About a month ago, we spoke with Dr. Prabhakar Patil of Compact Power, Inc. about CPI's lithium-ion battery technology. We didn't want to miss the chance to chat in person during the SAE Congress this week, so we stopped by the CPI booth. The reason most AutoblogGreen readers would be following the fortunes of CPI is the company's work with GM on the Chevy Volt (CPI, along with A123 Systems, are supplying the test battery packs for the Volt. BTW, the Volt/Malibu mules are on the track) but Dr. Patil again mentioned that CPI is working with other, unnamed OEMs. We're anxious to learn more about that.But let's talk about the battery deal we do know about. Based on the packs currently being tested in the Volt, Dr. Patil estimated that a li-ion battery that could move an electric car 100 miles between charges would weigh about 800 pounds. This is double what the Volt's batteries weigh, but would get you 2.5 times the Volt's EV-only distance, because the Volt's batteries reserve some power for the hybrid operations. Regenerative braking can get you the rest of the way. Considering all the studies that show that most people drive well-under 50 miles a day, carrying around all that extra weight for capacity that won't often get used doesn't make a lot of sense, he said. Patil also sees the benefits of the recent CARB ZEV mandate decision. Give a listen.
In the CPI booth was the company's ER2 racer which was setting speed records back in 2002. The ER2 uses an 11 kWh li-ion battery pack and a 165 kW AC induction motor to go from 0-60 in 3.2 seconds. More details here.
1. Once again, GM with their overweight battery packs.
800 pounds = 363 kilograms
100 miles in 363 kilograms is 0.275 mi/kg.
The Volt consumes 200Wh/mi, so 55Wh/kg battery density. I.e., just over half the energy density of the individual cells. Meaning that structural elements on the pack are making up almost as much mass as the batteries themselves.
By comparison, if I remember the numbers correctly, Tesla's cells were ~140Wh/kg, and the packs were ~110Wh/kg. And Tesla had to do a lot more intricate thermal management than the Volt will have to, too, since they're using much more volatile laptop batteries.
Look -- if we're going to be wasting this much weight on the packs, rather than the batteries, perhaps our research shouldn't be going into more energy dense batteries -- perhaps it should be going into *lighter packs*.
Posted at 12:41PM on Apr 17th 2008 by KarenRei