{"paper_id":"2bf85145-485b-47cb-830f-aed4ac6af5fa","body_text":"Activating Free Volume of Polymeric Aggregates toward Advanced Hard Carbon for Sodium Storage | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Activating Free Volume of Polymeric Aggregates toward Advanced Hard Carbon for Sodium Storage Xunhui Xiong, Jianhao Lin, Zhishan Liao, Yike Liu, Bote Zhao, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7799184/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Constructing closed pore structure through precursor modification has been regarded as an effective route for boosting plateau capacity in hard carbon (HC) anodes for sodium-ion batteries (SIBs). However, the mechanistic role of polymer aggregation behavior in the closed pore formation in polymer-derived HCs remains poorly understood. Herein, flexible chain conformation has been incorporated into phenolic resin network to weaken the aggregated state and promote closed pores formation in the polymer-derived HC for the first time. During the stepwise immersion in an ethanol/water solvent, the extension of crystalline domains in polyethylene glycol segments can reduce the multichain aggregation as well as activate more free volumes within the polymer backbone. More free volumes can mitigate pyrolytic cross-linking reactions and facilitate the multiple releasing of volatile byproducts, which construct plentiful closed pore structure with ultra-small pore size during pyrolysis. As a result, the as-obtained HC anode demonstrates a high reversible capacity (357.9 mAh g − 1 at 0.1 C), enhanced rate performance (168.9 mAh g − 1 at 5 C) as well as excellent cycling stability over 2000 cycles at 4 C. This work provides a valuable insight into aggregate chemistry toward the development of high-performance HC anodes for advanced SIBs. Physical sciences/Energy science and technology/Energy storage/Batteries Physical sciences/Chemistry/Electrochemistry/Batteries Physical sciences/Materials science/Materials for energy and catalysis/Batteries free volume aggregate chemistry hard carbon closed pores sodium-ion batteries Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Technological expectations for sodium-ion batteries (SIBs) have been sparked by the abundant sodium resources, superior fast-charging capability as well as excellent low-temperature performance, which has made SIBs become promising complement to lithium-ion batteries. 1 However, the larger atomic size and different ionization behavior of Na + have brought serious challenges for the advancement of SIBs, particularly in the concerns over the high-capacity and durable anodes. 2 – 4 Among the various reported anodes, hard carbon (HC) shows greatly practical prospect owing to the merit of cost-effectiveness, low operating voltage and outstanding Na-storage capacity. 5 , 6 Unlike the traditional graphite anode, the active Na-storage sites in HC anodes root in their complex pseudo-graphite domains and internal nanopores structure, leading to a slope region (> 0.1 V) and a plateau region (< 0.1 V) in the sodiation voltage profile. 7 Recently, substantial reports have highlighted the significance of closed pore structure to realize sodium pore-filling process, which can contribute to the low-potential plateau capacity in HC anodes. 8 , 9 Obviously, the development of HC anodes with large plateau capacity is imperative to obtain high-energy-density SIBs for practical applications. Among the different precursors to prepare HC anodes, the synthetic polymer precursors possess the merits of high carbon yield, definite molecular constituent as well as excellent structure designability, and tremendous pore engineering strategies have been explored to prepare HC anodes with large plateau capacity via regulating the composition of polymer precursors. 10, 11 For instance, a co-interfering chemistry of the phenolic resin precursor have been proposed through introducing coordinated Zn 2+ cations and organic carboxylate anions, which can promote the curvature of carbon layers and realize the closure of nanopores in resin-derived HCs. 12 Besides, incorporating pitch coating with pre-oxidized phenolic resin has been developed to increase the disorder degree of pseudo-graphitic phase and enrich closed pore structure during pyrolysis, resulting in an improved plateau capacity of 242.8 mAh g − 1 for the obtained HC anode. 13 Despite of these great successes, the effect of polymer precursor structure on the formation of closed pores in the as-derived HCs remains unclear. Thereafter, various molecular design strategies have been developed during the polymerization process of polymer precursors to construct abundant closed pores in the HCs. 14 – 16 For example, the introduction of twisted benzene ring via polycondensation reaction can greatly enhance the thermal stability of polyimide chains, which effectively suppress the rearrangement of carbon layer and facilitate the closed pore formation during carbonization. 17 However, the chemically grafted groups in the polymer precursors show notable limitation in controlling the closed pore content and deliver low Na-storage capacity (< 320 mAh g − 1 ). Moreover, the underlying influence of polymeric aggregation on closed pore formation has not been explored. Generally, the polymeric network suffers from the multichain aggregation driven by strong molecular interactions, leading to denser chain packing as well as robust spatial constraints. 18 According to our previous work, the existence of narrow free volume between neighboring chains in polymer precursor could inhibit the formation of closed pores during the carbonization process. 19 Thus, activating more free volume in polymeric aggregates in the early molecular structural design may be a promising strategy to construct well-developed micropore structure in the resultant HCs, which has not yet reported in the previous polymer-derived HC anodes. Recently, the incorporation of flexible chain conformation in conjugated polymer showed considerable potentials to tune the polymer aggregation behavior in solution. 20 The flexible chain segments possess excellent mobility and form the expanded random coils in a good solvent, which can disrupt the molecular packing of polymer aggregates. 21 Inspired by this observation, a phenolic resin network linked with polyethylene glycol (PEG200, M n =200) segments has been designed in this work to activate the free volume of polymeric aggregates and construct abundant closed pores in the as-derived HC anode for SIBs. Driving by hydrogen-bonding interactions, the linked flexible PEG200 chains can spontaneously form crystalline domains during the curing process, which possesses hidden lengths in the cured phenolic network. When undergoing stepwise immersion processes in the ethanol/water solvent, the reduced bonding interactions between the internal PEG200 domains along with the extending of hidden lengths can weaken the aggregated chains, causing greatly increased free volume within the polymer backbones. More free volume can enlarge the gap distance within chain aggregates, which can mitigate pyrolytic cross-linking reactions and inhibit the over-graphitization of carbon layer during the carbonization process, resulting in the formation of well-developed closed pore in the final HC sample. When evaluated as an anode for SIB, the as-obtained HC exhibits a reversible capacity (357.9 mAh g − 1 at 0.1 C) with an enhanced plateau capacity contribution, an improved rate performance as well as excellent cycling stability over 2000 cycles at 4 C. This work inspires the exploration on aggregate chemistry to develop polymer-derived HC anodes with high plateau capacity towards advanced SIBs. Results Preparation and characterization of the PPR aggregates From polymer topology perspective, the original phenolic resin network is inevitably entrapped by multistrand aggregation driven by the intramolecular interactions, which could fold or entwin the polymer backbones into dense cluster. 22 To control their aggregation behavior, the soft PEG200 chains with tunable extensibility are chosen as links to construct a dynamic phenolic resin network (Fig. 1 a), which can spontaneously form crystalline domains during the following curing process because of the hydrogen-bonding interactions. Unlike phenolic resin with the rigid polymer backbones, the PEG200 crystalline domains could be flexibly zipped or extended as a transition switch to contribute to the hidden lengths. 23 To support our hypothesis, flexible PEG200 chain segments were grafted on the phenolic resin backbones (denoted as PPR) through one-step esterification reaction at 60°C. As illustrated in Supplementary Fig. 1, the generated carboxyl groups during the ring-opening reaction of maleic anhydride can provide extra cross-linking sites and hence induce a further esterification reaction with hydroxyl groups in phenolic resin and PEG200. Then the liquid components were observed to be spontaneously converted into PPR piece, as shown in the optical photographs in Supplementary Fig. 2. For comparison, the cured phenolic resin without PEG200 (denoted as PR) was also prepared under the identical condition. Fourier transform infrared (FTIR) spectroscopy was firstly employed to verify the crosslinking reaction (Fig. 1 b). Compared with the FTIR spectrum of pure phenolic resin, the PPR precursor show an enhanced intensity of -C = O group (1719 cm − 1 ), indicating maleic anhydride ring-opening followed by the esterification reaction with the hydroxy groups of phenolic resin. 24 Meanwhile, the emerging -C-O-C- groups (1095 cm − 1 ) with signal blueshift can be observed in the PPR precursor when compared with PEG200, demonstrating that the PEG200 chains have been covalently grafted within phenolic resin backbones. 25 Owing to the excellent miscibility between phenolic resin backbones and PEG200 segments, the PPR precursor shows higher optical transparency than the PR precursor (Supplementary Fig. 3). Besides, arising from the strong plasticization effect of PEG200 chains, 26 PPR network possesses excellent flexibility, which can be further proved by the mechanical properties analysis in Fig. 1 c. Distinguished from the PR precursor, an impressive gelation-like behavior for the PPR precursor can be verified by the tensile modulus down to 0.84 MPa, indicating that PEG200 segments have successfully induce the transition from rigidity to super-soft in phenolic resin aggregates. Furthermore, the breaking strain in PPR experiences an exceptional enhancement over 160%, demonstrating that the dynamic and adaptable slip of PEG crystalline domains can gradually extend the hidden lengths and thus survive large deformation. 27 Besides, the chains mobility of the PPR aggregates was revealed by glass transition temperature (T g ), which can be evaluated from the peaks of loss factor (tan δ) curves through dynamic mechanical analysis (DMA) test (Fig. 1 d and Supplementary Fig. 4). 28 Compared with PR precursor, a lower T g of 28.2°C in the PPR precursor indicates a less restriction from the intermolecular interactions as well as more mobile molecular chain. 29 , 30 The excellent extensibility and mobility for the PPR network with flexible PEG200 segments are favorable for the subsequent solvent immersion process to inhibit the over-aggregation of polymer chains. The weakly aggregated transition of PPR aggregates in solution To fully exert the hidden length of PEG200 segments in the PPR precursor, PPR underwent stepwise immersion processes in the ethanol and water, respectively. As shown in Fig. 2 a and Supplementary Fig. 5, the strongly aggregated PPR precursor experiences a significant swelling of 30% after immersed in ethanol. However, PPR precursor experiences obvious shrinkage after the direct volatilization of ethanol (denoted as PPR-S), resulting in the recovery of the strongly aggregated state. To stabilize the swelling-state aggregates, water exchange was employed to induce the phase separation owing to the poor hydrophilicity of phenolic resin backbones, 28 leading to a color change transition from orange transparent to opaque white. In contrast, a less obvious shape variation can be observed for PR precursor during the water exchange process, indicating that the unique transition behavior could be tuned by interactive network with both hydrophilic and hydrophobic segments (Supplementary Fig. 6). The as-formed PPR aggregates after dual-solvent immersion (denoted as PPR-W) shows no obvious shrinkage of polymer backbones after drying, which can be unexpectedly broken into pieces during falling ball test (Supplementary Fig. 7). The notable brittleness transition symbolizes the absence of energy dissipation within PPR-W aggregates, implying that the dual-solvent immersion process can significantly weaken the multichain aggregation of PPR network. 31 To further illustrate the above solution-responsive aggregation behavior, the geometrical information of PPR-S and PPR-W aggregates were investigated by small-angle X-ray scattering (SAXS) analysis. As shown in Fig. 2 b, the significant scatting peak can be attributed to the crystalline domains of PEG200 chains, 32 which is associated with the change of hidden length. Compared with PPR-S aggregates, the position of scattering peak in PPR-W aggregates experiences a remarkable shift to lower q value and the average inter-domains distance is prominently increased to 27.3 nm from 6.7 nm according to Bragg equation (d = 2π/q max ). The enhanced inter-domains distance indicates that the dual-solvent immersion process enables to weaken interchain interactions to extend hidden length from PEG200 crystalline domains and thus reduces the multichain aggregation. Their different interchain packing was further explored by X-ray diffraction (XRD) patterns (Fig. 2 c), in which the broad peaks in the 2θ range of 15–25° illustrate the relative extent of crystallinity. Compared with the PPR-S aggregates, the obviously attenuative peak intensity in PPR-W aggregates demonstrates the destruction of PEG200 crystalline domains and weakly aggregated state in PPR-W network. Notably, the extension of hidden lengths in PEG200 segments can reduce the aggregation, which also affect the spatial configuration of polymeric aggregates. The spatial configuration of PPR-W aggregates was further evaluated from positron annihilation lifetime spectroscopy (PALS), which can effectively reveal the free volume distribution within the polymeric aggregates. As shown in Fig. 2 d and Supplementary Fig. 8, 𝜏 3 stands for the lifetime of triplet spin-state positronium, which could be used to evaluate the free volume and correlate with the average cavity size by the Tao-Eldrup model. 