Solid polymer electrolytes regulated by ion-dipole interactions for high voltage lithium batteries

Abstract

Solid polymer electrolytes (SPEs) with wide electrochemically stable window and high lithium-ion transference number (t_Li⁺) are a requirement for high energy density lithium batteries. Here, we construct a copolymer electrolyte (PDA) with ether-ester bifunctional groups that exhibits a low highest occupied molecular orbital (HOMO) energy level by in situ polymerization. Compared to the poly(1,3-dioxolane) (PDOL) pure polyether electrolyte, the weakening of the ion-dipole interaction between lithium salt and polymer in the PDA electrolyte promotes the formation of a “weak solvation” structure. Therefore, the electrolyte achieves high oxidative stability (4.6 V vs. Li⁺/ Li with a standard leakage current of 10 μA), high Li⁺ transference number (0.60), and importantly, derives a stable LiF-rich composition on high voltage cathode surface. Which ultimately enables stable cycling of Li||LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) batteries at a range of 3.0–4.3 V. This work provides a fundamental understanding of the design of antioxidant SPEs to achieve high energy density lithium batteries.