Date Posted: 10/21/2012 12:29:15 PM
Posted By: sashoo Membership Level: Silver Total Points: 382
For quite some time now, designers of batteries have been searching for the next outstanding thing in the technology of energy storage that could, even, be a replacement to the batteries of lithium ion. These batteries are utilised in almost everything today - ranging from cars to smartphones to laptops. It goes without saying that the designers, may have rethought about the current li-ion batteries. The researchers of Northwestern University have redesigned a battery of lithium ion that is, not only, capable of holding the charge of the latest batteries on the market, but it also charges tenfolds faster.And what's the magic? It's actually in the reengineered anode that addresses the two paramount concerns holding li-ion batteries - charge rate and energy capacity. These batteries function through a chemical reaction, whereby, the lithium ions are interchanged between the two battery ends - the cathode and the anode. As the device burns energy, ions move from their storage area (from the anode to the cathode) via an electrolyte. During this process, there is transfer of electrical charge to the device as the ions initiate the transition via the electrolyte. But when the battery charges, the motion of the ions occurs in the opposite direction (from cathode to anode).The design of the current anode is based on sheets of graphene which are, basically, carbon layers that are one atom thick - the sheets provide storage for the lithium ion. But the charging rate of these anodes is rather low as they are capable of, just, storing a single lithium per six carbon atoms. On the other hand, silicon, which has been experimented on by designers, holds four atoms of lithium per silicon atom. It, however, has a tendency of significantly contracting and expanding during the process of charging. Consequently, it gets fragmented, naturally reducing the anode's lifetime.A design that is based on graphene reduces the charge rate too. The graphene sheets have an ultra thin, yet, exceptionally long geometry and, as such, the lithium ions undergo a long trip as they force their way towards the edges of these sheets. Which is why a bottleneck kind of ion forms around the anode's edges, significantly slowing down the charge rate.The team from Northwestern University significantly sailed through these problems by first rethinking the anode, then the hybrid (graphene-silicon) incorporation. No wonder the design facilitates a double boost of both charge rate and energy capacity. Initially the team sandwiched silicon layers between the sheets of graphene, a thing that allowed vast numbers of lithium ion to settle there. And beware that the silicon still contracts and expands during the charging and discharging process, but the anode is held together by graphene's flexibility. This means that it doesn't matter when the silicon gets fragmented, it will obviously stay in place, and greater charge will be held by the anode.This university team then drilled tiny holes (a diameter of 10 to 20 nanometers) in sheets of graphene by use of chemical oxidation. The reason it did this was to enable the lithium ions move via the graphene, rather than going way around the anode's edges - where traffic jams occurred. This shortcut lets lithium ions quickly pile in the anode during charging, resulting in a tenfold charge rate.And that is just for the anode. In their next plan, the researchers are to rethink about the cathode so as to make it most effective and efficient. It, certainly, goes without saying the improved li-ion battery could, probably, in the next 3 to 5 years, hit the market place.
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