Mechanically Stable UV‐Crosslinked Polyester‐Polycarbonate Solid Polymer Electrolyte for High‐Temperature Batteries

Abstract Due to the mechanism with which solid polymer electrolytes use to conduct ions, these materials are generally more suitable for high‐temperature applications where the ionic conductivity is sufficient and where liquid electrolytes show insufficient stability. To enable high‐temperature cycling of polymer electrolytes, the mechanical stability has to be improved. Herein, we report successful long‐term cycling of a solid polyester‐polycarbonate – poly(ϵ‐caprolactone‐co‐trimethylene carbonate) (poly(CL‐co‐TMC)) – electrolyte cross‐linked through the addition of multifunctional acrylates and the use of UV‐irradiation, allowing stable cycling of cells for more than 100 cycles at 80 °C, with good rate capabilities (0.2 mA cm⁻²) and Coulombic efficiencies exceeding 99 %. Both the mechanical properties and the ionic conductivity of the mechanically stabilized poly(CL‐co‐TMC) were investigated and optimized to reduce the frequency dependence of the moduli while still achieving an acceptable ionic conductivity at elevated temperature. These results indicate that the poly(CL‐co‐TMC) system can straight‐forwardly be modified to allow for higher‐temperature applications.