Balancing Solvation Ability of Polymer and Solvent in Gel Polymer Electrolytes for Efficient Lithium Metal Batteries

Gel polymer electrolytes (GPEs) show practical potential in lithium metal batteries (LMBs), but their development is hindered by insufficient understanding of Li⁺ solvation chemistry and its impact on ion transport and solid electrolyte interphase (SEI) formation. By regulating the solvation abilities of polymer and solvent, this work explores the relationships between GPE composition, Li⁺ coordination structures, Li⁺ transference number, and interphase chemistry. The GPE combining weakly coordinated solvents with strongly coordinating polymer results in strong Li⁺-polymer attachment, leading to sluggish ion transport. Employing strongly chelating solvents causes complete Li⁺-polymer detachment, forming micelle structures that obstruct ion transport. The GPE with both weakly coordinated solvent fluoroethylene carbonate (FEC) and polymer 1H,1H,2H,2H-tridecafluoro-n-octyl acrylate (TFOA) enables optimal interactions between Li⁺ and polymer/solvent, facilitating partial Li⁺-polymer detachment and aggregates (AGGs) generation, avoiding micelle formation. This promotes efficient Li⁺ transport and anion-derived SEI generation. The resulting GPE achieves 99.2% Coulombic efficiency (CE) in Cu||Li cells and enables 4.5 V LiNi_0.8Mn_0.1Co_0.1O₂||Li to demonstrate 81% capacity retention after 140 cycles. These findings provide valuable insights for further advanced GPE design.