Revealing the Pnma crystal structure and ion-transport mechanism of the Li3YCl6 solid electrolyte

Chloride solid electrolytes represented by Li3YCl6 excel simultaneously in ionic conductivity, deformability, and oxidative stability; their structure-property relationship would provide guiding principles for designing high-performance solid electrolytes. Here, we report that the prototype system Li3YCl6 does not exhibit the P3¯m1 symmetry as commonly believed. This structure occurs only when the material partially decomposes at an overly high annealing temperature of 550°C. With the decomposition being suppressed at 450°C, the material shows a Pnma symmetry instead. Based on this orthorhombic structure, the ion-transport mechanism is clarified through neutron diffraction and first-principles computation. Guided by the established structure-property relationship, the efficient ion transport previously achievable only in the low-crystallinity state is realized in highly crystalline materials. The all-solid-state cells formed by this high-crystallinity material and LiNi0.8Mn0.1Co0.1O2 deliver performance exceeding most reported Li3YCl6-based cells; under 3 C at 25°C, the capacity retention is above 80% for 780 cycles. [Display omitted] •Li3YCl6 is reported to have a Pnma structure, not the common P3¯m1 structure•The ion-transport mechanism of Li3YCl6 is established on the basis of Pnma structure•Guided by this finding, the Li-ion conductivity is significantly improved Hu et al. report that the original structural model used to describe the prototype chloride solid electrolyte Li3YCl6 may be incorrect. Considering this finding, they redetermine the crystal structure and establish the ion-transport mechanism accordingly. Guided by the clarified structure-property relationship, the Li-ion conductivity is subsequently improved.