Redox Potential Paradox in NaxMO2 for Sodium-Ion Battery Cathodes

Yusuke Nanba, Tatsumi Iwao, Benoit Mortemard De Boisse, Wenwen Zhao, Eiji Hosono, Daisuke Asakura, Hideharu Niwa, Hisao Kiuchi, Jun Miyawaki, Yoshihisa Harada, Masashi Okubo, Atsuo Yamada

Research output: Contribution to journalArticlepeer-review

56 Citations (Scopus)


Raising the operating potential of the cathode materials in sodium-ion batteries is a crucial challenge if they are to outperform state-of-the-art lithium-ion batteries. Although the layered transition metal oxides, NaMO2 (M: transition metal), are the most promising cathode materials owing to their high theoretical capacity with much more stable nature than Li1-xMO2 system, factors influencing the redox potential have not yet been fully understood. Here, we identify redox potential paradox, E(Ni3+/Ni2+) > E(Ni4+/Ni3+), in an identical structural framework, namely, NaTi4+0.5Ni2+0.5O2 and NaFe3+0.5Ni3+0.5O2, which is induced by transition of the oxides from Mott-Hubbard to negative charge-transfer regimes. The origin of the unusually low E(Ni4+/Ni3+) is the surprisingly large contribution (over 80%) of oxygen orbital to the redox reaction, of which the primary effect on the electrochemical property is demonstrated for the first time, providing a firm platform to design better cathodes for advanced sodium-ion batteries.

Original languageEnglish
Pages (from-to)1058-1065
Number of pages8
JournalChemistry of Materials
Issue number4
Publication statusPublished - 2016 Feb 23
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry


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