Mechanically Engineered Wood Hard Carbon Anodes Achieving 94% Initial Coulombic Efficiency for High Performance Sodium‐Ion Batteries

Hard carbon (HC) is recognized as a viable anode candidate for sodium‐ion batteries (SIBs), its widespread adoption is frequently restricted by low reversible capacity, poor initial Coulombic efficiency (ICE) and inferior rate performance. Herein, a mechanical pretreatment technique, followed by carbonization, is presented to modify the microstructure of basswood‐derived HC for excellent Na + storage performance. The mechanical processing followed by carbonization of basswood transforms its biopolymer structure into a HC with smaller pseudo‐graphitic domains, increased closed porosity, and wider interlayer spacing compared to the untreated samples. This distinctive microstructure enhances low‐voltage plateau Na + storage and accelerates reaction kinetics. This microstructure design delivers three benefits; high‐rate Na + transport, consistent (de)intercalation, and minimized undesirable electrolyte decomposition. The optimized HC sample demonstrates a substantial reversible capacity of 324 mAh g −1 at 0.1 C, an exceptional ICE of 94.1%, impressive rate performance of 238.8 mAh g −1 at 10 C, and remarkable capacity retention of 84.24% after 500 cycles. Density functional theory simulations demonstrate improved Na+ adsorption energies and charge distribution in the modified carbon framework, supporting rapid ion movement and higher electrochemical stability.