Available online at www.sciencedirect.comJournal of Power Sources 178 (2008) 801–806Short communicationA study on the electrochemical characteristics ofLiFePO4cathode forlithium polymer batteries by hydrothermal methodEn Mei Jina, Bo Jina,b, Dae-Kyoo Juna, Kyung-Hee Parka,Hal-Bon Gua,∗, Ki-Won KimcaDepartment ofElectrical Engineering, Chonnam National University, Gwangju 500-757, South KoreabCollege ofMaterials Science and Engineering, Jilin University, 130025 Changchun, ChinacITRC for Energy Storage and Conversion, Gyeongsang National University, 660-701 Jinju, South KoreaReceived 14 July 2007; received in revised form 11 September 2007; accepted 24 September 2007Available online 29 September 2007AbstractPhospho-olivine LiFePO4cathode materials were preparedby hydrothermal reaction at 150?C. Carbon blackwas addedto enhance the electricalconductivity of LiFePO4. LiFePO4-C powders (0, 3, 5 and 10wt.%) were characterized by X-ray diffraction (XRD) and transmission electronmicroscope (TEM). LiFePO4-C/solid polymer electrolyte (SPE)/Li cells were characterized electrochemically by charge/discharge experiments ata constant current density of 0.1 mAcm−2in a range between 2.5 and 4.3 V vs. Li/Li+, cyclic voltammetry (CV) and ac impedance spectroscopy.The results showed that initial discharge capacity of LiFePO4was 104mAhg−1. The discharge capacity of LiFePO4-C/SPE/Li cell with 5 wt.%carbon black was 128 mAhg−1at the first cycle and 127 mAhg−1after 30 cycles, respectively. It was demonstrated that cycling performance ofLiFePO4-C/SPE/Li cells was better than that ofLiFePO4/SPE/Li cells.© 2007 Elsevier B.V. All rights reserved.Keywords: LiFePO4; Carbon black; Hydrothermal method; Solid polymer electrolyte1. IntroductionLithium polymer batteries are widely used in potentialpower sources for portable electronic devices such as cellu-lar telephones, lap-top computers and cameras. The successfulcommercialization of Li-ion gel polymer batteries for portableelectronic devices has led to other applications where the sizeandweightofbatteries are important. Aconsiderable investmentinthis batterytechnologythatutilizes LiCoO2cathodes has beenmade [1–3]. However, low-cost cathode materials are requiredfor many applications such as in electrical vehicles (EVs) andhybrid electric vehicles (HEVs) [4,5].Recently, phosphates LiMPO4(M=Co, Mn, Fe andNi) cath-ode materials, whichprovide highpotentials andgoodreversiblecapacities over 150mAhg−1in practical uses [6]. Among thisseries of materials, LiFePO4is a low-cost material and highly∗Corresponding author. Tel.: +82 62 530 0740; fax: +82 62 530 0077.E-mail address: hbgu@chonnam.ac.kr (H.-B. Gu).compatible to the environment. LiFePO4 has a highly stablethree-dimensional frameworkdue to strong P–O covalent bondsin (PO4)3−polyanion, which prohibits the liberation ofoxygen[7–10]. These characteristics provide an excellent safety underabuseconditions ofthebatteries. Phospho-olivineLiFePO4havebeen intensively investigated because of its high stability, lowcost, high compatibility with environment [11,12]. However, itis difficult to attain its full capacity because its electronic con-ductivity is very low, and diffusion of Li+ion in the olivinestructure is slow. The two ways ofelectronic conductive carboncoating and particle size reduction have been used to improveelectronic conductivity of LiFePO4[13–16]. Various syntheticmethodssuchassolid-statereaction, sol–gelroute,hydrothermalreaction, co-precipitation method have been successfully usedfor these strategies and the synthesis of single-phase LiFePO4[17–20].In this paper, phosphor-olivine LiFePO4 cathode materialwas prepared by hydrothermal reaction. In order to enhance theelectricalconductivityofLiFePO4, carbonblackwasaddedafterhydrothermal reaction. 25PVDF-LiClO4EC10PC10as polymer0378-7753/$ – see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.jpowsour.2007.09.073
