Solvent-free processing of solid state electrodes based on a plastic crystal electrolyte system

Succinonitrile (SN) has long been known as a useful additive in polymer electrolytes and lately as an electrolyte basis for solid state Li-ion batteries. However, the processing of such a material into corresponding composite electrodes has yet to be addressed in depth. We studied here several paths, comparing an infiltration method to the more scalable and therefore industry-relevant extrusion-based processing route. The latter has the advantage of solvent-free processing as well as reducing the numbers of processing steps from the base materials to the electrode foil and improving the achievable porosity fill rate. The electrodes consists of state of the art NCM-622 (cathode) and LTO (anode) active material mixed with an SN-based polymer mixture: a backbone polymer such as PAN and ionic salts such as Li-TFSI provide ionic conductivity. Finally, due to fiber reinforcement of the electrolyte with glassfiber nonwoven a mechanical stability during processing, reduction of short circuits and a fixed electrolyte thickness could be achieved. According to our design considerations the cell can reach an energy density of 590 Wh/L based on these components. A benchmark infiltration process is compared to the new preparation process: the mixing of all the components into a homogeneous electrode paste using a kneading machine with high shear stress. The active material content can be maximized by processing the material at an optimal temperature where the electrolyte mix exhibits a low-viscosity behavior. We characterize the corresponding product from a composition and structure standpoint with SEM and EDX analyses as well as porosity measurements. We further analyze the complete cells from an electrochemical standpoint with C-rate capability and cell longevity.