Highly Conductive Li7La3Zr2O12/PVDF Composite Polymer Electrolyte for Rechargeable Lithium Ion Batteries

Abstract

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.