Solvent-free and scalable mechanochemical synthesis of high-performance sulfide solid electrolytes

Along the path of developing and establishing solid-state batteries, especially based on sulfides, the demand for upscaled production processes highly increases. Regarding the synthesis of sulfide solid electrolytes, solvent-based processes predominate, whereas dry mechanochemical processes are reported as promising regarding product quality but mainly not scalable. Based on a previous work, which investigated and improved the mechanochemical synthesis of Li3PS4, this study aims to investigate the potential of a continuous and upscaled synthesis of sulfides, such as Li3PS4, Li6PS5Cl and Li5.5PS4.5Cl1.5, in a dry operated stirred media mill. In order to achieve the desired crystallinity of argyrodites after mechanochemical processing, a subsequent heat-treatment under argon atmosphere was conducted. Phase composition, morphology, ionic conductivity and performance of solid electrolytes in laboratory cells were characterized to evaluate suitable process conditions, follow the phase formation and evaluate the final product quality. New insights into the process-structure-property relationships were gained through upscaled experiments from the hundred grams up to the kilogram scale. As previously identified in lab-scale, the process is mainly affected by rotational speed. Additionally, dwell times, achieved through multi-passage processing, production atmosphere and thermal treatment were of high significance. As a result, a scalable and continuous mechanochemical synthesis for sulfide solid electrolytes was developed and demonstrated. High ionic conductivities of up to 5 mScm-1 for Cl-rich argyrodites, measured at room temperature and a pressure of 50 MPa, were achieved and cells performed with high capacity of 170 mAh g-1NCM after 30 cycles and exceptional C-rate performance of 143 mAh g-1NCM at 2C.