Dual-salt reinforced polyacrylonitrile-based composite solid electrolyte for stable lithium metal batteries

Composite solid electrolytes (CSEs) have exhibited considerable promise in the advancement of solid-state lithium batteries, attributed to their inherent safety, straightforward manufacturing processes, and flexibility. Nevertheless, the practical applications of CSEs are constrained by their low ionic conductivity and insufficient interfacial compatibility. Herein, we proposed a strategy for modulating Li⁺ conduction and interfacial compatibility by incorporating Lithium bis(trifluoromethanesulfonyl)imide/Lithium bis(oxalate)borate (LiTFSI/LiBOB) dual salts in polyacrylonitrile-based CSE. The optimized CSE with a LiTFSI/LiBOB molar ratio of 1:3 (F/B-1:3) exhibits a high ionic conductivity of 4.11 × 10^-4 S cm^-1 (30 °C) and Li-ion transference number of 0.68. This can be attributed to the increased concentration of dissociated Li⁺ resulting from the interaction among dual salts, polymer, and aerogel fillers. Moreover, the F/B-1:3 electrolyte induces the formation of a solid electrolyte interface (SEI) layer containing LiF/Li₃N/B-O species, promoting uniform Li deposition and strengthening the compatibility between F/B-1:3 electrolyte and Li metal anode. As a result, the Li|F/B-1:3|Li symmetrical cell exhibits outstanding cycling stability with over 1600 h at 0.1 mA cm^-2 without short circuits. Noteworthy, the assembled Li|F/B-1:3|NCM811 cell demonstrates a capacity retention of 86.5 % after 200 cycles and an average coulombic efficiency of 99.87 % at 1C.