N/S co-doped carbon coated nickel sulfide as a cycle-stable anode for high performance sodium-ion batteries

Abstract

Transition-metal sulfides (TMDSs) stand out as promising Na-storage anodes due to their high theoretical capacities, low cost and non-toxic. However, the low realizable capacity and poor cycling performance severely hinder their large-scale applications. To achieve high reversible capacity with strong rate capability and long cycle life, N/S co-doped carbon coated NiSx (NiSx-NSC) was prepared via a facile and green calcination method, using thiourea as the nitrogen and sulfur sources. The as-prepared NiSx-NSC exhibits high reversible capacity of 338.4 mAh g−1, outstanding rate capability of 201 mAh g−1 at 2 A g−1 and superior long-term cycling stability of 99.5% capacity retention over 300 cycles, suggesting one of the best Na-storage performances for nickel sulfide. First-principle calculations and EIS characterizations confirm that compared to the pure carbon coated NiSx, the N/S co-doping can modify the electronic structure of the composite to improve the high electronic and ionic transfer kinetics, leading to remarkable Na storage performances.