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中国科技论文在线
Enhanced electrochemical performances of CuCrO2–CNTs
nanocomposites anodes by in–situ hydrothermal synthesis
for lithium ion batteries# 5
Xiao-Dong Zhu
1
, Jing Tian
2
, Shi-Ru Le
1
, Jin-Run Chen
2
, Ke-Ning Sun
1**
(1. Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology,
Harbin, Heilongjiang 150080, China;
2. Department of Chemistry, Harbin Institute of Technology, Harbin, Heilongjiang, 150001,
China) 10
Foundations: the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20102302120051)
and Open Project of State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of
Technology ()
Brief author introduction:Xiao-Dong Zhu (1979-),male,associate professor, Research interest: Materials for lithium
ion battery and Solid Oxide Fuel Cells
Correspondance author: Ke-Ning Sun (1964-),male,Professor,Main research is Lithium Ion Batteries. E-mail:
Abstract: The CuCrO2–carbon nano–tubes (CNTs) nanocomposites synthesized by 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
( C) after 140 cycles. The electrochemical performances of CuCrO2 anodes are improved
remarkably by adding 5–20 wt% CNTs. The CuCrO2–CNTS composite anodes maintain a specific 15
capacity of 742 mAh g
-1
after 60 cycles ( C) when the CNTs proportion is over 10 wt%. Even at 1 C
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 20
performance.
Key words: Lithium–ion batteries; Carbon nanotubes; Composite materials; Cycling performance; 3D
network
0 Introduction 25
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 30
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 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 35
cycling performance. However, the dispersible uniformity of CNTs in CuCrO2 was subjected to
restrictive because the CuCrO2–CNTs composite anodes were prepared by mechanical mixing method.
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中国科技论文在线
In this study, the nanosized CuCrO2–CNTs composites were successfully synthesized by an in–situ
hydrothermal method. And this method afforded an anode material with high capacity and good cycle
ability by combining the framework of CNTs with CuCrO2 of high capacity. 40
1 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 45
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 M. Next, the above mixture was transferred 50
into a 50 mL autoclave, and kept at 210℃ for 60 h until a black sedimen was formed. It was washed
with deionized water to be neutral, dried, ground and sieved, and then vacuum–dried at 120℃ 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–2–pyrrolidone
(NMP) into homogeneous slurry. The resulting paste was cast on a copper current collector. The coin 55
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=1:1 (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
– (versus Li/Li+) using Land 2000T (China) battery tester at room temperature. All batteries 60
were charged and discharged at C 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 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) 65
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
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symmetry delafossite structure with R–3m space group.
70
75
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 V, then present a long voltage plateau near V 80
and an inclined curve from to 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 85
active CuCrO2, and possibly interfacial lithium storage
[5].
0 400 800 1200
0
1
2
3
V
o
lt
ag
e
(
V
)
Capacity (mAh g
-1
)
0 50 100 150
300
600
900
1200
1500
Cycle number
C
a
p
a
c
it
y
(
m
A
h
g
-1
)
Typical initial charge/discharge curves (a) and capacity vs. cycle number plot (b) of CuCrO2
anode.
Fig. 2b shows the cycling performance curves of CuCrO2. These curves are tested at C except for 90
the initial 10 cycles at C. The discharge capacity of the second cycle is 589 mAh g
–1
, much lower
Fig. 1 XRD pattern of the CuCrO2.
10 20 30 40 50 60 70 80
20
40
60
80
100
120
(2 0 2)
(1 0 4)
(0 1 8)
(1 1 0)
( 0 0 6 )
(0 1 2)
2-theta/deg.
In
te
n
si
ty
/a
.u
.
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than that of the initial discharge capacity. It can be also noticed that discharge capacities of CuCrO2 has
a high irreversible capacity 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 95
capacity reaches 304 mAh g
–1
after 140 cycles at C 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 described below:
CuCrO2 +4Li
+
+4e
–→ Cu + Cr + 2Li2O (1)
2Cu + 4Li2O +2Cr ↔ Cu2O + Cr2O3 +8Li
+
+8e
–
(2) 100
The structure of CuCrO2 can be described as alternating layers of edge–sharing Cr
III
O6 octahedra and
linking to each other by Cu
I
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 105
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 decreases and then
increases with the discharge/charge cycles. 110
To enhance the electric connectivity of anode materials, it is an interesting concept to compound
CuCrO2 and CNTs to form a 3D 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%, 20 wt% CNTs, respectively.
