Achieving over 200 Wh kg-1 Sodium-Ion Pouch Cell by Quantitative Engineering of Hard Carbon Pores

Achieving over 200 Wh kg-1 Sodium-Ion Pouch Cell by Quantitative Engineering of Hard Carbon Pores | 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 Achieving over 200 Wh kg-1 Sodium-Ion Pouch Cell by Quantitative Engineering of Hard Carbon Pores Yan Yu, Zhihao Chen, Jialong Shen, Wenjie Deng, Yingshan Huang, and 10 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6761243/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 Energy-dense sodium-ion batteries (SIBs) offer lithium-free, cost-effective solutions for grid-scale energy storage. However, the structural complexity of hard carbon (HC) anodes hinders the establishment of a clear structure-performance relationship, leading current HC exhibit insufficient performance when paired with advanced cathodes. In this study, we precisely adjusted the content and size of closed pores in HC using an economical, extensible rosin-assisted pore-promoting strategy and quantified the effective pore volume for sodium storage through small-angle X-ray scattering experiments. We show that optimizing the closed pore size to increase the effective pore volume is key to enhancing the electrochemical performance of HC. By controlling the size (~ 2 nm) of closed pores, we enhance the Na clusters filled volume fraction of HC, resulting in an extended low-potential plateau (<0.1 V vs. Na + /Na) and higher sodium storage capacity. Additionally, we established a positive correlation between the plateau capacity of HC and the effective pore volume. Consequently, the 4.5 Ah pouch-type sodium-ion batteries assembled with optimized HC here (areal capacity, 2.8 mAh cm -2 ) achieved a high energy density of 202 Wh kg -1 , with over 80% capacity retention after 500 cycles at 0.5C. This research provides a solution for realizing low-cost, advanced sodium-ion batteries. Physical sciences/Energy science and technology/Energy storage/Batteries Physical sciences/Materials science/Materials for energy and catalysis/Batteries Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Main The abundance and widely distributed sodium resources make sodium-ion batteries (SIBs) a feasible option for environmentally sustainable and cost-effective large-scale energy storage systems 1 – 4 . However, the commercialization of SIBs is still challenged by poor electrochemical performance and high costs, particularly for active materials. Significant efforts are being devoted to developing and optimizing cost-effective, high-performance electrode materials, including cathodes (layered transition metal oxides 5 , Prussian blue analogs 6 , and polyanionic compounds 7 ) and anodes (hard carbon), to advance the industrialization of SIBs. While significant progress has been achieved in cathode materials—particularly layered oxides demonstrating competitive specific capacities (> 160 mAh g − 1 ) and elevated average voltages (> 3.2 V vs. Na⁺/Na)—with corresponding pouch-type full cells exceeding 165 Wh kg − 15, 8 , the development of high-energy-density sodium-ion batteries remains constrained by a persistent challenge: the absence of high-performance hard carbon (HC) anode. Current anode limitations directly compromise energy density metrics, rendering state-of-the-art SIBs still lagging behind commercial LiFePO 4 ||graphite battery (~ 180 Wh kg − 1 ) 9 . HC is a type of amorphous carbon composed of sp 2 and sp 3 hybridized carbon atoms, with a complex structure featuring pores, defects and curved graphene platelets 10 , 11 . The typical electrochemical curve of HC anodes can be divided into a sloping region (> 0.1 V vs. Na⁺/Na) and a plateau region (< 0.1 V vs. Na⁺/Na), with the latter being a key factor determining the operating voltage and energy density of the full cell ( Supplementary Fig. 1 ) 12 , 13 . It has been noted that increasing the closed pore content of HC can enhance its plateau capacity, and many studies have focused on increasing the size and number of closed pores. For example, Yang et al. 14 utilized chemical vapor deposition (CVD) of methane on porous carbon (PC) to increase sodium storage nanopore content, thereby promoting plateau capacity. The addition of pore-forming agents, such as CO 2 15 , ethanol 16 , MgO 17 , KOH 18 , ZnO 19 , has also been widely used as an effective strategy. However, the inherent structural complexity of HC often leads to insufficient control over the formation of closed pores, causing the electrochemical performance of HC to remain below expectations, particularly under high load conditions that fulfill the industrial requirements of SIBs 20 – 23 . Moreover, there is still a lack of fundamental understanding and rational design regarding the relationship between HC’s closed pore structure and sodium-storage behavior. In this study, we utilized an esterification reaction to incorporated rosin acid into the polymer chains of biomass precursors (cellulose, hemicellulose, and lignin). During subsequent aromatization and carbonization processes, the decomposition of rosin generates gases and creates spatial hindrance, allowing precise control over the closed pore structure of the HC (Fig. 1 and Supplementary Fig. 2 ). By quantifying the effective pore volume of HC for sodium storage and the Na clusters filled volume fraction, we demonstrated that the pore size is the key factor determining the Na + pore filling behavior. Specifically, smaller pore sizes ( 2 nm) are detrimental to sodium storage, as larger Na clusters are thermodynamically unstable. In addition, we found that the plateau capacity of HC is directly proportional to the effective pore volume (the product of Na clusters filled volume fraction and closed pore volume). As a result, Pine HC with an average pore size of 1.91 nm exhibited the highest Na clusters filled volume fraction (51.2%), corresponding to an effective pore volume of 0.033 cm³·g − 1 . The reversible sodium storage capacity reached 336 mAh g − 1 (with 74.2% in the plateau region) and an initial Coulombic efficiency (ICE) of 92.2%, outperforming existing commercial HC. At high areal capacities (2.79/2.74 mAh cm − 2 ), the 4.5 Ah pouch-type sodium-ion batteries, with Pine HC as the anode and NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM111) as the cathode, achieved a high energy density of over 202 Wh kg − 1 , with more than 80% capacity retention after 500 cycles. Pyrolysis of pine wood To elucidate the mechanism of rosin-assisted pore-promoting strategy, we employed biomass containing rosin acid (e.g., waste pine wood) as a precursor for HC production as a demonstration. The distribution of rosin in pine wood was visualized using Scanning electron microscopy (SEM) combined with Raman microscopy. The pine wood exhibited the characteristic porous structure typical of natural wood, with pore widths of approximately 10 − 40 µm (Fig. 2 a). Raman mapping revealed that rosin was localized within these pore walls, permeating the entire matrix of the pine wood (Fig. 2 b,c), with a content of about 3 wt% ( Supplementary Table 1 ). To explore the role of rosin in pyrolysis, the rosin-free wood (RF wood) was obtained by Soxhlet extraction method ( Supplementary Fig. 3 ). The transverse relaxation distribution of the low-field nuclear magnetic resonance (LF-NMR) spectra of RF wood showed the absence of the rosin signal, indicating successful extraction ( Supplementary Fig. 4 ). Furthermore, the 13 C solid-state NMR (ssNMR) spectra reveal the structural evolution of pine wood and RF wood during pyrolysis (Fig. 2 d). After heat treatment, all samples were subjected to Soxhlet extraction to remove unreacted rosin, except for the pristine sample. The chemical shift signals of pristine-pine wood at 0 − 50 ppm are attributed to the C − H groups of rosin, whereas the signals corresponding to cellulose, hemicellulose, and lignin are found in the 50 − 185 ppm range ( Supplementary Table 2 ) 24 . The 200°C-pine wood sample retained degraded rosin, indicating that a portion of the rosin had been grafted onto the polymer chains and could not be extracted by solvent. Compared to 200°C-RF wood, the 200°C-pine wood exhibited stronger signals for ester carbon (173 ppm) and polycyclic aromatic carbon (128 ppm) 25 . This implies that esterification reactions occurred between rosin and the hydroxyl groups present in cellulose/hemicellulose/lignin, which compromised the thermal stability of the polymer chains, as confirmed by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results ( Supplementary Figs. 5 and 6 ). With an increase in carbonization temperature, cellulose and hemicellulose were observed to undergo pyrolysis and aromatization first (250 − 300°C). The ester signal of pine wood remained higher than that of RF wood. At 400°C, lignin and rosin were fully degraded and converted into polycyclic aromatic hydrocarbons and oxygenated aromatic hydrocarbons. Further, we investigated the decomposition mechanism of pine wood and RF wood by thermogravimetric analysis coupled with FTIR (TGA-FTIR). The TGA curves of pine wood revealed a notable initial weight loss between 200 − 280°C, primarily due to the esterification with rosin and the partial thermal degradation of cellulose, as evidenced by the gas signals (H 2 O, CO 2 , and CH 4 , etc.) detected in FTIR spectra (Fig. 2 e and Supplementary Table 3 ). The second weight loss occurred between 300 − 400°C, signifying further pyrolysis of cellulose, hemicellulose, and lignin, during which the carbon matrix underwent intramolecular cyclization and intermolecular aromatization 26 . During this stage, a substantial amount of the hydrogen and oxygen was removed, releasing more gases and organics compounds (ethers (C − O−C), aldehydes (C = O), and alkanes (C − C), etc.). 