The effect of HCl on achieving pure Li3InCl6 by water-mediated synthesis process

Lithium indium chloride 'Li3InCl6 (LIC)' has been demonstrated to be a good electrolyte for solid-state lithium batteries. However, in the water-mediated synthesis process, the LIC precursor was inevitably subjected to slight oxidation during drying because of that the LIC is extremely easy bonded with water. In this study, a dilute hydrochloric acid (HCl) was introduced in the water-mediated synthesis process. The results showed that a pure LIC sample was obtained successfully in the case of 5 wt% HCl, and an optimum Li+ ionic conductivity of 1.94 mS∙cm−1 was achieved. The assembled all-solid-state lithium-ion battery LIC@LiCoO2/LIC/Li6PS5Cl/In-Li had a high charge specific capacity of 163.2 mAh·g−1 at 0.05 C. The Coulombic efficiency remained above 98% after 20 cycles. Further analysis indicated that the hydrates of HCl(H2O)2 and HCl(H2O)3 were observed in the sample after drying at 100 ℃ for 4 h, and they were disappeared after drying at 200 ℃ for 4 h. Therefore, it suggested that HCl was better at absorbing free water molecules than LIC, as a result it prevented LIC from being oxidized during drying process. In contrast, samples without HCl showed In(OH)3 impurities after drying at 143 ℃ for 4 h, which led to the appearance of final oxide impurities in LIC.