Ca Mobility in NASICON Battery Materials Studied from First-Principles

Batteries using multivalent charge carriers present a promising alternative to traditional Li-ion technology, offering the potential for higher energy densities and often relying on more abundant elements. However, their ion mobility within the electrolyte and cathode is generally lower than that of monovalent carriers due to stronger electrostatic interactions, heightening the need for materials that can provide high ion mobility. NASICON materials are known for their high ion mobility with monovalent carriers such as lithium and sodium and are widely used as solid electrolytes. In this computational study, we investigate two NASICON materials in particular with respect to their ion mobility for the bivalent charge carrier calcium, focusing on how the transition metal's atomic size in the NASICON material influences the height of the migration barrier and the properties of the materials as a solid electrolyte or electrode material. We found both materials to be good candidates for solid electrolytes with sufficiently low ion migration barriers. We confirm that the triangular faces of the octahedra along the reaction path whose size scales with the radii of the transition metal atoms act as the bottlenecks for migration.