Cosolvent‐Assisted Formation of Charged Ion‐Solvent Clusters and Solid Electrolyte Interphase for High‐Performance Magnesium Metal Batteries

Abstract High‐performance magnesium electrolyte is crucial for the practical application of rechargeable Mg batteries. Herein, a bis(2,2,2‐trifluoroethyl) ether (BTFE) cosolvent is introduced into the chlorine‐containing Mg electrolytes. Theoretical calculations and experimental characterizations reveal that the positive electrostatic potential distributed around the hydrogen atoms in a BTFE molecule could interact with Cl − and facilitate the formation of charged, instead of neutral, ion‐solvent clusters in the BTFE cosolvated magnesium lithium chloride complex (MLCC) electrolyte, which helps to lift its ionic conductivity. The modified solvation structure also lowers the lowest unoccupied molecular orbital energy level of the ion‐solvent clusters, facilitating the in situ formation of solid electrolyte interphase. Using the BTFE cosolvated MLCC electrolyte, reversible Mg plating/stripping can be achieved at 20 mA cm −2 in a Mg//Mg cell, and an ultra‐long cycle life of 1200 h can be achieved at 5 mA cm −2 . The new electrolyte also enables high capacity retention of 160 mAh g −1 after 800 cycles for a Mg//CuS full cell, or super‐long cycle life of over 10 000 cycles at 80 C for a Mg//Mo 6 S 8 full cell. The merits of BTFE cosolvent, universally applicable to other chlorine‐containing Mg electrolytes, open a way to develop practical Mg battery electrolytes.