Content of research

This research is for the development of a process of the purification of metallic sodium containing impurities by electrorefining. Metallic sodium from used sodium-sulfur batteries is used as a source material. By placing the metallic sodium in the upper left (anode) of an electrolysis cell model (Fig. 1) and applying current, the sodium ions dissolve in the electrolyte and only the sodium is deposited on the high-purity sodium (cathode) layer on the upper right. This process can be operated at 200°C or less. The high-purity sodium obtained by this electrolysis is pure enough to be used as a raw material for batteries and growth medium of semiconductor crystal. Since Japan is dependent on foreign countries for sodium resources, we believe that this technology will be widely applied in the future.

Potential for social implementation

• ・High-purity sodium can be used as a raw material for batteries, a catalyst in organic chemical synthesis, a flux in GaN semiconductor manufacturing, and a cooling medium for reactor.

Appealing points to industry and local governments

・The properties of ionic liquids, which are electrolytes, affect the purity and production rate of sodium. Since ionic liquids are still expensive, we would like to collaborate with companies which can develop cheaper ionic liquids.
・I would like to try to achieve high purity of active metals other than sodium. In particular, I would like to utilize this method for the domestic circulation of metals that are heavily dependent on imports from overseas.