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Copper nanofiber-networked cobalt oxide composites for high performance Li-ion batteries.

Nam SH, Kim YS, Shim HS, Kim JG, Bae Kim W - Nanoscale Res Lett (2011)

Bottom Line: We prepared a composite electrode structure consisting of copper nanofiber-networked cobalt oxide (CuNFs@CoOx).The copper nanofibers (CuNFs) were fabricated on a substrate with formation of a network structure, which may have potential for improving electron percolation and retarding film deformation during the discharging/charging process over the electroactive cobalt oxide.Such enhanced Li-ion storage performance may be associated with modified electrode structure at the nanoscale, improved charge transfer, and facile stress relaxation from the embedded CuNF network.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Chemdan-gwagiro, Buk-gu, Gwangju 500-712, South Korea. wbkim@gist.ac.kr.

ABSTRACT
We prepared a composite electrode structure consisting of copper nanofiber-networked cobalt oxide (CuNFs@CoOx). The copper nanofibers (CuNFs) were fabricated on a substrate with formation of a network structure, which may have potential for improving electron percolation and retarding film deformation during the discharging/charging process over the electroactive cobalt oxide. Compared to bare CoOxthin-film (CoOxTF) electrodes, the CuNFs@CoOxelectrodes exhibited a significant enhancement of rate performance by at least six-fold at an input current density of 3C-rate. Such enhanced Li-ion storage performance may be associated with modified electrode structure at the nanoscale, improved charge transfer, and facile stress relaxation from the embedded CuNF network. Consequently, the CuNFs@CoOxcomposite structure demonstrated here can be used as a promising high-performance electrode for Li-ion batteries.

No MeSH data available.


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Galvanostatic mode at 0.15C. The potential curves of (a) the initial cycling profiles; (b) the specific capacity with cycling number; (c) the rate performance test for various C-rates of 0.15 to 3C.
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Figure 3: Galvanostatic mode at 0.15C. The potential curves of (a) the initial cycling profiles; (b) the specific capacity with cycling number; (c) the rate performance test for various C-rates of 0.15 to 3C.

Mentions: To investigate the influence of CuNFs on the Li ions storage performance of the CoOx, we conducted galvanostatic discharge/charge processes. Figure 3a shows the first and second discharge/charge voltage profiles at a constant 0.15C between the voltages of 2.5 and 0.01 V (vs. Li+/Li). Both CoOxTF and CuNFs@CoOxexhibit the plateau around 1.0 V in the first discharge curve. This is associated with the following electrochemical reaction [14] of Co3O4 + 8Li+ + 8e- → 4Li2O + 3Co. The CuNFs@CoOx seems to have a little bit larger irreversible capacity of ca. 240 mAh g-1 compared to the bare CoOxTF, which could be caused by the enlarged contact area between the electrolyte and electrode material [7]. Although the CuNFs@CoOxelectrode indicated a conversion profile similar to that of the CoOxTF, the capacity was ca. 30% higher than that of the bare CoOxTF, as shown in Figure 3b. The highly rugged microstructure of CuNFs@CoOxmight be responsible for the increased reaction sites along the CuNF network, making the electrochemical reaction more efficient with Li ions, because the electrochemical performance can be dependent on the textual characteristics of the electrodes [15]. In addition, it was also reported that the incorporation of nanostructure into a Li host matrix exhibited an enhanced reversible capacity [8,16]. The coulombic efficiency (the ratio of the number of charges that enter the electrode to the number that can be extracted from the electrode) was more than 90% except for the initial few cycles, which suggests that the inserted Li ions were reversibly extracted. Figure 3c shows the current density dependence on the discharge capacities of the CoOxTF and CuNFs@CoOxat 0.15, 0.3, 0.6, 1.2, 2.5, and 3C-rates. The capacity of the CoOxTF decreased rapidly with increasing current density, which is consistent with previously reported results [15,17], whereas the CuNFs@CoOxwas able to maintain 50% of its initial capacity even at 3C-rate. Such enhanced performance of the CuNFs@CoOxcan be attributed to the improvement of the electrical conductivity of the CoOxby the embedded CuNF network, which creates an efficient electron percolation path between the current collector and the active material [8].


