Electrolytes for Supercapacitors

Electrolytes play a pivotal role in the performance, efficiency, and longevity of supercapacitors (SCs) by enabling ion transport between electrodes. This chapter comprehensively explores electrolyte systems, including aqueous, organic, ionic liquid, and solid-state electrolytes, detailing their material properties, electrochemical stability windows, ionic conductivity, and compatibility with various electrode materials. Key selection factors such as voltage range, thermal stability, viscosity, and safety considerations are thoroughly examined. The chapter also discusses advanced techniques for evaluating electrolyte performance, including cyclic voltametry (CV), Electrochemical Impedance Spectroscopy (EIS), and capacitance retention analysis. Challenges such as limited electrochemical stability, toxicity, and restricted ionic mobility are addressed, alongside promising advancements in hybrid electrolytes, deep eutectic solvents (DESs), and polymer gel-based systems. By integrating theoretical models, experimental findings, and comparative analyses, this chapter offers valuable insights into the strategic design of electrolytes for next-generation SCs. The ongoing development of innovative electrolyte materials is driving advancements in energy storage, enhancing power density, flexibility, and environmental sustainability.