Modeling of Li diffusion in nanocrystalline Li-Si anode material

To quantify the Li diffusion behavior in nanocrystalline anode materials for lithium-ion batteries (LIBs), a hybrid model of the first principles calculation and diffusion kinetics was developed. The dependence of the Li diffusion on the electronic structure, solute concentration, grain size and temperature was described for the nanocrystalline Li-Si system. In contrast to conventional polycrystalline materials in which the activation barrier for Li diffusion decreases with the increase of concentration before amorphization, there exists a coordination effect of the solute concentration and grain size on the Li diffusion in nanocrystalline materials. A maximum diffusion coefficient can be obtained in the nanocrystalline Li-Si by a combination of the concentration and grain size, which is increased by two orders of magnitude from that in the coarse-grained counterpart. The present work advanced the understanding of the Li diffusion mechanisms during lithiation/delithiation of LIBs and may facilitate the development of nanocrystalline anode materials.