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Structural, Transport and Electrochemical Properties of LiFePO4 Substituted in Lithium and Iron Sublattices (Al, Zr, W, Mn, Co and Ni)

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      Abstract

      LiFePO 4 is considered to be one of the most promising cathode materials for lithium ion batteries for electric vehicle (EV) application. However, there are still a number of unsolved issues regarding the influence of Li and Fe-site substitution on the physicochemical properties of LiFePO 4. This is a review-type article, presenting results of our group, related to the possibility of the chemical modification of phosphoolivine by introduction of cation dopants in Li and Fe sublattices. Along with a synthetic review of previous papers, a large number of new results are included. The possibility of substitution of Li + by Al 3+, Zr 4+, W 6+ and its influence on the physicochemical properties of LiFePO 4 was investigated by means of XRD, SEM/EDS, electrical conductivity and Seebeck coefficient measurements. The range of solid solution formation in Li 1−3 x Al x FePO 4, Li 1−4 x Zr x FePO 4 and Li 1−6 x W x FePO 4 materials was found to be very narrow. Transport properties of the synthesized materials were found to be rather weakly dependent on the chemical composition. The battery performance of selected olivines was tested by cyclic voltammetry (CV). In the case of LiFe 1− y M y PO 4 (M = Mn, Co and Ni), solid solution formation was observed over a large range of y (0 < y ≤ 1). An increase of electrical conductivity for the substitution level y = 0.25 was observed. Electrons of 3 d metals other than iron do not contribute to the electrical properties of LiFe 1− y M y PO 4, and substitution level y > 0.25 leads to considerably lower values of σ. The activated character of electrical conductivity with a rather weak temperature dependence of the Seebeck coefficient suggests a small polaron-type conduction mechanism. The electrochemical properties of LiFe 1− y M y PO 4 strongly depend on the Fe substitution level.

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      Most cited references 58

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      Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides

       R. D. Shannon (1976)
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        Phospho-olivines as Positive-Electrode Materials for Rechargeable Lithium Batteries

         A. K. Padhi (1997)
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          Electronically conductive phospho-olivines as lithium storage electrodes.

          Lithium transition metal phosphates have become of great interest as storage cathodes for rechargeable lithium batteries because of their high energy density, low raw materials cost, environmental friendliness and safety. Their key limitation has been extremely low electronic conductivity, until now believed to be intrinsic to this family of compounds. Here we show that controlled cation non-stoichiometry combined with solid-solution doping by metals supervalent to Li+ increases the electronic conductivity of LiFePO4 by a factor of approximately 10(8). The resulting materials show near-theoretical energy density at low charge/discharge rates, and retain significant capacity with little polarization at rates as high as 6,000 mA x g(-1). In a conventional cell design, they may allow development of lithium batteries with the highest power density yet.
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            Author and article information

            Affiliations
            Department of Hydrogen Energy, Faculty of Energy and Fuels, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Krakow, Poland; E-Mails: akulka1986@ 123456o2.pl (A.K.); anna.milewska@ 123456agh.edu.pl (A.M.); wojciech.zajac@ 123456agh.edu.pl (W.Z.); xi@ 123456agh.edu.pl (K.S.)
            Author notes
            [* ]Author to whom correspondence should be addressed; E-Mail: molenda@ 123456agh.edu.pl. ; Tel.: +48-12-617-2522; Fax: +48-12-617-2522.
            Journal
            Materials (Basel)
            Materials (Basel)
            materials
            Materials
            MDPI
            1996-1944
            29 April 2013
            May 2013
            : 6
            : 5
            : 1656-1687
            5452508
            10.3390/ma6051656
            materials-06-01656
            © 2013 by the authors.

            licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license ( http://creativecommons.org/licenses/by/3.0/).

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