Pomegranate Points Way To Silicon-Based Li-Ion Battery

Science describes nature, but science also borrows from nature. We’ve heard about a solar leafa smart watch inspired by buzzing insects, a hybrid car inspired by water, self-cleaning glass inspired by a carnivorous plant, a scooter steering system inspired by horses, a building design inspired by a bird … you get the idea.

The latest in the parade of nature-inspired technological advances is a next-generation lithium-ion battery concept inspired by the pomegranate. It’s a concept that could result in “smaller, lighter and more powerful batteries for products like cell phones, tablets and electric cars,” its developers say.

pomegranate battery

Illustration via SLAC/Greg Stewart

According to the U.S. Department of Energy’s SLAC National Accelerator Laboratory, an electrode “designed like a pomegranate” that includes “silicon nanoparticles clustered like seeds in a tough carbon rind … overcomes several remaining obstacles to using silicon for a new generation of lithium-ion batteries.”

Silicon is an attractive anode material in batteries because it has greater charge-holding capacity than the graphite, or carbon, that is used in batteries today. But heretofore, in attempting to put it to work, the “brittle silicon swells and falls apart during battery charging, and it reacts with the battery’s electrolyte to form gunk that coats the anode and degrades its performance,” SLAC said.

To overcome this issue, the SLAC/Stanford crew used silicon nanowires or nanoparticles that are so small, they can’t break into anything smaller. These silicon nanoparticles were then encased in carbon “yolk shells” that can expand and shrink, then packed together like seeds in a pomegranate. “Each cluster has a carbon rind that holds it together, conducts electricity and minimizes reactions with the battery’s electrolyte that can degrade performance,” SLAC said.

Now, we should wave a bit of a caution flag here: Yi Cui, the associate professor at Stanford University and SLAC who led the research, said “a couple of challenges remain” on this concept. Cui as well as anyone knows that progress in the laboratory on batteries is not quickly translated to manufacturing and the market. Cui was a founder of Amprius, the Silicon Valley startup that began stalking silicon-based li-ion batteries in 2008. As Greentech Media’s Jeff St. John recently reported, the company only in the past year has begun producing its first-generation battery, one that uses a mixed silicon/carbon technology.

The challenges the researchers face with the pomegranate plan? “They need to simplify the process and find a cheaper source of silicon nanoparticles,” SLAC said. “One possible source is rice husks: They’re unfit for human food, produced by the millions of tons and 20 percent silicon dioxide by weight. According to Liu, they could be transformed into pure silicon nanoparticles relatively easily, as his team recently described in Scientific Reports.”

The research behind the battery is written up in the peer-reviewed scientific journal Nature Nanotechnology.

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.