Two Dimensional Li Diffusion in Ion-Conductive Lithium Lanthanum Titanates

The lower the dimensionality of diffusion, the faster anisotropic diffusion is expected to be realized. However, lithium lanthanum titanates solid electrolytes shows the opposite trend to this expectation. To understand this puzzling fact, we carried out microscale analysis of the Li occupancy behavior by first-principles calculations. A cooperative Li movement provides an opportunity to avoid simultaneous occupancy by two Li ions in the same La A-site defect. This result suggests a one-to-one correspondence between Li and La A-site defects. It enabled us to interpret the diffusion properties of this system and indicates a potential advantage of two dimensional Li diffusion. (C) 2013 The Electrochemical Society. All rights reserved.