New Rechargeable Magnesium Battery System
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Ramat-Gan, Israel May 4, 2004; A
new and revolutionary rechargeable Magnesium battery system has been
developed for heavy-load applications such as high performance PEVs. A
team of scientists under the direction of Dr. Doron Aurbach at the
Chemistry Department of Israel's Bar-Ilan University has developed a
rechargeable magnesium battery system that can be recycled many
thousands of times with extremely low capacity fading.
This
is a "green" and safe battery technology, meaning it is environmentally
non-toxic as well as being non-explosive. It is also very lightweight
and incredibly cheap to produce. Magnesium is the seventh most abundant
metal on earth so it's an ideal material for making into batteries. It
has a repoted energy density of 60 Wh/Kg. Unlike nickel-metal-hydride
technology, this magnesium battery system demonstrates virtually NO
self discharge! This means that once charged, the pack can be left in a
charged state for long periods of time without damage. This should make
the batteries very attractive to sales outlets as they can sit on a
shelf indefinitely without harm unlike most current batteries which
have a limited shelf life. Dr. Aurbach's team also reports the battery
has an operating temperature of -20C to 60C and possesses a
stable
almost constant voltage of 1.2V per cell. This is hugely significant as
it means that these cells should not suffer from reduced range in
colder climates. Lead acid technology can lose half of its practical
range or more in sub 0C temperatures. The constant cell voltage of
1.2V per cell matches very well with applications in 6V multiples (5 x
1.2V cells) which includes most EV applications.
Aurbach and colleagues began by using pure magnesium anodes. But
magnesium metal is too brittle to fashion into the thin sheets that are
needed for these cells. So instead the researchers now use an alloy of
magnesium called AZ-31, which is 3% aluminium and 1% zinc. This
provides both the flexibility to form into thin sheets as well as
incredible durability so that the anodes don't get consumed in the
discharge/recharge process.
For the cathode, the team needed to use or create a material full of
tiny gaps into which magnesium ions can fit. The researchers had
previously discovered that magnesium ions can pass in and out of a type
of molybdenum sulphide, called Mo6S8. They make this material from a
version containing copper, then replace the copper with magnesium. At
first they used electricity to replace the copper with magnesium, but
as this is not a practical way to make commercial batteries, they have
perfected a way of replacing the copper using a cost efficient chemical
reaction instead.
The final ingredient in this new battery is the electrolyte. Aurbach's
team uses a polymer gel, an organic liquid, and a chemical that reacts
favorably with magnesium facilitating the efficient transfer of the
magnesium ions.
The biggest advantage of these new cells are the extremely long life
and durability of the cells themselves. Every other battery technology
consumes the battery as part of the discharge/recharge process. This
gives them an extremely limited shelf life. Lead acid batteries are
typically good for a year or less under daily 80% depth of discharge
usage. While nickel-metal-hydride cells and lithium-ion cells are
supposed to last longer, in reality they are not delivering the
thousands of cycles that the chemistry promises. Some only last for a
matter of months due to charging and temperature issues, and these
chemistries have other problems as well. These new Magnesium cells do
no consume themselves as part of their normal cycle process. This means
that the cells will last more than 20 years of daily full discharge
usage. Your batteries should outlast any vehicle you put them into, and
cycle #5000 will deliver just as much range as cycle #50. Imagine
batteries that last for decades (instead of months) and never get weak!
That's exactly what this technology promises.
Dr.
Aurbach said he feels confident that with additional research, the new
battery's energy density can be increased to rival or surpass that of
lithium-ion! "Lead acid, lithium-ion and nickel-metal-hydride batteries
do not have a long enough useful lifespan," said Aurbach. "In addition,
there are very important safety and toxicity issues to consider when
using those technologies to collect and store megawatts of energy.
Because magnesium batteries are non-explosive, non-toxic, do not
self-discharge and have a virtually limitless cycle life, they appear
to be the best choice over all other existing energy storage systems."
"Magnesium batteries can be engineered for any electrically powered
device which might benefit from the availability of a non-portable
battery able to undergo thousands of charge/discharge cycles," said
Meir Ezra, president and CEO of Idea One, the US company that will be
marketing the cells. "Such applications could include electric cars,
golf carts, electrically powered forklifts and utility vehicles, and
electrically powered scooters and bicycles, to name a few."
Currently, kilo-per-kilo, the new magnesium batteries are capable of
generating roughly twice the amount of energy as their lead-acid
counterpart, but only half the energy of lithium-ion batteries. Aurbach
and his team are currently researching methods to increase the energy
density of their magnesium battery so it will produce as much or more
power than the lithium-ion batteries which Aurbach helped invent and
which now power millions of portable electronic and communications
devices throughout the world.
"It took us several decades to come up with a good rechargeable lithium
battery - the lithium-ion system," said Dr. Aurbach. "Because we have
so many years of experience with Lithium science and battery
electrochemistry, I can speculate we may quite quickly develop a
magnesium battery with a comparable or greater energy density than is
now available from Lithium batteries."
This
may just be the radical battery technology breakthrough that we have
all been waiting for. Because these cells can handle heavy loads both
into and out of them, they are ideal for high performance electric
scooters, bicycles, motorcycles, and cars. They also provide rapid
recharging capabilities making them a nearly ideal battery system.
Hopefully, since this technology is being developed outside of North
America, this battery technology will be brought to the international
market very rapidly and we will see the benefit of it across the entire
EV segment within a very few years.
Click
here to read Professor Aurbach's biography
Click here to visit the Bar-Ilan
University Chemistry department website
Click
here for a 1.6MB PDF update sent to V is for Voltage from Dr. Aurbach's
team