Decoupling the Ionic Conductivity and Elastic Modulus of Gel Electrolytes: Fully Zwitterionic Copolymer Scaffolds in Lithium Salt/Ionic Liquid Solutions

摘要

A critical barrier to overcome in the development of solid-state electrolytes for lithium batteries is the trade-off between sacrificing ionic conductivity for enhancement of mechanical stiffness. Here, a physically cross-linked, polymer-supported gel electrolyte consisting of a lithium salt/ionic liquid solution featuring a fully zwitterionic (ZI) copolymer network is introduced for rechargeable lithium-based batteries. The ZI scaffold is synthesized using a 3:1 molar ratio of 2-methacryloyloxyethyl phosphorylcholine and sulfobetaine vinylimidazole, and the total polymer content is varied between 1.1 and 12.5 wt%. Room-temperature ionic conductivity values comparable to the base liquid electrolyte (approximate to 1 mS cm(-1)) are achieved in ZI copolymer-supported gels that display compressive elastic moduli as large as 14.3 MPa due to ZI dipole-dipole cross-links. Spectroscopic characterization suggests a change in the Li+ coordination shell upon addition of the zwitterions, indicative of strong Li(+center dot center dot center dotbold)ZI group interactions/bold. Li+ transference number measurements reveal an increase in Li+ conductivity within a ZI gel electrolyte (tLi+ nearly doubles). ZI gels display enhanced stability against Li metal, dendrite suppression, and suitable charge-discharge performance in a graphite|lithium nickel cobalt manganese oxide cell. Fully ZI polymer networks in nonvolatile, ionic liquid-based electrolytes represent a promising approach toward realizing highly conductive, mechanically rigid gels for lithium battery technologies.