26 Beyond 400°C, the weight change stabilized, although continuous CO 2 was released due to the cracking and reformation of carbonyl groups (C = O) after esterification, a process that facilitates the formation of the porous structure in the carbon matrix. In the case of RF wood, a significant mass loss solely occurred between 300 − 400°C, attributable to the pyrolysis of polymer chains (Fig. 2 f). The amount of CO 2 released during subsequent carbonization was lower compared to pine wood. Ab initio molecular dynamics (AIMD) simulations were conducted to further elucidate the impact of rosin on the pore structure of the carbon matrix. Unlike pure carbon, the gases generated from rosin pyrolysis create spatial hindrance and form numerous cavities within the carbon network (Fig. 2 g, Supplementary Fig. 7 and Table 4 ). Even after the removal of these gases, the pores (highlighted in orange) remained stable during subsequent simulated annealing. These findings suggest that the esterification reaction with rosin altered the decomposition mechanisms of pine wood, thereby promoting the formation of the nanopore structure of HC. Characterization the structure of Pine HC Pine wood and RF wood, treated at 200°C, were carbonized at a high temperature of 1300°C, then crushed and graded to produce Pine HC and RF HC, respectively ( Supplementary Fig. 8 ). In addition, to obtain HC with different closed pore structures, we prepared Pine HC variants with varying rosin content (Pine HC-x%, x = 1, 6, 10). XRD patterns revealed that all Pine HCs and RF HC are amorphous, as evidenced by broad (002) and (100) diffraction peaks, which is consistent with results of selected area electron diffraction (SAED) and wide-angle X-ray scattering (WAXS) ( Supplementary Figs. 9–11 ). Structure parameters are detailed in Supplementary Table 5 . Raman spectra showed that the I D /I G value increased with the rise in rosin content ( Supplementary Fig. 12 ). The I D /I G ratio increased from 1.80 in RF HC to 2.12 in Pine HC-10%, suggesting that the esterification with rosin enhances the defect concentration and reduces the graphitization degree of HC. This increase in structural disorder aids in the diffusion and storage of Na + ions 27 . X-ray photoelectron spectroscopy (XPS) analysis further confirms that Pine HC-10% (6.4%) and Pine HC (5.8%) contains a higher oxygen content and more ester (− COOR) groups compared to RF HC (5.2%) ( Supplementary Fig. 13 ). High-resolution transmission electron microscopy (HRTEM) reveals the microstructure of Pine HC and RF HC: both materials consisting of disorderly intertwined curved graphene platelets, which form nanocarbon layers and closed pores (Fig. 3 a,b). Notably, Pine HC contains more and larger closed pores compared to RF HC, indicating that rosin promotes the formation of these nanopores. Additionally, we examined the nanopore structure (including open and closed pores) of all Pine HCs and RF HC using small-angle X-ray scattering (SAXS). Significant differences in scattering intensity at around 0.1 Å −1 were observed between the HCs ( Supplementary Fig. 14 ). Calculations based on the Teubner-Strey model reveal that Pine HC (1.91 nm) has a larger average pore diameter than RF HC (1.24 nm) (Fig. 3 c and Supplementary Table 6 ) 28 , consistent with the TEM observations. As the rosin content reached to 10% (Pine HC-10%), the average pore size further increased to 2.73 nm. As a complement to SAXS, we measured the true density of all Pine HCs and RF HC (Fig. 3 d). The skeletal densities of Pine HC-10%, Pine HC-6%, Pine HC, Pine HC-1%, and RF HC were 1.81, 1.90, 1.97, 2.02, and 2.09 g cm − 3 , respectively, with corresponding closed pore volumes of 0.110, 0.084, 0.065, 0.053, and 0.036 cm 3 g − 1 . These findings suggest that the introduction of rosin results in larger closed pore sizes and volumes compared to RF HC. Furthermore, the Brunauer-Emmett-Teller (BET) surface area and open pore structure of HCs were characterized by nitrogen adsorption experiments. The rosin esterification influenced the surface structure of HC: Pine HC showed a BET surface area of 16.7 m 2 g − 1 , in contrast to RF HC’s 9.0 m 2 g − 1 (Fig. 3 e, Supplementary Fig. 15 and Supplementary Table 7 ). Pine HC-10%, with the highest rosin content, exhibits the largest BET surface area of 52.4 m 2 g − 1 . The corresponding pore size distribution indicates that the higher specific surface area of Pine HC is mainly due to a greater number of pores in the 0.5 − 1.5 nm range compared to RF HC. It has been reported that these pores around 1 nm are difficult for the electrolyte to fully diffuse into and wet, thus would not significantly affect the ICE of Pine HC 29 . In contrast, Pine HC-10% possesses more open pores in the 1.5 − 5 nm range than Pine HC, which could potentially exacerbate the irreversible decomposition of the electrolyte. Electrochemical performance of Pine HC The sodium storage performance of all Pine HCs and RF HC was evaluated in a half-cell configuration using an ester electrolyte (Fig. 4 a, Supplementary Figs. 16 and 17 ). Pine HC-1% (with 1% rosin content) shows improved electrochemical performance compared to RF HC, with discharge capacity rising from 282 to 316 mAh g − 1 , and ICE increasing from 89.2–90.3%. Pine HC achieves a balance of high ICE (92.2%) and high capacity (341 mAh g − 1 ). Pine HC-6% has the highest capacity at 347 mAh g − 1 , but its ICE drops to 88.2%. Due to irreversible Na + loss caused by excessive specific surface area, the ICE of Pine HC-10% further decreases to 83.1%. A detailed analysis was conducted on the electrochemical performance differences among Pine HCs and RF HC, revealing that the increased plateau capacity is the main factor for the superior overall capacity of Pine HCs (Fig. 4 b). As the rosin content increased (from 0–6%), the plateau capacity rose from 201 mAh g − 1 in RF HC to 259 mAh g − 1 in Pine HC-6%, an increase of 29%, with the corresponding plateau region percentage rising to 74.7%. Further increasing the rosin content to 10% resulted in a decrease in both reversible capacity and plateau capacity, which is due to excessive open pores and larger closed pores that are unfavorable for sodium storage. The rate performance of Pine HC (best overall electrochemical performance) and RF HC was further compared. Pine HC exhibited excellent rate performance and cycling stability, achieving reversible capacities of 322.6, 280.3, 224.9, 171.4, and 105.5 mAh g − 1 at current densities of 50, 100, 150, 200, and 300 mA g − 1 , respectively (Fig. 4 c and Supplementary Fig. 18 ). In terms of cycling performance, the capacity retention exceeded 92% after 200 cycles at 100 mA g − 1 ( Supplementary Fig. 19 ). The electrochemical kinetics of sodium storage in Pine HC and RF HC were investigated through galvanostatic intermittent titration technique (GITT) and cyclic voltammetry (CV) measurements. Analysis of GITT profiles indicated that, in the slope region (> 0.1 V), Pine HC possessed higher Na + ion diffusion coefficients (D Na+ ) compared to RF HC ( Supplementary Fig. 20 ). This suggests that the improved pore structure facilitates Na + diffusion to the interlayer and edge sites of HC. In the plateau region (< 0.1 V), the sodium storage mechanism transitions to closed pores filling (discuss later). This transition causes the D Na+ of Pine HC and RF HC to first decrease and then increase 30 . Moreover, CV curves at different scan rates demonstrate that Pine HC shows reduced voltage polarization and a higher capacitive contribution compared to RF HC ( Supplementary Fig. 21 ), reflecting a faster Na + diffusion kinetics. Owing to its pore-rich structure, Pine HC exhibits significant advantages in both specific capacity and ICE over previously reported HC anodes (Fig. 4 d and Supplementary Table 8 ) 18 , 31 – 43 . Additionally, this pore-promoting strategy has been applied to a variety of cellulose-based biomasses. By immersing raw materials (e.g., cypress wood, corncobs, and wheat straw, etc.) in an ethanol solution of rosin, followed by identical heat treatment and carbonization processes, we synthesized various biomass-derived HCs. Compared to the original samples, the rosin-modified samples showed a 10 − 20% increase in capacity and a 3 − 5% improvement in ICE (Fig. 4 e, Supplementary Fig. 22 and Table 9 ). Subsequently, the compatibility of Pine HC anode with various cathodes, including NFM111, Na 3 V 2 (PO 4 ) 3 (NVP), Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 (NFPP), and Na 2 MnFe(CN) 6 (PBA), was evaluated in pouch cells. Within a voltage range of 1.5 − 4 V, the NFM111||Pine HC pouch cell demonstrated a high ICE of 87.7% ( Supplementary Fig. 23 ), resulting in an energy density of 244.4 Wh kg − 1 (based on the total weight of active cathode and anode materials). Cyclic stability testing was conducted under conditions of 1C discharge current and voltage window of 1.5 − 3.8 V. The results showed that the capacity retention of NFM111||Pine HC pouch cell after 500 cycles was 86.3%, reflecting outstanding cycle stability (Fig. 4 f and Supplementary Fig. 24 ). Furthermore, the NVP||Pine HC, NFPP||Pine HC, and PBA||Pine HC pouch cells exhibited impressive electrochemical performance, manifesting ICEs of 80.5%, 80.0%, and 79.1%, and energy densities of 201.1, 165.1, and 258.8 Wh kg − 1 , respectively ( Supplementary Figs. 25–27 ). After 200 cycles, their capacity retentions were 82.5%, 81.5%, and 80.0%, respectively ( Supplementary Figs. 28–30 ). These results indicate that Pine HC can be effectively paired with various cathode materials, showcasing its excellent potential for practical applications. Structural evolution during the first sodiation of Pine HC To explore the structural evolution of Pine HC during the first discharge process, in situ SAXS experiments were performed (Fig. 5 a and Supplementary Fig. 31 ). The scattering intensity is directly related to the square of the difference in scattering length density (ΔSLD) between the carbon matrix and the pores. Therefore, SAXS can determine whether Na + ions are intercalating into the carbon matrix or filling the closed pores. As sodiation progresses, the scattering intensity of the closed pores in Pine HC initially exhibits a slight increase (slope region) followed by a significant decrease (plateau region) (Fig. 5 b,c). For quantification and comparison, ΔSLD between the carbon matrix and the pores at different states of discharge (SODs) was obtained by fitting SAXS data. The sodium storage mechanism of Pine HC can be divided into two stages: before reaching 30% SOD (the slope region), the ΔSLD increased from 20.4×10 − 6 to 21.3×10 − 6 Å −2 , which indicates that Na + adsorption/intercalation enhances the SLD of the carbon matrix, as the SLD of closed pores is zero (Fig. 5 d) 14 . From 30–100% SOD (the plateau region), ΔSLD drops from 21.3×10 − 6 to 17.2×10 − 6 Å −2 , suggesting that Na + ions enter and fill the closed pores. These two stages were also captured by in situ XRD and in situ Raman experiments ( Supplementary Figs. 32 and 33 ). In the slope region of sodiation, Pine HC exhibited a weakening of the (002) diffraction peak and a red shift of the G-band, disclosing that Na + ion adsorb/intercalate into the carbon layers and electrons occupy the π* anti-bonding band of the graphene platelets. 