Phase Study of Lithium-Niobium-Tantalum Oxides as Cathode Coating Materials

Although all-solid-state batteries (ASSBs) exhibit great potential for providing high energy density and enhanced battery safety, the stability of electrode−electrolyte interfaces is still a serious challenge. Niobate and tantalate materials have been widely applied as coating materials to mitigate the interfacial reactivities in ASSBs, especially amorphous LiMO₃ (M=Nb or Ta) with high ionic conductivities and appreciable electronic resistance.¹ Compared with pure LiMO₃ (M=Nb or Ta), partially-crystallized Li-Nb-Ta oxides were found to show even higher ionic conductivity and higher permittivity, which can be more effective for fast charge-transfer reactions at the cathode/electrolyte interfaces in ASSBs.² However, the mechanism behind Nb/Ta mixing and the improved properties needs to be further understood.

Leveraging a combination of density functional theory, cluster expansion formalism, grand canonical Monte Carlo (gcMC) simulations, and machine-learned molecular dynamics, we reveal the phase transition nature of LiTa_1-xNb_xO₃ and the improved Li-ion conduction properties brought by Nb/Ta mixing. As studied in our previous work, the crystalline Li-M-O coating contains mixtures of LiMO₃ and Li₃MO₄, and we extend the mixing study into Li₃MO₄ as well.³ Our investigation of the phase behavior and the structure-property relationships in the Li-Nb-Ta oxides helps to develop more suitable synthesis protocols to maximize the functional properties of these coating materials.

References:
1. Glass, A. M., Nassau, K. & Negran, T. J. Ionic conductivity of quenched alkali niobate and tantalate glasses. J. Appl. Phys. 49, 4808–4811 (1978).
2. Yada, C. et al. A High-Throughput Approach Developing Lithium-Niobium-Tantalum Oxides as Electrolyte/Cathode Interlayers for High-Voltage All-Solid-State Lithium Batteries. J. Electrochem. Soc. 162, 722–726 (2015).
3. Chen, H., Deng, Z., Li, Y. & Canepa, P. On the Active Components in Crystalline Li-Nb-O and Li-Ta-O Coatings from First Principles. Chem. Mater. 35, 5657–5670 (2023).