Triple‐Layered Noncombustible PEO‐Based Solid Electrolyte for Highly Safe Lithium‐Metal Batteries

Lithium-metal batteries are currently recognized as promising next-generation technologies owing to their high energy density. Solid polymer electrolytes, particularly those based on polyethylene oxide (PEO), are lauded for their leakage resistance, safety, and flexible design. Despite the ongoing fire safety- and ionic conductivity-related concerns, a novel noncombustible solid polymer electrolytes with superior ionic conductivities are introduced here with additive decabromodiphenyl ethane and zeolite. To enhance the mechanical strength and ensure soft interactions at the electrode interface, a triple-layer structure with self-extinguishing properties and robust ionic conductivity is proposed. Notably, the softness at the electrode interface intensifies as the LiTFSI concentration increases; this higher concentration negatively impacts PEO crystallinity, enhancing the ionic conductivity owing to the presence of free Li⁺ and TFSI^- ions. This novel electrolyte can achieve a conductivity of 1.5 mS cm^-1 at 60 °C, maintain anodic stability up to 4.8 V, and exhibit flame retardancy. Furthermore, adding LiTFSI at 60% relative to PEO is shown to reduce LiF formation on the surface, enhancing anode stability. The [LiFePO₄/triple-layered electrolyte/Li] lithium-metal batteries are capable of an initial capacity of 153 mAh g^-1, sustained superior capacity retention of 87.9%, and high Coulombic efficiency (99.6%) over 1000 cycles at a 1C rate.