Investigation of Structure, Ionic Conductivity and Electrochemical Stability of Halogen-substitution in solid-state ion conductor Li3YBrxCl6-x

The materials Li3YX6 (X = Cl, Br) are Li-ion conductors to be used as solid electrolytes in all solid-state batteries. Solid electrolytes ideally have high ionic conductivity and (electro)chemical compatibility with the electrodes. It was proven that introducing Br to Li3YCl6 increases ionic conductivity, but, according to thermodynamic calculations, should also reduce oxidative stability. In this paper, the trade-off between ionic conductivity and electrochemical stability in Li3YBrxCl6-x (x = 0 – 6) is investigated. The results show that, while Br-rich materials are more conductive (5.36 10-3 S/cm at 30°C for x = 4.5), the oxidative stability is lower (3V compared to 3.5V). Small Br content (x = 1.5) doesn’t affect oxidative stability but substantially increases ionic conductivity compared to pristine Li3YCl6 (2.1 compared to 0.049 10-3 S/cm at 30°C). This work highlights that optimization of substitutions in the anion-framework provide prolific and rational avenues for tailoring the properties of solid electrolytes.