The Effects of Self-Discharge on the Performance of Symmetric Electric Double-Layer Capacitors and Active Electrolyte-Enhanced Supercapacitors: Insights from Modeling and Simulation

• Published in: Journal of electronic materials 2017-02, Vol.46 (2), p.1163-1189
• Main Authors: Ike, Innocent S., Sigalas, Iakovos, Iyuke, Sunny E.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Electrolytes; Electronics; Electronics and Microelectronics; Instrumentation; Materials Science; Optical and Electronic Materials; Solid State Physics
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-016-5053-9

The effects of self-discharge on the performance of symmetric electric double-layer capacitors (EDLCs) and active electrolyte-enhanced supercapacitors were examined by incorporating self-discharge into electrochemical capacitor models during charging and discharging. The sources of self-discharge in capacitors were side reactions or redox reactions and several impurities and electric double-layer (EDL) instability. The effects of self-discharge during capacitor storage was negligible since it took a fully charged capacitor a minimum of 14.0 days to be entirely discharged by self-discharge in all conditions studied, hence self-discharge in storage condition can be ignored. The first and second charge–discharge cycle energy efficiencies η E 1 and η E 2 of a capacitor of electrode effective conductivity α 1  = 0.05 S/cm with only EDL instability self-discharge with current density J VR  = 1.25 × 10 −3  A/cm 2 were 72.33% and 72.34%, respectively. Also, energy efficiencies η E 1 and η E 2 of a similar capacitor with both side reactions and redox reactions and EDL instability self-discharges with current densities J VR  = 0.00125 A/cm 2 and J VR 1  = 0.0032 A/cm 2 were 38.13% and 38.14% respectively, compared with 84.24% and 84.25% in a similar capacitor without self-discharge. A capacitor with only EDL instability self-discharge and that with both side reactions and redox reactions and EDL instability self-discharge lost 9.73 Wh and 28.38 Wh of energy, respectively, through self-discharge during charging and discharging. Hence, EDLCs charging and discharging time is significantly dependent on the self-discharge rate which are too large to be ignored.