24October2017

Nano-Micro Letters

CoFe2O4-graphene Nanocomposites Synthesized through An Ultrasonic Method with Enhanced Performances as Anode Materials for Li-ion Batteries

Yinglin Xiao, Xiaomin Li, Jiantao Zai*, Kaixue Wang, Yong Gong, Bo Li, Qianyan Han and Xuefeng Qian*

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Nano-Micro Letters, , Volume 6, Issue 4, pp 307-315

Publication Date (Web): September 13, 2014 (Article)

DOI:10.1007/s40820-014-0003-7

*Corresponding author. E-mail: xfqian@sjtu.edu.cn

 

Abstract

 


Figure discription XRD patterns (a) and Raman spectra (b) of CoFe2O4, CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550, repectively.

CoFe2O4-graphene nanocomposites (CoFe2O4-GNSs) were synthesized through a ultrasonic method and their electrochemical performances as Li-ion battery electrode were improved by annealing processes. The nanocomposites obtained at 350°C kept a high specific capacity of 1257 mAh g-1 even after 200cycles at 0.1 A g-1. Furthermore, the obtained materials also have better rate capability, and it can be maintained to 696, 495, 308 and 254 mAh g-1 at 1, 2, 5 and 10 A g-1, respectively. The improvement in the reversible capacity and cyclic stability can be attributed to the good electrical conductivity improved by annealing at appropriate temperature, the electrochemical nature of CoFe2O4 and GNSs during discharge-charge processes.


 

Keywords

Cobalt ferrite; Graphene; Anode materials; Lithium ion battery

 

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Introduction

 

With the advantages of large specific capacity, high energy density, long cycle life and environmental friendliness, lithium-ion batteries (LIBs) have become one of the predominant power sources for portable electronics in recent years [1-3]. However, the lower reversible storage capacity of carbon-based anode materials cannot match the demands for the practical applications in electric vehicles (EVs) and hybrid electric vehicles (HEVs) [4]. To meet the demands for these practical applications, the energy density, power density, cycle life and rate performances of rechargeable Li-ion batteries need to be improved urgently [2,5].Transition-metal oxides (MO, where M is Co, Ni, Mn, Fe, Zn or Cu) were found to be promising anode materials to replace carbonaceous anodes due to their higher theoretical reversible capacities [2,6] (such as 717 mAh g-1 of NiO [7], 1007 mAh g-1 of Fe2O3 [8], 755 mAh g-1 of MnO [9], 890 mAh g-1 of Co2O3 [10]). However, the huge volume changes during continuous charging/discharging processes would lead to the rapid disintegration of anodes caused by the induced mechanical stress and capacity fading upon cycling, which limited their further practical applications. To improve their electrochemical properties, especially for their cycling performances, decreasing particle size into nanometer, doping metal into binary compounds (e.g. Al or Co), or fabricating nanocomposites has been used to overcome these problems [11-14]. For example, Co3O4 nanorods/graphene nanocomposites had a discharge capacity of 1310 mAh g-1 at a rate of 100 mA-1 after 40 cycles [15], magnetite modified graphene nanosheets exhibited remarkably high reversible lithium storage capacity (1235 mAh g-1 at 0.2 A g-1 after 50 cycles), good rate capability (315 mAh g-1 at 10 A g-1) and improved cycling stability (450 mAh g-1 at 5 A g-1 after nearly 700 cycles) [3]. Recently, ternary oxide compounds, e.g. NiFe2O4, CuFe2O4, ZnFe2O4, ZnSnO4, ZnMn2O4 and et al, have attracted considerable attention because of their good cyclic stability [16,17]. For example, hollow CoFe2O4 nanospheres electrodes still kept more than 93.6% reversible capacity of the first cycle after 50 cycles. However, most of the ternary metal oxides suffer from the problem of poor electronic conductivity, and need to be modified by an electronically conductive agent, such as carbon nanotubes or graphene [18]. Graphene nanosheets (GNSs) with superior properties, e.g. superiorly electrical conductivity, chemical inertness and high surface area of over 2600 m2 g-1, attracted great interests in energy storage areas [19]. Thus the electrochemical performances of GNSs/transition-metal oxide nanocomposites would be improved due to their synergistic effects by combining the high capacity of transition-metal oxides and high surface area/conductivity of GNSs, especially for their rate capabilities and cycling performances [20,21].

 

As a kind of important magnetic materials, CoFe2O4 has been the subject of intense research for the potential applications in high-density storage, magnetic resonance imaging and drug-delivery technology [22]. Recently, CoFe2O4 or its composites used as anode materials for lithium-ion batteries becomes the hot topic of researches due to its higher theoretical reversible capacities [23], and some methods are developed [18,24,25]. For example, Xia and Liu et al synthesized CoFe2O4-graphene nanocomposites by solvothermal method with the improvement of cycle performances, but the rate capability still needed to be further improved.

 

Herein, CoFe2O4-graphene nanocomposites have been prepared by sonication-assisted process and further by annealing process at appropriate temperature. The sonication-assisted process can ensure well the dispersion of CoFe2O4 nanoparticles in reduced graphene oxide [26]. The following appropriate annealing process can improve carbon quality, optimize the interface of graphene/nanoparticles and further improve the conductivity of graphene matrix [20,27]. These combined effects make the obtained materials have better cyclic stability and rate capability compared with previous results.

