Direct laser writing of pure lignin on carbon cloth for highly flexible supercapacitors with enhanced areal capacitance

A facile and additive-free approach was developed to synthesize pure lignin-derived porous carbon for highly flexible supercapacitor electrodes. Lignin was simply melted on a carbon cloth, and then subjected to direct laser writing (DLW). It was found that lignin was transformed into 3D porous graphene while bonding on the carbon cloth. The fabricated materials (LCE) under different laser powers were all confirmed as having a sharp (002) peak with small d002 spacing from the XRD profile, and a high IG/ID ratio from Raman spectra. The LCEs showed promising capacitive behaviors in electrochemical testing. The best LCE (i.e., LCE40) possesses a CA of 786 mF cm−2, and it was further characterized by XPS and HRTEM to determine its compositional and structural information. Moreover, LCE40 had super flexibility attributed to carbon cloth as the substrate. The CA of the LCE after bending remained at 93–97% under different current densities. When assembled into symmetric solid-state supercapacitors, the LCE40-based device showed an areal capacitance of 148.6 mF cm−2, which is much superior to all other reported laser-induced lignin-derived carbon. This one-step process is innovative and simpler than any other porous carbon fabrication and provides a method for fabricating lignin-derived flexible supercapacitors.