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Cu electrode and its high performance for lithium-ion batteries
Materials Letters 122 (2014) 186–189
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
In situ synthesis of Co3O4/Cu electrode and its high performance for lithium-ion batteries Beibei Wang a, Gang Wang b, Hui Wang a,n a Key Laboratory of Synthetic and Natural Functional Molecule Chemistry (Ministry of Education), College of Chemistry & Materials Science, Northwest University, Xi'an 710069, PR China b National Key Laboratory of Photoelectric Technology and Functional Materials (Culture Base), National Photoelectric Technology and Functional Materials & Application International Cooperation Base, Institute of Photonics & Photon-Technology, Northwest University, Xi’an 710069, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 12 August 2013 Accepted 1 February 2014 Available online 8 February 2014
In this paper, we report the growth of Co3O4 micro-rod arrays on Cu substrate by a modified hydrothermal method. The obtained Co3O4/Cu shows that the formed Co3O4 micro-rods on Cu foil are 1–2 μm in diameter and 25 μm in length. When evaluated as electrode materials for lithium-ion batteries, the specific capacity of Co3O4/Cu materials remains over 0.8 mA h mg 1 after 50 cycles at 0.1 C. The superior electrochemical performance of the Co3O4/Cu electrode may be attributed to the close contact of Co3O4 micro-rod arrays on Cu substrate and the extra space between the neighboring arrays, which provide fast pathways and reduce volume expansion. & 2014 Elsevier B.V. All rights reserved.
Keywords: Cobalt oxide array Crystal structure Functional Lithium ion batteries
1. Introduction Lithium-ion batteries (LIBs) are now considered as a state-ofthe-art power sources for portable electronic devices due to their advantages of high energy density, high electromotive force and long lifespan [1]. Although graphite has served as a reliable anode material for commercial LIBs with high reversibility, its low capacity (372 mA h g 1) can not satisfy future requirements of the electronic devices [2]. With the ever-increasing need for energy density and power demands, considerable efforts have been made in finding new electrode materials for LIBs. Nowadays, transition metal oxides (such as NiO, Fe2O3 and Co3O4) have shown desirable properties as the fascinating anode materials [3–5]. Among the available metal oxide anodes, Co3O4 has attracted special attention because of its high theoretical lithium storage capacity (890 mA h g 1) [6]. However, Co3O4 usually suffers from the problems of low ionic and electronic conductivities, large volume change, and poor cycle stability when used as anode materials, which limit its potential application in LIBs. In order to improve the stability of Co3O4 anode and obtain better capacity retention and cycle life for the material, the growth of one-dimensional (1D) Co3O4 arrays with controlling uniform size and perfect crystalline structure on a variety of conductive substrates (which can be used directly as current collectors) for LIBs have been developed. Several advantages can be obtained on the novel architecture: (1) The extra free space between neighboring arrays allows
n
Corresponding author: Tel.: þ 86 29 88363115; fax: þ 86 29 88303798. E-mail address: [email protected] (H. Wang).
http://dx.doi.org/10.1016/j.matlet.2014.02.004 0167-577X & 2014 Elsevier B.V. All rights reserved.
the ease of electrolyte penetration and accommodates volume variation during Li þ insertion/extraction; (2) the direct attachment and close contact of Co3O4 active materials on the current substrate enable fast pathways for electron transport kinetics; and (3) the direct growth of Co3O4 arrays on conductive substrate can be processed directly for LIB assembly, without the addition of binders or conductive materials [7]. Although Co3O4 nano-wire and nano-belt arrays have been prepared successfully on various metallic substrates and exhibited excellent lithium storage properties, in situ synthesis of 1D Co3O4 micro-rod arrays on Cu foil has never been found in the reported literatures. Herein, we developed a facile hydrothermal method to grow Co3O4 micro-rod arrays directly on Cu foil (Co3O4/Cu, illustrated in Fig. 1(a)). The binder-free Co3O4/Cu material as an anode for LIBs was investigated. It was found that the material exhibits ultrahigh reversible capacity, good cycling stability and superior rate performance.
