Enhanced electrochemical performance and interdiffusion behavior of sodium ions in onion-derived freeze-dried and KOH-activated carbon for sodium-ion battery anodes

Biomass-derived carbon materials are widely regarded as promising anode materials for sodium-ion batteries (SIBs) owing to their environmental friendliness, high electronic conductivity, stability, and low cost. However, their commercial application is restricted because of their low capacities and poor cycling stabilities. Heteroatom doping and increasing the active specific surface area of carbon materials have proven to be key to solving these problems. In this study, a facile activation and annealing process combined with freeze drying and KOH treatment was used to successfully prepare nitrogen-doped onion-derived carbon materials (dried onion (DO) and freeze-dried onion (FDO)) with high specific surface areas. The obtained carbon materials exhibited excellent electrochemical performances as anodes for SIBs, delivering high discharge reversible capacities of 140.5 (DO) and 151.4 (FDO) mAh/g at a current density of 0.05 A/g after 30 cycles. The capacities reached 45 (DO) and 66 (FDO) mAh/g at 30 A/g. Specifically, FDO//Na3V2(PO4)3@C full cells achieved a reversible capacity of 43.9 mAh/g with a specific energy of 91.5 Wh kg-1 at 5 C after 1,000 cycles, indicating that it provides broad prospects for the energy storage system of SIBs.