Reconciling electrolyte donicity and polarity for lithium carbon fluoride batteries

Abstract

Among the existing electrochemical energy storage technologies, lithium carbon fluoride (Li°||CF_x) batteries have captured substantial attention owing to their surprisingly high energy density and low self-discharge rate. The features of nonaqueous electrolytes play an essential role in determining the electrochemical reactions of the CF_x cathode, subsequently affecting the electrochemical performances of Li°||CF_x batteries. Herein, differing from previous stereotypical perceptions, the fascinatingly entangled parameters of nonaqueous electrolytes, comprising permittivity, donicity, and polarity, are comprehensively investigated and reconciled by adopting the solution mixtures of 1,2-dimethoxyethane (DME) and propylene carbonate (PC). The results demonstrate that the higher donicity and moderate polarity of nonaqueous electrolytes (e.g., DME-rich electrolytes) favor the heterolytic dissociation of carbon–fluorine bonds, resulting in more complete electrochemical conversions of the CF_x cathode. This work provides new insights into the electrochemical reaction paths of the CF_x cathode and encourages the electrolyte design for high-energy batteries with other conversion-type electrode materials (e.g., sulfur and oxygen).