2. Experimental Synthesis of Co3O4/Cu: Typically, 0.624 g Co(NO3)2 6H2O, 0.159 g NH4F and 0.643 g CO(NH2)2 were dissolved in 30 ml distilled water and then stirred for 30 min. The homogeneous solution was then transferred into a 50 ml Teflon-lined autoclave. Subsequently a piece of Cu foil was immersed into the reaction solution with the interacted surface facing down and the top side of the substrate was protected from solution contamination through fixed glass slide. The autoclave was heated to 120 1C for 9 h. After that the Cu foil was taken down from the glass slide,
B. Wang et al. / Materials Letters 122 (2014) 186–189
187
2h
9h
(b)
25 μm
0.5 μm
5 μm
Fig. 1. (a) Schematic illustration of the growth of Co3O4 arrays on Cu foil. (b) XRD pattern. ((c)–(e)) SEM images of Co3O4 micro-rod arrays. Inset of (c) shows the optical photo of a Cu foil, an as-grown precursor sample, and an annealed Co3O4 micro-rod arrays (from left to right).
washed with distilled water and annealed at 400 1C for 2 h in Ar gas. The experiments were repeated for 10 times to obtain Co3O4/ Cu foils and to assure the work can be reproduced. After the annealing process, the synthesized Co3O4/Cu foils were cut into wafers of 16 mm in diameter. The loading density range of these active materials (Co3O4) on Cu foils was measured to be 1.5– 2.5 mg cm 2. Material characterization: The as-prepared products were characterized by X-ray diffraction (XRD, Rigaku), field emission gun scanning electron microscopy (FEI Quanta 400 FEG), and high-resolution transmission electron microscopy (HRTEM, JEOL JEM-2100). Electrochemical measurement: Electrochemical tests were performed by CR2430 coin cells with lithium foil as the counter and reference electrode. The Co3O4/Cu wafers of 16 mm were used directly for battery assembly, and other ancillary materials such as binders or conductive additives are not required. The electrolyte solution was prepared by dissolving 1 M LiPF6 in a mixture of dimethyl carbonate, diethyl carbonate and ethylene carbonate (1:1:1 by volume), and the separator was microporous polypropylene film. All cells were tested using an LAND battery programcontrol test system (CT 2001A, Wuhan Jinnuo Electronic Co. Ltd. of China). The AC impedance spectra of the cells were measured on an electrochemical workstation (CHI 660D).
3. Results and discussion XRD results show the crystal structure, phase and lattice of the as-prepared Co3O4 micro-rod arrays scratched from the Cu foil (Fig. 1(b)). All the diffraction peaks in the XRD pattern can be indexed to cubic Co3O4 phase (JCPDS no. 42-1467, space group: Fd3m). The Cu foil surface was uniformly covered by a dense layer of pink solid products after the growth, which turned to black via thermal treatment in Ar (Fig. 1(c), inset). The size and morphology of Co3O4 micro-rod arrays were measured by SEM. Fig. 1(c)– (e) shows the SEM images of Co3O4 micro-rod arrays on Cu foil with different magnification. The average diameter and length of the micro-rods are estimated to be about 1–2 μm and 25 μm. The cross-sectional SEM image reveals that Co3O4 micro-rod arrays are grown directly and closely contacted with Cu foil (Fig. 1(c)). High magnification image of the Co3O4 micro-rod reveals that the top of the micro-rod is rhombic (Fig. 1(e)). The detailed morphological and structural features of Co3O4 microrod were examined by TEM and HRTEM (Fig. 2). TEM images in Fig. 2(a) and (b) show that the Co3O4 consists of numerous interconnected small nanoparticles with size of 15–25 nm. Consistent with the observation in Fig. 1(d), the average diameter of Co3O4 micro-rod is in the range of 1–2 μm. An enlarged TEM image of Co3O4 micro-rod
