Sponge-like mesoporous CuO ribbon clusters as high-performance anode material for lithium-ion batteries

Sponge-like mesoporous CuO ribbon clusters as high-performance anode material for lithium-ion batteries

Materials Letters 91 (2013) 279–282 Contents lists available at SciVerse ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/m...

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Materials Letters 91 (2013) 279–282

Contents lists available at SciVerse ScienceDirect

Materials Letters journal homepage: www.elsevier.com/locate/matlet

Sponge-like mesoporous CuO ribbon clusters as high-performance anode material for lithium-ion batteries Y.F. Yuan a,b,n, Y.B. Pei a, J. Fang a, H.L. Zhu a, J.L. Yang a, S.Y. Guo a a b

College of Machinery and Automation, Zhejiang Sci-Tech University, Hangzhou 310018, People’s Republic of China State Key Lab of Silicon Materials, Zhejiang University, Hangzhou 310027, People’s Republic of China

a r t i c l e i n f o

abstract

Article history: Received 25 July 2012 Accepted 2 October 2012 Available online 10 October 2012

Hemispherical CuO clusters assembled by mesoporous nanocrystal ribbons are directly grown on Ni foam. As anode material of lithium-ion batteries, CuO ribbon clusters exhibit high specific capacity, high stability, and good rate performance, superior to commercial CuO powder. At 0.2 C, after 50 cycles, the discharge capacities are still 3 times that of commercial CuO, sustaining 81% discharge capacity of the 2nd cycle. At 0.5–4 C, the discharge capacity is 206–572 mAh g  1. The improved electrochemical performances result from the unique nano-assembled structure. & 2012 Elsevier B.V. All rights reserved.

Keywords: CuO cluster Anode material Nanocrystalline materials Energy storage and conversion

1. Introduction CuO is a competitive candidate in anode materials of lithiumion batteries (LIBs), and has the advantages of low cost, chemical stability, environmental friendly nature, high safety and high theoretical capacity (670 mAh g  1). However, electrode pulverization and the loss of electrical contact during repetitive cycling lead to dissatisfactory cycle life and poor rate performance, limiting the application of CuO [1,2]. At present, composite technology and nanotechnology are two main ways to improve electrochemical performances of CuO [3–6]. CuO/C [7], CuO/Fe2O3 nanocomposite [8], CuO nanosheet [9], CuO nanoflower [10], CuO nanotube [11] have been widely reported. In the nanomaterials, Li þ diffusion is much easier; reaction kinetics is faster; but during the Li uptake-release process, the strain still occurs. Nevertheless the strain is relatively small and readily accommodated. The composite of CuO and high conducting material can well disperse CuO material and cover the shortage of CuO low conductivity. However, the addition of a lot of conducting materials decreases the energy density and power density of the anode. The nano-assembly is a relatively novel technology to prepare electrode materials. It not only maintains the high activity of the nanomaterials, but also provides a good structure to accommodate the material strain. The few nanoassembled CuO materials have been reported by far.

n Corresponding author at: College of Machinery and Automation, Zhejiang Sci-Tech University, Hangzhou 310018, People’s Republic of China. Tel.: þ86 571 8684 3343. E-mail address: [email protected] (Y.F. Yuan).

0167-577X/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2012.10.007

Here, we adopt a simple two-step approach to grow CuO clusters assembled with sponge-like mesoporous nanocrystal ribbons on Ni foam. CuO ribbon clusters exhibit an enhanced electrochemical performance as the anode for LIBs.

2. Experimental In a typical procedure, 0.24 g Cu(NO3)2 and 1.2 g urea were dissolved into 100 ml deionized water. Stirred for 30 min, the mixed solution was transferred into a 100 ml Teflon-lined stainless steel autoclave. The clean Ni foam discs with a diameter of about 12 mm were then immersing into the solution, sealed and maintained at 95 1C for 10 h, and finally cooled down naturally to room temperature. The obtained nickel foam covered with the precursor was washed with deionized water for several times, dried at 60 1C for 5 h, and finally calcined at 350 1C for 5 h. The structures and the morphologies of as-prepared products were analyzed by powder X-ray diffractometer (Thermo, X0 TRA) with Cu Ka1 radiation (l ¼0.15406 nm), Field-emission scanning electron microscopy (FESEM, Zeiss, Ultra55) and Transmission electron microscope (TEM, JEOL, JEM-2100, 200 KV). The specific surface areas were characterized by adsorption–desorption of N2 (BET method) at the temperature of liquid nitrogen (77 K), with a Micromeritics instrument. Coin-type (CR2025) test cells were assembled in an argonfilled gloveboxs with the as-prepared CuO ribbon cluster as working electrodes, metallic Li foils as both reference and counter electrodes, 1 M LiPF6 in ethylene carbonate and diethylene carbonate with the volume ratio of 1:1 as the electrolyte, a polypropylene microporous film as a separator. For comparison,

