Rod-shaped monoclinic CoMo2S4 with exceptionally reversible phase conversion for sodium storage

Abstract Binary metal sulfides have gained wide attention for sodium storage materials benefiting from rich redox sites, high electrochemical activity and high electronic conductivity. However, poor cycle performance and structure reversibility still restrict their applications. Therefore, rational element combination with the exclusive preparation methods are of great significance. Herein, a rod-shaped CoMo2S4 (CMS) with a monoclinic phase was successfully synthesized and investigated as a new anode material for sodium-ion batteries. CMS exhibits promising cycle performance and rate capability (418.1 mAh g−1 at 0.5 A g−1 and 228.9 mAh g−1 at 8 A g−1). The investigation of detailed sodium storage mechanism for CMS reveals exceptionally reversible phase conversion between CMS and metallic Co/Mo phases without generating monometal sulfides (CoSx or MoSx) during discharge and charge processes. The synergistic catalytic effect of ultrafine Mo and Co nanoparticles on the decomposition of Na2S plays a vital role in the reversible phase transition of CMS, which provides new insights for the design of binary metal sulfide anodes for sodium-ion batteries.