A Comprehensive Review of Novel Emerging Electrolytes for Supercapacitors: Aqueous and Organic Electrolytes Versus Ionic Liquid-Based Electrolytes

Storage of energy is essential to meet the daily demand for powering portable devices. This necessitates the development of storage systems such as supercapacitors (SCs), batteries, and solar cells. SCs have garnered a lot of attention for their ability to provide a massive amount of power. Nevertheless, traditional mechanisms fall short of our expectations. Ionic liquids (ILs), the evolutionary green designer solvents, are efficient enough to substitute for conventional electrolytes such as aqueous or organic electrolytes in SCs. A limited potential window of aqueous electrolytes restricts the performance of high energy electrodes. In contrast, organic electrolytes with high volatility, flammability, and lack of tunability are not suitable for long-term and robust applications. Beneficial properties of ILs such as negligible volatility, high thermal, chemical, and electrochemical stability have overcome many restrictions in SCs and improved their overall performances. ILs can be used as standalone electrolyte or can be mixed with organic electrolytes, redox elements, and polymers to obtain electrolytes for SCs. The structure of anions and cations has been found to significantly influence overall electrochemical performances. ILs benefit SCs with a wider working voltage, temperature range, and better energy density. ILs have been utilized not only as electrolytes but also in the synthesis of electrode materials. Consequently, it is essential to discuss recent findings and the function of ILs in achieving higher-performing SCs. This review mainly highlights the most recent findings on the use of ILs-based electrolytes and electrodes in supercapacitors.