Researchers: Don’t Rule Out Lead-Acid Batteries Yet

Material costs make lithium-ion batteries uncompetitive with piston power, but the venerable lead-acid battery just might be the key to boosting the appeal of electrified vehicles.

So says Subhash Dhar, chairman and CEO of Troy, Mich.-based Energy Power Systems LLC. He tells AutoTech Daily that EPS is working on tweaks that can give lead-acid batteries the power of nickel-metal hydride batteries at one-third the price.

The challenge is price rather than technology, Dhar says, adding, "We still don't know how to make a [high-energy] battery for $150 per kilowatt-hour." He considers that price the breakeven point where all-electric drive becomes cost-competitive with a conventional IC engine. Lithium-ion batteries currently cost about $700 per kWh.

Dhar brings considerable credibility to the discussion. He is past president of ECD-Ovonics, the company that developed nickel-metal hydride batteries that displaced the original lead-acid batteries in the second-generation EV1 electric introduced by General Motors Co. in 1999. He's also past CEO of Envia Systems, a startup focused on advanced lithium-ion technology.

Dhar notes that materials represent about 70% of the cost of a lithium-ion battery, meaning that mass production won't significantly lower unit prices. Managing the temperature and current flow inside lithium-ion batteries also requires complex and costly controls.

Dhar acknowledges that superior energy density, which translates into the vehicle range on a single charge, makes lithium-ion batteries the superior choice for EVs. But he contends that lead-acid batteries which use a 154-year-old chemistry are a better option for hybrid powertrains, especially "mild" hybrids.

Mild hybrids capture energy from regenerative braking and use it to enhance IC engine torque and operate the stop-start system. He says a lead-acid chemistry is well suited to the repeated high-power charging and discharging a harsh duty cycle for lithium-based batteries.

Dhar says EPS also is developing a system that combines a high-power lead-acid battery with an energy-dense lithium ion battery to produce a system that is smaller and about half the cost of an all-lithium construction. This approach cuts the cost of plug-in battery systems.

The new design replaces conventional two-volt cells with plates strung in series to produce the required total voltage. The strings are then stacked in parallel to increase power output. Dhar says the architecture reduces internal resistance, improving both rapid charging and high-power discharging.

EPS also has demonstrated several ways to package such batteries. One is a long and flat design well suited for hybrids. An alternative spiral stack results in a compact cylindrical battery.

EPS is looking for production sites in Michigan. Dhar notes that the company's battery design is compatible with some existing lead-acid batterymaking facilities.