Abstract

Layered-oxide LiNi_xMn_yCo_1–x–yO₂ (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 LiNbO₃ and Li₃NbO₄ or of LiTaO₃ and Li₃TaO₄. 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 VacLi′ and antisite defects Nb_Li^•••• (Ta_Li^••••) combined into charge-neutral defect complexes. Even in defective crystalline LiNbO₃ (or LiTaO₃), we reveal poor Li-ion conduction properties. In contrast, Li₃NbO₄ and Li₃TaO₄ 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.