Commercialized LIBs have disadvantages such as overheating and catching on fire due to the utilization of liquid organic electrolytes. To expand the applications of LIBs, the development of solid-state lithium-ion conductive electrolyte materials, which are nonflammable, more durable for high temperature, more resistive to lithium dendrite and have wider electrochemical operating voltage window, is urgently needed.

Among the various types of solid-state lithium-ion conductive electrolyte candidates, the garnet-type Li₇La₃Zr₂O₁₂ (LLZO) has attracted significant attention due to its high ionic conductivity and superior electrochemical stability corresponding to a wide electrochemical window. By combine the sol-gel synthesis and high energy ball milling, we investigated the phase transition from tetragonal Li₇La₃Zr₂O₁₂ to cubic Li₇La₃Zr₂O₁₂ without subsequent high-temperature calcination. For the sample calcined at 900 °C for 6 h, X-ray diffraction measurement revealed that the ball milling treatment induces a direct phase transition from tetragonal Li₇La₃Zr₂O₁₂ to cubic Li₇La₃Zr₂O₁₂ without high-temperature heat treatment. However, in a comparative study, cubic Li₇La₃Zr₂O₁₂ can only be obtained after high-temperature calcination above 1180 °C. We hypothesize that the high energy ball milling promotes the accumulation of Li⁺ vacancy leading to this easy phase transition. This study establishes an efficient way to transform tetragonal Li₇La₃Zr₂O₁₂ to cubic Li₇La₃Zr₂O₁₂ at lower calcination temperature via high energy ball milling treatments.

In addition, dispersing cubic Li₇La₃Zr₂O₁₂ powders as active inorganic electrolyte fillers in polymer matrix to synthesize flexible and easy-to-process Li₇La₃Zr₂O₁₂/PVDF composite polymer electrolytes (CPEs) is also being investigated in order to enhance not only ionic conductivity but also mechanical properties and thermal stability of polymer electrolytes.