Olivine type LiFePO4 is used as a cathode material for Li-ion batteries because of
its high energy density (with capacity of 170 mAh/g and plateau voltage of 3.5 V
vs. Li+
/Li), stability, safety, environmental friendliness and low cost. However, the
low intrinsic electronic and ionic conductivity limits its application.Physical chemistry 2012 : 11th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 201

Jokić, Bojan M.

Jugović, Dragana

Milović, Miloš

Mitrić, Miodrag

Uskoković, Dragan

Repository of the Vinča Nuclear Institute (VinaR)

        Pon HYSICAL11th InterFundamentPhyUnder UnivePThe ConfProfesSeptemBe CHEMISnational Coal and Appsical Chem the auspicersity of Beroceeding      erence is desor  Ivan Dr        ber 24-28lgrade, Ser  TRY 2012nference lied Aspectistry s of the lgrade s dicated to aganić , 2012  bia   s of       ISBN 978-86-82475-27-9 Volume 1 ISBN 978-86-82475-28-6 Volume II  Title: PHYSICAL CHEMISTRY 2012 (Proceedings) Editors: S. Anić and Ž. Čupić Published by: Society of Physical Chemists of Serbia, Studenski trg 12-16, 11158, Belgrade, Serbia Publisher: Society of Physical Chemists of Serbia For Publisher: S. Anić, President of Society of Physical Chemists of Serbia Printed by: “Jovan” Priting and Publishing Company; 200 Copies; Number of pages: 6+ 497; Format: B5; Printing finished in September 2012.  Text and Layout: “Jovan”  200- Coppy printing  III CONTENTS  Volume 1 Organizers V Committees VI Sponsors VIII Professor Ivan Draganić IX Plenary lectures 1 Chemical Thermodynamics 35 Spectroscopy, Molecular Structure,  Physical Chemistry of Plasma 65 Kinetics, Catalysis  137 Nonlinear Dynamics  225 Electrochemistry  301 Biophysical Chemistry, Photochemistry,  Radiation Chemistry  337 Radiochemistry, Nuclear Chemistry  Material Science 415  Volume II Solid State Physical Chemistry 505 Macromolecular Physical Chemistry  515 Environmental Protection  Forensic Sciences Pharmaceutical Physical Chemistry 557 Phase Boundaries 667 Complex Compounds 681 General Physical Chemistry 707 Geophysical Chemistry 719 Education, History 731 Food Physical Chemistry 743 Free Topic 783 Index 791  H-07-P 441 SYNTHESIS AND STRUCTURAL PROPERTIES OF F-DOPED LiFePO4/C COMPOSITE M. Milović1, D. Jugović1, M. Mitrić2, B. Jokić3, D. Uskoković1  1Institute of Technical Sciences of SASA, Belgrade, Serbia 2Vinča Institute of Nuclear Sciences, University of Belgrade, Belgrade, Serbia 3Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Serbia Introduction Olivine type LiFePO4 is used as a cathode material for Li-ion batteries because of its high energy density (with capacity of 170 mAh/g and plateau voltage of 3.5 V vs. Li+/Li), stability, safety, environmental friendliness and low cost. However, the low intrinsic electronic and ionic conductivity limits its application.  Effects of cation doping on improving electrochemical performance of LiFePO4 has been widely studied and debated [1]. On the other hand, anion doping has not been sufficiently investigated. It is generally accepted that doping of LiFePO4 with fluorine would enhance its electrochemical performance. Several papers are dealing with the influence of small quantities of fluorine dopant on the properties of LiFePO4 [2, 3].  In this paper, we report on the impact of F doping on the crystal structure of LiFePO4/C composite obtained through the co-precipitation in molten stearic acid, a new method established by our group [4]. Experimental F-doped LiFePO4/C was synthesized by co-precipitation in molten stearic acid [4]. In the molten stearic acid, stoichiometric amounts of aqueous solutions of (NH4)2HPO4 and FeSO4·7H2O were added sequentially when precipitation occurred. Dry melt was reground and mixed with solid LiF, which served as both lithium and fluorine source. Thus obtained powder was calcined at temperature of 700°C for 3 hours in a slightly reductive atmosphere (Ar + 5%H2), then washed in distilled water and dried under vacuum. The properties of thus obtained powder were compared with the previously published data of the undoped one obtained under the same synthesis conditions, except for lithium salt [4]. X-ray diffraction data were collected on a Philips PW 1050 diffractometer with Cu-Kα1,2 radiation (Ni filter) at the room temperature. Measurements were done in 2θ range of 10-110° with scanning step width of 0.02° and 14 s times per step. Crystal structure refinement was based on the Rietveld full profile method [5] using the Koalariet computing program [6]. Chemical composition of the final compound was Li:Fe:P = 0.99:1.00:1.00 determined by inductively coupled plasma (ICP) analysis. The fluorine in the sample was detected with SA720 ion selective electrode (ISE).  