A Bulky Anions/Mutli‐Armed Polyethylene Glycol‐Based Composite Gel Electrolyte for Wide‐Temperature Lithium Metal Batteries

The revival of lithium metal batteries (LMBs) highlights the critical importance of enhancing ion transport kinetics and optimizing the interfacial robustness of the anode against cycling degradation. A central strategy in this context involves the development of polymer electrolytes with both high ion conductivities and favorable cation mobility across a broad operational temperature range. Here, an ultrarobust composite gel electrolyte (CGE), engineered from bulky anions and multi-armed polyethylene glycol polymers is reported, capable of promoting efficient lithium salt dissociation and ensuring stable ion deposition in LMBs. This CGE is achieved by blending of polyhedral oligomeric silsesquioxane octacarboxyphenyl lithium salt (POSS-COOLi) with a functionalized POSS derivative containing poly(ethylene glycol) chains. The electron-withdrawing POSS cages not only effectively suppress the freezing of ethylene oxide segments at low temperatures but also enhance the interaction between POSS framework and Li⁺ ions. The CGE at an O/Li molar ratio of 10:1 demonstrates excellent ionic conductivities (3.95 × 10^-4 S cm^-1 at 25 °C and 9.32 × 10^-5 S cm^-1 at -10 °C)-and high lithium transference number (0.85 at 25 °C and 0.73 at -10 °C). The Li/Li and Li/LiFePO₄ cells utilizing this CGE demonstrated superior cycling performance under low-temperature conditions. This breakthrough paves the way for the design of high-safety and low-temperature electrolytes.