XAFS Analysis

Abstract

All-solid-state batteries using nonflammable inorganic solid electrolytes are expected to have both high energy density and excellent safety and to have higher power density than current lithium-ion batteries. However, the actual power density of the all-solid-state batteries is often smaller than expected, due to factors such as the resistance at the electrode/solid-state electrolyte interface and/or the dispersion of the active material and solid-state electrolyte in the composite electrode. In order to improve the power density of the all-solid-state batteries, analytical methods with several space and time scales are necessary for clarification about the specific polarization factors of the all-solid-state batteries. In this chapter, we introduce the application of X-ray absorption fine structure (XAFS) analysis to the analysis of an interfacial structure between the cathode and solid electrolyte, and a reaction distribution in composite materials. Depth-resolved XAFS analysis proves that the electronic structure of the active material changed and a reactive layer formed at the interface between the active material and the solid electrolyte during charging and discharging, which leads to the increase of resistance. Two-dimensional XAFS analysis proves that the ionic conduction resistance increases the farther away from the solid electrolyte layer because of the large bending of the ionic path in the heterogeneous electrode, leading to large polarization. These XAFS analyses are powerful tools to understand the phenomena inside all-solid-state batteries and improve the performances.