Development of a high power lithium secondary battery for hybrid electric vehicles

摘要

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/Li_(1+x)Mn_2O_4). It used an improved cathode material and more advanced electrolyte. Cell performances of the Type II cell were evaluated and compared with a Type I cell of the same cell size, i.e. 400 (diameter) x 108 mm (length). The Type II 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 800 W at 45 percent SOC (state of charge) and 25 deg C, which was 1.3 times higher than that of the latter (600 W at around 40 percent), Moreover, the former had an input-output power of more than 100 W at -30 deg 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 percent SOC range and a storage test at 50 percent SOC were earned out at various temperatures for the Type II cell. Less than a 15 percent DCR (direct current resistance) increase was observed in the pulse mode cycle test after 450 K cycles at 50 deg C. No more than a 25 percent DCR increase was detected after 240 days in the 50 percent SOC storage test even at 65 deg C. The activation energies for capacity change and DCR change in the storage test were also estimated for the Type II cell.