Advancements in liquid and solid electrolytes for their utilization in electrochemical systems

Electrolyte is one of the key components, which plays an important role in various modern electrochemical energy storage devices. Electrode and electrolyte both are key factors which yield high capacitance value, power density and energy density for energy storage devices. This review article emphasizes an overview about classes of electrolyte. Various types of liquid electrolytes (organic, ionic liquid & aqueous) & solid electrolyte (polymer-based electrolytes) are also discussed. There are new compositions like deep eutectic solvent, which have also been discussed in detail, along with their advantages, merits, and demerits. This review also emphasizes recent research efforts in order to elucidate the next steps needed to develop a fundamental framework needed for a deeper understanding of DESs. It covers recent developments in DES research, frames outstanding scientific questions, and identifies promising research thrusts aligned with the advancement of the field towards understanding of these solvents. Natural polymers or starch-based polymer electrolytes are also discussed which are prepared using various methods like solution casting technique, sol-gel method, ionotropic gelation, spin coating and hot-press technique. Performance of polymer electrolyte is then discussed based on different parameters like conductivity, electrochemical stability window, thermal stability window and impedance spectroscopy. Performance indicators of supercapacitor and batteries have been compared for different kind of electrolytes. In the last section, important directions for future scope have been highlighted. • This review is written on novel electrolytes: “Deep Eutectic Solvents (DES)”. • The synthesis processes, properties and application of Deep Eutectic Solvents is discussed in detail. • The properties of DES are compared with polymer based electrolytes and Starch based sustainable and ecofriendly polymers. • Application of different types of polymer electrolytes in energy storage devices is discussed in detail.