How particle size affects consolidation behavior, strain and properties of Li6PS5Cl fast ionic conductors

Solid-state battery fabrication requires the densification of solid electrolytes to achieve optimal cycling performance and high energy density. However, the underlying compaction mechanisms of these electrolytes remain poorly understood. Here, we investigate the effect of pressure consolidation on the ionic conductor Li₆PS₅Cl with particle size distributions (PSD) ranging from 4 μm to 40 μm. Heckel analysis reveals that samples with smaller PSDs exhibit higher compressibility at lower pressures. X-ray diffraction peak profiling shows that applied pressure induces lattice strain, leading to peak broadening, while pair distribution function analysis demonstrates a reduction in coherence length upon pressing. Dark-field X-ray microscopy further provides spatially resolved orientation maps, uncovering intragranular structural variations within individual Li₆PS₅Cl agglomerates after compression. To better understand the origin of stress fluctuations, we performed discrete element method simulations using the experimental PSDs. The results indicate that smaller particles and broader PSDs experience higher stresses, whereas monodisperse systems do not exhibit significant stress fluctuations with position or particle size. This suggests that the high strain observed cannot be attributed solely to smaller particles, but rather to size inhomogeneity. Overall, these findings highlight that both particle size and its distribution play a critical role in processing solid electrolytes for solid-state batteries.

固态电池的制备需对固体电解质进行致密化处理，以实现最优的循环性能与高能量密度。然而，此类电解质的固有压实机制仍未得到充分阐明。本研究针对粒径分布（Particle Size Distribution，PSD）介于4 μm至40 μm之间的离子导体Li₆PS₅Cl，探究了压力固结工艺对其的影响。赫克尔分析结果显示，PSD更小的样品在低压下表现出更高的压缩性。X射线衍射峰轮廓分析表明，施加压力会引发晶格应变，导致衍射峰宽化；而对分布函数分析则显示，施压后相干长度有所缩短。暗场X射线显微镜进一步提供了空间分辨的取向图谱，揭示了压缩后单个Li₆PS₅Cl团聚体内部的晶粒结构变化。为更好地理解应力波动的起源，我们基于实验获取的PSD开展了离散元法模拟。模拟结果表明，粒径更小且PSD更宽的体系所受应力更高；而单分散体系则未出现随位置或粒径变化的显著应力波动。这意味着，观测到的高应变并非仅由小粒径颗粒所致，而是源于粒径分布的不均匀性。综上，本研究结果表明，颗粒尺寸及其分布在固态电池用固体电解质的制备工艺中均发挥着关键作用。