Though the use of silicon in lithium-ion batteries promises a whole new world of energy storage, it also poses several problems to a battery's durability and overall performance. A new electrode design inspired by clusters of pomegranate seeds and developed by researchers at the Department of Energy's National Accelerator Laboratory (SLAC) and Stanford University, overcomes some of these obstacles, bringing lighter and more powerful batteries closer to reality.

An anode (the part of the battery that stores energy while the battery is charging) made from silicon is able to store ten times the charge of graphite anodes used in today's lithium-ion batteries. This holds significant possibilities for extending the battery life of common gadgets such as cell phones, tablets and mobile phones, but there are various hurdles that must first be overcome.

The fragile nature of the silicon compared to graphite causes it to swell and eventually break while the battery is charging. It also reacts nastily to the electrolyte of the battery, causing a gunk to form on its coat and compromise the battery's performance. Previously, researchers have overcome these problems by using silicon nanoparticles, which are already too small break, and placing them in protective casings or "yolk shells" made from carbon, with enough spare room inside for them to swell and shrink without causing damage.

This latest breakthrough involved a microemulsion technique commonly seen in oil, paint and cosmetic industries whereby the researchers gathered the yolk shells into clusters. By then applying another coat of carbon around the cluster, the team created a stable and more efficient highway for electrical currents.

In addition, the "pomegranate" design reduces the surface area of the cluster to one tenth of the sum of the individual particles inside, in effect, decreasing the area exposed to the electrolyte and the amount of gunk, improving overall performance.

"While a couple of challenges remain, this design brings us closer to using silicon anodes in smaller, lighter and more powerful batteries for products like cell phones, tablets and electric cars," said Yi Cui, an associate professor at Stanford and SLAC who led the research.

The remaining obstacles identified by the researchers include the need to simplify the process and also finding a cheaper source of silicon nanoparticles. The team has earmarked rice husks as a possibility. Unfit for human food, there is an abundant supply and, according to the researchers, are 20 percent silicon dioxide by weight, meaning the husks could be easily transformed to pure silicon nanoparticles.

The team's findings were published in the journal Nature Nanotechnology.

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