Development of novel and ultrahigh-performance asymmetric supercapacitor based on redox electrode-electrolyte system

The conventional enhancement in capacitive performance that only relies on electrode materials is limited. Here, based on the system-level design principle, we explore the possibility of enhancing capacitance through both electrode and electrolyte. A novel and ultrahigh-performance asymmetric supercapacitor has been fabricated using two redox electrode systems. The positive electrode system consists of graphene supported Co(OH)2 nanosheet (Co(OH)2/GNS) electrode and mixed KOH and K3Fe(CN)6 aqueous electrolyte. And the negative electrode system comprises carbon fiber paper supported activated carbon (AC/CFP) electrode in mixed KOH and p-phenylenediamine (PPD) aqueous electrolyte. The novel asymmetric supercapacitor exhibits a significantly improved capacitive performance (specific capacitance of 204.5 Fg−1, operational voltage of 2.0 V) in comparison with that of the conventional asymmetric supercapacitor (66.8 Fg−1, 1.5 V) fabricated without redox electrolyte. The improvement is attributed high reversibility and conductivity of electrode materials and redox electrolyte, as well as the synergistic effect between the two electrode systems, resulting in a ultrahigh energy density (114.5 Whkg−1 at a power density of 1000 Wkg−1), excellent power density (4000 Wkg−1 at an energy density of 31.6 Whkg−1) and long-term cycling stability (after 20000 cycles, initial capacitance remains well). These encouraging results afford a facile and efficient way to fabricate ultrahigh-performance supercapacitors for the increasing demands on the energy storage devices.