Nonstoichiometry and Li-ion transport in lithium zirconate: The role of oxygen vacancies

Understanding Li-ion migration mechanisms and enhancing Li-ion transport in Li₂ZrO₃ (LZO) is important to its role as solid absorbent for reversible CO₂ capture at elevated temperatures, as ceramic breeder in nuclear reactors, and as electrode coating in high-voltage lithium-ion batteries (LIBs). Although defect engineering is an effective way to tune the properties of ceramics, the defect structure of LZO is largely unknown. This study reports the defect structure and electrical properties of undoped LZO and a series of cation-doped LZOs: (i) depending on their charge states, cation dopants can control the oxygen vacancy concentration in doped LZOs; (ii) the doped LZOs with higher oxygen vacancy concentrations exhibit better Li⁺ conductivity, and consequently faster high-temperature CO₂ absorption. In fact, the Fe (II)-doped LZO shows the highest Li-ion conductivity reported for LZOs, reaching 3.3 mS/cm at ~300°C that is more than 1 order of magnitude higher than that of the undoped LZO.