33 , 34 Form the fitting results (Fig. 2 e and Supplementary Table S1 ), PPR-W aggregates possess a longer 𝜏 3 lifetime (1.48 ns vs. 1.29 ns) than that of PPR-S aggregates, indicating that the weakly aggregated state can activate more free volume (51.69 Å 3 vs. 38.29 Å 3 ) owing to the extended hidden lengths of PEG segments. The lager space extension can be further verified by mercury intrusion porosimetry (MIP), in which the Hg was used as space occupier to fill the internal void volume. As displayed in Fig. 2 f and Supplementary Fig. 9, the PPR-W aggregates exhibit much higher total intrusion volume (0.416 mL g −1 ) than that of PPR-S aggregates (0.092 mL g −1 ), favoring the enhanced internal void space within PPR-W aggregates. All these results confirm that the change from strongly to weakly aggregated state in solution can realize less ordered molecular packing and activate more internal free volume without sacrificing the network connectivity (Fig. 2 g). The role of aggregation behavior in forming closed pore in hard carbon To explore the effect of polymeric aggregation behavior on the closed pore formation, PPR-S and PPR-W aggregates were calcinated at 1400°C, and the as-obtained HCs were denoted as PPR-S-1400 and PPR-W-1400, respectively. As shown in Supplementary Fig. 10, the color of both PPR-S and PPR-W changes to black after carbonization process, while the shrinkage degree of edge length from 2.8 cm to 1.8 cm in PPR-W aggregates is obviously larger than PPR-S aggregates. A clear morphological evolution can be further observed in the scanning electron microscopy (SEM). As shown in cross-section SEM images (Fig. 3 a and 3 c), a typical macropore morphology observed in both PPR-S and PPR-W aggregates can be attributed to the removal of polymer-poor phase within the backbones, which is consistent with the pore distribution of MIP results. When carbonized at 1400°C, both PPR-S-1400 and PPR-W-1400 experience pores shrinkage and macropore walls growth (Fig. 3 b and 3 d), but a greater decrement of macropore size can be observed for PPR-W-1400. The different carbonized shrinkage and morphological changes are highly correlated with the different aggregated states of the precursors. The thermogravimetric analysis (TGA) was further employed to investigate the pyrolysis behaviors of PPR-S and PPR-W aggregates. As shown in Fig. 3 e ~ f, the rapid decomposition of PPR-S and PPR-W aggregates occurred during the calcination process can be divided into three main temperature ranges from the derivative TGA. Specifically, the weight loss in stage I (< 180°C) is ascribed to the removal of absorbed water and small molecules. In stage II (180 ~ 300°C), the continuous mass loss of PPR-S and PPR-W aggregates can be determined to the decomposition of PEG200 segments according to the TGA curve. However, an extra DTG peaks in PPR-W can be observed at 280°C compared with PPR-S, indicating that more light fractions can be released in this temperature range for PPR-W. Obviously, activating more free volumes within PPR-W aggregates is beneficial to form a gas channel for releasing volatiles, which can be further verified by FTIR spectra at 300°C. Compared with PPR-S, the lower intensity of -C = O (1720 cm − 1 ) and C-O (1191 cm − 1 ) linkages can be observed in PPR-W aggregates (Supplementary Fig. 11a), indicating that larger free volumes in PPR-W aggregates can mitigate pyrolytic cross-linking reactions. Such relative sparsity feature allows volatile byproducts to rapidly escape and thus induce the pore formation in the early stages, while strongly aggregated state involves complex cross-linking to densify their backbones. Further increasing carbonization temperature over 300°C, similar sluggish pyrolytic cross-linking reactions in PPR-W can be proved by the weaker signal of -C = O and C-O groups than PPR-S in FTIR spectra at 400°C (Supplementary Fig. 11b), leading to multi-DTG peaks in stage III. As a result, the carbon yield of PPR-W aggregates from room temperature to 800°C is 46.32%, lower than that of PPR-S aggregates (53.67%). All these results demonstrate that the weakly aggregated state in PPR-W can activate more free volumes to mitigate pyrolytic reactions and realize the multiple releases of volatile byproducts, which may create abundant micropores in the final HC. N 2 adsorption and desorption test was conducted to confirm the effect of different pyrolysis behaviors on micropore distribution (Supplementary Fig. 12). Notably, PPR-W-1400 exhibits a larger number of micropores than PPR-S-1400, indicating that the gas channel formed by volatile byproducts can be eventually converted to nanopore structure, which is believed to facilitate the formation of closed pores in PPR-W-1400. High-resolution transmission electron microscopy (HRTEM) has also been used to reveal obvious distinctions in the pore structure for PPR-S-1400 and PPR-W-1400. As displayed in Fig. 3 g, the PPR-W-1400 sample possesses abundant closed pores, accompanied by the randomly curved carbon layer with large interlayer spacing (0.411 nm). In contrast, PPR-S-1400 sample is predominantly consisted of long and multilayer graphitic domains, resulting in insufficient closed pores distribution (Fig. 3 h). Much improved closed pore structure in PPR-W-1400 can be concretely characterized by the SAXS technique. As shown in Fig. 4 a, PPR-W-1400 exhibits a broad peak with stronger scattering intensity within the q range of 0.1 ~ 0.4 Å −1 , indicative of a higher content of internal closed-pore structure than PPR-S-1400. 35 Furthermore, the shift of peaks position towards higher q value in PPR-W-1400 signifies a smaller closed pore radius than PPR-S-1400, which can be calculated as 0.36 nm (vs. 0.58 nm PPR-S-1400) by fitting the SAXS data (Fig. 4 b and Supplementary Fig. 13). Fortunately, the relatively small closed nanopores can favor improved rate performance owing to weaker metallic state of Na-storage within the plateau region, which have been verified by previously reported works. 36 , 37 These findings indicate that the weakly aggregated state of PPR-W-1400 can induce the multiple releases of volatile byproducts to promote the formation of abundant closed pore structure with ultra-small pore size during the carbonization process. The differences in closed pore volume can be evaluated by the true density results, which selectively eliminates open pores and interparticle spaces for the quantification of closed pore volume. 38 As shown in Fig. 4 c, PPR-W-1400 exhibits a higher closed pore volume of 0.065 cm 3 g − 1 than PPR-S-1400 (0.041 cm 3 g − 1 ), indicating the advantage of the weakly aggregated state in construction of closed pore, which can provide efficient Na-storage active sites for enhancing plateau capacity. XRD patterns were also employed to evaluate the effect of aggregated state on microcrystalline structure of HC samples. As shown in Fig. 4 d, PPR-W-1400 and PPR-S-1400 exhibit two broad peaks at ~ 23° and ~ 43°, which can be corresponded to the (002) and (100) crystal planes of graphitic crystallites, respectively. 39 However, the (002) diffraction peak of PPR-W-1400 show an obvious shift toward lower angle, suggesting that the weakened aggregated state can expand the interlayer distance. Based on the Bragg’s law, the enlarged d (002) value of PPR-W-1400 is calculated to be 0.405 nm (vs. 0.381 nm for PPR-S-1400), which can ensure reversible Na + intercalation/deintercalation as well as fast ion diffusion kinetics. Meanwhile, the aromatic carbon ratio (37.9%) of PPR-W-1400 fitted from (002) peak (Supplementary Fig. 14) is obviously lower than that of PPR-S-1400 (42.3%), suggesting that the weakly aggregated state can inhibit over-graphitization to form turbostratic structure. 40 Raman spectra offer more structural information for different HC samples. As shown in Fig. 4 e and Supplementary Fig. 15, both of PPR-W-1400 and PPR-S-1400 exhibit typical D band (1350 cm − 1 ) and G band (1595 cm − 1 ), which are related to defective structure and graphitic domains, respectively. 41 However, PPR-W-1400 exhibits obvious weakened G band as well as much higher A D /A G value than that of PPR-S-1400, illustrating that more disordered graphitic structures have been generated in PPR-W-1400. All the results demonstrate that the weakly aggregated state can inhibit over aromatization reaction and increase disordered degree, which is in good accordance with HRTEM results. The chemical composition of HCs was further analyzed by X-ray photoelectron spectroscopy (XPS), in which both PPR-W-1400 and PPR-S-1400 samples present the mainly component of C and O species (Supplementary Fig. 16a). The C 1s spectra shows three fitted peaks centered at 284.8, 286.2, 288.9 eV, corresponding to C-C, C-O and O-C = O, respectively (Supplementary Fig. 16b). Among them, the C-O groups on surface of HCs could cause much irreversible reaction and reduced initial coulombic efficiency, which have been proved in previously reported works. 42 It is worth noting that the C-O content in PPR-W-1400 is relatively lower than that of PPR-S-1400, indicating that the less aggregated state can diminish the formation of C-O and thus suppress the irreversibility during the Na-storage. Furthermore, the O 1s spectra of PPR-W-1400 (Fig. 4 f) also delivers higher O-III (C = O) percentage (14.9%) compared to PPR-S-1400 (9.6%), which will be conducive to rapid transportation of Na + and increase the reversibility of Na + adsorption. 43 Based on the above discussion, the role of polymeric aggregates on the formation of closed pore structures in the resultant HCs can be summarized in Fig. 4 g. Specifically, the larger free volume activated by the weakly aggregated state can realize the multiple releasing of volatile byproducts, which can induce the formation of abundant closed pores. Besides, the weakly aggregated state is benefit to carbonized shrinkage, leading to ultra-small closed pores and large closed pore volume. Furthermore, the polymer with less aggregated state tends to form the turbostratic and disordered microstructure in HC during the carbonization process, accompanied with expanded interlayer spacing and more C═O groups. Electrochemical performance and sodium storage mechanism of hard carbon The sodium storage performances of as-prepared HCs anodes were evaluated in the half Na-ion cells, with a particularly focus on the effect of weakly aggregated state on plateau capacity. As shown in Fig. 5 a, the galvanostatic charge-discharge (GCD) curves show typical voltage profile with slope and plateau region, in which PPR-W-1400 delivers an impressive reversible capacity of 357.9 mAh g − 1 at 0.1 C (1C = 300 mA g − 1 ), much higher than that of 286.5 mAh g − 1 for PPR-S-1400. The analysis on the slope and plateau capacity contributions shows that PPR-W-1400 possesses a large plateau capacity of 259.7 mAh g − 1 (Fig. 5 b), much higher than that of PPR-S-1400 (~ 203.2 mAh g − 1 ). The improved plateau capacity supports the weakly aggregated state is beneficial to the formation of closed pore structure. Meanwhile, the slope capacity increase in PPR-W-1400 can be attributed to the higher -C = O content, which allows reversible Na + adsorption to realize higher initial coulombic efficiency (ICE) of 86.8% (vs. 81.8% for PPR-1400). 44 Furthermore, the PPR-W-1400 anode maintains a higher reversible capacity of 168.9 mAh g − 1 at 5 C (Fig. 5 c). This remarkable enhancement stems from the smaller closed pore size in PPR-W-1400, which is benefit to form the minor Na cluster with weaker metallic state and thus facilitates superb Na + transportation. 14 The cycling stability at 1 C rate shows an impressive capacity retention of 93.1% for PPR-W-1400 after 700 cycles, while PPR-S-1400 anode keeps a capacity retention of 88.2% (Fig. 5 d). At a higher current density of 4 C rate, PPR-W-1400 still maintains a higher capacity of 163.2 mAh g − 1 over 2100 cycles (Fig. 5 e). In sharp contrast, PPR-S-1400 only delivers a low capacity of 100.5 mAh g − 1 . These results indicate that the expanding interlayer spacing in the PPR-W-1400 can ensure the reversible Na + intercalation pathways during the intensive cycling processes, highlighting the critical role of weak aggregation engineering in achieving durable Na-storage performance. To better reveal the role of aggregated state in modulating the Na-storage behavior, PEG crystalline domains with different hidden lengths were grafted on the polymer precursor. As shown in Supplementary Fig. 17, the phenolic resin grafted with ethylene glycol (EG) or PEG400 (M n =400) were also prepared under same treatment condition, which were denoted as PR-EG and PR-PEG400, respectively. All the PR, PR-EG and PR-PEG400 precursors with or without dual-solvent immersion treatment were annealed at 1400°C. As shown in Fig. 5 f and Supplementary Fig. 18, the resultant HCs derived from the weakly aggregated state by extending the hidden lengths of EG or PEG segments demonstrates an enhanced specific capacity when compared with the corresponding strongly aggregated state. In contrast, the PR-derived HC anode shows no obvious growth of capacity after dual-solvent immersion process. Obviously, the absence of extensible hidden lengths in phenolic resin backbones cannot realize the weakly aggregated transition, as evidenced by SAXS and XRD results (Supplementary Fig. 19 ~ 20, Supporting Information), as well as impressive Na-storage capacity. Additionally, PPR-W-1400 anode demonstrates higher capacity than those samples grafted with the EG and PEG400. This is because the small molecular size endowed by EG delivers the limited hidden lengths, while the oversize macromolecular chain of PEG400 may cause lower crosslinking degree and excessive carbonized shrinkage. Both of them are not beneficial to release the free volume in the precursor and construct closed pores in the HC sample. Therefore, the rational control of polymeric aggregates can be a promising strategy to modulate the well-developed pore structure of HC, which demonstrates significantly superior Na-storage performance than most of previous reports on resin-derived HC anodes. [14–16, 45–51] To investigate the mechanism of the greatly improved Na-storage capability in the synthesized HC anodes, the in-situ XRD spectra were carried out to analyze the (002) diffraction peak of PPR-W-1400 during the sodiation/de-sodiation process (Fig. 6 a). In the sodiation process, no remarkable change can be observed in the range of 2.0 ~ 0.1 V for (002) peaks, suggesting that the adsorption behavior of Na + or the reaction between the functional groups such as -C = O on surface with Na + . With further sodiation goes on, the intensity of (002) peak experiences a gradual decrease from 0.1 to 0.01 V, demonstrating an intercalation chemistry with the formation of Na-C compound. 52 In the following desodiation process to 2.0 V, the (002) peak can fully return to the original intensity, demonstrating the excellent reversibility and structural stability of PPR-W-1400. More importantly, no obvious change of the (002) peak position can be observed for PPR-W-1400 sample during the whole charge/discharge process, whereas the PPR-S-1400 exhibits a significant leftward shift (Supplementary Fig. 21). These results indicate that the (002) plane in PPR-W-1400 sample has enough layer spacing (0.405 nm) to accommodate Na + , which can avoid expansion of carbon layer and enable the PPR-W-1400 to deliver impressive cycle stability at large current density. To further visualize the formation of pore-filling process, the ethanol solution containing 1% phenolphthalein was used to rinse the PPR-W-1400 electrode at different potentials. As shown in Fig. 6 b, a distinctive purplish-red and deepening color change can be observed in the phenolphthalein solution for PPR-W-1400 when the voltage discharged from 0.5 to 0.01 V, which verifies the formation of quasi-metallic Na inside the closed pores. 53 Moreover, the color of phenolphthalein solution becomes lighter in the following charged state of 0.5 V, further demonstrating the excellent reversibility of Na storage in PPR-W-1400 sample, which is consistent with the in-situ XRD result. To explore the reason for the impressively enhanced rate performances, the galvanostatic intermittent titration technique (GITT) was performed for PPR-W-1400 and PPR-S-1400 anodes. As shown in Fig. 6 c and Supplementary Fig. 22, all of the Na + diffusion coefficients (D Na + ) values show no significant change in the slope region, and then turn to “U” shape in the plateau region during the sodiation/de-sodiation process. 