PVP-Assisted Construction of CoS2 Anode Material with Combined N-Doping and Spatial Confinement Carbon Coating

PVP-Assisted Construction of CoS2 Anode Material with Combined N-Doping and Spatial Confinement Carbon Coating | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 19 January 2026 V1 Latest version Share on PVP-Assisted Construction of CoS2 Anode Material with Combined N-Doping and Spatial Confinement Carbon Coating Authors : Lisan Cui , Jianxiang Ding , You Li , Chunlei Tan [email protected] , Yixin Liu , Ming Liu , and Shenglong Yang Authors Info & Affiliations https://doi.org/10.22541/au.176881356.62874136/v1 144 views 41 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract The limited availability of lithium resources significantly constrains the sustainable development and large-scale application of lithium-ion batteries. Encouragingly, the abundance of sodium resources and their chemical similarity to lithium render sodium-ion batteries highly promising for large-scale energy storage applications. In this study, a nitrogen-doped carbon-encapsulated CoS 2 nano-anode material with core-shell interstitial voids (denoted as N-CoS 2 @C-PVP) was successfully fabricated via a rationally designed preparation process. By introducing PVP, which adsorbs onto the particle surface to form a protective layer, the spatial steric hindrance effect effectively inhibits particle agglomeration, thereby facilitating the synthesis of nanoparticles and the realization of nitrogen doping. Benefiting from the PVP protective layer, a carbon coating with a cavity structure was constructed during calcination and carbonization. This structural architecture effectively accommodates the repeated volume expansion and contraction of CoS 2 during sodiation/desodiation processes, thus enhancing the cycling stability of the material. The N-CoS 2 @C-PVP anode retains a discharge specific capacity of 377.55 mAh g -1 after 3000 cycles at 1 A g -1 , with a corresponding capacity retention of 62.61%, which is significantly superior to that of the PVP-free N-CoS 2 @C counterpart. Additionally, the synergistic effect between nano-sized CoS 2 particles and nitrogen doping enhances the specific capacity and rate capability of the material. PVP-Assisted Construction of CoS 2 Anode Material with Combined N-Doping and Spatial Confinement Carbon Coating Lisan Cui a,b , Jianxiang Ding a , You Li a , Chunlei Tan *,a,b , Yixin Liu a , Ming Liu a , and Shenglong Yang *,a,b a Guangxi Key Laboratory of Bamboo and Timber Structure Digital-Intelligent Construction, Energy-Efficient and Storage Materials Laboratory, Intelligent Environmental Protection Building Materials Laboratory, School of Civil Engineering and Architecture, Guangxi University of Science and Technology, Liuzhou, 545006, China b Guangxi Key Laboratory of Low Carbon Energy Materials, School of Chemical and Pharmaceutical Science, Guangxi Normal University, Guilin, 541004, China Keywords Sodium-ion batteries｜Nano-anode material｜CoS 2 ｜PVP Comprehensive Summary The limited availability of lithium resources significantly constrains the sustainable development and large-scale application of lithium-ion batteries. Encouragingly, the abundance of sodium resources and their chemical similarity to lithium render sodium-ion batteries highly promising for large-scale energy storage applications. In this study, a nitrogen-doped carbon-encapsulated CoS 2 nano-anode material with core-shell interstitial voids (denoted as N-CoS 2 @C-PVP) was successfully fabricated via a rationally designed preparation process. By introducing PVP, which adsorbs onto the particle surface to form a protective layer, the spatial steric hindrance effect effectively inhibits particle agglomeration, thereby facilitating the synthesis of nanoparticles and the realization of nitrogen doping. Benefiting from the PVP protective layer, a carbon coating with a cavity structure was constructed during calcination and carbonization. This structural architecture effectively