Electronic Conductive Paths in Cathode Composites for All-Solid-State Batteries Unraveled from Microscopic Local Resistance

Scanning spreading resistance microscopy (SSRM) is a powerful tool to evaluate microscopic electric properties. The ability to measure the electronic resistance properties in microscopic regions offers a promising route to extend our understanding of electronic transport and degradation mechanisms within electrodes for all-solid-state lithium-ion batteries. To date, however, it is unclear how the contact resistance of active materials and the network resistance of conductive additives affect the local resistance measured by SSRM when they are applied to composite materials. In this study, we investigate the local electronic resistance of LiNi0.5Co0.2Mn0.3O2 (NCM) cathode composites incorporating conductive additives with different contents using SSRM. Increasing conductive additive content decreases the local resistance of NCM domains owing to the reduction in contact resistance. The percolation phenomenon of the conductive additives was observed by SSRM. Moreover, we compare the resistance components and capacities from battery cycling and reveal the effect of contact resistance and network resistance on the battery performance. The cathode composites, where no percolation of conductive additives is formed, show higher capacity than the cathode composites, where percolation is formed. The capacity obtained in these electrodes is dominated by contact resistance, a measure that is unattainable by macroscopic techniques, rather than network resistance. This work provides fundamental insight into electrode design for optimizing electron transport.