Improved Capacitive Performance of High‐Voltage Electric Double‐Layer Capacitors by Electrolyte Optimization Using Hierarchically Porous Carbon Electrodes

Advancement of the voltage window with stringent safety concerns is an imperative strategy to enhance the energy densities and output power delivery of electrical double‐layer capacitors (EDLCs). Solid‐state, water‐in‐salt (WIS), and ionic liquid‐based electrolytes are attractive and ideal choices for high‐voltage EDLCs due to their superior voltage window, electrochemical performance, and predominant safety aspects. Mindful of this, the current report demonstrates the electrochemical performance of new nanoporous carbon electrodes derived from waste dry leaves of Swietenia macrophylla with a high specific surface area (SSA) (1834 m 2 g −1 ) in polymer–gel, WIS, and ionic liquids‐based electrolytes. Symmetric EDLC devices are fabricated using polymer gel solid‐state (PVA–Na 2 SO 4 ), ionic liquids (EMIMBF 4 ), and WIS (21 m LiTFSI) electrolytes with the electrochemical stability windows of (ESW) 2, 2.5, and 2 V, respectively. The assembled devices with Na 2 SO 4 /PVA, EMIMBF 4 , and 21 m LiTFSI (WIS) electrolytes‐based devices exhibit high energy densities of 40, 31, and 25 Wh kg −1 at 0.5 A g −1 and good output power delivery of 5, 6.23, and 3 kW kg −1 at 5 A g −1 with better cyclability features. Self‐discharging studies and systematic evaluation of high‐voltage EDLCs offer a sustainable method to develop high‐performance aqueous and diverse electrolyte‐based supercapacitors.