A Flexible Supercapacitor with High Energy Density Driven by MXene/Deep Eutectic Solvent Gel Polyelectrolyte

Limited by low operating voltages and insufficient understanding of the electrolyte component interaction mechanisms, electrochemical double-layer capacitors (EDLCs) exhibit unsatisfactory energy density and significant energy loss under low temperatures. Herein, we propose a new strategy for the synthesis of a green gel polymer electrolyte employing polyacrylamide (PAM) as a cross-linking network based on a Li-salt containing a deep eutectic solvent (DES). Remarkably, the addition of lignin and MXene contribute significantly to boost the performance of the device with DES gel polyelectrolyte, mainly through the Lewis acid-base interactions between the abundant functional groups (−F and −OH) and TFSI- group. We have also confirmed the occurrence of this interaction and the mechanism of improving conductivity and operating voltage by molecular dynamics simulations. Consequently, the device delivers a wide potential window of 0-2.4 V and the highest weight energy density of 42.6 Wh kg^-1. This work offers new insight into the fabrication of green and flexible devices with high energy density without producing electronic waste.