where I is the discharge current (A), and Δt is the discharge time (s). This equation gives capacity in Coulombs (C), although it is often converted to have units of mAh. The discharge energy, calculated via integration, is also a reliable performance metric to indicate the performance of all energy storage devices . We recommend that this is also reported for all supercapacitors. This approach should be used to calculate the energy and power of non-ideal devices, and is also applicable for ideal devices (SI Section 3). Both energy density and power density should only be calculated and reported for twoelectrode devices.