多孔碳纳米纤维负载TiO2锂电池负极材料_图文

1、Electrochemistry Communications 13(201110981101Contents lists available at ScienceDirectElectrochemistry Communicationsj o u r n a l h o m e p a g e :w ww. e l s ev i e r. c o m /l o c a t e /e l e c o mNanosized anatase titanium dioxide loaded porous carbon nano ber webs as anode materials for lith

2、ium-ion batteriesXiujuan Yang, Donghua Teng, Bingxue Liu, Yunhua Yu , Xiaoping YangKey Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, Chinaa r t i c l e i n f o a b s t r a c tNanosized anatase titanium dioxide lo

3、aded porous carbon nano bers (TiO2/PCNFswere prepared from electrospun TiO(OAc2/PAN/PMMAcomposite precursor bers with different amount of PMMA porogen, which were sequentially heat-treated in different environments. Electrochemical measurement results show that these as-prepared TiO 2/PCNFspresent h

4、igher cyclic reversible capacity than the TiO 2/CNFscounterpart (withoutPMMA porogen in its precursor bers. Among the as-prepared TiO 2/PCNFssamples, the representative TiO 2/PCNFs(themass ratio of PAN to PMMA is 3:1exhibits the best high-rate performance with a high stable capacity retention about

5、200mAhg 1at a current density as high as 800mAg 1. This novel TiO 2/PCNFscomposite material opens up a promising application in high-power lithium-ion batteries.Crown Copyright ©2011Published by Elsevier B.V. All rights reserved.Article history:Received 26May 2011Received in revised form 23June

6、 2011Accepted 11July 2011Available online 21July 2011Keywords:Titanium dioxidePorous carbon nano ber Electrospinning AnodeLithium-ion battery1. IntroductionAnatase TiO 2has been regarded as a promising high-rate anode material for 2V lithium-ion batteries due to its structural character-istics, low

7、cost, safety and especially the higher lithium intercalation potential to avoid the deposition of metallic lithium 14. Micro-sized bulk anatase TiO 2has poor ion and electron conductivity, which has limited its practical capacity and high-rate capability for reversible lithium insertion and extracti

8、on. So much attention has been paid to producing nanostructured and open-chanelled TiO 2materials, which can provide increased reaction active sites and short diffusion lengths for electron and lithium-ion transport, resulting in improved electrochemical performance 59. However, these nanosized part

9、i-cles usually suffer from serious agglomeration during lithium insertion and extraction, giving rise to poor cycling performance 10,11. Homogeneous dispersion of nanoparticles in a substrate is an effective way to resolve the aggregation problem 12,13. It has been demonstrated that electrospun-deri

10、ved carbon nano bers are prom-ising supports for nanostructured guest materials due to their large speci c surface area, good mechanical property, structural integrity, and high conductivity 14,15. Furthermore, introducing nano-porous structures into carbon nano bers can lead to highly-developed int

11、ernal surface area and more open-channels for ion and electron to migrate rapidly, leading to a superior rate performance 16,17. Accordingly, these porous carbon nano bers are excellent host substrate for active guest materials. However, to the best of ourknowledge, there has been no report on the l

12、ithium storage properties of TiO 2loaded porous carbon nano bers.In this work, nanosized anatase TiO 2loaded porous carbon nano bers (TiO2/PCNFswere facilely fabricated by electrospinning TiO(OAc2/PMMA/PANnano bers containing different amount of PMMA, followed by subsequent thermal treatments. The a

13、s-prepared TiO 2/PCNFswebs as anode materials for LIBs exhibit highly effective lithium storage even at high current rates. 2. ExperimentalA 3g of PAN copolymer bril (Mw=100,000g/mol,93.0wt.%acrylonitrile, 5.3wt.%methylacrylate, and 1.7wt.%itaconic acid, UK Courtaulds Co. and a certain amount of PMM

14、A (Mw=90,000g/molwere dissolved in 30.0ml dimethylformamide (DMFunder magnetic stirring in water bath at 50°Cfor 3h. Mass ratios of PAN to PMMA were 2:1,3:1and 5:1,respectively. A 3.6ml of tetrabutyl titanate Ti(OC4H 9 4was mixed to 2.4ml acetic anhydride to obtain TiO(OAc2solution, which was t

15、hen dropped slowly into each of the PAN:PMMA solutions. Strong magnetic stirring was applied for at least 24h to obtain homogeneous solutions, which were then electrospun following the previous study 18. The as-obtained electrospinning TiO(OAc2/PMMA/PANnano bers were stabilized in air at 280°Cf

16、or 5.5h, and carbonized in highly pure N 2at 600°Cfor 2h to obtain TiO 2/PCNFs.For comparison, TiO 2/CNFswere prepared according to the same procedures but without addition of PMMA into PAN solution (PAN:PMMA=1:0.Surface morphology and interior structure of samples were observed by eld-emission

17、 scanning electron microscopy (FESEM,Hitachi S-4700, 10kV and transmission electron microscopy (TEM,Corresponding author. Tel.:+861064427698; fax:+861064412084. E-mail address:yuyh(Y.H. Yu.1388-2481/$see front matter. Crown Copyright ©2011Published by Elsevier B.V. All rights reserved. doi: 10.

