Suw Charman-AndersonSep 15, 2011 18:14:22 IST
The lithium-ion (Li-ion) battery is the unsung hero of mobile technology, without which we'd all be tethered to the nearest power outlet.
The combination of Li-ion batteries and more efficient processors mean that new laptops can run all day on a single charge. To consider how far we've come, Tech journalist Alexis Madrigal recently estimated that if Apple's MacBook Air was as inefficient as computers 20 years ago, its battery would only last 2.5 seconds.
Now two improvements in Li-ion technology could make our battery-powered life safer, cooler and longer: A new polymer jelly could make batteries smaller, cheaper and safer, and new silicon anodes held together by seaweed extract could allow them to hold up to ten times more charge.
Researchers from the University of Leeds have created a new polymer gel which would replace the liquid electrolyte now used in most batteries. This liquid electrolyte can cause common battery problems, such as overheating and "thermal runaway", a rather euphemistic way of saying that the batteries have reached temperatures high enough to catch fire.
Laptop manufacturers have long struggled with thermal runaway. In 2006, Dell had to recall 4 million batteries after a number of their laptops caught fire, whilst Apple had to recall 1.8 mn batteries. Last year, 54,000 batteries were recalled by HP.
Traditional Li-ion batteries are made of a positive electrode (anode) separated by a porous film from a negative electrode (cathode). The ensemble is bathed in a liquid electrolyte, usually an organic solvent which is hazardous and flammable. The battery gets its name from the anode, which is made of lithium cobalt oxide.
The new gel is sandwiched between the anode and the cathode, removing the need for the separator, reducing bulk and cost. The electrodes are sealed together with the gel in between, creating a "highly-conductive strip that is just nanometres thick," so there is no excess electrolyte to catch fire. Says Professor Ward:
"The polymer gel looks like a solid film, but it actually contains about 70% liquid electrolyte. It's made using the same principles as making a jelly: you add lots of hot water to 'gelatine' - in this case there is a polymer and electrolyte mix - and as it cools it sets to form a solid but flexible mass."
In the meantime, researchers at the Georgia Institute of Technology and Clemson University have discovered a way to improve the anodes used in Li-ion batteries so that they can hold up to ten times more charge. Currently, anodes are made of graphite, despite the fact that silicon anodes hold more charge. Silicon anodes aren't used, however, because they degrade quickly. But a common food additive is set to change that.
Anodes are usually made by mixing graphite powder with a polymer binder which sticks it to a metal foil. Silicon is more effective than graphite at holding the ions that charge the battery, but they swell by up to four times as the battery charges, which cracks the binder and damages the anode.
The food additive, a binding agent made from brown algae of the sort also found in giant kelp forests, can be used to create a stable silicon anode. Although the silicon particles still swell, the binder stretches with them, preserving the integrity of the anode.
Even better, the alginate binder dissolves in water, removing the need for the solvents currently used to create graphite anodes. This means a cleaner and more environmentally friendly manufacturing process. The researchers think that it should be possible to simply swap in the new materials without having to change processes, which will make it easy for manufacturers to adopt.
Together, these advances could mean cooler, smaller, cheaper batteries that hold more charge. And that means cooler, cheaper devices that won't burn ears or thighs and will stay charged for longer. At last, we may end up with mobile devices that truly are mobile!
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