Applications of high power density lithium ion batteries

In 2003, we developed a new type of lithium ion battery for the light vehicle application, in which 14 cells of 7 Ah were integrated into a battery pack. It has the high rate discharge capability up to 5C rate (35 A), a energy density of 74 Wh kg−1, and the low temperature discharge capacity at −5 °C more than 90% of that at 25 °C. The life cycle test of 100% depth of discharge (DOD) at 35 °C showed the capacity fading around 10% after 500 cycles, which confirmed much longer practical life than 2 years. Recently, we have developed a new high power cell. It has the capacity of 5.5 Ah, and has the output power density of 3000 W kg−1 at 50% state of charge (SOC) and at 25 °C for 5 s discharge basis, and the input power density of 2200 W kg−1 at the same conditions. The new cells showed much less increase in direct current resistance (DCR) in both the cycle life test and the storage life test than the cells developed before, which consequently implied much longer calendar life than our previous ones developed in 2000.