Novel PEO-based composite electrolyte for low-temperature all-solid-state lithium metal batteries enabled by interfacial cation-assistance

Non-flammable succinonitrile (SN) is a promising plasticizer for lowering the working temperature of poly (ethylene oxide) (PEO)-based solid-state polymer electrolytes. However, its application is greatly impeded by the inherent instability interface toward the Li anode. Here, we report a novel PEO/SN-based composite solid-state electrolyte with a durable interface and high room-temperature ionic conductivity of 6.74×10⁻⁴ S cm⁻¹. By taking advantage of cation-assistance between La³⁺ cation in LLZTO and N atom in SN, reducing the active -C[tbnd]N groups or converting them to less reactive -C = N- groups, preventing the corrosion of lithium anode from SN. As a result, PEO/SN-based electrolyte displays highly stable Li plating/stripping cycling for over 1000 h at 0.1 mA cm⁻² at RT. Furthermore, the all-solid-state lithium metal batteries (ASSLBs) based on LiFePO₄ cathode deliver admirable cycling stability with a discharge capacity of 133 mAh g⁻¹ and high-capacity retention of 92.6% after 240 cycles at 0.5C at RT. Even at -10 °C, the batteries still can achieve excellent electrochemical performance. The unique Li⁺ ion conduction pathway is investigated by tracer-exchange ⁶Li NMR. This work proposes new insight via cation assistance to build a durable interface for the real application of PEO/SN-based electrolytes system in ASSLBs.