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).

Methods
See supporting information from published main text. https://doi.org/10.1021/acsmacrolett.4c00704 In short, polymers were synthesized via anionic polymerization and subsequently functionalized through multiple steps. Polymers were then blended with Li salts and characterized via thermal, electrochemical, and spectroscopic methods.