Electrochemical Properties of Cathode according to the Type of Sulfide Electrolyte and the Application of Surface Coating

The electrochemical performance of all-solid-state cells (ASSCs) based on sulfide electrolytes is critically affected by the undesirable interfacial reactions between oxide cathodes and sulfide electrolytes because of the high reactivity of sulfide electrolytes.Based on the concept that the interfacial reactions are highly dependent on the type of sulfide electrolyte, the electrochemical properties of the ASSCs prepared using three types of sulfide electrolytes were observed and compared.The Li 2 MoO 4 -LiI coating layer was also introduced to suppress the interfacial reactions.The cells using argyrodite electrolyte exhibited a higher capacity and Coulombic efficiency than the cells using 75Li 2 S-22P 2 S 5 -3Li 2 SO 4 and Li 7 P 3 S 11 electrolytes, indicating that the argyrodite electrolyte is less reactive with cathodes than other electrolytes.Moreover, the introduction of Li 2 MoO 4 -LiI coating on the cathode surface significantly enhanced the electrochemical performance of ASSCs because of the protection of coating layer.Pulverization of argyrodite electrolyte is also effective in increasing the capacity of cells because the smaller size of electrolyte particles improved the contact stability between the cathode and the sulfide electrolyte.The cyclic performance of cells was also enhanced by pulverized electrolyte, which is also associated with improved contact stability at the cathode/electrolyte.These results show that the introduction of Li 2 MoO 4 -LiI coating and the use of pulverized sulfide electrolyte can exhibit a synergic effect of suppressed interfacial reaction by the coating layer and improved contact stability owing to the small particle size of electrolyte.