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

## TL;DR

Adding phosphoric acid during preparation improves the performance of a solid-state electrolyte for lithium-ion batteries.

## Contribution

Demonstrates that using 1% H3PO4 during synthesis enhances ionic conductivity and battery stability in Li3InCl6.

## Key findings

- LIC samples made with 1% H3PO4 showed highest ionic conductivity of 1.15 × 10−3 S/cm.
- Batteries using this sample cycled stably for 14 cycles with high initial charge capacity.
- LIC samples contained LiIn(P2O7), which improves Li+ transport through its structure.

## Abstract

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.