Additionally, since the Si phase is approximated as a porous electrode, the inner stresses that are generated can no longer be directly related to the stresses between the explicit Si particles. Then, the equation of motion takes the form in stationary condition as following, where is Cauchy stress tensor: 0 = ∇ • Moreover, graphite, Si and CBD domains are treated as a linear elastic material. Hooke's law is used to describe the relation between the stress and strain tensors: