Design and Synthesis of Lignin-Based Flexible Supercapacitors

Due to the immense demand for flexible supercapacitors, it is important to develop low-cost and smarter solutions. To date, supercapacitors made of eco-friendly materials have been either expensive or of limited use. Herein, we report a solid-state, lightweight, low-cost, and plant-based supercapacitor for applications in flexible electronics. The asymmetric supercapacitor is made of MnO2 deposited on activated carbon and lignin as a substrate using hydrothermal deposition. With Al/AC/lig-MnO2 anode and Al/AC cathode, the supercapacitor is assembled using a poly(vinyl alcohol) (PVA)/H3PO4 gel electrolyte. Morphological characterization is conducted using microtomography and scanning electron microscope. Electrochemical performance is assessed using cyclic charge–discharge, cyclic voltammetry, and electrochemical impedance spectroscopy. A series of compositions of AC:lignin:MnO2 are optimized for best performance. After 2000 cycles, the specific capacitance obtained at 6.01 mA g–1 is 5.52 mF cm–2, which is up to 13 times reported. Retention is 98.7% after 1000 cycles and 97.5% after 2000 cycles. The maximum energy density, power density, and Coulombic efficiency obtained are 14.11 Wh kg–1, 1 kW kg–1, and 98%, respectively. The favorable electrochemical performance makes it useful for a wide variety of electronics. This new approach to fabricate electrodes from green sources, with constituent optimization and cost-effectiveness, marks an important step toward green energy technology development.