Lattice Dynamics of Superionic Conductors

固态电池更安全，可能更轻，具有更高的能量密度，并且比当前电池具有更长的寿命。固态电池使用必须以与液体电解质相当的速率传导离子的固态电解质。这种材料被称为快离子导体。固体中这种高离子传导的微观起源仍然知之甚少，特别是对于表现出相关或液体状扩散的系统。在这个早期阶段的报告中，我们认为，晶格动力学，更准确地说，非谐振动模式与大振幅和强方向性的扩散路径，必须发挥作用，在快速离子传导。我们强调如何晶格软化的振动模式提供了正是这些条件。然后，我们探讨这一假设在Li3N，一个简单的快离子导体，显示相关扩散。我们发现，使用第一性原理晶格动力学计算，有显着软化的某些振动模式指向的方向的扩散路径。这支持了我们的假设，晶格软化，和快速离子导电。它也可能解释相关扩散。我们预计我们的研究结果开辟了系统研究的晶格软化的超离子导体，这可能会变成一个高通量筛选的描述符。这将为更明智的固态电池设计提供一条高速公路，并加快整个实验室到产品的时间轴。

Solid state batteries are safer, potentially lighter, have a higher energy density, and have longer lifetimes than current batteries. A solid state battery uses a solid state electrolyte that must conduct ions at rates comparable to those of liquid electrolytes. Such materials are called fast ionic conductors. The microscopic origin of such high ionic conduction in solids is still poorly understood, in particular for systems that exhibit correlated, or liquid-like diffusion. In this early stage report, we argue that lattice dynamics, and more precisely anharmonic vibrational modes with large amplitudes and strong directionality towards the diffusion path, must play a role in fast ionic conduction. We highlight how the lattice softening of such vibrational modes provides exactly those conditions. Then, we explore this hypothesis in Li3N, a simple fast ionic conductor that shows correlated diffusion. We found, using first principles lattice dynamics calculations, that there is significant softening of certain vibrational modes pointing in the direction of the diffusion path. This supports our hypothesis that lattice softening, and fast ionic conduction are linked. It could potentially explain correlated diffusion too. We anticipate our findings to open the way for systematic studies of lattice softening in superionic conductors, which could potentially be turned into a descriptor for high-throughput screening. This would provide a highway for more informed design of solid state batteries, and speed up the whole lab-to-product timeline.