44 For the plateau region, these phenomena are less pronounced, suggesting that Na + intercalation is nearly saturated at this stage. During desodiation, the scattering intensity of Pine HC rises and nearly returns to its initial level, indicating high reversibility of sodium storage within the closed pores ( Supplementary Fig. 34 ). Ex situ 23 Na ssNMR further investigated the changes in the chemical state of Na. A sharp peak near − 10 ppm was observed, corresponding to the diamagnetic Na in the remaining electrolyte and SEI layer ( Supplementary Fig. 35 ) 45 . As more Na fills the closed pores (0.01-0 V), signals indicating quasi-metallic Na clusters appear, shifting to higher chemical shifts (from 868 ppm to 925 ppm). This is due to the increasing contribution of the Knight shift, which indicates the growing metallic character of Na. 46 Additionally, the presence of Na clusters was visualized by reacting sodiated Pine HC with a 1% phenolphthalein ethanol solution. When the electrode containing Na clusters is placed in the solution, bubbles (H 2 ) form and sodium ethoxide is produced, turning the solution red ( Supplementary Fig. 36 ). As the discharge depth increases, the redness of the solution deepens, suggesting an increase in the content of quasi-metallic Na clusters in the electrodes ( Supplementary Fig. 37 ). Effective pore volume and plateau region capacity To investigate the relationship between sodium storage capacity and closed pore structure, we conducted in situ SAXS experiments on all Pine HC samples and RF HC and calculated their Na clusters filled volume fraction after sodiation (Fig. 5 e, Supplementary Fig. 38 ). As the closed pore size increases (from 1.24 nm (RF HC) to 2.73 nm (Pine HC-10%)), the Na clusters filled volume fraction initially rises and then falls. An average pore size of 2 nm seems to be a critical point ( Supplementary Fig. 39 ); for small closed pores ( 2 nm), the filled volume fraction dropped significantly (26% for Pine HC-10%). We attribute this to two thermodynamic factors: HC defect concentration (I D /I G ) and Na cluster stability 47 . In HCs with small closed pores (RF HC, Pine HC-1%, and Pine HC), stable Na clusters form, and defect concentration induced by rosin enhances the filled volume fraction. Conversely, larger Na clusters are thermodynamically unstable, making formation difficult in HCs with large closed pores (Pine HC-6% and Pine HC-10%). Furthermore, we define these fillable closed pore volumes as effective pore volume (effective pore volume = filled volume fraction × closed pore volume) (Fig. 5 f). It is evident that the effective pore volume, rather than the entire closed pore volume of HC, provide the sodium storage capacity. By comparing the effective pore volume and the plateau capacity of HCs, we found a strong correlation between the two (R 2 > 0.96) (Fig. 5 g). Effective pore volume determines Na + plateau storage, indicating that optimizing closed pore size to increase filled volume fraction is crucial for improving HC electrochemical performance. Pilot production of Pine HC and high-energy pouch cells As a proof-of-concept, 3 kg of Pine HC were produced using pine sawdust ( Supplementary Fig. 40 ). The estimated production cost is $ 3.53 kg − 1 ( Supplementary Table 10 ), which is only 13% of the current commercial HC price (Kuraray Type 2, $ 27.5 kg − 1 ) and significantly lower than the low-cost synthesis HC benchmark ( $ 5 kg − 1 ). 48 Additionally, Pine HC and commercial HC were compared in a three-electrode pouch cells within the voltage window of 1.2 − 4.5 V (Fig. 6 a,b, Supplementary Figs. 41 and 42 ). The red and blue profiles illustrate the potential responses of the anode and cathode against the reference electrode (Na metal) under full cell conditions, respectively. Upon reaching the cut-off voltage, the cathode paired with Pine HC exhibited a lower potential of 4.53 V compared to that paired with commercial HC (4.57 V), thus reducing the risk of irreversible phase transitions, gas evolution, and electrolyte decomposition in the pouch cell 8 . More importantly, the NFM111||Pine HC cell achieved a specific energy density of 315.8 Wh kg − 1 (average voltage: 3.09 V), surpassing the 283.4 Wh kg − 1 (2.98 V) obtained by NFM111||Commercial HC cell (based on the total weight of active cathode and anode materials). The radar chart comparison highlights the advantages of Pine HC over commercial HC (Fig. 6 c and Supplementary Table 11 ). Furthermore, we fabricated a 4.5 Ah-laminated NFM111||Pine HC pouch cell with an energy density of 202 Wh kg − 1 (based on the weight of the entire cell) (Fig. 6 d,e and Supplementary Fig. 43 ). Detailed information about this cell is provided in Supplementary Table 12 . After 500 cycles at 90% depth of discharge (DOD), the capacity retention remains above 80% (Fig. 6 f and Supplementary Fig. 44 ). These results clearly demonstrate that Pine HC holds significant potential for industrial applications in SIBs. Conclusions To summary, we developed an economical, extensible rosin-assisted pore-promoting strategy to precisely engineer the content and size (1.2–2.7 nm) of nanopores in HC. Based on this, we deconstructed the relationship between sodium storage capacity and closed pore structure, demonstrating that pore size is the critical parameter governing Na filling: HC with smaller closed pore sizes ( 2 nm) hinders Na cluster formation, resulting in a lower Na clusters filled volume fraction. By optimizing defect concentration and closed pore size, the Na clusters filled volume fraction of the obtained Pine HC exceeds 50%, with a reversible sodium storage capacity of 336 mAh g − ¹ and an ICE of 92.2%. Furthermore, the fabricated 4.5 Ah-laminated NFM111||Pine HC pouch cell achieved a high energy density (exceeding 202 Wh kg − 1 ) and exhibited excellent cycling stability, with a capacity retention of 80.8% after 500 cycles. This work represents a promising development path for cost-effective, high-performance anodes for large-scale energy storage systems. Methods Synthesis of HC samples To prepare Pine HC, 50 g of pine waste wood (with 3 wt% rosin content) (Huadong Timber Market, Jinhua, Zhejiang) was first placed in a muffle furnace and heated at 200°C for 6 hours. Subsequently, it was carbonized at 1300°C for 2 hours in a box furnace under a nitrogen atmosphere. The resulting material was then ground using a jet mill and sieved through a 1000-mesh sieve to obtain Pine HC. The rosin was extracted from the pine wood using a Soxhlet extractor to produce rosin-free wood (RF wood), which was then subjected to the same process to obtain RF HC. RF wood was soaked in a rosin ethanol solution containing 1 wt%, 6wt% and 10 wt% rosin relative to the RF wood. After solvent removal, the wood underwent heat treatment, carbonization, and pulverization to produce Pine HC-1%, Pine HC-6% and Pine HC-10%. Other biomass precursors were also soaked in a rosin ethanol solution containing 3 wt% rosin of the precursor and then processed similarly to yield rosin-modified HCs. Commercial HC was obtained from Kuraray Co. Ltd., Japan. Electrochemical measurements The slurry containing active material, carbon black, and sodium carboxymethylcellulose (mass ratio 92:3:5) was coated on Cu foil to prepare HC electrodes, with deionized water as the solvent and maintaining an active material mass loading of 5 mg cm − 2 . The coin-type cells (CR2032) were assembled in an argon-filled glove box using sodium foil, glass fiber, and 1M NaPF 6 solution in a ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 by volume) as the counter electrode, separator, and electrolyte, respectively. Galvanostatic charge-discharge and GITT tests were performed using a Neware battery testing system (CT-4008T-5 V10 mA-164, Shenzhen, China) within a voltage range of 0 − 2.5V. The NFM111 cathode for pouch cells was purchased from Guangdong Canrd Co., Ltd., while the NVP, NFPP, and PBA cathodes were obtained from Hefei Kejing Co., Ltd. Both cathode and anode utilized Al foil as current collectors, with the cathode measuring 4.3×5.6 cm 2 and the anode measuring 4.5×5.8 cm 2 . The electrolyte consisted of a 1M NaPF 6 solution in a mixture of EC, propylene carbonate (PC), DMC, and ethyl methyl carbonate (EMC) (1:1:4:4 by volume) with 3% fluoroethylene carbonate (FEC) additive. A 12 µm polyethylene (PE) separator was employed. Three-electrode pouch cell was fabricated following the method described by Li et al. 49 and was evaluated using an electrochemical workstation (PARSTAT 4000A). Materials characterization The morphologies and structure of the samples were examined using SEM (CIQTEK SEM3100) and TEM (JEOL, 2100F). XRD analyses were conducted with a Rigaku, TTR-III diffractometer utilizing Cu Kα radiation, with in situ XRD patterns recorded every 7 minutes. Raman spectra and mappings were obtained via a WITec alpha300 R Raman imaging microscope equipped with a 532 nm excitation laser, with in situ Raman spectra collected every 10 minutes. XPS measurements were performed on a Thermo ESCALAB 250Xi spectrometer. TGA-FTIR (PerkinElmer TL-9000) was carried out in a N 2 atmosphere at a heating rate of 10°C min − 1 . The true density of the samples was determined using a JW-M100A analyzer with He as the analysis gas. 13 C and 23 Na ssNMR spectra were acquired at room temperature on a Bruker AVANCE III 400 WB spectrometer. For ex situ experiments, electrodes were collected from Cu foil, transferred into 1.3 mm rotors without rinsing, and sealed with Vespel caps to minimize air or moisture exposure. SAXS experiments were conducted on a SAXSpoint 2.0 equipped with a 50 W micro-focus X-ray source (1 mm × 1 mm). The Teubner-Strey model was applied using SasView 5.0.6 software to analyze and obtain nanopore structural information 28 . During in situ SAXS experiments, data were acquired every 30 minutes. Background data were obtained using a blank in situ cell, and the measured signal intensity was calibrated using glassy carbon as a reference standard. Based on the measured SLD of closed pores, the porosity of Pine HC, and the density of metallic Na, we estimated the filled volume fraction of Na clusters in HC 50 . Calculation methods We used Packmol software to randomly put the rosins and C atoms into a 20×20×20 Å 3 box 51 . The Ab-initio Molecular Dynamics (AIMD) calculations were carried out by using CP2K software 52 . Goedecker-Teter-Hutter (GTH) pseudopotentials were used to describe the core electrons and the exchange-correlation effects were represented by Perdew-Burke-Ernzerhof (PBE) functional 53 , 54 . The basis sets of H atom, C atom and O atom were DZVP-MOLOPT-SR-GTH-q1, DZVP-MOLOPT-SR-GTH-q4 and DZVP-MOLOPT-SR-GTH-q6, respectively. The energy cut-off was 300 Ry and energy convergence criterion was set to 1×10 − 5 Hartree. We used constant-volume (NVT) ensemble with a CSVR thermostat and opened OT method during the AIMD simulation 55 . The structure was first annealed at 2000 K with 0.3 fs time step and then annealed at 1500 K with 1.0 fs time step after removing rosins. The free volume and surface area of the final models were calculated and visualized using Multiwfn and VMD. Declarations Acknowledgements This work was supported by the National Natural Science Foundation of China (Nos. 51925207, 52225208, 52202322, 52102321, U23A20579, and 52302323), the National Synchrotron Radiation Laboratory (KY2060000173), the Joint Fund of the Yulin University and the Dalian National Laboratory for Clean Energy (Grant YLU-DNL Fund 2021002), the Fundamental Research Funds for the Central Universities (WK2060140026), the “Transformational Technologies for Clean Energy and Demonstration” Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA21000000), Hefei Municipal Natural Science Foundation (2022021), and China Postdoctoral Science Foundation (Nos. 2023M733361). We thank the USTC supercomputing center for providing computational resources for this project. This work was partially carried out at the Instruments Center for Physical Science, University of Science and Technology of China. Supercomputing facilities were provided by the Hefei Advanced Computing Center. Author information These authors contributed equally: Zhihao Chen, Jialong Shen, Hai Yang. Authors and Affiliations Hefei National Research Center for Physical Sciences at the Microscale, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Department of Materials Science and Engineering, CAS Key Laboratory of Materials for Energy Conversion, University of Science and Technology of China, Hefei, China. Zhihao Chen, Jialong Shen, Hai Yang, Yingshan Huang, Wenjie Deng, Yuhang Lou, Guanyin Gao & Yan Yu National Synchrotron Radiation Laboratory, Hefei, China Yan Yu School of Materials and Energy, Guangdong University of Technology, Guangzhou, 510006, China Xianhong Rui Contributions H.Y. and Y.Y. conceived the ideas. Z.C. synthesized the carbon and performed electrochemical measurements with support from Y.H., W.D., G.G., and G.G. H.Y. assembled the pouch cells. J.S. carried out the AIMD simulations. Z.C. wrote the manuscript, H.Y., X.R., and Y.Y contributing to the editing process. All authors were involved in the experimental analysis and have approved the final manuscript. Corresponding author Correspondence to Yan Yu. Ethics declarations Competing interests The authors declare no competing interests. References Hwang, J.Y., Myung, S.T. & Sun, Y.K. Sodium-ion batteries: present and future. Chem. Soc. Rev. 46 , 3529-3614 (2017). Zhao, Y. et al. Recycling of sodium-ion batteries. Nature Reviews Materials 8 , 623-634 (2023). Liu, T.F. et al. Exploring competitive features of stationary sodium ion batteries for electrochemical energy storage. Energy Environ. Sci. 12 , 1512-1533 (2019). Peng, J., Li, H., Chen, L. & Wu, F. Application of Liquid Metal Electrodes in Electrochemical Energy Storage. Precision Chemistry 1 , 452-467 (2023). Tang, Y. et al. Sustainable layered cathode with suppressed phase transition for long-life sodium-ion batteries. 