As shown in Fig. 3, the initial discharge capacity at of CC5, CC10 and CC20 is 1050, 1478 and 115
1625 mAh g
–1
, reparately, 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. And 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
reparately, much higher than that of CuCrO2–CNTs composite anodes prepared by mechanical 120
mixing method [3]. At high charge/discharge rates (1C), as shown in Fig. 3d, CC20 still exhibits a high
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中国科技论文在线
reversible specific capacity of 530 mAh g
–1
after 40 cycles.
125
130
Cyclic performances of CC5 at C (a), CC10 at (b), CC20 at (c) and CC20 at 1C (d). The inset 135
panels are SEM images of CC5 (a), CC10 (b) and CC20 (c).
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 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 140
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. 145
3 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 150
and the conductive network, which showed a high reversible specific capacity of 745 mAh g
–1
after 60
cycles ( C). Even at high charge/discharge rates (1C), the specific capacity retention was still as high
0 20 40 60
400
600
800
1000
Cycle number
C
ap
ac
it
y
(m
A
h
g
-1
)
0 20 40 60
400
800
1200
1600
Cycle number
C
ap
ac
it
y
(m
A
h
g
-1
)
0 20 40 60
400
800
1200
1600
C
ap
ac
it
y
(m
A
h
g
-1
)
Cycle number
(a)
0 10 20 30 40 50
400
800
1200
1600
C
ap
ac
it
y
(m
A
h
g
-1
)
Cycle number
(b)
(c) (d)
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中国科技论文在线
as 530 mAh g
–1
after 40 cycles with good rate property and stable electrode structure.
References
[1] Taberna P L, Mitra S, Poizot P, Simon P, Tarascon J M. High rate capabilities Fe3O4-based Cu 155
nano-architectured electrodes for lithium-ion battery applications [J]. Nature Materials, 2006, 5(7): 567-573.
[2] Lu L, Wang J Z, Zhu X B, Gao X W, Liu H K. High capacity and high rate capability of nanostructured
CuFeO2 anode materials for lithium-ion batteries [J]. Journal of Power Sources, 2011, 196(16): 7025-7029.
[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 [J]. Materials Letters, 2013, 97: 113-116. 160
[4] Zheng S F, Hu JS, Zhong LS, Song W G, Wan LJ, Guo Y G. Introducing Dual Functional CNT Networks
into CuO Nanomicrospheres toward Superior Electrode Materials for Lithium-Ion Batteries [J]. Chemistry of
Materials, 2008, 20(11): 3617-3622.
[5] Maier J, Nanoionics: ion transport and electrochemical storage in confined systems [J]. Nature Materials, 2005,
4(11): 805-815. 165
[6] Attili R N, Saxena R N, Carbonari A W. Delafossite oxides ABO(2) (A = Ag, Cu; B = Al, Cr, Fe, In, Nd, Y)
studied by perturbed–angular–correlation spectroscopy using a Ag–111(beta(–))Cd–111 probe [J]. Physical
Review B, 1998, 58(5): 2563-2569.
170
原位水热合成锂离子电池纳米复合负
极 CuCrO2–CNTs 增强其电化学性能
朱晓东1，田静2，乐士儒1，陈金润2，孙克宁1
（1. 哈尔滨工业大学基础与交叉科学研究院，哈尔滨 150080；
2. 哈尔滨工业大学化学系，哈尔滨 150001） 175
摘要：采用水热法原位合成了 CuCrO2–碳纳米管（CNTs）纳米复合物，作为锂离子电池负
极显示出了优越的容量保持率和循环性能。CuCrO2 由于较差的电导率和大的体积变化，它
的放电容量在 140 次循环后仅能保持 304mAh g-1 ( C)。通过加入 5–20 wt%的 CNTs，
CuCrO2负极的电化学性能得到了大幅提高。当 CNTs的比例超过 10 wt%时，CuCrO2–CNTs
复合负极在 60次循环后容量可以保持 742 mAh g-1。甚至在 1C 充放电倍率下，40次循环后180
容量仍然可以达到 530 mAh g-1。SEM 照片显示 CNTs 被均匀地分散在 CuCrO2 中形成 3D
网络。这种网络结构提供了良好的电导率，抑制了循环过程中的体积变化，从而提高了放电
比容量和循环性能。
关键词：锂离子电池；碳纳米管；复合材料；循环性能；3D 网络
中图分类号： 185
