Preparation of Lithium Sulfide-Based Cathode Materials and Application to All-Solid-State Batteries

Abstract

All-solid-state Li-S batteries with Li 2 S cathode active materials have attracted considerable attention owing to their high theoretical energy densities; however, the improvement of electron, ion conductivity and the activation of the redox reaction of Li 2 S is challenging owing to its insulating behavior. The addition of multivalent cations (such as Mg 2+ , Ca 2+ , Al 3+ , and Y 3+ ) to Li 2 S results in a higher discharge capacity, thereby improving the ionic conductivity and reactivity of Li 2 S. These cations can form solid solutions or nanocomposites, and may also exhibit catalytic activity. The ionic radii of Mg 2+ (0.57 Å) and Al 3+ (0.35 Å) are similar to that of Li + (0.59 Å); therefore, these additives are expected to form solid solutions. The ionic radius of Ca 2+ (1.0 Å) is larger than that of Li + (0.59 Å), resulting in the formation of CaS-Li 2 S nanocomposites. Y 3+ tends to segregate at the grain boundaries, while Y 3+ on the surface of Li 2 S particles exhibits catalytic effects. This review summarizes the effects of multivalent cation doping on the activation of Li 2 S-based cathode materials.