54 Nonetheless, it can be clearly observed that PPR-W-1400 exhibits a higher D Na + than PPR-S-1400 in the range of 0.01 ~ 0.1 V, which could be attributed to the unique pore structure with ultra-small closed pore size in PPR-W-1400. The faster Na + transfer kinetics in PPR-W-1400 can guarantee the high retention of plateau capacity when increasing to larger current density. Meanwhile, the PPR-W-1400 also displays a much smaller charge-transfer impedance (R ct ) than that of PPR-S-1400 (Fig. 6 d). These results illustrate that larger interlayer spacing in PPR-W-1400 are beneficial to high reaction kinetics for fast charge transfer, accounting well for the better rate performance. Encouraged by the superior electrochemical performances of PPR-W-1400 anode in the half cell, the full batteries were further assembled with the commercial Na 3 V 2 (PO 4 ) 3 (NVP) cathode (Fig. 6 e and Supplementary Fig. 23). The full cell can exhibit reversible capacity of 336.6, 274.8, 249.3, 230.8 mAh g − 1 (based on the mass of active anode materials) at 0.1, 0.7, 2 and 4 C rates, respectively (Fig. 6 f). In addition, the capacity retention rate of full cell is 85.4% over 100 cycles at 4 C (Fig. 6 g), demonstrating the potential of PPR-W-1400 for constructing high-performance energy storage devices. Discussion In summary, a phenolic resin network linked with flexible chain conformation has been proposed to weaken the polymeric aggregates to prepare high-performance polymer-derived HCs for the first time. The extension of crystalline domains in PEG segments can drive the transition from a strongly to weakly aggregated state during the stepwise immersion process, resulting in increasing the free volume within the phenolic resin network. More free volumes can mitigate pyrolytic cross-linking reactions and realize the multiple releasing of volatile byproducts, ultimately promoting the formation of abundant closed pores during carbonization process. As a result, the as-prepared HC anode exhibited a high plateau capacity of 259.7 mAh g -1 at 0.1C, improved rate performance (168.9 mAh g -1 at 5C) as well as superior cycling stability over 2100 cycles at 4C. Our work offers a new perspective on polymer aggregation topology to construct closed pore structure in the polymer-derived HC for high-performance SIBs. Methods Materials All the materials were purchased from commercial sources and used without further purification. Phenol-formaldehyde resin (Water solubility, Macklin, solid content ~70 %), Polyethylene glycol (PEG) (Aladdin, M w =200 & 400), Ethylene glycol (EG) (Macklin, 99 %), Maleic anhydride (Macklin, 99 %). Fabrication of the hard carbon samples 1.31 g of phenolic resin liquid was mixed with 1.22 mL PEG200, then 0.3 g maleic anhydride were added to the mixture. Next, the solution was diluted with deionized water to 5 mL of total volume followed by continuous stirring to form homogeneous solution. The mixed solution was poured into block-like silicon mold sealed with cling film and cured at 60 °C for 14 h. Then, the solidified block was obtained and denoted as PPR precursor by removing mold. The PPR precursor was sequentially immersed with ethanol solvent for 2 days and water solvent for 2 days, and dried at 60 °C to obtain a pink white block of final PPR-W aggregates, while the PPR precursor with only ethanol immersion was noted as PPR-W aggregates. The precursors were directly carbonized at 1400 °C for 1 h in a tube furnace under argon flow with a temperature rate of 2 °C/min, where the obtained hard carbons derived from PPR-W and PPR-S were denoted as PPR-W-1400 and PPR-S-1400, respectively. For comparison, the cured phenolic resin without PEG200, with EG and with PEG400 under identical preparation process was noted as PR-W/S-1400, PR-EG-W/S-1400 and PR-PEG400-W/S-1400, respectively. Materials Characterization Fourier transform infrared (FTIR) spectra were recorded using Thermo Nicolet IS5. Small-angle X-ray scattering (SAXS) was carried out by a Xenocs Xeuss 2.0 with a Cu-Kα source. Positron annihilation lifetime spectroscopy (PALS) was recorded by AMETEK PLS-SYSTEM. Tensile properties were determined using an CL-200 N electronic universal testing machine at the cross-head speed of 50 mm/min. The storage modulus (E'), loss modulus (E\"), and loss factor (tan δ) of precursors were determined using DMA (TA DMA850, USA) in compression mode (temperature range: 25~120 °C; heating rate:2°C min -1 ; frequency:1Hz). The character structural information of the samples was analyzed by X-ray diffraction analyzer (XRD, Bruker D8 advanced, Cu, Kα, λ=1.5418 Å) and Raman spectrometer (LabRam HR Evolution). Specific surface area was tested by N 2 adsorption-desorption (Micromeritics ASAP 2460). The pore volume was tested by mercury intrusion porosimetry (MIP, Micromeritics AutoPore9605). The true densities of hard carbon samples were measured via helium gas pycnometry with the Micromeritics AccuPyc II 1340. The pyrolysis behavior of precursors was acquired on Thermogravimetric analysis (TGA, Perkin Elmer STA6000). The morphology of the samples was observed by Transmission electron microscope (TEM, JEM-2100Plus) and Scanning electron microscope (SEM, Hitachi SU8010). The composition of the sample surface was characterized by X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha). In-situ XRD was carried out during charge/discharge cycle using in-situ cell (LIB-XRD, Beijing Scistar Technology Co. Ltd, China). Electrochemical Measurements CR2032 coin cells were assembled in an Ar-filled glove box (H 2 O, O 2 < 0.01 ppm) for testing the electrochemical performance of samples. Hard carbon powder (80%), acetylene black (10%) and sodium alginate (10 wt%) were ground by adding the proper amount of H 2 O to form a homogeneous slurry. And the slurry was coated on the Cu foil and dried at 80 °C for 12 h in a vacuum oven. The obtained working electrode was cut into 13 mm disks with a mass loading of 1.5~2 mg/cm 2 . For half-cells, CR2032 coin cells were assembled using hard carbon anode as working electrode, Na disk as a counter electrode and glass fiber (Whatman) as separator. 1 M NaPF 6 in DIGLYME=100 Vol% (DoDochem) was used as ether-based electrolyte. The half-cells were tested within the voltage range of 0.002-2 V. For full-cells, Na 3 V 2 (PO 4 ) 3 (NVP, Shenzhen Kejing), acetylene black and polytetrafuoroethylene (PVDF) were mixed with the ratio of 8:1:1, and the mass loading of cathode disks with a diameter of 10 mm was 7~8 mg/cm 2 . The capacity ratio of anode/cathode was 1.1/1. 1 M NaPF 6 in DIGLYME=100 Vol% as electrolyte. Before assembling PPR-W-1400//NVP full-cell, PPR-W-1400 anode was precycled for 5 cycles at 0.1 C in the half-cells. The full-cells were tested within the voltage range of 3.8-2 V. Galvanostatic charge-discharge and galvanostatic intermittent titration technique (GITT) tests were carried out on LAND2001CT battery testing system. The diffusion coefficient of Na + (D Na + ) at PPR-W-1400 and PPR-S-1400 electrode can be calculated based on Fick's second law from GITT results. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed on electrochemical workstation (CHI660a, Shanghai Chenhua). Declarations Acknowledgements The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (52322406, 52264035), the Natural Science Foundation of Guangdong Province, China (2024A1515010827) and the Double Thousand Plan in Jiangxi Province (jxsq2023101061). Author contributions J.L. and X.X. conducted the experiments and designed the project and wrote the manuscript. Z.L., Y.L. and B.Z. J.W. analyzed the results. Competing interests The authors declare no competing interests. Additional information Supplementary information The online version contains supplementary material available from the author. Correspondence and requests for materials should be addressed to Xunhui Xiong. Data availability The data that support the findings of this study are available within the article and its Supplementary Information files. All other relevant data supporting the findings of this study are available from the corresponding authors upon reasonable request. References Nayak, P. K., Yang, L., Brehm, W. & Adelhelm, P. From Lithium-ion to sodium-ion batteries: advantages, challenges, and surprises. Angew. Chem. Int. Ed. 57 , 102-120 (2018). Fang, Z. et al. Root-growth-inspired self-morphology-evolution of microsized bismuth surrounded by microsized hard carbon for stabilized sodium-ion storage. Adv. Mater. 37 , 2412636 (2025). Ma, X. et al. General and scalable fabrication of core-shell metal sulfides@C anchored on 3D N-doped foam toward flexible sodium ion batteries. Small 15 , 1903259 (2019). Si, W. et al. Hollow structured medium entropy transition metal selenide CoNiFe-Se@NC enables high performance of sodium-ion batteries. Green Chem. 27 , 2150-2159 (2025). Pei, B. et al. Hard carbon for sodium-ion batteries: from fundamental research to practical applications. Adv. Mater. 2504574 (2025). Yang, Y. et al. Recent advances of high-rate hard carbon anodes for sodium-ion batteries: correlations between performance and microstructure. Adv. Funct. Mater. e14132 (2025). Kitsu Iglesias, L. et al. Microstructure-dependent sodium storage mechanisms in hard carbon anodes. Small 21 , 2505561 (2025). Jian, W. et al. Elucidation of the sodium-ion storage behaviors in hard carbon anodes through pore architecture engineering. ACS Nano 19 , 22201-22216 (2025). Zhang, Y. et al. Redefining closed pores in carbons by solvation structures for enhanced sodium storage. Nat. Commun. 16 , 3634 (2025). Liu, J. et al. Boosting sodium-ion storage in hard carbon via polyethylene glycol cross-linked phenolic resin. Electrochim. Acta 535 , 146572 (2025). Cheng, M.-G. et al. Preparation of enriched closed-pores hard carbon for high-Performance sodium-ion batteries by the poly(vinyl butyral) template method. ACS Appl. Energy Mater. 7 , 3452-3461 (2024). Hou, Z. et al. Expediting sodium energy of hard carbon by cation/anion co-interfering chemistry. Adv. Funct. Mater. 35 , 2505468 (2025). Xiao, S. et al. Insight into the role of closed-rore size on rate capability of hard carbon for fast-charging sodium-ion batteries. Adv. Mater. 37 , 2501434 (2025). Zhao, Y. et al. Closed-pore hard carbon nanospheres via aldol condensation for sodium storage. ACS Appl. Nano Mater. 8 , 2785-2796 (2025). Zhang, X. et al. Molecular engineering to regulate the pseudo-graphitic structure of hard carbon for superior sodium energy storage. Small 20 , 2311778 (2024). Zhou, H. et al. Microstructure regulation of resin-based hard carbons via esterification cross-linking for high-performance sodium-ion batteries. Inorg. Chem. Front. 10 , 2404-2413 (2023). Nie, F. et al. “Spatial twist engineering”: breathing new life into polyimide-derived hard carbon for high-performance sodium-ion batteries. J. Energy Chem. 111 , 383-392, (2025). Zhang, Z. et al. NIR clusteroluminescence of non-conjugated phenolic resins enabled by through-space interactions. Angew. Chem. Int. Ed. 62 , e202306762 (2023). Lin, J. et al. Steric hindrance engineering to modulate the closed pores formation of polymer-derived hard carbon for high-performance sodium-ion batteries. Angew. Chem. Int. Ed. 63 , e202409906 (2024). Xiong, M. et al. Efficient n-doping of polymeric semiconductors through controlling the dynamics of solution-state polymer aggregates. Angew. Chem. Int. Ed. 60 , 8189-8197 (2021). Wang, C. J. et al. Bottlebrush hydrogels with hidden length: super-swelling and mechanically robust. Adv. Funct. Mater. 34 , 2410905 (2024). Cui, K. et al. Phase Separation behavior in tough and self-healing polyampholyte hydrogels. Macromolecules 53 , 5116-5126 (2020). Yang, Y., Ru, Y., Zhao, T. & Liu, M. Bioinspired multiphase composite gel materials: from controlled micro-phase separation to multiple functionalities. Chem 9 , 3113-3137 (2023). Xue, B. et al. Strong, tough, rapid-recovery, and fatigue-resistant hydrogels made of picot peptide fibres. Nat. Commun. 14 , 2583 (2023). Cavusoglu, J. & Çaylı, G. Polymerization reactions of epoxidized soybean oil and maleate esters of oil-soluble resoles. J. Appl. Polym. Sci. 132, 41457 (2015). Liu, J., Chen, R., Wang, C., Zhao, Y. & Chu, F. Synthesis and characterization of polyethylene glycol-phenol-formaldehyde based polyurethane composite. Sci. Rep. 9 , 19545 (2019). Sheng, Y. et al. Engineering water-stiffening polymers via PEG-sidechain-mediated microphase separation. Adv. Funct. Mater. 34 , 2401999 (2024). Xu, L., Qiao, Y. & Qiu, D. Coordinatively stiffen and toughen hydrogels with adaptable crystal-domain cross-linking. Adv. Mater. 35 , 2209913 (2023). Yang, Z. et al. Robust liquid crystal semi-interpenetrating polymer network with superior energy-dissipation performance. Nat. Commun. 15 , 9902 (2024). Cheng, J. et al. Sterically hindered organogels with self-healing, impact response, and high damping properties. Adv. Mater. 36 , 2411700 (2024). Li, E. et al. Tailoring the gating effect of organic cage via a porous liquid approach. Adv. Funct. Mater. 35 , 2413668 (2025). Xu, W. et al. Optimization of the thermally conductive low-k polymer dielectrics based on multisource free-volume effects. ACS Appl. Mater. Interfaces 16 , 16809-16819 (2024). Li, Y. et al. Regulating pore structure of hierarchical porous waste cork-derived hard carbon anode for enhanced Na storage performance. Adv. Energy Mater. 9 , 1902852 (2019). Li, Y. et al. Origin of fast charging in hard carbon anodes. Nat. Energy 9 , 134-142 (2024). Huang, J. et al. Fabrication of lignin-derived high-rate hard carbon anodes for sodium-ion batteries. Chem. Eng. Sci. 319 , 122343 (2026). Tang, Z. et al. Revealing the closed pore formation of waste wood-derived hard carbon for advanced sodium-ion battery. Nat. Commun. 14 , 6024 (2023). Huang, Y. et al. Reconfiguring terminal species of bituminous coal to steer hard carbon toward high-capacity and fast sodium storage. Angew. Chem. Int. Ed. 64 , e202423864 (2025). Xue, Y. et al. Substitution index-prediction rules for low-potential plateau of hard carbon anodes in sodium-ion batteries. Adv. Mater. 37 , 2417886 (2025). Cui, J. et al. Repair surface defects on biomass derived hard carbon anodes with N-doped soft carbon to boost performance for sodium-ion batteries. Adv. Energy Mater. 15 , 2502082 (2025). Xie, F. et al. Screening heteroatom configurations for reversible sloping capacity promises high-power Na-ion batteries. Angew. Chem. Int. Ed. 61 , e202116394 (2022). Liu, Y. et al. Molecular engineering of pore structure/interfacial functional groups toward hard carbon anode in sodium-ion batteries. Energy Storage Mater. 75 , 104008 (2025). Zheng, J. et al. Unveiling the microscopic origin of irreversible capacity loss of hard carbon for sodium-ion batteries. Adv. Energy Mater. 14 , 2303584 (2024). Xiao, S. et al. Insight into the role of closed-pore size on rate capability of hard carbon for fast-charging sodium-ion batteries. Adv. Mater. 37 , 2501434 (2025). Sun, D. et al. Rationally regulating closed pore structures by pitch coating to boost sodium storage performance of hard carbon in low-voltage platforms. Adv. Funct. Mater. 34 , 2403642 (2024). Xu, R. et al. Hard carbon anodes derived from phenolic resin/sucrose cross-linking network for high-performance sodium-ion batteries. Battery Energy 2 , 20220054 (2023). Zhang, G. et al. Tailoring a phenolic resin precursor by facile pre-oxidation tactics to realize a high-initial-coulombic-efficiency hard carbon anode for sodium-ion batteries. ACS Appl. Mater. Interfaces 13 , 31650-31659 (2021). Chen, Z. et al. Polymer-based hard carbons with enhanced initial coulombic efficiency for practical sodium storage. Ind. Eng. Chem. Res. 64 , 7349-7359 (2025). Guo, L. et al. Spatial configuration engineering of phenolic resins to tune the closed pores of hard carbon for enhanced plateau-capacity sodium storage. Chem. Eng. J. 512 , 162478 (2025). Ma, Q. et al. Research on the controlled synthesis of phenolic resin-based carbon microspheres and their sodium storage behavior. ChemistrySelect 10 , e202500414 (2025). Li, X. et al. C60 to Modulate the closed pore structures of hard carbon for high-performance Sodium-ion batteries. ACS Nano 19 , 14829-14838 (2025). Wang, Y. et al. Lowering energy barriers of free radicals facilitates defect-suppressed carbon layers of hard carbon. Small 36 , e06923 (2025). Eren, E. O. et al. An enhanced three-stage model for sodium storage in hard carbons. Energy Environ. Sci. 18 , 7859-7868 (2025). Fu, W. et al. Constructing accessible closed nanopores in coal-derived hard carbon for sodium-ion batteries. Small 21 , 2411376 (2025). Additional Declarations There is NO Competing Interest. Supplementary Files Supportinginformation.docx Supporting information Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-7799184\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":true,\"archivedVersions\":[],\"articleType\":\"Article\",\"associatedPublications\":[],\"authors\":[{\"id\":537125507,\"identity\":\"686f2d40-9107-4ace-885a-5fca7b41cf4b\",\"order_by\":0,\"name\":\"Xunhui Xiong\",\"email\":\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1ElEQVRIie3PMQrCMBSA4Uihk5C1RXqHQCA6SHuVlkAnD5CxIDjaVW9REJxTMrgEumZwqEtnRzdNSl3TjIL5IfCG95EEAJ/vV8v1gdO8qJxJbFa5MzEh7koglCTq2T29dGJYPcE2aXgw9DYSn0qKcjnQqypJxEGJGx6ukfU9Kmj74iAoUctQE1E0XA82knVtxQ3BtTTkPU8QoOMtKQI7Q/g8idT4F5HrAW8kovgsQmIlsJYkfjGRwVo8FGNpcrztByv5VlTTOwEIXPZ1meOez+fz/WMfz4dMm9Y7CjgAAAAASUVORK5CYII=\",\"orcid\":\"https://orcid.org/0000-0002-5858-9247\",\"institution\":\"South China University of Technology\",\"correspondingAuthor\":true,\"prefix\":\"\",\"firstName\":\"Xunhui\",\"middleName\":\"\",\"lastName\":\"Xiong\",\"suffix\":\"\"},{\"id\":537125508,\"identity\":\"7216f90f-912e-406b-a37f-d6895d21ea6e\",\"order_by\":1,\"name\":\"Jianhao Lin\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Jianhao\",\"middleName\":\"\",\"lastName\":\"Lin\",\"suffix\":\"\"},{\"id\":537125509,\"identity\":\"6cabc17e-81bc-410d-ad16-512074def971\",\"order_by\":2,\"name\":\"Zhishan Liao\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"South China University of Technology\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Zhishan\",\"middleName\":\"\",\"lastName\":\"Liao\",\"suffix\":\"\"},{\"id\":537125510,\"identity\":\"8875354c-ec2c-432d-9159-faed44318875\",\"order_by\":3,\"name\":\"Yike Liu\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Guizhou Institute of Technology\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Yike\",\"middleName\":\"\",\"lastName\":\"Liu\",\"suffix\":\"\"},{\"id\":537125511,\"identity\":\"4ef47b84-5bc1-44b2-90cc-ea5c877d000e\",\"order_by\":4,\"name\":\"Bote Zhao\",\"email\":\"\",\"orcid\":\"https://orcid.org/0000-0003-1236-6862\",\"institution\":\"South China University of Technology\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Bote\",\"middleName\":\"\",\"lastName\":\"Zhao\",\"suffix\":\"\"},{\"id\":537125512,\"identity\":\"5ffe1bc0-f733-4e02-867c-acb104a2ed38\",\"order_by\":5,\"name\":\"Jiexi Wang\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Central South University\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Jiexi\",\"middleName\":\"\",\"lastName\":\"Wang\",\"suffix\":\"\"}],\"badges\":[],\"createdAt\":\"2025-10-07 11:46:38\",\"currentVersionCode\":1,\"declarations\":\"\",\"doi\":\"10.21203/rs.3.rs-7799184/v1\",\"doiUrl\":\"https://doi.org/10.21203/rs.3.rs-7799184/v1\",\"draftVersion\":[],\"editorialEvents\":[],\"editorialNote\":\"\",\"failedWorkflow\":false,\"files\":[{\"id\":94825922,\"identity\":\"7de5c358-1bef-488d-8855-62ad4d8e864a\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:50:50\",\"extension\":\"docx\",\"order_by\":0,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":3859421,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"manuscript.docx\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/00b1fc8990f16adb4b67ff7d.docx\"},{\"id\":94820842,\"identity\":\"4ffa7475-7b09-4aac-8e59-0f06936df9d0\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"json\",\"order_by\":1,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":7215,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"NCOMMS2580112.json\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/0e8f7366b9d6af7600486f01.json\"},{\"id\":94826259,\"identity\":\"25210401-7221-4f15-82a3-d8415a6ecc31\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:51:17\",\"extension\":\"docx\",\"order_by\":2,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":21586645,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"Supportinginformation.docx\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/6c83ad92f060ecece63dc6e1.docx\"},{\"id\":94820845,\"identity\":\"b5e077e2-c753-4db1-9835-c2fe0161876e\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"xml\",\"order_by\":3,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":114316,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"NCOMMS25801120enriched.xml\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/26fe0f8d30efce75d9630f05.xml\"},{\"id\":94820846,\"identity\":\"939ea131-fd58-4928-909c-089bf2117768\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":4,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":303837,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"floatimage1.