where V / / is the volume of the positive electrode, negative electrode and separator, respectively, in mm 3 , and similarly, 𝜀 / / , is the porosity (in fraction). Finally, to calculate the gravimetric energy density of the cell, the mass of each component of the cell and the energy of the cell need to be calculated. To find the mass of each component, the corresponding density of the component is taken, and the volume of the specific component is used. For example,