近日，美国杜克大学的Olivier Delaire及其研究团队取得一项新进展。他们揭示了固态锂电解质的类液体动力学。相关研究成果已于2025年1月6日在国际知名学术期刊《自然—物理学》上发表。
据悉，超离子材料是介于物质的晶态和液态之间的一种状态。尽管其在固态电池或热电装置等潜在应用方面引起了广泛关注，但超离子材料中观察到的快离子扩散，究竟是否反映出类似液态的动力学行为，或者可动离子的跳跃是否与更传统的晶格声子存在固有耦合，目前仍尚不清楚。
该研究团队揭示了固态电解质候选材料——超离子化合物Li6PS5Cl中，离子扩散从晶格振动到弛豫动力学的转变。通过结合非弹性和准弹性中子散射测量，以及基于第一性原理的机器学习分子动力学模拟，研究人员发现超离子态下的振动态密度，强烈偏离了晶格动力学德拜定律所预期的二次方行为。
超离子动力学源自过阻尼的声子准粒子，产生了液态中瞬时简正模特有的线性态密度。此外，研究人员还表明，晶格声子与Li+扩散瓶颈的动态呼吸作用相耦合，使得扩散系数提高了一个数量级。因此，这项研究结果为超离子材料在未来能量存储，和转换技术中的应用提供了新见解。
附：英文原文
Title: Liquid-like dynamics in a solid-state lithium electrolyte
Author: Ding, Jingxuan, Gupta, Mayanak K., Rosenbach, Carolin, Lin, Hung-Min, Osti, Naresh C., Abernathy, Douglas L., Zeier, Wolfgang G., Delaire, Olivier
Issue&Volume: 2025-01-06
Abstract: Superionic materials represent a regime intermediate between the crystalline and liquid states of matter. Despite the considerable interest in potential applications for solid-state batteries or thermoelectric devices, it remains unclear whether the fast ionic diffusion observed in superionic materials reflects liquid-like dynamics or whether the hops of mobile ions are inherently coupled to more conventional lattice phonons. Here we reveal a crossover from crystalline vibrations to relaxational dynamics of ionic diffusion in the superionic compound Li6PS5Cl, a candidate solid-state electrolyte. By combining inelastic and quasi-elastic neutron-scattering measurements with first-principles-based machine-learned molecular dynamics simulations, we found that the vibrational density of states in the superionic state strongly deviates from the quadratic behaviour expected from the Debye law of lattice dynamics. The superionic dynamics emerges from overdamped phonon quasiparticles to give rise to a linear density of states characteristic of instantaneous normal modes in the liquid state. Further, we showed that the coupling of lattice phonons with a dynamic breathing of the Li+ diffusion bottleneck enables an order-of-magnitude increase in diffusivity. Thus, our results shed insights into superionics for future energy storage and conversion technologies.
DOI: 10.1038/s41567-024-02707-6
Source: https://www.nature.com/articles/s41567-024-02707-6