Wet-Spinning Assembly of Flexible, Ultratough, and Conductive Alkali Lignin Functionalized Graphene Oxide Composite Fibers for Fiber-Shaped Supercapacitor

Graphene-based fibers (GBFs) are attractive for next-generation wearable electronics due to their potentially high mechanical strength, superior flexibility, and conductivity. However, for most fiber electrodes reported so far, a graphene fiber with high capacity and sufficient toughness for direct machine weaving or knitting has yet to be developed. Here, alkali lignin (AL) was dispersed by graphene oxide (GO) aqueous solution by mechanical stirring without any surfactants to afford stable AL/GO aqueous inks. AL could be intercalated into GO sheets by strong noncovalent interactions such as hydrogen bonding and π–π stacking, and the steric hindrance effect of the AL chains could effectively prevent the π–π stacking of GO nanosheets. Thus, hyperelastic GO-AL fibers (GOF-AL) could be assembled by wet-spinning of the as-prepared AL/GO aqueous inks at room temperature. The results suggest that AL can act as a binder and dispersant for graphene sheets and can facilitate the rearrangement of the fiber's microstructure. Significantly, reduced GO-AL fibers (rGOF-AL) showed enhanced tensile strength and breakage elongation with a tensile strength limit of 310 MPa, ∼2 times higher than pure reduced GO fibers (rGOF), and with an elongation at break of 16%, ∼1.7 times higher than pristine rGOF. Using H2SO4-poly(vinyl alcohol) (PVA) gel as the electrolyte, the rGOF-AL electrodes were further fabricated into a flexible solid-state supercapacitor. The rGOF-AL-based fiber-shaped supercapacitor (rGOF-AL FSC) showed high capacitive performances (46.5 mF cm–2 at 0.5 mA cm–2 and 94.0% capacitance retention over 1000 cycles). The current rGOF-AL with excellent tensile and electrical conductivity was recyclable and ecologically friendly, highlighting a promising prospect for high-value usage of lignin.