On the Active Components in Crystalline Li–Nb–O and Li–Ta–O Coatings from First Principles

Layered-oxide LiNi x Mn y Co 1– x – y O 2 (NMC) positive electrodes with high nickel content deliver high voltages and energy densities. However, a high nickel content, e.g., x = 0.8 (NMC811), can lead to high surface reactivity, which can trigger thermal runaway and gas generation. While claimed safer, all-solid-state batteries still suffer from high interfacial resistance. Here, we investigate niobate and tantalate coating materials, which can mitigate the interfacial reactivities in Li-ion and all-solid-state batteries. First-principles calculations reveal the multiphasic nature of Li–Nb–O and Li–Ta–O coatings, containing mixtures of LiNbO 3 and Li 3 NbO 4 or of LiTaO 3 and Li 3 TaO 4 . The concurrence of several phases in Li–Nb–O or Li–Ta–O modulates the type of stable native defects in these coatings. Li–Nb–O and Li–Ta–O coating materials can favorably form lithium vacancies Vac Li ′ and antisite defects Nb Li •••• (Ta Li •••• ) combined into charge-neutral defect complexes. Even in defective crystalline LiNbO 3 (or LiTaO 3 ), we reveal poor Li-ion conduction properties. In contrast, Li 3 NbO 4 and Li 3 TaO 4 that are introduced by high-temperature calcinations can provide adequate Li-ion transport in these coatings. Our in-depth investigation of the structure–property relationships in the important Li–Nb–O and Li–Ta–O coating materials helps to develop more suitable calcination protocols to maximize the functional properties of these niobates and tantalates.