Molecular dynamics simulations of cathoderglass interface behavior: effect of orientation on phase transformation, Li migration, and interface relaxation

Ž . The molecular dynamics MD computer simulation technique has been used to study electrolytercathode interfaces formed in Li-based thin film oxide solid state ionic devices at the atomistic level. The solid electrolytes are lithium silicate glasses while the cathodes are V O or WO crystals. The work presented in this paper will focus on the behavior at the glassrV O interface. The MD 2 5 3 2 5 simulation technique has been successfully used to simulate a variety of silicate glasses and glass surfaces, with results consistent with a variety of experimental data. The simulations of the vanadia crystal reproduce the experimental crystal structures, vibrational frequency, and the appropriate phase transition of V O as Li ions enter the crystal. The simulations have also shown that Li transport into the crystal 2 5 Ž . is affected by the orientation of the crystal at the interface as well as by surface roughness. While the crystal oriented with the 001 planes parallel to the crystalrglass interface shows the appropriate phase transition to the d-LiV O phase as Li ions enter the crystal, the 2 5 Ž . work presented here shows that the crystal oriented with the 100 planes parallel to the interface does not transform. The difference is attributed to the effect of interface bonding between the ions in the first crystal layer and those in the glass surface. The simulations show a relaxation occurring in a lithium metasilicate glass electrolyte but not in a lithium disilicate electrolyte. In addition, relaxation at the interface between a roughened glass surface and the crystal creates a distortion in the crystal planes in immediate contact with the glass that creates an induced strain in the crystal. q 2000 Elsevier Science S.A. All rights reserved.