Investigating the impact of solid electrolyte particle size/void shape in modulating lithium-ion conduction pathways within graphite composite electrodes using in situ X-ray computed tomography

Abstract

Although all-solid-state batteries (ASSBs) have superior safety and higher energy density than conventional lithium-ion batteries (LIBs), concern regarding inadequate power density originate from the poor Li-ion conduction in composite electrode, especially at high C-rate. Tortuosity of solid electrolyte (SE) within the composite electrode has been considered as one of the major components which influence their electrochemical performance. However, research based on structural information for composite electrodes under actual pressure conditions is not sufficient. Here, we investigated the effect of solid electrolyte particle size on the voids and tortuosity of solid electrolyte in composite electrode and electrochemical performance of composite electrodes using in situ X-ray computed tomography. The results showed that fine Li₃PS₄ resulted in better packing and lowering tortuosity to increasing pressure compared to large Li₃PS₄, which enhanced the electrochemical performance, especially at higher pressure. A detailed analysis on shapes of voids revealed that plate-like voids with low elongation and flatness disappeared and more spherical voids with high elongation and flatness were emerged as external pressure increased. In addition, the voids in the composite electrode using fine Li₃PS₄ particles were less likely to interfere with Li-ion conduction pathways, which improved overall battery performance. This study highlights the important role of SE particle size in optimizing ASSB performance through improved microstructural properties.