accommodates the repeated volume expansion and contraction of CoS 2 during sodiation/desodiation processes, thus enhancing the cycling stability of the material. The N-CoS 2 @C-PVP anode retains a discharge specific capacity of 377.55 mAh g -1 after 3000 cycles at 1 A g -1 , with a corresponding capacity retention of 62.61%, which is significantly superior to that of the PVP-free N-CoS 2 @C counterpart. Additionally, the synergistic effect between nano-sized CoS 2 particles and nitrogen doping enhances the specific capacity and rate capability of the material. * E-mail: [email protected] ; [email protected] Background and Originality Content The rapid expansion of the lithium-ion batteries (LIBs) industry poses a severe supply challenge for upstream lithium mineral resources [1-2] . Based on current consumption trends, projections indicate that globally proven lithium reserves will be inadequate to satisfy the projected demand from electric vehicles and a wide array of electronic devices over the next few decades [3-5] . Sodium and lithium belong to the same main group of the periodic table and exhibit similar physicochemical properties. [6-7] . In addition to the natural abundance of sodium, this renders sodium-ion batteries (SIBs) an extremely promising alternative to lithium-ion batteries (LIBs) [8] . Nevertheless, Sodium ions (1.02 Å) possess a considerably larger ionic radius in comparison with lithium ions (0.76 Å) [9] , which renders them unable to intercalate and deintercalate within the interlayer spacing (d = 0.335 nm) of traditional carbon materials., thereby significantly limiting their performance in SIBs [10-12] . Consequently, there is a pressing need to develop new anode materials to promote the development of SIBs technology [13-14] . Metal-sulfur bonds (M-S) in metal sulfides (e.g., FeS, ZnS, MoS₂) exhibit greater covalent character and lower bond strength than their metal-oxygen (M-O) counterparts, due to the lower electronegativity of sulfur [15] . This inherent characteristic facilitates the breaking and reformation of M-S bonds in electrochemical reactions, leading to markedly improved reaction kinetics. Consequently, metal sulfides, which combine high reversible capacity with superior sodium-ion transport properties, stand out as ideal anode candidates for high-energy-density sodium-ion batteries [16] . Notably, cobalt sulfide (CoS 2 ) features both superior electrical conductivity and a high theoretical specific capacity (870 mAh·g⁻¹), making it a promising candidate for high-performance sodium-ion batteries [17] . However, during repeated sodium intercalation and deintercalation, the CoS 2 anode undergoes severe structural degradation and pulverizes due to substantial volume strain [18] . This structural instability directly leads to a rapid increase in irreversible capacity and poor rate performance. Therefore, targeted structural design and modulation of the CoS 2 anode is considered an effective strategy to address its performance degradation during cycling, which is caused by volume expansion and poor conductivity [19] . In recent years, combining carbon materials with nanostructured anodes has been a proven strategy to boost reaction kinetics and cycling performance [20-21] . Among these, the adoption of hollow porous carbon-coated nano-sized active materials can not only effectively enhance the mechanical strength of the active materials and alleviate their volume variation during the charge/discharge process, but also suppress the agglomeration of electroactive nanoparticles, thereby improving the cycling stability of the electrode [22] . Furthermore, the nanoscale structural configuration enables the active material to expose a greater number of electrochemically active sites, thereby boosting the pseudocapacitive behavior of the material [23] . Yin et al. fabricated porous carbon nanofibers integrated with CoS 2 nanoparticles. As a conductive matrix, carbon nanofibers can not only construct a stable electron transport