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, ClO₄⁻ 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||LiCoO₂ 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.