H2V3O8与石墨烯复合材料应用到锂离子电池.

1、D0l:10.1002/cplu.201300331Syn thesis of H 2V 30 8/ReducedGraphe ne Oxide Composite as a Promisi ng Cathode Material for Lithium-Io n BatteriesKai Zhu, aXiao Yan, aYo ngquan Zha ng, aYuhui Wang, aA nyu Su, aXiaofei Bie, aDo ng Zhang, aFei Du, aCh un zho ng Wang, a,bGa ng Chen, a,ba nd Yingjin Wei*aIn

2、 troduct ionIn rece nt years, electricity gen eratio n from wind and solar en ergy has improved greatly with because of the contributions made by global scientists. 1In addition, hybrid electric vehicles (HEVshave bee n recog ni zed as replaceme nts for fuel vehicles in the near future to reduce fos

3、sil fuel con sumpti on and CO 2emissi ons. All these gree n-en ergy tech niq ues n eed to be sup-ported with large-scale en ergy-storage devices. It is gen erally accepted that lithium-i on batteries are the most suitable en ergy-storage systems among the various possibilities. 2,3However, it is dif

4、ficult for the traditional LiCoO 2cathode to meet the in creas ing dema nds of large-scale lithium-i on batter-ies in the aspects of en ergy/powerde nsities, safety, and price. 4,5Therefore, the search for new cathode materials has become a serious issue for the next generation of lithium-ion batter

5、ies.Va nadium oxides such as V 20 5, VO 2, V 20 5n H 20 xerogel, b -AgVO 3, and LiV 30 8, with typical ope n-layered structures, allow the in tercalati on of guest molecules or cations into the layers. 6,7In lithium-ion batteries, these open-layered structures offer much higher specific en ergies th

6、a n many other cathode materials such as LiCoO 2and LiFePO 4. Ano ther van adium oxide, H 2V 30 8, has bee n reported as a promisi ng cathode ma-terial since 2006. 8In recent years, several attempts have beenmade to prepare H 2V 30 8nano materials to improve its electro-chemical properties.8 -2It ha

7、s been reported that H 2V 30 8nanobelts exhibit a very high initial discharge capacity of 373mA h g a 1. 10However, the cycle life and rate capability of the material are greatly restricted because of its large irreversi-ble capacity and low electro nic conductivity. 9The electronic conductivities o

8、f electrode materials can be improved through their comb in ati on with highly con ductive carb on aceous mate-rials.13,14Rece ntly, composite electrodes that in terc onnect nano structured electrode materials with graphene have at-tracted much attention. 15In general, the graphene in the composite

9、electrodes can act both as con ductive cha nn els and as an elastic buffer to accommodate the volume cha nge that occurs duri ng repeated lithium uptake and removal, simulta ne-ously preve nti ng the aggregatio n of nan oparticles and the crack ing or crumbling of the electrode materials. 15-8There-

10、fore, it seems to be an ideal rei nforci ng comp onent for compo-site electrodes. Many graphe ne-based electrode materials such as V 20 5/graphe ne,19V 20 5n H 20 xerogel/graphe ne,20TiO 2/gra- phe ne, 21S nO 2/graphe ne,22Co 30 4/graphe ne,23a nd Fe 30 4/gra-phe ne 24have bee n reported so far, all

11、 of which showed im-proved electrochemical properties with respect to their prist in e coun terparts. However, to the best of our kno wledge, no nanostructured H 2V 30 8/graphe necomposite material has yet bee n reported.Herein, a H 2V 30 8/reducedgraphe ne oxide (RG0composite cathode was fabricated

12、 through a simple approach, as illustrat-ed in Figure 1a. Graphene oxides prepared through a modified Hummers method were mixed with HV0 4formed from the re-actio n of V 20 5and H 20 2. Un der hydrothermal con diti ons, the composites selfassembled into H 2V 30 8/RG0 nano structures, in which the el

13、ectro n tran sport through the H 2V 30 8nanowires was improved owing to the presence of the highlycyclic performance, and rate capability. The man high discharge capacities of 256 and 117 mAhg ftnt densities of 0.1 dnd 1 Ag , respectively, with capacity fading after fifty charge/discharge cycles, ta

14、mmeiry and electrochemical impedance spearos that the superioT electrochemical performance of 卜 can be attributed to the cooperation of RGO, wh(t better mechdrical flexibility higher electronic candi smaMer charge-transfer resistance,HjVjOu no wires wrapped by reduced graphene oxide (RGO) are synthe

15、sized successfully through a simple hydrothermal process. The siructuraf properties of the samples are charseter- ized by X-ray diffracdon, Kanning electron microscopy transmission electron microscopy, ftaman scattertng, and X*ray pho- loelectron spe匚i he RGO nanosheets modify the suf faces of the H

16、jVjOu nanowires through V-C linkages. The HjVjOu/RGO composite exhibits a remarkably enhanced elec- nochemkdl performance in terms of its reversible capacity,con ductiveaK. Zhu, X. Ya n, Y. Zha ng, Y. Wang, A. Su, Dr. X. Bie, Dr. D. Zha ng. Dr. F. Du,Prof. Dr. C. Wang, Prof. Dr. G. Che n, Prof. Dr.

