Salt-Solvent-Polymer Interactions Influence Lithium Salt Distribution in Thermoplastic Vulcanizate Electrolytes

Lithium ion mobility in solvent-doped solid polymer electrolytes depends on interactions between the salt, the polymer and absorbed solvents. This work presents novel electrolytes based on thermoplastic vulcanizates which have been shown to possess the mechanical and electrochemical stability of the elastomeric phase along with the mobility and processability of the thermoplastic phase. Although modest ionic conductivities were obtained for the as-prepared electrolytes, the addition of lithium salt-containing solvents improved conductivity by about 2 orders of magnitude. The presence of multiple lithium salt dissociating phases raises questions regarding the distribution of lithium salt in the electrolyte and the participation of each phase in ion conduction. Ionic conductivity, NMR spectroscopy measurements of salt distribution and ion mobility and vibrational spectroscopy of lithium-coordinating functional groups showed that lithium salts exist in a solvent-swelled polymer phase wherein ionic conductivity depends on a combination of lithium salt distribution, solvent-polymer interactions and local-scale polymer mobility.