network to enhance the electrical conductivity of the composite, but also provide a buffering space to mitigate the volume expansion of CoS 2 during cycling. Electrochemical measurements revealed that the composite maintained a reversible capacity of 384.6 mAh g -1 after 800 cycles at 1.0 A g -1 , thus verifying its superior rate performance and cycling stability [24] . Li et al. employed the sacrificial template method to assemble Ti 3 C 2 T x MXene nanosheets into thin-walled hollow spheres, on which MOF-derived CoS 2 nanoparticles embedded in nitrogen-doped carbon were uniformly anchored (denoted as MXene@CoS 2 /NC). This material exhibits exceptional sodium-ion storage performance, delivering a reversible specific capacity of 620 mAh g⁻¹ at 200 mA g -1 , and maintaining a capacity of 394 mAh g⁻¹ even at a high current density of 5 A g -1 [25] . Inspired by these recent findings, a nitrogen-doped carbon-encapsulated CoS₂ nanoanode with core-shell interstitial voids (denoted as N-CoS 2 @C-PVP) was successfully synthesized via a unique process design, which exhibits excellent electrochemical performance. The technique innovatively introduces polyvinylpyrrolidone (PVP), which possesses distinctive physicochemical properties, during the precursor synthesis stage. PVP adsorbs onto the particle surfaces to form a protective layer, effectively suppressing particle agglomeration via steric hindrance while simultaneously restricting particle growth, thereby achieving precise control over nanoparticle dimensions. During the high-temperature treatment, the PVP protective layer is carbonized, which together with the externally coated carbon forms a cavity structure. This structural configuration effectively mitigates the volume expansion of CoS 2 particles during charge-discharge cycles, thereby markedly enhancing the cycling stability of the material. Furthermore, the introduction of PVP enables nitrogen doping, thereby further boosting the electrochemical performance of the resultant material. This work provides novel insights into the development of anode materials for sodium-ion batteries. Results and Discussion Preparation of N-CoS 2 @C-PVP materials Figure 1a shows the synthesis procedure of the N-CoS 2 @C-PVP and N-CoS 2 @C materials. The precursor was first synthesized via the co-precipitation method, followed by coating with dopamine hydrochloride, and the final product was obtained through one-step calcination and sulfidation. The control sample was prepared by the identical procedure without the addition of PVP. Figure 1 Diagram of fabricating for N-CoS 2 @C-PVP and N-CoS 2 @C materials (a), Mechanisms for the enhanced Na + storage performance and cycling stability of N-CoS 2 @C-PVP during sodiation/desodiation process (b). Structural characterizations Figure 2a-b illustrates SEM images of the N-CoS 2 @C material. The material suffered from large particle size and severe aggregation, while the introduction of PVP significantly improved the dispersion of the resulting product and effectively confined its particle size to the nanometer scale (Figure 2c-d). As shown in Figure 2e-f, both materials were found to contain Co, S, C, and N elements. Notably, the nitrogen content of N-CoS₂@C-PVP is substantially higher than that of N-CoS₂@C, demonstrating that the incorporation of PVP efficiently elevates the nitrogen doping level of the material. Figure 2 SEM images of N-CoS 2 @C (a, b), N-CoS 2 @C-PVP (c, d), and EDS mapping images of N-CoS 2 @C (e), N-CoS 2 @C-PVP (f). Figure 3a displays XRD patterns of the as-prepared N-CoS 2 @C-PVP and N-CoS 2 @C. The intense diffraction peaks observed for both materials confirm the presence of distinct crystalline structures in the synthesized products. The positions of the diffraction peaks match the standard pattern of CoS 2 (PDF#97-005-3067), confirming the successful synthesis of hexagonal CoS 2 . Moreover, the full width at half maximum (FWHM) of the diffraction peaks corresponding to N-CoS₂@C-PVP (0.2982 nm) is broader