Care and Feeding of Battery-Electric Cars
Why aren’t there more battery-electric vehicles on the road? After all, they’re cleaner than clean (especially if you ignore where the electricity that charges them comes from) and they are a driver’s dream -- quiet to the point of silence, comfortable and, perhaps surprisingly, fast. But they do have an Achilles’ heel: Batteries are very, very expensive, and they wear out, so replacement involves yet more expense. That’s why the makers of hybrids, plug-in hybrids and the new battery-electric vehicles are very careful about the way they treat those batteries.
Like babies, batteries don’t want to be too hot or too cold. They prosper best when things are just right. To that end, the all-new Ford Focus Electric, which debuts in the U.S. late next year and in Europe in 2012, will be powered by an advanced lithium-ion battery that uses liquid that is heated and cooled to help maximize battery life.
The nickel-metal hydride batteries used in vehicles such as the Toyota Prius like to be coddled. However, the nurturing required by the Prius battery is nothing in comparison to that of the lithium-ion-battery systems that will be used in vehicles like the Chevrolet Volt electric car and the Ford Focus battery electric. Thermal management is critical to the success of all-electric vehicles, because extreme temperatures can affect performance, reliability, safety and durability. Ford chose an advanced active liquid-cooling-and-heating system to regulate the temperature of its lithium-ion-battery packs, which are designed to operate under a range of ambient conditions. You might think of it the same way you think of coolant running through your engine and into the radiator.
“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 Electrification Programs and Engineering at Ford. “Active liquid systems are more effective than air systems at regulating lithium-ion-battery temperature. As a result, the active liquid system on Focus Electric will play a key role in providing our customers with the best performance possible.”
Of course, your car’s coolant doesn’t run through the radiator when it’s at rest. But in the Focus Electric, the active liquid-cooling-and-heating system automatically preconditions the battery-pack temperature during daily recharging. When the vehicle is plugged into the power grid, its system will be able to warm up the battery on cold days and cool it down on hot days.
How does it actually work? The active liquid system heats or chills coolant before pumping it through the battery-cooling system. This loop regulates temperature throughout the system against external conditions like the 100-degree day or minus-10-degree night. On hot days, chilled water absorbs heat from the batteries, 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 accept energy efficiently and provide enough power to get up that next hill.
“Extreme temperatures impact a battery’s life and performance, making it crucial to have an effective cooling and heating system to regulate temperature for these demanding applications,” says Anand Sankaran, executive technical leader of Energy Storage and HV Systems at Ford.
Of course, using an active system like this is more complex than relying on ambient conditions to do most of the work. But as we move toward the first sales in years of electric vehicles from major manufacturers, engineers are finding they can’t achieve the durability customers require without going to greater lengths.