A Japanese research team developed a high-energy-density magnesium (Mg) rechargeable battery that can replace existing lithium (Li)-ion rechargeable batteries.

The team includes Yoshiharu Uchimoto and Yuuki Orikasa, professor and assistant professor, respectively, at the Graduate School of Human and Environmental Studies, Kyoto University; Hiroshi Kageyama, professor at the Graduate School of Engineering, Kyoto University; and Cedric Tassel, assistant professor at Hakubi Center, Kyoto University. The team developed the battery in collaboration with Japan Synchrotron Radiation Research Institute (JASRI).

The main components of the battery are Mg, iron (Fe) and silicon (Si), which are abundantly available, realizing a low cost. In the development of the battery, the research team used the high-brightness synchrotron radiation of the "SPring-8" large-scale synchrotron radiation facility to clarify the mechanism of the battery's charge/discharge reaction.

As a positive-electrode material, the team employed a polyanion compound, which stabilizes crystal structure with Si-O bond. It ensured the diffusion of Mg ions by finely controlling the crystal structure with electrochemical treatment. Also, as a positive-electrode material that has high cycling characteristics, MgFeSiO4 was selected.

The charge/discharge curve of the battery shows that the capacity density of the positive electrode is twice as high as that of the positive electrode of existing Li-ion batteries (160mAh/g). For the electrolyte of the battery, Mg(TFSI)2 and Triglyme were combined. It can be used together with a Mg negative electrode and has a high oxidation stability.

The research team prototyped a rechargeable battery by using the newly-developed positive electrode and electrolyte. Its theoretical energy density is about seven times higher than that of existing Mg rechargeable batteries. It also eliminates the need to use the Grignard reagent, which is chemically unstable, or halogen ions, which are corrosive.