All-solid-state rechargeable battery is one of the candidates of post-lithium-ion batteries. In recent years, the intrinsic charge-discharge performance of active materials and the ionic conductivity of solid electrolytes have dramatically improved; however, the dynamic behavior of carrier ion in the composite electrode has not been understood for the performance of battery pack. If the transport number in the solid electrolyte is almost one, it is considered that salt concentration distribution does not occur in principle. Due to this advantage, the thicker electrodes can be realized for all-solid-state rechargeable battery. However, as far as the authors know, the direct observation of carrier ions during operation of all-solid state rechargeable batteries has not been reported. This is because it is difficult to observe the behavior of lithium ions which are general carrier ions but are light elements. Therefore, in this research, as a model of all-solid-state rechargeable batteries, we used silver ion conductor which shows much high ionic conductivity. The dynamic behavior of silver ion in solid electrolyte and electrode during battery operation was investigated by high energy X-ray imaging method with synchrotron radiation.

Ag₆I₄WO₄ was used as the solid electrolyte, and in the case of the electrolyte observation, silver used as both electrodes. The pressed cell component was sliced with the thickness of 300 mm. In the case of the electrode observation, TiTe₂ was used as the working electrode and silver was used as the counter electrode. X-ray transmission imaging measurements were performed in SPring-8.

Compared with the reference samples of Ag_6+xI₄WO₄ (x = 0, 0.06, 0.17, 0.31), it was shown that noticeable ion concentration distribution similar to that of the battery using the organic electrolytic solution as the electrolyte during charge / discharge does not occur. On the other hand, dendrite growth in the solid electrolyte due to silver deposition and reaction distribution in the electrode were observed. In this presentation, we will provide the direct observation of silver ion diffusion in composite electrode.