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B. Wang et al. / Materials Letters 122 (2014) 186–189
20 nm
200 nm
(220)
d(220)=2.86 Å
(311)
(111)
d(111)= 4.7 Å [220]
d(311)=2.43 Å
[311] 5 nm
[111]
2 nm
Fig. 2. ((a)–(c)) TEM images of a Co3O4 micro-rod. (d) HRTEM image of the area marked with red rectangle in (c) and corresponding FFT images (inset). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
with well lattice fringes is shown in Fig. 2(c). Fig. 2(d) presents a magnified HRTEM image of the region marked in Fig. 2(c) and corresponding fast-Fourier-transform (FFT) pattern. The marked interplanar spacings are measured to be 2.86, 4.67, and 2.43 Å, corresponding to the (2 2 0), (1 1 1), and (3 1 1) crystal planes of Co3O4. The lithium storage properties of Co3O4 micro-rod arrays as anode materials for LIBs were investigated in the potential range of 0.005–3.0 V (versus Li/Li þ ). The initial five charge/discharge curves of Co3O4/Cu electrode are shown in Fig. 3(a). For the first discharge curve, a distinct plateau located at 1.1 V and one unclear plateau at 1.35 V can be observed, which can be ascribed to the reduction process of CoO to Co and Co3O4 to CoO, as well as the formation of amorphous Li2O (Co3O4 þ8Li þ þ8e ¼4Li2Oþ 3Co). For the first charge, a voltage plateau at around 1.9–2.5 V is recorded, corresponding to the process of the reversible oxidation of Co to Co3O4 and the decomposition of the Li2O matrix. The initial discharge and charge capacities of Co3O4 are found to be 1.5 and 1.0 mA h mg 1 at 0.1 C, respectively. Accordingly, the coulombic efficiency of Co3O4 in the first cycle can be calculated to be 66%. These values are higher than the theoretical capacity of Co3O4, which is attributed to the formation of solid electrolyte interphase (SEI) film and the decomposition of electrolytes [8]. Fig. 3(b) shows reversible capacity versus cycle number for Co3O4 micro-rod array electrode. As can be seen in Fig. 3(b), from the second cycle onwards, the Co3O4 electrode exhibits slightly capacity decay and around 80% of the initial reversible capacity can be retained over 50 cycles at 0.1 C (0.8 mA h mg 1 at the 50th cycle). As shown in Fig. 3(c), after the electrode cycled at 0.1 C for 10 cycles, the applied current density is increased stepwise to 4 C. The reversible capacity of Co3O4/Cu electrode is about 1.0, 0.8, 0.7,
0.5 and 0.4 mA h mg 1 at current densities of 0.25, 05, 1, 2 and 4 C, respectively. The above results indicate that the rate performance of the Co3O4/Cu electrode is excellent. The Nyquist plots of the Co3O4/Cu electrode before and after 3 charge/discharge cycles are shown in Fig. 3(d). As shown in the figure, both of the samples before and after 3 cycles have the same shapes of Nyquist plots, composed of a depressed semicircle in the high frequency region and a sloped line in the low-frequency region. In general, the smaller of a semicircle is, the lower the charge transfer resistance of an electrode is. Obviously, the diameter of the semicircle for Co3O4/Cu electrode after three cycles is smaller than that of the fresh cell, indicating lower charge-transfer resistance of the Co3O4/ Cu electrode after a few cycles. The high reversible capacity, good cycling stability, and high rate capability can be attributed to the unique structure of Co3O4. The close contact of Co3O4 micro-rod arrays on Cu foil allows direct 1D pathway for electron transport. Additionally, the extra space between neighboring micro-rods can provide structural flexibility for volume change.
