Structure Regulation of Hard Carbon with Enriched Semi‐Closed Ultramicropores for Enhanced Rapid Sodium Storage

Abstract Regulating the microstructure of hard carbon (HC) anodes has emerged as a popular strategy to enhance the application potential of sodium‐ion batteries (SIBs). However, the low platform capacity and inferior rate property remain significant barriers to their further development. Herein, HC materials with abundant ultramicropores (0.3‐0.8 nm) are prepared employed epoxy resin and zinc acetate as precursors. Benefiting from the abundant hydroxyl and epoxy groups, the synergistic generation of simple aromatic free radicals and the precipitated ZnO promote the cross‐linking between precursor molecules during the first‐step pyrolysis, alter the twisting and folding of carbon layers during high‐temperature calcniantion, thereby precisely regulating the micropore structure of HC. Owing to its abundant ultramicropore structure and the boosted Na + transfer dynamics, the optimal anode demonstrates a superior plateau capacity of 256.2 mAh g −1 at 30 mA g −1 (408.0 mAh g −1 reversible capacity) and rate capability of 317.0 mAh g −1 at 1 A g −1 , outperforming most other resin‐derived carbon materials. In situ Raman combined with in situ XRD testing results demonstrate that the well‐designed HC presents a typical “adsorption‐intercalation‐pore filling” sodium storage mechanism. This work provides a theoretical basis and experimental guidance for high‐performance HC derived from epoxy resin, which is essential for advancements in SIBs.