A new method to create long-lasting, rechargeable batteries for smartphones, laptops and other electronic devices has been devised by researchers.
The team showed how a coating that makes high capacity silicon electrodes more durable could lead to a replacement for lower-capacity graphite electrodes.
"Understanding how the coating works gives us an indication of the direction we need to move in to overcome the problems with silicon electrodes," said materials scientist Chongmin Wang of the Department of Energy's Pacific Northwest National Laboratory in US.
Thanks to its high electrical capacity potential, silicon is one of the hottest things in lithium ion battery development these days, researchers said.
Replacing the graphite electrode in rechargeable lithium batteries with silicon could increase the capacity ten-fold, making them last many hours longer before they run out of juice.
However, silicon electrodes are not very durable - after a few dozen recharges, they can no longer hold electricity.
Researchers have been using electrodes made up of tiny silicon spheres about 150 nanometres wide - about a thousand times smaller than a human hair - to overcome some of the limitations of silicon as an electrode.
The small size lets silicon charge quickly and thoroughly - an improvement over earlier silicon electrodes - but only partly alleviates the problem.
Last year, materials scientist Chunmei Ban and her colleagues at the National Renewable Energy Laboratory in Golden, Colorado, and the University of Colorado, Boulder
found that they could cover silicon nanoparticles with a rubber-like coating made from aluminium glycerol.
The coated silicon particles lasted at least five times longer - uncoated particles died by 30 cycles, but the coated ones still carried a charge after 150 cycles.
Researchers did not know how this coating improved the performance of the silicon nanoparticles.
The nanoparticles naturally grow a hard shell of silicon oxide on their surface, much like stainless steel forms a protective layer of chromium oxide on its surface.
The team discovered that, without the alucone coating, the oxide shell prevents silicon from expanding and limits how much lithium the particle can take in when a battery charges.
At the same time, they found that the alucone coating softens the particles, making it easier for them to expand and shrink with lithium.
Microscopic images showed the rubbery alucone replaces the hard oxide. That allows the silicon to expand and contract during charging and discharging, preventing fracturing.
The study was published in the journal ACS Nano.