In situ preparation of nonflammable phosphorus-containing gel polymer electrolyte for lithium metal battery with enhanced interfacial stability and safety

The large-scale application of lithium metal batteries (LMBs) is restricted by the safety issues, particularly the flammablility of liquid electrolyte and the growth of lithium dendrites. Herein, a novel phosphorus-containing gel polymer electrolyte (GPE) was prepared in situ via thiol–ene click chemistry of ethyl di[2-(acryloyloxy) ethyl] phosphate and di- and tri-thiol monomers directly inside the battery. The GPEs exhibits exceptional flame retardancy and effectively reduces the risk of thermal runaway of batteries with GPE, maintaining high ionic conductivity of 1.42 × 10^-3 S cm⁻¹ at room temperature. The polymer skeleton contributes to the formation of inorganic/organic hybrid solid electrolyte interface (SEI) layer, which can effectively enhance interface stability and suppress the formation of lithium dendrites. As a results, the fabricated LiFePO₄/GPE-3/Li cells exhibited excellent rate performance and stable cycling, retaining 90 % of capacity at 0.5C after 800 cycles. Furthermore, LiCoO₂/GPE-3/Graphite full cells demonstrate a capacity retention of 95.7 % at 0.2C after 50 cycles within the voltage range of 3.0–4.45 V, confirming the superior cycling stability of GPE-3 in high-voltage, high-capacity battery systems. This work presents a GPE that not only enhances the safety of LMBs but also significantly improves their electrochemical performance, offering a promising solution for the practical application of high-energy–density LMBs.