18、1016/j.elecom.2011.07.007X.J. Yang et al. /Electrochemistry Communications 13(2011109811011099Hitachi H-800, 200kV. The average diameters of TiO 2/PCNFsand TiO 2/CNFswere calculated from 100laments based on the FESEM images using Image J software analyzer. The crystal structure was examined by X-ray

19、 diffraction (XRD,Rigaku D/max2500VB2+/PC,Cu K , =0.154nm.Electrochemical tests were performed using 2025coin cells with lithium as counter electrode and Celgard 2300membrane as separator under ambient temperature. The test cells were assembled as our previous study 14. Galvanostatic charge and disc

20、harge were conducted using a battery tester (LANDCT2001A at different current densities of 25, 50, 100, 200, 400and 800mAg 1over the potential range from 0.001to 3.00V. Cyclic voltammetry (CV,0.1-3V, 0.1mVs 1 was performed using an electrochemical working station (VersaSTAT3.3. Result and discussion

21、Fig. 1shows FESEM and TEM images of representative as-prepared TiO 2/PCNFs(PAN:PMMA=3:1and TiO 2/CNFs(PAN:PMMA=1:0.As shown in Fig. 1a and b, the as-prepared samples exhibit a long brous morphology and relatively uniform diameters. Compared to the TiO 2/CNFswith a diameter distribution of 400500nm (

22、Fig. 1b, the TiO 2/PCNFs(Fig. 1a has a much larger diameter in the range of 700800nm due to the addition of PMMA, which has a lower spinability (theability to form bers than PAN 19. Moreover, the decomposition of PMMA and the shrinkage of PAN made TiO 2/PCNFshave much rougher and grooved surface tha

23、n TiO 2/CNFs.Fig. 1c and d shows the SEM images of cross sections of TiO 2/PCNFsand TiO 2/CNFs.Since the elongated PMMA phase decomposes, hollow cores with an average channel diameter of about 20nm are created within a single TiO 2/PCNFsber (Fig. 1c. In addition, the TEM image of TiO 2/PCNFs(Fig. 1e

24、 indicates that long but discontinuous hollow channels are well-developed along the ber axial direction. However, for the TiO 2/CNFs,no visible pores are found in the cross section (Fig. 1d or within a single ber (Fig. 1f. Both the TiO 2/PCNFsand the TiO 2/CNFspresent uniform dark regions, which sug

25、gest the presence and well dispersion of TiO 2in the support of PCNFs or CNFs. The weight percentages of TiO 2in all the TiO 2/PCNFsand TiO 2/CNFssamples are 2530%calculated from quantitative thermogravimetric analysis (TGA,not shown here and energy-dispersive X-ray spectroscopy (EDX,not shown here

26、semi-quantitative data.Fig. 2shows XRD patterns of TiO 2/PCNFs(PAN:PMMA=3:1and TiO 2/CNFs.Both of the samples have broad diffraction peaks near 25°,corresponding to (002crystallographic plane, which indicate the disorder structure of typical carbon materials (JCPDSNo. 130148. Moreover, the othe

27、r diffraction peaks are nearly the same, which proves that the crystal phase and grain size of TiO 2are little affected by the PMMA porogen. The XRD results indicate that the nanoparticles in the samples have a typical anatase phase structure (JCPDSNo. 211272 with highly oriented (101crystal planes

28、at 25.4°,and theirFig. 1. Surface morphology FESEM images of (aTiO 2/PCNFsand (bTiO 2/CNFs.Cross-sectional FESEM images of (cTiO 2/PCNFsand (dTiO2/CNFs.TEM images of (eTiO 2/PCNFsand (fTiO 2/CNFs(TiO2/PCNFs:PAN:PMMA=3:1;TiO 2/CNFs:PAN:PMMA=1:0.1100X.J. Yang et al. /Electrochemistry Communicatio

29、ns 13(201110981101Fig. 2. XRD patterns of (aTiO 2/PCNFs(PAN:PMMA =3:1and (bTiO 2 /CNFs.average grain sizes are about 13nm calculated by Debye Scherrer equation according to the deconvoluted TiO 2patterns.The as-prepared TiO 2/PCNFsand TiO 2/CNFsare in the form of exible webs, so they were directly u

30、sed as electrodes without adding any binder or conductor in electrochemical measurements. Fig. 3a shows the rst charge discharge voltage pro les of the TiO 2/PCNFs(PAN:PMMA=5:1,3:1,and 2:1and TiO 2/CNFs(PAN:PMMA=1:0at a current density of 25mAg 1between a voltage of 0.001and 3.00V. All the TiO 2/PCN

31、Fssamples exhibit higher initial charge capacities and especially higher coulombic ef ciencies than TiO 2/CNFs. The representative TiO 2/PCNFs(PAN:PMMA=3:1presents the rst charge capacity of 687.2mAh g 1and coulombic ef ciencies of 76.3%,while the TiO 2/CNFsonly have the corresponding values of 576.

