Recent progress for all solid state battery using sulfide and oxide solid electrolytes

All solid state batteries (ASSB) have been researched by many groups in order to realize safe and high energy density rechargeable batteries. There are mainly two types of inorganic electrolytes used for ASSB: sulfides and oxides. We will review the recent advances in ASSB with oxide electrolytes. At first, the status of solid electrolytes will be discussed from the viewpoints of Li+ conductivity, chemical and electrochemical stability and compatibility with Li metal anode. In practical, the garnet electrolyte Li7La3Zr2O12 (LLZO), widely regarded as the most promising solid electrolyte, will be focused. Second, since it is very difficult to attach electrode layers to a LLZO pellet due to its surface nature, some deposition techniques, e.g. chemical vapor deposition and physical vapor deposition, are used for electrode fabrication. Here, a new aerosol deposition technique to deposit cathode layer onto LLZO electrolyte is introduced. In addition, the wettability between LLZO and the most promising anode material, Li metal, is discussed. Finally, we would like to discuss the internal short circuit problem of ASSB due to Li metal penetration through LLZO pellet during charge and discharge processes. The understanding of this phenomenon is very important to realize practical ASSBs.