H2V3O8与石墨烯复合材料应用到锂离子电池.docx

1、H2V3O8与石墨烯复合材料应用到锂离子电池DOI:10.1002/cplu.201300331Synthesis of H 2V 3O 8/ReducedGraphene Oxide Composite as a Promising Cathode Material for Lithium-Ion BatteriesKai Zhu, aXiao Yan, aYongquan Zhang, aYuhui Wang, aAnyu Su, aXiaofei Bie, aDong Zhang, aFei Du, aChunzhong Wang, a,bGang Chen, a,band Yingji

2、n Wei*aIntroductionIn recent years, electricity generation from wind and solar energy has improved greatly with because of the contributions made by global scientists. 1In addition, hybrid electric vehicles (HEVshave been recognized as replacements for fuel vehicles in the near future to reduce foss

3、il fuel consumption and CO 2emissions. All these green-energy techniques need to be sup-ported with large-scale energy-storage devices. It is generally accepted that lithium-ion batteries are the most suitable energy-storage systems among the various possibilities. 2,3However, it is difficult for th

4、e traditional LiCoO 2cathode to meet the increasing demands of large-scale lithium-ion batter-ies in the aspects of energy/powerdensities, safety, and price. 4,5Therefore, the search for new cathode materials has become a serious issue for the next generation of lithium-ion batteries.Vanadium oxides

5、 such as V 2O 5, VO 2, V 2O 5n H 2O xerogel, b -AgVO 3, and LiV 3O 8, with typical open-layered structures, allow the intercalation of guest molecules or cations into the layers. 6,7In lithium-ion batteries, these open-layered structures offer much higher specific energies than many other cathode ma

6、terials such as LiCoO 2and LiFePO 4. Another vanadium oxide, H 2V 3O 8, has been reported as a promising cathode ma-terial since 2006. 8In recent years, several attempts have beenmade to prepare H 2V 3O 8nanomaterials to improve its electro-chemical properties. 812It has been reported that H 2V 3O 8

7、nanobelts exhibit a very high initial discharge capacity of 373mA h g 1. 10However, the cycle life and rate capability of the material are greatly restricted because of its large irreversi-ble capacity and low electronic conductivity. 9The electronic conductivities of electrode materials can be impr

8、oved through their combination with highly conductive carbonaceous mate-rials. 13,14Recently, composite electrodes that interconnect nanostructured electrode materials with graphene have at-tracted much attention. 15In general, the graphene in the composite electrodes can act both as conductive chan

9、nels and as an elastic buffer to accommodate the volume change that occurs during repeated lithium uptake and removal, simultane-ously preventing the aggregation of nanoparticles and the cracking or crumbling of the electrode materials. 1518There-fore, it seems to be an ideal reinforcing component f

10、or compo-site electrodes. Many graphene-based electrode materials such as V 2O 5/graphene,19V 2O 5n H 2O xerogel/graphene,20TiO 2/gra-phene, 21SnO 2/graphene,22Co 3O 4/graphene,23and Fe 3O 4/gra-phene 24have been reported so far, all of which showed im-proved electrochemical properties with respect

11、to their pristine counterparts. However, to the best of our knowledge, no nano-structured H 2V 3O 8/graphenecomposite material has yet been reported.Herein, a H 2V 3O 8/reducedgraphene oxide (RGOcomposite cathode was fabricated through a simple approach, as illustrat-ed in Figure 1a. Graphene oxides

12、 prepared through a modified Hummers method were mixed with HVO 4formed from the re-action of V 2O 5and H 2O 2. Under hydrothermal conditions, the composites self-assembled into H 2V 3O 8/RGOnanostructures, in which the electron transport through the H 2V 3O 8nanowires was improved owing to the pres

13、ence of the highly conductiveaK. Zhu, X. Yan, Y. Zhang, Y. Wang, A. Su, Dr. X. Bie, Dr. D. Zhang, Dr. F. Du,Prof. Dr. C. Wang, Prof. Dr. G. Chen, Prof. Dr. Y. WeiKey Laboratory of Physics and Technology for Advance Batteries Ministry of Education, College of PhysicsJilin University, Changchun 130012

14、(P. R. China Fax:(+86 431-85155126E-mail:yjweibProf. Dr. C. Wang, Prof. Dr. G. ChenState Key Laboratory of Surperhard Materials Jilin University, Changchun 130012(P. R. ChinaCHEM PLUS CHEM FULL PAPERSRGO nanosheets (Figure1b. Moreover, RGO suppressed the structural degradation of H 2V 3O 8during cha

15、rge/discharge,im-proving the electrochemical performance of the material signif-icantly.Results and Discussion The phase and composition of the as-obtained H 2V 3O 8andH 2V 3O 8/RGOproducts were analyzed by XRD as depicted inFigure 2. All the XRD peaks can be indexed readily to the or-thorhombic cry

16、stalline phase of H 2V 3O 8(spacegroup:Pnam . 25No characteristic peaks from impurities of other vanadiumoxides are detected, which indicates that the products consistof a pure H 2V 3O 8phase. The calculated lattice parameters ofthe products are a =9.373(3,b =16.939(7,c =3.649(6 forthe pristine samp

