In this age of smartphones and tablets, batteries are the life force that makes the world go round. Scientists are continually looking for ways to make batteries more efficient and powerful. Last year, for instance, a team of Singaporean researchers developed a new type of Li-ion battery that can be charged to 70-percent of its total capacity in a matter of 2 minutes. As part of a new project, scientists at Vanderbilt University have devised yet another innovative technique, by which a smartphone battery can be fully charged in less than 30 seconds!
Recently published in the journal ACS Nano, the research is based on the existing knowledge that adding quantum dots (basically, nanocrystals about 10,000 times smaller than the width of a single human hair) to a regular smartphone battery actually improves its efficiency to a large extent. However, one problem with this approach is that, more often than not, the newly-gained efficiency lasts only for a few recharge cycles. In this new research, the scientists have found an ingenious way to eliminate the problem.
According to the team, using quantum dots made of iron pyrite can not only reduce the battery’s charging time, but also increase its lifespan to dozens of cycles. What makes this breakthrough all the most significant is the fact that iron pyrite is one of the most abundant materials found in the earth’s surface. Generated as a byproduct of coal production, the substance is quite cheap and, is commonly known as fool’s gold, thanks to its sparkling gold-like luster. Speaking about the research, Cary Pint, an assistant professor at the university’s Mechanical Engineering Department, says:
Researchers have demonstrated that nanoscale materials can significantly improve batteries, but there is a limit. When the particles get very small, generally meaning below 10 nanometers (40 to 50 atoms wide), the nanoparticles begin to chemically react with the electrolytes and so can only charge and discharge a few times. So this size regime is forbidden in commercial lithium-ion batteries.
To determine the size of the crystals best suited for this technology, the researchers added millions of differently-sized iron pyrite particles to lithium button batteries, similar to the ones used in wrist watches, LED flashlights and pocket calculators. Super-small nanocrystals, around 4.5 nanometers in size, were found to substantially enhance the batteries’ rate and cycling capacities. This, according to the scientists, was brought about by iron pyrite’s unique ability to change forms, as a way of storing energy. Unlike standard batteries, where lithium stores energy without altering the material that contains it, the iron pyrite nanocrystals in the new battery change into iron and lithium-sulfur (or sodium-sulfur) compounds. Pint elaborates:
You can think of it like vanilla cake. Storing lithium or sodium in conventional battery materials is like pushing chocolate chips into the cake and then pulling the intact chips back out. With the interesting materials we’re studying, you put chocolate chips into vanilla cake and it changes into a chocolate cake with vanilla chips.
As Anna Douglas, a graduate student at the university and the study’s lead author, explains, energy storage in iron pyrite-based batteries relies on the diffusion of iron atoms. Since iron diffuses rather slowly, the size of the pyrite particles should be smaller than the iron’s diffusion length. Using ultra-small particles actually ensures that the iron can easily move to the surface, while the lithium (or sodium) in the battery reacts with the sulfurs present in the fool’s gold. According to Pint, the development of efficient batteries is entirely dependent on our understanding of chemical storage mechanisms and the effect of nanocrystals on them. He adds:
The batteries of tomorrow that can charge in seconds and discharge in days will not just use nanotechnology, they will benefit from the development of new tools that will allow us to design nanostructures that can stand up to tens of thousands of cycles and possess energy storage capacities rivaling that of gasoline. Our research is a major step in this direction.
The study was partially funded by the National Science Foundation.