Atomic-scale factors that control the rate capability of nanostructured\n amorphous Si for high-energy-density batteries

Nanostructured Si is the most promising high-capacity anode material to\nsubstantially increase the energy density of Li-ion batteries. Among the\nremaining challenges is its low rate capability as compared to conventional\nmaterials. To understand better what controls the diffusion of Li in the\namorphous Li-Si alloy, we use a novel machine-learning potential trained on\nmore than 40,000 ab-initio calculations and nanosecond-scale molecular dynamics\nsimulations, to visualize for the first time the delithiation of entire LiSi\nnanoparticles. Our results show that the Si host is not static but undergoes a\ndynamic rearrangement from isolated atoms, to chains, and clusters, with the Li\ndiffusion strongly governed by this Si rearrangement. We find that the Li\ndiffusivity is highest when Si segregates into clusters, so that Li diffusion\nproceeds via hopping between the Si clusters. The average size of Si clusters\nand the concentration range over which Si clustering occurs can thus function\nas design criteria for the development of rate-improved anodes based on\nmodified Si.\n