PEI–LiTFSI electrolytes for electrochromic devices: Characterization by differential scanning calorimetry and viscosity measurements

Polymer electrolytes containing poly(ethylene imine) (PEI) and lithium bis(trifluoromethylsulfonyl) imide (LiTFSI) can serve as model electrolytes for electrochromic devices. Such electrolytes were characterized by differential scanning calorimetry, conductivity, and viscosity measurements. The glass transition temperature (Tg) and viscosity of the PEI–LiTFSI electrolytes have minima at a [N]:[Li] ratio of 100:1. Both Tg and viscosity increased at high salt concentrations. The temperature dependences of ionic conductivity and viscosity followed an Arrhenius equation with parameters depending only weakly on the salt concentration. The fluid behavior of the electrolytes could be reconciled with the Bingham plastic model with parameters being functions of salt concentration.