Tailoring a Glass Network Structure through Addition of Transition Metal Oxides to Enhance Ionic Conductivity in Phosphate Glasses

Abstract

In the development of oxide glass-based electrolytes and electrodes for solid-state batteries, high ionic conductivity represents an ultimate challenge. One way of increasing the ionic conductivity in these materials is to increase the mobility of ions through the addition of transition metal oxides. In this study, we report a significant enhancement of lithium-ion conductivity due to structural changes induced by addition of WO₃ and MoO₃. Despite the potential of WO₃ and MoO₃ to induce polaronic (electronic) conductivity, these glasses are purely ionic conductors. The increase in lithium-ion conductivity is approximately 5 and 4 orders of magnitude with addition of up to ≈40 mol % WO₃ and MoO₃, respectively. A detailed structural analysis shows that the increase in the mobility of Li⁺ ions is related to a strong facilitating effect of tungstate and molybdate units in the glass network. Moreover, this study also discusses similarities and differences in the dynamics of lithium and sodium ions in phosphate glasses containing WO₃ and MoO₃, and shows that the addition of WO₃ can enhance the cathode performance of these glasses in both lithium-ion and sodium-ion batteries.