The holy grail of battery design

Battery cathodes have long been made of Lithium. Anodes (the part of the battery that discharges the electrons to race around their circuit) are another story.

During charging, the positively charged lithium ions in the electrolyte are attracted to the negatively charged anode, and the lithium accumulates on the anode. Today, the anode in a lithium ion battery is actually made of graphite or silicon.

Engineers would like to use lithium for the anode, but so far they have been unable to do so. That’s because the lithium ions expand as they gather on the anode during charging.

All anode materials, including graphite and silicon, expand somewhat during charging, but not like lithium. Researchers say that lithium’s expansion during charging is “virtually infinite” relative to the other materials. Its expansion is also uneven, causing pits and cracks to form in the outer surface, like paint on the exterior of a balloon that is being inflated.

The resulting fissures on the surface of the anode allow the precious lithium ions to escape, forming hair-like or mossy growths, called dendrites. Dendrites, in turn, short circuit the battery and shorten its life.

Stanford scientists have solved this problem, using carbon nano spheres that sit on top of the lithium anode.

The Stanford team’s nanosphere layer resembles a honeycomb: it creates a flexible, uniform and non-reactive film that protects the unstable lithium from the drawbacks that have made it such a challenge. The carbon nanosphere wall is just 20 nanometers thick. It would take about 5,000 layers stacked one atop another to equal the width of single human hair.

This means batteries that don’t degrade with repeated charge/discharge cycles, and batteries that are an order of magnitude more efficient. This also means a safer battery (no more battery overheating), much longer and more efficient phone batteries, and electric cars that can go 300 miles on a charge.