Microstructure Regulation of Hard Carbon through a Sacrificial Pore-Forming Strategy for High-Rate Sodium Storage

Hard carbon is considered one of the most promising anode materials for sodium-ion batteries due to its high structural tunability, low working potential, and stable cycling stability. However, the trade-off relationship between sloping capacity and plateau capacity in the regulation of specific surface area, pore structure, and interlayer spacing limits the improvement of its rate performance and sodium storage capacity. To address this issue, based on a green phenolic resin precursor system, this work introduces polyvinylpyrrolidone (PVP) as a "sacrificial pore-forming agent" to regulate the evolution of the surface structure and pores of hard carbon. Research indicates that PVP undergoes vigorous decomposition during high-temperature carbonization, significantly inhibiting the ordered stacking of graphitic microcrystals via an in situ gas-phase etching effect, and inducing the formation of abundant surface defects, open channels, and closed-pore structures. The optimized hard carbon sample, HC-PVP-10%, exhibits a high reversible capacity of 335 mAh g^-1 at 0.1 C and maintains competitive rate performance of 235 mAh g^-1 at a high rate of 5 C. Structural characterizations such as X-ray diffraction and Raman, electrochemical performance analysis, and density functional theory calculation results collectively confirm that the material follows an "adsorption-intercalation-filling" sodium storage mechanism. This work not only deepens the fundamental understanding of the structure-property relationships of hard carbon materials but also provides insights for the preparation of next-generation high-energy-density and fast-charging sodium-ion battery anodes.