Polyethylene glycol-based waterborne polyurethane as solid polymer electrolyte for all-solid-state lithium ion batteries

An environmental friendly waterborne polyurethane (WPU) dispersion was synthesized from polyethylene glycol (PEG), hexamethylene diisocyanate (HDI), diethylene glycol (DEG) and dimethylol propionic acid (DMPA). Solid polymer electrolytes based on WPU and LiTFSI were fabricated via an organic solvent free process. The LiTFSI salts were found to be dissolved in WPU by the coordination of Li+ ion with carbonyl and ether group in WPU. The as-prepared WPU showed a semi-crystalline structure and became amorphous after adding lithium salts. The ionic conductivities increased with the increase of salt concentration and followed the Arrhenius behavior. The 20 wt% LiTFSI in WPU electrolyte showed a superior comprehensive performance with an ionic conductivity of 7.3 × 10−4 and 2.2 × 10−3 S cm−1 at 60 °C and 80 °C. All-solid-state LiFePO4/SPE/Li cell using this electrolyte exhibited an initial discharge capacity of 151 mAh g−1 at 0.1C under 60 °C. All of these results demonstrate that this new WPU-based solid polymer electrolyte is a promising environmentally friendly candidate for all-solid-state lithium ion batteries.