Reveal The Active Components of Crystalline Li-Nb-O and Li-Ta-O Coatings

As widely applied coating materials for high-voltage positive electrode materials, niobate and tantalate materials can mitigate the interfacial reactivities in Li-ion and all-solid-state batteries. Although crystalline LiMO₃ (M=Nb, Ta) coatings show substantial enhancements in the battery electrochemical performances, there exists an apparent contradiction between the low Li-ion conductivity of crystalline LiMO₃ coating and the good rate capabilities achieved in these cells.^1,2 This contradiction needs to be well understood to optimize the functional properties of crystalline niobates and tantalates. Leveraging a combination of density functional theory, empirical bond valence mapping, nudged-elastic band calculations, and machine learning molecular dynamics, we reveal the multiphasic nature of Li–M–O coatings, containing mixtures of LiMO₃ and Li₃MO₄. The concurrence of several phases in Li–M–O modulates the type of stable native defects in these coatings. Li–M–O coating materials can form favorably lithium vacancies and antisite defects combined into charge-neutral defect complexes. Even in defective crystalline LiMO₃, we reveal poor Li-ion conduction properties. In contrast, Li₃MO₄ introduced by high-temperature calcinations can provide adequate Li-ion transport in these coatings. However, the occurrence of intrinsic defects in niobates (and tantalates) remains conditional to the coexistence of LiMO₃ and Li₃MO₄ at synthesis conditions, which regulates the availability of Li vacancies. Our in-depth investigation of the structure-property relationships in the important Li–M–O coating materials helps to develop more suitable calcination protocols to maximize the functional properties of these niobates and tantalates.³<br/><br/>References<br/>1. Glass, A. M., Nassau, K. & Negran, T. J. Ionic conductivity of quenched alkali niobate and tantalate glasses. <i>J. Appl. Phys.</i> <b>49</b>, 4808–4811 (1978).<br/>2. Xin, F. <i>et al.</i> What is the Role of Nb in Nickel-Rich Layered Oxide Cathodes for Lithium-Ion Batteries? <i>ACS Energy Lett.</i> <b>6</b>, 1377–1382 (2021).<br/>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. <i>Chem. Mater.</i> <b>35</b>, 5657–5670 (2023).