Even for typical EDLC materials there is an asymmetry in the electrochemical behaviour for the cations and anions due to the difference in ion sizes with respect to pore diameter19. This results in unequal specific capacitances (in Farads per gram) for positive (csp+) and negative electrodes (csp−); that is, csp−≠csp+. Therefore, to maintain the stable voltage condition of V−=V+, the weights of the electrodes (m− and m+) should be unequal to compensate for the different specific capacitance values: . Since the current response for pseudocapacitive or battery materials varies with applied potential (Fig. 1c,d), the general case of combining two different electrochemical materials will produce an asymmetric energy storage cell.