Batteries for Electric Vehicles
The electric vehicle battery pack performs the same function as the gasoline tank in a conventional vehicle: it stores the energy needed to operate the vehicle. Battery packs usually contain 10 to 52 individual 6-, 8-, or 12-volt batteries similar to the starter battery used in gasoline vehicles. While a gasoline tank can store the energy to drive 300-500 miles before refilling, the current generation of batteries will only store enough energy to drive 50 to 150 miles between recharging.
| Energy Density (Whr/kg) | Power Density (W/kg) | Life Cycles per Battery | Cost ($) | |
|---|---|---|---|---|
| Current lead acid | 35 | 150 | 500 | 150 |
| USABC mid-term goals | 80 | 150 | 600 | 250 |
| USABC long-term goals | 200 | 400 | 1,000 | 100 |
| Impact on vehicle performance | Range | Acceleration | Life-cycle cost; replacement period | Acquisition cost; battery replacement cost |
The range of an electric vehicle (the distance traveled between recharging) depends on the energy stored in the battery pack. Just as the amount of gasoline can be increased by installing a larger gas tank, the amount of stored electrical energy can also be increased by increasing the number and/or size of batteries in the battery pack. However, when batteries are added, the weight is increased and the spaced used by the battery pack increases. Because of this weight and space penalty, there is a limit to the number of batteries that can be used for any given vehicle.
To increase the range and improve the performance of electric vehicles, batteries are being developed that can store larger amounts of energy with the same weight and volume. The United States Advanced Battery Consortium (USABC) was established to develop the next generation electric vehicle batteries. The members of the USABC include the big three U.S. automobile manufacturers, the Electric Power Research Institute, battery manufacturers, and the United States Department of Energy (DOE).
| Energy Density (Wh/kg) | Power Density (w/kg) | Life Cycles per Battery | |
|---|---|---|---|
| Advanced lead acid | 48 | 150 | 800 |
| GM Ovonic nickel-metal hydride | 70 | 220 | 600 |
| SAFT nickel-metal hydride | 70 | 150 | 1,500 |
| SAFT lithium ion | 120 | 230 | 600 |
| Lithium polymer | 150 | 350 | 600 |
| Zebra sodium-nickel chloride | 86 | 150 | 1000 |
When the USABC long-term goals (chart, above) are met, batteries will be available to provide electric vehicles with ranges greater than 200 miles and a battery life greater than 100,000 miles.
Independent of the battery development efforts supported by the USABC, the Advanced Lead Acid Battery Association, an association of lead acid battery manufacturers, is supporting development programs to improve the near-term performance of the lead acid battery.
Battery systems being supported by the USABC to meet the midterm goals include nickel metal hydride battery technologies. The USABC is also supporting battery systems to meet the long-term goals. The two systems being investigated are the lithium polymer and the lithium-ion battery systems.