Room-temperature Operation of All-solid-state Chloride-ion Battery with Perovskite-type CsSn_0.95Mn_0.05Cl₃ as a Solid Electrolyte (Supporting Information)

Perovskite-type CsSnCl₃ is an attractive candidate for use as a solid electrolyte in all-solid-state chloride-ion batteries because it exhibits high ionic conductivity. However, perovskite-type CsSnCl₃ is metastable at room temperature and easily undergoes a phase transition to a stable phase. Here, we prepared perovskite-type CsSn_0.95Mn_0.05Cl₃, in which the Sn²⁺ in CsSnCl₃ is partly substituted with Mn²⁺, via a mechanical milling method. Differential scanning calorimetry showed that the perovskite-type CsSn_0.95Mn_0.05Cl₃ is stable to −15 °C. Moreover, it exhibits a high chloride ionic conductivity of 2.0 × 10⁻⁴ S cm⁻¹ at 25 °C. We demonstrated the room-temperature operation of an all-solid-state chloride-ion battery with a BiCl₃ cathode, an Sn anode, and CsSn_0.95Mn_0.05Cl₃ as the electrolyte. The first discharge capacity of the all-solid-state cell at room temperature was 169 mAh g⁻¹ based on the weight of BiCl₃. X-ray diffraction and X-ray photoelectron spectroscopic analyses confirmed that the reaction mechanism of the cell is derived from the redox reaction of BiCl₃ and Sn.