A Novel Potassium Salt Regulated Solvation Chemistry Enabling Excellent Li-Anode Protection in Carbonate Electrolytes

Abstract

In lithium-metal batteries (LMBs), the compatibility of Li anode and conventional lithium hexafluorophosphate-(LiPF₆ ) carbonate electrolyte is poor owing to the severe parasitic reactions. Herein, to resolve this issue, a delicately designed additive of potassium perfluoropinacolatoborate (KFPB) is unprecedentedly synthesized. On the one hand, KFPB additive can regulate the solvation structure of the carbonate electrolyte, promoting the formation of Li⁺ FPB^- and K⁺ PF₆ ^- ion pairs with lower lowest unoccupied molecular orbital (LUMO) energy levels. On the other hand, FPB^- anion possesses strong adsorption ability on Li anode. Thus, anions can preferentially adsorb and decompose on the Li-anode surface to form a conductive and robust solid-electrolyte interphase (SEI) layer. Only with a trace amount of KFPB additive (0.03 m) in the carbonate electrolyte, Li dendrites' growth can be totally suppressed, and Li||Cu and Li||Li half cells exhibit excellent Li-plating/stripping stability upon cycling. Encouragingly, KFPB-assisted carbonate electrolyte enables high areal capacity LiCoO₂ ||Li, LiNi_0.8 Co_0.1 Mn_0.1 O₂ (NCM811)||Li, and LiNi_0.8 Co_0.05 Al_0.15 O₂ (NCA)||Li LMBs with superior cycling stability, showing its excellent universality. This work reveals the importance of designing novel additives to regulate the solvation structure of carbonate electrolytes in improving its interface compatibility with the Li anode.

Keywords: carbonate electrolytes; interface compatibility; lithium-anode protection; novel additives; solvation structure.