than that of N-CoS₂@C (0.2564 nm), suggesting that N-CoS 2 @C-PVP has smaller crystallite sizes. As demonstrated in Figure 3b and 3d, the N-CoS 2 @C-PVP material exhibits a significantly larger specific surface area (52.583 m 2 g -1 ), which is approximately 50 times greater than that of N-CoS 2 @C (1.547 m 2 g -1 ). This can be mainly attributed to the introduction of PVP, which effectively regulates and promotes the formation of nanostructured particles. The larger specific surface area facilitates the exposure of more active sites, thereby enhancing sodium ion storage. Furthermore, the pore size distributions of both N-CoS 2 @C-PVP and N-CoS 2 @C are predominantly composed of mesopores (Figure 3c and 3e). The abundant mesoporous structure provides extra accommodation space for ions and effectively mitigates volume expansion during charge-discharge processes, thereby enhancing the capacity and rate capability. The survey XPS spectra of both N-CoS 2 @C-PVP and N-CoS 2 @C samples confirm the presence of Co, S, C, and N (Figure 3f). Interestingly, the N 1s signal intensity in N-CoS 2 @C-PVP is slightly higher than that in N-CoS 2 @C, indicating that the introduction of PVP contributes a small amount of additional nitrogen to the material. The peaks at 778.3 eV and 780.9 eV are attributed to the Co 2p 3/2 and Co 2p 1/2 energy levels in CoS 2 , respectively, while their respective satellite peaks are detected at 785.3 eV and 803.5 eV. (Figure 3g) [26] . Notably, the N-CoS 2 @C material, the signals at 778.3 eV and 780.9 eV can be further ascribed to CoOₓ species, whereas such oxidized state signals are not significantly observed in the N-CoS 2 @C-PVP sample. This is mainly due to the protective coating formed by PVP on the particle surfaces during the precursor preparation process, which effectively suppresses the oxidation of the Co element. Figure 3h shows that the peak at 162.4 eV can be assigned to the S 2p 3/2 level in Co-S species [27] , while the two peaks observed at 169.1 eV and 170.5 eV are assigned to the S 2p 3/2 and S 2p 1/2 levels in a C x SO y structure, respectively [28] . In addition, the peak located at 164.6 eV is assigned to the S 2p 3/2 level in C-S bonds, indicating that sulfur has been successfully incorporated into the carbon layer [29] . As evidenced by Figure 3i, the binding energies at 284.6 eV and 286.3 eV correspond to sp² and sp³ hybridized carbon, respectively, while the peak at 288.5 eV can be attributed to the N-C bond [30] . Compared with N-CoS 2 @C, N-CoS 2 @C-PVP exhibits a larger peak area at the N-C bond position, indicating an increase in nitrogen content within the material. Figure 3j reveals that N-CoS 2 @C-PVP contains both pyridinic-N and graphitic-N, the excess pyridinic-N species are supplied by PVP [27] . Figure 3k displays the Raman spectra of N-CoS 2 @C and N-CoS 2 @C-PVP materials. For N-CoS 2 @C, distinct characteristic peaks of CoS 2 are observed, while no obvious carbon (C) peak is detected. In contrast, the N-CoS 2 @C-PVP material shows weaker CoS 2 peaks along with a clear C peak. This observed difference can be predominantly ascribed to the larger particle size of N-CoS 2 @C, which results in the Raman measurement area being dominated by CoS 2 signals, thereby failing to capture the carbon signal regions. Thermogravimetric analysis (Figure S1) revealed that the mass fractions of carbon and cobalt disulfide (CoS 2 ) in the N-CoS 2 @C-PVP composite were quantified as 54.2% and 45.8%, respectively. In contrast, the corresponding mass fractions of carbon and CoS 2 in the N-CoS 2 @C composite are 49.6% and 50.1%, respectively [31] . Figure 3 XRD pattern (a), Nitrogen adsorption-desorption isotherms b, d), pore size distribution c, e), XPS spectrum (f), Co 2p region (g), S 2p region (g), C 1s region (i), N 1s region (j), and Raman spectra (k) of the N-CoS 2 @C-PVP and N-CoS 2 @C. HRTEM and HAADF-STEM further studied the fine structures of N-CoS 2 @C and N-CoS 2 @C-PVP. The TEM images in figure 4a and 4i reveal