Novel waterborne polyurethane based electrolytes for lithium batteries-(IV). The influence of DMPA/PEG ratios on conductivity

Three waterborne polyurethane (WPU) films with the molar ratios of dimethylol propionic acid (DMPA) to polyethylene glycol (PEG) at 0.1, 1, and 3 were prepared by using our modified acetone process. The effects of DMPA/PEG on conductive behavior were investigated by comparing the ionic conductivity of these dry films, their gel-type films, and gel-type electrolytes. The gel-type films and gel-type electrolytes were prepared by impregnating the dry films with 50 wt% propylene carbonate (PC) and 1M LiClO₄/PC, respectively. The ionic conductivity was determined by running alternating current (AC) impedance with stainless steel (SS)/dry film/SS and Li/gel film/Li cells. Differential scanning calorimetry (DSC) and polarizing microscopy (PM) were employed for material characterization to explain the reason for different conductivities. The room temperature conductivities of gel-type films and gel-type electrolytes are ~10^-5 S/cm and ~10^-4 S/cm, respectively.