Simple and scalable solvent-free PEO based electrolyte fabrication by kneading for all solid state lithium sulfur batteries

PEO is the most investigated polymer for battery solid electrolytes, and continues to be considered state of the art to this day. It is often prepared by tape casting in a solvent-based process. However, solvent-free production of battery electrolytes has become a prominent topic in the recent years in science and industry. This is due to the elimination of one process step – the evaporation of a solvent – sparing production time, material, energy, solvent disposal and thus substantially reducing the production costs. Herein we propose the quick and simple solvent-free preparation of a PEO-LiTFSI electrolyte by kneading on a larger scale with reduced production times compared to conventional solvent based techniques. 50 g of electrolyte are produced at 60 °C within ∼15 min of kneading and another ∼5 min for calendering at 120 °C, whilst for the solvent-based solid electrolyte processing, ∼1.5 h followed by drying over night was required to prepare one solid electrolyte film. The processing and properties of the electrolyte are thoroughly discussed, comparing different conducting salts, polymer molecular weights and polymer–salt concentrations that are evaluated by EIS at different temperatures. An SEM and 4K light microscope-supported post mortem analysis was performed to provide insights on the surface processes of the electrodes that occur during galvanostatic cycling. Moreover, we report the first application of this solvent-free based PEO solid electrolyte in Li–S cells with different electrolyte thicknesses at 50 °C.