The Synergistic Effect of Anion: Design of Stable Ether Electrolytes for Li Metal Batteries Beyond 4.6 V

Abstract Improving the compatibility of ether electrolytes with high voltage condition is the key to realize high energy density lithium metal batteries (LMBs) with stable cycling, in which constructing a good cathode electrolyte interphase (CEI) is very important. Herein, a special synergistic effect of anion is found with a CEI‐forming agent solvent, which significantly improves the oxidation resistance of conventional ether electrolytes. In this work, ClO 4 − is chosen for its strong adsorption ability, and fluoroethylene carbonate (FEC) is the CEI‐forming agent. The interaction between them regulates the decomposition of anions and solvents on the cathode surface. As revealed by various tests, a thin, robust, and homogeneous CEI is generated, which ensures a stable 1,2‐dimethoxyethane (DME)‐based electrolyte to normally work in a Li||LiCoO 2 cell for 1000 cycles at a high cut‐off voltage of 4.5 V (>80% capacity retention). Differing from common approaches to enhance the oxidative stability of ether‐based electrolytes, this model relies only on the synergistic effect of a simple anion (adsorbent) and film‐forming agent, enabling the stable cycling of the cell using the conventional ether‐based electrolytes even at 4.65 V cut‐off voltage. The design strategy provides important guidelines for the implementation of ether‐based LMBs with high energy density under high voltages.