4. Conclusions We have demonstrated the direct growth of cubic-phase crystal Co3O4 micro-rod arrays on Cu substrate by a modified hydrothermal approach. When evaluated as an anode for LIBs, Co3O4/Cu exhibited a high initial discharge capacity of 1.5 mA h mg 1 at 0.1 C, which was maintained at 0.8 mA h mg 1 after 50 cycles. The as-prepared Co3O4 micro-rod arrays have potential application as
2000
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Capacity retention
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Potential vs. Li/Li+ (V)
B. Wang et al. / Materials Letters 122 (2014) 186–189
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After 3 cycles
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250 200 150 100 50 0
0
0
10
20
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100 150 200 250 300 350 400
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Fig. 3. (a) The charge/discharge profiles of Co3O4/Cu electrode. (b) Cycling performance and capacity retention of Co3O4/Cu electrode. (c) Rate performance of Co3O4/Cu electrode. (d) The impedance plots of Co3O4/Cu micro-rod electrode.
anode materials in LIBs due to the simple synthesis method and high capacity. Acknowledgements This work was supported by the financial supports of the National Natural Science Foundation of China (nos. 21301140 and 21061130551), the Natural Science Foundation of Shaanxi Province (nos. 2013JQ2004 and 2012JQ6019), the Foundation of the Education Committee of Shaanxi Province (no. 2013JK0671), and Northwest University Cross-discipline Fund for Postgraduate Students (YZZ13037).
References [1] Armand M, Tarascon JM. Nature 2008;451:652–7. [2] Buqa H, Goers D, Holzapfel M, Spahr ME, Novak P. J Electrochem Soc 2005;152: A474–A481. [3] Abbas SM, Hussain ST, Ali S, Munawar KS, Ahmad N, Ali N. Mater Lett 2013;107:158–61. [4] Liu ZL, Tay SW. Mater Lett 2012;72:74–7. [5] Fan S, Liu XJ, Li YF, Yan EY, Wang CH, Liu JH, Zhang Y. Mater Lett 2013;91:291–3. [6] Tummala R, Guduru RK, Mohanty PS. J Power Sources 2012;199:270–7. [7] Jiang J, Li YY, Liu JP, Huang XT, Yuan CZ, Lou XW, et al. Adv Mater 2012;24:5166–80. [8] Wang J, Yang N, Tang H, Dong Z, Jin Q, Yang M, et al. Angew Chem Int Ed 2013;52:6417–20.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
In situ synthesis of Co3O4/Cu electrode and its high performance for lithium-ion batteries Beibei Wang a, Gang Wang b, Hui Wang a,n a Key Laboratory of Synthetic and Natural Functional Molecule Chemistry (Ministry of Education), College of Chemistry & Materials Science, Northwest University, Xi'an 710069, PR China b National Key Laboratory of Photoelectric Technology and Functional Materials (Culture Base), National Photoelectric Technology and Functional Materials & Application International Cooperation Base, Institute of Photonics & Photon-Technology, Northwest University, Xi’an 710069, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 12 August 2013 Accepted 1 February 2014 Available online 8 February 2014
In this paper, we report the growth of Co3O4 micro-rod arrays on Cu substrate by a modified hydrothermal method. The obtained Co3O4/Cu shows that the formed Co3O4 micro-rods on Cu foil are 1–2 μm in diameter and 25 μm in length. When evaluated as electrode materials for lithium-ion batteries, the specific capacity of Co3O4/Cu materials remains over 0.8 mA h mg 1 after 50 cycles at 0.1 C. The superior electrochemical performance of the Co3O4/Cu electrode may be attributed to the close contact of Co3O4 micro-rod arrays on Cu substrate and the extra space between the neighboring arrays, which provide fast pathways and reduce volume expansion. & 2014 Elsevier B.V. All rights reserved.