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commercial CuO powder was used to prepare test cells: the slurry consist of 80 wt% CuO powder, 10 wt% acetylene black and 10 wt% polyvinylidene fluoride (PVDF) was dispersed in N-methlypyrrolidinone (NMP), and then coated onto Ni foam with 12 mm diameter, dried at 120 1C for 12 h and then pressed at a pressure of 10 MPa. All the cells were aged for 12 h before measurement. The cyclic voltammetry and galvanostatic discharge–charge tests were carried out on an electrochemical station (Gaoss Union, EC550) between 0 and 3.0 V at a scan rate of 0.2 mV s  1 and LAND battery test system in the range of 0.02–3.0 V (vs. Li/Li þ ), respectively. All the tests were performed at room temperature (25 1C).



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3. Results and discussion Fig. 1(a) is XRD patterns of the precursor and the final products. The precursor is Cu2(OH)2CO3 (ICDD 41–1390), while the final products is pure monoclinic CuO (ICDD 45–0937). SEM images show that CuO directly grows on the nickel foam, presenting hemispherical clusters (Fig. 1b). These hemispherical clusters consist of many CuO ribbons with 15–30 mm in the length, 100–1000 nm in the width, 60–120 nm in the thickness (Fig. 1c). The microstructure of CuO ribbon is further analyzed by TEM (Fig. 1d and e). Fig. 1(d) displays that CuO ribbon is assembled by numerous nanocrystals. Their crystalline plane can be clearly seen in HRTEM image (Fig. 1e). The nanocrystals

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Fig. 1. (a) XRD patterns of the precursor and the final product, (b) low and (c) high resolution SEM images, (d) TEM and (e) HRTEM images of CuO ribbon clusters.

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size ranges from about 20 to 40 nm. Lots of mesopores with about 10 nm in diameter exists among these nanocrystals, forming a 3-D network mesopore structure, leading to a final sponge-like mesopore CuO ribbon. The formation of mesoporous network is due to heat decomposition of the precursor Cu2(OH)2CO3. Fig. 2 shows electrochemical properties of CuO ribbon clusters. Fig. 2(a) is the first three cyclic voltammograms (CV) of CuO

ribbon clusters. In the first cathodic process, four reduction peaks appear at  1.82 V, 0.95 V, 0.6 V, and 0.5 V. It corresponds to a multi-step electrochemical reaction of CuO, related to the formation of CuII1  xCuIxO1  x/2 solid solution, reduction to Cu2O, further reduction to Cu and Li2O, and the final formation of solid electrolyte interface (SEI) film [12]. Three anodic peaks at  0.7, 2.5 and 2.7 V are attributed to the slight decomposition of organic

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Fig. 2. First three CV curves of (a) CuO ribbon clusters and (b) commercial CuO; (c) Galvanostatic discharge/charge curves of CuO ribbon clusters; (d) Cycling discharge/ charge performances of CuO ribbon clusters and commercial CuO at 0.2 C; (e) Rate capacity at the different rates; (f) SEM image of the fully charged CuO ribbon clusters after 50 cycles.

