Highly Conductive Ester-Based Solid Electrolyte Exhibiting Remarkable Stability for Safe, Sustainable, and High-Performance Lithium Metal Batteries

Abstract

Since the 1970s, polymer electrolytes (PEs) such as poly(ethylene oxide) (PEO) have been extensively studied to address the instability and safety issues associated with lithium metal electrodes. However, these conventional PEs suffer from low lithium transference numbers and narrow electrochemical stability windows. In this work, we introduce innovative solid-state PEs based on crosslinked poly(butyl malonate) (CPBM) and lithium salts. Unlike traditional PEO-based PEs, the CPBM-based PEs are fully amorphous and self-standing, offering a suite of superior electrochemical properties. Notably, they exhibit comparable ionic conductivities to PEO-based PEs but achieve significantly higher lithium transference numbers and an impressive limiting current density enabling efficient ion transport. Another remarkable feature of our CPBM-based PEs is their wide electrochemical stability window, extending up to 4.7 V vs. Li/Li⁺ and an excellent stability with lithium metal. These substantial improvements in electrochemical stability have been rigorously validated through long-term cycling stability tests, including Li stripping/plating and full cells with LiFePO₄ (LFP) and Mn-rich LiMn₀.6Fe₀.4PO₄ (LMFP) electrodes. We firmly believe the polymalonate-based PEs represent a pioneering solution to overcome the limitations inherent in PEO-based PEs and paves a way to safe, high-performance lithium metal batteries, marking a significant leap forward in battery technology.