Pomegranate-Inspired Batteries Could Power Future

Batteries with pomegranate-like silicon nanoparticle anodes could be used in lithium-ion batteries of the future, researchers said.

Stanford University and the Department of Energy's SLAC National Accelerator Laboratory found that using electrodes with silicon nanoparticles clustered in a carbon shell are a better way to employ silicon anodes in lithium-ion batteries. The latest design is inspired by seeds in a pomegranate.

Silicon has been widely regarded as the most promising substance for anodes in next generation batteries.

"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, lead author of the study.

"Experiments showed our pomegranate-inspired anode operates at 97 percent capacity even after 1,000 cycles of charging and discharging, which puts it well within the desired range for commercial operation," Cui said in a news release.

Lithium-ion batteries work by moving electrons between cathode (positive electrode) and anode (negative electrode). Charging a battery causes electrons to shift towards the anode. Once the charge gets over, the electrons go back to the cathode.

Replacing graphite with silicon in batteries could increase their storage capacity. However, a major flaw with silicon anodes is that they tend to swell and break during charging. Also, they react with the electrolyte in the battery to form a slimy substance (gunk).

In a previous research paper, Cui and team demonstrated that using silicon nanoparticles can solve the breakage problem. They showed that keeping these nanoparticles in carbon yolk shells gives them enough space to expand during charging.

In the present study, researchers tweaked battery design by encasing the carbon yolk shells in a tough carbon rind. The second layer of carbon holds the clusters together and provides a path for electrical currents.

The pomegranate-like design also solves the problem with gunk; clusters are tightly packed, which reduces the surface area of the anode exposed to the electrolyte.

There are two more problems that Cui and team need to solve to make silicon anodes viable; they need to simplify process and find a good source of silicon nanoparticles.

According to the researchers, rice husks might be a good source for silicon nanoparticles. Rice husks are 20 percent silicon dioxide by weight. Researchers recently described how the husk could be used to source nanoparticles.

The study is published in the journal Nature Nanotechnology.