Researchers at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory has invented an electrode designed like a pomegranate with silicon nanoparticles clustered like seeds in a tough carbon rind, that they say overcomes several obstacles to using silicon for a new generation of lithium-ion batteries.

A novel battery electrode features silicon nanoparticles clustered like pomegranate seeds in a tough carbon rind. (Credit: Greg Stewart/SLAC)

Experiments showed our pomegranate-inspired anode operates at 97 percent capacity even after 1,000 cycles of charging and discharging, they explained.

Silicon anodes, where energy is stored when a battery charges, could store 10 times more charge than the graphite anodes in today’s rechargeable lithium-ion batteries, but they also have major drawbacks: silicon is brittle, swells, and falls apart during battery charging, and it reacts with the battery’s electrolyte to form a substance that coats the anode and degrades its performance.

Using a microemulsion technique, they gathered tiny pieces into clusters, and coated each cluster with a second, thicker layer of carbon. These carbon rinds hold the pomegranate clusters together and provide a sturdy highway for electrical currents. And since each pomegranate cluster has just one-tenth the surface area of the individual particles inside it, a much smaller area is exposed to the electrolyte, thereby reducing the amount of muck that forms to a manageable level.

Although the clusters are too small to see individually, together they form a fine black powder that can be used to coat a piece of foil and form an anode. Lab tests showed that pomegranate anodes worked well when made in the thickness required for commercial battery performance.

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