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Unraveling the storage mechanism in organic carbonyl electrodes for sodium-ion batteries.

Wu X, Jin S, Zhang Z, Jiang L, Mu L, Hu YS, Li H, Chen X, Armand M, Chen L, Huang X - Sci Adv (2015)

Bottom Line: We take Na2C6H2O4 as an example to unravel the mechanism.It consists of alternating Na-O octahedral inorganic layer and π-stacked benzene organic layer in spatial separation, delivering a high reversible capacity and first coulombic efficiency.The experiment and calculation results reveal that the Na-O inorganic layer provides both Na(+) ion transport pathway and storage site, whereas the benzene organic layer provides electron transport pathway and redox center.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.

ABSTRACT
Organic carbonyl compounds represent a promising class of electrode materials for secondary batteries; however, the storage mechanism still remains unclear. We take Na2C6H2O4 as an example to unravel the mechanism. It consists of alternating Na-O octahedral inorganic layer and π-stacked benzene organic layer in spatial separation, delivering a high reversible capacity and first coulombic efficiency. The experiment and calculation results reveal that the Na-O inorganic layer provides both Na(+) ion transport pathway and storage site, whereas the benzene organic layer provides electron transport pathway and redox center. Our contribution provides a brand-new insight in understanding the storage mechanism in inorganic-organic layered host and opens up a new exciting direction for designing new materials for secondary batteries.

No MeSH data available.


Related in: MedlinePlus

Resolved crystal structure of Na2C6H2O4.(A) XRD pattern and Rietveld refinement of Na2C6H2O4 sample. The black (red) line represents the experimental (calculated) data. The residual discrepancy is shown in yellow. The refinement is preformed in the P–1 space group. Inset shows the molecular structure. (B to D) Schematic illustration of the triclinic Na2C6H2O4 (B) layered structure (green color refers to Na-O octahedron), (C) along the a axis and (D) along the b axis. For clarity, 2,5-DBQ molecules and sodium ions are expressed using tubes and balls in (D).
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Figure 1: Resolved crystal structure of Na2C6H2O4.(A) XRD pattern and Rietveld refinement of Na2C6H2O4 sample. The black (red) line represents the experimental (calculated) data. The residual discrepancy is shown in yellow. The refinement is preformed in the P–1 space group. Inset shows the molecular structure. (B to D) Schematic illustration of the triclinic Na2C6H2O4 (B) layered structure (green color refers to Na-O octahedron), (C) along the a axis and (D) along the b axis. For clarity, 2,5-DBQ molecules and sodium ions are expressed using tubes and balls in (D).

Mentions: The crystal structure of this compound was resolved in an ab initio manner from powder diffraction data. To solve this problem, we used 2,5-DBQ dianion and sodium cation as independent motifs in a simulated annealing approach; an initial structure is obtained, then corrected by density functional theory (DFT) geometry optimization, and finally refined via the Rietveld method. As shown in Fig. 1A, the final structure obtained after refinement produced an excellent fit to the diffraction pattern, with Rp = 2.75% and Rwp = 3.70%. The compound crystallizes in a centrosymmetric triclinic system (space group P–1), with lattice constants of a = 3.5229(2) Å, b = 6.0240(3) Å, c = 7.3975(4) Å, α = 74.269(2), β = 81.823(2), γ = 93.870(2), and V = 148.6 Å3. The detailed crystallographic information is listed in table S2. Figure 1B displays a typical layered structure of Na2C6H2O4, where an Na-O inorganic layer and parallel-orientated benzene organic layer are alternately arranged along the c direction. For each 2,5-DBQ molecule, all of four carbonyl groups with very similar bond lengths of 1.2792 and 1.2769 Å are extended outward from the benzene ring layer and coordinated to sodium atoms, whereas the two C–H bonds are left inside the layer. This similar bond length of all C–O bonds gives a new insight in understanding the structure, which cannot be described as discrete C=O and C–O bonds (hereafter “carbonyl”), but all belong to the same conjugation. Each sodium atom is coordinated with six oxygen atoms (two from the same 2,5-DBQ molecule and the remaining four are from different 2,5-DBQ molecules) with the Na-O distance range from 2.3433 to 2.5543 Å to form the Na-O octahedron. The inorganic layer consists of Na-O octahedrons connected through edge sharing. Moreover, each carbonyl is coordinated with three different sodium atoms above and below the benzene ring plane. The sodium atoms are arranged in S line along the a axis, forming a possible one-dimensional (1D) Na+ ion transport pathway as corroborated later. The parallel-stacked benzene rings through π interaction are along the a axis, and the distance between neighboring benzene rings is 3.157 Å (Fig. 1D). The inorganic and organic layers are connected by oxygen atoms to form the layered structure.


