High Voltage Window of the Symmetrical Electrochemical Capacitor Made By Using Dual Redox Additives Enhanced Quasi-Solid like Electrolyte

Abstract

Recently, researchers have shown an increased interest in redox-active electrolyte because of its high performance and simple fabrication. However, most studies have only focused on aqueous electrolyte system, while suffering from limiting potential window of the electrochemical capacitor(EC) due to water decomposition voltage at 1.23 V. In addition, leakage problem results in safety concern in liquid system. In the light of this, we introduce dual redox additives TEMPO and pBQ into PVDFHFP-BMIMTFSI-EC quasi-solid like polymer electrolyte (QSPE) as dual redox active electrolyte (RQSPE). The TEMPO and pBQ enable rapid charge transfer and highly solubility in ionic liquid, promoting the synergic effect of electric double layer capacitance(EDLC) and redox reaction. The coupling of battery-like reversible redox reaction and supercapacitor-like EDLC leads to provide high energy density and power density at the same time. The electrochemical properties of the fabricated EC involving RQSPE electrolyte and carbon electrodes are compared to those of the EC using QSPE without redox additives. The excellent specific energy of 61.12 Wh kg-1 is exhibited by the EC with RQSPE, which is over three times higher than the one without redox additives. In addition, the specific power density of the EC with RQSPE is up to 3.43 kW kg-1 at 17.10 Wh kg-1. Furthermore, the addition of redox additives can expand the voltage window of the EC to 3 V, while the EC without such additives has less value of 2.5 V. The ionic conductivity of the electrolyte is 8.85 mS cm-1, also indicating that adding redox additives have positive effect to the mobility of electrolyte. Finally, the EC with RQSPE exhibits stable cycling stability over 2000 charge/discharge cycles. Figure 1