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.