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Supplementary Files SIPineHCforSIBsCZH20250527.docx SUPPLEMENTARY INFO 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-6761243","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":466636297,"identity":"f368b3e0-5161-4548-8cfb-0fcbf8279377","order_by":0,"name":"Yan 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microporous formation in biomass hard carbon.\u003c/strong\u003e The diagram only shows cellulose chain, but the hydroxyl groups on hemicellulose and lignin can also esterify with rosin.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6761243/v1/d465b5f9451dc8f874086ad2.png"},{"id":84080241,"identity":"703b095a-ba04-49c1-9366-2cc92799af5b","added_by":"auto","created_at":"2025-06-06 13:58:52","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":309772,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePyrolysis mechanisms of pine wood.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e-\u003cstrong\u003ec\u003c/strong\u003e, SEM image, Raman mapping image, and corresponding Raman spectra of pine wood. Raman color mapping is based on the C=C characteristic peak of rosin (black dashed line) at 1653 cm\u003csup\u003e-1\u003c/sup\u003e. Scale bars, 40 μm. \u003cstrong\u003ed\u003c/strong\u003e, \u003csup\u003e13\u003c/sup\u003eC CP/MAS solid-state NMR spectra of pine wood and RF wood at different pyrolysis temperatures.\u003cstrong\u003e e\u003c/strong\u003e,\u003cstrong\u003ef\u003c/strong\u003e, TGA-FTIR spectra of pine wood (\u003cstrong\u003ee\u003c/strong\u003e) and RF wood (\u003cstrong\u003ef\u003c/strong\u003e). The TGA curves are shown on the left and the FTIR spectra on the right are derived from the gases released during the pyrolysis of samples. \u003cstrong\u003eg\u003c/strong\u003e, Snapshots of rosin pyrolysis and gases release from the carbon matrix, which induces the formation of microporous structures. The pores in the carbon matrix are shown in orange.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6761243/v1/37223f9e50b287a2a23cc83e.png"},{"id":84078736,"identity":"9cb2ba51-f889-4603-a8ef-59f51a6361dd","added_by":"auto","created_at":"2025-06-06 13:42:52","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":289879,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePore structure characterization of Pine HCs and RF HC.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e,\u003cstrong\u003eb\u003c/strong\u003e, HRTEM images of Pine HC (\u003cstrong\u003ea\u003c/strong\u003e) and RF HC (\u003cstrong\u003eb\u003c/strong\u003e). Scale bars, 5 nm. On the right side are the structures resulting from refinements against \u003cem\u003eL\u003c/em\u003e\u003csub\u003e\u003cem\u003ea\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eL\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e002\u003c/em\u003e\u003c/sub\u003e of the HC. \u003cstrong\u003ec\u003c/strong\u003e, The average closed pore size obtained from SAXS profiles. \u003cstrong\u003ed\u003c/strong\u003e, True density (skeletal density) and the corresponding closed pore volume of Pine HCs, RF HC, and graphite. \u003cstrong\u003ee\u003c/strong\u003e, The BET surface area and the corresponding pore size distribution.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6761243/v1/e181994952747f3801fcac7c.png"},{"id":84078735,"identity":"f1cdc2f6-6735-4157-9895-cc80fa699b71","added_by":"auto","created_at":"2025-06-06 13:42:52","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":174925,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical performance of Pine HCs and RF HC anodes.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e, Galvanostatic charge-discharge profiles of Pine HCs and RF HC at 30 mA g\u003csup\u003e-1\u003c/sup\u003e. \u003cstrong\u003eb\u003c/strong\u003e, Comparison of the plateau and slope capacity ratio in the 2nd discharge profiles. \u003cstrong\u003ec\u003c/strong\u003e, Rate capability of Pine HC and RF HC under various current densities ranging from 30 to 300 mA g\u003csup\u003e-1\u003c/sup\u003e. \u003cstrong\u003ed\u003c/strong\u003e, Comparison of the reversible capacity and ICE of Pine HC with the reported HC anodes.\u003cstrong\u003e e,\u003c/strong\u003e Electrochemical performance of various biomass-derived rosin-modified HCs in terms of their reversible capacity and ICE. \u003cstrong\u003ef\u003c/strong\u003e, Cycling performance of the NFM111||Pine HC pouch cell under a discharge current of 1C.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6761243/v1/29a8b9e9dc7904e8d4290652.png"},{"id":84078739,"identity":"b738f754-4929-4977-8e61-94ea9f35c849","added_by":"auto","created_at":"2025-06-06 13:42:52","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":215242,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eIn situ SAXS studies for sodium storage mechanism in Pine HC anodes. a\u003c/strong\u003e, Schematic illustration of the experimental set-up for in situ SAXS. \u003cstrong\u003eb\u003c/strong\u003e,\u003cstrong\u003ec\u003c/strong\u003e, In situ SAXS profiles of Pine HC electrode during the slope capacity region (\u003cstrong\u003eb\u003c/strong\u003e) and the plateau capacity region (\u003cstrong\u003ec\u003c/strong\u003e) for the first sodiation. Curves with various color represent different discharge states. \u003cstrong\u003ed\u003c/strong\u003e, Magnitude of the average different in scattering length density (ΔSLD) between the carbon matrix and the closed pores upon different states of discharge (SOD) and the corresponding discharge curves. Insert: Schematic diagram of sodium storage stages in the slope and plateau capacity regions of Pine HC, where red spheres indicate adsorbed or intercalated Na\u003csup\u003e+\u003c/sup\u003e, and blue spheres indicate pore filled Na\u003csup\u003e+\u003c/sup\u003e. \u003cstrong\u003ee\u003c/strong\u003e, Calculated Na clusters filled volume fraction in the plateau region of Pine HC. \u003cstrong\u003ef\u003c/strong\u003e, Effective pore volumes of HCs determined from in situ SAXS experiments. \u003cstrong\u003eg\u003c/strong\u003e, Liner fit between the effective pore volume and the plateau capacity of HCs.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6761243/v1/a2d9375d8dd3db26d8cdd572.png"},{"id":84078740,"identity":"a20db550-58bb-4634-9e4e-e85ea9b7b7fc","added_by":"auto","created_at":"2025-06-06 13:42:52","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":180800,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe advantages of Pine HC over commercial HC and the high energy density achieved in Ah-level pouch cells.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e,\u003cstrong\u003eb\u003c/strong\u003e, Electrochemical profiles of the NFM111||Pine HC (\u003cstrong\u003ea\u003c/strong\u003e) and NFM111||Commercial HC (\u003cstrong\u003eb\u003c/strong\u003e) measured in three-electrode pouch cell within 1.2−4.5 V with an N/P (negative/positive capacity) ratio of 1.12 (reference electrode: Na metal). \u003cstrong\u003ec\u003c/strong\u003e, Radar chart comparing the electrochemical performance in pouch cell and cost effectiveness of Pine HC and commercial HC. \u003cstrong\u003ed\u003c/strong\u003e-\u003cstrong\u003ef\u003c/strong\u003e, 4.5 Ah-laminated NFM111||Pine HC pouch cell with an energy density of 202 Wh kg\u003csup\u003e-1\u003c/sup\u003e: photograph that successfully powered a smartphone to 93% capacity (\u003cstrong\u003ed\u003c/strong\u003e), the charge-discharge profiles within 1.2−4.5 V (\u003cstrong\u003ee\u003c/strong\u003e), and the cycling performance at 0.5C within 1.5−4.2 V (\u003cstrong\u003ef\u003c/strong\u003e). Scale bar, 5 cm.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6761243/v1/7514392873a97b7d6f52fa90.png"},{"id":86971207,"identity":"70cd01db-f11b-41a2-9e88-3af7ccc0b58d","added_by":"auto","created_at":"2025-07-17 18:58:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2769268,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6761243/v1/8d9dfa56-05a2-4aea-a7ae-a88b6d856a0b.pdf"},{"id":84078743,"identity":"92b0185a-2f1e-4fdd-96f5-cd907e1c18f7","added_by":"auto","created_at":"2025-06-06 13:42:52","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":10530523,"visible":true,"origin":"","legend":"SUPPLEMENTARY INFO","description":"","filename":"SIPineHCforSIBsCZH20250527.docx","url":"https://assets-eu.researchsquare.com/files/rs-6761243/v1/4697b9bd64b4a46959ebf3c4.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Achieving over 200 Wh kg-1 Sodium-Ion Pouch Cell by Quantitative Engineering of Hard Carbon Pores","fulltext":[{"header":"Main","content":"\u003cp\u003eThe abundance and widely distributed sodium resources make sodium-ion batteries (SIBs) a feasible option for environmentally sustainable and cost-effective large-scale energy storage systems\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. However, the commercialization of SIBs is still challenged by poor electrochemical performance and high costs, particularly for active materials. Significant efforts are being devoted to developing and optimizing cost-effective, high-performance electrode materials, including cathodes (layered transition metal oxides\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e, Prussian blue analogs\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, and polyanionic compounds\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e) and anodes (hard carbon), to advance the industrialization of SIBs. While significant progress has been achieved in cathode materials\u0026mdash;particularly layered oxides demonstrating competitive specific capacities (\u0026gt;\u0026thinsp;160 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and elevated average voltages (\u0026gt;\u0026thinsp;3.2 V vs. Na⁺/Na)\u0026mdash;with corresponding pouch-type full cells exceeding 165 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;15, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e, the development of high-energy-density sodium-ion batteries remains constrained by a persistent challenge: the absence of high-performance hard carbon (HC) anode. Current anode limitations directly compromise energy density metrics, rendering state-of-the-art SIBs still lagging behind commercial LiFePO\u003csub\u003e4\u003c/sub\u003e||graphite battery (~\u0026thinsp;180 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e9\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eHC is a type of amorphous carbon composed of sp\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e and sp\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e hybridized carbon atoms, with a complex structure featuring pores, defects and curved graphene platelets\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. The typical electrochemical curve of HC anodes can be divided into a sloping region (\u0026gt;\u0026thinsp;0.1 V vs. Na⁺/Na) and a plateau region (\u0026lt;\u0026thinsp;0.1 V vs. Na⁺/Na), with the latter being a key factor determining the operating voltage and energy density of the full cell (\u003cb\u003eSupplementary Fig.