17、Y. WeiKey Laboratory of Physics and Tech no logy for Adva nee Batteries Mini stry ofEducati on, College of PhysicsJilin University, Changchun 130012(P. R. China Fax:(+86 431-85155126E-mail:yjweibProf. Dr. C. Wang, Prof. Dr. G. ChenState Key Laboratory of Surperhard Materials Jili n Uni versity, Chan

18、 gch un130012(P. R. Chi naCHEM PLUS CHEM FULLPAPERSRGO nano sheets (Figurelb. Moreover, RGO suppressed the structural degradati on of H 2V 3O 8duri ng charge/discharge,im-pro ving the electrochemical performa nee of the material sig nif-ica ntly.Results and Discussi on The phase and compositi on of

19、the as-obta ined H 2V 3O 8a ndH 2V 3O 8/RGOproducts were an alyzed by XRD as depicted inFigure 2. All the XRD peaks can be indexed readily to the or-thorhombic crystalline phase of H 2V 3O 8(spacegroup:Pnam . 25No characteristic peaks from impurities of other van adiumoxides are detected, which in d

20、icates that the products con sistof 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 sample, and a =9.353(1,b =16.932(0,c =3.646(4 for the H 2V 3O 8/RGOcomposite, which are in good agreeme nt with previously reported values

21、 (JCPDS,No. 85-2401. The slight differe nces in the lattice parameters may be caused by differe nt hydrothermal con diti ons with/withoutthe additi on of graphe ne oxide soluti on. In addition, a small dif-fraction peak can be observed at 26.58for H 2V 3O 8/RGO,which is absent for the pristine mater

22、ial. This additional peak can be indexed to the disordered 002stacking layers of RGO, 19,26indi-cating that the composite is fabricated successfully through the prese nt syn thetic route. For the determ in ati on of the exact amount of RGO, thermogravimetric an alysis (TGAwas per-formed on H 2V 3O 8

23、and the H 2V 3O 8/RGOcomposite (Figure3.For the prist ine H 2V 3O 8, the weight loss of 4.4wt %before 6008C is caused by the decompositio n of H 2V 3O 8. A largerweight loss of 10.7wt %is observed for H 2V 30 8/RG0,whichmay be attributed to the combusti on of RGO together with the decompositi on of

24、H2V 3O 8. On the basis of these results, the mass conten t of RGO in the H 2V 30 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/RGO products. The prist ine sample con sists of a large nu mber of un iform nano wires with a high aspect ratio:50-20

25、0nm in width and several micrometers in len gth. From the SEM image of H 2V 3O 8/RGO,it is ap pare nt that the H 2V 3O 8nano-wires are dispersed on the RGO layer. The graphe ne oxides, with abundant fun cti onal groups such as hy-droxyl, carboxyl, and carb onyl groups, attach easily onto the surface

26、 of H 2V 3O 8and are conv erted to re-duced graphe ne oxides duri ng hydrothermal treat-me nt. In the mean time, the H 2V 3O 8nano wires help preve nt the RGO from un it ing in the reduct ion pro-cess. This nano architectured wrapp ing layer of RGO sheets formed on the H 2V 3O 8surface can act as an

27、 electr onic con ductive skin. For further characteriza-ti on 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-ored intimately on the RGO sheets. In this case, it is anticipated that once the electr

28、 ons arrive atIF 吏=7=m-PDF#!7Q10MV05026/StirriBy5 s(IA.Oj RGORGO Figure 1. a Schematic of the sy nthesis route for the H 2V 3O 8a nd H 2V 3O8/RGOmaterials, and b the ideal electro n tran sportatio n pathway in the H 2V 3O 8/RGOrrlyAI 胡 UMUPDF#851020304050607026 / degreescomposite.Figure 2. XRD patte

29、rns of pristine H 2V 30 8and the H 2V 30 8/RGOcompositecompared withthe sta ndard XRD pattern for H 2V 30 810203040nn 1 a.(PDF#85-2401.Figure 3. TGA curves of pure H 2V 30 8and the H 2V 3O 8/RGOcomposite.they can tran sfer quickly to the H 2V 30 8nano wires. Thus, an im-proved electricalcon ductivit

