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Viable aluminium-ion battery is safe, durable and flexible

07 April 2015

A new aluminium-ion battery developed by researchers at Stanford University could replace many of the lithium-ion and alkaline batteries in wide use today.

The researchers demonstrate the flexibility of their aluminium-ion battery (image courtesy of Stanford University)

This first high-performance aluminium battery, comprising an aluminium anode and a graphite cathode, is fast-charging, long-lasting, flexible and inexpensive. 

"We have developed a rechargeable aluminium battery that may replace existing storage devices, such as alkaline batteries, which are bad for the environment, and lithium-ion batteries, which occasionally burst into flames," says Hongjie Dai, a professor of chemistry at Stanford. "Our new battery won't catch fire, even if you drill through it."

Dai and his colleagues describe their novel aluminium-ion battery in the April 6 advance online edition of the journal, Nature

Aluminium has long been an attractive material for batteries, mainly because of its low cost, low flammability and high-charge storage capacity. For decades, researchers have tried unsuccessfully to develop a commercially viable aluminium-ion battery.  A key challenge has been finding materials capable of producing sufficient voltage after repeated cycles of charging and discharging.

"People have tried different kinds of materials for the cathode," says Dai. "We accidentally discovered that a simple solution is to use graphite. In our study, we identified a few types of graphite material that give us very good performance."

For the experimental battery, the Stanford team placed the aluminium anode and graphite cathode, along with an ionic liquid electrolyte, inside a flexible polymer-coated pouch.

"The electrolyte is basically a salt that's liquid at room temperature, so it's very safe," says Stanford graduate student Ming Gong, co-lead author of the Nature study.

"In our study, we have videos showing that you can drill through the aluminium battery pouch, and it will continue working for a while longer without catching fire," Dai says. "But lithium batteries can go off in an unpredictable manner  – in the air, the car or in your pocket. Besides safety, we have achieved major breakthroughs in aluminium battery performance."

One example is ultra-fast charging. The Stanford team reported "unprecedented charging times" of down to one minute with the aluminium prototype.

Durability is another important factor. The Stanford battery was able to withstand more than 7,500 charge cycles without any loss of capacity. By comparison, a typical lithium-ion battery lasts about 1,000 cycles.

"Another feature is its flexibility," Gong says. "You can bend it and fold it, so it has the potential for use in flexible electronic devices."

"Millions of consumers use 1.5-volt AA and AAA batteries," Dai says. "Our rechargeable aluminium battery generates about two volts of electricity. That's higher than anyone has achieved with aluminium."

While the Stanford battery produces about half the voltage of a typical lithium battery, the researchers believe that improving the cathode material could eventually increase its voltage and energy density.

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