Size and Surface Effects on Stress-Diffusion Coupling in Silicon Nanowire Electrodes

The development of diffusion-induced stresses (DIS) in amorphous alloy nanowire-based Li-ion battery electrodes is analyzed using a finite deformation model with full diffusion/stress coupling. The analyses reveal significant contributions to the driving force for diffusion by stress gradients, an effect much stronger than those seen in cathode lattices, but so far neglected for alloy-based anodes. A significant contribution of surface to overall stresses is also found. The long-term DIS is determined by charging rate, nanowire radius, and Li mobility modulated by stress effects. Stress-enhanced diffusion (SED) is negligible when lithium concentration is low, leading to significantly higher DIS levels in the early stage of a charging cycle. This finding points out the need to use lower charging rates in the initial stages of charging cycles of amorphous lithium alloy anodes.