Development of a Solid‐Liquid Hybrid Electrolyte Composed of LiTa 2 PO 8 and [C 2 mim][FSA]–Li[FSA] Ionic Liquid for Rechargeable Lithium Metal Batteries

ABSTRACT Although LiTa 2 PO 8 (LTPO) is a promising solid electrolyte for the safe utilization of Li metal anodes, non‐uniform solid‐solid contact at the electrode interface restricts Li + ion conduction and leads to high interfacial resistance. To address this issue, this study investigates the performance of an ionic liquid (IL)‐LTPO hybrid electrolyte prepared by coating the surface of LTPO with a 66.7–33.3 mol% 1‐ethyl‐3‐methylimidazolium bis(fluorosulfonyl)amide ([C 2 mim][FSA])–lithium bis(fluorosulfonyl)amide (Li[FSA]) IL. The introduction of the IL layer successfully maintained a low interfacial resistance even after 2000 cycles. However, the interfacial resistance increases after 3000 cycles at 1.77 mA cm −2 for 60 s, likely due to depletion of the IL, which is necessary for the formation and maintenance of the IL‐derived solid electrolyte interphase (SEI) layer on the Li surface. The chemical stability of the IL‐coated LTPO hybrid electrolyte toward Li metal is examined. LTPO undergoes discoloration upon contact with Li metal, and the reaction is accelerated by the presence of an IL at the Li metal | LTPO interface. This phenomenon is triggered by the reduction of Ta 5+ species in LTPO.