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

Abstract

Layered-oxide $\mathrm{LiN}{\mathrm{i}}_{\mathrm{x}}\mathrm{M}{\mathrm{n}}_{\mathrm{y}}\mathrm{C}{\mathrm{o}}_{1-\mathrm{x}-\mathrm{y}}{\mathrm{O}}_2$ (NMC) positive electrodes with high Nickel content, deliver high voltages and energy densities. However, a high nickel content, e.g., $x$ = 0.8 (NMC 811), 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 $\mathrm{LiNb}{\mathrm{O}}_3$ and $\mathrm{L}{\mathrm{i}}_3\mathrm{Nb}{\mathrm{O}}_4$, or of $\mathrm{LiTa}{\mathrm{O}}_3$ and $\mathrm{L}{\mathrm{i}}_3\mathrm{Ta}{\mathrm{O}}_4$. 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 form favorably lithium vacancies $\mathrm{Va}{\mathrm{c}}_{\mathrm{Li}}^{{}^{\prime }}$ and antisite defects $\mathrm{N}{\mathrm{b}}_{\mathrm{Li}}^{\bullet \bullet \bullet \bullet }$ ($\mathrm{T}{\mathrm{a}}_{\mathrm{Li}}^{\bullet \bullet \bullet \bullet }$) combined into charge-neutral defect complexes. Even in defective crystalline $\mathrm{LiNb}{\mathrm{O}}_3$ (or $\mathrm{LiTa}{\mathrm{O}}_3$), we reveal poor Li-ion conduction properties. In contrast, $\mathrm{L}{\mathrm{i}}_3\mathrm{Nb}{\mathrm{O}}_4$ and $\mathrm{L}{\mathrm{i}}_3\mathrm{Ta}{\mathrm{O}}_4$ 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.

Cited by in corpus (1)

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