Enhanced Polysulfides Adsorption and Conversion for High Coulombic Efficiency Sodium‐Ion Batteries

Abstract

AbstractTransition metal sulphides based on conversion reaction mechanism have attracted much attention as anode materials for sodium‐ion batteries owing to their theoretical specific capacity and potential long lifespan. The unsatisfactory Coulombic efficiency, however, inhabits the cycling lifespan due to the intermediate polysulfide formation (Na2Sx; 4≤x≤6) and chain reactions. To enhance the polysulfide polysulfide adsorption capability and capacity, a hybrid with synergistic sodium storage and polysulfide adsorption capability was designed, in which massive CoS2 nanoparticles (CoS2 NP) were utilized as electrons supplier to enhance the adsorption energy of three‐dimensional nitrogen‐doped carbon (3D‐NC) framework towards sodium polysulfide. Combining the experimental and computational results, the encapsulated CoS2 can dramatically optimize the local electronic structure and function as a powerful electron reservoir to increase the effective adsorption to Na2Sx (4≤x≤6). Meanwhile, the electron transferring between CoS2 NP and 3D‐NC can facilitate the conversion of Na2S to Na2Sx. An ultra‐high initial Coulombic efficiency of 98.05 % and 98.38 % can be achieved at current densities of 0.06 A g−1 and 0.4 A g−1, respectively. Beneficial from the high reversible capability, a superior cycling lifespan is obtained up to 800 long cycles at current densities of 0.6 A g−1.