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/267c08c1495b6c36880b65ab.png\"},{\"id\":94820851,\"identity\":\"5fd755a5-928b-403f-b65c-7ad9f1be9eaa\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":5,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":653040,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"floatimage2.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/9ea63d15bb56ce6ed5565537.png\"},{\"id\":94820852,\"identity\":\"a6b786c5-9954-4786-ab54-dc10de403dbd\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":6,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":1269696,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"floatimage3.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/aa17a5ae3e6e5fd1dba37365.png\"},{\"id\":94820854,\"identity\":\"6dd41bde-dd07-4766-a09f-90963b21f341\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":7,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":435597,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"floatimage4.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/17885e1e776160ac5778422c.png\"},{\"id\":94820859,\"identity\":\"e0168a23-b0c1-48d9-89ab-e3b314d4674a\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":8,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":464161,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"floatimage5.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/bc91fa2c67dd01dcbcc79d65.png\"},{\"id\":94820862,\"identity\":\"8666b1e0-6a3f-45d2-ab1d-9e2f31c317eb\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":9,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":657424,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"floatimage6.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/19e16c7474a51410f94f1860.png\"},{\"id\":94826419,\"identity\":\"7c594e6c-025e-47d8-bbe5-7df2fb377281\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:51:41\",\"extension\":\"png\",\"order_by\":10,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":68837,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"Onlinefloatimage1.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/8324bc614965b63e3f2ebbc4.png\"},{\"id\":94820847,\"identity\":\"08bae106-ff33-4119-bb27-3dc920d96308\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":11,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":123766,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"Onlinefloatimage2.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/3b4f5d7cba5e6aa88cf5d7c8.png\"},{\"id\":94826004,\"identity\":\"fae63b8a-8ba2-41ce-b0e7-5f54b2c11ccf\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:50:54\",\"extension\":\"png\",\"order_by\":12,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":221291,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"Onlinefloatimage3.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/0feeb5f39506eb0a3fe3ed7d.png\"},{\"id\":94826311,\"identity\":\"d6949d54-e6a6-4133-8731-6fbc3d5cc69f\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:51:24\",\"extension\":\"png\",\"order_by\":13,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":104829,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"Onlinefloatimage4.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/f3964c5008e1d78801fa43aa.png\"},{\"id\":94820857,\"identity\":\"ee58606d-fe1b-42d9-9755-a84994efe2d9\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":14,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":105714,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"Onlinefloatimage5.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/a95ee3a0ea99740f464b0341.png\"},{\"id\":94826037,\"identity\":\"795cfa61-6356-40e3-bffc-4eaea6786658\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:50:57\",\"extension\":\"png\",\"order_by\":15,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":122926,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"Onlinefloatimage6.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/2dedc89e9898ebf83e7b2b04.png\"},{\"id\":94826386,\"identity\":\"9fc8b331-6e3a-4d0c-a36b-435bfc6a06c9\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:51:31\",\"extension\":\"xml\",\"order_by\":16,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":112871,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"NCOMMS25801120structuring.xml\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/829c8ac6936564602b2a116a.xml\"},{\"id\":94820863,\"identity\":\"8fd70197-73b9-4400-952c-7ced5e205d86\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"html\",\"order_by\":17,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"acdc-reference\",\"size\":120974,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"earlyproof.html\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/a695b5eb52893692959cdd38.html\"},{\"id\":94820841,\"identity\":\"0d7c36a3-bfb0-4f38-8f0c-4d57ab6f47ab\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":1,\"title\":\"Figure 1\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":303837,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eThe design and mechanical property of PPR aggregates\\u003c/strong\\u003e. \\u003cstrong\\u003ea\\u003c/strong\\u003e Dynamic model scheme of the PPR phenolic aggregates with PEG200 crystalline domains as hidden lengths. \\u003cstrong\\u003eb\\u003c/strong\\u003e FTIR spectra of PPR, PEG200 and pure phenolic resin. \\u003cstrong\\u003ec\\u003c/strong\\u003e Tensile stress-strain curves for PR and PPR. \\u003cstrong\\u003ed\\u003c/strong\\u003eLoss factor (tan δ) curves for PR and PPR aggregates at 25~120 °C by DMA in compression mode (frequency:1 Hz).\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage1.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/5c2ea5d639b80d3b0e4af73c.png\"},{\"id\":94820840,\"identity\":\"54c06deb-0424-4f2b-9202-1bcb6b7c3132\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":2,\"title\":\"Figure 2\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":653040,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eThe aggregation behavior of PPR precursor in stepwise immersion process\\u003c/strong\\u003e. \\u003cstrong\\u003ea\\u003c/strong\\u003e Photographs of the dynamic evolution of PPR aggregates during only ethanol uptake and dual-solvent uptake process. \\u003cstrong\\u003eb\\u003c/strong\\u003e SAXS patterns, (\\u003cstrong\\u003ec\\u003c/strong\\u003e) XRD patterns, (\\u003cstrong\\u003ed\\u003c/strong\\u003e) PALS spectra, (\\u003cstrong\\u003ee\\u003c/strong\\u003e) 𝜏\\u003csub\\u003e3\\u003c/sub\\u003e lifetime and free volume and (\\u003cstrong\\u003ef\\u003c/strong\\u003e) Pore size distribution with intrusion volume of PPR-W and PPR-S aggregates; \\u003cstrong\\u003eg\\u003c/strong\\u003e Illustration of the dynamic evolution of the aggregated state by the dual-solvent uptake process.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage2.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/74921f046dcd3f181b6fd090.png\"},{\"id\":94820844,\"identity\":\"5d72f7c0-ea57-48a4-94fd-b87e734c9c50\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":3,\"title\":\"Figure 3\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":1269696,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eThe carbonization process of precursors with different aggregation behaviors\\u003c/strong\\u003e. Cross-section SEM images of (\\u003cstrong\\u003ea\\u003c/strong\\u003e) PPR-W, (\\u003cstrong\\u003eb\\u003c/strong\\u003e) PPR-W-1400, (\\u003cstrong\\u003ec\\u003c/strong\\u003e) PPR-S and (\\u003cstrong\\u003ed\\u003c/strong\\u003e) PPR-S-1400. \\u003cstrong\\u003ee\\u003c/strong\\u003e TGA curves of PPR-S, PPR-W and PEG200. \\u003cstrong\\u003ef\\u003c/strong\\u003e DTG curves of PPR-S and PPR-W. HRTEM images of (\\u003cstrong\\u003eg\\u003c/strong\\u003e) PPR-W-1400 and (\\u003cstrong\\u003eh\\u003c/strong\\u003e) PPR-S-1400.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage3.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/7e75c3ec8087018f451b7dc1.png\"},{\"id\":94820849,\"identity\":\"8d1c2bbb-2e90-4881-9fe0-ae581640d869\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":4,\"title\":\"Figure 4\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":435597,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eAnalysis of structural information in different HCs\\u003c/strong\\u003e. \\u003cstrong\\u003ea\\u003c/strong\\u003e SAXS patterns, (\\u003cstrong\\u003eb\\u003c/strong\\u003e) Pore size distribution curve obtained from fitting the SAXS data, (\\u003cstrong\\u003ec\\u003c/strong\\u003e) Closed pore volume calculated from true density, (\\u003cstrong\\u003ed\\u003c/strong\\u003e) XRD patterns, (\\u003cstrong\\u003ee\\u003c/strong\\u003e) Raman spectra and (\\u003cstrong\\u003ef\\u003c/strong\\u003e) High-resolution XPS spectra of O 1s of PPR-W-1400 and PPR-S-1400. \\u003cstrong\\u003eg\\u003c/strong\\u003e Structural evolution under the influence of the strongly or weakly aggregated state.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage4.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/98bbded977dcf3f133db0bd9.png\"},{\"id\":94820843,\"identity\":\"3b6e534e-4e63-4c7b-96b5-a0426148268f\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"png\",\"order_by\":5,\"title\":\"Figure 5\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":464161,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eElectrochemical performances of different HCs\\u003c/strong\\u003e. The (\\u003cstrong\\u003ea\\u003c/strong\\u003e) initial discharge/charge curves, (\\u003cstrong\\u003eb\\u003c/strong\\u003e) 2\\u003csup\\u003end\\u003c/sup\\u003e discharge capacity contributed from slope and plateau region, (\\u003cstrong\\u003ec\\u003c/strong\\u003e) Rate performance and Cycling performance at (\\u003cstrong\\u003ed\\u003c/strong\\u003e) 1 C and (\\u003cstrong\\u003ee\\u003c/strong\\u003e) 4 C for PPR-W-1400 and PPR-S-1400 anodes. \\u003cstrong\\u003ef\\u003c/strong\\u003e The specific capacity of different HC samples derived from strongly and weakly aggregated state. \\u003cstrong\\u003eg\\u003c/strong\\u003e Comparison of Na-storage performance with the previously reported resin-derived HCs anodes.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage5.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/b7ebe61532471216398abd22.png\"},{\"id\":94825727,\"identity\":\"0f62a5b8-8cb5-43b7-be74-8bb17b52bac5\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:50:38\",\"extension\":\"png\",\"order_by\":6,\"title\":\"Figure 6\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":657424,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eSodium storage mechanism and full cell.\\u003c/strong\\u003e \\u003cstrong\\u003ea\\u003c/strong\\u003e In-situ XRD spectra of PPR-W-1400 anode. \\u003cstrong\\u003eb\\u003c/strong\\u003e Optical photographs of PPR-W-1400 anode at different potential stage soaked in ethanol solution containing 1% phenolphthalein. \\u003cstrong\\u003ec\\u003c/strong\\u003e Na\\u003csup\\u003e+\\u003c/sup\\u003e diffusion coefficients at sodiation process estimated from GITT curves and (\\u003cstrong\\u003ed\\u003c/strong\\u003e) Nyquist plots for PPR-W-1400 and PPR-S-1400 anodes. \\u003cstrong\\u003ee\\u003c/strong\\u003e The schematic illustration of the full cell configuration, (\\u003cstrong\\u003ef\\u003c/strong\\u003e) Charge/discharge curves at different current densities and (\\u003cstrong\\u003eg\\u003c/strong\\u003e) Cycling performance at 4 C for PPR-W-1400//NVP full cell.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"floatimage6.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/3ccc0023293b298fd0e53238.png\"},{\"id\":99311212,\"identity\":\"27027c86-2833-44cb-9124-f7587e8457e3\",\"added_by\":\"auto\",\"created_at\":\"2025-12-31 16:14:08\",\"extension\":\"pdf\",\"order_by\":0,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"manuscript-pdf\",\"size\":4700363,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"manuscript.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/396a67d7-b3ac-4ed9-b4b2-d8ad7b0188d0.pdf\"},{\"id\":94820856,\"identity\":\"05a184e4-21a7-4167-9dac-e160bba2ff04\",\"added_by\":\"auto\",\"created_at\":\"2025-10-31 06:04:01\",\"extension\":\"docx\",\"order_by\":1,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"supplement\",\"size\":21586645,\"visible\":true,\"origin\":\"\",\"legend\":\"Supporting information\",\"description\":\"\",\"filename\":\"Supportinginformation.docx\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-7799184/v1/7e4da89693756a50fadd6ef7.docx\"}],\"financialInterests\":\"There is \\u003cb\\u003eNO\\u003c/b\\u003e Competing Interest.\",\"formattedTitle\":\"Activating Free Volume of Polymeric Aggregates toward Advanced Hard Carbon for Sodium Storage\",\"fulltext\":[{\"header\":\"Introduction\",\"content\":\"\\u003cp\\u003eTechnological expectations for sodium-ion batteries (SIBs) have been sparked by the abundant sodium resources, superior fast-charging capability as well as excellent low-temperature performance, which has made SIBs become promising complement to lithium-ion batteries.\\u003csup\\u003e\\u003cspan citationid=\\\"CR1\\\" class=\\\"CitationRef\\\"\\u003e1\\u003c/span\\u003e\\u003c/sup\\u003e However, the larger atomic size and different ionization behavior of Na\\u003csup\\u003e+\\u003c/sup\\u003e have brought serious challenges for the advancement of SIBs, particularly in the concerns over the high-capacity and durable anodes.\\u003csup\\u003e\\u003cspan additionalcitationids=\\\"CR3\\\" citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR4\\\" class=\\\"CitationRef\\\"\\u003e4\\u003c/span\\u003e\\u003c/sup\\u003e Among the various reported anodes, hard carbon (HC) shows greatly practical prospect owing to the merit of cost-effectiveness, low operating voltage and outstanding Na-storage capacity.\\u003csup\\u003e\\u003cspan citationid=\\\"CR5\\\" class=\\\"CitationRef\\\"\\u003e5\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR6\\\" class=\\\"CitationRef\\\"\\u003e6\\u003c/span\\u003e\\u003c/sup\\u003e Unlike the traditional graphite anode, the active Na-storage sites in HC anodes root in their complex pseudo-graphite domains and internal nanopores structure, leading to a slope region (\\u0026gt;\\u0026thinsp;0.1 V) and a plateau region (\\u0026lt;\\u0026thinsp;0.1 V) in the sodiation voltage profile.\\u003csup\\u003e\\u003cspan citationid=\\\"CR7\\\" class=\\\"CitationRef\\\"\\u003e7\\u003c/span\\u003e\\u003c/sup\\u003e Recently, substantial reports have highlighted the significance of closed pore structure to realize sodium pore-filling process, which can contribute to the low-potential plateau capacity in HC anodes.\\u003csup\\u003e\\u003cspan citationid=\\\"CR8\\\" class=\\\"CitationRef\\\"\\u003e8\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR9\\\" class=\\\"CitationRef\\\"\\u003e9\\u003c/span\\u003e\\u003c/sup\\u003e Obviously, the development of HC anodes with large plateau capacity is imperative to obtain high-energy-density SIBs for practical applications.