Achieving interfacial stability in lithium metal batteries by PEO/PSBMA-based gel polymer membrane using aqueous solvent

Utilizing high-capacity lithium anodes becomes the most effective strategy to enhance the energy density of lithium metal batteries (LMBs). The associated safety issues can be effectively addressed by employing gel polymer electrolytes (GPEs). Although traditional polyethylene oxide (PEO) based GPE exhibits good compatibility with lithium anodes, its lower oxidative decomposition potential (< 4 V) restricts its application in 4.2 V LMBs. To extend the oxidative stability of PEO, we propose a PEO blended GPE that incorporates the water-soluble zwitterionic polymer, poly(sulfobetaine methacrylate) (PSBMA), synthesized via free-radical polymerization. The blended polymer membrane was fabricated using electrospinning with water as the solvent. The environmentally friendly membrane with porous fiber structure shows the increased ionic conductivity of 1.8 × 10^‐3 S cm^‐1 for PPA25-GPE (PEO: PSBMA = 75 %: 25 %), compared to 1.0 × 10^‐3 S cm^‐1 for PEO based GPE. Furthermore, the oxidative potential of PPA25-GPE is extended to 5 V vs Li/Li⁺. The superior film-forming ability and wettability properties of PSBMA, attributed to its zwitterionic groups, improve the interfacial compatibility between GPE and electrodes, contributing to the cyclic performance of the assembled battery. A Li||Li symmetric cell delivers a stable lifespan of over 2500 h at 0.5 mA cm^‐2 with a fixed areal capacity of 0.5 mAh cm^‐2, while the LiNi_0.8Co_0.15Al_0.05O₂/Li cell exhibits excellent cycling stability and rate capability up to 4.5 V. Consequently, the environmentally friendly nature and electrochemical stability of GPE facilitates the further development of high-energy density LMBs.