Argonne Lab Develops PEDOT Cathode Coating Improving Lithium-Ion Batteries

May 16, 2019 by Scott McMahan

Scientists working at the U.S. Department of Energy's (DOE) Argonne National Laboratory have developed a new cathode coating. They used an oxidative chemical vapor deposition technique to deposit the coating that can help keep a lithium-ion battery's cathode electrically and ionically conductive.

Additionally, the coating works to ensure the battery remains safe after many cycles and helps resolve several other issues at the same time.

"The coating we've discovered really hits five or six birds with one stone." Khalil Amine, Argonne distinguished fellow and battery scientist.

Amine and his team encapsulated particles of Argonne's pioneering nickel-manganese-cobalt (NMC) cathode material with a sulfur-containing polymer called PEDOT. (See image above of PEDOT coating shown in thin blue mesh cross-section, image courtesy of Argonne National Laboratory). This polymer gives the cathode a layer of protection from the battery's electrolyte as the battery charges and discharges.

Unlike conventional coatings, which are limited to protecting the exterior surface of the micron-sized cathode particles and leaving the interior vulnerable to cracking, the PEDOT coating could penetrate to the interior of the cathode particle, adding an additional layer of shielding.

Although PEDOT blocks the chemical interaction between the battery and the electrolyte, it does allow the essential transport of lithium ions and electrons that the battery requires to function.

"This coating is essentially friendly to all of the processes and chemistry that makes the battery work and unfriendly to all of the potential reactions that would cause the battery to degrade or malfunction," said Argonne chemist Guiliang Xu, the first author of the research.

The coating also mostly blocks another reaction that results in deactivating the battery's cathode. In this reaction, the cathode material transforms into another form called spinel. ​"The combination of almost no spinel formation with its other properties makes this coating a very exciting material," Amine said.

The PEDOT material also showed the ability to prevent oxygen release, an important factor in NMC cathode material degradation at high voltage. ​"This PEDOT coating was also found to be able to suppress oxygen release during charging, which leads to better structural stability and also improves safety," Amine said.

Amine noted that the scientists could probably scale up the coating for nickel-rich NMC-containing batteries. ​"This polymer has been around for a while, but we were still surprised to see that it has all of the encouraging effects that it does," he said.

With the applied coating, the researchers believe that the NMC-containing batteries could either run at higher voltages, have longer lifetimes, or both.

For the research, the scientists used two DOE Office of Science User Facilities at Argonne; the Advanced Photon Source (APS) and the Center for Nanoscale Materials (CNM). They took in situ high-energy X-ray diffraction measurements at beamline 11-ID-C of the APS, and focused ion beam lithography and transmission electron microscopy at the CNM.

A paper detailing the study, ​"Building ultra-conformal protective layers on both secondary and primary particles of layered lithium transition metal oxide cathodes," appeared in the online edition of Nature Energy on May 13. Other Argonne-based authors of the paper included Yuzi Liu, Xiang Liu, Han Gao, Minghao Zhuang, Yang Ren and Zonghai Chen. Researchers from Indiana University-Purdue University Indianapolis, Drexel University, and four Chinese universities also collaborated.

The research was funded via DOE's Office of Science, Office of Basic Energy Sciences, and the Vehicle Technologies Office of the Office of Energy Efficiency and Renewable Energy.