Lead-Acid Batteries Seek New Role in Hybrids, Plug-Ins

Using a souped-up version of a chemistry that's been around since the days of Edison, a Detroit-area startup wants to slash the costs of batteries for hybrids and plug-in cars.

Energy Power Systems (EPS) says it has boosted the power density and cycle life of the venerable lead-acid battery, without touching the low costs that made it desirable in the first place. With the new technology, batteries for mild hybrids and plug-in cars could cost less than half of what they do today, the company says.

Subhash Dhar, chairman, CEO, and founder of EPS, said in an interview:

The concept has always been to start with a chemistry that gives you high energy density, and then hope you can reduce the cost. But the industry has never made much progress in terms of cost. So we turned it upside down -- we started with low cost and improved the technology, so we can get the performance without disturbing the cost structure.

Energy Power Systems (EPS) proposes replacement of a 16-kWh lithium-ion battery, like the one in the Chevy Volt, with a 9-kWh lithium pack and a high-power, 3.5-kWh lead-acid pack.
(Source: EPS)

In truth, the energy numbers of EPS' batteries are puny compared to that of today's lithium-ion batteries. Whereas, lithium-ion typically checks in around 150 Wh/kg, the EPS battery is 40 Wh/kg. But that doesn't worry Dhar. The EPS battery is not targeted at high energy (which translates to driving range in an EV), but is instead focused on power density. Power density is far more important for full hybrids, mild hybrids, and micro-hybrids, since those vehicles can extend their range by burning gasoline, Dhar told us. "When you realize that energy isn't critical, and power is critical, you can boost the power and not worry about disturbing the fundamental low-cost structure of lead-acid," he said.

That's why his company has lifted the power density of lead-acid from about 200 W/kg to 1,600 W/kg. Cycle life has similarly been improved by a factor of five.

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