Study of the morphology control and solid solution behaviour of Olivine LiMPO4 (M = Fe, Mn, and Co)

Abstract

Lithium iron phosphate (LiFePO4) is one of the most promising cathode materials for lithium ion rechargeable batteries. It has a high theoretical specific capacity (170 mAh/g) and operating potential (3.45 V vs. Li+/Li). Additionally, the material is extremely stable thermally and electrochemically at ambient conditions, which is very suitable to be used in electric vehicles. However, the electronic and ionic conductivities of the material are quite low, which limits the power performance of the batteries. In the last decade, extensive work was reported on various methods to improve the electronic conductivity extrinsically, for example carbon coating, metallic additives and molecular wiring. Nevertheless, energy density of the cells will be reduced because of non-electrochemically active nature of the additives. In principle, electronic and ionic conductivities can be boosted intrinsically. One of the methods is to increase the number of charge carriers in the material, for instance in two-phase solid solution system LiαFePO4/Li1-βFePO4 or single solid solution phase LixFePO4. Since the formation of solid solution has been reported to be size dependent, it is highly desired to know how to synthesize LiFePO4 particles with different sizes. In this study, we have used hydrothermal synthesis and polyol process to control the size of LiMPO4 (M: Fe, Mn, and Co) particles. We will present how we prepare particles with different sizes. Moreover, the solid solution properties of various sizes of LiMPO4 (M: Mn and Fe) were studied. The result will be presented. Part of the preliminary findings have been published in the peer-reviewed journals or conference presentations: 1) Journal of Materials Chemistry [Ellis B.; Kan W. H.; Makahnouk W. R. M.; Nazar L. F. J. Mater. Chem. 2007, 17 (30) 3248., 2) Journal of the American iv Chemical Society [Lee K. T.; Kan W. H.; Nazar L. F. J. Am. Chem. Soc. (submitted)], 3) Material Research Society Meeting [Kan W. H.; Maunders C.; Badi S.; Ellis B.; Botton G.; Nazar L. F. MRS Fall Meeting 2008 in Boston]