Halides of the family Li₃MX₆ (M = Y, In, Sc and so on, X = halogen) are emerging solid electrolyte materials for all-solid-state Li-ion batteries. They show greater chemical stability and wider electrochemical stability windows than existing sulfide solid electrolytes, but have lower room-temperature ionic conductivities. Here we report the discovery that the superionic transition in Li₃YCl₆ is triggered by the collective motion of anions, as evidenced by synchrotron X-ray and neutron scattering characterizations and ab initio molecular dynamics simulations. Based on this finding, we used a rational design strategy to lower the transition temperature and thus improve the room-temperature ionic conductivity of this family of compounds. We accordingly synthesized Li₃YCl_xBr_6−x and Li₃GdCl₃Br₃ and achieved very high room-temperature conductivities of 6.1 and 11 mS cm⁻¹ for Li₃YCl_4.5Br_1.5 and Li₃GdCl₃Br₃, respectively. These findings open new routes to the design of room-temperature superionic conductors for high-performance solid batteries.

Li₃MX₆ 家族的卤化物（M = Y、In、Sc 等，X = 卤素）是用于全固态锂离子电池的新兴固体电解质材料。与现有的硫化物固体电解质相比，它们表现出更高的化学稳定性和更宽的电化学稳定性窗口，但具有较低的室温离子电导率。在这里，我们报告了 Li_{3YCl 6} 中的超离子跃迁是由阴离子的集体运动触发的发现，同步加速器 X 射线和中子散射表征以及从头分子动力学模拟证明了这一点。基于这一发现，我们使用了合理的设计策略来降低转变温度，从而提高了该族化合物的室温离子电导率。因此，我们合成了 Li₃YCl_xBr _6-x 和 Li₃GdCl₃Br₃，并为 Li₃YCl_4.5Br_1.5 和 Li₃GdCl₃Br₃ 实现了 6.1 和 11 mS ^cm-1 的非常高的室温电导率分别。这些发现为高性能固体电池的室温超离子导体的设计开辟了新的途径。