Strong kinetics-stress coupling in lithiation of Si and Ge anodes

Coupling between transport kinetics of chemical participants and mechanical stress is a universal phenomenon in numerous chemo-physical processes. In this Letter, we present a set of in-situ   transmission electron microscopy studies along with atomistically informed continuum mechanics modeling to evidence the strong coupling between lithiation kinetics and stress generation and failure of silicon (Si) and germanium (Ge) electrodes. On the one hand, we show that anisotropic lithiation in crystalline Si (cc-Si) leads to anisotropic swelling and surface fracture, in contrast to isotropic lithiation, isotropic swelling, and tough behavior in cc-Ge and amorphous Si (aa-Si). On the other, we demonstrate that lithiation self-generated stress leads to lithiation retardation and externally applied bending breaking the lithiation symmetry in cc-Ge nanowires. Our studies shed lights on the design of durable high-performance lithium ion batteries.