Strong stress-enhanced diffusion in amorphous lithium alloy nanowire electrodes

Diffusion-induced stress (DIS) development and stress-enhanced diffusion (SED) in amorphous lithium alloy nanowire battery electrodes are investigated using a finite deformation model, accounting for full two-way coupling between diffusion and stress evolution. Analytical solutions are derived using a perturbation method. The analyses reveal significant contributions to the driving force for diffusion by stress gradient, an effect much stronger than those seen in cathode lattices but so far has been neglected for alloy-based anodes. The contribution of stress to diffusion is small at low lithium concentrations, this lack of SED leads to significantly higher DIS levels in early stages of a charging cycle. As lithium concentration increases, SED becomes more pronounced, leading to lower DIS levels. The long-term DIS level in the material scales with charging rate, nanowire radius, and the mobility of Li ions as modulated by the effect of stress. The solutions obtained provide guidance for lowering stresses during charging. In particular, lower charging rates should be used during the initial stages of charging cycles. (c) 2011 American Institute of Physics. [doi:10.1063/1.3530738]