Investigation of Structure, Ionic Conductivity, and Electrochemical Stability of Halogen Substitution in Solid-State Ion Conductor Li(3)YBr(x)Cl(6–x)

[Image: see text] Li(3)YX(6) (X = Cl, Br) materials are Li-ion conductors that can 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 Li(3)YCl(6) 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 Li(3)YBr(x)Cl(6–x) halogen-substituted compounds is investigated. The compositions of Li(3)YBr(1.5)Cl(4.5) and Li(3)YBr(4.5)Cl(1.5) are reported for the first time, along with a consistent analysis of the whole Li(3)YBr(x)Cl(6–x) (x = 0–6) tie-line. 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 (∼3 V compared to ∼3.5 V). Small Br content (x = 1.5) does not affect oxidative stability but substantially increases ionic conductivity compared to pristine Li(3)YCl(6) (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.