Molecular Dynamics Simulations of Li Insertion in a Nanocrystalline V 2 O 5 Thin Film Cathode
The behavior of lithium ion diffusion from an electrolyte into a polycrystalline layered cathode has been studied using molecular dynamics computer simulations. Lithium silicate glass was the model solid electrolyte whilethe cathode was a nanocrystalline vanadia with amorphous V 2 O 5 intergranular films (IGF) between the crystals. Nanosized V 2 O 5 crystals were aligned with their (001) planes parallel to electrolyte/cathode interface, rotated 90° from each other around this interface's normal in order to present two different orientations between the crystal planes for lithium intercalation via the amorphous vanadia IGF. A series of nanocrystalline vanadia cathodes with different IGF thicknesses was simulated to examine the effects of the IGF thickness on lithium transport into the cathodes. Results showed preferential diffusion of Li from the electrolyte into the amorphous vanadia IGF, with some of those Li diffusing into the crystalline V 2 O 5 from the IGF. Results also showed easier lithium diffusion from the IGF into the V 2 O 5 crystal along the (010) direction than along the (100) direction. Additionally, an optimum IGF thickness of 2.5-3.0 nm is suggested as being neither too thick to decrease the capacity of the cathode nor too thin to impede the transport of lithium from glassy electrolyte into the cathode.
Molecular Dynamics Simulation of the Effect of Crystal Orientation on Lithium‐Ion Diffusion at the V 2 O 5 / Li2SiO3 Interface
The molecular dynamics computer simulation technique was used to determine the effect of the orientation of the V 2 O 5 crystal (cathode) on Li-ion transport across the electrolyte/cathode interface for solid-state thin-film batteries and electrochromic devices. Simulations of the intercalation of lithium ions from a lithium metasilicate glass into V 2 O 5 crystals oriented with the (001) and (010) planes parallel to the interface were performed. The simulations showed that lithium ions have better mobility into the (010) oriented interface than the (001) oriented interface. Energy barriers for Li motion in the and directions were determined to be 0.87 eV vs. 2.47 eV in V 2 O 5 and 0.81 eV vs. 1.79 eV in δ-LiV 2 O 5 , respectively. The higher energy barrier in the direction causes the accumulation of lithium ions between the crystal planes. For approximately the same amount of volume, the (010) V 2 O 5 /glass interface and an amorphous V 2 O 5 /glass interface contain 46 and 45% more lithium ions, respectively, than the (001) V 2 O 5 /glass interface.
Molecular dynamics simulations of a-alumina and ?-alumina surfaces
Molecular dynamics simulations of crystalline aluminum oxide were performed for α-Al2O3 and γ-Al2O3 phases. Both bulk crystals and surfaces of each phase were studied. For each of the surfaces, several possible atomic terminations were examined and surface energies, density profiles, and atom configurations have been calculated. It was found that due to processes of surface relaxation and reconstruction some terminations of the α-alumina surfaces become more likely to appear. For γ-alumina, the occurrence of cation vacancies in the crystal structure has a significant influence on surface morphology. On the surfaces, additional active sites were observed which are not predicted by idealized models which omit vacancies.