Keywords: Cobalt oxide array Crystal structure Functional Lithium ion batteries
1. Introduction Lithium-ion batteries (LIBs) are now considered as a state-ofthe-art power sources for portable electronic devices due to their advantages of high energy density, high electromotive force and long lifespan [1]. Although graphite has served as a reliable anode material for commercial LIBs with high reversibility, its low capacity (372 mA h g 1) can not satisfy future requirements of the electronic devices [2]. With the ever-increasing need for energy density and power demands, considerable efforts have been made in finding new electrode materials for LIBs. Nowadays, transition metal oxides (such as NiO, Fe2O3 and Co3O4) have shown desirable properties as the fascinating anode materials [3–5]. Among the available metal oxide anodes, Co3O4 has attracted special attention because of its high theoretical lithium storage capacity (890 mA h g 1) [6]. However, Co3O4 usually suffers from the problems of low ionic and electronic conductivities, large volume change, and poor cycle stability when used as anode materials, which limit its potential application in LIBs. In order to improve the stability of Co3O4 anode and obtain better capacity retention and cycle life for the material, the growth of one-dimensional (1D) Co3O4 arrays with controlling uniform size and perfect crystalline structure on a variety of conductive substrates (which can be used directly as current collectors) for LIBs have been developed. Several advantages can be obtained on the novel architecture: (1) The extra free space between neighboring arrays allows
n
Corresponding author: Tel.: þ 86 29 88363115; fax: þ 86 29 88303798. E-mail address: [email protected] (H. Wang).
http://dx.doi.org/10.1016/j.matlet.2014.02.004 0167-577X & 2014 Elsevier B.V. All rights reserved.
the ease of electrolyte penetration and accommodates volume variation during Li þ insertion/extraction; (2) the direct attachment and close contact of Co3O4 active materials on the current substrate enable fast pathways for electron transport kinetics; and (3) the direct growth of Co3O4 arrays on conductive substrate can be processed directly for LIB assembly, without the addition of binders or conductive materials [7]. Although Co3O4 nano-wire and nano-belt arrays have been prepared successfully on various metallic substrates and exhibited excellent lithium storage properties, in situ synthesis of 1D Co3O4 micro-rod arrays on Cu foil has never been found in the reported literatures. Herein, we developed a facile hydrothermal method to grow Co3O4 micro-rod arrays directly on Cu foil (Co3O4/Cu, illustrated in Fig. 1(a)). The binder-free Co3O4/Cu material as an anode for LIBs was investigated. It was found that the material exhibits ultrahigh reversible capacity, good cycling stability and superior rate performance.
2. Experimental Synthesis of Co3O4/Cu: Typically, 0.624 g Co(NO3)2 6H2O, 0.159 g NH4F and 0.643 g CO(NH2)2 were dissolved in 30 ml distilled water and then stirred for 30 min. The homogeneous solution was then transferred into a 50 ml Teflon-lined autoclave. Subsequently a piece of Cu foil was immersed into the reaction solution with the interacted surface facing down and the top side of the substrate was protected from solution contamination through fixed glass slide. The autoclave was heated to 120 1C for 9 h. After that the Cu foil was taken down from the glass slide,
B. Wang et al. / Materials Letters 122 (2014) 186–189
187
2h
9h
(b)
25 μm
0.5 μm
5 μm
Fig. 1. (a) Schematic illustration of the growth of Co3O4 arrays on Cu foil. (b) XRD pattern. ((c)–(e)) SEM images of Co3O4 micro-rod arrays. Inset of (c) shows the optical photo of a Cu foil, an as-grown precursor sample, and an annealed Co3O4 micro-rod arrays (from left to right).
washed with distilled water and annealed at 400 1C for 2 h in Ar gas. The experiments were repeated for 10 times to obtain Co3O4/ Cu foils and to assure the work can be reproduced. After the annealing process, the synthesized Co3O4/Cu foils were cut into wafers of 16 mm in diameter. The loading density range of these active materials (Co3O4) on Cu foils was measured to be 1.5– 2.5 mg cm 2. Material characterization: The as-prepared products were characterized by X-ray diffraction (XRD, Rigaku), field emission gun scanning electron microscopy (FEI Quanta 400 FEG), and high-resolution transmission electron microscopy (HRTEM, JEOL JEM-2100). Electrochemical measurement: Electrochemical tests were performed by CR2430 coin cells with lithium foil as the counter and reference electrode. The Co3O4/Cu wafers of 16 mm were used directly for battery assembly, and other ancillary materials such as binders or conductive additives are not required. The electrolyte solution was prepared by dissolving 1 M LiPF6 in a mixture of dimethyl carbonate, diethyl carbonate and ethylene carbonate (1:1:1 by volume), and the separator was microporous polypropylene film. All cells were tested using an LAND battery programcontrol test system (CT 2001A, Wuhan Jinnuo Electronic Co. Ltd. of China). The AC impedance spectra of the cells were measured on an electrochemical workstation (CHI 660D).