H-07-P 442 Results and Discussion X-ray powder diffraction pattern (Fig. 1) was used for phase identification and structural analysis. Olivine type LiFePO4 was obtained as a major phase with FeS as an impuritiy phase. There is no evidence of a crystalline carbon, so internal carbon could be treated as a contribution to the background. The structure of F-doped LiFePO4 has been refined in the space group Pnma (D2h16) in olivine type with following crystallographic positions: Li+ ions in special crystallographic position 4a [0,0,0] with local symmetry ī;  Fe2+ and P5+ ions occupy two different crystallographic 4c positions [x,0.25,z]  with local symmetry m; O2- ions occupy three different crystallographic positions: additional two 4c positions and one general 8d position [x,y,z] with local symmetry 1.  The Rietveld refinement results (Table 1 and 2) indicate decreased lattice parameters and primitive cell volume compared with the undoped sample synthesized under the same conditions [4]. This finding is an evidence that F− ions are successfully incorporated in the lattice, since F− ions are smaller than O2− ions (rVI(F−) = 1.33 Å, rVI(O2−) = 1.40 Å). There are three kinds of O sites (namely O1, O2, and O3) in the lattice that may be occupied by fluorine separately or randomly. The best refinement was accomplished when O2 site was allowed to be occupied by fluorine ions. The calculated value of dopant concentration matches well with the chemical composition of the powder. Furthermore, doping with fluorine resulted in increased crystallite size. The Rietveld refinement also showed additional electron density on the lithium sites indicating so-called "anti-site" defect in which Li ion (on the M1 site) and Fe ion (on the M2 site) are interchanged.  Fig. 1. The observed (•), calculated (-), anddifference (bottom) X-ray diffraction data of F-doped LiFePO4/C taken at room temperature;vertical markers bellow the diffraction patternindicate positions of possible Bragg reflections; theFig. 2. Scanning electron microscopyimage of F-doped LiFePO4/C preparedvia co-precipitation method. H-07-P 443 Table 1. The final results of the structural refinement for undoped [4] and F-doped LiFePO4.  Lattice parameters [Å] Primitive cell volume [Å3] Mean crystallite size [nm] Li site occ. by Fe O2 site occ. by F R factor [%] LiFePO4 a = 10.3279(3) V = 291.68(9) 75(10) 0.020(5) - Rwp = 4.49 b = 6.0096(2) c = 4.6994(1) F-doped LiFePO4 a = 10.3340(2) V = 291.49(8) 150(9) 0.027(3) 0.04(1) Rwp =  2.07 b = 6.0086(1) c = 4.6943(3) Table 2. Fixed and refined atomic coordinates. Fractional coordinates LiFePO4 F-doped LiFePO4 x y z x y z Li (4a) 0 0 0 0 0 0 Fe (4c) 0.2820(3) 0.25 0.9749(4) 0.2820(2) 0.25 0.9724(8) P (4c) 0.0924(4) 0.25 0.4140(6) 0.0939(6) 0.25 0.4155(6) O(1) (4c) 0.1039(6) 0.25 0.7343(7) 0.1076(9) 0.25 0.7331(2) O(2) (4c) 0.4563(6) 0.25 0.2100(7) 0.4650(9) 0.25 0.2126(6) O(3) (8d) 0.1682(1) 0.0426(7) 0.2828(6) 0.1691(9) 0.0365(9) 0.2804(5) The typical SEM image of as-prepared F-doped LiFePO4/C composite is presented in Fig. 2. It shows wide particle size distribution, with increased particle size compared to the undoped powder. Apparently, F substitution catalyzes the growth of the primary particles. By comparing mean particle size estimated from SEM image (Fig. 2.) with mean crystallite size (Table 1) it can be concluded that particles are polycrystalline composed of a number of crystallites. Conclusion F-doped lithium iron phosphate powder was successfully synthesized by facile co-precipitation in molten stearic acid followed by thermal treatment. Crystal structure refinement showed that doping with fluorine ions preserves olivine structure. According to the Rietveld refinement fluorine ions occupy separately O2 oxygen site. Scanning electron microscopy showed that F substitution catalyzes the growth of the primary particles. References [1] J. W. Fergus, J. Power Sources, 2010, 195, 939-954. [2] F. Lu, Y. Zhou, J. Liu, Y. Pan, Electrochim. Acta, 2011, 56, 8833-8838. [3] M. Pan, X. Lin, Z. Zhou, J. Solid State Electrochem., 2011, 16, 1615-1621. [4] D. Jugović et. al., J. Power Sources, 2011, 196, 4613-4618. [5] H. M. Rietveld, J. Appl. Cryst., 1969, 2, 65-71. [6] R. W. Cheary, A. Coelho, J. Appl. Cryst., 1992, 25, 109-121. CIP Volume I  CIP - Каталогизација у публикацији Народна библиотека Србије, Београд  544(082) 621.35(082) 66.017/.018(082)  MEĐUNARODNA konferencija iz fundamentalne i  primenjene fizičke hemije (11 ; 2012 ;        Beograd)    Physical Chemistry 2012 : proceedings.     #Vol. #1 / 11th International Conference on   Fundamental and Applied Aspects of Physical   Chemistry, September 24-28, 2012, Belgrade ;  [editors S.[Slobodan] Anić and Ž.[Željko]     Čupić ; organized by Society of Physical      Chemists of Serbia ... et al.]. - Belgrade :  Society of Physical Chemists of Serbia, 2012  (Belgrade : Jovan). - VI, 498 str. : ilustr.  ; 24 cm  "The Conference is dedicated to Professor     Ivan Draganić" --> nasl. str. - Tiraž 200. - Bibliografija uz svaki rad.  ISBN 978-86-82475-27-9 1. Društvo fizikohemičara Srbije (Beograd) a) Физичка хемија - Зборници b)             Електрохемијско инжењерство - Зборници c)  Наука о материјалима - Зборници COBISS.SR-ID 193432332            

Synthesis and structural properties of F-doped LiFePO4/C composite

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Synthesis and structural properties of F-doped LiFePO4/C composite

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