Functional Sulfate Additive‐Derived Interfacial Layer for Enhanced Electrochemical Stability of PEO‐Based Polymer Electrolytes

Solid‐state electrolyte batteries have attracted significant interest as promising next‐generation batteries due to their achievable high energy densities and nonflammability. In particular, curable polymer network gel electrolytes exhibit superior ion conductivity and interfacial adhesion with electrodes compared to oxide or sulfide solid electrolytes, bringing them closer to commercialization. However, the limited electrochemical stability of matrix polymers, particularly those based on poly (ethylene oxide) (PEO), presents challenges in achieving stable electrochemical performance in high‐voltage lithium metal batteries. Here, these studies report a sulfate additive‐incorporated thermally crosslinked gel‐type polymer electrolyte (SA‐TGPE) composed of a PEO‐based polymer matrix and a functional sulfate additive, 1,3‐propanediolcyclic sulfate (PCS), which forms stable interfacial layers on electrodes. The electrode‐electrolyte interface modified by the PCS enhances the electrochemical stability of the polymer electrolyte, effectively alleviating decomposition of the PEO‐based polymer matrix on the cathode. Moreover, it also mitigates side reactions of the Ni‐rich NCM cathode and dendrites of lithium metal anode. These studies provide a novel perspective by utilizing interfacial modification through electrolyte additives to resolve the electrochemical instability of PEO‐based polymer electrolytes in high‐voltage lithium metal batteries. Polyethylene oxide (PEO)‐based gel‐type polymer electrolytes (GPEs) face challenges due to their limited electrochemical stability in high voltages. An artificial electrode‐electrolyte interface derived from a functional sulfate additive, 1,3‐propanediolcyclic sulfate, demonstrates exceptional stability on the high‐voltage cathode (LiCoO2, Ni‐rich NCM) and lithium metal anode. This mitigates the oxidative degradation of the PEO‐based polymer matrix, enhancing the electrochemical stability of the GPE.