Poly (ethylene oxide) (PEO)-based polymer electrolytes show the prospect in all-solid-state lithium metal batteries; however, they present limitations of low room-temperature ionic conductivity, and interfacial incompatibility with high voltage cathodes. Therefore, a salt engineering of 1, 1, 2, 2, 3, 3-hexafluoropropane-1, 3-disulfonimide lithium salt (LiHFDF)/LiTFSI system was developed in PEO-based electrolyte, demonstrating to effectively regulate Li ion transport and improve the interfacial stability under high voltage. We show, by manipulating the interaction between PEO matrix and TFSI⁻-HFDF⁻, the optimized solid-state polymer electrolyte achieves maximum Li⁺ conduction of 1.24 × 10⁻⁴ S cm⁻¹ at 40 °C, which is almost 3 times of the baseline. Also, the optimized polymer electrolyte demonstrates outstanding stable cycling in the LiFePO₄/Li and LiNi_0.8Mn_0.1Co_0.1O₂/Li (3.0–4.4 V, 200 cycles) based all-solid-state lithium batteries at 40 °C.