Stanford researchers have developed a flexible aluminium battery that charges in under a minute and may be safer than lithium-ion models. The downside is that it has a lower voltage than most rechargeable batteries.

Rather than a solid casing, the battery consists of a pouch filled with two metals and a liquid. The anode is aluminium, while the cathode is made of graphite, both of which are comparatively light and cheap. The electrolyte is a salt that is liquid at room temperature.

To improve the performance, the researchers designed the battery by using the graphite in foam form. That allows easy access by the ions to the spaces between each of the ultra-thin layers of the graphite, in turn speeding up the charging process.

One advantage is that the battery should have a longer life-span than existing models, with the researchers saying it should run through 7,500 complete charging cycles without losing capacity. That compares with only a few hundred cycles in some popular smartphone batteries.

The design is also said to reduce the chances of a short-circuit that could lead to overheating and even explosion. Indeed, the researchers even found the battery continued working for a short period after they drilled right through it.

The main limitation is that the prototype battery only delivers two volts. That’s more than a standard disposable or rechargeable AA battery, but only around half that delivered by lithium-ion batteries. For the moment the researchers have been testing by connecting two batteries to a phone via an adapter, but they believe there’s room to get more volts from a battery that can fit in an ordinary phone slot.