\\u003c/p\\u003e\\u003cp\\u003eAmong the different precursors to prepare HC anodes, the synthetic polymer precursors possess the merits of high carbon yield, definite molecular constituent as well as excellent structure designability, and tremendous pore engineering strategies have been explored to prepare HC anodes with large plateau capacity \\u003cem\\u003evia\\u003c/em\\u003e regulating the composition of polymer precursors.\\u003csup\\u003e10,\\u003cspan citationid=\\\"CR10\\\" class=\\\"CitationRef\\\"\\u003e11\\u003c/span\\u003e\\u003c/sup\\u003e For instance, a co-interfering chemistry of the phenolic resin precursor have been proposed through introducing coordinated Zn\\u003csup\\u003e2+\\u003c/sup\\u003e cations and organic carboxylate anions, which can promote the curvature of carbon layers and realize the closure of nanopores in resin-derived HCs.\\u003csup\\u003e\\u003cspan citationid=\\\"CR11\\\" class=\\\"CitationRef\\\"\\u003e12\\u003c/span\\u003e\\u003c/sup\\u003e Besides, incorporating pitch coating with pre-oxidized phenolic resin has been developed to increase the disorder degree of pseudo-graphitic phase and enrich closed pore structure during pyrolysis, resulting in an improved plateau capacity of 242.8 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e for the obtained HC anode.\\u003csup\\u003e\\u003cspan citationid=\\\"CR12\\\" class=\\\"CitationRef\\\"\\u003e13\\u003c/span\\u003e\\u003c/sup\\u003e Despite of these great successes, the effect of polymer precursor structure on the formation of closed pores in the as-derived HCs remains unclear. Thereafter, various molecular design strategies have been developed during the polymerization process of polymer precursors to construct abundant closed pores in the HCs.\\u003csup\\u003e\\u003cspan additionalcitationids=\\\"CR15\\\" citationid=\\\"CR13\\\" class=\\\"CitationRef\\\"\\u003e14\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR15\\\" class=\\\"CitationRef\\\"\\u003e16\\u003c/span\\u003e\\u003c/sup\\u003e For example, the introduction of twisted benzene ring \\u003cem\\u003evia\\u003c/em\\u003e polycondensation reaction can greatly enhance the thermal stability of polyimide chains, which effectively suppress the rearrangement of carbon layer and facilitate the closed pore formation during carbonization.\\u003csup\\u003e\\u003cspan citationid=\\\"CR16\\\" class=\\\"CitationRef\\\"\\u003e17\\u003c/span\\u003e\\u003c/sup\\u003e However, the chemically grafted groups in the polymer precursors show notable limitation in controlling the closed pore content and deliver low Na-storage capacity (\\u0026lt;\\u0026thinsp;320 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e). Moreover, the underlying influence of polymeric aggregation on closed pore formation has not been explored.\\u003c/p\\u003e\\u003cp\\u003eGenerally, the polymeric network suffers from the multichain aggregation driven by strong molecular interactions, leading to denser chain packing as well as robust spatial constraints.\\u003csup\\u003e\\u003cspan citationid=\\\"CR17\\\" class=\\\"CitationRef\\\"\\u003e18\\u003c/span\\u003e\\u003c/sup\\u003e According to our previous work, the existence of narrow free volume between neighboring chains in polymer precursor could inhibit the formation of closed pores during the carbonization process.\\u003csup\\u003e\\u003cspan citationid=\\\"CR18\\\" class=\\\"CitationRef\\\"\\u003e19\\u003c/span\\u003e\\u003c/sup\\u003e Thus, activating more free volume in polymeric aggregates in the early molecular structural design may be a promising strategy to construct well-developed micropore structure in the resultant HCs, which has not yet reported in the previous polymer-derived HC anodes. Recently, the incorporation of flexible chain conformation in conjugated polymer showed considerable potentials to tune the polymer aggregation behavior in solution.\\u003csup\\u003e\\u003cspan citationid=\\\"CR19\\\" class=\\\"CitationRef\\\"\\u003e20\\u003c/span\\u003e\\u003c/sup\\u003e The flexible chain segments possess excellent mobility and form the expanded random coils in a good solvent, which can disrupt the molecular packing of polymer aggregates.\\u003csup\\u003e\\u003cspan citationid=\\\"CR20\\\" class=\\\"CitationRef\\\"\\u003e21\\u003c/span\\u003e\\u003c/sup\\u003e Inspired by this observation, a phenolic resin network linked with polyethylene glycol (PEG200, M\\u003csub\\u003en\\u003c/sub\\u003e=200) segments has been designed in this work to activate the free volume of polymeric aggregates and construct abundant closed pores in the as-derived HC anode for SIBs. Driving by hydrogen-bonding interactions, the linked flexible PEG200 chains can spontaneously form crystalline domains during the curing process, which possesses hidden lengths in the cured phenolic network. When undergoing stepwise immersion processes in the ethanol/water solvent, the reduced bonding interactions between the internal PEG200 domains along with the extending of hidden lengths can weaken the aggregated chains, causing greatly increased free volume within the polymer backbones. More free volume can enlarge the gap distance within chain aggregates, which can mitigate pyrolytic cross-linking reactions and inhibit the over-graphitization of carbon layer during the carbonization process, resulting in the formation of well-developed closed pore in the final HC sample. When evaluated as an anode for SIB, the as-obtained HC exhibits a reversible capacity (357.9 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e at 0.1 C) with an enhanced plateau capacity contribution, an improved rate performance as well as excellent cycling stability over 2000 cycles at 4 C. This work inspires the exploration on aggregate chemistry to develop polymer-derived HC anodes with high plateau capacity towards advanced SIBs.\\u003c/p\\u003e\"},{\"header\":\"Results\",\"content\":\"\\u003cdiv id=\\\"Sec3\\\" class=\\\"Section2\\\"\\u003e\\u003ch2\\u003ePreparation and characterization of the PPR aggregates\\u003c/h2\\u003e\\u003cp\\u003eFrom polymer topology perspective, the original phenolic resin network is inevitably entrapped by multistrand aggregation driven by the intramolecular interactions, which could fold or entwin the polymer backbones into dense cluster.\\u003csup\\u003e\\u003cspan citationid=\\\"CR21\\\" class=\\\"CitationRef\\\"\\u003e22\\u003c/span\\u003e\\u003c/sup\\u003e To control their aggregation behavior, the soft PEG200 chains with tunable extensibility are chosen as links to construct a dynamic phenolic resin network (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003ea), which can spontaneously form crystalline domains during the following curing process because of the hydrogen-bonding interactions. Unlike phenolic resin with the rigid polymer backbones, the PEG200 crystalline domains could be flexibly zipped or extended as a transition switch to contribute to the hidden lengths.\\u003csup\\u003e\\u003cspan citationid=\\\"CR22\\\" class=\\\"CitationRef\\\"\\u003e23\\u003c/span\\u003e\\u003c/sup\\u003e To support our hypothesis, flexible PEG200 chain segments were grafted on the phenolic resin backbones (denoted as PPR) through one-step esterification reaction at 60\\u0026deg;C. As illustrated in Supplementary Fig.\\u0026nbsp;1, the generated carboxyl groups during the ring-opening reaction of maleic anhydride can provide extra cross-linking sites and hence induce a further esterification reaction with hydroxyl groups in phenolic resin and PEG200. Then the liquid components were observed to be spontaneously converted into PPR piece, as shown in the optical photographs in Supplementary Fig.\\u0026nbsp;2. For comparison, the cured phenolic resin without PEG200 (denoted as PR) was also prepared under the identical condition.\\u003c/p\\u003e\\u003cp\\u003eFourier transform infrared (FTIR) spectroscopy was firstly employed to verify the crosslinking reaction (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003eb). Compared with the FTIR spectrum of pure phenolic resin, the PPR precursor show an enhanced intensity of -C\\u0026thinsp;=\\u0026thinsp;O group (1719 cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e), indicating maleic anhydride ring-opening followed by the esterification reaction with the hydroxy groups of phenolic resin.\\u003csup\\u003e\\u003cspan citationid=\\\"CR23\\\" class=\\\"CitationRef\\\"\\u003e24\\u003c/span\\u003e\\u003c/sup\\u003e Meanwhile, the emerging -C-O-C- groups (1095 cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e) with signal blueshift can be observed in the PPR precursor when compared with PEG200, demonstrating that the PEG200 chains have been covalently grafted within phenolic resin backbones.\\u003csup\\u003e\\u003cspan citationid=\\\"CR24\\\" class=\\\"CitationRef\\\"\\u003e25\\u003c/span\\u003e\\u003c/sup\\u003e Owing to the excellent miscibility between phenolic resin backbones and PEG200 segments, the PPR precursor shows higher optical transparency than the PR precursor (Supplementary Fig.\\u0026nbsp;3). Besides, arising from the strong plasticization effect of PEG200 chains,\\u003csup\\u003e26\\u003c/sup\\u003e PPR network possesses excellent flexibility, which can be further proved by the mechanical properties analysis in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003ec. Distinguished from the PR precursor, an impressive gelation-like behavior for the PPR precursor can be verified by the tensile modulus down to 0.84 MPa, indicating that PEG200 segments have successfully induce the transition from rigidity to super-soft in phenolic resin aggregates. Furthermore, the breaking strain in PPR experiences an exceptional enhancement over 160%, demonstrating that the dynamic and adaptable slip of PEG crystalline domains can gradually extend the hidden lengths and thus survive large deformation.\\u003csup\\u003e\\u003cspan citationid=\\\"CR26\\\" class=\\\"CitationRef\\\"\\u003e27\\u003c/span\\u003e\\u003c/sup\\u003e Besides, the chains mobility of the PPR aggregates was revealed by glass transition temperature (T\\u003csub\\u003eg\\u003c/sub\\u003e), which can be evaluated from the peaks of loss factor (tan δ) curves through dynamic mechanical analysis (DMA) test (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003ed and Supplementary Fig.\\u0026nbsp;4).\\u003csup\\u003e\\u003cspan citationid=\\\"CR27\\\" class=\\\"CitationRef\\\"\\u003e28\\u003c/span\\u003e\\u003c/sup\\u003e Compared with PR precursor, a lower T\\u003csub\\u003eg\\u003c/sub\\u003e of 28.2\\u0026deg;C in the PPR precursor indicates a less restriction from the intermolecular interactions as well as more mobile molecular chain.\\u003csup\\u003e\\u003cspan citationid=\\\"CR28\\\" class=\\\"CitationRef\\\"\\u003e29\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR29\\\" class=\\\"CitationRef\\\"\\u003e30\\u003c/span\\u003e\\u003c/sup\\u003e The excellent extensibility and mobility for the PPR network with flexible PEG200 segments are favorable for the subsequent solvent immersion process to inhibit the over-aggregation of polymer chains.\\u003c/p\\u003e\\u003cp\\u003e\\u003c/p\\u003e\\u003c/div\\u003e\\n\\u003ch3\\u003eThe weakly aggregated transition of PPR aggregates in solution\\u003c/h3\\u003e\\n\\u003cp\\u003eTo fully exert the hidden length of PEG200 segments in the PPR precursor, PPR underwent stepwise immersion processes in the ethanol and water, respectively. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003ea and Supplementary Fig.\\u0026nbsp;5, the strongly aggregated PPR precursor experiences a significant swelling of 30% after immersed in ethanol. However, PPR precursor experiences obvious shrinkage after the direct volatilization of ethanol (denoted as PPR-S), resulting in the recovery of the strongly aggregated state. To stabilize the swelling-state aggregates, water exchange was employed to induce the phase separation owing to the poor hydrophilicity of phenolic resin backbones,\\u003csup\\u003e28\\u003c/sup\\u003e leading to a color change transition from orange transparent to opaque white. In contrast, a less obvious shape variation can be observed for PR precursor during the water exchange process, indicating that the unique transition behavior could be tuned by interactive network with both hydrophilic and hydrophobic segments (Supplementary Fig.\\u0026nbsp;6). The as-formed PPR aggregates after dual-solvent immersion (denoted as PPR-W) shows no obvious shrinkage of polymer backbones after drying, which can be unexpectedly broken into pieces during falling ball test (Supplementary Fig.\\u0026nbsp;7). The notable brittleness transition symbolizes the absence of energy dissipation within PPR-W aggregates, implying that the dual-solvent immersion process can significantly weaken the multichain aggregation of PPR network.\\u003csup\\u003e\\u003cspan citationid=\\\"CR30\\\" class=\\\"CitationRef\\\"\\u003e31\\u003c/span\\u003e\\u003c/sup\\u003e\\u003c/p\\u003e\\u003cp\\u003eTo further illustrate the above solution-responsive aggregation behavior, the geometrical information of PPR-S and PPR-W aggregates were investigated by small-angle X-ray scattering (SAXS) analysis. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003eb, the significant scatting peak can be attributed to the crystalline domains of PEG200 chains,\\u003csup\\u003e32\\u003c/sup\\u003e which is associated with the change of hidden length. Compared with PPR-S aggregates, the position of scattering peak in PPR-W aggregates experiences a remarkable shift to lower q value and the average inter-domains distance is prominently increased to 27.3 nm from 6.7 nm according to Bragg equation (d\\u0026thinsp;=\\u0026thinsp;2π/q\\u003csub\\u003emax\\u003c/sub\\u003e). The enhanced inter-domains distance indicates that the dual-solvent immersion process enables to weaken interchain interactions to extend hidden length from PEG200 crystalline domains and thus reduces the multichain aggregation. Their different interchain packing was further explored by X-ray diffraction (XRD) patterns (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003ec), in which the broad peaks in the 2θ range of 15\\u0026ndash;25\\u0026deg; illustrate the relative extent of crystallinity. Compared with the PPR-S aggregates, the obviously attenuative peak intensity in PPR-W aggregates demonstrates the destruction of PEG200 crystalline domains and weakly aggregated state in PPR-W network. Notably, the extension of hidden lengths in PEG200 segments can reduce the aggregation, which also affect the spatial configuration of polymeric aggregates.\\u003c/p\\u003e\\u003cp\\u003eThe spatial configuration of PPR-W aggregates was further evaluated from positron annihilation lifetime spectroscopy (PALS), which can effectively reveal the free volume distribution within the polymeric aggregates. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003ed and Supplementary Fig.\\u0026nbsp;8, \\u0026#120591;\\u003csub\\u003e3\\u003c/sub\\u003e stands for the lifetime of triplet spin-state positronium, which could be used to evaluate the free volume and correlate with the average cavity size by the Tao-Eldrup model.\\u003csup\\u003e\\u003cspan citationid=\\\"CR32\\\" class=\\\"CitationRef\\\"\\u003e33\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR33\\\" class=\\\"CitationRef\\\"\\u003e34\\u003c/span\\u003e\\u003c/sup\\u003e Form the fitting results (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003ee and Supplementary Table \\u003cspan refid=\\\"MOESM1\\\" class=\\\"InternalRef\\\"\\u003eS1\\u003c/span\\u003e), PPR-W aggregates possess a longer \\u0026#120591;\\u003csub\\u003e3\\u003c/sub\\u003e lifetime (1.48 ns vs. 1.29 ns) than that of PPR-S aggregates, indicating that the weakly aggregated state can activate more free volume (51.69 \\u0026Aring;\\u003csup\\u003e3\\u003c/sup\\u003e vs. 38.29 \\u0026Aring;\\u003csup\\u003e3\\u003c/sup\\u003e) owing to the extended hidden lengths of PEG segments. The lager space extension can be further verified by mercury intrusion porosimetry (MIP), in which the Hg was used as space occupier to fill the internal void volume. As displayed in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003ef and Supplementary Fig.\\u0026nbsp;9, the PPR-W aggregates exhibit much higher total intrusion volume (0.416 mL g\\u003csup\\u003e\\u0026minus;1\\u003c/sup\\u003e) than that of PPR-S aggregates (0.092 mL g\\u003csup\\u003e\\u0026minus;1\\u003c/sup\\u003e), favoring the enhanced internal void space within PPR-W aggregates. All these results confirm that the change from strongly to weakly aggregated state in solution can realize less ordered molecular packing and activate more internal free volume without sacrificing the network connectivity (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003eg).