Interfacial Resistance and Degradation Behavior of Uncoated Single-Crystal-like and Polycrystalline NCM523 in All-Solid-State Batteries Analyzed by Three-Electrode Cells

Abstract All-solid-state batteries are promising as safe and high energy density power sources but often suffer from short cycle life due to insufficient solid|solid contact at the electrode|electrolyte interface. It has been reported that the conventional polycrystalline (PC) positive electrode materials need coating to suppress the interfacial reaction with sulfide-based solid electrolytes, while single-crystal-like (SC) materials can be cycled without coating. In this study, the behavior of uncoated SC and PC NCM523 electrodes was comparatively examined in sulfide-based all-solid-state cells using three-electrode cells to resolve the interfacial resistive components and relate them to cycling performance. By employing a chemically reduced Li4Ti5O12 reference electrode, four resistive components were separated, allowing the charge-transfer resistance and the interparticle contact-related resistance to be evaluated independently. The SC cell showed high cycling stability, whereas the capacity of the PC cell once decreased and partially recovered afterward, which was confirmed to be reproducible. With detailed impedance analysis, the capacity loss of the PC cell was chiefly assigned to an increase in the charge-transfer resistance, and the partial recovery was correlated with a contact-related resistance among the NCM523 particles. Both resistive components were kept low in the SC cell, leading to the higher cycling stability of the SC cell.