AbstractLi-ion-conducting chloride solid electrolytes receive considerable attention due to their physicochemical characteristics such as high ionic conductivity, deformability and oxidative stability. However, the raw materials are expensive, and large-scale use of this class of inorganic superionic conductors seems unlikely. Here, a cost-effective chloride solid electrolyte, Li₂ZrCl₆, is reported. Its raw materials are several orders of magnitude cheaper than those for the state-of-the-art chloride solid electrolytes, but high ionic conductivity (0.81 mS cm^–1 at room temperature), deformability, and compatibility with 4V-class cathodes are still simultaneously achieved in Li₂ZrCl₆. Moreover, Li₂ZrCl₆ demonstrates a humidity tolerance with no sign of moisture uptake or conductivity degradation after exposure to an atmosphere with 5% relative humidity. By combining Li₂ZrCl₆ with the Li-In anode and the single-crystal LiNi_0.8Mn_0.1Co_0.1O₂ cathode, we report a room-temperature all-solid-state cell with a stable specific capacity of about 150 mAh g^–1 for 200 cycles at 200 mA g^–1.