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

• • Li/Li symmetric cells with DN-FRQSPE achieve stable cycling beyond 2000 h without dendrite formation, directly addressing the short-circuit failure mode that limits conventional liquid electrolytes to <80 cycles in full-cell configurations. • • Li|DN-FRQSPE|LiFePO4 full cells retain 93% capacity after 200 cycles at 0.2C, corresponding to a 0.035% decay per cycle, which translates to a projected 10-year operational lifespan for stationary storage applications. • • The charge–discharge plateau gap remains only 0.13 V after 100 cycles, indicating low interfacial resistance and excellent compatibility between the DN-FRQSPE and both Li-metal anode and LFP cathode, a critical metric for high round-trip efficiency. • • XPS analysis shows suppressed Fe2+ to Fe3+ conversion in the LFP cathode with DN-FRQSPE, whereas liquid electrolytes cause continuous Fe3+ accumulation and capacity fade, demonstrating the electrolyte's role in stabilizing cathode–electrolyte interfaces.