Criteria appointing the highest acceptable cell voltage of asymmetric supercapacitors

This communication discusses the criteria for appointing the highest acceptable cell voltage of asymmetric supercapacitors. An electrochemical capacitor (EC) consisting of graphene anode and activated Mn3O4 cathode is employed as the model system. The capacitive performances of this asymmetric EC are evaluated by cyclic voltammetric, charge/discharge and electrochemical impedance spectroscopic (EIS) analyses. The criteria for appointing the highest appropriate cell voltage of asymmetric ECs with excellent reversibility and capacitor-like behaviour are proposed.

► This work establishes the criteria appointing the highest practical cell voltage of asymmetric supercapacitors.
► EIS is a powerful tool in evaluating the highest practical cell voltage of asymmetric supercapacitors.
► The most important criterion is the phase angle of resultant cell capacitance (− 80° in the complex plan) in EIS.
► Energy efficiency can be considered as an approximate indicator of capacitor or non-capacitor like behaviour.