(Keynote) Sulfide Electrolytes Based on the LGPS Related Materials

Abstract

All-solid-state is an ideal form of batteries. The solid electrolyte is a key issue for the development of all-solid-state batteries. Among the electrolytes proposed, the sulphide system is a candidate because of its high ionic conductivity. The LGPS (Li10GeP2S12) electrolyte exhibits a high bulk conductivity of over 10- 2 S cm-1 at room temperature and are promising for applications requiring batteries with high power and energy densities [1]. Moreover, material variations of the LGPS electrolytes provided suitable combinations of the electrodes and the electrolyte. For example, the LGPS-group materials, such as Li9.54Si1.74P1.44S11.7Cl0.3 and Li9.6P3S12, provided high power and high energy density to the all-solid-state cells [2]. These results clearly derive from the intrinsic nature of the solid electrolytes, indicating the advantages of the all-solid-state devices over conventional electrochemical devices.Systematic substitutions of the constituent elements were examined after the first report of Li10GeP2S12. The simplest substitution system was Si and Sn analogs. Solid solutions of the Ge-Si, Ge-Sn, and Si-Sn systems were examined. Among the substitution systems, the lithium tin-silicon system with Li10.35[Sn0.27Si1.08]P1.65S12 showed the high ionic conductivity which is comparable to the original LGPS material. On the other hand, the LGPS-type structre was also appered in the L-P-S ternary system. Li9.6P3S12 with the LGPS-type showed high electrochemical stability which might be used for low potential ranges such as Li and carbon anode.Partial substituteions of the anion-site were also studied for the halogen and oxygen systems. The oxygen and halogen substitution generally improved the electrochemical stabilities. Actually, the oxygen doped Li-P-S-O system showed higher electrochemical stability. Based on a wide composition range of the materials search, the LGPS materials were also found in the Li-A-P-S-X (A: Si, Ge, Sn, X:halogen) and Li-P-S-X (X: halogen) systems. For example, Li9.54Si1.74P1.44S11.7Cl0.3 showed the higest conductivity of 25 mScm-1 at room temperature. The halogen substitution systems of the L-P-S-X systems were also developed and this system had higher electrochemical stability.The present study summarizes the materials varieties and formation ranges of the LGPS materials in these ternary and quarternary sytems. In addition to the materials variety, the electrolyte-electrode combination which is another important parameter to achieve high battery characteristics is summarized. We also shows the properties of the all-solid-state cells using these LGPS-type solid electrolytes with various anode and cathode systems.