There are a number of different types of batteries that are used in conventional and advanced vehicles, described below.
Lead-acid batteries can be designed to be high power and are inexpensive, safe, and reliable. A recycling infrastructure is in place for them. But low specific energy, poor cold temperature performance, and short calendar and cycle life are still impediments to their use. Advanced high-power lead-acid batteries are being developed for HEV applications.
Nickel-Metal Hydride Batteries
Nickel-metal hydride batteries, used routinely in computer and medical equipment, offer reasonable specific energy and specific power capabilities. Their components are recyclable, but a recycling structure is not yet in place. Nickel-metal hydride batteries have a much longer life cycle than lead acid batteries and are safe and abuse-tolerant. These batteries have been used successfully in production electric vehicles and recently in low-volume production HEVs. The main challenges with nickel-metal hydride batteries are their high cost, high self-discharge and heat generation at high temperatures, the need to control losses of hydrogen, and their low cell efficiency.
Lithium Ion Batteries
The lithium ion batteries are rapidly penetrating into laptop and cell-phone markets because of their high specific energy. They also have high specific power, high-energy efficiency, good high-temperature performance, and low self-discharge. Components of lithium ion batteries could also be recycled. These characteristics make lithium ion batteries suitable for HEV applications. However, to make them commercially viable for HEVs, further development is needed including improvement in calendar and cycle life, higher degree of cell and battery safety, abuse tolerance, and acceptable cost.
Lithium Ion Polymer Batteries
Lithium ion polymer batteries with high specific energy, initially developed for cell phone applications, also have the potential to provide high specific power for HEV applications. The other key characteristics of the lithium polymer are safety, and good cycle life. The battery could be commercially viable if the cost is lowered and higher specific power batteries are developed.
Although nickel-cadmium batteries, used in many electronic consumer products, have higher specific energy and better life cycle than lead-acid batteries, they do not deliver sufficient power and are not being considered for HEV applications. Cadmium is a heavy metal that is toxic which reduces its desirability for use in hybrid applications.
NREL's Energy Storage team conducts research and development on many of these different types of batteries to improve their performance and life-cycle costs.