\u0026nbsp;1\u003c/b\u003e)\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. It has been noted that increasing the closed pore content of HC can enhance its plateau capacity, and many studies have focused on increasing the size and number of closed pores. For example, Yang et al.\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e utilized chemical vapor deposition (CVD) of methane on porous carbon (PC) to increase sodium storage nanopore content, thereby promoting plateau capacity. The addition of pore-forming agents, such as CO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e15\u003c/sup\u003e, ethanol\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, MgO\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e, KOH\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, ZnO\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, has also been widely used as an effective strategy. However, the inherent structural complexity of HC often leads to insufficient control over the formation of closed pores, causing the electrochemical performance of HC to remain below expectations, particularly under high load conditions that fulfill the industrial requirements of SIBs\u003csup\u003e\u003cspan additionalcitationids=\"CR21 CR22\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Moreover, there is still a lack of fundamental understanding and rational design regarding the relationship between HC\u0026rsquo;s closed pore structure and sodium-storage behavior.\u003c/p\u003e \u003cp\u003eIn this study, we utilized an esterification reaction to incorporated rosin acid into the polymer chains of biomass precursors (cellulose, hemicellulose, and lignin). During subsequent aromatization and carbonization processes, the decomposition of rosin generates gases and creates spatial hindrance, allowing precise control over the closed pore structure of the HC (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e \u003cb\u003eand Supplementary Fig.\u0026nbsp;2\u003c/b\u003e). By quantifying the effective pore volume of HC for sodium storage and the Na clusters filled volume fraction, we demonstrated that the pore size is the key factor determining the Na\u003csup\u003e+\u003c/sup\u003e pore filling behavior. Specifically, smaller pore sizes (\u0026lt;\u0026thinsp;2 nm) are favorable for the formation of Na clusters, and appropriately increasing defect concentration can help increase the Na clusters filled volume fraction. Larger pore sizes (\u0026gt;\u0026thinsp;2 nm) are detrimental to sodium storage, as larger Na clusters are thermodynamically unstable. In addition, we found that the plateau capacity of HC is directly proportional to the effective pore volume (the product of Na clusters filled volume fraction and closed pore volume). As a result, Pine HC with an average pore size of 1.91 nm exhibited the highest Na clusters filled volume fraction (51.2%), corresponding to an effective pore volume of 0.033 cm\u0026sup3;\u0026middot;g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The reversible sodium storage capacity reached 336 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (with 74.2% in the plateau region) and an initial Coulombic efficiency (ICE) of 92.2%, outperforming existing commercial HC. At high areal capacities (2.79/2.74 mAh cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), the 4.5 Ah pouch-type sodium-ion batteries, with Pine HC as the anode and NaNi\u003csub\u003e1/3\u003c/sub\u003eFe\u003csub\u003e1/3\u003c/sub\u003eMn\u003csub\u003e1/3\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (NFM111) as the cathode, achieved a high energy density of over 202 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, with more than 80% capacity retention after 500 cycles.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003ePyrolysis of pine wood\u003c/h3\u003e\n\u003cp\u003eTo elucidate the mechanism of rosin-assisted pore-promoting strategy, we employed biomass containing rosin acid (e.g., waste pine wood) as a precursor for HC production as a demonstration. The distribution of rosin in pine wood was visualized using Scanning electron microscopy (SEM) combined with Raman microscopy. The pine wood exhibited the characteristic porous structure typical of natural wood, with pore widths of approximately 10\u0026thinsp;\u0026minus;\u0026thinsp;40 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Raman mapping revealed that rosin was localized within these pore walls, permeating the entire matrix of the pine wood (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb,c), with a content of about 3 wt% (\u003cb\u003eSupplementary Table\u0026nbsp;1\u003c/b\u003e). To explore the role of rosin in pyrolysis, the rosin-free wood (RF wood) was obtained by Soxhlet extraction method (\u003cb\u003eSupplementary Fig.\u0026nbsp;3\u003c/b\u003e). The transverse relaxation distribution of the low-field nuclear magnetic resonance (LF-NMR) spectra of RF wood showed the absence of the rosin signal, indicating successful extraction (\u003cb\u003eSupplementary Fig.\u0026nbsp;4\u003c/b\u003e). Furthermore, the \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC solid-state NMR (ssNMR) spectra reveal the structural evolution of pine wood and RF wood during pyrolysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). After heat treatment, all samples were subjected to Soxhlet extraction to remove unreacted rosin, except for the pristine sample. The chemical shift signals of pristine-pine wood at 0\u0026thinsp;\u0026minus;\u0026thinsp;50 ppm are attributed to the C\u0026thinsp;\u0026minus;\u0026thinsp;H groups of rosin, whereas the signals corresponding to cellulose, hemicellulose, and lignin are found in the 50\u0026thinsp;\u0026minus;\u0026thinsp;185 ppm range (\u003cb\u003eSupplementary Table\u0026nbsp;2\u003c/b\u003e)\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. The 200\u0026deg;C-pine wood sample retained degraded rosin, indicating that a portion of the rosin had been grafted onto the polymer chains and could not be extracted by solvent. Compared to 200\u0026deg;C-RF wood, the 200\u0026deg;C-pine wood exhibited stronger signals for ester carbon (173 ppm) and polycyclic aromatic carbon (128 ppm)\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. This implies that esterification reactions occurred between rosin and the hydroxyl groups present in cellulose/hemicellulose/lignin, which compromised the thermal stability of the polymer chains, as confirmed by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results (\u003cb\u003eSupplementary Figs.\u0026nbsp;5 and 6\u003c/b\u003e). With an increase in carbonization temperature, cellulose and hemicellulose were observed to undergo pyrolysis and aromatization first (250\u0026thinsp;\u0026minus;\u0026thinsp;300\u0026deg;C). The ester signal of pine wood remained higher than that of RF wood. At 400\u0026deg;C, lignin and rosin were fully degraded and converted into polycyclic aromatic hydrocarbons and oxygenated aromatic hydrocarbons.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurther, we investigated the decomposition mechanism of pine wood and RF wood by thermogravimetric analysis coupled with FTIR (TGA-FTIR). The TGA curves of pine wood revealed a notable initial weight loss between 200\u0026thinsp;\u0026minus;\u0026thinsp;280\u0026deg;C, primarily due to the esterification with rosin and the partial thermal degradation of cellulose, as evidenced by the gas signals (H\u003csub\u003e2\u003c/sub\u003eO, CO\u003csub\u003e2\u003c/sub\u003e, and CH\u003csub\u003e4\u003c/sub\u003e, etc.) detected in FTIR spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee \u003cb\u003eand Supplementary Table\u0026nbsp;3\u003c/b\u003e). The second weight loss occurred between 300\u0026thinsp;\u0026minus;\u0026thinsp;400\u0026deg;C, signifying further pyrolysis of cellulose, hemicellulose, and lignin, during which the carbon matrix underwent intramolecular cyclization and intermolecular aromatization\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. During this stage, a substantial amount of the hydrogen and oxygen was removed, releasing more gases and organics compounds (ethers (C\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;C), aldehydes (C\u0026thinsp;=\u0026thinsp;O), and alkanes (C\u0026thinsp;\u0026minus;\u0026thinsp;C), etc.).\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e Beyond 400\u0026deg;C, the weight change stabilized, although continuous CO\u003csub\u003e2\u003c/sub\u003e was released due to the cracking and reformation of carbonyl groups (C\u0026thinsp;=\u0026thinsp;O) after esterification, a process that facilitates the formation of the porous structure in the carbon matrix. In the case of RF wood, a significant mass loss solely occurred between 300\u0026thinsp;\u0026minus;\u0026thinsp;400\u0026deg;C, attributable to the pyrolysis of polymer chains (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). The amount of CO\u003csub\u003e2\u003c/sub\u003e released during subsequent carbonization was lower compared to pine wood. Ab initio molecular dynamics (AIMD) simulations were conducted to further elucidate the impact of rosin on the pore structure of the carbon matrix. Unlike pure carbon, the gases generated from rosin pyrolysis create spatial hindrance and form numerous cavities within the carbon network (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg, \u003cb\u003eSupplementary Fig.\u0026nbsp;7 and Table\u0026nbsp;4\u003c/b\u003e). Even after the removal of these gases, the pores (highlighted in orange) remained stable during subsequent simulated annealing. These findings suggest that the esterification reaction with rosin altered the decomposition mechanisms of pine wood, thereby promoting the formation of the nanopore structure of HC.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eCharacterization the structure of Pine HC\u003c/h2\u003e \u003cp\u003ePine wood and RF wood, treated at 200\u0026deg;C, were carbonized at a high temperature of 1300\u0026deg;C, then crushed and graded to produce Pine HC and RF HC, respectively (\u003cb\u003eSupplementary Fig.