United States. Scientists at the U.S. Department of Energy's (DOE) Argonne National Laboratory developed a new cathode coating for lithium-ion batteries, which keeps it electrically and ionically conductive, while retaining the battery's level of safety after numerous charge and discharge cycles.
The development was done by using an oxidative chemical vapor deposition technique, which can help to solve at the same time these and various other potential problems with this type of batteries. "The coating we've discovered actually kills five or six birds with one stone," says Khalil Amine, an Argonne member and battery scientist.
In the research, Amine and his fellow researchers took particles from the nickel-manganese-cobalt (NMC) cathode material developed by Argonne and encapsulated them with a sulfur-containing polymer called PEDOT. This polymer gives the cathode a layer of protection against the battery electrolyte, as it is charged and discharged.
Unlike conventional coatings, which protect the outer surface from micron-sized cathode particles and leave the inside vulnerable to cracking, the PEDOT coating had the ability to penetrate the inside of the cathode particle, adding an additional layer of shielding.
In addition, although it avoids the chemical interaction between the battery and the electrolyte, it does allow the necessary transport of lithium ions and electrons that the battery requires to operate.
"This coating is essentially friendly to all the processes and chemistry that makes the battery work and is not friendly to all the potential reactions that could cause the battery to degrade or malfunction," explains Argonne chemist Guiliang Xu, an author of the research.
The coating also largely prevents another reaction that causes the battery cathode to be deactivated. In this reaction, the cathode material is converted into another form called spinel. "The combination of almost no spinel formation with its other properties makes this coating a very exciting material," says Amine, who further notes that the coating could be expanded for use in nickel-rich NMC-containing batteries.
With the coating applied, the researchers believe that batteries containing NMC could operate at higher voltages, thereby increasing their energy production, having a longer lifespan, or both.