Copper nanofiber-networked cobalt oxide composites for high performance Li-ion batteries.

Nam SH, Kim YS, Shim HS, Kim JG, Bae Kim W - Nanoscale Res Lett (2011)

Galvanostatic mode at 0.15C. The potential curves of (a) the initial cycling profiles; (b) the specific capacity with cycling number; (c) the rate performance test for various C-rates of 0.15 to 3C.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211358&req=5

Figure 3: Galvanostatic mode at 0.15C. The potential curves of (a) the initial cycling profiles; (b) the specific capacity with cycling number; (c) the rate performance test for various C-rates of 0.15 to 3C.
Mentions: To investigate the influence of CuNFs on the Li ions storage performance of the CoOx, we conducted galvanostatic discharge/charge processes. Figure 3a shows the first and second discharge/charge voltage profiles at a constant 0.15C between the voltages of 2.5 and 0.01 V (vs. Li+/Li). Both CoOxTF and CuNFs@CoOxexhibit the plateau around 1.0 V in the first discharge curve. This is associated with the following electrochemical reaction [14] of Co3O4 + 8Li+ + 8e- → 4Li2O + 3Co. The CuNFs@CoOx seems to have a little bit larger irreversible capacity of ca. 240 mAh g-1 compared to the bare CoOxTF, which could be caused by the enlarged contact area between the electrolyte and electrode material [7]. Although the CuNFs@CoOxelectrode indicated a conversion profile similar to that of the CoOxTF, the capacity was ca. 30% higher than that of the bare CoOxTF, as shown in Figure 3b. The highly rugged microstructure of CuNFs@CoOxmight be responsible for the increased reaction sites along the CuNF network, making the electrochemical reaction more efficient with Li ions, because the electrochemical performance can be dependent on the textual characteristics of the electrodes [15]. In addition, it was also reported that the incorporation of nanostructure into a Li host matrix exhibited an enhanced reversible capacity [8,16]. The coulombic efficiency (the ratio of the number of charges that enter the electrode to the number that can be extracted from the electrode) was more than 90% except for the initial few cycles, which suggests that the inserted Li ions were reversibly extracted. Figure 3c shows the current density dependence on the discharge capacities of the CoOxTF and CuNFs@CoOxat 0.15, 0.3, 0.6, 1.2, 2.5, and 3C-rates. The capacity of the CoOxTF decreased rapidly with increasing current density, which is consistent with previously reported results [15,17], whereas the CuNFs@CoOxwas able to maintain 50% of its initial capacity even at 3C-rate. Such enhanced performance of the CuNFs@CoOxcan be attributed to the improvement of the electrical conductivity of the CoOxby the embedded CuNF network, which creates an efficient electron percolation path between the current collector and the active material [8].

Bottom Line: We prepared a composite electrode structure consisting of copper nanofiber-networked cobalt oxide (CuNFs@CoOx).The copper nanofibers (CuNFs) were fabricated on a substrate with formation of a network structure, which may have potential for improving electron percolation and retarding film deformation during the discharging/charging process over the electroactive cobalt oxide.Such enhanced Li-ion storage performance may be associated with modified electrode structure at the nanoscale, improved charge transfer, and facile stress relaxation from the embedded CuNF network.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Chemdan-gwagiro, Buk-gu, Gwangju 500-712, South Korea. wbkim@gist.ac.kr.

ABSTRACT
We prepared a composite electrode structure consisting of copper nanofiber-networked cobalt oxide (CuNFs@CoOx). The copper nanofibers (CuNFs) were fabricated on a substrate with formation of a network structure, which may have potential for improving electron percolation and retarding film deformation during the discharging/charging process over the electroactive cobalt oxide. Compared to bare CoOxthin-film (CoOxTF) electrodes, the CuNFs@CoOxelectrodes exhibited a significant enhancement of rate performance by at least six-fold at an input current density of 3C-rate. Such enhanced Li-ion storage performance may be associated with modified electrode structure at the nanoscale, improved charge transfer, and facile stress relaxation from the embedded CuNF network. Consequently, the CuNFs@CoOxcomposite structure demonstrated here can be used as a promising high-performance electrode for Li-ion batteries.

No MeSH data available.


Related in: MedlinePlus