Continuous Li⁺ Coordination Polymer Electrolyte for Fast Li⁺ Migration, Stable Electrolyte Interphases, and Safe Quasi-Solid Lithium Metal Batteries.

Abstract

The advancement of quasi-solid lithium metal batteries strongly hinges on attaining fast Li⁺ transport, stable electrode/electrolyte interphases, and high safety. The present study reports a high-continuous Li⁺ coordination polymer electrolyte composed of a poly(1,3,5-trioxane) (PTXE) skeleton and mixed solvent of triethyl phosphate (TEP) and fluoroethylene carbonate (FEC). The continuous ether chains (-[C-O]_<i>n</i>-) in PTXE coordinated with binary solvents and anions of dual lithium salt (TFSI^- and DFOB^-) optimize the solvent structure and establish rapid Li⁺ migration, achieving high Li⁺ conductivity (1.87 mS cm^-1 at 25 °C) and Li⁺ transference number (0.64) prior to the liquid electrolyte. Simultaneously, via the synergistic induction and regulation exerted by polymer chain segments on the coordination of solvents and anions around Li⁺, phosphorus- and fluorine-rich cathodic and anodic electrolyte interphases are formed. Furthermore, flame-retardant TEP significantly improves the thermal stability at high temperature (60 °C) as well as under harsh mechanical testing. The assembly of a lithium metal battery with high loading mass of LiNi_0.6Co_0.2Mn_0.2O₂ (10 mg cm^-2) and ultrathin Li (50 μm) exhibits a high capacity retention rate of 87.1% with 120 cycles. Furthermore, a large-capacity pouch cell (7 Ah) with Li||LiNi_0.8Co_0.1Mn_0.1O₂ (40 mg cm^-2) achieves high reversible capacity (6.58 Ah) with a high energy density of 505 Wh kg^-1.