An advanced lithium-ion battery that uses heated and cooled liquid to maximize battery life and extend its gas-free driving range will power the new Ford Focus Electric car.
Thermal management of lithium-ion battery systems is critical to the success of all-electric vehicles because extreme temperatures can affect performance, reliability, safety and durability. The active-liquid cooling and heating system on the Focus Electric will regulate the temperature of its lithium-ion battery packs, which are designed to operate under a range of ambient conditions.
"All-electric vehicles do not have a conventional engine on board, so it is critical we maximize the performance of the battery under various operating temperatures," says Sherif Marakby, director of Ford's electrification program and engineering. "Active liquid systems are more effective than air systems at regulating lithium-ion battery temperature."
Active-liquid cooling and heating also enable the Focus Electric to automatically precondition the battery pack temperature during daily recharging. When the vehicle is plugged into the power grid, the vehicle system will be able to warm up the battery on cold days and cool it down on hot days. While air-cooling methods work well for many of today's smaller car-battery systems, the larger, more complex lithium-ion battery technology of the Focus Electric calls for an aggressive thermal management system.
The active-liquid system heats or chills a coolant before pumping it through the battery cooling system. This loop regulates temperature throughout the system against external conditions.
On hot days, chilled water absorbs battery heat, dispersing it through a radiator before pumping it through the chiller again. On cold days, heated water warms the batteries, gradually bringing the system's temperature to a level that allows it to efficiently accept charge energy and provide enough discharge power for expected vehicle performance.
Liquid cooling also plays a role in charging the vehicle. When the Focus is plugged in for recharging, the vehicle control system automatically will precondition the battery, if needed, to the optimal temperature before accepting charge. If the battery is already at the optimal temperature, the system automatically will accept charge and maintain an optimal temperature.
The Focus Electric will have an expected range of up to 100 miles and use no gasoline at all. It will be built at Ford's retooled Michigan Assembly Plant.