Mechanism of charge transport in lithium thiophosphate

Lithium ortho-thiophosphate (Li₃PS₄) has emerged as a promising candidate for solid-state-electrolyte batteries, thanks to its highly conductive phases, cheap components, and large electrochemical stability range. Nonetheless, the microscopic mechanisms of Li-ion transport in Li₃PS₄ are far to be fully understood, the role of PS₄ dynamics in charge transport still being controversial. We build machine learning potentials targeting state-of-the-art DFT references (PBEsol, r²SCAN, and PBE0) to tackle this problem in all known phases of Li₃PS₄ (α, β and γ), for large system sizes and timescales. We discuss the physical origin of the observed superionic behavior of Li₃PS₄: the activation of PS₄ flipping drives a structural transition to a highly conductive phase, characterized by an increase of Li-site availability and by a drastic reduction in the activation energy of Li-ion diffusion. We also rule out any paddle-wheel effects of PS₄ tetrahedra in the superionic phases–previously claimed to enhance Li-ion diffusion–due to the orders-of-magnitude difference between the rate of PS₄ flips and Li-ion hops at all temperatures below melting.
This archive provides all the relevant data and input files that were used to fit the ML interatomic potentials used in this work, along with the relevant Density-Functional Theory calculations that were used for the training set construction, the validation of the ML models and the calculation of the electronic band structure of the β and γ structure. Furthermore, it provides input files of all the molecular dynamics trajectories needed to investigate Li-ion diffusion properties of Li₃PS₄ and the rotational dynamics of PS₄ tetrahedra. Finally, it provides the raw data to reproduce the figures of the manuscript associated with this archive.

锂正硫代磷酸盐（Li₃PS₄）因其高导电相、低廉的组成成分以及宽泛的电化学稳定性范围，已成为固态电解质电池的有力候选者。尽管如此，锂离子在Li₃PS₄中的微观传输机制尚未得到全面理解，PS₄动态在电荷传输中的作用仍存在争议。本研究构建了针对最先进密度泛函理论参考（PBEsol、r²SCAN和PBE0）的机器学习势，以解决Li₃PS₄（α、β和γ相）所有已知相态、大系统规模和时间尺度上的这一问题。我们探讨了Li₃PS₄观测到的超离子行为的物理起源：PS₄翻转的激活驱动结构向高导电相的转变，该相态以锂位点的增加和锂离子扩散活化能的显著降低为特征。我们还排除了在所有低于熔点的温度下，PS₄四面体的桨轮效应——先前声称可增强锂离子扩散——由于PS₄翻转速率与锂离子跳跃速率之间数量级的差异。此档案提供了所有用于拟合本研究中使用的机器学习原子间势能的相应数据和输入文件，以及用于构建训练集、验证机器学习模型和计算β和γ结构的电子能带结构的密度泛函理论计算。此外，它还提供了所有用于研究Li₃PS₄锂离子扩散性质和PS₄四面体旋转动力学所需的分子动力学轨迹的输入文件。最后，它提供了用于再现与该档案相关的手稿中图表的原始数据。