\u0026nbsp;8\u003c/b\u003e). In addition, to obtain HC with different closed pore structures, we prepared Pine HC variants with varying rosin content (Pine HC-x%, x\u0026thinsp;=\u0026thinsp;1, 6, 10). XRD patterns revealed that all Pine HCs and RF HC are amorphous, as evidenced by broad (002) and (100) diffraction peaks, which is consistent with results of selected area electron diffraction (SAED) and wide-angle X-ray scattering (WAXS) (\u003cb\u003eSupplementary Figs.\u0026nbsp;9\u0026ndash;11\u003c/b\u003e). Structure parameters are detailed in \u003cb\u003eSupplementary Table\u0026nbsp;5\u003c/b\u003e. Raman spectra showed that the I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e value increased with the rise in rosin content (\u003cb\u003eSupplementary Fig.\u0026nbsp;12\u003c/b\u003e). The I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e ratio increased from 1.80 in RF HC to 2.12 in Pine HC-10%, suggesting that the esterification with rosin enhances the defect concentration and reduces the graphitization degree of HC. This increase in structural disorder aids in the diffusion and storage of Na\u003csup\u003e+\u003c/sup\u003e ions\u003csup\u003e27\u003c/sup\u003e. X-ray photoelectron spectroscopy (XPS) analysis further confirms that Pine HC-10% (6.4%) and Pine HC (5.8%) contains a higher oxygen content and more ester (\u0026minus;\u0026thinsp;COOR) groups compared to RF HC (5.2%) (\u003cb\u003eSupplementary Fig.\u0026nbsp;13\u003c/b\u003e).\u003c/p\u003e \u003cp\u003eHigh-resolution transmission electron microscopy (HRTEM) reveals the microstructure of Pine HC and RF HC: both materials consisting of disorderly intertwined curved graphene platelets, which form nanocarbon layers and closed pores (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea,b). Notably, Pine HC contains more and larger closed pores compared to RF HC, indicating that rosin promotes the formation of these nanopores. Additionally, we examined the nanopore structure (including open and closed pores) of all Pine HCs and RF HC using small-angle X-ray scattering (SAXS). Significant differences in scattering intensity at around 0.1 \u0026Aring;\u003csup\u003e\u0026minus;1\u003c/sup\u003e were observed between the HCs (\u003cb\u003eSupplementary Fig.\u0026nbsp;14\u003c/b\u003e). Calculations based on the Teubner-Strey model reveal that Pine HC (1.91 nm) has a larger average pore diameter than RF HC (1.24 nm) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec \u003cb\u003eand Supplementary Table\u0026nbsp;6\u003c/b\u003e)\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e, consistent with the TEM observations. As the rosin content reached to 10% (Pine HC-10%), the average pore size further increased to 2.73 nm. As a complement to SAXS, we measured the true density of all Pine HCs and RF HC (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). The skeletal densities of Pine HC-10%, Pine HC-6%, Pine HC, Pine HC-1%, and RF HC were 1.81, 1.90, 1.97, 2.02, and 2.09 g cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, respectively, with corresponding closed pore volumes of 0.110, 0.084, 0.065, 0.053, and 0.036 cm\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. These findings suggest that the introduction of rosin results in larger closed pore sizes and volumes compared to RF HC. Furthermore, the Brunauer-Emmett-Teller (BET) surface area and open pore structure of HCs were characterized by nitrogen adsorption experiments. The rosin esterification influenced the surface structure of HC: Pine HC showed a BET surface area of 16.7 m\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, in contrast to RF HC\u0026rsquo;s 9.0 m\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, \u003cb\u003eSupplementary Fig.\u0026nbsp;15 and Supplementary Table\u0026nbsp;7\u003c/b\u003e). Pine HC-10%, with the highest rosin content, exhibits the largest BET surface area of 52.4 m\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The corresponding pore size distribution indicates that the higher specific surface area of Pine HC is mainly due to a greater number of pores in the 0.5\u0026thinsp;\u0026minus;\u0026thinsp;1.5 nm range compared to RF HC. It has been reported that these pores around 1 nm are difficult for the electrolyte to fully diffuse into and wet, thus would not significantly affect the ICE of Pine HC\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. In contrast, Pine HC-10% possesses more open pores in the 1.5\u0026thinsp;\u0026minus;\u0026thinsp;5 nm range than Pine HC, which could potentially exacerbate the irreversible decomposition of the electrolyte.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eElectrochemical performance of Pine HC\u003c/h3\u003e\n\u003cp\u003eThe sodium storage performance of all Pine HCs and RF HC was evaluated in a half-cell configuration using an ester electrolyte (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, \u003cb\u003eSupplementary Figs.\u0026nbsp;16 and 17\u003c/b\u003e). Pine HC-1% (with 1% rosin content) shows improved electrochemical performance compared to RF HC, with discharge capacity rising from 282 to 316 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and ICE increasing from 89.2\u0026ndash;90.3%. Pine HC achieves a balance of high ICE (92.2%) and high capacity (341 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Pine HC-6% has the highest capacity at 347 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, but its ICE drops to 88.2%. Due to irreversible Na\u003csup\u003e+\u003c/sup\u003e loss caused by excessive specific surface area, the ICE of Pine HC-10% further decreases to 83.1%. A detailed analysis was conducted on the electrochemical performance differences among Pine HCs and RF HC, revealing that the increased plateau capacity is the main factor for the superior overall capacity of Pine HCs (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). As the rosin content increased (from 0\u0026ndash;6%), the plateau capacity rose from 201 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in RF HC to 259 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in Pine HC-6%, an increase of 29%, with the corresponding plateau region percentage rising to 74.7%. Further increasing the rosin content to 10% resulted in a decrease in both reversible capacity and plateau capacity, which is due to excessive open pores and larger closed pores that are unfavorable for sodium storage. The rate performance of Pine HC (best overall electrochemical performance) and RF HC was further compared. Pine HC exhibited excellent rate performance and cycling stability, achieving reversible capacities of 322.6, 280.3, 224.9, 171.4, and 105.5 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at current densities of 50, 100, 150, 200, and 300 mA g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec \u003cb\u003eand Supplementary Fig.\u0026nbsp;18\u003c/b\u003e). In terms of cycling performance, the capacity retention exceeded 92% after 200 cycles at 100 mA g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (\u003cb\u003eSupplementary Fig.\u0026nbsp;19\u003c/b\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe electrochemical kinetics of sodium storage in Pine HC and RF HC were investigated through galvanostatic intermittent titration technique (GITT) and cyclic voltammetry (CV) measurements. Analysis of GITT profiles indicated that, in the slope region (\u0026gt;\u0026thinsp;0.1 V), Pine HC possessed higher Na\u003csup\u003e+\u003c/sup\u003e ion diffusion coefficients (D\u003csub\u003eNa+\u003c/sub\u003e) compared to RF HC (\u003cb\u003eSupplementary Fig.\u0026nbsp;20\u003c/b\u003e). This suggests that the improved pore structure facilitates Na\u003csup\u003e+\u003c/sup\u003e diffusion to the interlayer and edge sites of HC. In the plateau region (\u0026lt;\u0026thinsp;0.1 V), the sodium storage mechanism transitions to closed pores filling (discuss later). This transition causes the D\u003csub\u003eNa+\u003c/sub\u003e of Pine HC and RF HC to first decrease and then increase\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. Moreover, CV curves at different scan rates demonstrate that Pine HC shows reduced voltage polarization and a higher capacitive contribution compared to RF HC (\u003cb\u003eSupplementary Fig.\u0026nbsp;21\u003c/b\u003e), reflecting a faster Na\u003csup\u003e+\u003c/sup\u003e diffusion kinetics. Owing to its pore-rich structure, Pine HC exhibits significant advantages in both specific capacity and ICE over previously reported HC anodes (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed \u003cb\u003eand Supplementary Table\u0026nbsp;8\u003c/b\u003e)\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan additionalcitationids=\"CR32 CR33 CR34 CR35 CR36 CR37 CR38 CR39 CR40 CR41 CR42\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e. Additionally, this pore-promoting strategy has been applied to a variety of cellulose-based biomasses. By immersing raw materials (e.g., cypress wood, corncobs, and wheat straw, etc.) in an ethanol solution of rosin, followed by identical heat treatment and carbonization processes, we synthesized various biomass-derived HCs. Compared to the original samples, the rosin-modified samples showed a 10\u0026thinsp;\u0026minus;\u0026thinsp;20% increase in capacity and a 3\u0026thinsp;\u0026minus;\u0026thinsp;5% improvement in ICE (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee, \u003cb\u003eSupplementary Fig.\u0026nbsp;22 and Table\u0026nbsp;9\u003c/b\u003e).\u003c/p\u003e \u003cp\u003eSubsequently, the compatibility of Pine HC anode with various cathodes, including NFM111, Na\u003csub\u003e3\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e (NVP), Na\u003csub\u003e4\u003c/sub\u003eFe\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eP\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e (NFPP), and Na\u003csub\u003e2\u003c/sub\u003eMnFe(CN)\u003csub\u003e6\u003c/sub\u003e (PBA), was evaluated in pouch cells. Within a voltage range of 1.5\u0026thinsp;\u0026minus;\u0026thinsp;4 V, the NFM111||Pine HC pouch cell demonstrated a high ICE of 87.7% (\u003cb\u003eSupplementary Fig.\u0026nbsp;23\u003c/b\u003e), resulting in an energy density of 244.4 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (based on the total weight of active cathode and anode materials). Cyclic stability testing was conducted under conditions of 1C discharge current and voltage window of 1.5\u0026thinsp;\u0026minus;\u0026thinsp;3.8 V. The results showed that the capacity retention of NFM111||Pine HC pouch cell after 500 cycles was 86.3%, reflecting outstanding cycle stability (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef \u003cb\u003eand Supplementary Fig.\u0026nbsp;24\u003c/b\u003e). Furthermore, the NVP||Pine HC, NFPP||Pine HC, and PBA||Pine HC pouch cells exhibited impressive electrochemical performance, manifesting ICEs of 80.5%, 80.0%, and 79.1%, and energy densities of 201.1, 165.1, and 258.8 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively (\u003cb\u003eSupplementary Figs.\u0026nbsp;25\u0026ndash;27\u003c/b\u003e). After 200 cycles, their capacity retentions were 82.5%, 81.5%, and 80.0%, respectively (\u003cb\u003eSupplementary Figs.\u0026nbsp;28\u0026ndash;30\u003c/b\u003e). These results indicate that Pine HC can be effectively paired with various cathode materials, showcasing its excellent potential for practical applications.