Pyrazine-Linked 2D Covalent Organic Frameworks as Coating Material for High-Nickel Layered Oxide Cathodes in Lithium-Ion Batteries

The high specific capacity in excess of 200 mAh g(-1) and low dependence on cobalt have enhanced the research interest on nickelrich layered metal oxides as cathode materials for lithium-ion batteries for electric vehicles. Nonetheless, their poor cycle life and thermal stability, resulting from the occurrence of cation mixing between the transitionmetal (TM) and lithium ions, are yet to be fully addressed to enable the widespread and reliable use of these materials. Here, we report a two-dimensional (2D) pyrazine-linked covalent organic framework (namely, Pyr-2D) as a coating material for nickel-rich layered cathodes to mitigate unwanted TM dissolution and interfacial reactions. The Pyr-2D coating layer, especially the 2D planar morphology and conjugated atomic configuration of Pyr-2D, protects the electrode surface effectively during cycling without sacrificing the electric conductivity of the host material. As a result, Pyr-2D-coated nickel-rich layered cathodes exhibited superior cyclability, rate performance, and thermal stability. The present study highlights the potential ability of 2D conjugated covalent organic frameworks to improve the key electrochemical properties of emerging battery electrodes.