Extending the Frontiers of Lithium-Ion Conducting Oxides: Development of Multicomponent Materials with γ-Li₃PO₄-Type Structures

Complex compositional control is typically required in developing ionic conductors to tune their lattice size and the number of carriers. Moreover, compositional complexity may affect their ion-conducting properties. Therefore, in this study, lithium superionic conductors (LISICONs) with γ-Li3PO4-type structures were developed in quasi-ternary (Li-M-M′-M″-O) systems to elucidate the multicomponent effects. Among the compounds examined, Li3.68(Ge0.6V0.36Ga0.04)O4 in the Li4GeO4–Li3VO4–Li5GaO4 ternary system exhibited the highest ionic conductivity (1.5 × 10–4 S cm–1) at 298 K, with extremely low activation energy (∼0.26 eV). Moreover, the ternary systems showed a trend in which those with framework cations with larger ionic radii exhibited enhanced conductive properties. Additionally, the changes in ionic conductivity associated with the ionic radius were larger in ternary systems than those in binary systems. A significant decrease in activation energy, in particular, was observed using multicomponent systems. The formation of a multicomponent framework facilitated compositional and structural optimization, yielding enhanced ion-conducting properties, and advanced the order of optimal ionic conductivities of existing LISICON systems from 10–5 to 10–4 S cm–1.