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.