Water adsorption on the surface of Ni- and Co-based layer-structured cathode materials for lithium-ion batteries

Ni-based layer-structured cathode materials are more vulnerable to moisture than conventional LiCoO₂ cathodes, adsorbing more water and easily forming LiOH on the surface. This study investigated the moisture adsorption mechanism on the surface of layer-structured cathodes. The behavior of water molecules on LiCoO₂ and LiNiO₂ surfaces were simulated and the structural and chemical changes during the adsorption process were analyzed by first-principles methods. It was found that the adsorption occurs via two types of mechanism: one involving ionic interactions between Li on the crystal surface and O in the adsorbate, and the other involving covalent bonding between the transition metal (TM) on the surface and O in the adsorbate, which restores the coordination of the TM by recovering its broken bonds. The difference between the water adsorption behaviors of Ni-based and Co-based layer-structured cathodes was found to be mainly due to the ionic-interaction-driven adsorption on the (003) surface.