The
high specific capacity in excess of 200 mAh g–1 and
low dependence on cobalt have enhanced the research interest
on nickel-rich 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 transition-metal (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.
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