Degradable and recyclable polyesters and polycarbonates for next-generation sustainable solid-state lithium metal batteries

With the rapid growth of the portable electronics and electric vehicle markets, there is an urgent demand for lithium-ion batteries with higher energy density and improved safety. Solid polymer electrolytes (SPEs) are considered a key solution to the safety concerns of conventional liquid electrolytes, owing to their superior flexibility, processability, and interfacial compatibility. However, traditional poly(ethylene oxide) (PEO) based electrolytes suffer from low room-temperature ionic conductivity, a narrow electrochemical window, and a low lithium-ion transference number. These limitations make them unsuitable for high-voltage lithium metal batteries. In recent years, polyesters and polycarbonates have emerged as promising next-generation SPE matrix materials, leveraging the unique chemistry of their carbonyl (C=O) groups to deliver high dielectric constants, wide voltage windows, and moderate Li + coordination. More importantly, the chemical tunability of these polymers opens new pathways toward addressing sustainability challenges across the full battery lifecycle. This review systematically covers recent progress in polyester- and polycarbonate-based SPEs that are designed to be degradable and, in selected cases, closed-loop recyclable for solid-state lithium metal batteries. Starting from molecular design principles and ion transport dynamics, we examine the latest strategies for boosting electrochemical performance, including copolymerization, side-chain engineering, crosslinked network topology optimization, and the use of lithium salts as multifunctional catalysts. Representative material systems are categorized by their structural features and electrochemical metrics, with a focus on electrode/electrolyte interfacial chemistry and sustainable strategies for degradation, monomer recovery, and closed-loop recycling. The review concludes with a critical outlook on future directions, oriented toward overcoming barriers to industrial adoption.