Bendy battery promises safe, speedy charging

Scientists have built a flexible aluminium battery which they say could be a cheap, fast-charging and safe alternative to current designs, the BBC reports.

The battery consists of a soft pouch containing aluminium for one electrode, and a graphite foam for the other - all surrounded by a special liquid salt.

It can recharge in less than a minute and is very safe and durable compared to lithium-ion batteries, but currently only delivers about half the voltage.

The work appears in the journal Nature.

The researchers say it has advantages over lithium-ion batteries, common in electronic devices like smartphones, as well as traditional alkaline batteries.

"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," said senior author Prof Hongjie Dai from Stanford University in California.

"Our new battery won't catch fire, even if you drill through it."

In fact, a video made by the research team shows that the battery even continues to work for a short period after being punished in this way.

We may not expect batteries to withstand such treatment routinely - but this demonstration certainly sets the new design apart from lithium-ion batteries, which have faced safety concerns including recent bans on air transport.

Because it is lightweight and inexpensive, aluminium has attracted interest from battery engineers for many years, but it has never yielded a viable product.

Key to the new discovery was the choice of material for the other, positive electrode (the cathode) to go with aluminium for the negative electrode (or anode). Graphite - a form of carbon in which the atoms form thin, flat sheets - turned out to deliver very good performance, while also being similarly lightweight, cheap and widely available.

To connect the two electrodes, the pouch is filled with liquid.

"The electrolyte is basically a salt that's liquid at room temperature, so it's very safe," said PhD student Ming Gong, another of the study's authors. This contrasts with the flammable electrolytes used in lithium-ion batteries.