Improving the ionic conductivity of Li1+Al Ge2-(PO4)3 solid electrolyte for all-solid-state batteries using microstructural modifiers

Although lithium-ion batteries are recognized as the most suitable power source for electric vehicles, they continue to pose a severe safety issue mainly arising from the use of flammable electrolytes. To improve safety, various types of solid electrolytes are explored as potential alternatives due to their non-flammability, high stability, and a wide electrochemical window. In particular, Li1+xAlxGe2-x(PO4)3 (LAGP) has many strengths such as a high total Li+ conductivity and low sensitivity against Li metal anode. Despite these benefits, practical use of LAGP is hindered by a significant loss of total Li+ conductivity due to large grain boundary resistance and interfacial resistance. As an effective way to increase the total Li+ conductivity of LAGP, we propose microstructural engineering with the structural modifiers (B2O3 and Bi2O3) with different functionalities. During synthesis, B2O3 facilitates the grain growth of LAGP, thereby reducing the number of grain boundaries. At the same time, Bi2O3 promotes the densification of LAGP with the advancement of its structural integrity. As a result of synergetic effect, the total Li+ conductivity of LAGP can be effectively improved at room temperature. Furthermore, we demonstrate positive effects of the tailored microstructure of LAGP on the electrochemical performance of all-solid-state batteries.