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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

Crystal structures of Na3C6H2O4 and Na4C6H2O4.(A to F) Schematic illustration of Na3C6H2O4 (A) layered structure (yellow color refers to Na-O square pyramid, and green color refers to Na-O octahedron), (C) along the a axis and (E) along the b axis, and Na4C6H2O4 (B) layered structure (yellow color refers to Na-O square pyramid), (D) along the a axis and (F) along the b axis. For clarity, 2,5-DBQ molecules and sodium ions are expressed using tubes and balls in (E) and (F).
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Figure 5: Crystal structures of Na3C6H2O4 and Na4C6H2O4.(A to F) Schematic illustration of Na3C6H2O4 (A) layered structure (yellow color refers to Na-O square pyramid, and green color refers to Na-O octahedron), (C) along the a axis and (E) along the b axis, and Na4C6H2O4 (B) layered structure (yellow color refers to Na-O square pyramid), (D) along the a axis and (F) along the b axis. For clarity, 2,5-DBQ molecules and sodium ions are expressed using tubes and balls in (E) and (F).

Mentions: These three compounds show great structural resemblance and regular evolution of lattice constants. The structure can be described as an alternative stacking of 2,5-DBQ molecular layers with Na-O layers along the c axis. It can be seen from Fig. 5 (A and B) that the layered structure stays intact during Na insertion. It is clear that the inserted sodium atoms are stored in the inorganic layer of Na-O polyhedrons, which also provides a transport pathway for Na+ ions along the ab plane. Upon sodium insertion, the coordination environments of both sodium atoms and carbonyl groups change dramatically. In Na2C6H2O4, all the sodium atoms are coordinated with six oxygen atoms from five adjacent 2,5-DBQ molecules and the carbonyl group is coordinated with three different sodium atoms. Whereas for the fully discharged compound Na4C6H2O4, the two symmetry-independent sodium atoms are each coordinated with five oxygen atoms in a square pyramidal geometry to form the inorganic layer, the coordination number of carbonyl group by sodium atoms is increased to five. The structure of Na3C6H2O4 shows a transient state between the Na2C6H2O4 and Na4C6H2O4 phases. As shown in Fig. 5 (C and D), the three sodium atoms reside in two independent sites within the unit cell of Na3C6H2O4, that is, one Na1 atom (purple, 1g) in six coordinated octahedral environment and two Na2 atoms (pink, 2i) in five coordinated pyramidal environment to form an inorganic layer with alternative octahedrons and square pyramids along the b direction (see more in fig. S6). The change of sodium atom positions in this process is shown in fig. S7. The angle between the identical benzene ring plane and the bc plane decreases with Na insertion, and the benzene ring rotates around its center, as shown in Fig. 6. The distance between neighboring benzene rings significantly expands to 3.282 and 3.734 Å, respectively (note that C-O and C-C lengths are shown in table S5). From the above discussion, Na insertion leads to the obvious movement of all oxygen and benzene rings.


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)

Crystal structures of Na3C6H2O4 and Na4C6H2O4.(A to F) Schematic illustration of Na3C6H2O4 (A) layered structure (yellow color refers to Na-O square pyramid, and green color refers to Na-O octahedron), (C) along the a axis and (E) along the b axis, and Na4C6H2O4 (B) layered structure (yellow color refers to Na-O square pyramid), (D) along the a axis and (F) along the b axis. For clarity, 2,5-DBQ molecules and sodium ions are expressed using tubes and balls in (E) and (F).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Crystal structures of Na3C6H2O4 and Na4C6H2O4.(A to F) Schematic illustration of Na3C6H2O4 (A) layered structure (yellow color refers to Na-O square pyramid, and green color refers to Na-O octahedron), (C) along the a axis and (E) along the b axis, and Na4C6H2O4 (B) layered structure (yellow color refers to Na-O square pyramid), (D) along the a axis and (F) along the b axis. For clarity, 2,5-DBQ molecules and sodium ions are expressed using tubes and balls in (E) and (F).
Mentions: These three compounds show great structural resemblance and regular evolution of lattice constants. The structure can be described as an alternative stacking of 2,5-DBQ molecular layers with Na-O layers along the c axis. It can be seen from Fig. 5 (A and B) that the layered structure stays intact during Na insertion. It is clear that the inserted sodium atoms are stored in the inorganic layer of Na-O polyhedrons, which also provides a transport pathway for Na+ ions along the ab plane. Upon sodium insertion, the coordination environments of both sodium atoms and carbonyl groups change dramatically. In Na2C6H2O4, all the sodium atoms are coordinated with six oxygen atoms from five adjacent 2,5-DBQ molecules and the carbonyl group is coordinated with three different sodium atoms. Whereas for the fully discharged compound Na4C6H2O4, the two symmetry-independent sodium atoms are each coordinated with five oxygen atoms in a square pyramidal geometry to form the inorganic layer, the coordination number of carbonyl group by sodium atoms is increased to five. The structure of Na3C6H2O4 shows a transient state between the Na2C6H2O4 and Na4C6H2O4 phases. As shown in Fig. 5 (C and D), the three sodium atoms reside in two independent sites within the unit cell of Na3C6H2O4, that is, one Na1 atom (purple, 1g) in six coordinated octahedral environment and two Na2 atoms (pink, 2i) in five coordinated pyramidal environment to form an inorganic layer with alternative octahedrons and square pyramids along the b direction (see more in fig. S6). The change of sodium atom positions in this process is shown in fig. S7. The angle between the identical benzene ring plane and the bc plane decreases with Na insertion, and the benzene ring rotates around its center, as shown in Fig. 6. The distance between neighboring benzene rings significantly expands to 3.282 and 3.734 Å, respectively (note that C-O and C-C lengths are shown in table S5). From the above discussion, Na insertion leads to the obvious movement of all oxygen and benzene rings.

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