Lignin Cellulose Nanofibrils as an Electrochemically Functional Component for High‐Performance and Flexible Supercapacitor Electrodes

Abstract The increasing demand for wearable electronics has driven the development of supercapacitor electrode materials toward enhanced energy density, while being mechanically strong, flexible, as well as environmentally friendly and low‐cost. Taking advantage of faradaic reaction of quinone groups in natural lignin that is covalently bound to the high‐strength cellulose nanofibrils, the fabrication of a novel class of mechanically strong and flexible thin film electrodes with high energy storage performance is reported. The electrodes were made by growing polyaniline (PANI) on flexible films composed of lignin‐containing cellulose nanofibrils (LCNF) and reduced graphene oxide (rGO) nanosheets at various loading levels. The highest specific capacitance was observed for the LCNF/rGO/PANI electrode with 20 wt% rGO nanosheets (475 F g −1 at 10 mV s −1 and 733 F g −1 at 1 mV s −1 ), which represented a 68 % improvement as compared to a similar electrode made without lignin. In addition, the LCNF/rGO(20)/PANI electrode demonstrated high rate performance and cycle life (87 % after 5000 cycles). These results indicated that LCNF functioned as an electrochemically active multifunctional component to impart the composite electrode with mechanical strength and flexibility and enhanced overall energy storage performance. LCNF/rGO(20)/PANI electrode was further integrated in a flexible supercapacitor device, revealing the excellent promise of LCNF for fabrication of advanced flexible electrodes with reduced cost and environmental footprint and enhanced mechanical and energy storage performances.