Loading ...
Sorry, an error occurred while loading the content.
 

Metal Mix Boosts Batteries by Kimberly Patch

Expand Messages
  • RemyC
    From: http://trnmag.com/Stories/2002/100202/Metal_mix_boosts_batteries_100202.html Metal mix boosts batteries October 2/9, 2002 By Kimberly Patch, Technology
    Message 1 of 1 , Dec 25, 2004
      From:
      http://trnmag.com/Stories/2002/100202/Metal_mix_boosts_batteries_100202.html

      Metal mix boosts batteries
      October 2/9, 2002
      By Kimberly Patch, Technology Research News

      A truly good battery should be made of relatively inexpensive materials,
      store a significant amount of electricity, and discharge this energy as
      quickly as an electrical device needs it. And in a world that's increasingly
      contaminated by the residues of technology, it should be rechargeable and
      nontoxic.

      The common lithium batteries that power portable electronic devices like
      laptop computers and cell phones use lithium metal oxide electrodes. Five
      years ago, scientists discovered a cheaper, nontoxic lithium electrode --
      lithium iron phosphate. But initial promise turned to disappointment when
      the material turned out to be a bad conductor, and so could not discharge
      electricity at rates high enough to be useful.

      Researchers from the Massachusetts Institute of Technology have now shown
      that doping, or mixing, lithium iron phosphate with positive ions of another
      metal can drastically boost the material's conductivity. Ions are atoms that
      have fewer or more electrons than electrically neutral atoms and so have a
      positive or negative charge.

      The doping metal increased the conductivity of the lithium iron phosphate by
      100 million times, making it an even better conductor than standard lithium
      metal oxide electrodes, according to Yet-Ming Chiang, a professor of
      materials science and engineering at the Massachusetts Institute of
      Technology.

      The raw materials that go into the compound are only about one-quarter the
      cost of those that make up lithium metal oxide electrodes and the compound
      is nontoxic, Chiang said. The material gives a battery an extremely high
      rate of charge and discharge, "while at the same time being low in materials
      cost and very safe," he said.

      Lithium iron phosphate batteries could bring on a new class of devices that
      would bridge the gap between super capacitors, which deliver short bursts of
      high power, but can only store limited amounts of total energy, and
      batteries, which have the opposite trade-off, said Chiang.

      The material promises to improve batteries for electric and hybrid cars,
      backup power for implantable medical devices, and fuel cells, according to
      Chiang.

      Batteries generate electricity when the pair of materials that make up the
      bulk of the battery react chemically, with one material giving up electrons
      and the other material gaining electrons. Rather than flowing directly from
      one material to the other, however, the electric current leaves the battery
      through one electrode and returns through another.

      Connecting an electronic device between a battery's electrodes, which act as
      gatekeepers that determine how quickly the electricity flows, powers the
      device.

      Batteries made with the researchers' new electrode material would deliver
      voltage similar to conventional lithium batteries, but the material's better
      conductivity allows for much higher power density, or rate of charge and
      discharge, said Chiang. A cell containing the new electrode could be charged
      or discharged in as little as three minutes, while typical batteries might
      require a half-hour or more, he said.

      This is important for electric vehicles because they need a high rate of
      energy to accelerate and because they need to store electricity quickly in
      order to reuse breaking energy, said Chiang. "Battery power density is
      required for rapid acceleration and also to accept the regenerative breaking
      energy when someone slams on the brakes," he said.

      The material could also eventually be used as electrodes for electrochemical
      applications like fuel-cells and membranes for separating hydrogen gas,
      according to Chiang. "These are other applications that require rapid
      electron transport as well as ion transport -- in these cases the ion is
      hydrogen rather than lithium as in the battery," he said.

      The team synthesized more than 50 different mixtures by adding different
      metals and baking the samples at temperatures as high as 850 degrees Celsius
      in order to change the crystal structure of the material to improve its
      conductivity, said Chiang. The metals included magnesium, aluminum,
      titanium, zirconium, niobium, and tungsten. The challenges were getting the
      additive to be uniformly distributed in the crystal lattice of the lithium
      iron phosphate at the right positions in the lattice to have the necessary
      effect on conductivity, he said.

      They knew they were on to something when something strange happened.
      "Lithium iron phosphate is normally medium gray color, not surprising for an
      electronic insulator," Chiang said. When one of the samples came out
      jet-black, "we realized that something special had happened," he said.
      "Highly conductive materials are usually either metallic in luster -- gold,
      silver, copper, aluminum -- or black in color -- carbon, oxide
      superconductors, magnetic ferrites."

      The material has a nanoporous crystal structure, said Chiang. Nanoporous
      materials contain holes nearly as small as atoms. "The nanoporous structure
      allows for rapid lithium transport into the electrode without impeding the
      electronic conductivity," he said.

      The formulation has proven very stable in abuse tests. This is "especially
      important for batteries that pack a lot of energy and will be used under a
      wide range of temperatures and electrical conditions," Chiang said.

      Lithium iron phosphate is also the basic formulation of a mineral found in
      the earth's mantle. Both this and the dopants the researchers added are
      considered nontoxic compared to nickel-cadmium or lead acid batteries, said
      Chiang. "We expect no environmental issues concerned with disposal," he
      said.

      The new type of lithium iron phosphate "looks like a major breakthrough,"
      said John Owen, a reader in electrochemistry at the University of
      Southampton in England for. "This discovery will certainly bring forward the
      arrival of a new type of lithium battery in its the next year or two," he
      said.

      Once the scope and mechanism of the effect are fully understood, "the way
      will be open to use a similar technique to improve many other materials in
      the field of energy conversion, [including] fuel cells and solar cells," he
      said.

      If the result turns out to be reliable, then this is most certainly
      interesting, said Josh Thomas a professor of solid-state electrochemistry at
      Uppsala University in Sweden, and director of the university's Advanced
      Battery Centre. The material "is at the absolute front line... in
      implementing new materials for developing better, cleaner, more powerful
      batteries for ever larger applications -- ultimately for traction
      applications in electric and electric/hybrid vehicles," he said.

      The researchers are currently working to understand exactly how the material
      conducts so well, said Chiang. "We want to understand the crystal chemistry
      and mechanisms of conduction in this material at a deeper level, to know
      where the atoms and electrons are and why the conduction is as high as it
      is," he said. The researchers are also planning to investigate similar
      compounds, he said.

      Because batteries based on the new electrode can use existing materials for
      the rest of the battery, the material could find its way into products
      within two years, Chiang said.

      Chiang is co-founder of A123Systems, which has licensed the technology from
      MIT and is working to commercialize it, according to Chiang.

      Chiang's research colleagues were Sung-Yoon Chung and Jason T. Bloking. They
      published the research in the September 22, 2002 issue of Nature Materials.
      The research was funded by the Department of Energy (DOE).
    Your message has been successfully submitted and would be delivered to recipients shortly.