A Review of Redox Electrolytes for Supercapacitors

Abstract

Supercapacitors (SCs) have attracted widespread attention due to their short charging/discharging time, long cycle life, and good temperature characteristics. Electrolytes have been considered as a key factor affecting the performance of SCs. They largely determine the energy density based on their decomposition voltage and the power density from their ionic conductivity. In recent years, redox electrolytes obtained a growing interest due to an additional redox activity from electrolytes, which offers an increased charge storage capacity in SCs. This article summarizes the latest progress in the research of redox electrolytes, and focuses on their properties, mechanisms, and applications based on different solvent types available. It also proposes potential solutions for how to effectively increase the energy density of the SCs while maintaining their high power and long life.

Role of dual redox additivesKI/VOSO4in manganese ammonium phosphate at graphene quantum dots for supercapattery

“…17 For instance, Akinwolemiwa et al, and Li et al dispersed KBr and KI as redox initiators in AC supercapacitors to achieve both electric double-layer capacitance (EDLC) and Nernstian charge storage kinetics in a single system. 18 Similarly, various redox additives other than halides, for example, K 4 Fe(CN) 6 , 19 VOSO 4 , 20 hydroquinone, 21 p-phenylenediamine, 19 p-aminophenol, 22 indigo carmine, 23 methylene blue, 24 lignosulfonates, 25 and so forth are also used to improve the specific capacitances of supercapacitor electrodes. This impeccably influences redox additives on hybrid electrodes' intended use in SUPAT systems also.…”

A Redox-Mediator-Integrated Flexible Micro-Supercapacitor with Improved Energy Storage Capability and Suppressed Self-Discharge Rate

“…Especially, RMs can show high flexibility and mechanical/chemical stability when they are mixed with a gel electrolyte, as well as provide easy diffusion in the gel electrolyte. The addition of RMs plays pivotal roles in enhancing the performance of supercapacitors due to the induced electrochemical Faradaic redox reactions on the surface of electrodes, which can store more electron charges compared to double-layer capacitance [27,28]. Thus, the total capacitance of supercapacitors with redox mediators can store energy by both electric double layer capacitance and the pseudocapacitance working in parallel.…”

Iodide Electrolyte-Based Hybrid Supercapacitor for Compact Photo-Rechargeable Energy Storage System Utilising Silicon Solar Cells

“…Energies 2021, 14, 2708 2 of 14 Among the recent attempts to improve the energy density of supercapacitors, the strategy of aqueous redox electrolyte hybrid energy storage (REHES) has received a significant attention due to the simplicity of the system's construction, low cost of electrode materials/electrolyte and environmental friendliness [8][9][10]. In general, the aqueous-redox system exhibits a mixed charge-discharge mechanism; the charge is stored in the electrical double layer at the porous carbon/electrolyte interface, and also as a result of localised valence electron transfer due to the presence of electroactive redox couple in the electrolyte.…”