LEAD-ACID BATTERIES GET NEW LOOK-SEE-----Carl Schwab

Using a souped-up version of a chemistry that’s been around since the days of Edison, a Detroit area start-up wants to slash the costs of batteries for hybrids and PHVs. The new company, EPS, (Energy Power Systems) claim it has boosted the POWER density (not to be confused with ENERGY density) and cycle-life of the venerable lead-acid battery, without touching the low costs that made it desirable in the first place.

SOME BACKGROUND—The lead-acid battery technology is basic to the fact that every car has a starter which by all standards is a horrible battery load. But it is serendipity. The starter motor while starting the ICE has to produce very high torque and good speed. This requires very high battery current. Once the ICE has started the battery must be recharged quickly at a high charge rate to replace the depleted charge. Lead-acid can do both---deliver very high current for a short period and then accept a very high recharge current to replace the depleted charge. This is a demanding POWER load. So people expect about 5-7 years of service from a lead-acid battery that has a nominal Amp-hr capacity of say 90 Ahr at a reasonable cost. What EPS is attempting to do is combine an EV battery pack in 2 parallel parts; one with POWER density and one with ENERGY density i.e. one for acceleration/braking and the other for electric range. Other experimenters have had simuliar ideas combining a SuperCap with Li-ion. EPS just may have something here.

Subhash Dhar, CEO and founder of EPS has said, “The industry has never made much progress in terms of reducing cost. So we are turning it upside down---start with low cost and improve the technology to get performance without disturbing the basic cost. EPS has achieved this end to the point POWER density of the lead-acid has improved from 200W/kg to 1600 W/kg while simultaneously improving the cycle-life by a factor 5 to 1. As an example, Dhar says he can replace the 16 kWh li-ion battery in the Chevy VOLT with  3.4 kWh lead-acid and a 9 kWh li-ion pack. By doing this, he believes EPS can cut the battery pack cost for a VOLT from $12,800 to under $6,000---BIG saving.

Some several years ago the writer participated in a test program for the GM IMPACT/EV1. The battery technology was lead-acid based and manufactured by ElectorSource, a Texas company. Their main claim to fame was significant weight reduction and the promise of only one battery pack replacement for 100,000miles. Replacement cost for the pack was $2,500(! circa 1995). It appears that Dhar/EPS has built upon the ElectroSource experience and produced considerable improvement in the life of the pack. BTW the lead-acid side of the hybrid pack does NOT require cell-balancing. The EPS battery is not targeted at high ENERGY (which translates to driving range in an EV), but instead focused on POWER density. POWER density is more important for hybrids, mild hybrids, and micro-hybrids, since they can extend their range by burning gasoline. What Mr. Dhar, EPS, is doing is replacing the projected function of SuperCap pack in a much lower cost lead-acid package---should sell.

It is the writer’s opinion that a change like this will help the PHV performance making it even more efficient to use electric energy for the daily trips and reserving the ICE operation for longer trips and reduce the cost of hybrid–type small car.

INTERESTING----

Comments

[koen weijand]

we would need a lightweigth portable generator for the long trips and take it out for the domectic short trips. we could share one generator with one or more neighbours..