Organic Cationic-Coordinated Perfluoropolymer Electrolytes with Strong Li+-Solvent Interaction for Solid State Li-Metal Batteries

Abstract

The practical application of solid-state polymer lithium-metal batteries (LMBs) is plagued by the inferior ionic conductivity of the applied polymer electrolytes (PEs), which is caused by the coupling of ion transport with the motion of polymer segments. Here, solvated molecules based on ionic liquid and lithium salt with strong Li⁺-solvent interaction are inserted into an elaborately engineered perfluoropolymer electrolyte via ionic dipole interaction, extensively facilitating Li⁺ transport and improving mechanical properties. The intensified formation of solvation structures of contact ion pairs and ionic aggregates, as well as the strong electron-withdrawal properties of the F atoms in perfluoropolymers, give the PE high electrochemical stability and excellent interfacial stability. As a result, Li||Li symmetric cells demonstrate a lifetime of 2500 h and an exceptionally high critical current density above 2.3 mA cm^-2, Li||LiFePO₄ batteries exhibit consistent cycling for 550 cycles at 10 C, and Li||uncoated LiNi_0.8Co_0.1Mn_0.1O₂ cells achieve 1000 cycles at 0.5 C with an average Coulombic efficiency of 98.45 %, one of the best results reported to date based on PEs. Our discovery sheds fresh light on the targeted synergistic regulation of the electro-chemo-mechanical properties of PEs to extend the cycle life of LMBs.

Keywords: Electrochemical stability; Flexible electronics; Ionic conductivity; Lithium-metal batteries; Perfluoropolymer electrolytes.