Effects of Li contents on the stability, electronic and Li-ion diffusion properties of Li3xLa(2/3)-x(1/3)-2xTiO3 surface

LLTO is a promising solid-state electrolyte for Li-ion batteries. We studied the effect of Li contents on the stability, electronic and Li-ion diffusion properties of LLTO surface based on first-principles and molecular dynamics simulations. We considered both Li-poor and Li-rich LLTO surfaces. Results show that La/O/Li-terminated LLTO(001) is the most stable crystal surface. Further, LLTO(001) surface gives better stability when Li contents are 0.17, 0.29, and 0.38 for Li-poor phase, while 0.33, 0.40, and 0.45 for Li-rich phase among the considered Li contents. Electronic structure calculations infer that both Li-poor and Li-rich LLTO(001) surfaces occur the transition from conductor to semiconductor with the increase of Li contents. Besides, we found that Li-ion always remains two dimensional diffusion path for different Li contents. As Li contents increase from 0.17 to 0.38 for Li-poor LLTO(001) surface, Li-ion diffusion coefficient increases gradually and Li-ion diffusion barrier decreases from 0.58 eV to 0.42 eV. Differently, when Li contents increase from 0.33 to 0.45 for Li-rich LLTO(001) surface, it does not follow a monotonic trend for both diffusion coefficient and diffusion barrier of Li-ion. In this case, Li-ion diffusion coefficient is the largest and Li-ion diffusion barrier is the lowest (0.30 eV) when Li contents are 0.40. Thus, our study suggests that by varying Li contents, the stability, band gap, and Li-ion diffusion performance of LLTO(001) can be altered favourably. These advantages can inhibit the formation of lithium dendrites on the LLTO(001) surface.