SAE Congress '08: Q&A with Dr. Patil of Compact Power
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.
Reader Comments (Page 1 of 1)
KarenRei 12:41PM (4/17/2008)
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*.
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Amtoro 4:24PM (4/17/2008)
He mentions that it makes no sense to make customers pay for a larger battery pack that they will never use fully, but the reality is that when you have a larger pack and do not deplete it every time, means it will take you longer to go through the total cycles the battery can deliver before it needs to be replaced. so, at the end, you're paying for a longer life or larger range but never paying for something you will never use.
If I'm wrong, open my eyes please :)
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Kevin Nugent 6:51PM (4/17/2008)
That guy sounds like an idoit "pay for something you will never use" Its the conveniance you idiot . Suppose you drive 30 miles including to work and back , then you go to the grosser y store and you only have 5 miles left. Suppose your grandmother s sick and just was rushed to the hospital . What are you going to say ??? I have to go home and recharge?? Case and point the more miles the better.
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Chris M 3:12AM (4/18/2008)
IIRC, the Tesla battery pack (ESS) complete with cooling and safety features was about 900 lbs, 408 Kg, and stored 53 Kwh, the energy density of the ESS is about 130 wh per kg.
Seems strange that a 800 lb pack could only get 100 miles, when the Tesla Roadster 900 lb pack gets 220 miles. That discrepancy could be explanied by the CPI batteries having a lower energy density, and their use in a much bigger, heavier, and less aerodynamic vehicle than the Roadster.
Kevin Nugent: How would having to make an emergency drive right when you needed to recharge be any different than having to make an emergency drive right when you need to make a detour to refill the gas tank? In both cases, the prudent thing to do is not let your reserves drop too low. Also, a Plug-in hybrid like the Volt will be able to drive for hundreds of miles after the 40 mile EV range, thanks to the range extender engine and gas tanks. BTW, in an emergency, it might be better to call 911 and wait for an ambulance, rather than trying to drive the patient there yourself.
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KarenRei 12:19PM (4/18/2008)
"the energy density of the ESS is about 130 wh per kg. "
Then it must be 130Wh/kg and 160Wh/kg. I just remember that they're about 30Wh/kg apart.
"That discrepancy could be explanied by the CPI batteries having a lower energy density"
A123 cells are about 100Wh/kg or so. I don't know what LG Chem's cells are like, but I assume they're similar. Sure, 100Wh/kg is less than Tesla's 160Wh/kg, but it's not *that* much less. They're getting ~55Wh/kg here. That's a ridiculously heavy pack.
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