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IEEE's Intro to Lithium Batteries for PHEVs

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  • Felix Kramer
    Although this story starts out talking about the Volt, it focuses mainly on batteries, and is an excellent introduction. It s from the IEEE, the Institute of
    Message 1 of 1 , Jan 7 8:12 PM
      Although this story starts out talking about the
      Volt, it focuses mainly on batteries, and is an
      excellent introduction. It's from the IEEE, the
      Institute of Electrical and Electronics
      Engineers, which last year called PHEVs a
      "downright irresistable solution"

      Lithium Batteries for Hybrid Cars
      By: John Voelcker

      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.

      -- -- -- -- -- -- -- -- -- -- -- --
      Felix Kramer fkramer@...
      Founder California Cars Initiative
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