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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

Electrochemical properties of disordered and ordered Na2RuO3.Galvanostatic cycling curves recorded at 30 mA g−1 for (a) disordered and (b) ordered Na2RuO3 with the first cycle highlighted in blue. Insets show the coordination environment of Na at x=1.0 for each phase. (c) Capacity retentions for (blue squares) disordered and (red circles) ordered Na2RuO3.
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f3: Electrochemical properties of disordered and ordered Na2RuO3.Galvanostatic cycling curves recorded at 30 mA g−1 for (a) disordered and (b) ordered Na2RuO3 with the first cycle highlighted in blue. Insets show the coordination environment of Na at x=1.0 for each phase. (c) Capacity retentions for (blue squares) disordered and (red circles) ordered Na2RuO3.

Mentions: Having demonstrated the differences between O- and D-Na2RuO3 in terms of the in-plane ordering and stacking sequences of the [Na1/3Ru2/3]O2 slabs, the Na+ (de)intercalation properties of both materials were studied to clarify the influence of the honeycomb ordering. Figure 3a,b shows the charge–discharge curves measured between 1.5 and 4.0 V versus Na/Na+ at 30 mA g−1 (a rate of ∼C/5). Here charging is an anodic process (Na deintercalation) and discharging is a cathodic process (Na intercalation). D-Na2RuO3 (Fig. 3a) delivers a reversible capacity of 135 mAh g−1, corresponding to (de)intercalation of 1.0 Na+, which is consistent with our previous report19. In contrast, the reversible capacity of O-Na2RuO3 exceeds 180 mAh g−1, indicating reversible (de)intercalation of 1.3 Na+, beyond a Ru5+/Ru4+ one-electron redox process. This behaviour is in agreement with that of Na2RuO3 reported by Rozier et al.20. Importantly, the voltage profile of O-Na2RuO3 significantly differs from the S-shaped voltage profile of D-Na2RuO3. O-NaxRuO3 (0.7≤x≤2) exhibits a staircase-like charge profile with a first voltage plateau around 2.5 V for 1.0≤x≤2.0 and a second voltage plateau around 3.6 V for 0.7≤x≤1.0; the second voltage plateau is related to the extra capacity of O-Na2RuO3, which exceeds that of the Ru5+/Ru4+ one-electron reaction. Although the plateau at 3.6 V shows gradual narrowing with repeating the cycles presumably due to slight loss of the crystallinity (Supplementary Fig. 1a,b), O-Na2RuO3 shows excellent capacity retention of 160 mAh g−1 after 50 cycles (Fig. 3c), which indicates the remarkable stability of the redox processes that contribute to the increased capacity. Indeed, the voltage plateau around 3.6 V is clearly observed for every charge process, suggesting occurrence of the accumulative oxygen redox reaction (Supplementary Fig. 1c,d)18. Therefore, the available capacity significantly exceeds one-electron redox reaction for O-Na2RuO3 even after 50 cycles. It is surprising that the in-plane honeycomb-type cation ordering in O-Na2RuO3 is solely responsible for the drastic changes in the electrochemical properties that results in 30% higher capacity. To the best of our knowledge, this is the first demonstration of the critical role of honeycomb-type cation ordering in [A1/3M2/3]O2 slabs in determining the primary electrochemical properties.


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)

Electrochemical properties of disordered and ordered Na2RuO3.Galvanostatic cycling curves recorded at 30 mA g−1 for (a) disordered and (b) ordered Na2RuO3 with the first cycle highlighted in blue. Insets show the coordination environment of Na at x=1.0 for each phase. (c) Capacity retentions for (blue squares) disordered and (red circles) ordered Na2RuO3.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4837481&req=5

f3: Electrochemical properties of disordered and ordered Na2RuO3.Galvanostatic cycling curves recorded at 30 mA g−1 for (a) disordered and (b) ordered Na2RuO3 with the first cycle highlighted in blue. Insets show the coordination environment of Na at x=1.0 for each phase. (c) Capacity retentions for (blue squares) disordered and (red circles) ordered Na2RuO3.
Mentions: Having demonstrated the differences between O- and D-Na2RuO3 in terms of the in-plane ordering and stacking sequences of the [Na1/3Ru2/3]O2 slabs, the Na+ (de)intercalation properties of both materials were studied to clarify the influence of the honeycomb ordering. Figure 3a,b shows the charge–discharge curves measured between 1.5 and 4.0 V versus Na/Na+ at 30 mA g−1 (a rate of ∼C/5). Here charging is an anodic process (Na deintercalation) and discharging is a cathodic process (Na intercalation). D-Na2RuO3 (Fig. 3a) delivers a reversible capacity of 135 mAh g−1, corresponding to (de)intercalation of 1.0 Na+, which is consistent with our previous report19. In contrast, the reversible capacity of O-Na2RuO3 exceeds 180 mAh g−1, indicating reversible (de)intercalation of 1.3 Na+, beyond a Ru5+/Ru4+ one-electron redox process. This behaviour is in agreement with that of Na2RuO3 reported by Rozier et al.20. Importantly, the voltage profile of O-Na2RuO3 significantly differs from the S-shaped voltage profile of D-Na2RuO3. O-NaxRuO3 (0.7≤x≤2) exhibits a staircase-like charge profile with a first voltage plateau around 2.5 V for 1.0≤x≤2.0 and a second voltage plateau around 3.6 V for 0.7≤x≤1.0; the second voltage plateau is related to the extra capacity of O-Na2RuO3, which exceeds that of the Ru5+/Ru4+ one-electron reaction. Although the plateau at 3.6 V shows gradual narrowing with repeating the cycles presumably due to slight loss of the crystallinity (Supplementary Fig. 1a,b), O-Na2RuO3 shows excellent capacity retention of 160 mAh g−1 after 50 cycles (Fig. 3c), which indicates the remarkable stability of the redox processes that contribute to the increased capacity. Indeed, the voltage plateau around 3.6 V is clearly observed for every charge process, suggesting occurrence of the accumulative oxygen redox reaction (Supplementary Fig. 1c,d)18. Therefore, the available capacity significantly exceeds one-electron redox reaction for O-Na2RuO3 even after 50 cycles. It is surprising that the in-plane honeycomb-type cation ordering in O-Na2RuO3 is solely responsible for the drastic changes in the electrochemical properties that results in 30% higher capacity. To the best of our knowledge, this is the first demonstration of the critical role of honeycomb-type cation ordering in [A1/3M2/3]O2 slabs in determining the primary electrochemical properties.

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