A lithium secondary battery (Type II cell) for hybrid electric vehicles (HEV) was developed on the basis of previous battery techniques (Type I cell with amorphous carbon/Li1+xMn2O4). It used an improved cathode material and more advanced electrolyte. Cell performances of the Type 11 cell were evaluated and compared with a Type I cell of the same cell size, i.e. 40 phi (diameter) x 108 mm (length). The Type 11 cell discharged 5.9 Ah, which was 1.5 times higher than the amount discharged by the Type I cell (3.8 Ah). The former had an input-output power of 800W at 45% SOC (state of charge) and 25 degrees C, which was 1.3 times higher than that of the latter (600W at around 40%). Moreover, the former had an input-output power of more than 100 W at -30 degrees C, though the Type I cell output power was only 50 W. A pulse charge-discharge cycle test with 167 W input and 260 W output for a 30-70% SOC range and a storage test at 50% SOC were carried out at various temperatures for the Type II cell. Less than a 15% DCR (direct current resistance) increase was observed in the pulse mode cycle test after 450 K cycles at 50 degrees C. No more than a 25% DCR increase was detected after 240 days in the 50% SOC storage test even at 65 degrees C. The activation energies for capacity change and DCR change in the storage test were also estimated for the Type 11 cell. (c) 2005 Elsevier B.V. All rights reserved.