These use a magnesium metal anode and could have two to three times the energy density of the best lithium-ion batteries. In addition, tests have shown they hold the majority of their charge over 3,000 charge cycles, many more than today’s smartphone batteries. Magnesium is also cheap and abundant. However, the technology is still unproven. To be truly useful, researchers need to find a suitable cathode, something that has held back previous efforts. And this is where his computational approach comes in.
Prof Ceder and his colleagues have virtually screened more than 12,000 materials. Those that show potential are synthesized and tested. At least four materials are now being studied in detail. He claims that one cathode material has already demonstrated performance that would create batteries with greater energy density than today's lithium ion technology. He will not reveal more details, but it is enough to have attracted significant interest from investors and the US military. He has also established a start-up called Pellion Technologies to exploit the technology, initially for use in cars. However, if he is successful the technology could trickle down to mobile phones in years to come.
Apple juice
If and when it does, it may have to compete with another powerful contender for your future phone – the fuel cell. Like batteries, these convert chemical energy into electricity through a chemical reaction. However, these work more like tiny engines, converting the chemical energy from a fuel – an alcohol, say - into electricity through a chemical reaction with oxygen. And like an engine, they continue to run providing there is enough fuel and oxygen flowing through them.
They are an old technology dating back to the 19th Century and were successfully used to power elements of the early Gemini and Apollo space missions, for example. But they have now caught the attention of phone manufacturers because they have a high energy density. Simply put, fuels contain lots of energy. For example, hydrogen contains nearly 150 times the energy of an equivalent weight of lithium. However, to be workable they need to be small and have an easily rechargeable reservoir for fuel.
To build these, researchers are focusing on so-called MEMs technology - miniaturized mechanical devices and structures built using the patterning and etching techniques pioneered to build early computer chips. These are already used to make everything from solar cells to flat-screen TVs. Crucially, these techniques have advanced to the point where they can now be used to construct complex 3D structures – such as the networks of channels and pipes necessary for a tiny fuel cell.
The technology can be expensive, with precious metals such as platinum and palladium used to speed up chemical reactions, and hydrogen sources, even when compressed or in liquid form, taking up a lot of space. There are also the practicalities of having to moving and storing the fuel necessary to charge your phone on the go, not to mention the potential problems of handling potentially toxic fuels to make a phone call.
However, companies such as NEC and Toshiba have already shown off prototype fuel cells for mobiles. And in December 2011, news that Apple had filed two more patent applications for fuel cells for portable electronic devices reignited interest. The applications showed the company is proposing the use of reducing agent sodium borohydride, which when mixed with water generates pure hydrogen, and that they would be used alongside a battery to cut down on size, weight and cost. The documents suggest the technology could power devices for "days or even weeks".
But, according to St Andrew’s Prof Bruce, we should not get too excited yet. “In the longer term there are these radical technologies which could transform energy storage for consumer electronics applications,” he says. But, for the next few years, he believes, lithium-ion batteries are here to stay. Better remember to pack that charger.
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