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Enhanced electrochemical performances of CuCrO2–CNTs nanocomposites anodes by in-situ hydrothermal synthesis for lithium ion batteries
Materials Letters 107 (2013) 147–149
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Enhanced electrochemical performances of CuCrO2–CNTs nanocomposites anodes by in-situ hydrothermal synthesis for lithium ion batteries Xiao-Dong Zhu a,b,c, Jing Tian c, Shi-Ru Le b,c, Jin-Run Chen c, Ke-Ning Sun a,b,c,n a
State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, Heilongjiang 150090, China Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin, Heilongjiang 150080, China c Department of Chemistry, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China b
art ic l e i nf o
a b s t r a c t
Article history: Received 29 March 2013 Accepted 30 May 2013 Available online 6 June 2013
The CuCrO2–carbon nanotubes (CNTs) nanocomposites synthesized by the in-situ hydrothermal method exhibit excellent specific capacity retention and cyclic performances. Due to the poor conductivity and large volume variation of CuCrO2, its discharge capacity only remains 304 mAh g–1 (0.2C) after 140 cycles. However, the electrochemical performances of CuCrO2 anodes are improved remarkably by adding 5– 20 wt% CNTs. The CuCrO2–CNTs composite anodes maintain a specific capacity of 742 mAh g−1 after 60 cycles (0.2C) when the CNTs proportion is over 10 wt%. Even at 1C charge/discharge rates, they still exhibit high capacity retention of 530 mAh g−1 after 40 cycles. The SEM micrographs show that CNTs are dispersed well within the CuCrO2 matrix to form a 3D network. Such a network structure provides good electrical conductivity and restrains the volume variations during the cycling processes, which collaboratively improve the discharge specific capacity and cycling performance. & 2013 Elsevier B.V. All rights reserved.
Keywords: Lithium-ion batteries Carbon nanotubes Composite materials Cycling performance 3D network
1. Introduction Discovering novel electrode materials with better performance is the key to develop the advanced Lithium-ion batteries (LIBs). Transition metal oxides with high specific capacity (600– 800 mAh g−1) are attractive anode materials to replace the conventional graphite [1]. Recently, some delafossite oxides, such as CuFeO2 and CuCrO2 have shown reversible reaction with Li [2,3]. However, these novel anode materials may possess poor electrochemical performance owing to poor conductivity and huge volume changes of active materials during lithium insertion/ extraction [2,4]. We improved remarkably the electrochemical performances of CuCrO2 anodes by replacing the ordinary conductive agent with CNTs [3]. The addition of CNTs in CuCrO2 anode contributed to the formation of a 3D conductive network. Such a networks structure has pivotal effects to improve the composite conductivity and restrain the volume variations during cycling processes, which collaboratively improve the discharge specific capacity and cycling performance. However, the dispersible uniformity of CNTs in CuCrO2 was subjected to restrictive as the
n Corresponding author at: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, Heilongjiang 150090, China. Tel./fax: +86 451 86412153. E-mail address: [email protected] (K.-N. Sun).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.05.137
