If you can make a battery out of a piece of citrus, why not a crustacean? Scientists at Stanford University are taking a look at the nanostructure of crab shells to create better lithium-ion batteries. The scientists first put a series of shells through a chemical process that turned them into hollow carbon nanotubes. They then stuffed these tiny tubes with sulfur and silicon, and tested them as electrodes. They found that not only did the anode and cathode hold a good amount of their charge after several hundred testing cycles, but the crab shells could help form a cheap, renewable base for batteries.
Most lithium-ion batteries use lithium cobalt oxide in their cathodes and cobalt anodes. However, if they used silicon as the anode and sulfur as the cathode, they could potentially increase their storage capacity by 10 times. Unfortunately, the materials cause the electrodes to expand and contract so much when reacting with the electrolyte that they eventually crack and make for very short battery life. To prevent this from happening, researchers have attempted to place the sulfur and silicon inside nanostructures like carbon nanofibers.
Yi Cui and a team of scientists at Stanford observed that crab shells could act as frameworks for the electrodes instead of carbon. The shells consist of tiny channels only 70nm wide and are perfect to house the electrodes. To test their technique, Cui and colleagues purchased stone crabs from a local Chinese grocery store. After isolating the nanofibers, they filled them with either sulfur or silicon. They then ran the electrodes through 200 charge and discharge cycles. The saw that the electrode with the sulfur kept 60% of its storage capacity and the one with silicon maintained 95%. Most cellphone batteries hold 80% of their charge after 500 cycles, although a full comparison cannot be made as Cui’s tests were just with electrodes and not full batteries.
The food industry throws away 500,000 tons of crab shells each year, and using the waste stream as a source for battery production would not only help to deal with disposal, but create more efficient batteries from a more renewable source.
Images via Stanford and Wikicommons user Andrea Westmoreland.