Lithium Batteries for Hybrid Cars

By: John Voelcker
http://spectrum.ieee.org/jan07/4848/2

Chevrolet's Volt is the first series hybrid
concept car shown by a major manufacturer. In a
series hybrid, the engine's only job is to crank
a generator; electric power does all the rest of the work.

In late November General Motors announced plans
to release a vehicle that will be able to go long
distances in electric-only mode. It thus became
the first U.S. company to commit to producing a
so-called plug-in hybrid design—one that has
batteries so capacious that they can be recharged
not only by the engine but also from wall current
in the garage. It represents the next way station
along the path to an all-electric vehicle.

Troy Clarke, president of GM North America, told
IEEE Spectrum that a plug-in version of the
Saturn Vue Green Line sport-utility vehicle could
hit dealer lots 24 months after the launch, in
2009, of a standard hybrid version using GM's
"two-mode hybrid" transmission. He would not,
however, commit to a specific date or even a year.

Tellingly, GM has not yet announced where it will
get the lithium-ion batteries that any plug-in
requires. Only such batteries-the kind used in
laptops-pack enough energy to sustain
electric-only mode for 32 kilometers (20 miles),
the range generally regarded as necessary. In a
statement released on 4 January, in the runup to
the Detroit Motor Show, the company did say that
it had agreed to support the battery technology
programs of two joint ventures, and that it would
also assess the technologies of other, unnamed companies.

Beyond plug-ins: the Volt

Although plug-in hybrids involve larger
batteries, their fundamental design hardly varies
from that of other, mechanical-drive cars. More
radical is the “series hybrid electric” car,
which powers the wheels with electric motors and
uses the onboard combustion engine only to run a
backup generator that recharges the batteries as needed.

The Chevrolet Volt, unveiled to the press on 7
January at Detroit’s North American International
Auto Show, is the first-ever series hybrid
concept car shown by a major manufacturer. For an
animated tour of its innards, click here. Its
1.0-liter, 3-cylinder turbocharged engine runs an
onboard 53-kilowatt generator that recharges a
16-kilowatthour lithium-ion battery made of 80
four-volt cells. The battery pack’s volume is 100
L, one-third as much as the lead-acid batteries
in GM’s 1990s-issue electric car, the EV1. GM’s
targeted maximum weight for the pack is 180
kilograms (400 pounds). The company also wants
the battery to last at least 10 years, through 4,000 full-discharge cycles.

The battery pack would charge in less than 6.5
hours, power a 120-kW electric motor delivering
320 newton-meters of peak torque, and go 64 km
(40 miles) in all-electric mode on battery charge
alone. The 12-gallon gasoline tank would add an
additional 965 km (600 miles) to that range.

“We don’t have a battery pack yet,” said Tony
Posawatz, the vehicle line director. He confirmed
that the vehicle shown in Detroit doesn’t yet run.

Lithium ion: light and cheap

Everything thus depends on the pace of
development of lithium-ion batteries. Right now
they’re the only candidate for the job, because
they store more than twice as much energy (110 to
130 watt hours per kilogram) as the next-best
technology, the nickel-metal-hydride (NiMH)
batteries in today’s gas-electric hybrids. The
reason: lithium is the lightest solid element, so
it’s easily portable. What’s more, it’s cheap.

To make lithium-ion batteries practical for
mass-produced electric-drive vehicles, new
technologies must increase the energy the
batteries store and the speed with which they can
discharge it. They must also lengthen cycle life
to 15 years or 241 000 km (150 000 miles)—the
average life of a vehicle. Finally, they must keep the cost as low as possible.

The technology has advanced quickly, says Mark
Duvall, manager of technology development for
electric transportation at the Electric Power
Research Institute, in Palo Alto, Calif. He’s
“impressed and bullish” on the prospects for new
lithium variants, some of which EPRI has tested to ascertain their cycle lives.

The first production car to use lithium-ion
batteries was the Toyota Vitz CVT 4, a small car
sold only in Japan. It used a four-cell, 12
ampere-hour lithium-ion battery pack to power its
electric accessories and restart the engine after
idle stop. More recently, Tesla Motors, in San
Carlos, Calif., has offered the Tesla Roadster,
an all-electric sports car that uses 6831
lithium-ion cells, each roughly the size of a
double-A battery. They give the car up to 400 km
(250 miles) of range, as well as the breathtaking
acceleration of 0 to 100 kilometers per hour (0
to 60 miles per hour) in less than 4 seconds.

Why use so many little cells? First, because
they’re readily available, and second, because
current lithium technology is susceptible to
thermal runaway—a problem underlined recently by
flaming laptops—and larger cells mean greater
risk. The Tesla’s 410-kg (900-pound) battery pack
is stuffed not only with cells but also with
sensors and control logic designed to detect and isolate any misbehaving cell.

