Imagine an amazing cellphone battery that lasts a whole week on one charge and takes a mere 15 minutes to recharge from flat. Sounds like science fiction or a dodgy claim, right? Well, incredibly, it isn't, but we will have to wait three to five years for such a wonder. Current high-end smartphones usually have to be recharged once a day, because battery technology really hasn't advanced enough to keep up with their increasing power demands. The same is also true of course, of anything else that uses batteries, such as laptops and electric cars. In the latter case, the batteries cost thousands, go flat pretty quickly, take an age to recharge and don't have that great a working lifetime. No wonder electric cars are still shunned by people that want real performance and practicality from their cars.

But all these frustrating limitations are set to end, if research with the catchy name of "In-Plane Vacancy-Enabled High-Power Si-Graphene Composite Electrode for Lithium-Ion Batteries" published in the November 2011 issue of Advanced Energy Materials is anything to go by. The lead author of this article (paywall) is Harold H Kung, who is professor of chemical and biological engineering in the McCormick School of Engineering and Applied Science. He also is a Dorothy Ann and Clarence L. Ver Steeg Distinguished Research Fellow. So, a pretty bright bod, then. He has written in the article:

We have found a way to extend a new lithium-ion battery's charge life by 10 times. Even after 150 charges, which would be one year or more of operation, the battery is still five times more effective than lithium-ion batteries on the market today.

That's amazing. Really amazing and the kind of breakthrough the world has been waiting impatiently for, for years. So, how has this been achieved? There are two main problems that have been overcome - and overcome in one fell swoop.Explained in simple terms that one can understand over a rushed breakfast after having spilled the coffee, is that when charging a lithium-ion battery, the speed at which the anode can absorb lithium ions is very low, therefore making charging times lengthy. Also, the capacity of the battery to hold charge is limited by the charge density, or how many lithium ions can be packed into the anode or cathode. This affects how long the battery lasts before it goes distressingly flat and that powerful high end smartphone turns into a beautifully crafted paperweight. Or you plug the charger in.

These limitations come about due to the multiple single atom thick graphene sheets that are used to make the anode in the batteries, because of the length of time the ions take to cross them and be snuggled between these sheets, all nice and comfy, is quite long. These limitations can be overcome by using silicon instead of graphene - yes, the same abundant material used to make computer chips, eliminating one source of shortage of raw material. Silicon has the wonderful ability to allow fast charging by allowing lithium ions a free pass to their resting place within the anode and also has a large capacity to store them, solving both problems in one. But, as always, there's a gotcha and things aren't so simple. The silicon expands and contracts significantly during the charging process, which causes it to fragment and lose its charge holding capacity, making it useless.

The problem was solved by the research team, by blending the use of graphene and silicon. They made a sandwich of two graphene sheets, with clusters of silicon used as the yummy filler. This allows for a much greater number of lithium atoms in the electrode, while the graphene allows the silicon to expand and contract as it requires, as Kung explained:

Now we almost have the best of both worlds. We have much higher energy density because of the silicon, and the sandwiching reduces the capacity loss caused by the silicon expanding and contracting. Even if the silicon clusters break up, the silicon won't be lost.

This however, isn't the whole story. The research team were able to speed up recharge by a massive ten times, by creating what they call "in-plane defects" in the graphene, which gives the lithium ions a shortcut into the anode and be stored there by reaction with the silicon. These 'defects' are actually tiny holes of around 10 to 20 nm in size, which are dotted around the graphene sheet.

Finally, it doesn't matter how fancy or high performance the battery is, if it has the tendency to burn or explode. The researchers are now looking into developing an electrolyte which will allow it to automatically shut off at high temperatures, while having the benefit of being reversible. This safety system could prove vital in electric cars in cases of short circuits or damage due to road accidents.

Just think, you could be on the train where there's no mains power and be playing the latest Call of Duty blockbuster on battery power on your high-powered laptop for three or four hours. At the end of the journey, the batteries would still have a lot of charge left in them and a recharge of say, 30-60 minutes would be enough to fully refresh them. Yup, amazing. The other side effect of course, is that all those small batteries such as the AA size, D size etc may suddenly cost a whole lot more, as sales reduce significantly, but this is a relatively small price to pay for such incredible performance improvements.

For a fuller explanation of how these batteries work - requiring extended concentration and strong coffee - see the source article at Northwestern University. It's a very good read.