 

2 Experimental section

 

2.1 Synthesis of graphite oxide (GO), CoFe2O4 and CoFe2O4-GNSs nanocomposites

 

GO was synthesized from natural graphite by the modified Hummer’s method [28]. CoFe2O4 was synthesized as following: 1.4 mmol of CoCl2·6H2O, 2.52 mmol of FeCl3·6H2O and 1.2 g of NaOH were mixed and dissolved in 40 mL distilled water after being sonicated for 30 mins, and then transferred into a Teflon-line autoclave and maintained at 180°C for 12 h. Final products were separated by centrifugation and dried in 80°C.

 

CoFe2O4-GNSs nanocomposites were synthesized as following: 0.2 g of GO was added into 50 mL water and sonicated for 30 mins, and then 0.5 g of CoFe2O4 was added into the solution, and sonicated for another 30 mins. Finally, 10 mL of hydrazine hydrate was added into the mixtures and sonicated for 60 mins. The resulted products were centrifuged and washed by distilled water, and then dried in 80°C. The obtained samples were further annealed at selected temperature (e.g. 350, 550°C) for 60 mins at a heating rate of 10°C min-1 in the N2, which were named as CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 according to their annealing temperature.

 

2.2 Characterizations

 

The obtained products were characterized by XRD (Shimadzu XRD-6000, CuKα, 40 kV, 30 mA). Raman spectra were recorded on a Super LabRam-II spectrometer with a holographic grating of 1800 g mm-1. Morphology of samples was investigated using a transmission electron microscopy (TEM) system (JEOL, JEM-2100). Thermogravimetric (TG) analysis was carried out under air on a Perkin-Elmer 7 instrument to determine the weight ratio of GNSs to CoFe2O4. Nitrogen adsorption-desorption measurement was conducted at 77.7 K on a Micromeritics ASAP 2010 anolyzer.

 

2.3 Lectrochemical testing

 

Working electrodes were prepared by mixing a slurry containing 80% active material (CoFe2O4-GNSs nanocomposites), 10% acetylene black, 10% polymer binder (polyvinylidene difluoride, PVDF) on copper foil according to previous works [29,30], and then dried in a vacuum oven at 60°C for 12 h. Electrolyte consisted of a solution of 1 mol L-1 of LiClO4 in ethylene carbonate (EC)/diethylene carbonate (DEC) (1:1 vol%). Charge-discharge cycles of cells were evaluated between 0.01 and 3 V at a current density of 100 mA g-1 for the first cycle using a battery test system (LAND CT2001A model, Wuhan Jinnuo Electronics, Ltd.). All tests were performed at room temperature. Electrochemical impedance spectroscopy (EIS) was performed using an Ametek PARSTAT 2273 electrochemistry workstation.

 

3 Results and discussion

 

XRD patterns of the obtained CoFe2O4, CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites are shown in Fig. 1a, all main diffraction peaks can be readily indexed to rhombohedral CoFe2O4 (JCPDS card No. 79-1744, space group: R-3m, a=5.94 Å). In the Raman spectra of CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites, the two weak peaks at 1325 cm-1 and 1600 cm-1 are assigned to the D band and G band of graphene, respectively [30],and their relative intensity (ID/IG ratio) relates the quantity of restoration of the sp2 carbon [31,32], and the restoration of the sp2 carbon results in the increasing of conductivity of GNSs [33,34]. From Fig. 1b, one can see that the ID/IG ratio increases with the increase of annealing temperature because of the removing of oxygen containing groups [33,34]. Interestingly, the D peak of GNSs in CoFe2O4-GNSs-350 nanocomposites shows obvious red-shift, revealing the stronger interactions between CoFe2O4 nanoparticles and GNSs after being annealed at 350°C. This phenomenon usually derives from the dielectric confinement effect of transition metal oxide on GNSs. However, if the annealing temperature is increased to 550°C, the interactions would become weaker due to the removing of functional group and the enlarged particle size of CoFe2O4 nanoparticles. As a result, the position of D band of CoFe2O4-GNSs-550 shows similar position with that of CoFe2O4-GNSs.

 

Figure 1 Caption XRD patterns (a) and Raman spectra (b) of CoFe2O4, CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550, repectively.

Figure 1 XRD patterns (a) and Raman spectra (b) of CoFe2O4, CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550, repectively.

 

Figure 2 shows the TEM images of CoFe2O4, CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites, and HRTEM images of CoFe2O4 nanoparticles. From Fig. 2a, one can see that CoFe2O4 nanoparticles with the size about 20 nm are main products. The 2.96 Å interplane distance corresponds to the (1 -2 0) crystal plane and the 2.96 Å lattice spacing corresponds to the (1 1 0) planes of rhombohedral CoFe2O4 in Fig. 2b-c, and the angle of 90° between (1 1 0) and (1 -2 0) planes matches well with its crystal structure (shown in Fig. S1), implying that the obtained CoFe2O4 nanoparticles are crystalline well. As shown in the TEM images of CoFe2O4-GNSs nanocomposites (Fig. 2d), CoFe2O4 nanoparticles disperse homogenously on the paper-like graphene nanosheets, which can prevent the stack of GNSs layers and form a 3D laminated structure. From the TEM images of CoFe2O4-GNSs-350 nanocomposites (Fig. 2e), more close contact of CoFe2O4 nanoparticles with GNSs can be observed, which is beneficial to increase the conductivity of electrodes, ensures the fast and sustained transportation of electrons in electrodes and enhances Li-ion diffusion rate during electrochemical reaction. However, more coalescence would happen along the grain boundaries of CoFe2O4 nanoparticles with increasing calcination temperature (Fig. 2f) [35], which would lead to lower capacities because of longer diffusion length of Li-ion and poor conductivity of electrode. Nitrogen adsorption/disadsorption isotherms of CoFe2O4, CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 (Fig. 3) reveal their specific surface area of 24.04, 137.13, 106.23 and 55.64 m2 g-1, respectively. The extra surface area of CoFe2O4-GNSs nanocomposites over CoFe2O4 is derived from graphene nanosheets. Compared with CoFe2O4-GNSs nanocomposites, the annealing process would lead to smaller specific surface area because of the shrink of GNSs and/or agglomeration of CoFe2O4 nanoparticles, and CoFe2O4-GNSs-550 nanocomposite has the lowest specific surface area [33,36,37].

