5 Facts: Chevy Volt Batteries

There's no doubt that the only real impediment to the widespread commercialization of electric vehicles and PHEVs is the extraordinarily expensive battery pack that's required to make them run. So where does that leave us?

The most high profile example of this challenge is presented by Chevrolet's groundbreaking Volt concept that's now on the road to production. From the start, General Motors officials and those close to the Chevy Volt program have made no secret that for GM's wonder car to come to fruition with the promised 40 mile electric only range, the lithium-ion battery is the key. GM is working around the clock internally and with outside suppliers to meet its November 2010 target deadline for production launch of the Volt. While that's still a ways off, in real time it is right around the corner. Our recent visit to the General Motors Technical Center where the Volt is being designed and developed showed us just how far along the Volt's battery program has come. Here's what we know:

Lithium-Ion Battery Fits to a 'T'
Battery suppliers are developing the Volt's battery based on the original "T" configuration found in the concept. The shape is a scaled down version of the T-battery GM used in the EV-1 electric car 10 years ago. It places battery mass down the center tunnel of the car and under the rear seat area to optimize the Volt's center of gravity, which should help handling dynamics. At GM's Tech Center, we were shown a side-by-side comparison of the EV-1's battery pack and the lithium-ion T-battery being developed for the Volt. The past decade of battery development has led to dramatic improvements in size, weight, and power. The older EV-1 T-battery dwarfed the similarly shaped Volt battery pack, and at 1,200 pounds weighed more than three times that of the 375 pound Volt pack.

GM is Working with Multiple Battery Suppliers
General Motors is wisely keeping its options open when it comes to a battery source for the production Volt. Officially, there are two contracts. One of these is with A123 Systems for a nanophosphate lithium-ion unit with cylindrical cells. The other is with Compact Power for a large stacked wafer, manganese oxide structured lithium-ion configuration. Compact Power is a division of the electronics giant LG. The competition is intense as battery technology advances and certainly a breakthrough technology from other sources would quickly be put into the mix.

Battery Life Cycle Testing Well Underway
The GM Tech Centers in Warren, Michigan and Mainz-Kastel, Germany have been testing the advanced lithium-ion batteries for over six months now in accelerated life and durability test regimes. Test cycles are designed to compress 10 years of real-world driving into a time schedule that works in tandem with the rest of the Volt development program. Laboratory battery cycling equipment is programmed to mimic end user driving styles, draining the batteries with draws for various speeds and load conditions.

Thermal Dynamic Testing on Track
Alongside the battery cycling equipment, GM is running test cells to put the battery packs through extreme temperature tests and cycles to see how they will perform in the real world. These test cells, which resemble large walk-in freezers, can cool or heat the batteries while they're being cycled to match any atmospheric operating condition Volt owners will encounter.

Charge Range Optimized for Longevity
The Volt program's 40 mile electric drive goal is dictating every parameter of the development process. The balancing act on the battery side is to make the 40 miles while keeping the battery in a state of charge that delivers long battery life. With the nickel-metal-hydride cells used in most current hybrid applications, batteries live in a relatively narrow 65 to 45 percent state of charge. The current Li-ion battery packs operating in the Volt program are charged to approximately 80 percent of their capacity and allowed to discharge to 30 percent of capacity before recharge.