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layer, and the stepwise oxidation process of Cu to Cu2O and CuO [7,13]. At the 2nd and 3rd cycles, CV curves coincide with each other well, indicating that the electrode reactions become more reversible. Compared with CV curves of commercial CuO (Fig. 2b), the cathodic peak potentials of CuO ribbon clusters are higher, and the potential interval between anodic and cathodic peaks is smaller, indicating better electrochemical reversibility. CuO ribbon clusters have larger-area anodic and cathodic peaks; these peaks are more obvious and show clearer peak fine structure, indicating higher electrochemical activity. Fig. 2(c) displays the galvanostatic discharge–charge curves of CuO ribbon clusters measured at 0.2 C (1 C is 670 mAh g  1). The plateaus on the voltage profiles coincide well with the cathodic and anodic peaks in the CV curves. The cycling discharge–charge performances at 0.2 C rate are illustrated in Fig. 2(d). The first discharge capacity, charge capacity and coulombic efficiency of CuO ribbon clusters are 934 mAh g  1, 638 mAh g  1 and 68%, much higher than 791 mAh g  1, 197 mAh g  1 and 25% of the commercial CuO. In the subsequent 49 cycles, coulombic efficiency of CuO ribbon clusters is always above 95%, and the discharge capacities are 3 times (at the 50th cycle) to 6 times (at the 6th cycle) those of commercial CuO, showing better electrochemical performances. After 50 cycles, CuO ribbon cluster can still sustain 81% discharge capacity of the 2nd cycle, presenting a high cycling stability. We compare rate capability of CuO ribbon clusters and commercial CuO powder in Fig. 2(e). Discharge capacity of CuO ribbon clusters is 572 mAh g  1 at 0.5 C after 10 cycles, and this value is slowly reduced to 485, 394, 285, and 206 mAh g  1 when the current rate is consecutively set at 1, 2, 3 and 4 C. At last, when current rate returns back to initial 0.5 C, the final discharge capacity is 430 mAh g  1, recovering 77% of the initial 0.5 C. The rate capability of CuO ribbon clusters is superior to that of the commercial CuO (120, 51, 22, 16, 15 and 96 mAh g  1 at 0.5, 1, 2, 3, 4 and 0.5 C, respectively). The improved electrochemical performance is attributed to the unique nanocrystal-assembled mesoporous ribbon cluster structure. The small size ( 21.6 nm, obtained by the calculation of XRD data) of CuO nanocrystals shortens diffusion route of Li þ ; while large specific surface area (SSA) offers more reaction sites. SSA of CuO ribbon cluster is 17.0 m2 g  1, while that of the commercial CuO is only 0.1 m2 g  1. The connection among the nanocrystals is also tight (Fig. 1d), offering a good electrical conductivity. Therefore, the electrochemical kinetics is enhanced. The 3-D network mesoporous provides the most sufficient contact between CuO and the electrolyte, insuring high efficient utilization of large specific surface of CuO nanocrystals. As a result, CuO ribbon clusters show higher electrochemical activity and rate performance, and deliver higher discharge capacity. This structure also has good buffer ability. The pulverization of CuO particles

arising from large volume change can be greatly suppressed, and CuO ribbon cluster structure can be well maintained, which is confirmed by SEM image (Fig. 2f) of CuO ribbon clusters after 50 cycles. The high stability of material structure can remarkably increase cycling stability of CuO.

4. Conclusions As the anodic material of LIBs, CuO ribbon clusters show high discharge capacity, good cycling stability and enhanced rate performance, being a high-performance anode material. The excellent electrochemical performance could be attributed to its unique structure. The small size, large specific surface and tight contact of CuO nanocrystals lead to high electrochemical activity and good charge–discharge performance. The 3-D network mesoporous structure well buffers the volume variations, enhancing cycling stability of CuO. The present work provides an effective material structure for other transition metal oxides.

Acknowledgments This work was supported by Zhejiang Provincial Natural Science Foundation (No. LQ12E02010); Visiting Scholar Foundation of State Key Lab of Silicon Materials, Zhejiang University (SKL2012-8); National Natural Science Foundation of China (No. 51002140); Foundation of New Century 151 Talent Engineering of Zhejiang Province (2010) and Innovation Team Project of Zhejiang Province (No.2009R50005).

References [1] Feng JK, Xia H, Lai MO, Lu L. Mater Res Bull 2011;46:424. [2] Debart A, Dupont L, Poizot P, Leriche JB, Tarascon JM. J Electrochem Soc 2001;148:A1266. [3] Li C, Wei W, Fang SM, Wang HX, Zhang Y, Gui YH, et al. J Power Sources 2010;195:2939. [4] Choi CS, Park YU, Kim H, Kim NR, Kang K, Lee HM. Electrochim Acta 2012;70:98. [5] Barreca D, Carraro G, Gasparotto. A, Maccato C, Cruz-Yusta M, Gomez-Camer JL, et al. ACS Appl Mater Interfaces 2012;4:3610. [6] Chen X, Zhang NQ, Sun KN. J Mater Chem 2012;22:13637. [7] Huang XH, Wang CB, Zhang SY, Zhou F. Electrochim Acta 2011;56:6752. [8] Garcia-Tamayo E, Valvo M, Lafont U, Locati C, Munao D, Kelder EM. J Power Sources 2011;196:6425. [9] Wang ZY, Su FB, Madhavi S, Lou XW. Nanoscale 2011;3:1618. [10] Xiang JY, Tu JP, Yuan YF, Wang XL, Huang XH, Zeng ZY. Electrochim Acta 2009;54:1160. [11] Xiang JY, Tu JP, Huang XH, Yang YZ. J Solid State Electrochem 2008;12:941. [12] Garcia-Tamayo E, Valvo M, Lafont U, Locati C, Munao D, Kelder EM. J Power Sources 2011;196:6425. [13] Lu LQ, Wang Y. Electrochem Commun 2012;14:82.