3. Results and discussion XRD results show the crystal structure, phase and lattice of the as-prepared Co3O4 micro-rod arrays scratched from the Cu foil (Fig. 1(b)). All the diffraction peaks in the XRD pattern can be indexed to cubic Co3O4 phase (JCPDS no. 42-1467, space group: Fd3m). The Cu foil surface was uniformly covered by a dense layer of pink solid products after the growth, which turned to black via thermal treatment in Ar (Fig. 1(c), inset). The size and morphology of Co3O4 micro-rod arrays were measured by SEM. Fig. 1(c)– (e) shows the SEM images of Co3O4 micro-rod arrays on Cu foil with different magnification. The average diameter and length of the micro-rods are estimated to be about 1–2 μm and 25 μm. The cross-sectional SEM image reveals that Co3O4 micro-rod arrays are grown directly and closely contacted with Cu foil (Fig. 1(c)). High magnification image of the Co3O4 micro-rod reveals that the top of the micro-rod is rhombic (Fig. 1(e)). The detailed morphological and structural features of Co3O4 microrod were examined by TEM and HRTEM (Fig. 2). TEM images in Fig. 2(a) and (b) show that the Co3O4 consists of numerous interconnected small nanoparticles with size of 15–25 nm. Consistent with the observation in Fig. 1(d), the average diameter of Co3O4 micro-rod is in the range of 1–2 μm. An enlarged TEM image of Co3O4 micro-rod
188
B. Wang et al. / Materials Letters 122 (2014) 186–189
20 nm
200 nm
(220)
d(220)=2.86 Å
(311)
(111)
d(111)= 4.7 Å [220]
d(311)=2.43 Å
[311] 5 nm
[111]
2 nm
Fig. 2. ((a)–(c)) TEM images of a Co3O4 micro-rod. (d) HRTEM image of the area marked with red rectangle in (c) and corresponding FFT images (inset). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
with well lattice fringes is shown in Fig. 2(c). Fig. 2(d) presents a magnified HRTEM image of the region marked in Fig. 2(c) and corresponding fast-Fourier-transform (FFT) pattern. The marked interplanar spacings are measured to be 2.86, 4.67, and 2.43 Å, corresponding to the (2 2 0), (1 1 1), and (3 1 1) crystal planes of Co3O4. The lithium storage properties of Co3O4 micro-rod arrays as anode materials for LIBs were investigated in the potential range of 0.005–3.0 V (versus Li/Li þ ). The initial five charge/discharge curves of Co3O4/Cu electrode are shown in Fig. 3(a). For the first discharge curve, a distinct plateau located at 1.1 V and one unclear plateau at 1.35 V can be observed, which can be ascribed to the reduction process of CoO to Co and Co3O4 to CoO, as well as the formation of amorphous Li2O (Co3O4 þ8Li þ þ8e ¼4Li2Oþ 3Co). For the first charge, a voltage plateau at around 1.9–2.5 V is recorded, corresponding to the process of the reversible oxidation of Co to Co3O4 and the decomposition of the Li2O matrix. The initial discharge and charge capacities of Co3O4 are found to be 1.5 and 1.0 mA h mg 1 at 0.1 C, respectively. Accordingly, the coulombic efficiency of Co3O4 in the first cycle can be calculated to be 66%. These values are higher than the theoretical capacity of Co3O4, which is attributed to the formation of solid electrolyte interphase (SEI) film and the decomposition of electrolytes [8]. Fig. 3(b) shows reversible capacity versus cycle number for Co3O4 micro-rod array electrode. As can be seen in Fig. 3(b), from the second cycle onwards, the Co3O4 electrode exhibits slightly capacity decay and around 80% of the initial reversible capacity can be retained over 50 cycles at 0.1 C (0.8 mA h mg 1 at the 50th cycle). As shown in Fig. 3(c), after the electrode cycled at 0.1 C for 10 cycles, the applied current density is increased stepwise to 4 C. The reversible capacity of Co3O4/Cu electrode is about 1.0, 0.8, 0.7,