30、y of the composite would be ex-pected. The high-resoluti on 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 30 8. The local structures of the materials were studied further through Rama n scatteri ng experime

31、nts, as show n in Figure 5, together with that of pure graphe ne oxide. Note that the Rama n patter ns of H 2V 30 8/RG0a nd graphe ne oxide are multi-plied by ten because of their rather weak peak inten sities. The basic structural un its of H 2V 30 8are composed of VO 6octahedra and VO 5trig onal b

32、ipyramids, which form the V 30 8layers by shari ng edges. 11The Raman spectra of H 2V 30 8can be ana-lyzed in terms of internal and ex-ternal vibrations (similarlyto those of most vanadium oxides. The internal modes can be described as stretchi ng and ben d-i ng vibrati ons of the Va 0 bon ds. These

33、 vibrati ons giverise to the high-freque ncy Rama n bands above 200cma 1. The exter nal modes can beviewed as relative motio ns of the V 30 8layers, which are located at low fre-que ncies below 200cm a 1. The in ternal a nd external vibratio ns of pristi ne H 2V 30 8a nd H 2V30 8/RG0 appear at the s

34、ame posi-ti ons with in an error of 2cma 1, in dicati ng that theRGO in the composite does not in flue nce the local structure of H 2V 30 8. There are two prominent Raman peaks at 1330cm a land1601cm a 1for the H 2V 30 8/RGOcomposite, which are absent for the pristine H 2V 30 8. These ad-ditional pe

35、akscorrespond to the D and G bands of RG0. 24Theinten sity ratio of the D to G bands (I D /I G is a measure of disor-der in carb on-based materials. The I D /I G value of graphene oxide is calculated to be 0.86. After the reducti on of graphe ne oxide, defects in the resulta nt RG0 in crease owing t

36、o fragme n- tati on along the reactive site, a larger nu mber of edges, and so on. This results in broader D and G ban ds, and the I D /I G ratio of500100015002000RamHn Shirt /cm 1a 1, whRGO in creases to 1.15. In additi on, there is a dist in ctive peak at 876cm caused by the V a C linkage between

37、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 scatteri ng backgro und of the H 2V 3O 8/RGOcomposite is very strong, and the Rama n peaks are much we

38、aker than those of pristine H 2V 3O 8. Even though many factors can affect the inten sities of Rama n spectra, we can rule out the effects of measureme nt con diti ons here because all the experime nts were performed un der the same con diti ons (in clud in gsample amount, laser power, scattering ti

39、me, etc. Therefore, the dif-ferences in Raman intensity can only be attributed to the in-trinsic properties of the samples. It is clear from the Rama n spectra that the local structure of H 2V 3O 8is not cha nged upon the additi on of RGO. However, most of the in cide nt phot onsare absorbed by RGO

40、because of its high electronic conductivi-ty, so only a small fraction of the phot ons are scatteredby Figure 4. SEM images of a prist ine H 2V 3O 8a nd b the H 2V 3O 8/RGOcomposite. c TEM and d HRTEM images of theH 2V 3O 8/RGOcomposite.Figure 5. Raman spectra of prist ine H 2V 3O 8, the H 2V 3O 8/R

41、GOcomposite, andgraphe ne oxide (GO.The Raman patterns of H 2V 3O 8/RGOa nd graphe neoxide are multiplied by ten because of their rather weak peak inten sities.H 2V 3O 8. Therefore the overall Rama n in ten sity is decreased sig-n ifica ntly.The chemical compositi ons and states of the H 2V 3O 8/RGO

42、composite and graphe ne oxide were inv estigated through X-ray photoelectro n spectroscopy (XPS.TheXPS survey spec-trum in Figure 6a reveals that the H 2V 30 8/RG0sample con sists of van adium, oxyge n, and carb on eleme nts. Hydroge n is not observed because it is not sen sitive to XPS. The V 2p 3/

43、2(Fig-ure 6b core level peak can be divided into three constituents, corresponding to V 5+(517.8eV, V 4+(516.2eV, 11and the Va C bond(516.9eV. 28Quan tificati on of the peak areas shows that the surface ratio of V 5+/V4+isapproximately two, which is very close to the chemical stoichiometry of V 5+/V

44、4+in H 2V 30 8. The C 1s XPS peak of graphe ne oxide (Figure6c contains four typical components corresp onding to the carb on atoms in functional groups:the nono xyge nated C ring (284.7eV, and the hydroxyl or epoxide (286.4eV, carbo nyl (287.1eV, and carboxyl (288.6eV groups. 29This suggests that a

