Suppression of Potasside Reaction in Localized High Concentration Electrolytes Utilizing Fluorine-Substituted Benzene as Bifunctional Additive for Potassium-Metal Batteries

Localized high-concentration electrolytes (LHCEs) have unique solvation structures that do not affect the original salt–solvent coordination from highly concentrated electrolytes. LHCEs enable a wide electrochemical voltage window and mitigate the extensive dendritic growth of metallic anodes. However, in K metal batteries, LHCE undergoes undesirable side reactions because of potasside (K–), triggering aggressive chemistry with a diluent, represented as hydrofluoroethers (HFEs), eventually resulting in poor cycle life. In this study, 1, 3, 5-trifluorobenzene (TFB) was introduced as a functional additive to prevent the parasitic K– reaction. The three symmetrically substituted fluorines prevented TFB from disrupting the as-formed solvation structure of LHCE located in the outer sphere. This characteristic increases the reaction energy barrier between K– and HFE, suppressing the deterioration of the metal anode by adding only 3 wt.% of TFB in LHCE. Moreover, TFB preferentially decomposes at each electrode because of its molecular energy level and increases the reversibility of the cell, reducing unnecessary consumption of electrolytes with a stable interface. This study discusses a novel method to prevent the K– reaction at the electrolyte level and the utilization of LHCE in K batteries to pursue higher energy densities, sustaining the advantage of using a metal anode.