Anion Donicity of Liquid Electrolytes for Lithium Carbon Fluoride Batteries

Abstract The increasing demand for high‐energy powers have greatly incentivized the development of lithium carbon fluoride (Li||CFx) cells. Five kinds of non‐aqueous liquid electrolytes with various kinds of lithium salts (LiX, X=PF6−, TFSI−, BF4−, ClO4−, and CF3SO3−) were comparatively studied. Intriguingly, the LiBF4‐based electrolyte show relatively moderate ionic conductivities; yet, the corresponding Li||CFx cells deliver the highest discharge capacities among them. A combination of morphological and compositional analyses of the discharge CFx cathode suggest that the moderate donicity of BF4− anion is accountable for favoring the breakdown of C−F bonds, and subsequently forming crystalline lithium fluoride as the main discharge products. This work brings not only fresh understanding on the role of salt anions for Li||CFx cells, but also inspire the electrolyte design for other conversion‐type (sulfur and/or organosulfur) cathode materials desired for high‐energy applications.