In situ polymerization of an electrochemically stable dual-salt gel polymer electrolyte for lithium ion batteries†

Abstract

Lithium-ion batteries with solid state electrolytes (SSEs) have improved safety and electrochemical properties; however, the interfacial compatibility between SSEs and electrodes is suboptimal, adversely affecting battery performance. Herein, we report a lithium hexafluorophosphate (LiPF₆) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dual salt gel polymer electrolyte (GPE) by in situ polymerization of 1,3-dioxolane (DOL) within a liquid electrolyte composed of an ethylene carbonate environment-friendly solvent. The LiPF₆ and LiTFSI concentrations have significant influences on the formation of the interface and the uniformity of composition in the GPE, which affect the degree of polymerization, ionic conductivity, and lithium ion transference number. The optimized GPE (15P15T) exhibits a wide electrochemical stability window up to 5.0 V vs. Li⁺/Li. Additionally, the Li‖15P15T GPE‖Li cell demonstrates a high stability against the stripping/plating test for over 2000 h at a current density of 1.0 mA cm⁻², while the liquid electrolyte (LE) fails from 600 h. The assembled Li‖15P15T GPE‖LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cell exhibits better cycling performance compared to the Li‖NCM811 cell with the LE. This work provides a reliable approach toward high voltage lithium-ion batteries with enhanced safety and performance.