\u003c/p\u003e\n\u003ch3\u003eStructural evolution during the first sodiation of Pine HC\u003c/h3\u003e\n\u003cp\u003eTo explore the structural evolution of Pine HC during the first discharge process, in situ SAXS experiments were performed (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea \u003cb\u003eand Supplementary Fig.\u0026nbsp;31\u003c/b\u003e). The scattering intensity is directly related to the square of the difference in scattering length density (ΔSLD) between the carbon matrix and the pores. Therefore, SAXS can determine whether Na\u003csup\u003e+\u003c/sup\u003e ions are intercalating into the carbon matrix or filling the closed pores. As sodiation progresses, the scattering intensity of the closed pores in Pine HC initially exhibits a slight increase (slope region) followed by a significant decrease (plateau region) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb,c). For quantification and comparison, ΔSLD between the carbon matrix and the pores at different states of discharge (SODs) was obtained by fitting SAXS data. The sodium storage mechanism of Pine HC can be divided into two stages: before reaching 30% SOD (the slope region), the ΔSLD increased from 20.4\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e to 21.3\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e \u0026Aring;\u003csup\u003e\u0026minus;2\u003c/sup\u003e, which indicates that Na\u003csup\u003e+\u003c/sup\u003e adsorption/intercalation enhances the SLD of the carbon matrix, as the SLD of closed pores is zero (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed)\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. From 30\u0026ndash;100% SOD (the plateau region), ΔSLD drops from 21.3\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e to 17.2\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e \u0026Aring;\u003csup\u003e\u0026minus;2\u003c/sup\u003e, suggesting that Na\u003csup\u003e+\u003c/sup\u003e ions enter and fill the closed pores. These two stages were also captured by in situ XRD and in situ Raman experiments (\u003cb\u003eSupplementary Figs.\u0026nbsp;32 and 33\u003c/b\u003e). In the slope region of sodiation, Pine HC exhibited a weakening of the (002) diffraction peak and a red shift of the G-band, disclosing that Na\u003csup\u003e+\u003c/sup\u003e ion adsorb/intercalate into the carbon layers and electrons occupy the π* anti-bonding band of the graphene platelets.\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e For the plateau region, these phenomena are less pronounced, suggesting that Na\u003csup\u003e+\u003c/sup\u003e intercalation is nearly saturated at this stage. During desodiation, the scattering intensity of Pine HC rises and nearly returns to its initial level, indicating high reversibility of sodium storage within the closed pores (\u003cb\u003eSupplementary Fig.\u0026nbsp;34\u003c/b\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eEx situ \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003eNa ssNMR further investigated the changes in the chemical state of Na. A sharp peak near \u0026minus;\u0026thinsp;10 ppm was observed, corresponding to the diamagnetic Na in the remaining electrolyte and SEI layer (\u003cb\u003eSupplementary Fig.\u0026nbsp;35\u003c/b\u003e) \u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e. As more Na fills the closed pores (0.01-0 V), signals indicating quasi-metallic Na clusters appear, shifting to higher chemical shifts (from 868 ppm to 925 ppm). This is due to the increasing contribution of the Knight shift, which indicates the growing metallic character of Na.\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e Additionally, the presence of Na clusters was visualized by reacting sodiated Pine HC with a 1% phenolphthalein ethanol solution. When the electrode containing Na clusters is placed in the solution, bubbles (H\u003csub\u003e2\u003c/sub\u003e) form and sodium ethoxide is produced, turning the solution red (\u003cb\u003eSupplementary Fig.\u0026nbsp;36\u003c/b\u003e). As the discharge depth increases, the redness of the solution deepens, suggesting an increase in the content of quasi-metallic Na clusters in the electrodes (\u003cb\u003eSupplementary Fig.\u0026nbsp;37\u003c/b\u003e).\u003c/p\u003e\n\u003ch3\u003eEffective pore volume and plateau region capacity\u003c/h3\u003e\n\u003cp\u003eTo investigate the relationship between sodium storage capacity and closed pore structure, we conducted in situ SAXS experiments on all Pine HC samples and RF HC and calculated their Na clusters filled volume fraction after sodiation (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee, \u003cb\u003eSupplementary Fig.\u0026nbsp;38\u003c/b\u003e). As the closed pore size increases (from 1.24 nm (RF HC) to 2.73 nm (Pine HC-10%)), the Na clusters filled volume fraction initially rises and then falls. An average pore size of 2 nm seems to be a critical point (\u003cb\u003eSupplementary Fig.\u0026nbsp;39\u003c/b\u003e); for small closed pores (\u0026lt;\u0026thinsp;2 nm), the filled volume fraction increased with pore size (from 43.1% for RF HC to 51.2% for Pine HC). However, as pore size increased further (\u0026gt;\u0026thinsp;2 nm), the filled volume fraction dropped significantly (26% for Pine HC-10%). We attribute this to two thermodynamic factors: HC defect concentration (I\u003csub\u003eD\u003c/sub\u003e/I\u003csub\u003eG\u003c/sub\u003e) and Na cluster stability\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e. In HCs with small closed pores (RF HC, Pine HC-1%, and Pine HC), stable Na clusters form, and defect concentration induced by rosin enhances the filled volume fraction. Conversely, larger Na clusters are thermodynamically unstable, making formation difficult in HCs with large closed pores (Pine HC-6% and Pine HC-10%). Furthermore, we define these fillable closed pore volumes as effective pore volume (effective pore volume\u0026thinsp;=\u0026thinsp;filled volume fraction \u0026times; closed pore volume) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef). It is evident that the effective pore volume, rather than the entire closed pore volume of HC, provide the sodium storage capacity. By comparing the effective pore volume and the plateau capacity of HCs, we found a strong correlation between the two (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.96) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg). Effective pore volume determines Na\u003csup\u003e+\u003c/sup\u003e plateau storage, indicating that optimizing closed pore size to increase filled volume fraction is crucial for improving HC electrochemical performance.\u003c/p\u003e\n\u003ch3\u003ePilot production of Pine HC and high-energy pouch cells\u003c/h3\u003e\n\u003cp\u003eAs a proof-of-concept, 3 kg of Pine HC were produced using pine sawdust (\u003cb\u003eSupplementary Fig.\u0026nbsp;40\u003c/b\u003e). The estimated production cost is \u003cspan\u003e$\u003c/span\u003e3.53 kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (\u003cb\u003eSupplementary Table\u0026nbsp;10\u003c/b\u003e), which is only 13% of the current commercial HC price (Kuraray Type 2, \u003cspan\u003e$\u003c/span\u003e27.5 kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and significantly lower than the low-cost synthesis HC benchmark (\u003cspan\u003e$\u003c/span\u003e5 kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003csup\u003e48\u003c/sup\u003e Additionally, Pine HC and commercial HC were compared in a three-electrode pouch cells within the voltage window of 1.2\u0026thinsp;\u0026minus;\u0026thinsp;4.5 V (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea,b, \u003cb\u003eSupplementary Figs.\u0026nbsp;41 and 42\u003c/b\u003e). The red and blue profiles illustrate the potential responses of the anode and cathode against the reference electrode (Na metal) under full cell conditions, respectively. Upon reaching the cut-off voltage, the cathode paired with Pine HC exhibited a lower potential of 4.53 V compared to that paired with commercial HC (4.57 V), thus reducing the risk of irreversible phase transitions, gas evolution, and electrolyte decomposition in the pouch cell\u003csup\u003e \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e \u003c/sup\u003e. More importantly, the NFM111||Pine HC cell achieved a specific energy density of 315.8 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (average voltage: 3.09 V), surpassing the 283.4 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (2.98 V) obtained by NFM111||Commercial HC cell (based on the total weight of active cathode and anode materials). The radar chart comparison highlights the advantages of Pine HC over commercial HC (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec \u003cb\u003eand Supplementary Table\u0026nbsp;11\u003c/b\u003e). Furthermore, we fabricated a 4.5 Ah-laminated NFM111||Pine HC pouch cell with an energy density of 202 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (based on the weight of the entire cell) (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed,e \u003cb\u003eand Supplementary Fig.\u0026nbsp;43\u003c/b\u003e). Detailed information about this cell is provided in \u003cb\u003eSupplementary Table\u0026nbsp;12\u003c/b\u003e. After 500 cycles at 90% depth of discharge (DOD), the capacity retention remains above 80% (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef \u003cb\u003eand Supplementary Fig.\u0026nbsp;44\u003c/b\u003e). These results clearly demonstrate that Pine HC holds significant potential for industrial applications in SIBs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eTo summary, we developed an economical, extensible rosin-assisted pore-promoting strategy to precisely engineer the content and size (1.2\u0026ndash;2.7 nm) of nanopores in HC. Based on this, we deconstructed the relationship between sodium storage capacity and closed pore structure, demonstrating that pore size is the critical parameter governing Na filling: HC with smaller closed pore sizes (\u0026lt;\u0026thinsp;2 nm) can increase the Na clusters filled volume fraction by enhancing defect concentration, while HC with larger closed pores (\u0026gt;\u0026thinsp;2 nm) hinders Na cluster formation, resulting in a lower Na clusters filled volume fraction. By optimizing defect concentration and closed pore size, the Na clusters filled volume fraction of the obtained Pine HC exceeds 50%, with a reversible sodium storage capacity of 336 mAh g\u003csup\u003e\u0026minus;\u003c/sup\u003e\u0026sup1; and an ICE of 92.2%. Furthermore, the fabricated 4.5 Ah-laminated NFM111||Pine HC pouch cell achieved a high energy density (exceeding 202 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and exhibited excellent cycling stability, with a capacity retention of 80.8% after 500 cycles. This work represents a promising development path for cost-effective, high-performance anodes for large-scale energy storage systems.