The stabilities of olivine LiFePO4 and spinel LiMn2O4 in a LiPF6-based electrolyte were investigated by means of atomic absorption spectroscopy. At 85°C a significant increase in Mn/Fe dissolution was observed in comparison to 60°C stored cathode materials. However, the comparison indicates a much lower solubility of the LiFePO4 versus LiMn2O4. This result shows a new advantage of LiFePO4 as a promising alternative cathode.