CuCrO2–CNTs composite anodes were prepared by the mechanical mixing method. In this study, the nanosized CuCrO2–CNTs composites were successfully synthesized by an in-situ hydrothermal method. This method afforded an anode material with high capacity and good cycle ability by combining the framework of CNTs with CuCrO2 of high capacity. 2. Experiment CuCrO2 nanoparticles were prepared by a hydrothermal reaction, and then assembled into the half-cell for the charge/discharge tests. First, 6 mmol Cr(NO3)3 9H2O was dissolved in 25 mL deionized water with magnetic stirring. Then, certain amount of acid-treated MWCNTs (5 wt%, 10 wt%, and 20 wt%. vs. theoretical formation weight of CuCrO2) was dispersed in chromium nitrate solution by ultrasonic vibration for 30 mins. 18 mmol NaOH was dispersed in 10 mL deionized water, and the solution was dropped slowly into the above mixture with sustained stirring, then Cr (OH)3 sediment could be observed at the bottom. 3 mmol Cu2O was added into the mixture with strong stirring for 10 h for homogeneous mixing. Thereafter a certain amount of NaOH was dropped into the mixture continuously until its concentration was up to 2.5 M. Next, the above mixture was transferred into a 50 mL autoclave, and kept at 210 1C for 60 h until a black sediment was
X.-D. Zhu et al. / Materials Letters 107 (2013) 147–149
3. Result and discussion The XRD pattern of the CuCrO2 sample is shown in Fig. 1. It can be seen that the main diffraction peaks are in perfect agreement with the JCPDF file No. 39-0247 (rhombohedral), such as (006), (012) and (110). It does not show any diffraction peaks due to starting precursors or foreign phases, such as CuCr2O4, Cu2O and Cr2O3. Analysis of these patterns showed that the material possesses a hexagonal symmetry delafossite structure with R-3m space group. Fig. 2a shows the initial charge/discharge curve of the CuCrO2 anode. As shown in the Fig. 2, the voltage falls rapidly from the open potential to 0.7 V, then present a long voltage plateau near 0.7 V and an inclined curve from 0.5 to 0.005 V. The initial discharge and charge capacities of the CuCrO2 anode are about 1392 and 641 mAh g−1, respectively. The high irreversible capacity is attributed to the irreversible reactions at the surface, such as the electrolyte decomposition and the formation of a solid electrolyte interface (SEI) layer [4], the reduction of the adsorbed impurities on the CuCrO2 surfaces, the initial formation of lithium oxide due to the presence of some residual OH groups in the surface of active CuCrO2, and possibly interfacial lithium storage [5]. Fig. 2b shows the cycling performance curves of CuCrO2. These curves are tested at 0.2C except for the initial 10 cycles at 0.1C. The discharge capacity of the second cycle is 589 mAh g−1, much lower than that of the initial discharge capacity. It can be also noticed that discharge capacities of CuCrO2 has a high irreversible capacity
120 100
Intensity/a.u.
(0 1 2)
80
(006) (1 1 0)
60
(1 0 4)
(0 1 8)
(2 0 2)
40 20 10
20
30
40
50
60
2-theta/deg. Fig. 1. XRD pattern of the CuCrO2.
70
80
3
Voltage (V)
formed. The black sedimen was washed with deionized water to be neutral, dried, ground and sieved, and then vacuum-dried at 120 1C for 2 h. Electrochemical performance was carried out with a CR 2032 coin cell. The candidate active material was mixed with 10 wt % polyvinylidene fluoride (PVDF) binder and N-methyl-2pyrrolidone (NMP) into homogeneous slurry. The resulting paste was cast on a copper current collector. The coin cell was made using CuCrO2–CNTs as a cathode, lithium metal foil as an anode, Celgard 2400 as separators and 1 M LiPF6 as in EC:DMC ¼1:1 (volume ratio) solvent used as an electrolyte, and assembled in an argon–filled glove box. Charge/discharge measurements were carried out at different C-rates over the potential range of 0.01–3.0 (vs. Li/Li+) using Land 2000T (China) battery tester at room temperature. All batteries were charged and discharged at 0.1C for the initial 10 cycles to be activated. The particle morphology of the powders after sintering was obtained using a scanning electron microscopy (SEM).