that the particle size of the N-CoS 2 @C-PVP material is smaller than that of N-CoS 2 @C. As presented in Figure 4b and 4j, A dense coating layer was observed on the surface of both materials, which effectively suppresses volume expansion and enhances electrical conductivity. It is noteworthy that in the N-CoS 2 @C-PVP material, there is a distinct gap between the particles and the carbon coating layer. This structural characteristic helps to alleviate the strain induced by volume variation in CoS 2 particles during charge-discharge processes. HAADF-STEM image reveals regions exhibiting that both materials exhibit clear lattice fringes, with the interplanar spacings of 0.300 nm and 0.334 nm (N-CoS 2 @C), and 0.306 nm and 0.338 nm (N-CoS 2 @C-PVP), respectively (Figure 4c-h and 4k-p). Among them, the N-CoS 2 @C-PVP material has a slightly larger interlayer spacing compared to N-CoS 2 @C. This expanded interlayer spacing facilitates the storage and extraction of Na ions. Figure 4 TEM images (a, i), HRTEM image (b, j), HAADF-STEM image (g, k), ABF-STEM image (d, l), the corresponding IFT image of the selected area (e, g, m, o), and lattice spacing (f, h, n, p) of N-CoS 2 @C and N-CoS 2 @C-PVP. Electrochemical performance Cyclic voltammetry (CV) was utilized to characterize Na + ions deintercalation and intercalation behaviors (Figure 5a-b), with measurement performed over a voltage range of 0.01-3.0 V at 0.1 mV s -1 . A prominent reduction peak around 0.71 V was observed, which is attributed to the conversion of CoS 2 to metallic Co and Na 2 S (CoS 2 + 4Na + + 4e - ↔ Co + 2Na 2 S) as well as the formation of the solid electrolyte interface (SEI) for both N-CoS 2 @C and N-CoS 2 @C-PVP. The reduction peaks observed around 0.89 V and 1.43 V are primarily ascribed to the transformation of CoS 2 into metallic Co and Na 2 S [26] . An additional oxidation peak is observed for N-CoS 2 @C at 1.91 V, which corresponds to the transformation process from NaₓCoS 2 to metallic cobalt and eventually to CoS 2 . The potential difference between oxidation and reduction peaks ( ΔE OR = E O -E R ) reflects both the reversibility of the electrode reaction and the extent of polarization [32] . The smaller ∆E OR of N-CoS 2 @C-PVP indicates higher electrochemical reversibility and faster reaction kinetics, primarily attributed to its smaller nanoparticles, which facilitate lithium-ion transport. Furthermore, the smaller ∆E OR also reflects the lower polarization degree of the N-CoS 2 @C-PVP electrode during charge-discharge processes, thus suppressing the occurrence of parasitic side reactions and significantly enhancing the structural stability of the material. The main charge-discharge plateaus observed in the galvanostatic charge-discharge profiles of the electrode materials correspond to the redox peaks in the cyclic voltammetry curves, respectively. The charge-discharge profiles of the N-CoS 2 @C-PVP electrode exhibit a higher degree of overlap than those of the N-CoS 2 @C electrode, indicating that the N-CoS 2 @C-PVP electrode possesses superior structural stability (Figs. 5c–d). The initial Coulombic efficiencies of N-CoS 2 @C and N-CoS 2 @C-PVP are 94.1% and 98.4%, respectively. The lower initial Coulombic efficiency of N-CoS 2 @C is primarily attributed to its larger particle size, which requires the consumption of more active Na for the formation of the SEI film (Figure S2). Figure 5e presents the rate performance of the N-CoS 2 @C and N-CoS 2 @C-PVP from 0.1 A g⁻¹ to 5.0 A g⁻¹. At low current density (0.1 A g⁻¹), the discharge specific capacities of the two material electrodes are 551.6 mAh g -1 and 724.8 mAh g -1 , respectively, with a capacity difference of 173.2 mAh g -1 . Notably, the discharge specific capacities of the two material electrodes are measured to be 221.3 mAh g -1 and 534.2 mAh g -1 at a high current density (5.0 A g⁻¹), respectively, with the capacity difference expanding to 312.9 mAh g -1 , indicating that the N-CoS 2 @C-PVP electrode material possesses a