A research group led by Professor Atsuo Yamada and Associate Professor Masashi Okubo of the Department of Chemical Systems Engineering, Graduate School of Engineering, the University of Tokyo has developed a positive electrode for sodium-ion batteries, which are candidates for next-generation batteries that do not use rare elements such as lithium. Announced that it was done.
So far, as for the positive electrode used in the sodium ion battery, compounds that charge and discharge by the oxidation / reduction reaction of transition metals (iron and manganese) have been studied.However, the amount of current that can be charged and discharged is suppressed to a low level by the amount of transition metal contained in the substance, which is the cause of the inability to supply power for a long time.
This time, the research group found that a layered oxide having a honeycomb-like structure composed of sodium, a transition metal, and an oxide ion can be charged and discharged by an oxidation / reduction reaction of the oxide ion.Conventionally, it has been considered that a stable reaction does not occur in this type of reaction due to the dissociation of oxygen and changes in the crystal structure.In this study, due to the cooperative structural distortion of the oxide ion and the transition metal generated in the honeycomb structure, the electrons of the oxide ion strongly interact with each other, resulting in a chemical state that promotes oxidation and reduction. It was found by detailed analysis.As a result of actually applying the obtained reaction as a positive electrode of a sodium ion battery, it is possible to store 1.4 times more electricity than the conventional positive electrode that extracts electrons only from transition metals, and it can also charge and discharge. It was found that the characteristics of the battery did not deteriorate at all even after repeated use, and the reaction was very stable and usable.
The realization of charging and discharging by oxide ions contained in a large amount in substances is expected to accelerate the development of sodium-ion batteries, reduce the cost of electric vehicles, and break away from the state of being dependent on scarce resources. ..