2
1
0
0
400
800
1200
Capacity (mAh
g-1)
50
100
1500
Capacity (mAh g-1)
148
1200 900 600 300 0
150
Cycle number Fig. 2. Typical initial charge/discharge curves (a) and capacity vs. cycle number plot (b) of CuCrO2 anode.
loss compared with the first cycles. The discharge capacity continues decreasing as subsequent cycles. After 10 cycles, the specific capacity retention is about 284 mAh g−1. The discharge behavior of CuCrO2 shows an active process during subsequent cycles. The discharge capacity reaches 304 mAh g−1 after 140 cycles at 0.2C charge/discharge rates. The reaction of the nanostructured CuCrO2 with Li can be compared with the CuFeO2 and CuCo2O4 [1]. The electrochemical reaction of CuCrO2 can be described below: CuCrO2+4Li++4e−- Cu+Cr+2Li2O
(1)
2Cu+4Li2O+2Cr2Cu2O+Cr2O3+8Li++8e−
(2)
The structure of CuCrO2 can be described as alternating layers of edge-sharing CrIIIO6 octahedra and linking to each other by CuI in the O–Cu–O dumbbell configuration [6]. During the first discharge/charge cycle, most CuCrO2 material is decomposed to Cu2O and Cr2O3, which are located at different layers. This will lead to the pulverization of particles and destruction of the electric connectivity for anode materials, which results in the degradation of discharge capacity from 2th to 10th cycles. The in situ formed Cu and Cr particles from Eq. (1) become smaller during the cycles due to the electrochemical milling effect. These smaller particles can reduce the activation energy of the phase inversion and enhance the reversibility of the reactions (Eq. (2)), thus the discharge capacity is improved increasingly. So the specific capacity of Cu–Cr–O compounds firstly decrease and then increases with the discharge/charge cycles. To enhance the electric connectivity of anode materials, it is an interesting concept to compound CuCrO2 and CNTs to form a 3D
X.-D. Zhu et al. / Materials Letters 107 (2013) 147–149
149
Capacity (mAh g-1)
Capacity (mAh g-1)
1600 1000
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1600 1200 800 400
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Fig. 3. Cyclic performances of CC5 at 0.2C (a), CC10 at 0.2C (b), CC20 at 0.2C (c) and CC20 at 1C (d). The inset panels are SEM images of CC5 (a), CC10 (b) and CC20 (c).
network, achieving a charming synergistic effect. Fig. 3 shows cycling performance curves of CuCrO2–CNTs with different CNTs proportion. CC5, CC10 and CC20 represent CuCrO2–CNTs composites with 5 wt%, 10 wt%, and 20 wt% CNTs, respectively. As shown in Fig. 3, the initial discharge capacity at 0.2C of CC5, CC10 and CC20 is 1050, 1478 and 1625 mAh g−1, respectively, while that of the second cycle is 602, 702 and 788 mAh g−1. After 10 cycles, the specific capacity retention of CC5, CC10 and CC20 is 463, 635 and 673 mAh g−1, much higher than that of CuCrO2. From 11th cycle the CuCrO2–CNTs composite anodes show longer active process even until 70th cycle. The discharge capacity of CC10 and CC20 reaches 745 mAh g−1 and 742 mAh g−1 separately, much higher than that of CuCrO2–CNTs composite anodes prepared by the mechanical mixing method [3]. At high charge/discharge rates (1C), as shown in Fig. 3d, CC20 still exhibits a high reversible specific capacity of 530 mAh g−1 after 40 cycles. The discharge capacity of CNTs can not be the reason for the increase of the discharge capacity. Because it only retains 85 mAh g−1 at a discharge current of 0.5 mA h at 30th cycle in our experiment. The inset SEM images in Fig. 3 show that the microstructures of CC5, CC10, and CC20. CNTs are dispersed well within the CuCrO2 matrix. CuCrO2 reunions can be restrained and the composite networks structures evolve when the CNTs proportion is over 10 wt%. Such a networks structure has pivotal effects to improve the composite conductivity and restrain the volume variations during cycling processes [4], which collaboratively improve the discharge specific capacity and cycling performance, and exhibits excellent high rate discharge performance. 4. Conclusion The CuCrO2–CNTs nanocomposites with excellent reversible specific capacity and cyclic performances were fabricated by an in-situ hydrothermal method. The addition of CNTs contributed to the formation of a conductive network, which facilitates to the
restrain of the buffer area during volume expansion. The improvement of the electrochemical property is due to the good conductivity of CNTs and the conductive network, which showed a high reversible specific capacity of 745 mAh g−1 after 60 cycles (0.2C). Even at high charge/discharge rates (1C), the specific capacity retention was still as high as 530 mAh g−1 after 40 cycles with good rate property and stable electrode structure.
