Lithium diffusion study in Li₂MnO₃ and Li_1.17Ni_0.17Mn_0.67O₂: a combined experimental and computational approach

A theoretical and experimental diffusivity study of Li₂MnO₃ and Li_1.17Ni_0.17Mn_0.67O₂ has been carried out to investigate the effect of Mn, Ni and surrounding atoms on Li⁺ diffusion and to understand how the Li⁺ diffusion trajectory changes with different charge spheres. It is observed that due to the presence of Ni in Li_1.17Ni_0.17Mn_0.67O₂, the activation energy reduces in all the possible diffusion paths, which helps in faster Li⁺ diffusion. This study brings a new physical insight into Li⁺ diffusion based on elliptical and straight diffusion trajectories. In Li_1.17Ni_0.17Mn_0.67O₂, the Li⁺ diffusion mechanism in different paths based on 2b, 2c and 4h Wyckoff sites of Li has been discussed. Experimentally, the galvanostatic intermittent titration technique is adopted to identify the diffusion coefficient of Li⁺. The diffusion coefficient of both the compounds varies in different voltage ranges. For L₂MnO₃, diffusion varies from 10^-11 to 10^-13 cm² s^-1, whereas for Li_1.17Ni_0.17Mn_0.67O₂, diffusion varies from 10^-9 to 10^-11 cm² s^-1 in the voltage range of 3.7-4.7 V.