Vanderbilt graduate student Anna Douglas holding one of the batteries that she has modified by adding millions of quantum dots made from iron pyrite, fool’s gold. Credit: John Russell, Vanderbilt University
If you add quantum dots – nanocrystals 10,000X smaller than the width of a human hair – to a smartphone battery it will charge in 30 seconds, but the effect only lasts for a few recharge cycles. However some Vanderbilt University researtchers have found a way to overcome this problem: Making the quantum dots out of iron pyrite ie as fool’s gold, can produce batteries that charge quickly and work for dozens of cycles.
Iron pyrite is one of the most abundant materials in the earth’s surface. It is produced in raw form as a byproduct of coal production and is so cheap that it is used in lithium batteries that are bought in the store and thrown away after a single use. Despite all their promise, researchers have had trouble getting nanoparticles to improve battery performance.
“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.”
Nanocrystals with quantum-confined length scales are often considered impractical for metal-ion battery electrodes due to the dominance of solid-electrolyte interphase (SEI) layer effects on the measured storage properties. Here we demonstrate that ultrafine sizes (∼4.5 nm, average) of iron pyrite, or FeS2, nanoparticles are advantageous to sustain reversible conversion reactions in sodium ion and lithium ion batteries.
METHOD: They added millions of iron pyrite quantum dots of different sizes to standard lithium button batteries like those that are used to power watches, automobile key remotes and LED flashlights. They got the most bang for their buck when they added ultrasmall nanocrystals that were about 4.5nm in size. These substantially improved both the batteries’ cycling and rate capabilities.
MOA: iron pyrite has a unique way of changing form into an iron and a lithium-sulfur (or sodium sulfur) compound to store energy. “This is a different mechanism from how commercial lithium-ion batteries store charge, where lithium inserts into a material during charging and is extracted while discharging – all the while leaving the material that stores the lithium mostly unchanged,” Douglas explained.
Thus the rules that forbid the use of ultrasmall nanoparticles in batteries no longer apply.”Instead of just inserting lithium or sodium ions in or out of the nanoparticles, storage in iron pyrite requires the diffusion of iron atoms as well. Unfortunately, iron diffuses slowly, requiring that the size be smaller than the iron diffusion length – something that is only possible with ultrasmall nanoparticles,” Douglas explained.
These ultrasmall nanoparticles have dimensions that allow the iron to move to the surface while the sodium or lithium reacts with the sulfurs in the iron pyrite. Understanding chemical storage mechanisms and how they depend on nanoscale dimensions is critical to enable the evolution of battery performance at a pace that stands up to Moore’s law and can support the transition to electric vehicles. http://news.vanderbilt.edu/2015/11/quantum-dots-made-from-fool%E2%80%99s-gold-boost-battery-performance/
Recent Comments