Effect of double and triple-doping of sulfur, nitrogen and phosphorus on the initial coulombic efficiency and rate performance of the biomass derived hard carbon as anode for sodium-ion batteries

Hard Carbons (HCs) are widely investigated as anode materials for Sodium-ion batteries (SIBs), for the abun-dance of the precursors and their easy synthesis. However, the intercalation of Na+ in the HCs is a big challenge for the design of high-performance SIBs. Heteroatom-doping can effectively facilitate the intercalation of Na+ in the anode material. Herein, a series of double and triple-atom phosphorus-nitrogen, phosphorus-sulfur, nitrogen -sulfur and phosphorus-nitrogen-sulfur in the camphor wood (Cmph) derived-HCs are fabricated, and their electrochemical performances as anodes for SIBs are investigated. The P-N-S-Cmph delivers high initial coulombic efficiency (ICE) of 70.74%%, an outstanding rate performance and good cycling stability, maintaining a specific capacity of 280 mAh g-1 at 2000 mA g-1 after 500 cycles. The excellent performances of the anode materials are assigned to the synergetic effect of the heteroatom-doping of S, N and P enlarging the interlayer spacing of the doped-Cmph-HCs, increasing the intercalation/deintercalation rate of Na+ in the HCs; disposing more active sites for the Na+ storage. In addition, sulfur can reversibly react with Na+, reducing the irreversible consumption of Na+ by the surface functional groups. This work presents a simple and effective method of designing high performance anode materials for SIBs.