Silicon has drawn a strong interest for its possible application as anode material for the next generation Li-ion batteries. The capacity of silicon is 10 times higher than graphite, however the kinetics of lithiation and delithiation of Si has not yet been fully understood. In this work, the temperature dependent diffusion coefficient of Li has been calculated, in bulk Si and LiSi phase, in the transition state theory framework. The energy barriers and pre-exponential factors have been obtained from total energy and phonon calculations, respectively, using the density functional theory (DFT). In LiSi case with multiple vacancy mediated diffusion pathways, kinetic monte carlo (KMC) simulations were used to calculate the effective diffusion coefficient.

Our results are in good agreement with the experimental data and suggest that in Li-Si system, quantum mechanical effects are only marginally significant. The current study shows a theoretical approach, which is computationally efficient and quantitatively accurate, to fill the gap due to limited studies of Li diffusion in lithiated Li_xSi phases.