17、le, and a =9.353(1,b =16.932(0,c =3.646(4 for the H 2V 3O 8/RGOcomposite, which are in good agreement with previously reported values (JCPDS,No. 85-2401. The slight differences in the lattice parameters may be caused by different hydrothermal conditions with/withoutthe addition of graphene oxide sol

18、ution. In addition, a small dif-fraction peak can be observed at 26.58for H 2V 3O 8/RGO,which is absent for the pristine material. This additional peak can be indexed to the disordered 002stacking layers of RGO, 19,26indi-cating that the composite is fabricated successfully through the present synth

19、etic route. For the determination of the exact amount of RGO, thermogravimetric analysis (TGAwas per-formed on H 2V 3O 8and the H 2V 3O 8/RGOcomposite (Figure3.For the pristine H 2V 3O 8, the weight loss of 4.4wt %before 6008C is caused by the decomposition of H 2V 3O 8. A largerweight loss of 10.7w

20、t %is observed for H 2V 3O 8/RGO,whichmay be attributed to the combustion of RGO together with the decomposition of H 2V 3O 8. On the basis of these results, the mass content of RGO in the H 2V 3O 8/RGOcomposite is estimat-ed to be 6.3wt %.Figure 4a,b shows SEM images of the H 2V 3O 8and H 2V 3O 8/R

21、GO products. The pristine sample consists of a large number of uniform nanowires with a high aspect ratio:50200nm in width and several micrometers in length. From the SEM image of H 2V 3O 8/RGO,it is apparent that the H 2V 3O 8nano-wires are dispersed on the RGO layer. The graphene oxides, with abun

22、dant functional groups such as hy-droxyl, carboxyl, and carbonyl groups, attach easily onto the surface of H 2V 3O 8and are converted to re-duced graphene oxides during hydrothermal treat-ment. In the meantime, the H 2V 3O 8nanowires help prevent the RGO from uniting in the reduction pro-cess. This

23、nanoarchitectured wrapping layer of RGO sheets formed on the H 2V 3O 8surface can act as an electronic conductive skin. For further characteriza-tion of the microstructure of the H 2V 3O 8/RGOcompo-site, TEM was performed as shown in Figure 4c. This shows clearly that the H 2V 3O 8nanowires are anch

24、-ored intimately on the RGO sheets. In this case, it is anticipated that once the electrons arrive at RGO Figure 1. a Schematic of the synthesis route for the H 2V 3O 8and H 2V 3O 8/RGOmaterials, and b the ideal electron transportation pathway in the H 2V 3O 8/RGO composite.Figure 2. XRD patterns of

25、 pristine H 2V 3O 8and the H 2V 3O 8/RGOcomposite compared withthe standard XRD pattern for H 2V 3O 8 (PDF#85-2401.Figure 3. TGA curves of pure H 2V 3O 8and the H 2V 3O 8/RGOcomposite. they can transfer quickly to the H 2V 3O 8nanowires. Thus, an im-proved electrical conductivity of the composite wo

26、uld be ex-pected. The high-resolution TEM image (Figure4d exhibits a lattice fringe corresponding to a d -spacing of 0.33nm, which is in agreement with the d 101spacing of H 2V 3O 8. The local structures of the materials were studied further through Raman scattering experiments, as shown in Figure 5

27、, together with that of pure graphene oxide. Note that the Raman patterns of H 2V 3O 8/RGOand graphene oxide are multi-plied by ten because of their rather weak peak intensities. The basic structural units of H 2V 3O 8are composed of VO 6octahedra and VO 5trigonal bipyramids, which form the V 3O 8la

28、yers by sharing edges. 11The Raman spectra of H 2V 3O 8can be ana-lyzed in terms of internal and ex-ternal vibrations (similarlyto those of most vanadium oxides. The internal modes can be de-scribed as stretching and bend-ing vibrations of the V O bonds. These vibrations give rise to the high-freque

29、ncy Raman bands above 200cm 1. The external modes can be viewed as relative motions of the V 3O 8layers, which are located at low fre-quencies below 200cm 1. The internal and external vibrations of pristine H 2V 3O 8and H 2V 3O 8/RGO appear at the same posi-tions within an error of 2cm 1, indicating

30、 that the RGO in the composite does not influence the local structure of H 2V 3O 8. There are two prominent Raman peaks at 1330cm 1and1601cm 1for the H 2V 3O 8/RGOcomposite, which are absent for the pristine H 2V 3O 8. These ad-ditional peaks correspond to the D and G bands of RGO. 24Theintensity ra

31、tio of the D to G bands (I D /I G is a measure of disor-der in carbon-based materials. The I D /I G value of graphene oxide is calculated to be 0.86. After the reduction of graphene oxide, defects in the resultant RGO increase owing to fragmen-tation along the reactive site, a larger number of edges

32、, and so on. This results in broader D and G bands, and the I D /I G ratio of RGO increases to 1.15. In addition, there is a distinctive peak at 876cm 1, which is caused by the V C linkage between RGO and H 2V 3O 8. According to previous reports, such a bridge be-tween the active material and RGO may produce a synergistic effect that improves the lithium-storage behavior. 27Further-more, the scattering background of the H 2V 3O 8/RGOcomposite is very strong, and the Raman peaks are much weake