Anion Donicity of Liquid Electrolytes for Lithium Carbon Fluoride Batteries

The increasing demand for high-energy powers have greatly incentivized the development of lithium carbon fluoride (Li||CF_x ) cells. Five kinds of non-aqueous liquid electrolytes with various kinds of lithium salts (LiX, X=PF₆ ^- , TFSI^- , BF₄ ^- , ClO₄ ^- , and CF₃ SO₃ ^- ) were comparatively studied. Intriguingly, the LiBF₄ -based electrolyte show relatively moderate ionic conductivities; yet, the corresponding Li||CF_x cells deliver the highest discharge capacities among them. A combination of morphological and compositional analyses of the discharge CF_x 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||CF_x cells, but also inspire the electrolyte design for other conversion-type (sulfur and/or organosulfur) cathode materials desired for high-energy applications.