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The structure of the cathode material for sodium ion secondary batteries developed this time. This material is called eldfellite.
Prof. John Goodenough of the University of Texas at Austin announced that, in the field of sodium (Na) secondary batteries, it has developed a long life and high safety cathode material. Papers have been published in academic journals. Goodenough developed lithium cobalt oxide (LiCoO2), a cathode material, in 1980, which opened the way for the practical application of lithium (Li) ion secondary batteries. He is also known worldwide. Goodenough is an active 92-year-old researcher.
The sodium ion secondary battery may become a new type of secondary battery that replaces a lithium ion secondary battery. R&D in this area is now the hottest time. Because Na has much more resources than Li, it is expected to significantly increase battery production and reduce costs. However, in terms of performance such as capacity density, there have been many problems related to lithium ion secondary batteries and durability.
This time, Goodenough et al. developed a cathode material NaFe(SO4)2 for sodium ion secondary batteries. Also called Eldfellite, this is a natural mineral resource. The feature is that the capacity density is about two-thirds of the positive electrode material for lithium ion secondary batteries, but the durability is higher than the original. The skeleton of the material developed this time consists of Na, Fe and oxygen atoms O, but the skeleton is not easily broken down even if sodium ions are repeatedly introduced.
The capacity density as a positive electrode material is theoretically 99 mAh/g. In actual measurement, after repeated charge and discharge 80 times, it is still 78 mAh/g, and the Coulomb efficiency is close to 100%. The average potential difference of the positive electrode material with respect to Na/sodium ion is about 3V.
Due to the low capacity density, the research team did not consider this material to be the final solution. Even so, Preetam Singh, the first author of this paper who wrote the paper, said that "this material will become the basis of cathode materials, and it is believed that it will eventually promote the practical use of sodium ion secondary batteries." (Reporter: Nozawa Tetsuo)
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