Covalent Organic Frameworks-Enhanced Ionic Conductivity of Polymeric Ionic Liquid-Based Ionic Gel Electrolyte for Lithium Metal Battery

Abstract

Ionic gel electrolyte (IGE) is considered as the promising next-generation safe electrolyte for lithium metal battery (LMB). Herein, the stable crystalline porous material TPB-DMTP-COF (TPB, triphenylbenzene; DMTP, dimethoxy terephthaldehyde), added in the polymeric ionic liquid/ionic liquid (PIL/IL)-based IGE was studied as high ionic liquid loading filler, providing a fast ion channel to enhance ionic conductivity for better performance of LMB. The ionic conductivity of the composite PIL/IL-based IGE with TPB-DMTP-COF at 30 °C is 0.28 mS cm–1, ∼2.2 times higher than the PIL/IL-based IGE without COF and reaches 1.26 mS cm–1 at 60 °C. The enhanced ionic conductivity can be attributed to the higher content of ILs in the composite IGE with TPB-DMTP-COF, the breaking of Coulombic ordering of ILs, and the faster diffusion of the anions of ILs in the pore center of TPB-DMTP-COF, revealed by molecular dynamics simulation. The better rate performance and long cycle (up to 800 at 1 C) of the composite IGE with COFs was obtained through the charge–discharge test. These findings indicate that the IGE obtained in this work has considerable advantages as promising electrolytes for LMBs.