Sustainable Fabrication of a Practical Hard Carbon Anode for a Sodium-Ion Battery with Unprecedented Long Cycle Life

Boosting the application of sodium-ion batteries (SIBs) requires the development of economical and high-performance anode materials. Here, we report a low-cost, environmentally friendly, and scalable preparation method to prepare hard carbon (HC) from a corn starch precursor by bioenzymatic action. This strategy can effectively inhibit the serious foaming of starch during pretreatment and make the internal microstructure of HC have a larger interlayer distance, a more disordered structure, and higher C═O content. As an anode for SIB, the enzymatic-assisted synthesis of HC has a high reversible capacity of 346 mAh·g–1, an initial Coulombic efficiency (ICE) of up to 91%, and a remarkably enhanced sodium-ion transport kinetics of 271 mAh·g–1 at 5C. Moreover, it displays extremely high retention of 92% after 2500 cycles at 1C and 93% after 6500 cycles at 3C. Such HC reaches all of the performance indicators for anode materials as well as a low surface area, demonstrating the advancement of this synthetic strategy in fabricating practical HC. In addition, the full-cell, by coupling with a Na3V2(PO4)3 (NVP) cathode, delivers a high capacity of 323 mAh·g–1 at 1C from the anode side, an outstanding rate capability of 313 mAh·g–1 at 5C, and good cycling performance. These satisfactory electrochemical properties, combined with renewable resources and scalable synthesis routes, enable the present HC to become a practical SIB anode.