Unraveling the storage mechanism in organic carbonyl electrodes for sodium-ion batteries.

Wu X, Jin S, Zhang Z, Jiang L, Mu L, Hu YS, Li H, Chen X, Armand M, Chen L, Huang X - Sci Adv (2015)

Resolved crystal structure of Na2C6H2O4.(A) XRD pattern and Rietveld refinement of Na2C6H2O4 sample. The black (red) line represents the experimental (calculated) data. The residual discrepancy is shown in yellow. The refinement is preformed in the P–1 space group. Inset shows the molecular structure. (B to D) Schematic illustration of the triclinic Na2C6H2O4 (B) layered structure (green color refers to Na-O octahedron), (C) along the a axis and (D) along the b axis. For clarity, 2,5-DBQ molecules and sodium ions are expressed using tubes and balls in (D).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4643786&req=5

Figure 1: Resolved crystal structure of Na2C6H2O4.(A) XRD pattern and Rietveld refinement of Na2C6H2O4 sample. The black (red) line represents the experimental (calculated) data. The residual discrepancy is shown in yellow. The refinement is preformed in the P–1 space group. Inset shows the molecular structure. (B to D) Schematic illustration of the triclinic Na2C6H2O4 (B) layered structure (green color refers to Na-O octahedron), (C) along the a axis and (D) along the b axis. For clarity, 2,5-DBQ molecules and sodium ions are expressed using tubes and balls in (D).
Mentions: The crystal structure of this compound was resolved in an ab initio manner from powder diffraction data. To solve this problem, we used 2,5-DBQ dianion and sodium cation as independent motifs in a simulated annealing approach; an initial structure is obtained, then corrected by density functional theory (DFT) geometry optimization, and finally refined via the Rietveld method. As shown in Fig. 1A, the final structure obtained after refinement produced an excellent fit to the diffraction pattern, with Rp = 2.75% and Rwp = 3.70%. The compound crystallizes in a centrosymmetric triclinic system (space group P–1), with lattice constants of a = 3.5229(2) Å, b = 6.0240(3) Å, c = 7.3975(4) Å, α = 74.269(2), β = 81.823(2), γ = 93.870(2), and V = 148.6 Å3. The detailed crystallographic information is listed in table S2. Figure 1B displays a typical layered structure of Na2C6H2O4, where an Na-O inorganic layer and parallel-orientated benzene organic layer are alternately arranged along the c direction. For each 2,5-DBQ molecule, all of four carbonyl groups with very similar bond lengths of 1.2792 and 1.2769 Å are extended outward from the benzene ring layer and coordinated to sodium atoms, whereas the two C–H bonds are left inside the layer. This similar bond length of all C–O bonds gives a new insight in understanding the structure, which cannot be described as discrete C=O and C–O bonds (hereafter “carbonyl”), but all belong to the same conjugation. Each sodium atom is coordinated with six oxygen atoms (two from the same 2,5-DBQ molecule and the remaining four are from different 2,5-DBQ molecules) with the Na-O distance range from 2.3433 to 2.5543 Å to form the Na-O octahedron. The inorganic layer consists of Na-O octahedrons connected through edge sharing. Moreover, each carbonyl is coordinated with three different sodium atoms above and below the benzene ring plane. The sodium atoms are arranged in S line along the a axis, forming a possible one-dimensional (1D) Na+ ion transport pathway as corroborated later. The parallel-stacked benzene rings through π interaction are along the a axis, and the distance between neighboring benzene rings is 3.157 Å (Fig. 1D). The inorganic and organic layers are connected by oxygen atoms to form the layered structure.

Bottom Line: We take Na2C6H2O4 as an example to unravel the mechanism.It consists of alternating Na-O octahedral inorganic layer and π-stacked benzene organic layer in spatial separation, delivering a high reversible capacity and first coulombic efficiency.The experiment and calculation results reveal that the Na-O inorganic layer provides both Na(+) ion transport pathway and storage site, whereas the benzene organic layer provides electron transport pathway and redox center.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.

ABSTRACT
Organic carbonyl compounds represent a promising class of electrode materials for secondary batteries; however, the storage mechanism still remains unclear. We take Na2C6H2O4 as an example to unravel the mechanism. It consists of alternating Na-O octahedral inorganic layer and π-stacked benzene organic layer in spatial separation, delivering a high reversible capacity and first coulombic efficiency. The experiment and calculation results reveal that the Na-O inorganic layer provides both Na(+) ion transport pathway and storage site, whereas the benzene organic layer provides electron transport pathway and redox center. Our contribution provides a brand-new insight in understanding the storage mechanism in inorganic-organic layered host and opens up a new exciting direction for designing new materials for secondary batteries.

No MeSH data available.


Related in: MedlinePlus