stable structure. In Figure 5f, the cycling performance profiles tested at 0.2 A g⁻¹ show that the two electrode materials exhibit discharge capacities of 364.98 mAh g⁻¹ and 785.76 mAh g⁻¹ after 100 cycles. Furthermore, In Figure 5g, the N-CoS₂@C-PVP electrode retains a discharge specific capacity of 377.55 mAh g⁻¹ after 3000 cycles at 1.0 A g⁻¹, with capacity retention rates of 62.61%. However, the discharge specific capacity of N-CoS₂@C is only 175 mAh g -1 after 500 cycles. It can be seen that the structural stability of the N-CoS 2 @C-PVP electrode is more prominent at high current densities. Figure 5 CV curves (0.1 mV s -1 ) (a-b), discharge/charge curves (0.1 A·g⁻ 1 ) (c-d), rate capability (e), cycling performances (0.1 A·g⁻ 1 , 1.0 A·g⁻ 1 ) (f, g) of the N-CoS 2 @C and N-CoS 2 @C-PVP materials. Figure 6a-b present GITT profiles and calculated Na + diffusion curves of the two electrodes. The calculated D Na + of the N-CoS 2 @C-PVP is 1.98×10 -12 cm 2 S -1 , which is one order of magnitude higher than that of the N-CoS 2 @C electrode (5.3×10 -13 ). Thus, it is evident that the nanoparticle structure shortens the Na⁺ transport pathway and facilitates a faster ion diffusion rate. The improvement of reaction kinetic characteristics was investigated by electrochemical impedance spectroscopy (EIS). N-CoS 2 @C and N-CoS 2 @C-PVP exhibit a lower impedance after 100 cycles, indicating the formation of a stable SEI film on the materials (Figure 6c-d). The results from the fitting calculation are listed in Table S1. After 100 cycles, the R Ω and R ct are 2.72 Ω and 10.34 Ω for the N-CoS 2 @C-PVP electrode , respectively, both of which are lower than those of the N-CoS 2 @C electrode (5.64 Ω and 14.17 Ω) . With increasing scan rates, all curves show similar shapes, which indirectly indicates favorable reaction kinetics and low polarization (Figure 6e-f). The shift in redox peaks intensifies with increasing scan rates, which can be ascribed to ohmic limitations and intrinsic electrochemical kinetics. In general, the correlation between peak current ( i ) and sweep rate ( v ) follows a power-law relationship. i=aν b Eq. 1 log ( i )= b log ( ν )+log ( a ) Eq. 2 Derived from fitted log( i )–log( v ) plots, the b value serves as a standard indicator for differentiating the energy storage mechanisms of electrode materials. As shown in Figure 6g-h, the values for peaks 1 to 5 of the N-CoS 2 @C-PVP electrode are 0.87, 0.92, 0.97, 0.82 and 0.51, respectively, and the N-CoS 2 @C material are 0.84, 0.95, 0.65, 0.49 and 0.89, indicating that the two materials follow a diffusion-controlled and surface-controlled mechanism. The relationship between scan rate and specific capacitance contribution is described by Eq. 3. i = k 1 ν+ k 2 ν 1/2 Eq. 3 Where i is the current density at a fixed potential, k 1 and k 2 are constants corresponding to the slope and intercept of the fitted line between i / ν 0.5 and ν 0.5 , respectively. As depicted in Figure 6i–j, the capacitive-controlled contribution of the N-CoS 2 @C and N-CoS 2 @C-PVP electrode at scan rates from 0.6 - 1.6 mV s -1 , respectively. The N-CoS 2 @C electrode is 23.52, 24.56, 25.88, 29.34, 38.64 and 42.69, while the N-CoS 2 @C-PVP electrode is 64.37, 66.17, 69.27, 71.66, 72.95 and 77.48. The proportion of capacitive-controlled contribution increases with increasing scan rates, which affords a higher capacity at high current densities. The remarkable capacitive contribution of the N-CoS 2 @C-PVP electrode originate from its large specific surface area, which enhances the adsorption of Na⁺ ions. This excellent capacitive contribution facilitates rapid sodium-ion storage kinetics at high current densities, thereby yielding outstanding rate performance. Figure S3a-b illustrates the proportion of capacitive control contribution ratio of the two materials measured at 1.0 mV s -1 . The proportions of surface-controlled contribution (blue regions) are 25.88% and 69.27%, respectively, indicating that the capacitive storage of N-CoS 