Flexible and Interfacial Stable Composite Polymer Electrolyte Membrane for Solid‐State Lithium‐Oxygen Battery: Dispersion of Anti‐perovskite in Insulating Polyethylene Oxide

Abstract This study pioneers the first‐ever integration of an advanced composite polymer electrolyte (CPE) based on polyethylene oxide (PEO) and anti‐perovskite into solid‐state lithium‐oxygen batteries, highlighting its potential in revolutionizing battery performance. The anti‐perovskite Li ₂ OHCl (LOC) exhibits exceptional ionic conductivity of 1.8 × 10 ⁻³ S cm ⁻¹ . When combined with PEO, the CPE achieves ionic conductivities of 0.56 × 10 ⁻³ S cm ⁻¹ at 25 °C and 1.92 × 10 ⁻³ S cm ⁻¹ at 60 °C, seven times higher than conventional PEO membranes. With a lithium‐ion transference number of 0.698, this CPE stands among the best solid electrolytes reported. Compared to liquid electrolytes, lithium symmetric cell with CPE shows a voltage drop of 50% and stable cycling for over 1000 h, demonstrating excellent compatibility with lithium. Additionally, an in situ hybrid polymer electrolyte (HPE) at cathode forms a 3D electronic and ionic conducting network, expanding triple‐phase boundary. Therefore, solid‐state lithium‐oxygen batteries based on HPE/carbon nanotubes || CPE || Li achieve a discharge capacity of 9.5 mAh cm ⁻² and with 1000 h cycle life, nearly 50 times longer than original PEO membranes. This work establishes a new benchmark for lithium‐oxygen batteries, underscoring the transformative potential of anti‐perovskite CPEs in next‐generation energy storage technologies.