Effective mechanochemical synthesis of sulfide solid electrolyte Li3PS4 in a high energy ball mill by process investigation

Mechanochemical syntheses have a high potential as environmentally friendly and scalable processes. However, especially in case of solid electrolytes, these syntheses are reported as very time consuming with process times up to several days. In this study, the sulfide solid electrolyte Li3PS4 was successfully synthesized in less than 5h after a systematic variation and subsequently optimization of the process parameters in a high energy ball mill. The synthesized electrolyte samples were characterized according to their composition, morphology, particle size distribution and ionic conductivity. Therefore, a better understanding of the process-structure-property relations and process efficiency was achieved. Thus, the results allow a correlation between the stressing conditions and kinetic rates. The stressing conditions are mainly affected by process parameters such as rotational speed, grinding media size and grinding media filling ratio. The kinetic of the mechanochemical process is highly dependent on the normal power input by head-on collisions, leading to a reduction of conversion time with increasing specific power input. The different sets of investigated process parameters also exhibit systematic effects on the crystallinity and particle size distribution of the solid electrolytes. As a result, a highly enhanced process with lowest specific energy demand was achieved by using the largest grinding media with highest rotational speeds at medium grinding media filling ratio.