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

Abstract 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 MoS 2 @C electrodes is explored using both carbonate and ether‐based solvents. The MoS 2 @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 Fe 7 S 8 @C anodes, demonstrating an exact match between the TMSs and DME electrolytes.