High Voltage Lithium Ion Batteries Based on carbon/ LiMPO4 (M=Mn,Co,Ni) Composites J. Moralesa, R. Trócolia, R. Saint-Martinb, S. Frangerb, J. Santos Peñaa a Department of Inorganic Chemistry, University of Córdoba, 14071 Spain b Laboratoire de Physico-Chimie de l’Etat Solide, ICMMO, Université Paris Sud, 91405 Orsay Cedex, France Since the discovery of Padhi et al. , lithium transition metal phosphates with nominal formula LiMPO4 have attracted much attention as positive electrodes for lithium ion batteries. The most studied is LiFePO4, a cheap and environmentally friendly material that develops a flat plateau at 3.5V versus Li+/Li. The electrochemical activity of other members of the family (LiCoPO4 and LiMnPO4) has also been studied but in less detail as they are insulators. Recently, measurements on single crystals evidenced that for electrochemical purposes, electronic conduction is a more limiting factor compared with lithium ion diffusivity . Nevertheless, the voltage where divalent manganese or cobalt are oxidised is higher than for iron and therefore, cells based on both phosphates are attractive. This is specially important for LiNiPO4, where Ni(II) oxidation takes place at 5.1V vs Li+/Li. Recently, Graetzel et al.  proposed the ball-milling of carbon with nanosized LiMnPO4 in order to obtain a suitable electrode material. In this communication we present our results on three different phospholivines, LiMPO4 (M=Mn,Co,Ni). The three systems were obtained by heating stoichiometric mixtures of the corresponding divalent transition metal phosphate with Li3PO4 and subsequently heating at 800°C. Two different techniques were envisaged for the preparation of carbon/phosphate composites. First, powders were ball milled with almidon for 15h and subsequently heated under argon atmosphere at 600°C for 30 min. Under these conditions, the pyrolisis of almidon produced a carbon coating onto the phosphate particles. This procedure cannot be used for preparing C/LiNiPO4 composites as Ni(II) is reduced to Ni(0). The second procedure involves the ball-milling of super P carbon with the phosphates for 15 h. The electrodic materials have been characterised by different techniques, including XRD, HRTEM, FTIR, TG, DSC and XPS. Electrochemical impedance has been applied in order to know the total conductivity of the systems and discriminate different interfacial process. Electrochemical tests were conducted by using 1M LiPF6 in (PC,EC,DMC) electrolyte. 1. A. K. Padhi, K. S. Nanjundaswamy, and J. B. Goodenough, J. Electrochem. Soc. 144 (4) (1997) 1188- 1194. 2. J. Santos-Peña, R. Saint-Martin, L. Pinsard-Gaudart, and S. Franger, Solid State Sciences (submitted). 3. D. Wang, H. Buqa, M. Crouzet, G. Deghenghi, T. Drezen, I. Exnar, N.-H. Kwon, J. H. Miners, L. Poletto, and M. Graetzel, J. Power Sourc. 189 (2009) 624-628.
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