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New direction for lithium batteries: Graphene coating can help improve energy density and battery life

Scientists from the United States and South Korea recently jointly studied the root causes of degradation of cathode materials for high-energy-density lithium batteries (LIBs) and developed graphene-based strategies to mitigate these degradation mechanisms and improve battery performance.

The study was jointly conducted by researchers from Northwestern University, Clemson University, and Sejong University in South Korea. Mark Hersam, an important author of the study, said: Most degradation mechanisms in LIBs occur on the electrode surface in contact with the electrolyte. We try to understand the chemical properties of these surfaces and then develop strategies to minimize degradation.

Specifically, the researchers used surface chemical characterization as a strategy to identify and minimize residual hydroxide and carbonate impurities during the synthesis of NCA (nickel, cobalt, aluminum) nanoparticles. They realized that the LIB cathode surface must first be prepared by appropriate annealing, a process in which the cathode nanoparticles are heated to remove surface impurities and then locked into the desired structure by an atomic layer-thick graphene coating.

The results show that cathodes made with graphene-coated NCA nanoparticles have excellent electrochemical properties, including low impedance, high rate performance, high volumetric energy and power density, and long cycle life. The graphene coating also acts as a barrier between the electrode surface and the electrolyte, further improving battery life.

Although the researchers believe that the graphene coating itself is sufficient to improve performance, their results show that it is very important to pre-anneal the cathode material in order to optimize its surface chemistry before applying the graphene coating.

It is reported that the research may be valuable for many emerging applications, especially electric vehicles and grid-scale energy storage for renewable energy sources such as wind and solar.

In addition, while this work focuses on nickel-rich LIB cathodes, this approach can also be extended to other energy storage electrodes, such as sodium-ion or magnesium-ion batteries, which contain nanostructured materials with high surface areas. Therefore, this work establishes a clear path to achieve high-performance, nanoparticle-based energy storage devices.

Our method can also be used to improve the performance of anodes in LIBs and related energy storage technologies. Ultimately, you want to optimize both the anode and cathode to achieve the best battery performance. Hersam added.

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