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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

Reaction mechanisms of disordered and ordered Na2RuO3.Schematic representation of the structural changes during charge–discharge for disordered Na2RuO3 and ordered Na2RuO3. Ordered Na2RuO3 can distort cooperatively to raise the energy level of the antibonding σ* orbital of the O–O bond, leading to the oxygen redox reaction. Disordered Na1RuO3 cannot accommodate the RuO6 distortion due to strain frustration, which prevents the oxygen redox reaction.
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f5: Reaction mechanisms of disordered and ordered Na2RuO3.Schematic representation of the structural changes during charge–discharge for disordered Na2RuO3 and ordered Na2RuO3. Ordered Na2RuO3 can distort cooperatively to raise the energy level of the antibonding σ* orbital of the O–O bond, leading to the oxygen redox reaction. Disordered Na1RuO3 cannot accommodate the RuO6 distortion due to strain frustration, which prevents the oxygen redox reaction.

Mentions: In the refined structure of O-Na1RuO3 (R space group, a=5.2492(1) Å and c=15.6201(6) Å), the Na site in the [Na1/3Ru2/3]O2 slabs is vacant, which means Na was extracted from the [Na1/3Ru2/3]O2 slabs prior to the Na layers. In this very unique, stable intermediate ilmenite-type Na1RuO3, all NaO6 octahedra in the Na layer share faces with a RuO6 octahedron and a ‘□O6' octahedron of the adjacent [□1/3Ru2/3]O2 slabs (□: Na vacancy). As shown in Fig. 4a, the interlayer distance of O-Na1RuO3 (5.2067(2) Å) is much shorter than that of D-Na1RuO3 (5.591(4) Å) as a result of substantial displacement of Na in the Na layer towards □O6 octahedra by Coulombic attraction (Fig. 4b). Importantly, the RuO6 octahedron is strongly distorted: the shortest neighbouring O–O distance is 2.580(4) Å, whereas the longest is 3.080(6) Å (Fig. 5 and Supplementary Table 3).


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)

Reaction mechanisms of disordered and ordered Na2RuO3.Schematic representation of the structural changes during charge–discharge for disordered Na2RuO3 and ordered Na2RuO3. Ordered Na2RuO3 can distort cooperatively to raise the energy level of the antibonding σ* orbital of the O–O bond, leading to the oxygen redox reaction. Disordered Na1RuO3 cannot accommodate the RuO6 distortion due to strain frustration, which prevents the oxygen redox reaction.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: Reaction mechanisms of disordered and ordered Na2RuO3.Schematic representation of the structural changes during charge–discharge for disordered Na2RuO3 and ordered Na2RuO3. Ordered Na2RuO3 can distort cooperatively to raise the energy level of the antibonding σ* orbital of the O–O bond, leading to the oxygen redox reaction. Disordered Na1RuO3 cannot accommodate the RuO6 distortion due to strain frustration, which prevents the oxygen redox reaction.
Mentions: In the refined structure of O-Na1RuO3 (R space group, a=5.2492(1) Å and c=15.6201(6) Å), the Na site in the [Na1/3Ru2/3]O2 slabs is vacant, which means Na was extracted from the [Na1/3Ru2/3]O2 slabs prior to the Na layers. In this very unique, stable intermediate ilmenite-type Na1RuO3, all NaO6 octahedra in the Na layer share faces with a RuO6 octahedron and a ‘□O6' octahedron of the adjacent [□1/3Ru2/3]O2 slabs (□: Na vacancy). As shown in Fig. 4a, the interlayer distance of O-Na1RuO3 (5.2067(2) Å) is much shorter than that of D-Na1RuO3 (5.591(4) Å) as a result of substantial displacement of Na in the Na layer towards □O6 octahedra by Coulombic attraction (Fig. 4b). Importantly, the RuO6 octahedron is strongly distorted: the shortest neighbouring O–O distance is 2.580(4) Å, whereas the longest is 3.080(6) Å (Fig. 5 and Supplementary Table 3).

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