Saying a lithium-ion battery would perform better than a lead-acid type if not for very cold weather is somewhat akin to saying your favorite sports team would have won the game had it just played better.
That is not the analogy A123 Systems is drawing for its 12-V Li-ion technology, however. A123’s message is more direct: Li-ion technology at anything but extremely low temperatures is a better solution than the lead-acid type for mass savings and all-around functionality.
“Because lithium-ion batteries can be more deeply discharged, they allow the engine to be turned off and on more frequently in stop/start systems,” said Jeff Kessen, a mechanical engineer who serves as A123’s Director of Automotive Marketing. “But [brake energy] regeneration is where the value proposition gets quite a bit stronger.”
Li-ion battery chemistry doesn’t degrade to the extent lead-acid does when accepting charge, and so the former is a better solution for the coupling of stop/start with brake re-gen, Kessen told Automotive Engineering. A123 labels such dual capability "microhybrid."
In a session on low-voltage electrification at The Battery Show 2014 in Novi, MI, Kessen spoke of three particular A123 Li-ion applications (click on arrow at top right of the main photo on this page to see a relevant chart). One is a simple alternative to the lead-acid starter battery. This application, which he said offers a fuel-economy improvement of 5 to 10%, is the one he focused on most. Kessen touched on a dual system for hybrid-vehicle applications using a 48-V Li-ion battery for hybridization tasks and a 12-V lead-acid type for engine cranking (fuel-economy benefit of about 15%).
There is also a dual system for microhybrid applications using one 12-V Li-ion battery for hybridization and one 12-V lead-acid battery for engine cranking (fuel-economy benefit of about 5 to 10%).
“There’s still a lot of untapped potential at the 12-V level” in terms of delivering a fuel-economy benefit, he said. The payoff for such systems may not be great, but neither is the investment required. And so “spending less to implement a fuel economy gain from a 12-volt system makes sense,” he asserted, as part of an OEM’s larger technology strategy to keep pace with ever-stiffening fuel-economy regulations.
The European Union’s ban on lead in vehicle electronics may be extended to batteries, which currently are exempted, according to Kessen, who noted that the most recent exemption expires in 2015. There has been enough progress in Li-ion viability in the past five years that “I think there is some possibility that a [lead] phase-out might be regulated in some way,” he said.
There’s no legislating away frigid weather in many parts of the world, and so from Kessen’s point of view cold-cranking performance is Li-ion’s “biggest frontier to be bridged”—that and cost. Given the same capacity, an Li-ion battery is about three times more expensive than lead-acid, but about half the weight, he said. “Auto manufacturers are scratching and clawing for a single pound or half a pound. So to get 20 pounds in one design change is fairly significant.”
In comparison to other Li-ion strategies involving higher voltages and dual battery systems, the big advantage for an OEM in switching to a single 12-V Li-ion battery is that they can do it “without tearing up the vehicle electrical architecture” while also enjoying the mass, life, brake regen, and additional functionality that come from a battery technology offering higher capacity, said Kessen.
For single 12-V battery applications, A123 has had an Li-ion product on the market for three years based on the company's AMP20 prismatic cells, and it continues to improve cold-cranking performance (click on arrow for chart). Kessen said the company has expended great effort over the past 18 months in its third-generation product. Available soon in samples, it will equal or better lead-acid AGM (absorbent glass mat) in the EN -18°C cold-crank test—and at a capacity of only 60 a·h (vs. 80 a·h for its second-generation product).
“Certainly it’s still true that lead-acid holds up better as the temperature goes down even further, but we’ve come quite a long ways in this dimension,” he said.
A123 has expanded capabilities beyond its indigenous lithium-iron-phosphate (LFP) technology via acquisitions to nickel-manganese-cobalt and lithium-titanate. “That’s not to say LFP has run out of steam in terms of stop/start—quite to the contrary,” said Kessen.
Pointing to a chart (click on arrow), he noted that A123 was able to significantly improve the power performance of the company’s base Nanophosphate PHEV technology by 79% via changes in the mechanical design of the cell (meaning revisions to the electrode), with no changes to cell chemistry. The result was what A123 calls Nanophosphate HEV, a technology that is employed by BMW, among others, Kessen said.
While continuing to pursue improvement in mechanical design, A123 for its Ultraphosphate technology has been focusing on chemistry changes. “This is a substantial accomplishment, which is still in the laboratory, he said.