Acknowledgments This work was supported by the Fundamental Research Funds for the Central Universities (Grant no. HIT. NSRIF. 2013.059), the National Natural Science Foundation of China (Grant no. 21246011 and 21103036), Open Project of State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology (No. QA201027), and the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20102302120051).
References [1] Taberna PL, Mitra S, Poizot P, Simon P, Tarascon JM. High rate capabilities Fe3O4-based Cu nano-architectured electrodes for lithium-ion battery applications. Nat Mater 2006;5:567–73. [2] Lu L, Wang JZ, Zhu XB, Gao XW, Liu HK. High capacity and high rate capability of nanostructured CuFeO2 anode materials for lithium–ion batteries. J Power Sources 2011;196:7025–9. [3] Zhu X-D, Tian J, Le S-R, Zhang N-Q, Sun K-N. Improved electrochemical performance of CuCrO2 anode with CNTs as conductive agent for lithium ion batteries. Mater Lett 2013;97:113–6. [4] Zheng SF, Hu JS, Zhong LS, Song WG, Wan LJ, Guo YG. Introducing dual functional CNT networks into CuO nanomicrospheres toward superior electrode materials for lithium-ion batteries. Chem Mater 2008;20:3617–22. [5] Maier J. Nanoionics: ion transport and electrochemical storage in confined systems. Nat Mater 2005;4:805–15. [6] Attili RN, Saxena RN, Carbonari AW. Delafossite oxides ABO(2) (A¼ Ag, Cu; B ¼Al, Cr, Fe, In, Nd, Y) studied by perturbed-angular-correlation spectroscopy using a Ag−111(beta(−))Cd−111 probe. Phys Rev B 1998;58:2563–9.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Enhanced electrochemical performances of CuCrO2–CNTs nanocomposites anodes by in-situ hydrothermal synthesis for lithium ion batteries Xiao-Dong Zhu a,b,c, Jing Tian c, Shi-Ru Le b,c, Jin-Run Chen c, Ke-Ning Sun a,b,c,n a
State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, Heilongjiang 150090, China Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin, Heilongjiang 150080, China c Department of Chemistry, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China b
art ic l e i nf o
a b s t r a c t
Article history: Received 29 March 2013 Accepted 30 May 2013 Available online 6 June 2013
The CuCrO2–carbon nanotubes (CNTs) nanocomposites synthesized by the in-situ hydrothermal method exhibit excellent specific capacity retention and cyclic performances. Due to the poor conductivity and large volume variation of CuCrO2, its discharge capacity only remains 304 mAh g–1 (0.2C) after 140 cycles. However, the electrochemical performances of CuCrO2 anodes are improved remarkably by adding 5– 20 wt% CNTs. The CuCrO2–CNTs composite anodes maintain a specific capacity of 742 mAh g−1 after 60 cycles (0.2C) when the CNTs proportion is over 10 wt%. Even at 1C charge/discharge rates, they still exhibit high capacity retention of 530 mAh g−1 after 40 cycles. The SEM micrographs show that CNTs are dispersed well within the CuCrO2 matrix to form a 3D network. Such a network structure provides good electrical conductivity and restrains the volume variations during the cycling processes, which collaboratively improve the discharge specific capacity and cycling performance. & 2013 Elsevier B.V. All rights reserved.
