| 研究実績の概要 |
As developed in the JSPS proposal, our JSPS project focuses on the development and understanding of new cathode materials involving oxygen redox for Li-ion and Na-ion batteries. During this first year, we focused our research on two materials that were expected to show a significant oxygen contribution: Na4Ir3O8 and Na2Mn3O7.
On one hand, Na4Ir3O8 did not show any reversible oxygen redox properties but showed interesting electrochemistry and structural behavior. Indeed, Na4Ir3O8 is, to our knowledge, the first example of a spinel-based cathode material for Na-ion batteries. Moreover, it showed tremendous structural stability upon cycling due to its very robust IrO6 framework. As a consequence, its volume expansion is lower than 2% upon removal of 3 Na+ per formula unit, making Na4Ir3O8 one of the few zero-strain cathode materials. Our study offers a new direction to develop more stable cathode materials for Na-ion batteries and our findings will soon submitted to a scientific journal.
On the other hand, Na2Mn3O7 showed interesting electrochemical properties owing to significant oxygen redox contribution. Our original approach consisted in incorporating transition metal vacancies in the pristine material in order to generate O orphaned orbitals that contribute to the redox reactions. Moreover, this process occurs at the high voltage of 4.1 V vs. Na and shows an unprecedented low polarization (hysteresis) and stability over time. Our results were just accepted for publication in Advanced Energy Materials (impact factor: 12.12).
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