32、5mAh g 1and 52.7%.The relative low coulombic ef ciency in the rst cycles is a general phenomenon for carbonaceous electrode materials as the existence of irreversible Li insertion sites and the formation of a solid electrolyte interphase (SEI20,21.Fig. 3b shows the representative cyclic voltammogram

33、s (CVof TiO 2/PCNFs(PAN:PMMA=3:1and TiO 2/CNFsat a 0.1mVs 1in the potential range of 0.13V. The broad current peaks below 1.0V are related with the complicated insertion of Li +into the carbon matrix and the formation of SEI lm 22. For the TiO 2/PCNFs,the peak at 0.4V associated with the formation o

34、f SEI lm is more obvious than that of TiO 2/CNFsdue to the existence of hollow cores and resultant larger internal surface area. In addition, a pair of redox peaks between 1.5V and 1.6V can be observed. This is a typical value for the Ti 4+/3+redox couple in an octahedral oxygen environment 23. The

35、broad charge potential peak at about 1.5V has a weakened intensity tendency during the discharge/chargecirculation, which can be ascribed to the different active lithium-ion insertion sites of anatase TiO 2and the spatial trap effect of TiO 2crystal lattice to lithium-ion.Fig. 3c indicates the cycli

36、ng performance of the as-prepared TiO 2/PCNFsand TiO 2/CNFsat different current densities of 25, 50, 100, 200, 400and 800mAg 1. It is interesting to note that except a few preliminary charge/dischargestages dominated by the forma-tion of SEI lms, the capacity of the TiO 2/PCNFsincrease as the amount

37、 of PMMA, but decrease when PAN:PMMA comes to 3:1.With an increase in PMMA amount, both the number of hollow cores and the diameter increase 19. The increased pore volume should promote the capacity of TiO 2/PCNFs,while the thickened diameter should be unfavorable to lithium-ion intercalation. There

38、fore, there should be an optimal PAN:PMMA ratio in the preparation of TiO 2/PCNFs.At the lower current densities below 200mAg 1, the TiO 2/PCNFs(PAN:PMMA=3:1have similar reversible capacities as the TiO 2/PCNFs(PAN:PMMA=5:1,but when the current density in-creases to 800mAg 1, the TiO 2/PCNFs(PAN:PMM

39、A=3:1exhibits higher reversible capacities than other TiO 2/PCNFs(PAN:PMMA=2:1Fig. 3. (aVoltage pro les of TiO 2/PCNFs(PAN:PMMA=2:1,3:1and 5:1and TiO 2/CNFs(PAN:PMMA=1:0at a current density of 25mAg 1; (bCyclic voltammograms of TiO 2/PCNFs(PAN:PMMA=3:1and TiO 2/CNFsat a scan rate of 0.1mVs 1; (cCycl

40、ing performance of TiO 2/PCNFs(PAN:PMMA=2:1,3:1and 5:1and TiO 2/CNFs(PAN:PMMA=1:0at different current densities of 25, 50, 100, 200, 400and 800mAg 1.and 5:1and the TiO 2/CNFs(PAN:PMMA=1:0.Although the capacity tends to decrease with increasing current density, the highest capacity of 200mAhg 1for th

41、e TiO 2/PCNFs(PAN:PMMA=3:1is still obtained at a current density as high as 800mAg 1. On the contrary, the poor cycle performance is inevitable and the discharge capacity is only kept at 20mAhg 1for the TiO 2/CNFs.This superior electrochem-ical performance of the TiO 2/PCNFs(PAN:PMMA=3:1comes from t

42、he combined merits of the unique hollow-core structure of the PCNFs support and the homogeneous dispersion of the nanosized TiO 2. The porous CNFs as an electronic conductor not only ensure good electrical contact during Li insertion/extractionprocess but also provide large electrode/electrolytecont

43、act area and short path length for both electron and lithium ion transports 17. As a result, the as-prepared TiO 2/PCNFswebs show a remarkable improved high-rate performance than TiO 2 /CNFs.X.J. Yang et al. /Electrochemistry Communications 13(20111098110111014. ConclusionsThe TiO 2/PCNFsand TiO 2/C

44、NFswebs directly used as anode materials for LIBs were prepared by electrospinning method and subsequent thermal treatments. The TiO 2/PCNFswebs combine nanosized anatase TiO 2and porous CNFs into one integral entity for lithium storage, exhibiting much higher reversible capacity especially at high

45、current density compared to the TiO 2/CNFs.However, these electrochemical properties of the TiO 2/PCNFswebs are highly dependent on their diameters and hollow core structure, which are closely related to the amount of the PMMA progen. By controlling the amount of the PMMA progen, the as-prepared TiO

46、 2/PCNFs(PAN:PMMA=3:1with a high reversible capacity (200mAhg 1 and good cycling stability at a current density up to 800mAg 1can be obtained.AcknowledgementThe authors acknowledge the nancial support from the National Natural Science Foundation of China (No.51072013. References1S.Y. Huang, L. Kavan

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