High-coincidence twin boundary in lithium battery material LiCoO ₂

High-coincidence twin boundary observed by scanning transmission electron microscopy in a thin film of LiCoO ₂ and characterized using atomistic simulation techniques is reported. The boundary can be described in coincidence site lattice theory as a near-Σ2 (11̄104̄)/(44̄01̄) θ =180° twist boundary. Using a two-body potential model the grain boundary excess energy was calculated to be very low (0.09 Jm ^-2), indicating high stability. Together with the surface energy of a (11̄04̄) terminated crystal, this gives a work of cohesion of 1.75 Jm ^-2, also consistent with a strongly bound interface. Although the layered structure is not drastically perturbed within the vicinity of the symmetrical grain boundary, small changes in the d-spacing within 4 to 5 planes (~0.6 nm) of the interface are associated with large changes in the Li ion migration energies.