Molecular simulation studies of lithium ion intercalation and diffusion in electrode and electrolyte materials

Computational chemistry studies based on quantum mechanics and molecular simulations are used to study the diffusion and intercalation of lithium ions in carbon and metal oxide electrodes and organic solvents-based electrolytes. The effect of the molecular interactions inside the solid and liquid phases and the solid-liquid interactions on thermodynamic, structural, and transport properties is evaluated by using molecular dynamics (MD) simulations and ab initio calculations.; Initially, the interactions of lithium ions with a model graphite cluster containing 32 carbon atoms are studied by ab initio methods. Li+ binds preferentially to armchair and basal plane sites in out-plane-locations, being these results in qualitative agreement with reported kinetic regions for the diffusion of Li+ ion graphite structures.; Secondly, MD studies are performed on 3D unit cell with periodic boundary conditions focusing on graphite-electrolyte systems. The liquid electrolyte consists of a mixture of cyclic organic carbonates and the salt LiPF ₆. Repulsive lithium-lithium inter and inter-layer interactions are predominant during the intercalation process for the modeled graphite (staging), in agreement with observed experimental results. Calculated solid phase lithium ion diffusivities are in the range 10−8–10 −9 cm2/s for the range 0–17 state of charge. The maximum interlayer spacing increase is found to be between 6–10% depending on the degree of intercalation. These results also confirmed reported experimental studies.; Finally, systems composed by carbon anodes-electrolyte-metal oxide phases are studied in 3D unit cells by using MD simulations. Structural changes, solid-liquid interatomic interactions, and diffusivities are evaluated. In the model amorphous carbon anode systems, the diffusion of lithium ions is slowed down and structural rearrangements lead to larger interlayer expansions which in turn yield larger capacity of lithium ion intercalation than in the graphite case. There is a spatial variation in the diffusion of lithium ions for the model LiCoO₂ cathodic phase, where the closer the ions are to the liquid-metal oxide interface the faster they diffuse; because of a significant increase in the interlayer spacing of the CoO₂ layers that compose the Li-metal oxide material.