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Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode.

Mortemard de Boisse B, Liu G, Ma J, Nishimura S, Chung SC, Kiuchi H, Harada Y, Kikkawa J, Kobayashi Y, Okubo M, Yamada A - Nat Commun (2016)

Bottom Line: Here using two polymorphs of Na2RuO3, we demonstrate the critical role of honeycomb-type cation ordering in Na2MO3.Ordered Na2RuO3 with honeycomb-ordered [Na(1/3)Ru(2/3)]O2 slabs delivers a capacity of 180 mAh g(-1) (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g(-1) (1.0-electron reaction).We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure, which induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2MO3 cathodes.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.

ABSTRACT
Sodium-ion batteries are attractive energy storage media owing to the abundance of sodium, but the low capacities of available cathode materials make them impractical. Sodium-excess metal oxides Na2MO3 (M: transition metal) are appealing cathode materials that may realize large capacities through additional oxygen redox reaction. However, the general strategies for enhancing the capacity of Na2MO3 are poorly established. Here using two polymorphs of Na2RuO3, we demonstrate the critical role of honeycomb-type cation ordering in Na2MO3. Ordered Na2RuO3 with honeycomb-ordered [Na(1/3)Ru(2/3)]O2 slabs delivers a capacity of 180 mAh g(-1) (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g(-1) (1.0-electron reaction). We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure, which induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2MO3 cathodes.

No MeSH data available.


Related in: MedlinePlus

Electronic structure changes of ordered Na2RuO3 upon charge.(a) States of charge of the samples for X-ray absorption spectroscopy. (b) Ruthenium L3-edge and (c) oxygen K-edge X-ray absorption spectra for various O-NaxRuO3 compositions: (i) x=2.0 (black), (ii) x=1.5 (blue), (iii) x=1.0 (green) and (iv) x=0.62 (red). The asterisked peak corresponds to O 2p-Na 3p. The calculated oxygen K-edge spectra for ordered Na2RuO3 (black) and ilmenite-type NaRuO3 (green) are also shown.
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f6: Electronic structure changes of ordered Na2RuO3 upon charge.(a) States of charge of the samples for X-ray absorption spectroscopy. (b) Ruthenium L3-edge and (c) oxygen K-edge X-ray absorption spectra for various O-NaxRuO3 compositions: (i) x=2.0 (black), (ii) x=1.5 (blue), (iii) x=1.0 (green) and (iv) x=0.62 (red). The asterisked peak corresponds to O 2p-Na 3p. The calculated oxygen K-edge spectra for ordered Na2RuO3 (black) and ilmenite-type NaRuO3 (green) are also shown.

Mentions: After the O3→O1 transition, O-Na2RuO3 delivers additional capacity, exceeding that of the Ru5+/Ru4+ one-electron reaction at the higher voltage plateau of around 3.7 V. To clarify the overall redox mechanism in O-Na2RuO3, we conducted Ru L3-edge and oxygen K-edge X-ray absorption spectroscopy (XAS) in the partial fluorescence yield mode at various charge depths (Fig. 6, Supplementary Figs 6 and 7). The Ru L3-edge XAS directly probes the 4d orbitals through the Laporte-allowed 2p→4d transition27. Furthermore, because the O 2p orbital strongly hybridizes with the Ru 4d orbital, oxygen K-edge XAS can be used to monitor the hole created on the O 2p and Ru 4d orbitals on charging28. Note that the probing depth of the partial fluorescence yield mode is about 100 nm; hence, the spectra are bulk sensitive29.


Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode.

Mortemard de Boisse B, Liu G, Ma J, Nishimura S, Chung SC, Kiuchi H, Harada Y, Kikkawa J, Kobayashi Y, Okubo M, Yamada A - Nat Commun (2016)

Electronic structure changes of ordered Na2RuO3 upon charge.(a) States of charge of the samples for X-ray absorption spectroscopy. (b) Ruthenium L3-edge and (c) oxygen K-edge X-ray absorption spectra for various O-NaxRuO3 compositions: (i) x=2.0 (black), (ii) x=1.5 (blue), (iii) x=1.0 (green) and (iv) x=0.62 (red). The asterisked peak corresponds to O 2p-Na 3p. The calculated oxygen K-edge spectra for ordered Na2RuO3 (black) and ilmenite-type NaRuO3 (green) are also shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837481&req=5

f6: Electronic structure changes of ordered Na2RuO3 upon charge.(a) States of charge of the samples for X-ray absorption spectroscopy. (b) Ruthenium L3-edge and (c) oxygen K-edge X-ray absorption spectra for various O-NaxRuO3 compositions: (i) x=2.0 (black), (ii) x=1.5 (blue), (iii) x=1.0 (green) and (iv) x=0.62 (red). The asterisked peak corresponds to O 2p-Na 3p. The calculated oxygen K-edge spectra for ordered Na2RuO3 (black) and ilmenite-type NaRuO3 (green) are also shown.
Mentions: After the O3→O1 transition, O-Na2RuO3 delivers additional capacity, exceeding that of the Ru5+/Ru4+ one-electron reaction at the higher voltage plateau of around 3.7 V. To clarify the overall redox mechanism in O-Na2RuO3, we conducted Ru L3-edge and oxygen K-edge X-ray absorption spectroscopy (XAS) in the partial fluorescence yield mode at various charge depths (Fig. 6, Supplementary Figs 6 and 7). The Ru L3-edge XAS directly probes the 4d orbitals through the Laporte-allowed 2p→4d transition27. Furthermore, because the O 2p orbital strongly hybridizes with the Ru 4d orbital, oxygen K-edge XAS can be used to monitor the hole created on the O 2p and Ru 4d orbitals on charging28. Note that the probing depth of the partial fluorescence yield mode is about 100 nm; hence, the spectra are bulk sensitive29.

Bottom Line: Here using two polymorphs of Na2RuO3, we demonstrate the critical role of honeycomb-type cation ordering in Na2MO3.Ordered Na2RuO3 with honeycomb-ordered [Na(1/3)Ru(2/3)]O2 slabs delivers a capacity of 180 mAh g(-1) (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g(-1) (1.0-electron reaction).We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure, which induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2MO3 cathodes.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan.

ABSTRACT
Sodium-ion batteries are attractive energy storage media owing to the abundance of sodium, but the low capacities of available cathode materials make them impractical. Sodium-excess metal oxides Na2MO3 (M: transition metal) are appealing cathode materials that may realize large capacities through additional oxygen redox reaction. However, the general strategies for enhancing the capacity of Na2MO3 are poorly established. Here using two polymorphs of Na2RuO3, we demonstrate the critical role of honeycomb-type cation ordering in Na2MO3. Ordered Na2RuO3 with honeycomb-ordered [Na(1/3)Ru(2/3)]O2 slabs delivers a capacity of 180 mAh g(-1) (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g(-1) (1.0-electron reaction). We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure, which induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2MO3 cathodes.

No MeSH data available.


Related in: MedlinePlus