 

Figure 2 Caption TEM images of bare CoFe2O4 (a); CoFe2O4-GNSs (d), CoFe2O4-GNSs-350 (e) and CoFe2O4-GNSs-550 (f). HRTEM images of CoFe2O4 (b, c).

Figure 2 TEM images of bare CoFe2O4 (a); CoFe2O4-GNSs (d), CoFe2O4-GNSs-350 (e) and CoFe2O4-GNSs-550 (f). HRTEM images of CoFe2O4 (b, c).

 

Figure 3 Caption Nitrogen adsorption/desorption isotherms of CoFe2O4 (a), CoFe2O4-GNSs (b), CoFe2O4-GNSs -350 (c) and CoFe2O4-GNSs -550 (d).

Figure 3 Nitrogen adsorption/desorption isotherms of CoFe2O4 (a), CoFe2O4-GNSs (b), CoFe2O4-GNSs -350 (c) and CoFe2O4-GNSs -550 (d).

 

 

The weight ratio of GNSs in CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites was evaluated by thermal gravimetric analysis (TGA) under air flow (Fig. 4). The final residues are CoFe2O4 [35,37], and the lost weight of CoFe2O4-GNSs may correspond to the oxidation of GNSs to CO2. According the changed weight of CoFe2O4, CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites, the weight percentage of GNSs in CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites is about 18, 17.5 and 15%, respectively.

 

Figure 4 Caption Thermogravimetry analyses (TGA) of CoFe2O4, CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550, respectively.

Figure 4 Thermogravimetry analyses (TGA) of CoFe2O4, CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550, respectively.

 

The electrochemical performances of the as-prepared CoFe2O4-GNSs nanocomposites as anode materials for LIBs were studied, cyclic voltammograms (CV) between 0 and 3.0 V at a scan rate of 0.005 V s-1 are shown in Fig. 5 a. In the 1st cycle, a smaller cathodic peak below 0.25 V (vs. Li/Li+) is associated with the reactions of Li intercalation into GNSs and the porous structure of CoFe2O4-GNSs nanocomposites. The large cathodic peak at 0.60 V (vs. Li/Li+) is associated with the reduction reactions of CoFe2O4 by Li during the first discharge process, which is similar to the previous reports [1]. This process can be expressed by following reaction:

 

CoFe2O4 + 8Li+ + 8e → Co + 2Fe + 4Li2O (1)

 

The anodic peak located at 1.70 V may be corresponding to the oxidation of metallic iron and cobalt, and it shifts positively to 1.75 V in the second and subsequent cycles; while the corresponding cathodic peak shifts to 0.7 V in the second cycles and then shifts to 0.85 V in the third cycles and subsequent cycles because of the polarization of electrode materials [38]. This process can be expressed by following reactions:

 

Co + Li2O → CoO + 2Li+ + 2e (2)

2Fe + 3Li2O → Fe2O3 + 6Li+ +6e (3)

 

In the second cycle, the peak at 1.5 V in the cathodic process can be attributed to the Faradic capacitance both on the surface and edge sites of GNSs [39,40]. After the 3rd cycle, reversible cathodic and anodic peaks are located at around 0.85 and 1.75 V because of the reversible oxidation/reduction processes during charge/discharge cycles, respectively. These processes can be expressed by following reaction:

 

Co + 2Fe + 4Li2O e1 CoO + Fe2O3 + 8Li (4)

 

Furthermore, the CV curves of CoFe2O4-GNSs electrode are stable and overlapped well, the integral area and peak intensity in the 5th cycle are close to that of the 4th cycle, implying that the electrochemical reversibility of the obtained nanocomposites is gradually built after the 3rd cycle and possesses good capacity retention [41].

 

Figure 5 Caption Cyclic voltammograms of CoFe2O4-GNSs nanocomposites (a) for the first five cycles between 3.00 and 0.01 V vs Li. Charge-discharge curves at 0.1 A g-1: CoFe2O4-GNSs (b), CoFe2O4-GNSs-350 (c) and CoFe2O4-GNSs-550 (d).

Figure 5 Cyclic voltammograms of CoFe2O4-GNSs nanocomposites (a) for the first five cycles between 3.00 and 0.01 V vs Li. Charge-discharge curves at 0.1 A g-1: CoFe2O4-GNSs (b), CoFe2O4-GNSs-350 (c) and CoFe2O4-GNSs-550 (d).

