The University of Tokyo has discovered a self-repairing electrode material that forms a stable structure by storing electricity.
The material is expected to increase the life of rechargeable batteries because it repeatedly repairs itself each time the battery is charged and, therefore, its performance does not lower.
A rechargeable battery stores electricity because ions are desorbed from its electrode material. The larger the number of ions desorbed from the electrode material, the more electricity the battery stores. However, when a large number of ions are desorbed from commonly-used electrode materials, the materials become unstable and their structures are changed (destroyed), drastically lowering their performance.
This time, the university found (1) that, when electrode material Na2MO3 (this time, M = Ru) is charged (when sodium ions are desorbed), structural disorder called stacking fault gradually disappears and (2) that, when the material is completely charged, it repairs itself and becomes completely free of structural disorder. And the university found that this spontaneous self-repairing also occurs after repeatedly charging and discharging the material.
When the structural change in the charging process is examined in detail by X-ray diffraction, it turned out that strong Coulomb attraction is generated between (1) holes formed after sodium ions are desorbed and (2) sodium ions remaining in the structure and that the attraction plays an important role. The ions and holes strongly attract each other, leading to the spontaneous shift to the structure with no disorder.
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