Better batteries through chemistry

The cathodes of current lithium-ion batteries are
made of lithium-cobalt metal oxide (LiCoO2). This
material is pricey, and it can become unstable
and release oxygen if the cell is overcharged.
One alternative is to replace the cobalt in the
cathodes with iron phosphates, which won’t
release oxygen under any charge and therefore will not burn.

A123Systems, in Watertown, Mass., first launched
a lithium-ion phosphate battery this past fall in
Black & Decker’s DeWalt power tools. A123Systems
claims its batteries can be recharged 10 times as
often as conventional lithium-ion designs, charge
to 90 percent capacity in 5 minutes, and charge
fully in less than 15 minutes. Conventional
lithium-ion models, by contrast, can take twice as long.

In May, the company unveiled a battery pack it
said could be ready for electric vehicle use
within three years. It’s smaller than a carton of
cigarettes and weighs barely 4.5 kg (10 lbs.),
one-fifth as heavy as an equivalent NiMH battery.
A123 is taking part in one of the two joint
ventures to which GM has awarded battery
development contracts. Its partner is Cobasys, of
Orion, Michigan, itself a joint venture of
Chevron Technology Ventures and Energy Conversion
Devices Inc. GM's other contract is with a joint
venture between Johnson Controls, of Milwaukee,
and Saft Advanced Power Systems, of Paris.

Austin, Texas–based Valence Technology also uses
iron-phosphate cathodes for its Saphion battery.
The technology is used in the Segway, the
self-stabilizing scooter, and in unofficial
conversions that aim to increase the range of a Toyota Prius.

Customarily, the anode of a lithium-ion battery
is made of graphite, which can store only a
limited amount of energy. Researchers at Sandia
National Laboratories, in Livermore, Calif., have
developed anodes using a composite of graphite
and silicon that can quadruple storage capacity.

Late this year, 3M Co., in St. Paul, Minn., will
deliver still another kind of anode, based on
amorphous silicon, which the company says will
store twice the energy of today’s lithium
batteries. Other researchers are trying to make
anodes of alloys of lithium and two other metals,
generally antimony mixed with either copper,
manganese, or indium. Such three-metal alloys
should also increase storage capacity.

Cells now being developed by Altair
Nanotechnologies, based in Reno, Nev., switch the
lithium from the cathode to the anode, forming a
compound called lithium-titanate spinel
(Li4Ti5O12). The company says that the cells
recharge in 3 minutes and deliver three times as
much power as the conventional design, and at a
great operating range of temperatures: –30 °C to
249 °C (–22 °F to 480 °F). It also says that its
batteries can keep on ticking after 9000
recharging cycles, compared with 1000 for
conventional cells. Altair’s battery, however, is not yet in production.

The big gamble

Once lithium batteries have met energy-storage,
power-delivery, durability, and cost goals, a
massive investment in manufacturing capacity will
be needed to produce them in bulk for use in
cars. But the market is crowded and competitive;
close to a dozen manufacturers have announced new
lithium battery technologies—with no guarantees
that automakers will buy. And that number omits
the in-house battery research that the major
automakers themselves are conducting.

Take Toyota, which builds the lion’s share of
hybrid vehicles globally. In 2005 it purchased
General Motors’ share of Fuji Heavy Industries
Ltd. (which manufactures Subarus)—in part,
analysts suggest, to get Fuji’s share of its
joint venture with Tokyo Electric Power to
develop automotive lithium batteries. Subaru has
already announced that in 2009 it will build and
sell the R1e, an electric version of its tiny R1
urban car that will use lithium-ion batteries.
Mitsubishi Motors, in Tokyo, will do much the
same with its “i” urban car, most likely using
batteries from Litcel, its joint venture with TDK Corp.

Analysts estimate the price premium for today’s
hybrids at roughly US $5000, some $3000 of which
goes to cover the cost of a NiMH battery pack. At
today’s gasoline and electricity prices, you’d
need six to 10 years of operation to pay it back.
But the analysts also say the hybrid premium
could fall to $2000 in five years ($1200 or more
of it the cost of lithium-ion batteries), which
would allow for a three-year payback.

The payback period could be longer for a plug-in
hybrid, because it would have larger, costlier
batteries—though fuel mileage is hard to
calculate. It all depends on how much of the
mileage is covered in electric mode, with power
taken from the grid, and how much in gasoline mode.

Powerful forces—global warming, possible carbon
taxes, global political instability—seem to be
lining up in ways that will bring us
electric-drive cars that will be feasible and
affordable for the first time ever. They won’t
arrive this year, or next year…but they’ll be
here sooner than you might think. It all comes
down to one question: when will the lithium-ion batteries be ready?

John Voelcker has written about automotive
technology, home building, and other topics for
20 years. He covered software and microprocessor
design for IEEE Spectrum from 1985 to 1990. A
connoisseur of vintage British automobiles, he
writes Spectrum’s annual “Top Ten Tech Cars” feature.