Co-Sinterable Lithium Garnet-Type Oxide Electrolyte with Cathode for All-Solid-State Lithium Ion Battery

     Lithium ion secondary batteries have been widely used as power sources for electric vehicle (EV), a mobile phone and etc., and are now indispensable for our daily lives. At the same time, safety of the batteries has been becoming an important issue with the progress of their performance, which recently motivated the researches on all-solid-state lithium ion batteries using solid electrolytes due to non-use of flammable organic liquid electrolytes. Especially, increasing attention has been paid to the use of garnet-type metal oxides (e.g. Li₇La₃Zr₂O₁₂ (LLZO) and its derivatives) as a solid electrolyte due to not only good chemical stability and high lithium ion conductivity but also the potential to construct a bi-polar structure for high capacity by a simple co-sintering process. However, it has been quite difficult to suppress chemical reactions of the electrolyte with an electrolyte during co-sintering, and it is now one of the most important issues to significantly lower the sintering temperature of the electrolyte.

     We investigated the development of a novel garnet-type oxide electrolyte, which is co-sinterable with a LiCoO₂ cathode, based on the strategy to enhance interdiffusion between LLZO grains and grain boundaries by an appropriate selection of dopants in LLZO and additives. The sintering temperature of LLZO drastically decreased to 790 ^oC with maintaining high lithium ion conductivity but without the reaction with a metal oxide cathode (LiCoO₂).

     In addition, an all-solid-state lithium ion battery was successfully prepared by co-sintering of the stacked cathode/electrolyte layer, and confirmed to function well as a secondary battery. These results opened the potential for fabrication of all-solid-state lithium ion batteries using oxide electrolytes by a simple and well-established co-sintering process.