Metal Mix Boosts Batteries by Kimberly Patch
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
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
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
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
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
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
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
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).