Thermal expansion and electrical conductivity of the battery material Li3NbO4 in the cation-ordered rocksalt phase

Abstract

Li₃NbO₄ is a host material for a family of high-capacity Li-excess cathodes with disordered rocksalt structure for lithium-ion batteries, where cation ordering significantly impacts electrochemical performance. It also has an important role in niobate coatings for lithium-ion battery cathodes. In ceramic form, it is also a potential candidate for tritium breeder blanket material in nuclear fusion reactors, operating at high temperatures. However, still very little is known about how the temperature or cation ordering affects Li₃NbO₄'s properties. Thus, here we report the thermal expansion and the DC electrical conductivity of highly cation-ordered Li₃NbO₄, as obtained by X-ray diffraction and impedance spectroscopy, respectively. The coefficient of thermal expansion increases from 20 × 10⁻⁶ K⁻¹ to 25 × 10⁻⁶ K⁻¹ between 300 K and 1150 K, falling between the values of the two most promising tritium breeder candidates and thus offering a comparable match with the reduced-activation ferritic-martensitic steel structural material. The DC conductivity ranges from ∼7 × 10⁻¹⁴ S/cm at room temperature to 8 × 10⁻⁶ S/cm at 673 K, with a bulk activation enthalpy of 0.76 eV, showing that high cation ordering makes Li₃NbO₄ a very good insulator. These results are expected to stimulate further investigations aiming to evaluate its suitability as a tritium breeder material, as well as comparative studies on fully or partially disordered Li₃NbO₄, to shed additional light on the role of cation ordering in Li₃NbO₄-based rocksalt cathodes and Li₃NbO₄-containing niobate coatings for lithium-ion batteries.