The battle to develop GM’s E-Flex electric vehicle architecture took a significant step forward when Compact Power (www.compactpower.com), a subsidiary of Korea’s LG Chem, delivered its first battery pack to the automaker. Compact Power and A123 Systems (see AD&P October, 2007) are the two main competitors to supply lithium-ion batteries to GM for its Chevrolet Volt and other E-Flex vehicles by the automaker’s late-2010 timeframe.
Unlike A123’s nanophosphate chemistry, Prabhakar Patil, Compact Power’s CEO, says his company’s design uses lithium manganese spinel cathode chemistry for improved thermal management, cost and reliability. “The benefit of the chemistry is that it provides a very good abuse tolerance, and the cost is better. Not only is manganese an abundant material, it is cheaper to manufacture thanks to lower processing costs and more consistency over higher volumes.” Compact Power manufactures its cells using a so-called “laminate flat package” while A123 utilizes a cylindrical design. Patil says his company’s approach requires fewer parts to manufacture and has improved thermal management characteristics over cylindrical packages. “If you try to make a vehicle-sized cylindrical cell, you will need electrodes up to 10 meters in length that are difficult to wind on a central spindle. Also, the heat generated from the center of cell would have to travel through nearly 100 layers of electrode, creating a big temperature gradient between the center and the outer layer of the cell.” Heat in the Compact Power laminate package, on the other hand, only has 16-20 layers to travel through, lowering the heat gradient by a factor of four, according to Patil. This may help the E-Flex architecture’s viability.
That’s because two obstacles could prevent moving the E-Flex battery to volume production by the late-2010 deadline: thermal management and cost. So while the Compact Power battery pack should have a less extreme temperature gradient, Patil says GM’s decision to manage battery temperature via liquid cooling faces packaging constraints. “Because of the power density, the cooling system is important and can affect the overall life of the battery pack,” he says. As for cost, Patil says GM should consider leasing the battery pack to customers in order to reduce the upfront acquisition cost. “Otherwise, the market will collapse if you pass the full cost of the battery onto the customer,” he says. Since the battery system will still be able to produce power at a reduced output at the end of its 10-year vehicle life expectancy, it could be used by utilities to provide back-up power to homes and other facilities in the event of a power outage, and generate additional revenue for automakers.