\\u003c/p\\u003e\\u003cp\\u003e\\u003c/p\\u003e\\n\\u003ch3\\u003eThe role of aggregation behavior in forming closed pore in hard carbon\\u003c/h3\\u003e\\n\\u003cp\\u003eTo explore the effect of polymeric aggregation behavior on the closed pore formation, PPR-S and PPR-W aggregates were calcinated at 1400\\u0026deg;C, and the as-obtained HCs were denoted as PPR-S-1400 and PPR-W-1400, respectively. As shown in Supplementary Fig.\\u0026nbsp;10, the color of both PPR-S and PPR-W changes to black after carbonization process, while the shrinkage degree of edge length from 2.8 cm to 1.8 cm in PPR-W aggregates is obviously larger than PPR-S aggregates. A clear morphological evolution can be further observed in the scanning electron microscopy (SEM). As shown in cross-section SEM images (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003ea and \\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003ec), a typical macropore morphology observed in both PPR-S and PPR-W aggregates can be attributed to the removal of polymer-poor phase within the backbones, which is consistent with the pore distribution of MIP results. When carbonized at 1400\\u0026deg;C, both PPR-S-1400 and PPR-W-1400 experience pores shrinkage and macropore walls growth (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003eb and \\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003ed), but a greater decrement of macropore size can be observed for PPR-W-1400. The different carbonized shrinkage and morphological changes are highly correlated with the different aggregated states of the precursors.\\u003c/p\\u003e\\u003cp\\u003eThe thermogravimetric analysis (TGA) was further employed to investigate the pyrolysis behaviors of PPR-S and PPR-W aggregates. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003ee\\u0026thinsp;~\\u0026thinsp;f, the rapid decomposition of PPR-S and PPR-W aggregates occurred during the calcination process can be divided into three main temperature ranges from the derivative TGA. Specifically, the weight loss in stage I (\\u0026lt;\\u0026thinsp;180\\u0026deg;C) is ascribed to the removal of absorbed water and small molecules. In stage II (180\\u0026thinsp;~\\u0026thinsp;300\\u0026deg;C), the continuous mass loss of PPR-S and PPR-W aggregates can be determined to the decomposition of PEG200 segments according to the TGA curve. However, an extra DTG peaks in PPR-W can be observed at 280\\u0026deg;C compared with PPR-S, indicating that more light fractions can be released in this temperature range for PPR-W. Obviously, activating more free volumes within PPR-W aggregates is beneficial to form a gas channel for releasing volatiles, which can be further verified by FTIR spectra at 300\\u0026deg;C. Compared with PPR-S, the lower intensity of -C\\u0026thinsp;=\\u0026thinsp;O (1720 cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e) and C-O (1191 cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e) linkages can be observed in PPR-W aggregates (Supplementary Fig.\\u0026nbsp;11a), indicating that larger free volumes in PPR-W aggregates can mitigate pyrolytic cross-linking reactions. Such relative sparsity feature allows volatile byproducts to rapidly escape and thus induce the pore formation in the early stages, while strongly aggregated state involves complex cross-linking to densify their backbones. Further increasing carbonization temperature over 300\\u0026deg;C, similar sluggish pyrolytic cross-linking reactions in PPR-W can be proved by the weaker signal of -C\\u0026thinsp;=\\u0026thinsp;O and C-O groups than PPR-S in FTIR spectra at 400\\u0026deg;C (Supplementary Fig.\\u0026nbsp;11b), leading to multi-DTG peaks in stage III. As a result, the carbon yield of PPR-W aggregates from room temperature to 800\\u0026deg;C is 46.32%, lower than that of PPR-S aggregates (53.67%). All these results demonstrate that the weakly aggregated state in PPR-W can activate more free volumes to mitigate pyrolytic reactions and realize the multiple releases of volatile byproducts, which may create abundant micropores in the final HC. N\\u003csub\\u003e2\\u003c/sub\\u003e adsorption and desorption test was conducted to confirm the effect of different pyrolysis behaviors on micropore distribution (Supplementary Fig.\\u0026nbsp;12). Notably, PPR-W-1400 exhibits a larger number of micropores than PPR-S-1400, indicating that the gas channel formed by volatile byproducts can be eventually converted to nanopore structure, which is believed to facilitate the formation of closed pores in PPR-W-1400. High-resolution transmission electron microscopy (HRTEM) has also been used to reveal obvious distinctions in the pore structure for PPR-S-1400 and PPR-W-1400. As displayed in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003eg, the PPR-W-1400 sample possesses abundant closed pores, accompanied by the randomly curved carbon layer with large interlayer spacing (0.411 nm). In contrast, PPR-S-1400 sample is predominantly consisted of long and multilayer graphitic domains, resulting in insufficient closed pores distribution (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig3\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003eh).\\u003c/p\\u003e\\u003cp\\u003e\\u003c/p\\u003e\\u003cp\\u003eMuch improved closed pore structure in PPR-W-1400 can be concretely characterized by the SAXS technique. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003ea, PPR-W-1400 exhibits a broad peak with stronger scattering intensity within the q range of 0.1\\u0026thinsp;~\\u0026thinsp;0.4 \\u0026Aring;\\u003csup\\u003e\\u0026minus;1\\u003c/sup\\u003e, indicative of a higher content of internal closed-pore structure than PPR-S-1400.\\u003csup\\u003e\\u003cspan citationid=\\\"CR34\\\" class=\\\"CitationRef\\\"\\u003e35\\u003c/span\\u003e\\u003c/sup\\u003e Furthermore, the shift of peaks position towards higher q value in PPR-W-1400 signifies a smaller closed pore radius than PPR-S-1400, which can be calculated as 0.36 nm (vs. 0.58 nm PPR-S-1400) by fitting the SAXS data (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003eb and Supplementary Fig.\\u0026nbsp;13). Fortunately, the relatively small closed nanopores can favor improved rate performance owing to weaker metallic state of Na-storage within the plateau region, which have been verified by previously reported works.\\u003csup\\u003e\\u003cspan citationid=\\\"CR35\\\" class=\\\"CitationRef\\\"\\u003e36\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR36\\\" class=\\\"CitationRef\\\"\\u003e37\\u003c/span\\u003e\\u003c/sup\\u003e These findings indicate that the weakly aggregated state of PPR-W-1400 can induce the multiple releases of volatile byproducts to promote the formation of abundant closed pore structure with ultra-small pore size during the carbonization process. The differences in closed pore volume can be evaluated by the true density results, which selectively eliminates open pores and interparticle spaces for the quantification of closed pore volume.\\u003csup\\u003e\\u003cspan citationid=\\\"CR37\\\" class=\\\"CitationRef\\\"\\u003e38\\u003c/span\\u003e\\u003c/sup\\u003e As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003ec, PPR-W-1400 exhibits a higher closed pore volume of 0.065 cm\\u003csup\\u003e3\\u003c/sup\\u003e g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e than PPR-S-1400 (0.041 cm\\u003csup\\u003e3\\u003c/sup\\u003e g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e), indicating the advantage of the weakly aggregated state in construction of closed pore, which can provide efficient Na-storage active sites for enhancing plateau capacity.\\u003c/p\\u003e\\u003cp\\u003eXRD patterns were also employed to evaluate the effect of aggregated state on microcrystalline structure of HC samples. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003ed, PPR-W-1400 and PPR-S-1400 exhibit two broad peaks at ~\\u0026thinsp;23\\u0026deg; and ~\\u0026thinsp;43\\u0026deg;, which can be corresponded to the (002) and (100) crystal planes of graphitic crystallites, respectively.\\u003csup\\u003e\\u003cspan citationid=\\\"CR38\\\" class=\\\"CitationRef\\\"\\u003e39\\u003c/span\\u003e\\u003c/sup\\u003e However, the (002) diffraction peak of PPR-W-1400 show an obvious shift toward lower angle, suggesting that the weakened aggregated state can expand the interlayer distance. Based on the Bragg\\u0026rsquo;s law, the enlarged d\\u003csub\\u003e(002)\\u003c/sub\\u003e value of PPR-W-1400 is calculated to be 0.405 nm (vs. 0.381 nm for PPR-S-1400), which can ensure reversible Na\\u003csup\\u003e+\\u003c/sup\\u003e intercalation/deintercalation as well as fast ion diffusion kinetics. Meanwhile, the aromatic carbon ratio (37.9%) of PPR-W-1400 fitted from (002) peak (Supplementary Fig.\\u0026nbsp;14) is obviously lower than that of PPR-S-1400 (42.3%), suggesting that the weakly aggregated state can inhibit over-graphitization to form turbostratic structure.\\u003csup\\u003e\\u003cspan citationid=\\\"CR39\\\" class=\\\"CitationRef\\\"\\u003e40\\u003c/span\\u003e\\u003c/sup\\u003e Raman spectra offer more structural information for different HC samples. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003ee and Supplementary Fig.\\u0026nbsp;15, both of PPR-W-1400 and PPR-S-1400 exhibit typical D band (1350 cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e) and G band (1595 cm\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e), which are related to defective structure and graphitic domains, respectively.\\u003csup\\u003e\\u003cspan citationid=\\\"CR40\\\" class=\\\"CitationRef\\\"\\u003e41\\u003c/span\\u003e\\u003c/sup\\u003e However, PPR-W-1400 exhibits obvious weakened G band as well as much higher A\\u003csub\\u003eD\\u003c/sub\\u003e/A\\u003csub\\u003eG\\u003c/sub\\u003e value than that of PPR-S-1400, illustrating that more disordered graphitic structures have been generated in PPR-W-1400. All the results demonstrate that the weakly aggregated state can inhibit over aromatization reaction and increase disordered degree, which is in good accordance with HRTEM results.\\u003c/p\\u003e\\u003cp\\u003e\\u003c/p\\u003e\\u003cp\\u003eThe chemical composition of HCs was further analyzed by X-ray photoelectron spectroscopy (XPS), in which both PPR-W-1400 and PPR-S-1400 samples present the mainly component of C and O species (Supplementary Fig.\\u0026nbsp;16a). The C 1s spectra shows three fitted peaks centered at 284.8, 286.2, 288.9 eV, corresponding to C-C, C-O and O-C\\u0026thinsp;=\\u0026thinsp;O, respectively (Supplementary Fig.\\u0026nbsp;16b). Among them, the C-O groups on surface of HCs could cause much irreversible reaction and reduced initial coulombic efficiency, which have been proved in previously reported works.\\u003csup\\u003e\\u003cspan citationid=\\\"CR41\\\" class=\\\"CitationRef\\\"\\u003e42\\u003c/span\\u003e\\u003c/sup\\u003e It is worth noting that the C-O content in PPR-W-1400 is relatively lower than that of PPR-S-1400, indicating that the less aggregated state can diminish the formation of C-O and thus suppress the irreversibility during the Na-storage. Furthermore, the O 1s spectra of PPR-W-1400 (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003ef) also delivers higher O-III (C\\u0026thinsp;=\\u0026thinsp;O) percentage (14.9%) compared to PPR-S-1400 (9.6%), which will be conducive to rapid transportation of Na\\u003csup\\u003e+\\u003c/sup\\u003e and increase the reversibility of Na\\u003csup\\u003e+\\u003c/sup\\u003e adsorption.\\u003csup\\u003e43\\u003c/sup\\u003e Based on the above discussion, the role of polymeric aggregates on the formation of closed pore structures in the resultant HCs can be summarized in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig4\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003eg. Specifically, the larger free volume activated by the weakly aggregated state can realize the multiple releasing of volatile byproducts, which can induce the formation of abundant closed pores. Besides, the weakly aggregated state is benefit to carbonized shrinkage, leading to ultra-small closed pores and large closed pore volume. Furthermore, the polymer with less aggregated state tends to form the turbostratic and disordered microstructure in HC during the carbonization process, accompanied with expanded interlayer spacing and more C═O groups.\\u003c/p\\u003e\\n\\u003ch3\\u003eElectrochemical performance and sodium storage mechanism of hard carbon\\u003c/h3\\u003e\\n\\u003cp\\u003eThe sodium storage performances of as-prepared HCs anodes were evaluated in the half Na-ion cells, with a particularly focus on the effect of weakly aggregated state on plateau capacity. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003ea, the galvanostatic charge-discharge (GCD) curves show typical voltage profile with slope and plateau region, in which PPR-W-1400 delivers an impressive reversible capacity of 357.9 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e at 0.1 C (1C\\u0026thinsp;=\\u0026thinsp;300 mA g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e), much higher than that of 286.5 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e for PPR-S-1400. The analysis on the slope and plateau capacity contributions shows that PPR-W-1400 possesses a large plateau capacity of 259.7 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003eb), much higher than that of PPR-S-1400 (~\\u0026thinsp;203.2 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e). The improved plateau capacity supports the weakly aggregated state is beneficial to the formation of closed pore structure. Meanwhile, the slope capacity increase in PPR-W-1400 can be attributed to the higher -C\\u0026thinsp;=\\u0026thinsp;O content, which allows reversible Na\\u003csup\\u003e+\\u003c/sup\\u003e adsorption to realize higher initial coulombic efficiency (ICE) of 86.8% (vs. 81.8% for PPR-1400).\\u003csup\\u003e\\u003cspan citationid=\\\"CR43\\\" class=\\\"CitationRef\\\"\\u003e44\\u003c/span\\u003e\\u003c/sup\\u003e Furthermore, the PPR-W-1400 anode maintains a higher reversible capacity of 168.9 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e at 5 C (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003ec). This remarkable enhancement stems from the smaller closed pore size in PPR-W-1400, which is benefit to form the minor Na cluster with weaker metallic state and thus facilitates superb Na\\u003csup\\u003e+\\u003c/sup\\u003e transportation.\\u003csup\\u003e14\\u003c/sup\\u003e The cycling stability at 1 C rate shows an impressive capacity retention of 93.1% for PPR-W-1400 after 700 cycles, while PPR-S-1400 anode keeps a capacity retention of 88.2% (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003ed). At a higher current density of 4 C rate, PPR-W-1400 still maintains a higher capacity of 163.2 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e over 2100 cycles (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003ee). In sharp contrast, PPR-S-1400 only delivers a low capacity of 100.5 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e. These results indicate that the expanding interlayer spacing in the PPR-W-1400 can ensure the reversible Na\\u003csup\\u003e+\\u003c/sup\\u003e intercalation pathways during the intensive cycling processes, highlighting the critical role of weak aggregation engineering in achieving durable Na-storage performance.\\u003c/p\\u003e\\u003cp\\u003eTo better reveal the role of aggregated state in modulating the Na-storage behavior, PEG crystalline domains with different hidden lengths were grafted on the polymer precursor. As shown in Supplementary Fig.\\u0026nbsp;17, the phenolic resin grafted with ethylene glycol (EG) or PEG400 (M\\u003csub\\u003en\\u003c/sub\\u003e=400) were also prepared under same treatment condition, which were denoted as PR-EG and PR-PEG400, respectively. All the PR, PR-EG and PR-PEG400 precursors with or without dual-solvent immersion treatment were annealed at 1400\\u0026deg;C. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig5\\\" class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003ef and Supplementary Fig.\\u0026nbsp;18, the resultant HCs derived from the weakly aggregated state by extending the hidden lengths of EG or PEG segments demonstrates an enhanced specific capacity when compared with the corresponding strongly aggregated state. In contrast, the PR-derived HC anode shows no obvious growth of capacity after dual-solvent immersion process. Obviously, the absence of extensible hidden lengths in phenolic resin backbones cannot realize the weakly aggregated transition, as evidenced by SAXS and XRD results (Supplementary Fig.