(Battery Division Research Award Address) Developments of New Ionic Conductors and Their Application to All-Solid-State Batteries

All-solid-state is an ideal form of battery. The all-solid-state battery offers an attractive option owing to their potential in improving the safety and achieving both high power and high energy densities. Despite extensive research efforts, the development of all-solid-state batteries still falls short of expectation largely because of the lack of suitable candidate materials for the electrolyte required for practical applications. Among the electrolytes proposed, the sulphide system is a candidate because of its high ionic conductivity1). The Li10GeP2S12 (LGPS) exhibits high bulk conductivity of over 10- 2 S cm-1 at room temperature and is promising for applications requiring batteries with high power and energy densities2). On the other hand, material variations may provide suitable combinations of the electrodes and the electrolyte. Specifically, new LGPS-type superionic conductors exhibit extremely high conductivity (25 mS cm-1, Li-Si-P-S-Cl system) and high stability (~0 V vs Li metal, Li-P-S system), which enable the generation of high power and ultrafast charging of all-solid-state cells with high energy densities3). The present study reviews the materials varieties and the materials design concepts of the solid electrolytes with the LGPS-type structures. The effects of conductivities and electrochemical stabilities of the electrolytes on the battery characteristics will be discussed. References 1) R. Kanno, et al., J. Electrochem. Soc., 148, (7), A742-A746 (2001). 2) N. Kamaya, et al., A. Mitsui, Nature Materials, 10, 682 (2011). 3) Y. Kato, et al., Nature Energy, 1, 201630, (2016).