“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."Jay Narayan, North Carolina State University

Researchers at North Carolina State University (NC State), in collaboration with battery testing researchers at the US Department of Energy’s Oak Ridge National Laboratory, have shown that extremely short pulses from a high-powered laser can cause tiny defects in lithium-ion battery materials – defects that can enhance battery performance.

The technique, called nanosecond pulsed laser annealing, lasts for only 100 nanoseconds and is generated by the same type of laser used for modern-day eye surgeries. The researchers tested the technique on graphite, a material widely used as the anode in lithium-ion batteries. They tested the technique in batches of 10 pulses and 80 pulses, and compared the differences in current capacity, as power is calculated by multiplying voltage by current.

Lithium-ion batteries are widely used in portable electronic devices and electric cars. With further improvements, these batteries could have an even greater impact on transportation and find use as storage devices for renewable energy sources like wind and solar.

The study produced a number of interesting results, said Jay Narayan, professor of materials science at NC State and corresponding author of a paper on this work in Carbon. 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.”

The researchers found that the current capacity increased by 20% when the optimal number of pulses was used, which was closer to 10 than 80. They also discovered, however, that too much of a good thing can be a bad thing, as too many defects in the graphite anodes can lead to problems.

“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.”

Narayan said that manufacturers should have the capability to use nanosecond pulsed laser annealing when producing both anodes and cathodes in lithium-ion batteries. “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.”

Together with colleagues at the University of Texas-Austin, Narayan has already shown that the same laser technique can also enhance cathode materials. They reported their findings in a paper in ACS Applied Materials and Interfaces.

“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.

This story is adapted from material from North Carolina State University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.