The overcharge behaviour of AlPO4-coated LiCoO2 cathodes as a function of coating thickness is investigated in Li-ion cells at 1 and 2C overcharging rates. The AlPO4 coating thickness is controlled by the concentration of the coating solution. During 1C-overcharging to l2V, the 5V plateau region, which is indicative of both electrolyte oxidation and an exothermic reaction between the electrolyte and the cathode, decreases with increasing AlPO4 coating thickness (AlPO4 concentration). Therefore, a Li-ion cell containing a P100-coated LiCoO2 cathode (AlPO4 coating thickness estimated as 1000Å) does not show the 5V plateau, and displays the lowest cell external temperature of 60°C, even at 12V. This suggests that the reaction at the 5V plateau strongly influences the final external temperature of the cell. When a higher current is applied (2C), cells with bare or P10-coated LiCoO2 cathodes either burst or explode, and reach external temperatures of over 275°C. By contrast, cells with P30 and P100-coated cathodes show only a swollen external appearance with temperature profiles similar to those at the 1C-overcharging rate.