Understanding ion transport mechanisms on the atomistic scale in solid-state electrolytes is crucial for the development of all-solid-state batteries. Li₇La₃Zr₂O₁₂ (LLZO) is a promising oxide solid electrolyte material, whose phase transition behavior and ion transport mechanisms have attracted significant research attention. Previous studies have primarily focused on ion transport in the cubic phase (intrinsic high-temperature phase or doped variants). In contrast, the tetragonal phase of LLZO, despite its close relationship with the cubic phase, has received less attention due to its relatively low ionic conductivity and high computational cost. A few recent computational studies have shown significant discrepancies in conductivity and activation energy between calculated and experimental values. Therefore, the unclear ion transport mechanisms in the tetragonal phase of LLZO are critical to understanding and designing oxide solid electrolytes. In this study, we employ state-of-the-art machine-learning-based neuroevolution potential molecular dynamics simulations to investigate the effects of lithium nonstoichiometry on the ionic conductivity and phase stability of LLZO. We demonstrate that small deviations from stoichiometry, particularly lithium deficiency, dramatically reduce the activation energy for Li⁺ diffusion in tetragonal LLZO from 1.227 to 0.425 eV, increasing room-temperature ionic conductivity by 10 orders of magnitude. The slight lithium nonstoichiometry, which commonly occurs during high-temperature synthesis, has a significant effect on ion transport in the tetragonal phase. Our findings highlight the crucial role of lithium nonstoichiometry and defect chemistry in enhancing LLZO performance and provide insights for the rational design of high-performance solid electrolytes through defect engineering.

中文翻译：

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锂非化学计量对四方石榴石型 Li7La3Zr2O12 中离子扩散的影响


了解固态电解质中原子尺度的离子传输机制对于全固态电池的开发至关重要。Li₇La₃Zr₂O₁₂ （LLZO） 是一种很有前途的氧化物固体电解质材料，其相变行为和离子传输机制引起了研究的广泛关注。以前的研究主要集中在立方相（本征高温相或掺杂变体）中的离子传输。相比之下，LLZO 的四方相尽管与立方相关系密切，但由于其相对较低的离子电导率和高计算成本而受到较少的关注。最近的一些计算研究表明，计算值和实验值之间的电导率和活化能存在显著差异。因此，LLZO 四方相中不清楚的离子传输机制对于理解和设计氧化物固体电解质至关重要。在这项研究中，我们采用最先进的基于机器学习的神经进化电位分子动力学模拟来研究锂非化学计量对 LLZO 离子电导率和相稳定性的影响。我们证明，与化学计量学的微小偏差，特别是锂缺乏，将四方 LLZO 中 Li⁺ 扩散的活化能从 1.227 降低到 0.425 eV，将室温离子电导率提高了 10 个数量级。高温合成过程中常出现的轻微锂非化学计量对四方相中的离子传输有显著影响。 我们的研究结果强调了锂非化学计量和缺陷化学在提高 LLZO 性能中的关键作用，并为通过缺陷工程合理设计高性能固体电解质提供了见解。