Converting a Metal-Coordinating Polymer to a Polymerized Ionic Liquid Improves Li⁺ Transport

Solid polymer electrolytes (SPEs) with mechanical strength and reduced flammability may also enable next-generation Li⁺ batteries with higher energy densities. However, conventional SPEs have fundamental limitations in terms of Li⁺ conductivity. While an imidazole functionalized polymer (PMS-Im) has been previously shown to have ionic conductivity related to the imidazole-Li⁺ coordination, herein we demonstrate that quaternization of this polymer to form an analogous imidazolium functionalized polymer (PMS-Im⁺) more efficiently solvates lithium salts and plasticizes the polymer. In addition, inverse Haven ratios as high as 10 indicate positively correlated Li⁺ transport, possibly due to percolation of nanochannels that significantly improve battery-relevant conductivity. From these combined effects, Li⁺ conductivity in PMS-Im⁺ (2.1 × 10^-5 S/cm) is over an order of magnitude greater than in PMS-Im at 90 °C (1.6 × 10^-6 S/cm).