Keywords: Lithium-ion batteries Carbon nanotubes Composite materials Cycling performance 3D network
1. Introduction Discovering novel electrode materials with better performance is the key to develop the advanced Lithium-ion batteries (LIBs). Transition metal oxides with high specific capacity (600– 800 mAh g−1) are attractive anode materials to replace the conventional graphite [1]. Recently, some delafossite oxides, such as CuFeO2 and CuCrO2 have shown reversible reaction with Li [2,3]. However, these novel anode materials may possess poor electrochemical performance owing to poor conductivity and huge volume changes of active materials during lithium insertion/ extraction [2,4]. We improved remarkably the electrochemical performances of CuCrO2 anodes by replacing the ordinary conductive agent with CNTs [3]. The addition of CNTs in CuCrO2 anode contributed to the formation of a 3D conductive network. Such a networks structure has pivotal effects to improve the composite conductivity and restrain the volume variations during cycling processes, which collaboratively improve the discharge specific capacity and cycling performance. However, the dispersible uniformity of CNTs in CuCrO2 was subjected to restrictive as the
n Corresponding author at: State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, Heilongjiang 150090, China. Tel./fax: +86 451 86412153. E-mail address: [email protected] (K.-N. Sun).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.05.137
CuCrO2–CNTs composite anodes were prepared by the mechanical mixing method. In this study, the nanosized CuCrO2–CNTs composites were successfully synthesized by an in-situ hydrothermal method. This method afforded an anode material with high capacity and good cycle ability by combining the framework of CNTs with CuCrO2 of high capacity. 2. Experiment CuCrO2 nanoparticles were prepared by a hydrothermal reaction, and then assembled into the half-cell for the charge/discharge tests. First, 6 mmol Cr(NO3)3 9H2O was dissolved in 25 mL deionized water with magnetic stirring. Then, certain amount of acid-treated MWCNTs (5 wt%, 10 wt%, and 20 wt%. vs. theoretical formation weight of CuCrO2) was dispersed in chromium nitrate solution by ultrasonic vibration for 30 mins. 18 mmol NaOH was dispersed in 10 mL deionized water, and the solution was dropped slowly into the above mixture with sustained stirring, then Cr (OH)3 sediment could be observed at the bottom. 3 mmol Cu2O was added into the mixture with strong stirring for 10 h for homogeneous mixing. Thereafter a certain amount of NaOH was dropped into the mixture continuously until its concentration was up to 2.5 M. Next, the above mixture was transferred into a 50 mL autoclave, and kept at 210 1C for 60 h until a black sediment was
X.-D. Zhu et al. / Materials Letters 107 (2013) 147–149
3. Result and discussion The XRD pattern of the CuCrO2 sample is shown in Fig. 1. It can be seen that the main diffraction peaks are in perfect agreement with the JCPDF file No. 39-0247 (rhombohedral), such as (006), (012) and (110). It does not show any diffraction peaks due to starting precursors or foreign phases, such as CuCr2O4, Cu2O and Cr2O3. Analysis of these patterns showed that the material possesses a hexagonal symmetry delafossite structure with R-3m space group. Fig. 2a shows the initial charge/discharge curve of the CuCrO2 anode. As shown in the Fig. 2, the voltage falls rapidly from the open potential to 0.7 V, then present a long voltage plateau near 0.7 V and an inclined curve from 0.5 to 0.005 V. The initial discharge and charge capacities of the CuCrO2 anode are about 1392 and 641 mAh g−1, respectively. The high irreversible capacity is attributed to the irreversible reactions at the surface, such as the electrolyte decomposition and the formation of a solid electrolyte interface (SEI) layer [4], the reduction of the adsorbed impurities on the CuCrO2 surfaces, the initial formation of lithium oxide due to the presence of some residual OH groups in the surface of active CuCrO2, and possibly interfacial lithium storage [5]. Fig. 2b shows the cycling performance curves of CuCrO2. These curves are tested at 0.2C except for the initial 10 cycles at 0.1C. The discharge capacity of the second cycle is 589 mAh g−1, much lower than that of the initial discharge capacity. It can be also noticed that discharge capacities of CuCrO2 has a high irreversible capacity
120 100
Intensity/a.u.
