Optimization of a Heterogeneous Ternary Li₃PO₄-Li₃BO₃-Li₂SO₄Mixture for Li-Ion Conductivity by Machine Learning

Mixing heterogeneous Li-ion conductive materials is one potential way to enhance Li-ion conductivity more than that of the parent materials. However, the huge number of possible compositions of parent materials impedes the development of an optimal mixture by using conventional methods. In this study, we employed machine learning to optimize the composition ratio of ternary Li3PO4-Li3BO3-Li2SO4 for Li-ion conductivity. We found the optimum composition of the ternary mixture system to be 25:14:61 (Li3PO4:Li3BO3:Li2SO4 in mol %), whose Li-ion conductivity is measured as 4.9 × 10-4 S/cm at 300 °C. Our X-ray structure analysis suggested that Li-ion conductivity of the mixed systems tends to be enhanced by the coexistence of two or more phases. Although the mechanism enhancing Li-ion conductivity is not simple, our results demonstrate the effectiveness of machine learning for the development of materials.