Composite Polymer Electrolyte Membrane for Efficient Anodic and Cathodic Processes for Quasi-Solid-State Lithium–Oxygen Batteries

Solid-state lithium–oxygen batteries are intensively researched for their superior energy density, operational stability, and safety over the liquid electrolyte analogues; however, they face several crucial challenges, such as instability of the lithium anode and high interfacial resistance for efficient oxygen redox reactions at the cathode. In this study, we designed and optimized a bilayer electrolyte membrane to protect the anode and facilitate efficient oxygen reduction (ORR) and oxygen evolution (OER) reactions at the cathode. The anode side had a copolymer (PVDF–HFP) with a lithium salt (LiTFSI), while the cathode side additionally contained varying amounts of LiTa₂PO₈ (LTPO) as solid electrolyte and SN as a plasticizer. The quasi-solid-state lithium–oxygen battery (QSSLOB) fabricated using the bilayer membrane having 20 wt % of LTPO, a small amount (∼30 μL) of liquid electrolyte (1 M LiTFSI/0.5 M LiI in TEGDME) at the cathode side delivered a discharge capacity (∼6885 mAh g^–1), excellent rate capability, and stable cycling (>424 cycles/100 mA g^–1 and 105 cycles/300 mA g^–1 at 25 °C) and outperformed several other control devices and reported QSSLOBs. A series of tests and inspections were undertaken to determine the factors contributing to the superior performance of the optimized device; together, these studies revealed a wide electrochemical stability window, superior lithium diffusion coefficient, favorable lithium transference number, excellent interfacial stability, and facile discharge–charge kinetics, leading to efficient lithium-ion transport and oxygen redox reactions, reduced oxygen crossover, and stable solid electrolyte interphase. The approach hereby could be a step forward for deployable LOBs in the beyond-lithium-ion battery scenario.