The concentration in the X direction which is perpendicular to the LCO interface is of interest. Therefore, the "symmetry" boundary conditions are used for top and bottom boundaries. The cobalt concentration at the LCO │Al2O3 interface (left-side boundary) is assumed 0.0524 mol/cm 3 . which is the cobalt concentration that can be provided by the LCO to the neighboring layer. No-flux boundary condition (concentration gradient equal to zero) is considered for LLZO's right face (right-side boundary).