Hybrid Car Batteries

Published on 18 Jan 2009

An energy storage system is an essential component in hybrid cars. Batteries used in hybrid cars should have high power (with high-peak and pulse-specific power), high specific energy at pulse power, high charge acceptance to maximize regenerative braking utilization, and long calendar and cycle life. See below to learn about hybrid car battery options, ultracapacitors (another energy storage device), and battery thermal management strategies.

Lead-Acid Batteries

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 hybrid car applications. 

Nickel-Cadmium Batteries

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 hybrid car 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 infrastructure 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 cars and recently in low-volume production hybrid cars . 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

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 hybrid car applications. However, to make them commercially viable for hybrid cars, further development is needed, including improvement in calendar and cycle life, higher degree of cell and battery safety, abuse tolerance, and acceptable cost.

Lithium Polymer Batteries

Lithium polymer batteries with high specific energy, initially developed for electric car applications, also have the potential to provide high specific power for hybrid car applications. The other key characteristics of the lithium polymer are safety and good cycle and calendar life. The battery could be commercially viable if the cost is lowered and higher specific power batteries are developed.

Ultracapacitors

Ultracapacitors are higher specific energy and power versions of electrolytic capacitors—devices that store energy as an electrostatic charge. They are electrochemical systems that store energy in a polarized liquid layer at the interface between an ionically conducting electrolyte and a conducting electrode. Energy storage capacity increases by increasing the surface area of the interface. Ultracapacitors are being developed as primary energy devices for power assist during acceleration and hill climbing, as well as recovery of braking energy. They are also potentially useful as secondary energy storage devices in HEVs, providing load-leveling power to chemical batteries. Additional electronics are required to maintain a constant voltage due to the low energy density.

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