\\u0026nbsp;19\\u0026thinsp;~\\u0026thinsp;20, Supporting Information), as well as impressive Na-storage capacity. Additionally, PPR-W-1400 anode demonstrates higher capacity than those samples grafted with the EG and PEG400. This is because the small molecular size endowed by EG delivers the limited hidden lengths, while the oversize macromolecular chain of PEG400 may cause lower crosslinking degree and excessive carbonized shrinkage. Both of them are not beneficial to release the free volume in the precursor and construct closed pores in the HC sample. Therefore, the rational control of polymeric aggregates can be a promising strategy to modulate the well-developed pore structure of HC, which demonstrates significantly superior Na-storage performance than most of previous reports on resin-derived HC anodes. \\u003csup\\u003e[14\\u0026ndash;16, 45\\u0026ndash;51]\\u003c/sup\\u003e\\u003c/p\\u003e\\u003cp\\u003e\\u003c/p\\u003e\\u003cp\\u003eTo investigate the mechanism of the greatly improved Na-storage capability in the synthesized HC anodes, the in-situ XRD spectra were carried out to analyze the (002) diffraction peak of PPR-W-1400 during the sodiation/de-sodiation process (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003ea). In the sodiation process, no remarkable change can be observed in the range of 2.0\\u0026thinsp;~\\u0026thinsp;0.1 V for (002) peaks, suggesting that the adsorption behavior of Na\\u003csup\\u003e+\\u003c/sup\\u003e or the reaction between the functional groups such as -C\\u0026thinsp;=\\u0026thinsp;O on surface with Na\\u003csup\\u003e+\\u003c/sup\\u003e. With further sodiation goes on, the intensity of (002) peak experiences a gradual decrease from 0.1 to 0.01 V, demonstrating an intercalation chemistry with the formation of Na-C compound.\\u003csup\\u003e\\u003cspan citationid=\\\"CR51\\\" class=\\\"CitationRef\\\"\\u003e52\\u003c/span\\u003e\\u003c/sup\\u003e In the following desodiation process to 2.0 V, the (002) peak can fully return to the original intensity, demonstrating the excellent reversibility and structural stability of PPR-W-1400. More importantly, no obvious change of the (002) peak position can be observed for PPR-W-1400 sample during the whole charge/discharge process, whereas the PPR-S-1400 exhibits a significant leftward shift (Supplementary Fig.\\u0026nbsp;21). These results indicate that the (002) plane in PPR-W-1400 sample has enough layer spacing (0.405 nm) to accommodate Na\\u003csup\\u003e+\\u003c/sup\\u003e, which can avoid expansion of carbon layer and enable the PPR-W-1400 to deliver impressive cycle stability at large current density. To further visualize the formation of pore-filling process, the ethanol solution containing 1% phenolphthalein was used to rinse the PPR-W-1400 electrode at different potentials. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003eb, a distinctive purplish-red and deepening color change can be observed in the phenolphthalein solution for PPR-W-1400 when the voltage discharged from 0.5 to 0.01 V, which verifies the formation of quasi-metallic Na inside the closed pores.\\u003csup\\u003e\\u003cspan citationid=\\\"CR52\\\" class=\\\"CitationRef\\\"\\u003e53\\u003c/span\\u003e\\u003c/sup\\u003e Moreover, the color of phenolphthalein solution becomes lighter in the following charged state of 0.5 V, further demonstrating the excellent reversibility of Na storage in PPR-W-1400 sample, which is consistent with the in-situ XRD result.\\u003c/p\\u003e\\u003cp\\u003eTo explore the reason for the impressively enhanced rate performances, the galvanostatic intermittent titration technique (GITT) was performed for PPR-W-1400 and PPR-S-1400 anodes. As shown in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003ec and Supplementary Fig.\\u0026nbsp;22, all of the Na\\u003csup\\u003e+\\u003c/sup\\u003e diffusion coefficients (D\\u003csub\\u003eNa\\u003c/sub\\u003e\\u003csup\\u003e+\\u003c/sup\\u003e) values show no significant change in the slope region, and then turn to \\u0026ldquo;U\\u0026rdquo; shape in the plateau region during the sodiation/de-sodiation process.\\u003csup\\u003e\\u003cspan citationid=\\\"CR53\\\" class=\\\"CitationRef\\\"\\u003e54\\u003c/span\\u003e\\u003c/sup\\u003e Nonetheless, it can be clearly observed that PPR-W-1400 exhibits a higher D\\u003csub\\u003eNa\\u003c/sub\\u003e\\u003csup\\u003e+\\u003c/sup\\u003e than PPR-S-1400 in the range of 0.01\\u0026thinsp;~\\u0026thinsp;0.1 V, which could be attributed to the unique pore structure with ultra-small closed pore size in PPR-W-1400. The faster Na\\u003csup\\u003e+\\u003c/sup\\u003e transfer kinetics in PPR-W-1400 can guarantee the high retention of plateau capacity when increasing to larger current density. Meanwhile, the PPR-W-1400 also displays a much smaller charge-transfer impedance (R\\u003csub\\u003ect\\u003c/sub\\u003e) than that of PPR-S-1400 (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003ed). These results illustrate that larger interlayer spacing in PPR-W-1400 are beneficial to high reaction kinetics for fast charge transfer, accounting well for the better rate performance.\\u003c/p\\u003e\\u003cp\\u003eEncouraged by the superior electrochemical performances of PPR-W-1400 anode in the half cell, the full batteries were further assembled with the commercial Na\\u003csub\\u003e3\\u003c/sub\\u003eV\\u003csub\\u003e2\\u003c/sub\\u003e(PO\\u003csub\\u003e4\\u003c/sub\\u003e)\\u003csub\\u003e3\\u003c/sub\\u003e (NVP) cathode (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003ee and Supplementary Fig.\\u0026nbsp;23). The full cell can exhibit reversible capacity of 336.6, 274.8, 249.3, 230.8 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e (based on the mass of active anode materials) at 0.1, 0.7, 2 and 4 C rates, respectively (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003ef). In addition, the capacity retention rate of full cell is 85.4% over 100 cycles at 4 C (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig6\\\" class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003eg), demonstrating the potential of PPR-W-1400 for constructing high-performance energy storage devices.\\u003c/p\\u003e\\u003cp\\u003e\\u003c/p\\u003e\"},{\"header\":\"Discussion\",\"content\":\"\\u003cp\\u003eIn summary, a phenolic resin network linked with flexible chain conformation has been proposed to weaken the polymeric aggregates to prepare high-performance polymer-derived HCs for the first time. The extension of crystalline domains in PEG segments can drive the transition from a strongly to weakly aggregated state during the stepwise immersion process, resulting in increasing the free volume within the phenolic resin network. More free volumes can mitigate pyrolytic cross-linking reactions and realize the multiple releasing of volatile byproducts, ultimately promoting the formation of abundant closed pores during carbonization process. As a result, the as-prepared HC anode exhibited a high plateau capacity of 259.7 mAh g\\u003csup\\u003e-1\\u003c/sup\\u003e at 0.1C, improved rate performance (168.9 mAh g\\u003csup\\u003e-1\\u003c/sup\\u003e at 5C) as well as superior cycling stability over 2100 cycles at 4C. Our work offers a new perspective on polymer aggregation topology to construct closed pore structure in the polymer-derived HC for high-performance SIBs.\\u003c/p\\u003e\"},{\"header\":\"Methods\",\"content\":\"\\u003cp\\u003e\\u003cstrong\\u003eMaterials\\u0026nbsp;\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eAll the materials were purchased from commercial sources and used without further purification. Phenol-formaldehyde resin (Water solubility, Macklin, solid content ~70 %), Polyethylene glycol (PEG) (Aladdin, M\\u003csub\\u003ew\\u003c/sub\\u003e=200 \\u0026amp; 400), Ethylene glycol (EG) (Macklin, 99 %), Maleic anhydride (Macklin, 99 %).\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFabrication of the hard carbon samples\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003e1.31 g of phenolic resin liquid was mixed with 1.22 mL PEG200, then 0.3 g maleic anhydride were added to the mixture. Next, the solution was diluted with deionized water to 5 mL of total volume followed by continuous stirring to form homogeneous solution. The mixed solution was poured into block-like silicon mold sealed with cling film and cured at 60 \\u0026deg;C for 14 h. Then, the solidified block was obtained and denoted as PPR precursor by removing mold. The PPR precursor was sequentially immersed with ethanol solvent for 2 days and water solvent for 2 days, and dried at 60 \\u0026deg;C to obtain a pink white block of final PPR-W aggregates, while the PPR precursor with only ethanol immersion was noted as PPR-W aggregates. The precursors were directly carbonized at 1400 \\u0026deg;C for 1 h in a tube furnace under argon flow with a temperature rate of 2 \\u0026deg;C/min, where the obtained hard carbons derived from PPR-W and PPR-S were denoted as PPR-W-1400 and PPR-S-1400, respectively.\\u003c/p\\u003e\\n\\u003cp\\u003eFor comparison, the cured phenolic resin without PEG200, with EG and with PEG400 under identical preparation process was noted as PR-W/S-1400, PR-EG-W/S-1400 and PR-PEG400-W/S-1400, respectively.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eMaterials Characterization\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eFourier transform infrared (FTIR) spectra were recorded using Thermo Nicolet IS5. Small-angle X-ray scattering (SAXS) was carried out by a Xenocs Xeuss 2.0 with a Cu-K\\u0026alpha; source. Positron annihilation lifetime spectroscopy (PALS) was recorded by AMETEK PLS-SYSTEM. Tensile properties were determined using an CL-200 N electronic universal testing machine at the cross-head speed of 50 mm/min. The storage modulus (E\\u0026apos;), loss modulus (E\\u0026quot;), and loss factor (tan \\u0026delta;) of precursors were determined using DMA (TA DMA850, USA) in compression mode (temperature range: 25~120 \\u0026deg;C; heating rate:2\\u0026deg;C min\\u003csup\\u003e-1\\u003c/sup\\u003e; frequency:1Hz). The character structural information of the samples was analyzed by X-ray diffraction analyzer (XRD, Bruker D8 advanced, Cu, K\\u0026alpha;, \\u0026lambda;=1.5418\\u0026nbsp;\\u0026Aring;) and Raman spectrometer (LabRam HR Evolution). Specific surface area was tested by N\\u003csub\\u003e2\\u003c/sub\\u003e adsorption-desorption (Micromeritics ASAP 2460). The pore volume was tested by mercury intrusion porosimetry (MIP, Micromeritics AutoPore9605). The true densities of hard carbon samples were measured via helium gas pycnometry with the Micromeritics AccuPyc II 1340. The pyrolysis behavior of precursors was acquired on Thermogravimetric analysis (TGA, Perkin Elmer STA6000). The morphology of the samples was observed by Transmission electron microscope (TEM, JEM-2100Plus) and Scanning electron microscope (SEM, Hitachi SU8010). The composition of the sample surface was characterized by X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha). In-situ XRD was carried out during charge/discharge cycle using in-situ cell (LIB-XRD, Beijing Scistar Technology Co. Ltd, China).\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eElectrochemical Measurements\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eCR2032 coin cells were assembled in an Ar-filled glove box (H\\u003csub\\u003e2\\u003c/sub\\u003eO, O\\u003csub\\u003e2\\u003c/sub\\u003e \\u0026lt; 0.01 ppm) for testing the electrochemical performance of samples. Hard carbon powder (80%), acetylene black (10%) and sodium alginate (10 wt%) were ground by adding the proper amount of H\\u003csub\\u003e2\\u003c/sub\\u003eO to form a homogeneous slurry. And the slurry was coated on the Cu foil and dried at 80 \\u0026deg;C for 12 h in a vacuum oven. The obtained working electrode was cut into 13 mm disks with a mass loading of 1.5~2 mg/cm\\u003csup\\u003e2\\u003c/sup\\u003e. For half-cells, CR2032 coin cells were assembled using hard carbon anode as working electrode, Na disk as a counter electrode and glass fiber (Whatman) as separator. 1 M NaPF\\u003csub\\u003e6\\u003c/sub\\u003e in DIGLYME=100 Vol% (DoDochem) was used as ether-based electrolyte. The half-cells were tested within the voltage range of 0.002-2 V. For full-cells, Na\\u003csub\\u003e3\\u003c/sub\\u003eV\\u003csub\\u003e2\\u003c/sub\\u003e(PO\\u003csub\\u003e4\\u003c/sub\\u003e)\\u003csub\\u003e3\\u003c/sub\\u003e (NVP, Shenzhen Kejing), acetylene black and polytetrafuoroethylene (PVDF) were mixed with the ratio of 8:1:1, and the mass loading of cathode disks with a diameter of 10 mm was 7~8 mg/cm\\u003csup\\u003e2\\u003c/sup\\u003e. The capacity ratio of anode/cathode was 1.1/1. 1 M NaPF\\u003csub\\u003e6\\u003c/sub\\u003e in DIGLYME=100 Vol% as electrolyte. Before assembling PPR-W-1400//NVP full-cell, PPR-W-1400 anode was precycled for 5 cycles at 0.1 C in the half-cells. The full-cells were tested within the voltage range of 3.8-2 V. Galvanostatic charge-discharge and galvanostatic intermittent titration technique (GITT) tests were carried out on LAND2001CT battery testing system. The diffusion coefficient of Na\\u003csup\\u003e+\\u003c/sup\\u003e (D\\u003csub\\u003eNa\\u003c/sub\\u003e\\u003csup\\u003e+\\u003c/sup\\u003e) at PPR-W-1400 and PPR-S-1400 electrode can be calculated based on Fick\\u0026apos;s second law from GITT results. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed on electrochemical workstation (CHI660a, Shanghai Chenhua).\\u0026nbsp;\\u003c/p\\u003e\"},{\"header\":\"Declarations\",\"content\":\"\\u003cp\\u003e\\u003cstrong\\u003eAcknowledgements\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (52322406, 52264035), the Natural Science Foundation of Guangdong Province, China (2024A1515010827) and the Double Thousand Plan in Jiangxi Province (jxsq2023101061).\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eAuthor contributions\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eJ.L. and X.X. conducted the experiments and designed the project and wrote the manuscript. Z.L., Y.L. and B.Z. J.W. analyzed the results.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eCompeting interests\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe authors declare no competing interests.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eAdditional information\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eSupplementary information\\u003c/strong\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003eThe online version contains supplementary material available from the author.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eCorrespondence\\u003c/strong\\u003e and requests for materials should be addressed to Xunhui Xiong.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eData availability\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe data that support the findings of this study are available within the article and its Supplementary Information files. All other relevant data supporting the findings of this study are available from the corresponding authors upon reasonable request.\\u003c/p\\u003e\"},{\"header\":\"References\",\"content\":\"\\u003col\\u003e\\n\\u003cli\\u003eNayak, P. K., Yang, L., Brehm, W. \\u0026amp; Adelhelm, P. From Lithium-ion to sodium-ion batteries: advantages, challenges, and surprises. \\u003cem\\u003eAngew. Chem. Int. Ed.\\u003c/em\\u003e \\u003cstrong\\u003e57\\u003c/strong\\u003e, 102-120 (2018).\\u003c/li\\u003e\\n\\u003cli\\u003eFang, Z. et al. Root-growth-inspired self-morphology-evolution of microsized bismuth surrounded by microsized hard carbon for stabilized sodium-ion storage. \\u003cem\\u003eAdv. Mater.\\u003c/em\\u003e \\u003cstrong\\u003e37\\u003c/strong\\u003e, 2412636 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eMa, X. et al. General and scalable fabrication of core-shell metal sulfides@C anchored on 3D N-doped foam toward flexible sodium ion batteries. \\u003cem\\u003eSmall\\u003c/em\\u003e \\u003cstrong\\u003e15\\u003c/strong\\u003e, 1903259 (2019).\\u003c/li\\u003e\\n\\u003cli\\u003eSi, W. et al. Hollow structured medium entropy transition metal selenide CoNiFe-Se@NC enables high performance of sodium-ion batteries. \\u003cem\\u003eGreen Chem.\\u003c/em\\u003e \\u003cstrong\\u003e27\\u003c/strong\\u003e, 2150-2159 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003ePei, B. et al. Hard carbon for sodium-ion batteries: from fundamental research to practical applications. \\u003cem\\u003eAdv. Mater.\\u003c/em\\u003e 2504574 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eYang, Y. et al. Recent advances of high-rate hard carbon anodes for sodium-ion batteries: correlations between performance and microstructure. \\u003cem\\u003eAdv. Funct. Mater.\\u003c/em\\u003e e14132 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eKitsu Iglesias, L. et al. Microstructure-dependent sodium storage mechanisms in hard carbon anodes. \\u003cem\\u003eSmall\\u003c/em\\u003e \\u003cstrong\\u003e21\\u003c/strong\\u003e, 2505561 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eJian, W. et al. Elucidation of the sodium-ion storage behaviors in hard carbon anodes through pore architecture engineering. \\u003cem\\u003eACS Nano\\u003c/em\\u003e \\u003cstrong\\u003e19\\u003c/strong\\u003e, 22201-22216 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eZhang, Y. et al. Redefining closed pores in carbons by solvation structures for enhanced sodium storage. \\u003cem\\u003eNat. Commun.