 

The discharge-charge voltage profiles of CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites at a current density of 0.1 A g-1 are shown in Fig. 5b-d. The platform at 0.85 V is associated with the reduction reaction of CoFe2O4 by Li during the first discharge process. The electrodes based on CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites with a coulombic efficiency of about 64%, 66% and 75% deliver a discharge capacity of 1509, 1508 and 959 mAh g-1 in the 1st cycle, respectively. The capacities are much larger than the theoretical value of CoFe2O4 (912 mAh g-1), in which the extra irreversible capacities can be attributed to the solid electrolyte interphase (SEI) films [42]. While they have a reversible discharge capacity of 973, 986 and 721 mAh g-1 in the 2nd cycle, and the extra reversible capacities can be attributed to the decomposition of organic electrolytes and the amorphism of CoFe2O4 nanoparticles. Similar phenomena also have been observed in other transition metal oxide [43]. Moreover, the efficiency of CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 rapidly increases to 95%, 95% and 96% in the 3rd cycle, respectively, and remains in the following cycles. Furthermore, the reversible capacities of CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites slightly increase from the 2nd cycle and reach to ~1086, 1071 and 839 mAh g-1 after 50 cycles, respectively, which could be ascribed to the gradual activation of GNSs in nanocomposites in the first several cycles. On the other hand, porous structure can form during discharge-charge processes (Fig. S2), and these in-situ formed porous also has a contribution to their reversible capacities [44,45]. Figure 6a shows the discharge-charge cycling performances of CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites at a current density of 0.1 A g-1. From Fig. 6a, one can see that the capacities of CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites at a current density of 0.1 A g-1 are about 973, 986 and 721 mAh g-1 in the 2nd cycle, respectively. And they still keep to 1086, 1071 and 839 mAh g-1 after 50 cycles, which is about 111%, 108% and 118% reversible capacity of the first cycle. The gradual increased capacity after the 50th cycle is attributed to the reversible polymerization/oligomerization of carbonates and alkyl carbonates (main components of electrolyte), which would further lead to form a reversible polymeric/gel films on nanocomposites [21,46]. Moreover, the capacity of CoFe2O4-GNSs-350 nanocomposites still keep to 1257 mAh g-1 after 200 cycles at the current of 0.1 A g-1 (Fig. S3a). The long term cyclic stability of all the nanocomposites can be due to the electrochemical nature of multiple metal oxide and well dispersion of CoFe2O4 nanoparticles in graphene matrix created by the sonication-assisted process.

 

The capacities of CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites at a current density of 1 A g-1 are 776, 775 and 525 mAh g-1 in the 2nd cycle, and keep to 436 mAh g-1, 596 mAh g-1 and 298 mAh g-1 after 180 cycles, (Fig. S3b) respectively. However, the capacity of CoFe2O4 nanoparticles only keep to 11 mA h g-1 after 180 cycles at the same conditions, only about 2% capacity of the first cycle. Figure 6b illustrates the rate capability of CoFe2O4-GNSs-350 nanocomposites at the current densities from 0.1 A g-1 to 10 A g-1. It can be seen that the reversible capacities keep to 1029, 696, 495 and 308 mA h g-1 at 0.1, 1, 2 and 5 A g-1, respectively, and CoFe2O4-GNSs-350 electrode can still keep a stable reversible capacity of 254 mAh g-1 even at the current density as high as 10 A g-1. Moreover, the capacities still keep to 294, 461, 638 and 1016 mAh g-1 when the current densities return to 5, 2, 1 and 0.1 A g-1, respectively, indicating the obtained CoFe2O4-GNSs-350 nanocomposites exhibit remarkable high lithium storage capacity with improved reversible cycling stability and superior rate capability. The better rate performances of the obtained CoFe2O4-graphene nanocomposites, compared with that of Xia (372 mAh g-1 at 2 A g-1) and Liu (440 mAh g-1 at 1.6 A g-1) may be due to the improved electrochemical performances, created by the properly annealed process.

 

Figure 6 Caption Electrochemical performances of CoFe2O4-GNSs nanocomposites: Circle stability at 0.1 A g-1 for CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 (a); Rate capability of CoFe2O4-GNSs-350 (b).

Figure 6 Electrochemical performances of CoFe2O4-GNSs nanocomposites: Circle stability at 0.1 A g-1 for CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 (a); Rate capability of CoFe2O4-GNSs-350 (b).

 

To further investigate the effects of GNSs in CoFe2O4-GNSs nanocomposites, Nyquist plots of CoFe2O4, CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites after 5 cycles are shown in Fig. 7. The Nyquist plot of CoFe2O4 shows a typical semicircle derived from the charge transfer impedance through the electrode/electrolyte interface, while the Nyquist plots of all nanocomposites have mutiple-semicircles because of the charge-transfer impedance through the interface of electrode/electrolyte and the inside charge-transfer impedances [47-49]. The electrode based on CoFe2O4-GNSs-350 nanocomposite has smallest multiple-semicircles, indicating its lowest charge-transfer impedance. Compared with the works of Xia and Liu [24,25], appropriate annealing process can improve the conductivity of the obtained CoFe2O4-GNSs nanocomposites because it can optimize the interfaces of graphene/nanoparticles and strongth the interactions between CoFe2O4 and GNSs [20,27]. However, high annealing temperature (550°C) would lead to the serious agglomeration of nanoparticles and further increase the resistance.

 

Figure 7 Caption Nyquist plots of CoFe2O4, CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 at 0.08 V vs. Li after 5 cycles.

