One-pot solvothermal synthesis of ZnFe2O4 nanospheres/graphene composites with improved lithium-storage performance
Graphical abstract
Introduction
Rechargeable lithium ion batteries (LIBs), which are based on the mechanism of Li+ intercalation into the cathode, have become the dominant power source for portable electronic devices, electric vehicles, smart grids, etc. [1], [2], [3]. Graphite is currently taken for standard anode material for LIBs. However, the relatively low theoretical capacity (372 mAh g−1) and the safety concern impede its application in high-energy LIBs [4]. Recently, zinc ferrite (ZnFe2O4) has attracted great attention due to its high theoretical capacity of about 1000 mAh g−1, which is two times higher than that of graphite [5], [6]. However, like other high capacity transition metal oxides, ZnFe2O4 shows rapid capacity fading because of poor conductivity and large volume expansion occurring in cycling process [7]. Therefore, the development of high-performance ZnFe2O4 electrode material with both good cycling stability and rate capability is essential for next-generation, high-power, and high-energy LIBs.
One approach to avoid the limitations of ZnFe2O4 is to hybridize with carbonaceous materials for improved conductivity and accommodation of the strain during volume change [8], [9], [10]. Graphene, as one of the special structures of carbon consisting of monolayers of hybridized carbon atoms arranged in a honeycombed network with six-membered rings, has been used as an excellent substrate to host active nanomaterials owing to its prominent thermal stability, superior electronic conductivity, remarkable structural flexibility, high specific surface area [14], and widespread potential applications in nanoscience and nanotechnology [11], [12], [13]. Recently, numerous graphene-based inorganic nanocomposites with metal [14], [15], metal oxides [16], [17] and sulfide [18], [19] have been successfully synthesized and showed enhanced properties of these host materials.
In this study, ZnFe2O4/graphene nanocomposites were synthesized through a facile solvothermal process, in which the formation of ZnFe2O4 nanoparticles, the reduction of graphene oxide (GO), and the uniform mixing of these two materials were accomplished in one step. The electrochemical tests showed that the ZnFe2O4/graphene nanocomposites exhibit obviously improved electrochemical properties compared with bare ZnFe2O4. The results indicate that the ZnFe2O4/graphene nanocomposites have great potential as anode material for the next generation high-performance LIBs.
Section snippets
Experiment
All the reagents used were of analytical purity and were used without further purification. Graphene oxide (GO) was synthesized from natural graphite powers by a modified Hummers method [20]. ZnFe2O4/graphene nanocomposites were prepared in a typical synthesis. 100 mg of GO was dispersed into 80 mL of ethylene glycol (EG) with sonication for 30 min. Then 10 mmol ferric chloride anhydrous (FeCl3), 5 mmol zinc acetate dihydrate (Zn(Ac)2·2H2O) and 4 g sodium acetate (NaAc) were added into the GO
Results and discussion
The XRD patterns of the as-prepared pure ZnFe2O4 and ZnFe2O4/graphene nanocomposites are shown in Fig. 1(a). All the diffraction peaks agree well with to a cubic structure of the ZnFe2O4 spinel (JCPDS No. 22-1010). According to the Debye–Scherrer equation, the average crystalline diameters for the obtained pure ZnFe2O4 and ZnFe2O4/graphene composite are about 20 nm and 10 nm, respectively. Besides, the (0 0 2) diffraction peak of graphene nanosheets located at about 24° in the XRD pattern is found
Conclusion
In summary, ZnFe2O4/graphene nanocomposites with uniformly dispersed ZnFe2O4 nanospheres on the graphene nanosheets have been successfully synthesized by a facile one-pot solvothermal route, and their electrochemical performances are investigated. The ZnFe2O4 nanospheres are composted of numerous nanoparticles around 10 nm. When evaluated as anode for LIBs, the as-prepared ZnFe2O4/graphene nanocomposites show improved cycling performance with a discharge capacity of 704.8 mAh g−1 after 50 cycles
Acknowledgment
This work was supported by the Program for New Century Excellent Talents in University of Ministry of Education of China (NCET-11-1081).
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