\\u003c/em\\u003e \\u003cstrong\\u003e16\\u003c/strong\\u003e, 3634 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eLiu, J. et al. Boosting sodium-ion storage in hard carbon via polyethylene glycol cross-linked phenolic resin. \\u003cem\\u003eElectrochim. Acta\\u003c/em\\u003e \\u003cstrong\\u003e535\\u003c/strong\\u003e, 146572 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eCheng, M.-G. et al. Preparation of enriched closed-pores hard carbon for high-Performance sodium-ion batteries by the poly(vinyl butyral) template method. \\u003cem\\u003eACS Appl. Energy Mater.\\u003c/em\\u003e \\u003cstrong\\u003e7\\u003c/strong\\u003e, 3452-3461 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eHou, Z. et al. Expediting sodium energy of hard carbon by cation/anion co-interfering chemistry. \\u003cem\\u003eAdv. Funct. Mater.\\u003c/em\\u003e \\u003cstrong\\u003e35\\u003c/strong\\u003e, 2505468 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eXiao, S. et al. Insight into the role of closed-rore size on rate capability of hard carbon for fast-charging sodium-ion batteries. \\u003cem\\u003eAdv. Mater.\\u003c/em\\u003e \\u003cstrong\\u003e37\\u003c/strong\\u003e, 2501434 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eZhao, Y. et al. Closed-pore hard carbon nanospheres via aldol condensation for sodium storage. \\u003cem\\u003eACS Appl. Nano Mater.\\u003c/em\\u003e \\u003cstrong\\u003e8\\u003c/strong\\u003e, 2785-2796 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eZhang, X. et al. Molecular engineering to regulate the pseudo-graphitic structure of hard carbon for superior sodium energy storage. \\u003cem\\u003eSmall\\u003c/em\\u003e \\u003cstrong\\u003e20\\u003c/strong\\u003e, 2311778 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eZhou, H. et al. Microstructure regulation of resin-based hard carbons via esterification cross-linking for high-performance sodium-ion batteries. \\u003cem\\u003eInorg. Chem. Front.\\u003c/em\\u003e \\u003cstrong\\u003e10\\u003c/strong\\u003e, 2404-2413 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003eNie, F. et al. \\u0026ldquo;Spatial twist engineering\\u0026rdquo;: breathing new life into polyimide-derived hard carbon for high-performance sodium-ion batteries. \\u003cem\\u003eJ. Energy Chem.\\u003c/em\\u003e \\u003cstrong\\u003e111\\u003c/strong\\u003e, 383-392, (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eZhang, Z. et al. NIR clusteroluminescence of non-conjugated phenolic resins enabled by through-space interactions. \\u003cem\\u003eAngew. Chem. Int. Ed.\\u003c/em\\u003e \\u003cstrong\\u003e62\\u003c/strong\\u003e, e202306762 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003eLin, J. et al. Steric hindrance engineering to modulate the closed pores formation of polymer-derived hard carbon for high-performance sodium-ion batteries. \\u003cem\\u003eAngew. Chem. Int. Ed.\\u003c/em\\u003e \\u003cstrong\\u003e63\\u003c/strong\\u003e, e202409906 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eXiong, M. et al. Efficient n-doping of polymeric semiconductors through controlling the dynamics of solution-state polymer aggregates. \\u003cem\\u003eAngew. Chem. Int. Ed.\\u003c/em\\u003e \\u003cstrong\\u003e60\\u003c/strong\\u003e, 8189-8197 (2021).\\u003c/li\\u003e\\n\\u003cli\\u003eWang, C. J. et al. Bottlebrush hydrogels with hidden length: super-swelling and mechanically robust. \\u003cem\\u003eAdv. Funct. Mater.\\u003c/em\\u003e \\u003cstrong\\u003e34\\u003c/strong\\u003e, 2410905 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eCui, K. et al. Phase Separation behavior in tough and self-healing polyampholyte hydrogels. \\u003cem\\u003eMacromolecules\\u003c/em\\u003e \\u003cstrong\\u003e53\\u003c/strong\\u003e, 5116-5126 (2020).\\u003c/li\\u003e\\n\\u003cli\\u003eYang, Y., Ru, Y., Zhao, T. \\u0026amp; Liu, M. Bioinspired multiphase composite gel materials: from controlled micro-phase separation to multiple functionalities. \\u003cem\\u003eChem\\u003c/em\\u003e \\u003cstrong\\u003e9\\u003c/strong\\u003e, 3113-3137 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003eXue, B. et al. Strong, tough, rapid-recovery, and fatigue-resistant hydrogels made of picot peptide fibres. \\u003cem\\u003eNat. Commun.\\u003c/em\\u003e \\u003cstrong\\u003e14\\u003c/strong\\u003e, 2583 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003eCavusoglu, J. \\u0026amp; \\u0026Ccedil;aylı, G. Polymerization reactions of epoxidized soybean oil and maleate esters of oil-soluble resoles. \\u003cem\\u003eJ. Appl. Polym. Sci.\\u003c/em\\u003e 132, 41457 (2015).\\u003c/li\\u003e\\n\\u003cli\\u003eLiu, J., Chen, R., Wang, C., Zhao, Y. \\u0026amp; Chu, F. Synthesis and characterization of polyethylene glycol-phenol-formaldehyde based polyurethane composite. \\u003cem\\u003eSci. Rep.\\u003c/em\\u003e \\u003cstrong\\u003e9\\u003c/strong\\u003e, 19545 (2019).\\u003c/li\\u003e\\n\\u003cli\\u003eSheng, Y. et al. Engineering water-stiffening polymers via PEG-sidechain-mediated microphase separation. \\u003cem\\u003eAdv. Funct. Mater.\\u003c/em\\u003e \\u003cstrong\\u003e34\\u003c/strong\\u003e, 2401999 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eXu, L., Qiao, Y. \\u0026amp; Qiu, D. Coordinatively stiffen and toughen hydrogels with adaptable crystal-domain cross-linking. \\u003cem\\u003eAdv. Mater.\\u003c/em\\u003e \\u003cstrong\\u003e35\\u003c/strong\\u003e, 2209913 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003eYang, Z. et al. Robust liquid crystal semi-interpenetrating polymer network with superior energy-dissipation performance. \\u003cem\\u003eNat. Commun.\\u003c/em\\u003e \\u003cstrong\\u003e15\\u003c/strong\\u003e, 9902 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eCheng, J. et al. Sterically hindered organogels with self-healing, impact response, and high damping properties. \\u003cem\\u003eAdv. Mater.\\u003c/em\\u003e \\u003cstrong\\u003e36\\u003c/strong\\u003e, 2411700 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eLi, E. et al. Tailoring the gating effect of organic cage via a porous liquid approach. \\u003cem\\u003eAdv. Funct. Mater.\\u003c/em\\u003e \\u003cstrong\\u003e35\\u003c/strong\\u003e, 2413668 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eXu, W. et al. Optimization of the thermally conductive low-k polymer dielectrics based on multisource free-volume effects. \\u003cem\\u003eACS Appl. Mater. Interfaces\\u003c/em\\u003e \\u003cstrong\\u003e16\\u003c/strong\\u003e, 16809-16819 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eLi, Y. et al. Regulating pore structure of hierarchical porous waste cork-derived hard carbon anode for enhanced Na storage performance. \\u003cem\\u003eAdv. Energy Mater.\\u003c/em\\u003e \\u003cstrong\\u003e9\\u003c/strong\\u003e, 1902852 (2019).\\u003c/li\\u003e\\n\\u003cli\\u003eLi, Y. et al. Origin of fast charging in hard carbon anodes. \\u003cem\\u003eNat. Energy\\u003c/em\\u003e \\u003cstrong\\u003e9\\u003c/strong\\u003e, 134-142 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eHuang, J. et al. Fabrication of lignin-derived high-rate hard carbon anodes for sodium-ion batteries. \\u003cem\\u003eChem. Eng. Sci.\\u003c/em\\u003e \\u003cstrong\\u003e319\\u003c/strong\\u003e, 122343 (2026).\\u003c/li\\u003e\\n\\u003cli\\u003eTang, Z. et al. Revealing the closed pore formation of waste wood-derived hard carbon for advanced sodium-ion battery. \\u003cem\\u003eNat. Commun.\\u003c/em\\u003e \\u003cstrong\\u003e14\\u003c/strong\\u003e, 6024 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003eHuang, Y. et al. Reconfiguring terminal species of bituminous coal to steer hard carbon toward high-capacity and fast sodium storage. \\u003cem\\u003eAngew. Chem. Int. Ed.\\u003c/em\\u003e \\u003cstrong\\u003e64\\u003c/strong\\u003e, e202423864 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eXue, Y. et al. Substitution index-prediction rules for low-potential plateau of hard carbon anodes in sodium-ion batteries. \\u003cem\\u003eAdv. Mater.\\u003c/em\\u003e \\u003cstrong\\u003e37\\u003c/strong\\u003e, 2417886 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eCui, J. et al. Repair surface defects on biomass derived hard carbon anodes with N-doped soft carbon to boost performance for sodium-ion batteries. \\u003cem\\u003eAdv. Energy Mater.\\u003c/em\\u003e \\u003cstrong\\u003e15\\u003c/strong\\u003e, 2502082 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eXie, F. et al. Screening heteroatom configurations for reversible sloping capacity promises high-power Na-ion batteries. \\u003cem\\u003eAngew. Chem. Int. Ed.\\u003c/em\\u003e \\u003cstrong\\u003e61\\u003c/strong\\u003e, e202116394 (2022).\\u003c/li\\u003e\\n\\u003cli\\u003eLiu, Y. et al. Molecular engineering of pore structure/interfacial functional groups toward hard carbon anode in sodium-ion batteries. \\u003cem\\u003eEnergy Storage Mater.\\u003c/em\\u003e \\u003cstrong\\u003e75\\u003c/strong\\u003e, 104008 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eZheng, J. et al. Unveiling the microscopic origin of irreversible capacity loss of hard carbon for sodium-ion batteries. \\u003cem\\u003eAdv. Energy Mater.\\u003c/em\\u003e \\u003cstrong\\u003e14\\u003c/strong\\u003e, 2303584 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eXiao, S. et al. Insight into the role of closed-pore size on rate capability of hard carbon for fast-charging sodium-ion batteries. \\u003cem\\u003eAdv. Mater.\\u003c/em\\u003e \\u003cstrong\\u003e37\\u003c/strong\\u003e, 2501434 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eSun, D. et al. Rationally regulating closed pore structures by pitch coating to boost sodium storage performance of hard carbon in low-voltage platforms. \\u003cem\\u003eAdv. Funct. Mater.\\u003c/em\\u003e \\u003cstrong\\u003e34\\u003c/strong\\u003e, 2403642 (2024).\\u003c/li\\u003e\\n\\u003cli\\u003eXu, R. et al. Hard carbon anodes derived from phenolic resin/sucrose cross-linking network for high-performance sodium-ion batteries. \\u003cem\\u003eBattery Energy\\u003c/em\\u003e \\u003cstrong\\u003e2\\u003c/strong\\u003e, 20220054 (2023).\\u003c/li\\u003e\\n\\u003cli\\u003eZhang, G. et al. Tailoring a phenolic resin precursor by facile pre-oxidation tactics to realize a high-initial-coulombic-efficiency hard carbon anode for sodium-ion batteries. \\u003cem\\u003eACS Appl. Mater. Interfaces\\u003c/em\\u003e \\u003cstrong\\u003e13\\u003c/strong\\u003e, 31650-31659 (2021).\\u003c/li\\u003e\\n\\u003cli\\u003eChen, Z. et al. Polymer-based hard carbons with enhanced initial coulombic efficiency for practical sodium storage. \\u003cem\\u003eInd. Eng. Chem. Res.\\u003c/em\\u003e \\u003cstrong\\u003e64\\u003c/strong\\u003e, 7349-7359 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eGuo, L. et al. Spatial configuration engineering of phenolic resins to tune the closed pores of hard carbon for enhanced plateau-capacity sodium storage. \\u003cem\\u003eChem. Eng. J.\\u003c/em\\u003e \\u003cstrong\\u003e512\\u003c/strong\\u003e, 162478 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eMa, Q. et al. Research on the controlled synthesis of phenolic resin-based carbon microspheres and their sodium storage behavior. \\u003cem\\u003eChemistrySelect\\u003c/em\\u003e \\u003cstrong\\u003e10\\u003c/strong\\u003e, e202500414 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eLi, X. et al. C60 to Modulate the closed pore structures of hard carbon for high-performance Sodium-ion batteries. \\u003cem\\u003eACS Nano\\u003c/em\\u003e \\u003cstrong\\u003e19\\u003c/strong\\u003e, 14829-14838 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eWang, Y. et al. Lowering energy barriers of free radicals facilitates defect-suppressed carbon layers of hard carbon. \\u003cem\\u003eSmall\\u003c/em\\u003e \\u003cstrong\\u003e36\\u003c/strong\\u003e, e06923 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eEren, E. O. et al. An enhanced three-stage model for sodium storage in hard carbons. \\u003cem\\u003eEnergy Environ. Sci.\\u003c/em\\u003e \\u003cstrong\\u003e18\\u003c/strong\\u003e, 7859-7868 (2025).\\u003c/li\\u003e\\n\\u003cli\\u003eFu, W. et al. Constructing accessible closed nanopores in coal-derived hard carbon for sodium-ion batteries. \\u003cem\\u003eSmall\\u003c/em\\u003e \\u003cstrong\\u003e21\\u003c/strong\\u003e, 2411376 (2025).\\u003c/li\\u003e\\n\\u003c/ol\\u003e\"}],\"fulltextSource\":\"\",\"fullText\":\"\",\"funders\":[],\"hasAdminPriorityOnWorkflow\":false,\"hasManuscriptDocX\":true,\"hasOptedInToPreprint\":true,\"hasPassedJournalQc\":\"\",\"hasAnyPriority\":true,\"hideJournal\":true,\"highlight\":\"\",\"institution\":\"\",\"isAcceptedByJournal\":false,\"isAuthorSuppliedPdf\":false,\"isDeskRejected\":\"\",\"isHiddenFromSearch\":false,\"isInQc\":false,\"isInWorkflow\":false,\"isPdf\":false,\"isPdfUpToDate\":true,\"isWithdrawnOrRetracted\":false,\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"researchsquare\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":true,\"externalIdentity\":\"\",\"sideBox\":\"\",\"snPcode\":\"\",\"submissionUrl\":\"/submission\",\"title\":\"Research Square\",\"twitterHandle\":\"researchsquare\",\"acdcEnabled\":true,\"dfaEnabled\":false,\"editorialSystem\":\"\",\"reportingPortfolio\":\"\",\"inReviewEnabled\":false,\"inReviewRevisionsEnabled\":true},\"keywords\":\"free volume, aggregate chemistry, hard carbon, closed pores, sodium-ion batteries\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-7799184/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-7799184/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"\\u003cp\\u003eConstructing closed pore structure through precursor modification has been regarded as an effective route for boosting plateau capacity in hard carbon (HC) anodes for sodium-ion batteries (SIBs). However, the mechanistic role of polymer aggregation behavior in the closed pore formation in polymer-derived HCs remains poorly understood. Herein, flexible chain conformation has been incorporated into phenolic resin network to weaken the aggregated state and promote closed pores formation in the polymer-derived HC for the first time. During the stepwise immersion in an ethanol/water solvent, the extension of crystalline domains in polyethylene glycol segments can reduce the multichain aggregation as well as activate more free volumes within the polymer backbone. More free volumes can mitigate pyrolytic cross-linking reactions and facilitate the multiple releasing of volatile byproducts, which construct plentiful closed pore structure with ultra-small pore size during pyrolysis. As a result, the as-obtained HC anode demonstrates a high reversible capacity (357.9 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e at 0.1 C), enhanced rate performance (168.9 mAh g\\u003csup\\u003e\\u0026minus;\\u0026thinsp;1\\u003c/sup\\u003e at 5 C) as well as excellent cycling stability over 2000 cycles at 4 C. This work provides a valuable insight into aggregate chemistry toward the development of high-performance HC anodes for advanced SIBs.\\u003c/p\\u003e\",\"manuscriptTitle\":\"Activating Free Volume of Polymeric Aggregates toward Advanced Hard Carbon for Sodium Storage\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2025-10-31 06:03:56\",\"doi\":\"10.21203/rs.3.rs-7799184/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"researchsquare\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":true,\"externalIdentity\":\"\",\"sideBox\":\"\",\"snPcode\":\"\",\"submissionUrl\":\"/submission\",\"title\":\"Research Square\",\"twitterHandle\":\"researchsquare\",\"acdcEnabled\":true,\"dfaEnabled\":false,\"editorialSystem\":\"\",\"reportingPortfolio\":\"\",\"inReviewEnabled\":false,\"inReviewRevisionsEnabled\":true}}],\"origin\":\"\",\"ownerIdentity\":\"58a73d65-39be-4761-92db-f6d4a7994766\",\"owner\":[],\"postedDate\":\"October 31st, 2025\",\"published\":true,\"recentEditorialEvents\":[],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"posted\",\"subjectAreas\":[{\"id\":57120456,\"name\":\"Physical sciences/Energy science and technology/Energy storage/Batteries\"},{\"id\":57120457,\"name\":\"Physical sciences/Chemistry/Electrochemistry/Batteries\"},{\"id\":57120458,\"name\":\"Physical sciences/Materials science/Materials for energy and catalysis/Batteries\"}],\"tags\":[],\"updatedAt\":\"2025-12-24T11:05:14+00:00\",\"versionOfRecord\":[],\"versionCreatedAt\":\"2025-10-31 06:03:56\",\"video\":\"\",\"vorDoi\":\"\",\"vorDoiUrl\":\"\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-7799184\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-7799184\",\"identity\":\"rs-7799184\",\"version\":[\"v1\"]},\"buildId\":\"8U1c8b4HqxoKbykW_rLl7\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}