We have been predicting the demise of the lead acid battery but
new developments are promising to extend this technology far into our
future. Combining the capacitor and lead acid battery results in a
battery that has the best of both worlds. This article from IEEE Spectrum
explains a capacitor lead acid hybrid from AxionEast Penn that
addresses the inherent weakness of the lead acid battery.
A Battery-Capacitor Hybrid—for Hybrids
By Prachi Patel-Predd
Engineers give lead-acid batteries a makeover by crossing them with
ultracapacitors
Lead-acid batteries are relics that haven’t changed much since
their invention nearly 150 years ago. Heavy and unable to
withstand rapid charge-discharge cycles, they are unsuitable for the
automotive world’s killer app, hybrid-electric vehicles. Hybrids
instead use expensive nickel-metal hydride (NiMH) batteries or,
experimentally, lithium batteries. But a new, souped-up version of
lead-acid batteries could change that, cutting the cost of hybrids and
also improving the function of power grids and a range of other
applications.
The new design combines lead-acid chemistry with ultracapacitors,
energy-storage devices that can quickly absorb and release a lot of
charge, which they store along the roughened surface of their
electrodes. Unlike ordinary lead-acid batteries, which are slowed by
the movement of chemicals within them, these could provide quick
bursts of power for acceleration and then recharge during braking, a
must for hybrid-electric and electric vehicles. A hybrid’s rapid
recharging cycles and high currents would destroy the lead electrodes
in standard batteries, because lead sulfate would build up on them. The
new batteries can go through at least four times as many charging
cycles as lead-acid batteries, and, crucially, would cost about a
quarter of NiMH batteries.
At least two lead-acid/ultracapacitor technologies are now poised
for market release. Battery giant East Penn Manufacturing Co., in Lyon
Station, Pa., licensed the technology for the UltraBattery in September
from Furukawa Battery, in Yokohama, Japan, which has already begun
manufacturing the devices. Researchers at Australia’s Commonwealth
Scientific and Industrial Research Organisation (CSIRO), who invented
the UltraBattery, tested it early this year in a Honda Insight hybrid,
which ran for 160 000 kilometers.
Meanwhile, Axion Power International, based in New Castle, Pa., has
developed a slightly different design, which it will test for U.S.
Marine Corps assault vehicles; the company got
US $1.2 million from the Department of Homeland Security in
October for the tests. A bank of 1000 of Axion’s batteries will also
soon be tested as a utility-grid buffer in upstate New York. Axion CEO
Thomas Granville says that the new technology “lets us get into
markets that have been in the past closed to lead-acid batteries.”
The new batteries’ advantage over standard lead‑acid batteries comes
from simple tweaks of the negative electrode. Instead of a lead
plate, Axion makes the electrode from activated carbon, the highly
porous, spongelike material used in ultracapacitor electrodes. When a
regular battery discharges, the lead electrode reacts with sulfate
ions, forming lead sulfate and creating protons and electrons. Axion’s
activated carbon electrode directly releases and adsorbs protons from
the sulfuric acid electrolyte during discharging and charging. The
batteries recharge four times as fast as conventional ones, Granville
says.
The UltraBattery is slightly different, says Lan Lam, project
manager of the battery work at CSIRO. The negative electrode is split
into two, one half made of lead and the other half of activated
carbon. The two halves are connected in parallel so that their
currents combine. This split-electrode design gives the battery the
best of both technologies, according to Lam. While activated carbon
provides quick energy bursts, it cannot store as much energy as the
lead-acid chemistry. The combination gives the UltraBattery an energy
capacity closer to that of a lead-acid battery than an ultracapacitor
could get alone, Lam says.
Both designs have a big cost advantage. “Nickel-metal hydride,
depending on the application, is as much as $800 to $1200 per
kilowatt-hour,” Granville says. “Axion’s battery costs $200 per
kilowatt-hour.”
These battery/ultracapacitor combinations will have to compete with
lithium-ion batteries as the successor to NiMH for hybrid vehicles.
Cost and safety, however, are still a concern for lithium.
Lithium-ion batteries can overheat, ignite, and even explode if
mistreated.
The lead-acid/ultracapacitor batteries have other advantages. They
are easier to recycle than NiMH or lithium, according to East Penn.
Lithium-ion batteries don’t have much usable metal, so they are
usually incinerated, while the nickel from NiMH batteries is consumed
in the steel industry. The military, meanwhile, is interested in
Axion’s batteries, not so much for hybrids but because they work at
temperatures as low as –50° C and weigh less than standard lead-acid
batteries, Granville says.
