Reconciling electrolyte donicity and polarity for lithium carbon fluoride batteries

Abstract

Among existing electrochemical energy storage technologies, lithium carbon fluoride (Li°||CFx) batteries have captured enormous 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 CFx cathode, and subsequently impacting the electrochemical performances of the Li°||CFx batteries. Herein, differing from previous stereotypical perceptions, the fascinatingly entangled parameters of non-aqueous electrolytes, enlisting permittivity, donicity, and polarity, are comprehensively investigated and reconciled, adopting the solution mixtures of 1,2-dimethoxyethane (DME) and propylene carbonate (PC). The results demonstrate that a 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 CFx cathode. This work not only brings a fresh mechanism understanding on the electrochemical reaction paths of CFx cathode, but also spurs the electrolyte design for high-energy batteries with other conversion-type electrode materials (e.g., sulfur, oxygen).