A scalable one-pot strategy for the development of polymer electrolytes adaptable to room-temperature high-voltage lithium batteries

Poly(ethylene oxide) (PEO) polymer electrolytes (PEs) have been commercially applied in LiFePO4||Li solid-state lithium batteries (SSLBs). However, it remains challenging to develop PEO-based PEs applicable to the high-voltage SSLBs with higher energy density, owing to the poor electrochemical stability of PEO. Herein, we report a scalable strategy for fabricating PEO-based PEs with high-voltage compatibility, by exploiting a new mechanism to stabilize the cathode-electrolyte interface in the high-voltage SSLBs. The protocol only involves a one-pot synthesis procedure to covalently crosslink the PEO chains, in the presence of high-content lithium bis(trifluoromethylsulphonyl)imide (LiTFSI) salts and N,N-dimethylformamide (DMF). LiTFSI-DMF supramolecular aggregates are formed and firmly embedded in the polymer network, endowing the PE with high room-temperature ionic conductivity. The dissociated and highly concentrated TFSI− anions can enter the Helmholtz layer close to the high-voltage cathode, leading to the formation of a thin and homogeneous cathode electrolyte interface (CEI), mainly composed of LiF, on the cathode. The CEI with high electrochemical stability can effectively stabilize the cathode-electrolyte interface, enabling long-term stable cycling of the high-voltage LiCoO2||Li and nickel-rich NCM622||Li batteries at room temperature. The simplicity and scalability of the strategy makes the reported PEO-based PE potentially applicable in high-voltage SSLBs in practice.