Nanocomposite polymer electrolytes were prepared by incorporating different amounts of zirconium oxide (Zr02) nanofiller to poly(vinylidene fluoride-co exafluoropropylene)-lithium trifluoromethane sulfonate (PVDF-HFP-LiCF3S03). X-ray diffraction (XRD) study has been carried out to investigate the structural features of the electrolyte films while a.c. impedance spectroscopy has been performed to investigate their electrical properties. The conductivity of nanocomposite polymer electrolyte systems is influenced by nanofiller concentration. The increase in conductivity is attributable to the increase in the fraction of amorphous region and the number of charge carriers and vice versa. The highest conductivity obtained is in the order of 10-3 S cm-1 for the system dispersed with 5 wt% of Zr02 nanofiller

Hashim Ali, S.A.

Ibrahim, S.

Mohamed, N.S.

UM Digital Repository

(;._)Advanced Materials Research Vols. 93-94 (2010) pp 489-492© (2010) Trans Tech Publications, Switzerlanddoi:1O.4028Iwww.scientific. netiAMR. 93-94. 489Characterization of PVDF-HFP-LiCF3S03-Zr02 Nanocomposite PolymerElectrolyte SystemsSalmiah Ibrahim 1,a, Siti Aishah Hashim Ali2,b, Nor Sabirin Mohamed!""Center for Foundation Studies in Science, University of Malaya, 50603 Kuala Lumpur, Malaysia21nstituteof Mathematical Sciences, Faculty of Science, University of Malaya, 50603 KualaLumpur, Malaysiaasalmiah01@um.edu.my, bsaishah@um.edu.my, cnsabirin@um.edu.myKeywords: conductivity, XRD, dielectricAbstract. Nanocomposite polymer electrolytes were prepared by incorporating different amountsof zirconium oxide (Zr02) nanofiller to poly(vinylidene fluoride-co-hexafluoropropylene)-lithiumtrifluoromethane sulfonate (PVDF-HFP-LiCF3S03). X-ray diffraction (XRD) study has been carriedout to investigate the structural features of the electrolyte films while a.c. impedance spectroscopyhas been performed to investigate their electrical properties. The conductivity of nanocompositepolymer electrolyte systems is influenced by nanofiller concentration. The increase in conductivityis attributable to the increase in the fraction of amorphous region and the number of charge carriersand vice versa. The highest conductivity obtained is in the order of 10-3 S cm-1 for the systemdispersed with 5 wt% of Zr02 nanofiller.IntroductionPolymer electrolytes are prorrusmg materials for electrochemical device applications, namelyrechargeable batteries, fuel cells, supercapacitors, hybrid power sources, display devices, sensorsetc [1-3]. This type of electrolytes has many advantages which include high ionic conductivity, highspecific energy, wide electrochemical stability window, light and easy processibility. In general, theconductivity of a polymer electrolyte increases as the degree of crystallinity decreases or in otherwords, as the flexibility of the polymeric backbone increases. One of the various methods that havebeen employed to enhance the conductivities of polymer-salt electrolytes is to form compositeelectrolyte systems by using organic or inorganic filler as additives. It has been reported that theaddition of fillers such as Al0203, Ti02, BaTi03 and Si02 yields significant enhancements inconductivities [4-9]. In these cases, the fillers may act as solid plasticizers or salt dissociationpromoters due to their high values of ferroelectricity. In this study, the authors have preparednanocomposite polymer electrolytes using PVDF-HFP copolymer as the host, LiCF3S03 as dopingsalt and Zr02 in nano size as the filler.Experimental MethodsThe polymer electrolyte systems studied in this work were prepared by mixing and stirring ofPVDF-HFP (Mw - 400,000 g mol") and LiCF3S03 of a fixed polymer:salt wt% ratio in N-NDimethyl formamide (DMF) to form solutions. The PVDF-HFP-LiCF3S03 solutions were thenadded with different