0.5 and 0.4 mA h mg 1 at current densities of 0.25, 05, 1, 2 and 4 C, respectively. The above results indicate that the rate performance of the Co3O4/Cu electrode is excellent. The Nyquist plots of the Co3O4/Cu electrode before and after 3 charge/discharge cycles are shown in Fig. 3(d). As shown in the figure, both of the samples before and after 3 cycles have the same shapes of Nyquist plots, composed of a depressed semicircle in the high frequency region and a sloped line in the low-frequency region. In general, the smaller of a semicircle is, the lower the charge transfer resistance of an electrode is. Obviously, the diameter of the semicircle for Co3O4/Cu electrode after three cycles is smaller than that of the fresh cell, indicating lower charge-transfer resistance of the Co3O4/ Cu electrode after a few cycles. The high reversible capacity, good cycling stability, and high rate capability can be attributed to the unique structure of Co3O4. The close contact of Co3O4 micro-rod arrays on Cu foil allows direct 1D pathway for electron transport. Additionally, the extra space between neighboring micro-rods can provide structural flexibility for volume change.
4. Conclusions We have demonstrated the direct growth of cubic-phase crystal Co3O4 micro-rod arrays on Cu substrate by a modified hydrothermal approach. When evaluated as an anode for LIBs, Co3O4/Cu exhibited a high initial discharge capacity of 1.5 mA h mg 1 at 0.1 C, which was maintained at 0.8 mA h mg 1 after 50 cycles. The as-prepared Co3O4 micro-rod arrays have potential application as
2000
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3 1st 2nd 3rd 4th 5th
2.5 2 1.5 1 0.5 0 0
100 1600
Capacity retention
800
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Potential vs. Li/Li+ (V)
B. Wang et al. / Materials Letters 122 (2014) 186–189
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Fig. 3. (a) The charge/discharge profiles of Co3O4/Cu electrode. (b) Cycling performance and capacity retention of Co3O4/Cu electrode. (c) Rate performance of Co3O4/Cu electrode. (d) The impedance plots of Co3O4/Cu micro-rod electrode.
anode materials in LIBs due to the simple synthesis method and high capacity. Acknowledgements This work was supported by the financial supports of the National Natural Science Foundation of China (nos. 21301140 and 21061130551), the Natural Science Foundation of Shaanxi Province (nos. 2013JQ2004 and 2012JQ6019), the Foundation of the Education Committee of Shaanxi Province (no. 2013JK0671), and Northwest University Cross-discipline Fund for Postgraduate Students (YZZ13037).
References [1] Armand M, Tarascon JM. Nature 2008;451:652–7. [2] Buqa H, Goers D, Holzapfel M, Spahr ME, Novak P. J Electrochem Soc 2005;152: A474–A481. [3] Abbas SM, Hussain ST, Ali S, Munawar KS, Ahmad N, Ali N. Mater Lett 2013;107:158–61. [4] Liu ZL, Tay SW. Mater Lett 2012;72:74–7. [5] Fan S, Liu XJ, Li YF, Yan EY, Wang CH, Liu JH, Zhang Y. Mater Lett 2013;91:291–3. [6] Tummala R, Guduru RK, Mohanty PS. J Power Sources 2012;199:270–7. [7] Jiang J, Li YY, Liu JP, Huang XT, Yuan CZ, Lou XW, et al. Adv Mater 2012;24:5166–80. [8] Wang J, Yang N, Tang H, Dong Z, Jin Q, Yang M, et al. Angew Chem Int Ed 2013;52:6417–20.