While much battery research of late has focused on finding alternative chemistries for lithium-ion batteries, other research is focused on making improvements to the current standard for energy storage so these type of devices perform better.
Some new research toward this end comes from Germany, where scientists have developed a process to investigate a key reason why lithium-ion batteries degrade related to metallic lithium that gets deposited on the anodes when charged too quickly. A long-time problem with these types of batteries, this can reduce battery lifespan, capacity, or even destroy the devices.
Scientists at the Technical University of Munich (TUM) and the Forschungszentrum Jülich have developed the first-ever process that can examine directly this phenomenon—called “lithium plating”—allowing for new strategies and materials to charge lithium-ion batteries more quickly and safely, they said.
Scientists in Germany have developed a process to investigate a key reason why lithium-ion batteries degrade related to metallic lithium that gets deposited on the anodes when charged too quickly. Pictured is a test cell developed to test the process, which can help improve the design of lithium-ion batteries. (Source: Tobias Schlösser / Forschungszentrum Jülich)
While researchers long have known that the depositing of metallic lithium at the anodes of lithium-ion batteries occurs—and is one of the primary factors that limits charging current—until now, they had no way to directly observe how and under which circumstances lithium plating takes place, said Josef Granwehr at the Jülich Institute of Energy and Climate Research, one of the researchers on the project.
“Using traditional methods of microscopy, we can only observe a battery after the fact, because it needs to be cut open,” he explained. “In the process, further reactions that distort the results become inevitable.”
Essential to the new method of observation is an electron paramagnetic resonance (EPR) spectroscopy process the researchers used, which is similar to nuclear magnetic resonance (NMR) spectroscopy with a key difference being that it focuses on electron spins rather than atomic nuclei, Granwehr said.
“Electrons are placed in an externally applied, static magnetic field,” he explained, with unpaired electrons in the sample “sounded out” using microwaves. In the magnetic field, these stimulate the electrons to flip, something scientists can measure by the associated drop in microwave radiation intensity.
In this way, EPR can differentiate between metallic lithium plating and lithium embedded in the graphite anodes, Granwehr said.
Researchers constructed a test cell with good electrochemical properties that also was compatible with the requirements of EPR spectroscopy, which was integral to being able to detect lithium plating, said Johannes Wandt, lead author on a paper researchers published in the journal Materials Today.
“The geometry is also important,” he explained. “Precise measurement results are contingent on the sample being exposed to the magnetic field but not the inevitably present electric field.”
The process now allows for the first-time researchers to identify the associated processes involved in lithium plating, which could lead them to develop safer and fast-charging protocols for lithium-ion batteries. It also is well-suited to test a variety of battery materials that can suppress lithium plating for the development of improved battery chemistries, researchers said.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years.