45、 relatively high degree of oxidati on was achieved duri ng preparati on through the Hummers method. After the hydrothermal treatme nt (Fig-ure 6d, the relative inten sities of the three oxyge n-containing fun cti onal groups decrease markedly, suggesti ng that the gra-phe ne oxide is reduced success

46、fully.The C 1s peak at 282.3eV is attributed to the Va C bond, 28which indicates that the H2V 30 8nanowires are anchored on the RGO sheets through a Va C linkage.Figure 7compares the CV curves of H 2V 30 8and H 2V 30 8/RG0in the voltage range 3.75-.5V at a scan rate of 0.05mV sa 1.For the pristine H

47、 2V 30 8, there are three reduction peaks in the first scan, which correspond to a series of structural transitions during the Li +intercalation pro-cess, as described in previous re-ports. 9The curre nt peaks become weaker and weaker in the subseque nt sca ns, in dicati ng continu ous capacity fadi

48、 ng and irreversible structural tran siti ons with repeated electrochemical react ions. In con trast, the H 2V 30 8/RG0composite shows much stron ger curre nt peaks in the first sca n. Moreover, the in te- grated area of the CV curve is larger, indicating a larger Li +ion capacity. Although the curr

49、ent peaks become weaker in the subsequent scans, they can still be distinguished afterfive sea ns. This implies that the H 2V 30 8/RGOcomposite has better structural and electrochemical reversibility tha n pristi ne H 2V 30 8.The electrochemical properties were characterized400Hindi ng毎肌 BSIC 522E2B

50、Biiidknu 附irergy阳、(WhVoJrgo1 1 * 2pJT-?.9.7白倉=o i -a20a為Binding EC IsZMJH 諸29QHind in p Encry.tfurtherFigure 6. a XPS survey spectrum of the H 2V 30 8/RG0composite. b V 2p XPS ofthe H 2V 30 8/RG0composite. c C 1sXPS of G0. d C 1s XPS of the H 2V 30 8/RG0Po =-_ l_Tf =u-0 卫冒iP1T2 3 + 4i I.i LJ )jn nnc

51、omposite.Figure 7. CV curves of a pristine H 2V 30 8and b the H 2V 30 8/RGOcomposite inthe in itial five cycles at a sca n rate of 0.05mV sa 1.through discharge/chargecycli ng experime nts. Figure 8dis-plays the voltage profiles of the materials at a curre nt den sity of 0.1A ga 1. It is clear that

52、the H 2V 308/RG0composite mai n-tai ns very good S-shaped voltage profiles, whereas those of H 2V 30 8become slope-like after the first cycle. These features corresp ond well with the CV measurements, again confirming that the RG0 in the composite helps the material maintain good electrochemical rev

53、ersibility. The in itial discharge/chargecapacities of the prist ine H 2V 30 8are 200a nd 169mA h ga 1, re-spectively. A small in itial Columbicefficie ncy of 84.5%is ob-ta ined owi ng to the irreversible structural tran siti ons, which give rise to some “ deadLi sites ” in the material. AftentoeRG0

54、, the firsta 1,discharge/chargecapacities of H 2V 30 8/RG0 in crease to 268a nd 256mA h g respectively, which are much higher than those of pristine H 2V 30 8. In addition, the Co-lumbic efficie ncy in creases to 95.5%.This in dicates that the RGO in the composite may suppress the irreversible elect

55、ro-chemical reacti ons of H 2V 3O 8.Figure 9shows the charge/dischargecapacities and Columb-ic efficie ncies of the materials over 50charge/dischargecycles. Both materials show fast capacity decay in the sec ond cycle. However, the capacity decay of H 2V 3O 8/RGO(7.8%is much smaller than that of pri

56、st ine H 2V 3O 8(25%at a curre nt den sity of 0.1A ga 1(Figure9a. Uponfurther cycli ng, the composite cathode shows almost no capacity decay, exhibit ing a high dis-charge capacity of 248mA h ga lafter 50cycles. In contrast, the pristine H 2V 3O8undergoes continuous capacity decay, decreas-es to 116

57、mA h ga lafter 50cycles. Withan in creased curre ntden sity of 1A ga 1(Figure9b, the reversible discharge capacity of pristi ne H 2V 3O8sudde nly decreases to 15mA h ga 1, whereas the H 2V 3O 8/RGOcomposite still has alarge discharge capacity of 117mA h ga 1. This in dicates that the H 2V 3O8/RGOcom

58、posite has a better rate performa nee tha n prist ine H 2V 3O 8.Electrochemical impeda nee spectroscopy was performed to study the kin etic properties of the materials. Figure 10a dis-plays the Nyquist plots of the materials at the state of charge of 3.75V. The high-freque ncy in tercepts, which corresp ond