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

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]n−) 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 LiNi0.6Co0.2Mn0.2O2 (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||LiNi0.8Co0.1Mn0.1O2 (40 mg cm–2) achieves high reversible capacity (6.58 Ah) with a high energy density of 505 Wh kg–1.