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*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

73 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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