Building a safe and stable rechargeable lithium-metal battery by applying a flame-retardant, double-network structural hybrid polyester-based quasi-solid-state polymer electrolyte
Rechargeable lithium-metal batteries (LMBs) offer high energy density but suffer from dendrite formation and parasitic reactions with liquid electrolytes, leading to safety hazards and poor cycling stability. Quasi-solid-state polymer electrolytes (QSPEs) mitigate these issues but often exhibit inadequate thermal stability and Li-metal compatibility. This work presents a double-network structural hybrid polyester-based flame-retardant quasi-solid-state polymer electrolyte (DN-FRQSPE) synthesized via one-step in situ UV curing polymerization. The first network is a loosely cross-linked flame-retardant P-N containing polyacrylate from N,N-bis(2-hydroxyethyl acrylate) aminomethyl phosphonic acid diethylester (BHAAPE); the second network is highly cross-linked PMMA. The DN-FRQSPE exhibits excellent electrochemical performance, flexibility, and flame retardancy. Li/Li symmetric cells demonstrate stable cycling exceeding 2000 h with dendrite-free morphology. Li|DN-FRQSPE|LiFePO4 full batteries deliver a capacity retention of 93% after 200 cycles at 0.2C (0.035% decay per cycle) and a charge–discharge plateau gap of only 0.13 V after 100 cycles. The solid-state system outperforms liquid counterparts, which short-circuit within 80 cycles. Post-mortem SEM and XPS analyses reveal suppressed Fe2+ to Fe3+ conversion and reduced electrode corrosion. This DN-FRQSPE design provides a viable pathway for safe, long-life lithium-metal batteries.