Old batteries, like old soldiers, never seem to die; they just fade away.
A team of researchers, led by Chongmin Wang at the Office of Science's Pacific Northwest National Lab (PNNL), recently figured out part of that answer for one type of high-performance battery. Lithium ion batteries are used in essential everyday electronics like cell phones and laptops, and adding the element nickel to their electrodes further improves their performance.
However, over time, their performance fades. The batteries take longer to charge and have to be charged up more frequently. Eventually, they barely work at all.
Image courtesy of Pacific Northwest National Laboratory (PNNL)
While manganese (blue) fills out this battery nanoparticle evenly, nickel (green) clumps in certain regions, interfering with the material's smooth operation.
Dr. Wang and his colleagues wondered why . . . and knew where to go for the tools to find out. They tapped into the Office of Science's world-class user facilities to take a closer look at what was happening at the molecular level. Specifically, they scoped out tiny particles – nanoparticles – with the same composition. The particles were so small, about 200 nanometers in size, that it would take some 300 of them together to form a particle the size of an average speck of dust. They were created by researchers at the Office of Science's Argonne National Lab (ANL) using a variety of different methods – see below for why.
Researchers took some fifty images of those nanoparticles using electron microscopes at PNNL's Environmental Molecular Sciences Laboratory and the National Center for Electron Microscopy at the Office of Science's Lawrence Berkeley National Laboratory. They found that the elements in the electrode (nickel, manganese and oxygen) formed rows – almost like lanes on a racetrack – between which the charged particles, the lithium ions, sped.
To the researcher's surprise, nickel proved to be a frenemy. While nickel can improve the performance of batteries, it can also clog the course. A bit like over-excited spectators at a race, nickel atoms sometimes slip out onto the lanes taken by the lithium ions during manufacturing, sprint down them, and then clump together at the finish. There's no way to disperse the bandits. As a consequence, the channel becomes clogged, fewer charges get through, and the battery fades.
That's where things stand at the moment. However, since the researchers used a variety of methods to produce the nanoparticles, they could find better ways to keep nickel on the sidelines. That would lead to improved battery performance, and indeed PNNL researchers are planning on doing more detailed experiments to see if particular manufacturing methods will create better electrodes.
There's a metaphor in there for the Office of Science at work: Old batteries may fade; but research recharges and renews.
The Department's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information please visit http://science.energy.gov/about. For more information about PNNL, please go to: http://www.pnnl.gov/.
Charles Rousseaux is a Senior Writer in the Office of Science.