Flexible Aluminum Battery for Smartphones

Would you be interested in a battery that takes only a second to charge up and is flexible enough to wrap around your smartphone? While manufacturers would be more interested in the flexibility feature, most users will welcome the quick charging time. At Stanford University, researchers claim to have developed such a battery from cheap, plentiful materials. It is flexible and charges up very fast as well.

The new aluminum battery has a foil anode made of flexible aluminum, a cathode of graphite foam and an electrolyte of liquid salt. Researchers at the Stanford University say they discovered this aluminum and graphite battery quite by accident, but have worked on their discovery to improve its performance, especially the graphite cathode part.

Compared to a lithium-ion battery, the aluminum battery with its porous graphite cathode offers only one-third the capacity at a terminal voltage of 2.5V. Therefore, two aluminum batteries must be used in series to power most devices requiring 5V. However, the aluminum battery has a property that gives it an edge over its lithium-ion rival – a very high Coulombic efficiency of above 95%. Researchers are currently engaged in optimizing the capacity and other desirable qualities to match or surpass those of lithium-ion batteries.

The aluminum battery uses a liquid electrolyte, making it cheap and nonflammable. This is an ionic liquid made by mixing two solid precursors – EMIC and AlCl3, where EMIC stands for 1-ethyl-3-methyl-imidazolium chloride and AlCl3 is aluminum chloride. While both compounds are individually solid, mixing them significantly lowers the melting point of the mixture so that it remains a liquid at room temperatures. The liquid electrolyte and the porous graphite electrode contribute to the super-fast recharging time, and the amount of current the aluminum battery can deliver.

The porous graphite foam cathode presents a large surface area, which is the governing factor for accessing the electrolyte. While charging, the large surface area presents a low energy barrier to the process of intercalation. The team expects the flexibility of the battery will be useful to manufacturers making flexible smartphones in the future.

The main attraction of the aluminum battery as compared to the lithium-ion batteries currently available is its capability of fast recharge. In fact, even the prototype reached 7.5 times the rate of charging of a commercial lithium-ion battery. Typically, lithium-ion batteries loose significant capacity after they have reached about 1000 recharge cycles. In comparison, an aluminum battery is capable of withstanding more than 7500 charges without any loss of capacity.

That makes the aluminum battery suitable for large installations such as storing solar energy during the day for release at night on the grid. These batteries are a perfect replacement for the lithium-ion batteries that occasionally burst into flames and for alkaline batteries that are bad for the environment. According to the researchers, even if someone were to drill through an aluminum battery, it will not catch fire.

At present, the only drawback is the terminal voltage. However, the researchers are optimistic that with a better cathode material, the aluminum battery can be made into a more powerful commercial battery.