Stable Cycling of All‐Solid‐State Lithium Metal Batteries Enabled by Salt Engineering of PEO‐Based Polymer Electrolytes

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 LiFePO 4 /Li and LiNi 0.8 Mn 0.1 Co 0.1 O 2 /Li (3.0–4.4 V, 200 cycles) based all‐solid‐state lithium batteries at 40 °C.