As a promising alternative to current commercial lithium-ion batteries, all-solid-state sodium-ion battery (ASS-SIB) requires solid electrolytes (SEs) with high Na ionic conductivity and good stability. Recently, lithium halide SEs have...

The enabling of all-solid-state lithium-ion batteries with high energy density requires the development of superionic solid electrolytes (SEs) with good chemical and electrochemical stability. Recently, Li₃YCl₆ and Li₃YBr₆ with high Li ion conductivity and good oxidation stability have attracted extensive attention. However, the effect of Li-ion concentration regulation on the performance of the materials is not clear so far. In this work, we study the structural, electronic and ionic diffusion properties of a series of Li_xYCl_3+x (x=2.14, 3, 4.2) and Li_xYBr_3+x (x=1.8, 3, 5) by using first-principles calculation based on density functional theory. The calculated results show that the Li-ion concentration has a significant effect on the properties of the materials, and with increasing of x value, higher Li-ion, more stable structure, larger band gap, and lower migration barrier, enabling the ability to tune the performance of the materials. In addition, the calculated results further show that Li₃YCl₆ and Li₃YBr₆ with the best balance of Li-ion carrier concentration and vacancy concentration exhibit the highest structural stabilities, the largest band gaps, and the lowest migration barriers among all similar structures. Our dindings provide a new strategy and idea for designing better-performance halide SEs.