Image: This illustration shows lithium ions (green) embedded in a graphite anode. see more 

Credit: (picture from Argonne National Laboratory.)

Researchers have discovered new problems that complicate fast charging.

As the saying goes, haste is not fast. Thanks to a new study designed to determine the cause of the decline in the performance of fast-charging lithium-ion batteries in electric vehicles, such maxims may be particularly applicable to batteries.

In a new study by the U.S. Department of Energy (DOE) Argonne National Laboratory, scientists discovered that one of the two terminals of a battery has interesting chemical behaviors when the battery is charged and discharged.

Lithium-ion batteries consist of a positively charged cathode and a negatively charged anode, which are separated by a material called an electrolyte, which moves lithium ions between them. The anode in these batteries is usually made of graphite-the same material as in many pencils. However, in lithium-ion batteries, graphite is assembled from small particles. Inside these particles, lithium ions can intercalate themselves in a process called intercalation. When the intercalation occurs correctly, the battery can be successfully charged and discharged.

However, when the battery is charged too fast, embedding becomes a tricky thing. Lithium ions do not enter the graphite smoothly, but tend to accumulate on the top of the anode surface, resulting in a “plating” effect, which may cause terminal damage to the battery (not a pun).

"Plating is one of the main reasons for battery performance impairment during fast charging," said Daniel Abraham, an Argonne battery scientist and author of the study. â <"When we quickly charge the battery, we find that in addition to the coating on the surface of the anode, reaction products are also accumulated in the electrode pores." Therefore, the anode itself will undergo a certain degree of irreversible expansion, which will damage the battery performance.

Using a technique called scanning electron nanodiffraction, Abraham from the University of Illinois at Urbana-Champaign and his colleagues observed another significant change in graphite particles. At the atomic level, the graphite atomic lattice at the edge of the particle is distorted due to repeated rapid charging, which hinders the embedding process. â <"Basically, what we are seeing is the distortion of the atomic network in graphite, which prevents lithium ions from finding their "home" inside the particles-instead, they are plated on the particles," he said.

"The faster we charge the battery, the more chaotic the atomic order of the anode, which will eventually prevent lithium ions from moving back and forth," Abraham said. â<"The key is to find a way to prevent this tissue loss or to modify the graphite particles in some way so that lithium ions can be inserted more effectively."

A paper based on this research, â<"Multi-length scale characterization of fast-charging lithium-ion battery anodes reveals a disordered increase in the edges of graphite particles", was published in the "Journal of the Electrochemical Society" on October 8.

In addition to Abraham, other authors of the study include Marco-Tulio Rodrigues of Argonne, and Zuo Jianmin and Saran Piedapasi of the University of Illinois at Urbana-Champaign. The research was funded by the US Department of Energy's Office of Science, and Pidaparthy's research was funded by the Office of Graduate Research (SCGSR) program, which aims to prepare graduate students for STEM careers that are critical to the Department of Energy's mission.

Argonne National Laboratory seeks to solve pressing national scientific and technological problems. As the first national laboratory in the United States, Argonne conducts cutting-edge basic and applied scientific research in almost all scientific disciplines. Argonne’s researchers work closely with researchers from hundreds of companies, universities, and federal, state, and municipal agencies to help them solve specific problems, elevate America’s scientific leadership, and prepare for a better future for the country. Argonne has employees from more than 60 countries and is managed by UChicago Argonne, LLC of the Office of Science of the U.S. Department of Energy.

The Office of Science of the U.S. Department of Energy is the largest supporter of basic research in the physical sciences of the United States, dedicated to solving some of the most pressing challenges of our time. For more information, please visit https://ener gy.gov/sc ience.

Journal of the Electrochemical Society

Multi-length-scale characterization of fast-charging lithium-ion battery anodes shows disorderly increase in the edges of graphite particles

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Johnathon Briggs US Department of Energy/Argonne National Laboratory jbriggs@anl.gov Office: (630) 252-8057

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Copyright © 2021 American Association for the Advancement of Science (AAAS)