amounts (1 to 8 wt%) of Zr02 nanofiller (particle size: 29-60 nm) and furtherstirred to form homogeneous solutions. The homogeneous solutions were then cast into glass Petridishes and allowed to evaporate slowly to form films. In this study, the PVDF-HFP:LiCF3S03 wt%ratio was fixed at 55:45. This is based on the authors' prior study which showed that this ratioyielded polymer-salt electrolyte system with the highest conductivity.Ionic conductivities of the polymer electrolyte systems were evaluated by impedance spectroscopyin the frequency range 42 Hz to 5 MHz using HIOKI 3532-50 LCR HiTester. In order to study theconductivity behaviour of the polymer electrolytes, the results of impedance measurements wereAll rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of thepublisher: Trans Tech Publications Ltd, Switzerland, WWW.ttp.net. (10: 202.185.78.6-21/12109,06:46:10){(Jn~ull(ommenl((mun490 Functionalized and Sensing Materialsalso presented in dielectric constant, Cr formalism. The structural features of the electrolytes studiedin this work were investigated by X-ray diffraction done in the scanning angle 28 from 10° to 60°using D8 Advance X-Ray Diffractometer-Bruker AXS with Cu-K, monocromatized radiation atroom temperature.Results and DiscussionThe XRD patterns of PVDF-HFP and PVDF-HFP-LiCF3S03 dispersed with different wt% of Zr02studied in this work are shown in Fig. 1. The XRD spectrum of PVDF-HFP-LiCF3S03 exhibits abroad peak at 28 of 20.2° corresponding to the PVDF crystalline peak [10]. The intensity of thispeak decreases with the increase in Zr02 nanofiller concentration up to 5 wt%. This indicates thatthe fraction of crystalline phase in the polymer matrix decreases with increasing nanofillerconcentration. However, further increase in filler concentration resulted in an increase in theintensity of the peak indicating an increase in the crystalline phase fraction in the polymer matrix.The peaks at 28.5°, 31.7° and 34.5°, which can be clearly seen in the XRD spectra ofnanocomposite electrolyte containing 7 wt% of nanofiller, correspond to Zr02 peaks. Peakscorresponding to the LiCF3S03 are not observed in all of the XRD spectra indicating that LiCF3S03is completely complexed in the polymer matrix.Fig. 1: XRD patterns of(a) PVDF-HFP and PVDF-HFP-LiCF3S03 containing (b) 0, (c) 1,(d) 5 and (e) 7 wt% of Zr02.10 20 40 50Fig. 2 depicts the variation of e, with frequency for PVDF-HFP-LiCF3S03-Zr02 nanocompositeelectrolytes. The value of Cj was obtained using the equation .where Co = coAlt, Co is the permittivity of free space, OJ is the angular frequency, Zr and Z, are thereal and imaginary parts of complex impedance obtained from impedance measurements.According to Bhide and Hariharan [11] and Mishra and Rao [12], the high values of dielectricconstant in the low frequency range as observed in Fig. 2 are assigned to the accumulation ofcharges at the electrode-electrolyte interfaces during the impedance measurements. As can be seenfrom this figure, the e, undergoes a gradual increase with increasing Zr02 nanofiller concentrationup to 5 wt% after which it decreases with further increase of nanofiller concentration. Since theconductivity in the electrolyte systems is attributable to the migration of Li+ ions, the increase in e,reflects the increase in the charge carrier concentration in the polymer matrix and vice versa.(1)(()II~uhAdvanced Materials Research Vols. 93-94 4913.00E+06 -,-------------------~•2.00E+06••... • •t.J • •• •1.00E+06 - • ••.. ,~~•• •.~•,,..O.OOE+OO2.00 3.00 4.00• (a)• (b)• (c)- (d)0-...5.00Log (J) (Hz)6.00Fig. 2: Frequency dependenceof dielectric constant forPVDF-HFP-LiCF3S03containing (a) 1, (b) 3, (c) 5and (d) 7 wt% of Zr02.7.00The variation of room temperature conductivity, (J as a function of Zr02 concentration is shown inFig. 