Zwitterionic metal covalent organic frameworks constructed from lithium salts to reinforce poly(ethylene oxide)/poly(propylene carbonate) composite polymer electrolytes

The active Li+ was coordinated with the zwitterionic part (squaric acid) of HUT4 by mechanical grinding to prepare a metal covalent organic framework HUT4Li, which was used as the filler of PEO and PPC composite polymer electrolytes (CPEs). The Li+ on the surface of HUT4Li can bind to oxygen atoms in PEO and PPC substrates as Lewis acid sites to promote Li+ transport. In addition, metal covalent organic frameworks with zwitterion ions (HUT4Li) can balance the uneven charge distribution of CPEs, cations capture anions in CPEs to accelerate the transport of Li+, and anions promote the dissolution of lithium salts and better distribute charge. Among them, the PEO-10%HUT4Li composite polymer electrolyte exhibited the best ion conductivity (3.4 x 10-3 S cm-1, 90 degrees C) and the highest lithium ion mobility (0.68, 60 degrees C). The PPC-10%HUT4Li composite polymer electrolyte has better ionic conductivity and a wider electrochemical window. The capacity retention rate of quasi-solid-state Li-S batteries with the PPC-10%HUT4Li electrolyte was 88.9% after 100 cycles at 0.2C. Li+ was coordinated with zwitterionic part (squaric acid) of HUT4 by mechanical grinding to form metal covalent organic frameworks (HUT4Li), which was used as filler of PEO and PPC to improve the ionic conductivity of composite polymer electrolytes.