ADVANCED X-RAY VISUALIZATION OF FUEL CELL AND LITHIUM ION BATTERY
Proton exchange membrane fuel cells (PEFC) and lithium ion secondary battery (LIB) are regarded as a promising alternative clean power sources for automobile applications, fuel cell vehicle (FCV) and electric vehicle (EV), respectively. PEFC and LIB needs higher performance, i.e., high current density to achieve cost reduction and downsizing for PEFC and higher specific capacity and rapid charge/discharge for LIB. In order to improve the performance, fundamental mechanism of the mass transport phenomena in PEFC and LIB under in-situ conditions need to be elucidated. We have developed a soft X-ray microscopy system, which is an advanced imaging system that could visualize water and Li ion in PEFC and LIB, respectively. It could be used in ordinary laboratories without synchrotron and neutron sources. Current density corresponds to liquid water production in fuel cell. It is noted that although H2O is produced at the catalyst layer, liquid water firstly appears near the cathode rib. Liquid water at the interface of MPL and catalyst layer is also observed. The concentration distributions of lithium ions inside the hard carbon negative electrode were able to be investigated. Density reduction caused by lithium intercalation was observed in the graphite negative electrode. These results suggest that transport phenomena in PEFC and LIB could be evaluated quantitatively by the advanced soft X-ray microscopy technique.