Hybrid electric vehicles (HEVs) contribute greatly to reducing CO2 emissions while achieving high fuel efficiency. A key component of HEVs is the rechargeable battery, and even higher performance, for example, smaller and lighter, is being sought after. The lithium-ion battery currently represents the ultimate@battery in terms of its high energy density; accordingly, we are researching ways to apply it in HEVs and electric vehicles (EVs).
Figure: Comparison of energy densities of rechargeable batteries
Hitachi commercialized the first-generation lithium-ion battery for HEVs in 2000. After that, we continued to improve the first-generation battery's positive and negative electrodes up until we commercialized the second-generation lithium-ion battery-with 30% improved power density-and fitted it in a "hybrid truck" in 2005. At present, while advancing our research on new materials and battery configurations, we are developing a high-performance lithium-ion battery as a substitute for the nickel-metal-hydride (NiMH) battery.
