Modeling mechanical interaction between Li dendrite growth and the solid-electrolyte interphase

SEI plays a critical role in Li-metal batteries, which control the electrodeposition/dissolution behavior at the Li surface. However, the fundamental questions as to how SEI moving and stress are generated at the surface of Lithium (Li) surface and impact Li dendrite growth in the dynamical process is still unclear. A general continuum mechano-electro-chemical phase-field Li dendrite-SEI model is first developed for the rigorous prediction of the dynamical mechanical interaction between Li dendrite growth and SEI. By transforming the implicit phase-field diffuse interface into an explicit SEI mechanical boundary condition, the electrochemical and mechanical degrees of freedom, including dynamical SEI moving, stress distribution, interfacial overpotential, and Li-dendrite morphology evolution are captured self-consistently. SEI mechanical aspect is achieved by presuming that the moving and deformation of the SEI is driven by the velocity difference which is induced by the non-uniform Li dendrite growth. To illustrate the model's applications, four cases are presented: (i) comparison of uniform and non-uniform Li deposition to clarify that the moving and mechanical stress are driven by the non-inhomogeneous growth velocity of deposits Li in the case of non-uniform Li deposit process; (ii) studying of SEI chemical properties, diffusion coefficient, and ionic conductivity to assess their influence on interfacial inhomogeneity and dendrite behavior; and (iii) evaluation of SEI heterogeneities in thickness and diffusivity, and (iv) Young's modulus to reveal their impact on stress concentration and interface instability. The results suggest that the SEI with uniform properties and a flat initial Li surface is favorable.