The effect of carbon coating on the properties of LiFePO4 particles is studied from magnetic measurements. Magnetization experiments are an excellent tool to detect very low concentrations of iron-based impurities (< 1 ppm) which are poisoning the phospho-olivine used as positive electrode mate- rial in rechargeable Li-ion batteries. The results indicate that I addition of 5% carbon withdraws traces of the Fe(III) phase such as Fe2P and/or Fe2O3. This carbothermal effect appears to be beneficial for long-term application of LiFePO4 materials in Li-ion batteries. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.