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis of HC samples\u003c/h2\u003e \u003cp\u003eTo prepare Pine HC, 50 g of pine waste wood (with 3 wt% rosin content) (Huadong Timber Market, Jinhua, Zhejiang) was first placed in a muffle furnace and heated at 200\u0026deg;C for 6 hours. Subsequently, it was carbonized at 1300\u0026deg;C for 2 hours in a box furnace under a nitrogen atmosphere. The resulting material was then ground using a jet mill and sieved through a 1000-mesh sieve to obtain Pine HC. The rosin was extracted from the pine wood using a Soxhlet extractor to produce rosin-free wood (RF wood), which was then subjected to the same process to obtain RF HC. RF wood was soaked in a rosin ethanol solution containing 1 wt%, 6wt% and 10 wt% rosin relative to the RF wood. After solvent removal, the wood underwent heat treatment, carbonization, and pulverization to produce Pine HC-1%, Pine HC-6% and Pine HC-10%. Other biomass precursors were also soaked in a rosin ethanol solution containing 3 wt% rosin of the precursor and then processed similarly to yield rosin-modified HCs. Commercial HC was obtained from Kuraray Co. Ltd., Japan.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical measurements\u003c/h2\u003e \u003cp\u003eThe slurry containing active material, carbon black, and sodium carboxymethylcellulose (mass ratio 92:3:5) was coated on Cu foil to prepare HC electrodes, with deionized water as the solvent and maintaining an active material mass loading of 5 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The coin-type cells (CR2032) were assembled in an argon-filled glove box using sodium foil, glass fiber, and 1M NaPF\u003csub\u003e6\u003c/sub\u003e solution in a ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 by volume) as the counter electrode, separator, and electrolyte, respectively. Galvanostatic charge-discharge and GITT tests were performed using a Neware battery testing system (CT-4008T-5 V10 mA-164, Shenzhen, China) within a voltage range of 0\u0026thinsp;\u0026minus;\u0026thinsp;2.5V.\u003c/p\u003e \u003cp\u003eThe NFM111 cathode for pouch cells was purchased from Guangdong Canrd Co., Ltd., while the NVP, NFPP, and PBA cathodes were obtained from Hefei Kejing Co., Ltd. Both cathode and anode utilized Al foil as current collectors, with the cathode measuring 4.3\u0026times;5.6 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e and the anode measuring 4.5\u0026times;5.8 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. The electrolyte consisted of a 1M NaPF\u003csub\u003e6\u003c/sub\u003e solution in a mixture of EC, propylene carbonate (PC), DMC, and ethyl methyl carbonate (EMC) (1:1:4:4 by volume) with 3% fluoroethylene carbonate (FEC) additive. A 12 \u0026micro;m polyethylene (PE) separator was employed.\u003c/p\u003e \u003cp\u003eThree-electrode pouch cell was fabricated following the method described by Li et al.\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e and was evaluated using an electrochemical workstation (PARSTAT 4000A).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eMaterials characterization\u003c/h2\u003e \u003cp\u003eThe morphologies and structure of the samples were examined using SEM (CIQTEK SEM3100) and TEM (JEOL, 2100F). XRD analyses were conducted with a Rigaku, TTR-III diffractometer utilizing Cu Kα radiation, with in situ XRD patterns recorded every 7 minutes. Raman spectra and mappings were obtained via a WITec alpha300 R Raman imaging microscope equipped with a 532 nm excitation laser, with in situ Raman spectra collected every 10 minutes. XPS measurements were performed on a Thermo ESCALAB 250Xi spectrometer. TGA-FTIR (PerkinElmer TL-9000) was carried out in a N\u003csub\u003e2\u003c/sub\u003e atmosphere at a heating rate of 10\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The true density of the samples was determined using a JW-M100A analyzer with He as the analysis gas. \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC and \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003eNa ssNMR spectra were acquired at room temperature on a Bruker AVANCE III 400 WB spectrometer. For ex situ experiments, electrodes were collected from Cu foil, transferred into 1.3 mm rotors without rinsing, and sealed with Vespel caps to minimize air or moisture exposure. SAXS experiments were conducted on a SAXSpoint 2.0 equipped with a 50 W micro-focus X-ray source (1 mm \u0026times; 1 mm). The Teubner-Strey model was applied using SasView 5.0.6 software to analyze and obtain nanopore structural information\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. During in situ SAXS experiments, data were acquired every 30 minutes. Background data were obtained using a blank in situ cell, and the measured signal intensity was calibrated using glassy carbon as a reference standard. Based on the measured SLD of closed pores, the porosity of Pine HC, and the density of metallic Na, we estimated the filled volume fraction of Na clusters in HC\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eCalculation methods\u003c/h2\u003e \u003cp\u003eWe used Packmol software to randomly put the rosins and C atoms into a 20\u0026times;20\u0026times;20 \u0026Aring;\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e box\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e. The Ab-initio Molecular Dynamics (AIMD) calculations were carried out by using CP2K software\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e. Goedecker-Teter-Hutter (GTH) pseudopotentials were used to describe the core electrons and the exchange-correlation effects were represented by Perdew-Burke-Ernzerhof (PBE) functional\u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e. The basis sets of H atom, C atom and O atom were DZVP-MOLOPT-SR-GTH-q1, DZVP-MOLOPT-SR-GTH-q4 and DZVP-MOLOPT-SR-GTH-q6, respectively. The energy cut-off was 300 Ry and energy convergence criterion was set to 1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e Hartree. We used constant-volume (NVT) ensemble with a CSVR thermostat and opened OT method during the AIMD simulation\u003csup\u003e\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e. The structure was first annealed at 2000 K with 0.3 fs time step and then annealed at 1500 K with 1.0 fs time step after removing rosins. The free volume and surface area of the final models were calculated and visualized using Multiwfn and VMD.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Natural Science Foundation of China (Nos. 51925207, 52225208, 52202322, 52102321, U23A20579, and 52302323), the National Synchrotron Radiation Laboratory (KY2060000173), the Joint Fund of the Yulin University and the Dalian National Laboratory for Clean Energy (Grant YLU-DNL Fund 2021002), the Fundamental Research Funds for the Central Universities (WK2060140026), the “Transformational Technologies for Clean Energy and Demonstration” Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA21000000), Hefei Municipal Natural Science Foundation (2022021), and China Postdoctoral Science Foundation (Nos. 2023M733361). We thank the USTC supercomputing center for providing computational resources for this project. This work was partially carried out at the Instruments Center for Physical Science, University of Science and Technology of China. Supercomputing facilities were provided by the Hefei Advanced Computing Center.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThese authors contributed equally: Zhihao Chen, Jialong Shen, Hai Yang.\u003c/p\u003e\n\u003cp\u003eAuthors and Affiliations\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHefei National Research Center for Physical Sciences at the Microscale, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Department of Materials Science and Engineering, CAS Key Laboratory of Materials for Energy Conversion, University of Science and Technology of China, Hefei, China.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eZhihao Chen, Jialong Shen, Hai Yang, Yingshan Huang, Wenjie Deng, Yuhang Lou, Guanyin Gao \u0026amp; Yan Yu\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNational Synchrotron Radiation Laboratory, Hefei, China\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYan Yu\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSchool of Materials and Energy, Guangdong University of Technology, Guangzhou, 510006, China\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eXianhong Rui\u003c/p\u003e\n\u003cp\u003eContributions\u003c/p\u003e\n\u003cp\u003eH.Y. and Y.Y. conceived the ideas. Z.C. synthesized the carbon and performed electrochemical measurements with support from Y.H., W.D., G.G., and G.G. H.Y. assembled the pouch cells. J.S. carried out the AIMD simulations. Z.C. wrote the manuscript, H.Y., X.R., and Y.Y contributing to the editing process. All authors were involved in the experimental analysis and have approved the final manuscript.\u003c/p\u003e\n\u003cp\u003eCorresponding author\u003c/p\u003e\n\u003cp\u003eCorrespondence to Yan Yu.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCompeting interests\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eHwang, J.Y., Myung, S.T. \u0026amp; Sun, Y.K. Sodium-ion batteries: present and future. \u003cem\u003eChem. Soc. Rev.\u003c/em\u003e \u003cstrong\u003e46\u003c/strong\u003e, 3529-3614 (2017).\u003c/li\u003e\n\u003cli\u003eZhao, Y. et al. 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However, the structural complexity of hard carbon (HC) anodes hinders the establishment of a clear structure-performance relationship, leading current HC exhibit insufficient performance when paired with advanced cathodes. In this study, we precisely adjusted the content and size of closed pores in HC using an economical, extensible rosin-assisted pore-promoting strategy and quantified the effective pore volume for sodium storage through small-angle X-ray scattering experiments. We show that optimizing the closed pore size to increase the effective pore volume is key to enhancing the electrochemical performance of HC. By controlling the size (~ 2 nm) of closed pores, we enhance the Na clusters filled volume fraction of HC, resulting in an extended low-potential plateau (\u0026lt;0.1 V vs. Na\u003csup\u003e+\u003c/sup\u003e/Na) and higher sodium storage capacity. Additionally, we established a positive correlation between the plateau capacity of HC and the effective pore volume. Consequently, the 4.5 Ah pouch-type sodium-ion batteries assembled with optimized HC here (areal capacity, 2.8 mAh cm\u003csup\u003e-2\u003c/sup\u003e) achieved a high energy density of 202 Wh kg\u003csup\u003e-1\u003c/sup\u003e, with over 80% capacity retention after 500 cycles at 0.5C. This research provides a solution for realizing low-cost, advanced sodium-ion batteries.\u003c/p\u003e","manuscriptTitle":"Achieving over 200 Wh kg-1 Sodium-Ion Pouch Cell by Quantitative Engineering of Hard Carbon Pores","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-06 13:42:47","doi":"10.21203/rs.3.rs-6761243/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","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":"3af1caaa-20c1-452d-80bc-da8e60450b1f","owner":[],"postedDate":"June 6th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":49545958,"name":"Physical sciences/Energy science and technology/Energy storage/Batteries"},{"id":49545959,"name":"Physical sciences/Materials science/Materials for energy and catalysis/Batteries"}],"tags":[],"updatedAt":"2025-07-17T18:50:16+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-06 13:42:47","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6761243","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6761243","identity":"rs-6761243","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}