Polarised QENS for determining the Haven Ratio in Lithium Solid State Electrolytes

All solid state batteries offer a potential route to address the poor range, slow charging, and safety issues associated with current liquid electrolyte batteries in cars, by utilizing metal anodes. However, reaching commercial SSBs is a multi-faceted problem with many limitations; one of which is the reduction in ionic conductivities as you go from liquid to solid electrolytes. Understanding the specific role of the prefactors that drive diffusion is vital for creating solid electrolytes with faster dynamics. One such prefactor is the Haven ratio, the ratio between ion and charge drive diffusion.
Here we will attempt to experimentally determine the microscopic Haven ratio by separating the coherent and incoherent dynamical structure factors of Li6PS5Cl (lithium-7 enriched). The incoherent scattering will represent single ion diffusion through the bulk structure, whilst coherent scattering will be presented if caterpillar diffusion is present. By isolating these two types of diffusive mechanisms, one will be able to accurately determine whether there is significantly more caterpillar diffusion than predicted by DFT calculations and whether the macroscopic Haven ratio is accurate. From this understanding, novel solid-state electrolytes for the electric vehicle market that optimize the Haven ratio, by maximizing the amount of charge-driven diffusion, will be synthesized.

全固态电池（All Solid State Batteries）为解决当前车用液态电解质电池存在的续航短板、充电缓慢及安全隐患问题提供了极具潜力的路径，其核心优势在于采用金属负极。然而，实现商业化全固态电池是一项多维度的复杂课题，存在诸多限制；其中之一便是从液态电解质切换为固态电解质时，离子电导率会出现显著下降。明确驱动离子扩散的前置因子的具体作用机制，对于开发具备更快离子动力学特性的固态电解质至关重要，而哈文比（Haven ratio）正是这类关键前置因子之一，其定义为离子扩散与电荷驱动扩散的比值。
本研究将通过分离富锂-7的Li₆PS₅Cl的相干与非相干动力学结构因子，实验测定微观哈文比。其中，非相干散射将表征体相结构内的单离子扩散过程，而若存在毛虫式扩散（caterpillar diffusion），则可通过相干散射观测到该扩散机制。通过分离这两类扩散过程，我们便能准确判断是否存在比密度泛函理论（Density Functional Theory, DFT）计算预测更多的毛虫式扩散，以及宏观哈文比是否准确可靠。基于这一研究结论，我们将合成面向电动汽车市场的新型固态电解质，通过最大化电荷驱动扩散的占比来优化哈文比性能。