Improved Electrochemical Performance of Sodium/Potassium-Ion Batteries in Ether-Based Electrolyte: Cases Study of MoS2@C and Fe7S8@C Anodes

Transition-metal sulfides (TMSs) are extensively investigated as anodes of low-cost sodium-ion batteries (SIBs) and potassium-ion batteries (KIBs) due to their abundant resources and high theoretical capacity. However, their poor cyclability and low initial coulombic efficiency (ICE) in ester-based electrolytes severely impede their application in SIBs and KIBs. To overcome these drawbacks, ether-based electrolytes are considered as alternatives, but its fundamental principle remains rarely reported and poorly understood. Herein, the electrochemical performance of MoS2@C electrodes is explored using both carbonate and ether-based solvents. The MoS2@C exhibits a higher ICE and Na/K-ion storage capacity (a reversible specific capacity of 625 mAh g(-1) with ICE of 80% for SIBs, and a capacity of 241 mAh g(-1) with ICE of 81% for KIBs, respectively) in dimethyl ether (DME) electrolytes than in ethylene carbonate and diethylene carbonate (EC/DEC) electrolytes. Experimental measurements and theoretical calculation show that the DME electrolytes help to optimize the solid-electrolyte interphase (SEI) composition, facilitate charge transport, reduce the energy barrier for Na/K-ions migration and reinforcing geometry architecture, thus endowing excellent electrochemical performance. Importantly, this electrolyte optimization solution can be extended to other TMSs, such as Fe7S8@C anodes, demonstrating an exact match between the TMSs and DME electrolytes.