Air-Sensitivity Study on LiNiO_{2} Layered Cathode Materials by Using Ab Initio Molecular Dynamics Simulations

Abstract

Nickel-rich layered oxides are important cathode materials for lithium batteries, but their effectiveness is compromised by air sensitivity. Using LiNiO_{2} as a prototype in ab initio molecular dynamics simulations, we find that oxygen active sites provide molecular orbitals and metal activation that work in synergy to form impurity hydroxyl and carbonate species in the presence of air. This mechanism successfully explains the high air sensitivity on the specific surfaces, the air-sensitivity transition after Li/Ni mixing, and the treatment effect of cation (Co and Mn) and anion (F and S) doping methods. Doping with sulfur ions proves to have the best protective effect against H_{2}O and CO_{2}. A series of first-principles calculations show that oxygen active sites originate from electron loss, and the activation effect of metals is limited by the type of elements, the number of coordination bonds, the coactivation effect and the Jahn-Teller distortion. While impurity formation is usually a localized phenomenon, the autoprotolysis of H_{2}O allows long-distance proton transport to support the hydrolysis reaction. The adsorption energy of H_{2}O and CO_{2} is not directly related to the air sensitivity, but is inversely proportional to the surface thermodynamic stability in the study of Li/Ni mixing. However, the concentration of Li/Ni mixing depends on the exposed surface, implying that the influence of Li/Ni mixing on air sensitivity and air adsorption capacity is uneven. Our studies contribute to realizing a cost-effective and convenient experimental strategy for treating air sensitivity of LiNiO_{2} cathode materials.