Computational Study of Li-ion Battery Cathode : Potential Development and Application

Abstract

Among several cathodes, Ni-rich LiNixMnyCozO2 (NMC) layered cathode structures are the most researched and used cathode materials for their high electrochemical performance. Especially, Ni is a key element to achieve a large capacity and reduced cost. To investigate these cathode materials and get insight, it is appropriate using large-scale atomistic simulations such as molecular dynamics (MD). At first, to simulate NMC cathode system, Li-Ni-O interatomic potential has been developed on the basis of the second nearest-neighbor modified embedded-atom method (2NNMEAM) formalism combined with a charge equilibration (Qeq) concept. This potential reproduces fundamental physical properties of the sub-systems’ (lithium-nickel and nickel oxide) as well as the lithium-nickel oxide ternary system in good agreement with experiments and first-principles calculations. The activation energy and diffusion coefficients for lithium migration in Li1-xNiO2 layered structures are also calculated by using this potential and the results show the same tendency as the experimental observations. Then, an 2NNMEAM + Qeq interatomic potential for the Li-Ni-Mn-Co-O quinary system is developed by newly developing or modifying interatomic potentials for sub-unary, binary and ternary systems. This potential is utilized to analyze the Li/Ni intermixing effect on Ni-rich cathode properties (lithium diffusion for rate properties, change in lattice parameter and internal stress for structural stability). The results demonstrate how cathode properties are affected by the intermixing and that controlling the intermixing will be particularly important in Ni-rich cathode materials. The quinary potential will also be useful for analyzing various material phenomena and designing cathode materials.