Figure 7 Nyquist plots of CoFe2O4, CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 at 0.08 V vs. Li after 5 cycles.

 

Based on above discussion, the improvement of electrochemical performances of CoFe2O4-GNSs nanocomposites can be contributed to their unique structure and electrochemical nature. Firstly, CoFe2O4 can transform into nanosized hybrid of Fe2O3/CoO during the first discharge process [1]. The in-situ formed hybrid of Fe2O3/CoO can combine with GNSs to form a porous structure, which can further accommodate its volume change and result in good stability of electrode. Similar phenomena have also been observed in MnFe2O4-GNSs naocomposites [50]. On the other hand, the in-situ formed nanosized Fe2O3 (CoO) can also act as the matrix of CoO (Fe2O3), which would prevent the aggregations of Fe2O3 (CoO), accommodate the volume change of active materials during discharge-charge processes and further improve their cycle stability. The obtained porous structure can accommodate its volume change and result in good stability of electrode [51]. Secondly, graphene nanosheets fabricated from the annealing process can increase the conductivity of electrodes, ensure the fast, sustain the transportation of electrons in electrodes and enhance Li-ion diffusion rate during electrochemical reaction. Thirdly, the annealing process can increase the interfaces of graphene/grain and grain/grain, and facilitate the ion/charge transfer during charge/discharge, which can be confirmed by EIS and TEM images. Furthermore, graphene nanosheets may also increase the BET surface area of nanocomposites and provide extra space for buffering the volumetric change, which would avoid the cracking of electrodes and maintain the structural integrity of electrodes during continuous charging/discharging. Finally, graphene nanosheets can also prevent the agglomeration CoFe2O4 nanoparticles because no larger nanoparticles are observed in Fig. 3d, which is also beneficial to improve the electrochemical performance of CoFe2O4-GNSs nanocomposites.

 

4 Conclusion

 

CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites have been synthesized through an ultrasonic and annealing process, and they exhibit different electrochemical performances of lithium storage capacity with improved reversible cycling stability and superior rate capability, e.g. the capacities of CoFe2O4-GNSs, CoFe2O4-GNSs-350 and CoFe2O4-GNSs-550 nanocomposites are about 1086, 1071 and 839 mAh g-1 in the 2nd cycles, and they still keep to 1128, 1148 and 839 mAh g-1 after 50 cycles, respectively. Moreover, CoFe2O4-GNSs-350 nanocomposites have the reversible capacities about 1257 mAh g-1 and 596 mA h g-1 even after 200/180 cycles at a current density of 0.1 A g-1 and 1 A g-1, respectively. Furthermore, the obtained CoFe2O4-GNSs-350 nanocomposites also have better rate capability, and it can be maintained to 308 and 254mAh g-1 at 5 and 10 A g-1, respectively. The long term cyclic stability can be due to the electrochemical nature and better dispersion of CoFe2O4 nanoparticles in graphene matrix created by the sonication-assisted process. Furthermore, proper annealing process can improve graphene quality and optimize the interfaces of graphene/grain and grain/grain and further improve the conductivity of obtained materials, which would further lead to the improved rate capability.

 

Acknowledgments

 

This work was supported by the Program of National Natural Science Foundation of China (21071097, 20901050), National Basic Research Program of China (2009CB930400), Shanghai Nano-Project (12nm0503502) and Minhang District Developing Project.

 

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[10] J.-G. Kang, Y.-D. Ko, J.-G. Park and D.-W. Kim, "Origin of capacity fading in nano-sized Co3O4 electrodes: electrochemical impedance spectroscopy study", Nanoscale Res. Lett. 3(10), 390-394 (2008). http://dx.doi.org/10.1007/s11671-008-9176-7

[11] G. Wang, Y. Chen, K. Konstantinov, M. Lindsay, H. Liu and S. Dou, "Investigation of cobalt oxides as anode materials for Li-ion batteries", J. Power Sources 109(1), 142-147 (2002). http://dx.doi.org/10.1016/S0378-7753(02)00052-6

[12] L. Liu, Y. Li, S. Yuan, M. Ge, M. Ren, C. Sun and Z. Zhou, "Nanosheet-based NiO microspheres: controlled solvothermal synthesis and lithium storage performances", J. Phys. Chem. C 114(1), 251-255 (2009). http://dx.doi.org/10.1021/jp909014w

[13] I. Issac, M. Scheuermann, S. M. Becker, E. G. Bardají, C. Adelhelm, D. Wang, C. Kübel and S. Indris, "Nanocrystalline Ti2/3Sn1/3O2 as anode material for Li-ion batteries", J. Power Sources 196(22), 9689-9695 (2011). http://dx.doi.org/10.1016/j.jpowsour.2011.07.046

[14] W. Li, G. Zhang, J. Li and Y. Lai, "NiFe2O4-based cermet inert anodes for aluminum electrolysis", JOM 61(5), 39-43 (2009). http://dx.doi.org/10.1007/s11837-009-0068-9

[15] L. Tao, J. Zai, K. Wang, H. Zhang, M. Xu, J. Shen, Y. Su and X. Qian, "Co3O4 nanorods/graphene nanosheets nanocomposites for lithium ion batteries with improved reversible capacity and cycle stability", J. Power Sources 202(15), 230-235 (2012). http://dx.doi.org/10.1016/j.jpowsour.2011.10.131