2 @C is predominantly governed by diffusion-controlled control, whereas that of N-CoS 2 @C-PVP is a surface-controlled process. Figure 6 GITT profiles and calculated Na + diffusion curves (a-b), Nyquist plots (c-d, before/after 100 cycles), CV curves at different scan rates (e-f), pseudocapacitive contribution (g-h) and log ( i ) -log ( v ) plots of cathodic/anodic peaks (i-j) for the N-CoS 2 @C and N-CoS 2 @C-PVP materials. Analysis of enhanced electrochemical performance To elucidate the enhancement mechanism of the core-shell interstitial voids on the electrochemical performance of the N-CoS 2 @C-PVP materials, further SEM and TEM characterizations were conducted on the N-CoS 2 @C-PVP and N-CoS 2 @C materials after 100 charge-discharge cycles. As observed from the SEM images, the particles in the N-CoS 2 @C-PVP composite remained relatively intact without obvious fragmentation after 100 cycles (Figure S4a). In contrast, severe pulverization occurred in the N-CoS 2 @C materials under the same cycling conditions (Figure S4c). This result demonstrates that the core-shell interstitial voids can effectively maintain the structural integrity of the material during repeated cycling processes. Furthermore, HRTEM images revealed that the square morphology of the particles was well-preserved. Meanwhile, the CoS 2 nanoparticles remained uniformly dispersed at the nanoscale even after multiple charge-discharge cycles (Figure S4b). The CoS 2 particles in the N-CoS 2 @C composite underwent severe pulverization and segregation after repeated cycling, with the formation of Na 2 S and Co also being detected (Figure S4d). The aforementioned results confirm that the N-CoS 2 @C-PVP electrode exhibits excellent structural stability. Simultaneously, the CoS 2 within this composite demonstrates remarkable reversibility and stability during the sodiation/desodiation processes (Figure 1b). Conclusions This paper presents a unique preparation process that successfully constructs a nitrogen-doped carbon-encapsulated CoS 2 nano-anode material with core-shell interstitial voids (N-CoS 2 @C-PVP). By introducing PVP, which adsorbs onto the particle surface to form a protective layer, the spatial steric hindrance effect effectively suppresses particle agglomeration, thereby enabling precise control over nanoparticle size. The material exhibits a large specific surface area (52.583 m²·g⁻¹) and demonstrates excellent electrochemical performance as an anode for sodium-ion batteries: at a high current density of 5.0 A g⁻¹, it delivers a discharge specific capacity of 534.2 mAh g⁻¹; and a discharge specific capacity of 377.55 mAh g⁻¹ is retained with a capacity retention rate of 62.61% after 3000 cycles at 1 A g⁻¹, significantly outperforming the PVP-free N-CoS 2 @C material (49.13 mAh·g -1 and 10.4%). Such outstanding cycling stability originates from the core-shell interstitial voids between the carbon layer and nano-size CoS 2 particles, which provide an effective buffer space for volume expansion of CoS 2 during charge-discharge processes. Additionally, the synergistic effect between the nano-sized CoS 2 particles and nitrogen doping boosts the material’s specific capacity and rate capability. This study offers theoretical reference for the rational design and development of high-performance anode materials for sodium-ion batteries. Experimental Firstly, two separate solutions were prepared: (1) 93.4 mg of Co(CH₃COO)₂·4H₂O was dissolved in 50 mL of deionized water ; (2) 83 mg of K₃[Co(CN)₆] and 1.5 g of PVP were dissolved in another 50 mL of deionized water. Subsequently, the two solutions were combined and stirred for 30 min,followed by aging for 24 h, and the precipitate was collected and dried. The dried product was then dispersed in a 10 mmol L-1 Tris(hydroxymethyl)aminomethane solution. Subsequently, 40 mg of dopamine hydrochloride was added to the mixture, and the mixture was stirred for 4 h. Upon completion of the reaction, the product was rinsed with deionized water and then