A high-flash-point quasi-solid polymer electrolyte for stable nickel-rich lithium metal batteries

In the exploration of next-generation high-energy–density batteries, lithium metal is regarded as an ideal candidate for anode materials. However, lithium metal batteries (LMBs) face challenges in practical applications due to the risks associated with organic liquid electrolytes, among which their low flash points are one of the major safety concerns. The adoption of high flash point quasi-solid polymer electrolytes (QSPE) that is compatible with the lithium metal anode and high-voltage cathode is therefore a promising strategy for exploring high-performance and high-safety LMBs. Herein, we employed the in-situ polymerization of poly (epoxidized soya fatty acid Bu esters-isooctyl acrylate-ditrimethylolpropane tetraacrylate) (PEID) to gel the liquid electrolyte that formed a PEID-based QSPE (PEID-QSPE). The flash point of PEID-QSPE rises from 25 to 82 °C after gelation, contributing to enhanced safety of the battery at elevated temperatures, whereas the electrochemical window increases to 4.9 V. Moreover, the three-dimensional polymer framework of PEID-QSPE is validated to facilitate the uniform growth of the solid electrolyte interphase on the anode, thereby improving the cycling stability of the battery. By employing PEID-QSPE, the Li|LiNi_0.9Co_0.05Mn_0.05O₂ cell achieved long-term cycling stability (Coulombic efficiency, 99.8%; >200 cycles at 0.1 C) even with a high cathode loading (∼5 mg cm⁻²) and an ultrathin Li (∼50 μm). This electrolyte is expected to afford inspiring insights for the development of safe and long-term cyclability LMBs.