A flame retardant and flexible gel polymer electrolytes for high temperature lithium metal batteries

In recent years, rechargeable lithium-ion batteries (LIBs) have been extensively studied and applied in portable electronics, electric vehicles, and new energy storage devices. Gel polymer electrolytes (GPEs), currently a research hotspot, inherit the high ionic conductivity of liquid electrolytes and great mechanical properties and safety of solid electrolytes, exhibiting great application potential. Herein, we demonstrate a flexible flame retardant GPE (PPC37) that forms a polymer network through intermolecular hydrogen bonding. During the charge–discharge cycle, the formation of a LiF-rich solid electrolyte interface (SEI) facilitates the uniform electrochemical deposition of Li⁺ and achieves a long life cycle without dendrites. PPC37 possesses high ionic conductivity (1.06 mS cm⁻¹ at 25 °C) and robust mechanical properties (198% fracture length and 2.43 MPa fracture strength). The Li|PPC37|LiFePO₄ batteries presented great cycling stability with an initial capacity of 151.9 mAh/g and a discharge capacity retention of 86.4% after 500 cycles at a high current density of 3C at 55 °C. The excellent thermal stability, interfacial stability, flame retardancy, flexibility and electrochemical stability demonstrated with PPC37 demonstrate the safety of high-temperature batteries, indicating their great application potential in flexible electronic devices and high-temperature environments.