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1266-CC05-02

Olivine-Carbon Nanofibrous Cathodes For Lithium Ion Batteries Yan L. Cheah, Song Y. Choy , Tingji Toh , Subodh Mhaisalkar and Madhavi Srinivasan* School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore. ABSTRACT Olivine (LiFePO4)-carbon nanofibre composites were synthesized through a combination of electrospinning and solvothermal methods. Morphology, distribution and crystal structure of these composites were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Electrochemical properties of synthesized LiFePO4carbon fibre composite cathodes have been studied in litium ion coin cells by means of galvanostatic cycling and cyclic voltammetry. Enhanced electronic conductivity was observed for the electrospun-LiFePO4 nanocomposites which was eight orders of magnitude higher than pristine LiFePO4. As compared to pristine LiFePO4, there was significant improvement in the specific capacity (~25% at 0.1C rate) of LiFePO4 – carbon nanofibre composites owing to their improved conductivity. INTRODUCTION Olivine lithium iron phosphate (LiFePO4) is a promising cathode material [1-3] owing to its low cost, low toxicity and safety. Although it possesses high theoretical capacity (170mAhg-1), its practical achievable capacity is less than 120mAhg-1 owing to low electronic conductivity (109 -10-10Scm-1) and low ionic diffusivity which prevents its large-scale application in electric vehicles (EVs) and hybrid electric vehicles (HEVs). The poor rate capability of LiFePO4 cathodes is an impediment to their applicability in lithium-ion batteries unless modifications are made to improve their low electronic conductivity and the slow lithium ion diffusion across the LiFePO4/FePO4 interface. Various approaches, such as conductive carbon coatings [4, 5], cosynthesis with carbon precursors [6, 7], decreasing particle size [8], cation doping [9-12], and carbon nanotubes (CNT) addition [13, 14] have been studied to improve LiFePO4 conductivity. Electrospinning is a method of production of nanofibres from polymeric liquids utilizing an electrostatic field. This involves use of high accelerating voltage to overcome surface tension of polymeric precursor solution resulting in a ejecting of a continuous jet, producing nanofibres on the collector upon evaporation of solvent[15-18]. Diameter and length of fibers can be controlled by varying parameters such as the flow-rate, accelerating voltage and also the needleto-collector plate distance [19-21]. Electrospinning is a promising method for electrode material synthesis as the resulting nanofibre mats have a large aspect ratio that would facilitate lithiumion transport due to small electronic resistance and short diffusion pathways, hence enabling higher rate lithium-ion storage capability, faster charge-discharge kinetics, and better cyclic stability. In this study, we have employed electrospinning and solvothermal methods to synthe