3. The figure reveals that the ionic conductivity increases with the increase in fillerconcentration and reaches a maximum value when the concentration of the nanofiller is 5 wt%. Theconductivity decreases for nanofiller concentration of greater than 5 wt%. Based on the results ofXRD and dielectric constant studies discussed earlier, the enhancement of conductivity can beattributed to the increase in the amorphous region and number of mobile ions in the nanocompositesystems and vice versa. This can be explained in terms of Lewis acid-base interactions amongPVDF, LiCF3S03 and Zr02 in the systems [13-15]. Such interactions produced greater number ofcharge carriers (Lt) and more amorphous region for charge carriers to transfer. Increasing thenanofiller concentration led to an increase in the number of charge carriers and amorphous fraction.Hence, the conductivity of nanocomposite increases as the concentration of nanofiller is increased.However, excessive addition of Zr02 filler resulted in the aggregation of the nanofiller particles.This is supported by the presences of Zr02 peaks in the XRD spectra. The aggregation ofnanoparticles reduced the effective number of nanofiller particles available for Lewis acid-baseinteractions. This explains the decrease in conductivity as shown in Fig.3.1.00E-02 .----------------------,1.00E-03I.OOE-04o 2 3 4 5 6 7Concentration erz-o, (%)Fig. 3: Variation of roomtemperature conductivity, as afunction of Zr02 concentration.8(1)"'UII~OIlUl,~nllOllta(!492 Functionalized and Sensing MaterialsConclusionThe enhancement of conductivity of the PVDF-HFP-LiCF3S03 upon addition of the Zr02 nanofillerup to 5 wt% electrolyte is attributed to the increase in amorphous region and concentration ofmobile ions. The decrease in conductivity of the electrolyte systems with high concentration of thenanofiller is due to the aggregation of filler particles that results in the increase in crystallinity anddecrease in number of charge carriers. The best conductivity of the order of 10-3S cm-1 is achievedwith the addition of 5 wt% of Zr02 to the PVDF HFP-LiCF3S03 system.References[1] M.B. Armand, Polymer Electrolyte Reviews I, J.R MacCallum and C.A Vincent (Eds) Elsevier,London (1987) p. 1.[2] C.A. Vincent, Prog of Solid State Chemistry Vol. 17 (1987), p. 145.[2] F.M. Gray Solid Polymer Electrolytes, Fundamental and Technological Applications VCHNew York (1991).[4] M. Morita, H. Noborio, N. Yoshimoto, M. Ishikawa, Solid State lonies Vol. 177 (2006), p. 715.[5] W. Wieczorek, J.R. Stevens, Z. Florjanczyk, Solid State lonics Vol .85 (1996), p. 67.[6] A.S. Best, A. Ferry, D.R. MacFarlane, M. Forsyth, Solid State lonics Vol. 126 (1999), p. 269.[7] H.Y. Sun, Y. Takeda, N. Imanishi, O. Yamamoto, HJ. Sohn, J. Electrochem. Soc. Vol. 147(2000), p. 2462.[8] J.-H. Shin, F. Alessandrini, S. Passerini, J. Electrochem. Soc. Vol. 152 (2005), p. A283.[9] J.M. Tarascon, A.S. Godz, C.N. Schmutz, F. Shukoki, P.C. Warren Solid State lonies Vol. 86(1996), p. 49.[10] N.S. Mohamed, S. Amir, S.A. Hashim Ali, International Journal of Materials Sciences Vol. 1(2006), p. Ill.[11] A. Bhide, K. Hariharan, European Polymer Journal Vol. 43 (2007), p. 4253.[12]R. Mishra and KJ. Rao, Solid State lonics Vol. 106 (1998), p. 113.[13]B. Natesan, N.K. Karan, R. S Katiyar, Physical Review E Vol. 74 (2006), p. 042801.[14] Y-J. Wang, D.Kim, Electrochimica Acta Vol. 52 (2007), p. 3181.[15] N.T.K Sundaram, T. Vasudevan, A. Subramania, J. Physics and Chemistry of Solids Vol. 68(2007), p. 264.«(,n\ul.lutnll'elll(QnUct

Characterization of PVDF-HFP-LiCF3S03-Zr02 nanocomposite polymer electrolyte systems

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Characterization of PVDF-HFP-LiCF3S03-Zr02 nanocomposite polymer electrolyte systems

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