The Effect of Phosphoric Acid on the Preparation of High-Performance Li3InCl6 Solid-State Electrolytes by Water-Mediated Synthesis

The halide solid-state electrolyte Li₃InCl₆ (LIC) is an excellent solid-state electrolyte for lithium-ion batteries. In this study, phosphoric acid (H₃PO₄) solution was added during the preparation of Li₃InCl₆ to obtain LIC samples with high ionic conductivity, and the effect of different concentrations of H₃PO₄ on increasing the ionic conductivity of LIC was investigated. The results showed that the LIC prepared in 1% H₃PO₄ had the least impurities and the highest ionic conductivity of 1.15 × 10^-3 S/cm, and the all-solid-state LiCoO₂-LIC/LIC-1%H₃PO₄/Li₆PS₅Cl/In/Li batteries assembled with this sample could be stably cycled for 14 cycles at 30 °C, presenting a high initial charge capacity of 128 mAh/g at 0.05 C. The Li-In/LPSC/LIC-1% H₃PO₄/LPSC/Li-In symmetric cell can be stably cycled at current densities of 0.05 mA/cm², 0.1 mA/cm², and 0.3 mA/cm². Further studies showed that LIC samples prepared in H₃PO₄ contained small amounts of LiIn(P₂O₇). The structure of LiIn(P₂O₇) is a continuous skeleton containing a large number of vacancies for Li⁺ transport, thus improving the ionic conductivity of LIC.