[16] Y. Ding, Y. Yang and H. Shao, "Synthesis and characterization of nanostructured CuFe2O4 anode material for lithium ion battery", Solid State Ionics 217(8), 27-33 (2012). http://dx.doi.org/10.1016/j.ssi.2012.04.021

[17] Z. Yuan, F. Huang, J. Sun and Y. Zhou, "An amorphous nanosized tin-zinc composite oxide as a high capacity anode material for lithium ion batteries", Chem. Lett. 31(3), 408-409 (2002). http://dx.doi.org/10.1246/cl.2002.408

[18] Y. Zhao, J. Li, Y. Ding and L. Guan, "Enhancing the lithium storage performance of iron oxide composites through partial substitution with Ni2+ or Co2+", J. Mater. Chem. 21(47), 19101-19105 (2011). http://dx.doi.org/10.1039/c1jm13263f

[19] D. Wang, R. Kou, D. Choi, Z. Yang, Z. Nie, J. Li, L.V. Saraf, D. Hu, J. Zhang and G. L. Graff, "Ternary self-assembly of ordered metal oxide- graphene nanocomposites for electrochemical energy storage", ACS Nano 4(3), 1587-1595 (2010). http://dx.doi.org/10.1021/nn901819n

[20] J. Zhu, Y. K. Sharma, Z. Zeng, X. Zhang, M. Srinivasan, S. Mhaisalkar, H. Zhang, H. H. Hng and Q. Yan, "Cobalt oxide nanowall arrays on reduced graphene oxide sheets with controlled phase, grain size, and porosity for Li-ion battery electrodes", J. Phys. Chem. C 115(16), 8400-8406 (2011). http://dx.doi.org/10.1021/jp2002113

[21] G. Zhou, D. W. Wang, F. Li, L. Zhang, N. Li, Z. S. Wu, L. Wen, G. Q. Lu and H. M. Cheng, "Graphene-wrapped Fe3O4 anode material with improved reversible capacity and cyclic stability for lithium ion batteries", Chem. Mater. 22(18), 5306-5313 (2010). http://dx.doi.org/10.1021/cm101532x

[22] Z. Chen and L. Gao, "Synthesis and magnetic properties of CoFe2O4 nanoparticles by using PEG as surfactant additive", Mater. Sci. Eng. B 141(1-2), 82-86 (2007). http://dx.doi.org/10.1016/j.mseb.2007.06.003

[23] P. Lavela and J. Tirado, "CoFe2O4 and NiFe2O4 synthesized by sol-gel procedures for their use as anode materials for Li ion batteries", J. Power Sources 172(1), 379-387 (2007). http://dx.doi.org/10.1016/j.jpowsour.2007.07.055

[24] H. Xia, D. Zhu, Y. Fu and X. Wang, "CoFe2O4-graphene nanocomposite as a high-capacity anode material for lithium-ion batteries", Electrochim. Acta, 83, 166-174 (2012). http://dx.doi.org/10.1016/j.electacta.2012.08.027

[25] S. Liu, J. Xie, C. Fang, G. Cao, T. Zhu and X. Zhao, "Self-assembly of a CoFe2O4/graphene sandwich by a controllable and general route: towards a high-performance anode for Li-ion batteries", J. Mater. Chem. 22(37), 19738-19743 (2012). http://dx.doi.org/10.1039/c2jm34019d

[26] W. T. L. Lim, Z. Zhong and A. Borgna, "An effective sonication-assisted reduction approach to synthesize highly dispersed Co nanoparticles on SiO2", Chem. Phys. Lett. 471(1-3), 122-127 (2009). http://dx.doi.org/10.1016/j.cplett.2009.02.041

[27] R. Yi, F. Dai, M. L. Gordin, H. Sohn and D. Wang, "Influence of silicon nanoscale building blocks size and carbon coating on the performance of micro-sized Si-C composite Li-ion anodes", Adv. Energy Mater. 3(11), 1507-1515 (2013). http://dx.doi.org/10.1002/aenm.201300496

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[29] H. Wang, C. Zhang, Z. Liu, L. Wang, P. Han, H. Xu, K. Zhang, S. Dong, J. Yao and G. Cui, "Nitrogen-doped graphene nanosheets with excellent lithium storage properties", J. Mater. Chem. 21(14), 5430-5434 (2011). http://dx.doi.org/10.1039/c1jm00049g

[30] J. Zhu, T. Zhu, X. Zhou, Y. Zhang, X. W. Lou, X. Chen, H. Zhang, H. H. Hng and Q. Yan, "Facile synthesis of metal oxide/reduced graphene oxide hybrids with high lithium storage capacity and stable cyclability", Nanoscale 3, 1084-1089 (2011). http://dx.doi.org/10.1039/c0nr00744g

[31] J. Liu, Z. Lin, T. Liu, Z. Yin, X. Zhou, S. Chen, L. Xie, F. Boey, H. Zhang and W. Huang, "Multilayer stacked low-temperature-reduced graphene oxide films: preparation, characterization, and application in polymer memory devices", Small 6(14), 1536-1542 (2010). http://dx.doi.org/10.1002/smll.201000328

[32] S. Stankovich, D. A. Dikin, R. D. Piner, K. A. Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu, S. T. Nguyen and R. S. Ruoff, "Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide", Carbon 45(7), 1558-1565 (2007). http://dx.doi.org/10.1016/j.carbon.2007.02.034

