Bendy Battery, Speedy Charge!

A team of US scientists have built a prototype of what could become the first viable aluminium battery to hit the commercial market. But that's not all - this battery is cheap, safe, flexible, and only takes a minute to charge! Unlike conventional batteries that sit in a hard casing, the electrodes (cathode and anode) sit in a soft pouch, which is filled with a liquid salt solution. Also unlike conventional batteries, the anode is made from aluminium and the cathode of a graphite foam that the team has developed. The Stanford University team in California said that their battery has many advantages over those other batteries. For example, common alkaline batteries, those that you use in most electronic toys or devices, often aren't rechargeable. Even when the batteries are reusable, they will eventually get thrown away and have a harmful effect on the environment. Lithium-ion batteries are becoming increasingly common, found in such devices as smartphones. But if the battery becomes too overheated or damaged, it can spontaneously catch fire, making it a safety hazard. So much so, in fact, that some airlines have banned the batteries from being transported through the air. "Our new battery won't catch fire, even if you drill into it," declared Professor Hongjie Dai. He is the senior author of a paper on the battery that has been published in the journal Nature. Of course, you might not expect your battery to withstand such rough treatment on a regular basis, but these things are good to know. Aluminium has been attracting the attention of battery engineers for years because it is lightweight and inexpensive. But up until now, the material hasn't yielded a viable product. "People have tried different kinds of materials for the cathode," explained Professor Dai. "We accidentally discovered that a simple solution is to use graphite, which is basically carbon." The team tried out different graphite materials to see which generated the best results, finding that foam works the best. The battery can only function when the two electrodes are connected, which happens when the pouch is filled with the liquid salt electrolyte solution. At room temperature, the electrolyte is essentially just salt in liquid form, making it very safe and not flammable, unlike the electrolytes found in lithium-ion batteries. The empty pockets in the graphite sponge allow ions in the solution easy access to the graphite, helping the battery to work faster. The prototype battery can work through more than 7,000 cycles of the ions transferring between the anode and cathode. It's incredibly impressive when you take into consideration that most lithium-ion batteries only last around 1,000 cycles, and it's also hundreds of times better than any other previous experimental batteries made using aluminium. So far, the only downside that the team has found with the battery is the voltage output, which is half that of a lithium-ion battery. However, this two-volt output is still better than the 1.5 volts of an alkaline battery. Professor Dai believes the voltage can be improved if the team plays about with the cathode material, but at the moment they all have very high hopes for their battery. After all, they did manage to charge a smartphone in only a minute when they strapped two of the pouch batteries together and plugged them into an adaptor. "Our battery has everything else [apart from high voltage output] you'd dream that a battery should have," said Professor Dai. "I see this as a new battery in its early days. It's quite exciting!"