Sodium-ion hybrid capacitor as next-generation battery －No more precious elements in batteries－
Xianfen Wang, Satoshi Kajiyama, Hiroki Iinuma, Eiji Hosono, Shinji Oro, Isamu Moriguchi, Masashi Okubo, Atsuo Yamada
Li-ion (lithium-ion) batteries, which power most portable electronics today, include precious elements such as lithium and cobalt. As a potential alternative to Li-ion batteries, Na-ion (sodium-ion) batteries have attracted much attention because of the abundance and low-cost of uniformly-distributed sodium. However, in order to realize a sodium-ion battery, a pair of compounds capable of intercalation (absorbing and releasing) of sodium ions is required for each of the negative and positive electrodes. In particular, development of a high-performance negative electrode is indispensable. The research group of Professor Atsuo Yamada and Associate Professor Masashi Okubo at the University of Tokyo, Graduate School of Engineering, Department of Chemical System Engineering, in collaboration with the research group of Professor Isamu Moriguchi at Nagasaki University Graduate School of Engineering, has clarified that a nanosheet compound comprising titanium and carbon is capable of sodium-ion intercalation. A prototype full cell with this nanosheet compound as a negative electrode in combination with an existing positive electrode material exhibited high-charge/discharge-rate capability, high capacity, and long cycle life, all of which are prerequisites for a next-generation battery technology. Part of this research was financially supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan under the "Elemental Strategy Initiative for Catalysis and Batteries" (ESICB; Principle researcher: Professor Yasuhiro Tanaka, Kyoto University Graduate School of Engineering) .