(0 1 2)
80
(006) (1 1 0)
60
(1 0 4)
(0 1 8)
(2 0 2)
40 20 10
20
30
40
50
60
2-theta/deg. Fig. 1. XRD pattern of the CuCrO2.
70
80
3
Voltage (V)
formed. The black sedimen was washed with deionized water to be neutral, dried, ground and sieved, and then vacuum-dried at 120 1C for 2 h. Electrochemical performance was carried out with a CR 2032 coin cell. The candidate active material was mixed with 10 wt % polyvinylidene fluoride (PVDF) binder and N-methyl-2pyrrolidone (NMP) into homogeneous slurry. The resulting paste was cast on a copper current collector. The coin cell was made using CuCrO2–CNTs as a cathode, lithium metal foil as an anode, Celgard 2400 as separators and 1 M LiPF6 as in EC:DMC ¼1:1 (volume ratio) solvent used as an electrolyte, and assembled in an argon–filled glove box. Charge/discharge measurements were carried out at different C-rates over the potential range of 0.01–3.0 (vs. Li/Li+) using Land 2000T (China) battery tester at room temperature. All batteries were charged and discharged at 0.1C for the initial 10 cycles to be activated. The particle morphology of the powders after sintering was obtained using a scanning electron microscopy (SEM).
2
1
0
0
400
800
1200
Capacity (mAh
g-1)
50
100
1500
Capacity (mAh g-1)
148
1200 900 600 300 0
150
Cycle number Fig. 2. Typical initial charge/discharge curves (a) and capacity vs. cycle number plot (b) of CuCrO2 anode.
loss compared with the first cycles. The discharge capacity continues decreasing as subsequent cycles. After 10 cycles, the specific capacity retention is about 284 mAh g−1. The discharge behavior of CuCrO2 shows an active process during subsequent cycles. The discharge capacity reaches 304 mAh g−1 after 140 cycles at 0.2C charge/discharge rates. The reaction of the nanostructured CuCrO2 with Li can be compared with the CuFeO2 and CuCo2O4 [1]. The electrochemical reaction of CuCrO2 can be described below: CuCrO2+4Li++4e−- Cu+Cr+2Li2O
(1)
2Cu+4Li2O+2Cr2Cu2O+Cr2O3+8Li++8e−
(2)
The structure of CuCrO2 can be described as alternating layers of edge-sharing CrIIIO6 octahedra and linking to each other by CuI in the O–Cu–O dumbbell configuration [6]. During the first discharge/charge cycle, most CuCrO2 material is decomposed to Cu2O and Cr2O3, which are located at different layers. This will lead to the pulverization of particles and destruction of the electric connectivity for anode materials, which results in the degradation of discharge capacity from 2th to 10th cycles. The in situ formed Cu and Cr particles from Eq. (1) become smaller during the cycles due to the electrochemical milling effect. These smaller particles can reduce the activation energy of the phase inversion and enhance the reversibility of the reactions (Eq. (2)), thus the discharge capacity is improved increasingly. So the specific capacity of Cu–Cr–O compounds firstly decrease and then increases with the discharge/charge cycles. To enhance the electric connectivity of anode materials, it is an interesting concept to compound CuCrO2 and CNTs to form a 3D
X.-D. Zhu et al. / Materials Letters 107 (2013) 147–149
149
Capacity (mAh g-1)
Capacity (mAh g-1)
1600 1000
800
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Fig. 3. Cyclic performances of CC5 at 0.2C (a), CC10 at 0.2C (b), CC20 at 0.2C (c) and CC20 at 1C (d). The inset panels are SEM images of CC5 (a), CC10 (b) and CC20 (c).
