Prabhakar Patil
Prabhakar Patil once oversaw the development of Ford Motor Company's Escape Hybrid program. Now he heads up one of the contractors hired by GM to help perfect the battery for the Chevrolet Volt extended range electric car.

Smart Move

Part one of two-part interview with Compact Power, Inc. CEO, Prabhakar Patil about their role in GM's Volt program.

By Bill Moore

Okay, let's get this out of the way right up front. Prabhakar Patil pronounces his first name 'pra bha kar' with the emphasis on the second syllable, not the first. I completely murdered his name in the opening to my telephone interview with him. Why can't these 'foreigners' have easy names like the rest of us: Peter, Paul, Pedro?

I jest, of course.

I normally ask my guests how to pronounce their name if I think I might not know it before starting the interview, but in Dr. Patil's case, I didn't. As Julie Roberts said in Pretty Woman, "big mistake.. huge."

Okay, so, now.... the last time I talked to anyone at Compact Power, Inc... and I'll call them CPI hereafter ... they were racing up Pikes Peak to prove an electric car could make the climb. They did, twice, breaking their own record, which I think still stands.

But if you want to get serious about participating in the car game, you'd better hustle your bustle out to Motown, which is precisely what the company did after the second run up the mountain, conveniently moving into a building just across the street from where GM, Chrysler and BMW were jointly developing their two-mode hybrid drive, which -- of course -- needs a good battery.

Now the company has a contract to deliver to GM a set of battery packs -- the number is proprietary -- based on lithium polymer cells developed by CPI's parent, LG Chem, the Korean conglomerate. LG makes the pouches -- we'll show you a picture in part two - and CPI creates the battery package, pictured below.

IN BRIEF: Synopsis of Interview

  • To establish their credibility as a young company, CPI twice raced to the top of Pikes Peak, demonstrating the weight and energy density advantage of their lithium batteries. They then participated in a small program with the US Advanced Battery Consortium, but realized that they needed to move more actively into automotive applications. To do this they packed up the company and relocated it from Colorado to Michigan, moving in a building across the street from the development center where GM, then-DaimlerChrsyler and BMW were working on their two-mode hybrid.

  • LG Chem, part of the Korean conglomerate LG Group, is the parent of CPI and supplies it with the lithium ion cells it uses to build completed battery modules and packs. CPI provides the engineering expertise to add the required battery brains; its thermal management and state-of-charge monitoring system. Patil says the CPI is setting itself up to become the "center of excellence" to carmakers, becoming their Tier One supplier for advanced battery systems.

  • Because the company is still, for all intents and purposes a start-up, it has the flexibility to adapt to the needs of the industry, but unlike most fledgling companies, it has the deep pockets of LG Chem it can draw on for financial support. LG Chem's strengths in material sciences is also a huge benefit. Batteries in general and lithium ion in particular are a strategic priority for LG Chem with 50 percent of its R&D budget devoted to electrical materials development, even though it represents only about 12 percent of the company's revenue. LG Chem manufactures some 30 million lithium cells of all types a month.

  • CPI is concentrating its electric car battery development efforts on what it calls its laminated flat pack cells for three reasons starting with thermal efficiency. The distance that heat in a battery has to travel is much shorter in a pouch type cell than a cylindrical type where the wound electrode can be up to 10 meters in length. This means the flat pack is four times more efficient thermally; the temperature difference between the core and the skin of the battery is one-quarter that of a cylindrical cell.

  • The second reason for using the flat packs is for manufacturing simplicity which translates into reliability. Winding a 10 meter long electrode into a conventional cylindrical cell poses mechanical stress issues because the winding can wobble like a "jelly roll." In the flat pack, the electrodes are laminated in place and don't move with respect to each other. This makes for a more "robust" manufacturing process with higher product yield and less waste; and that can translate into lower costs and better quality.

  • The third reason flat packs are preferred is because of their dramatically reduced part count compared to other types of lithium cells. This also makes for ease of manufacture and again lower cost.

  • This approach has been independently corroborated by Nissan who presented a paper at EVS 22 in Japan in 2006 that endorsed the laminated pack as the right direction to go for electric vehicle applications.

  • Lithium batteries tend to share some common characteristics: the anode tends to be made of a type of carbon-based material. It is on the cathode side that most of the variability comes into play. It can be a metal oxide like cobalt or iron phosphate, also referred to as olivine, which is what is used by A123. The cobalt provides high energy density, but can be volatile because it will release oxygen when it gets hot and that will feed what is known as thermal runaway when the battery literally goes into meltdown. To avoid this problem, LG Chem's cathode utilizes manganese oxide or spinel. Like olivine, it does not give off oxygen in the event of a thermal incident. Avoiding cobalt also makes the manufacturer less vulnerable to commodity availability and volatile pricing issues.

  • However, using spinel isn't without its trade-offs. It has a lower energy density than cobalt and it has "calendar-life" issues, meaning that regardless of how the battery is used, it will steadily lose its capacity to hold a charge over time. LG Chem believes it has solved both of these problems with a proprietary chemistry that blends spinel and three other elements to provide long calendar life and higher energy density.

  • The third advantage that the LG Chem cells used by CPI bring is its separator material. This is the plastic-like sheet that, as its name implies, separates the anode from the cathode. Patil explained that the reason so many lithium batteries where recalled last year was because microscopic debris found its way into the cells during manufacture. As the cells worked mechanically during use, the debris breached the separator material and allowed the cells to short. That local heating caused the separator to melt, which cascaded into cell failure and depending on the internal chemistry, thermal runaway.

  • CPI's cells use a proprietary separator that is mechanically six times stronger than conventional separator material. It also will not melt in the event of a short, which means the cells will not go into a runaway where temperatures can race to 700 degrees C. This improves the safety of the cell by solving the problem at its source rather than trying to rely on external devices.


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    Times Article Viewed: 12008
    Published: 19-Jul-2007


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