dried in an oven at 80 °C. Finally, the dried precursor and sublimed sulfur powder were placed separately in two crucibles at a mass ratio of 1:4 (with the precursor positioned downstream and the sulfur powder upstream), and calcined at 650 ℃ for 2 h under an argon/hydrogen mixed atmosphere, yielding the final N-CoS 2 @C-PVP material. Under otherwise identical experimental conditions, the sample prepared without the addition of PVP was used as a reference and labeled as N-CoS 2 @C. Characterization Surface morphology and elemental composition of the N-CoS 2 @C and N-CoS 2 @C-PVP were analyzed using a scanning electron microscope (SEM, Philips FEI Quanta 200 FEG) in conjunction with its equipped energy-dispersive X-ray spectroscopy (EDS). The lattice structure was investigated by transmission electron microscopy (TEM, Philips FEI Tecnai G2F30). The chemical states of the metals in the material were analyzed by X-ray photoelectron spectroscopy (XPS, Thermo Scientific Escalab 250 XI). Additionally, the crystal structure was characterized by X-ray diffraction (XRD, Rigaku D/Max-2500 V/PC) with Cu K α radiation (λ= 0.15406 nm). The specific surface area was measured via the Brunauer-Emmett-Teller (BET, NOVA-1200e, Quantachrome). Electrochemical measurements The electrode was composed of 70% active material (N-CoS 2 @C and N-CoS 2 @C-PVP), 15% super P (SP), and 15% carboxymethyl cellulose (CMC). A sodium-ion half-cell (CR2025) was assembled with an electrolyte of 1M NaPF 6 in DME for the evaluation of the electrode’s electrochemical performance. Galvanostatic charge-discharge tests were performed at 25 ℃ with a voltage window of 0.01-3.0 V (NEWARE CT-4008Tn, China). Electrochemical impedance spectroscopy (EIS) measurements were carried out over a frequency range of 0.01 Hz-100 kHz (DH7000C). Supporting Information Acknowledgement This research was supported by National Natural Science Foundation of China (52364035), Guangxi Natural Science Foundation (2025GXNSFHA069076), Guangxi Key Technologies R&D Program (GUIKE AB23075197), The Project to Improve the Basic Research Ability of Young and Middle-aged Teachers in Guangxi Universities (2024KY0367), Specific Research Project of Guangxi for Research Bases and Talents (2021AC19406), The Open Project Fund for Key Laboratory of Disaster Prevention & Mitigation and Prestress Technology of Guangxi Colleges and Universities (GXKDTJ011, GXKDTJ004), Opening Project of Guangxi Key Laboratory of Calcium Carbonate Resources Comprehensive Utilization (HZXYKFKT202203, HZXYKFKT202206), Guangxi Key Laboratory of Low Carbon Energy Materia (2021GXKLLCEM03, 2021GXKLLCEM02), Doctoral Fund of Guangxi University of Science and Technology（XIAOKEBO22z21, 22z22）. References [1] Dong, Y. L.; Huo, J. Y.; Xu, C. F.; Ji, D. Y.; Zhao, H. P.; Li, L. 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Keywords cos2 nano-anode material pvp sodium-ion batteries Authors Affiliations Lisan Cui Guangxi University of Science and Technology View all articles by this author Jianxiang Ding Guangxi University of Science and Technology View all articles by this author You Li Guangxi University of Science and Technology View all articles by this author Chunlei Tan [email protected] Guangxi University of Science and Technology View all articles by this author Yixin Liu Guangxi University of Science and Technology View all articles by this author Ming Liu Guangxi University of Science and Technology View all articles by this author Shenglong Yang Guangxi University of Science and Technology View all articles by this author Metrics & Citations Metrics Article Usage 144 views 41 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Lisan Cui, Jianxiang Ding, You Li, et al. PVP-Assisted Construction of CoS2 Anode Material with Combined N-Doping and Spatial Confinement Carbon Coating. Authorea . 19 January 2026. DOI: https://doi.org/10.22541/au.176881356.62874136/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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