network, achieving a charming synergistic effect. Fig. 3 shows cycling performance curves of CuCrO2–CNTs with different CNTs proportion. CC5, CC10 and CC20 represent CuCrO2–CNTs composites with 5 wt%, 10 wt%, and 20 wt% CNTs, respectively. As shown in Fig. 3, the initial discharge capacity at 0.2C of CC5, CC10 and CC20 is 1050, 1478 and 1625 mAh g−1, respectively, while that of the second cycle is 602, 702 and 788 mAh g−1. After 10 cycles, the specific capacity retention of CC5, CC10 and CC20 is 463, 635 and 673 mAh g−1, much higher than that of CuCrO2. From 11th cycle the CuCrO2–CNTs composite anodes show longer active process even until 70th cycle. The discharge capacity of CC10 and CC20 reaches 745 mAh g−1 and 742 mAh g−1 separately, much higher than that of CuCrO2–CNTs composite anodes prepared by the mechanical mixing method [3]. At high charge/discharge rates (1C), as shown in Fig. 3d, CC20 still exhibits a high reversible specific capacity of 530 mAh g−1 after 40 cycles. The discharge capacity of CNTs can not be the reason for the increase of the discharge capacity. Because it only retains 85 mAh g−1 at a discharge current of 0.5 mA h at 30th cycle in our experiment. The inset SEM images in Fig. 3 show that the microstructures of CC5, CC10, and CC20. CNTs are dispersed well within the CuCrO2 matrix. CuCrO2 reunions can be restrained and the composite networks structures evolve when the CNTs proportion is over 10 wt%. Such a networks structure has pivotal effects to improve the composite conductivity and restrain the volume variations during cycling processes [4], which collaboratively improve the discharge specific capacity and cycling performance, and exhibits excellent high rate discharge performance. 4. Conclusion The CuCrO2–CNTs nanocomposites with excellent reversible specific capacity and cyclic performances were fabricated by an in-situ hydrothermal method. The addition of CNTs contributed to the formation of a conductive network, which facilitates to the
restrain of the buffer area during volume expansion. The improvement of the electrochemical property is due to the good conductivity of CNTs and the conductive network, which showed a high reversible specific capacity of 745 mAh g−1 after 60 cycles (0.2C). Even at high charge/discharge rates (1C), the specific capacity retention was still as high as 530 mAh g−1 after 40 cycles with good rate property and stable electrode structure.
Acknowledgments This work was supported by the Fundamental Research Funds for the Central Universities (Grant no. HIT. NSRIF. 2013.059), the National Natural Science Foundation of China (Grant no. 21246011 and 21103036), Open Project of State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology (No. QA201027), and the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20102302120051).
References [1] Taberna PL, Mitra S, Poizot P, Simon P, Tarascon JM. High rate capabilities Fe3O4-based Cu nano-architectured electrodes for lithium-ion battery applications. Nat Mater 2006;5:567–73. [2] Lu L, Wang JZ, Zhu XB, Gao XW, Liu HK. High capacity and high rate capability of nanostructured CuFeO2 anode materials for lithium–ion batteries. J Power Sources 2011;196:7025–9. [3] Zhu X-D, Tian J, Le S-R, Zhang N-Q, Sun K-N. Improved electrochemical performance of CuCrO2 anode with CNTs as conductive agent for lithium ion batteries. Mater Lett 2013;97:113–6. [4] Zheng SF, Hu JS, Zhong LS, Song WG, Wan LJ, Guo YG. Introducing dual functional CNT networks into CuO nanomicrospheres toward superior electrode materials for lithium-ion batteries. Chem Mater 2008;20:3617–22. [5] Maier J. Nanoionics: ion transport and electrochemical storage in confined systems. Nat Mater 2005;4:805–15. [6] Attili RN, Saxena RN, Carbonari AW. Delafossite oxides ABO(2) (A¼ Ag, Cu; B ¼Al, Cr, Fe, In, Nd, Y) studied by perturbed-angular-correlation spectroscopy using a Ag−111(beta(−))Cd−111 probe. Phys Rev B 1998;58:2563–9.