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The study, performed in collaboration with battery testing researchers at the US Department of Energy’s Oak Ridge National Laboratory, showed that extremely short pulses from a high-powered laser can cause tiny performance-enhancing defects in lithium-ion battery materials.
The technique, called nanosecond pulsed laser annealing, lasts for only 100 nanoseconds. Researchers tested the technique on graphite, a widely used material in lithium-ion battery anodes. They tested the technique in batches of 10 pulses and 80 pulses, and compared the differences in current capacity.
The study showed some interesting results, said NC State’s Jay Narayan, corresponding author of a paper describing the work. Narayan pioneered the use of lasers to create and manipulate defects in semiconductors in work spanning more than four decades.
“Material defects can be a nuisance, but if you engineer them correctly you can make them an advantage,” he said. “This technique opens the door, so to speak, for lithium ions, so it enhances the current capacity. Graphite anodes consist of steps and grooves on the surface – creating more steps is like creating more doors for lithium ions to get in and get out, which is beneficial.
“The technique also creates defects called vacancies, which are missing atoms, and that helps provide more sites for lithium ions to come and go, which is related to the current capacity.”
Current capacity increased by 20% when the optimal number of pulses was used. Too many pulses led to problems, however.
“Lithium ion has a positive charge, so if it captures an electron it becomes lithium metal, and you don’t want that,” Narayan said. “Lithium metal shoots out tiny wire dendrites from the graphite anode and can cause a fire. So you want to make sure that a lithium ion doesn’t become a metal.”
Manufacturers should have the capability to use nanosecond pulse laser annealing when producing both anodes and cathodes, the other electrodes contained in batteries, Narayan said.
“These high-powered lasers exist, and you can treat anodes and cathodes within a microsecond,” Narayan said. “The cathodes or anodes are made on a sheet, which makes treatment relatively fast and easy.”
The study appeared in Carbon.
Narayan and colleagues at the University of Texas recently published another paper that used the same laser technique on cathode materials. Published in ACS Applied Materials and Interfaces, that study showed laser treatment enhanced cathode materials.
“Next, we are trying to eliminate the need for using more expensive materials, such as cobalt in battery cathodes, in order to make higher power and longer-lasting batteries,” Narayan said.
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