Gel Polymer Electrolytes Tailored with Low-Freezing-Point Plasticizers and Film-Forming Additives: Enabling Wide-Temperature-Range Operation of Lithium Metal Batteries

Poor low-temperature performance is one of the critical factors restricting the development of solid-state lithium–metal batteries (LMBs). Gel polymer electrolytes (GPEs), which incorporate liquid plasticizers into the polymer backbone, are regarded as one of the next-generation electrolytes to facilitate the development of LMBs for a wide-temperature range. Herein, we report a modified GPE with a semi-interpenetrating network, which is constructed via UV-initiated cross-linking of poly(ethylene oxide) (PEO) with tetraethylene glycol dimethyl ether monomers (TEGDME). Two types of plasticizers with low freezing points are introduced to coordinate the amorphous structure of polymer chains and also regulate ion migration at low temperatures. Fluoroethylene carbonate (FEC) is introduced as an additive for building a stable solid electrolyte interphase. As a result, a high ionic conductivity of 1.79 × 10–4 S cm–1 for the prepared PPBF-GPE can be achieved at room temperature. Benefiting from the favorable mechanical and electrochemical properties, the Li||Li symmetric cell exhibited stable cycling for over 1000 h at a current density of 0.1 mA cm–2. Accordingly, the assembled Li|PPBF-GPE|LiFePO4 cell can deliver outstanding cycling performance with a specific capacity of 87 mAh g–1 over 500 cycles at 0.2 C even at −10 °C. This work provides a reliable technical path for the design of high-performance polymer-based electrolytes over a wide temperature range and promotes the practical application of LMBs.