Modeling of stress generation in a spherical Si particle undergoing two-phase lithiation.^[30](a) Schematic of the two-phase model with a sharp phase boundary between the Si core anda-Li_3.75Si shell. (b) Numerical results showing the radial distribution of Li concentrationcnormalized by its maximum value at the fully lithiated state, and the radial distanceris normalized by the current radiusRof a partially lithiated particle which increases as lithiation proceeds. (c), (d) Numerical results showing the radial distribution of the von Mises effective stressσ_e, radial stressσ_r, and hoop stressσ_θ=σ_φ(normalized by Young’s modulus).