[33] C.-M. Chen, J.-Q. Huang, Q. Zhang, W.-Z. Gong, Q.-H. Yang, M.-Z. Wang and Y.-G. Yang, "Annealing a graphene oxide film to produce a free standing high conductive graphene film", Carbon 50(2), 659-667 (2012). http://dx.doi.org/10.1016/j.carbon.2011.09.022

[34] S. Mao, H. Pu and J. Chen, "Graphene oxide and its reduction: modeling and experimental progress", Rsc Adv. 2(7), 2643-2662 (2012). http://dx.doi.org/10.1039/c2ra00663d

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[36] J. M. Kim, W. G. Hong, S. M. Lee, S. J. Chang, Y. Jun, B. H. Kim and H. J. Kim, "Energy storage of thermally reduced graphene oxide", Int. J. Hydrog. Energy 39(8), 3799-3804 (2014). http://dx.doi.org/10.1016/j.ijhydene.2013.12.144

[37] J. B. Silva, W. D. Brito and N. D. Mohallem, "Influence of heat treatment on cobalt ferrite ceramic powders", Mater. Sci. Eng. B 112(2-3), 182-187 (2004). http://dx.doi.org/10.1016/j.mseb.2004.05.029

[38] L. Ji, Z. Tan, T. R. Kuykendall, S. Aloni, S. Xun, E. Lin, V. Battaglia and Y. Zhang, "Fe3O4 nanoparticle-integrated graphene sheets for high-performance half and full lithium ion cells", Phys. Chem. Chem. Phys. 13(15), 7170-7177 (2011). http://dx.doi.org/10.1039/c1cp20455f

[39] Y. Mai, D. Zhang, Y. Qiao, C. Gu, X. Wang and J. Tu, "MnO/reduced graphene oxide sheet hybrid as an anode for Li-ion batteries with enhanced lithium storage performance", J. Power Sources 216, 201-207 (2012). http://dx.doi.org/10.1016/j.jpowsour.2012.05.084

[40] K. Shu, C. Wang, M. Wang, C. Zhao and G. G. Wallace, "Graphene cryogel papers with enhanced mechanical strength for high performance lithium battery anodes", J. Mater. Chem. A 2(5), 1325-1331 (2014). http://dx.doi.org/10.1039/c3ta13660d

[41] S. Yin, Y. Zhang, J. Kong, C. Zou, C. M. Li, X. Lu, J. Ma, F. Y. C. Boey and X. Chen, "Assembly of graphene sheets into hierarchical structures for high-performance energy storage", ACS Nano 5(5), 3831-3838 (2011). http://dx.doi.org/10.1021/nn2001728

[42] F.-W. Yuan, H.-J. Yang and H.-Y. Tuan, "Alkanethiol-passivated Ge nanowires as high-performance anode materials for lithium-ion batteries: the role of chemical surface functionalization", ACS Nano 6(11), 9932-9942 (2012). http://dx.doi.org/10.1021/nn303519g

[43] H. Zhao, Z. Zheng, K.W. Wong, S. Wang, B. Huang and D. Li, "Fabrication and electrochemical performance of nickel ferrite nanoparticles as anode material in lithium ion batteries", Electrochem. Commun. 9(10), 2606-2610 (2007). http://dx.doi.org/10.1016/j.elecom.2007.08.007

[44] Z.-S. Wu, W. Ren, L. Wen, L. Gao, J. Zhao, Z. Chen, G. Zhou, F. Li and H.-M. Cheng, "Graphene anchored with Co3O4 nanoparticles as anode of lithium ion batteries with enhanced reversible capacity and cyclic performance", ACS Nano 4(6), 3187-3194 (2010). http://dx.doi.org/10.1021/nn100740x

[45] J. S. Chen and X. W. Lou, "Anatase TiO2 nanosheet: An ideal host structure for fast and efficient lithium insertion/extraction", Electrochem. Commun. 11(12), 2332-2335 (2009). http://dx.doi.org/10.1016/j.elecom.2009.10.024

[46] S. Laruelle, S. Grugeon, P. Poizot, M. Dolle, L. Dupont and J. Tarascon, "On the origin of the extra electrochemical capacity displayed by MO/Li cells at low potential", J. Electrochem. Soc. 149(5), A627-A634 (2002). http://dx.doi.org/10.1149/1.1467947

[47] T. Wei, F. Wang, J. Yan, J. Cheng, Z. Fan amd H. Song, "Microspheres composed of multilayer graphene as anode material for lithium-ion batteries", J. Electroanal. Chem. 653(1-2), 45-49 (2011). http://dx.doi.org/10.1016/j.jelechem.2011.01.010

[48] H. Liu, G. Wang, J. Liu, S. Qiao and H. Ahn, "Highly ordered mesoporous NiO anode material for lithium ion batteries with an excellent electrochemical performance", J. Mater. Chem. 21(9), 3046-3052 (2011). http://dx.doi.org/10.1039/c0jm03132a

[49] S. Yang, H. Song and X. Chen, "Electrochemical performance of expanded mesocarbon microbeads as anode material for lithium-ion batteries", Electrochem. Commun. 8(1), 137-142 (2006). http://dx.doi.org/10.1016/j.elecom.2005.10.035

[50] Y. Xiao, J. Zai, L. Tao, B. Li, Q. Han, C. Yu and X. Qian, "MnFe2O4-graphene nanocomposites with enhanced performances as anode materials for Li-ion batteries", Phys. Chem. Chem. Phys. 15(11), 3939-3945 (2013). http://dx.doi.org/10.1039/c3cp50220a

[51] J. Zai, K. Wang, Y. Su, X. Qian and J. Chen, "High stability and superior rate capability of three-dimensional hierarchical SnS2 microspheres as anode material in lithium ion batteries", J. Power Sources 196(7), 3650-3654 (2011). http://dx.doi.org/10.1016/j.jpowsour.2010.12.057

 

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[20] J. Zhu, Y. K. Sharma, Z. Zeng, X. Zhang, M. Srinivasan, S. Mhaisalkar, H. Zhang, H. H. Hng and Q. Yan, "Cobalt oxide nanowall arrays on reduced graphene oxide sheets with controlled phase, grain size, and porosity for Li-ion battery electrodes", J. Phys. Chem. C 115(16), 8400-8406 (2011). http://dx.doi.org/10.1021/jp2002113

[21] G. Zhou, D. W. Wang, F. Li, L. Zhang, N. Li, Z. S. Wu, L. Wen, G. Q. Lu and H. M. Cheng, "Graphene-wrapped Fe3O4 anode material with improved reversible capacity and cyclic stability for lithium ion batteries", Chem. Mater. 22(18), 5306-5313 (2010). http://dx.doi.org/10.1021/cm101532x

[22] Z. Chen and L. Gao, "Synthesis and magnetic properties of CoFe2O4 nanoparticles by using PEG as surfactant additive", Mater. Sci. Eng. B 141(1-2), 82-86 (2007). http://dx.doi.org/10.1016/j.mseb.2007.06.003

[23] P. Lavela and J. Tirado, "CoFe2O4 and NiFe2O4 synthesized by sol-gel procedures for their use as anode materials for Li ion batteries", J. Power Sources 172(1), 379-387 (2007). http://dx.doi.org/10.1016/j.jpowsour.2007.07.055

[24] H. Xia, D. Zhu, Y. Fu and X. Wang, "CoFe2O4-graphene nanocomposite as a high-capacity anode material for lithium-ion batteries", Electrochim. Acta, 83, 166-174 (2012). http://dx.doi.org/10.1016/j.electacta.2012.08.027

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[27] R. Yi, F. Dai, M. L. Gordin, H. Sohn and D. Wang, "Influence of silicon nanoscale building blocks size and carbon coating on the performance of micro-sized Si-C composite Li-ion anodes", Adv. Energy Mater. 3(11), 1507-1515 (2013). http://dx.doi.org/10.1002/aenm.201300496

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[33] C.-M. Chen, J.-Q. Huang, Q. Zhang, W.-Z. Gong, Q.-H. Yang, M.-Z. Wang and Y.-G. Yang, "Annealing a graphene oxide film to produce a free standing high conductive graphene film", Carbon 50(2), 659-667 (2012). http://dx.doi.org/10.1016/j.carbon.2011.09.022

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[41] S. Yin, Y. Zhang, J. Kong, C. Zou, C. M. Li, X. Lu, J. Ma, F. Y. C. Boey and X. Chen, "Assembly of graphene sheets into hierarchical structures for high-performance energy storage", ACS Nano 5(5), 3831-3838 (2011). http://dx.doi.org/10.1021/nn2001728

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Citation Information

Yinglin Xiao, Xiaomin Li, Jiantao Zai, Kaixue Wang, Yong Gong, Bo Li, Qianyan Han and Xuefeng Qian, CoFe2O4-graphene Nanocomposites Synthesized through An Ultrasonic Method with Enhanced Performances as Anode Materials for Li-ion Batteries. Nano-Micro Lett. 6(4), 307-315(2014). http://dx.doi.org/10.1007/s40820-014-0003-7

History

Received: 24 February 2014 / Revised: 16 May 2014 / Accepted: 19 May 2014

 


Additional Info

  • Type of Publishing: JOUR - Journal
  • Title:

    CoFe2O4-graphene Nanocomposites Synthesized through An Ultrasonic Method with Enhanced Performances as Anode Materials for Li-ion Batteries

  • Author: Yinglin Xiao, Xiaomin Li, Jiantao Zai, Kaixue Wang, Yong Gong, Bo Li, Qianyan Han and Xuefeng Qian
  • Year: 2014
  • Volume: 6
  • Issue: 4
  • Journal Name: Nano-Micro Letters
  • Publisher: OPEN ACCESS HOUSE SCIENCE & TECHNOLOGY
  • ISSN: 2150-5551
  • URL: http://dx.doi.org/10.1007/s40820-014-0003-7
  • Abstract:

    CoFe2O4-graphene nanocomposites (CoFe2O4-GNSs) were synthesized through a ultrasonic method and their electrochemical performances as Li-ion battery electrode were improved by annealing processes. The nanocomposites obtained at 350°C kept a high specific capacity of 1257 mAh g-1 even after 200 cycles at 0.1 A g-1. Furthermore, the obtained materials also have better rate capability, and it can be maintained to 696, 495, 308 and 254 mAh g-1 at 1, 2, 5 and 10 A g-1, respectively. The improvement in the reversible capacity and cyclic stability can be attributed to the good electrical conductivity improved by annealing at appropriate temperature, the electrochemical nature of CoFe2O4 and GNSs during discharge-charge processes.

  • Publish Date: Saturday, 13 September 2014
  • Start Page: 307
  • Endpage: 315
  • DOI: 10.1007/s40820-014-0003-7