Lignin Isolated from Poplar Wood for Porous Carbons as Electrode for High-Energy Renewable Supercapacitor Driven by Lignin/Deep Eutectic Solvent Composite Gel Polymer Electrolyte

The current challenge for supercapacitors based on sustainable materials is the difficulty of elevating energy density while maintaining the power density and capacitance retention. Herein, we demonstrate a strategy to boost the energy density of renewable all-lignin-based supercapacitors via sound design of lignin porous carbon electrodes isolated from poplar wood as well as employing lignin/deep eutectic solvent (DES) gel polymer electrolytes (GPEs) with a wide electrochemical window. The resulting device exhibits a remarkable specific capacitance of 181.5 F g –1 at 1 A g –1 and favorable capacitance retention of 80.2% at 5 A g –1 over 2000 cycles, which is attributed to the large specific surface area of 1125 m 2 g –1 as well as a high degree of graphitization possessed by the electrode materials and excellent conductivity of 13.5 S/m held by the DES gel polymer electrolytes. Furthermore, the supercapacitor delivers a maximum energy density of 40.8 Wh kg –1 and it remains 29.0 Wh kg –1 at an ultrahigh power density of 3.2 KW kg –1 .