Renewable symmetric supercapacitors assembled with lignin nanoparticles-based thin film electrolyte and carbon...

Lignin as a natural biopolymer is becoming increasingly in demand due to its eco-friendly properties, while lignin-based electrolyte with high conductivity and reliable durability for applications in supercapacitors is still challenging. Herein, a facile method to prepare lignin nanoparticles (LNPs)-based solid electrolyte thin film (LF) was proposed through chemical cross-linking reaction. The fabricated LF exhibited a distinctive spongy porous structure with the ionic conductivity of 3.26 mS cm^-1, demonstrating the exceptional flexibility and favorable mechanical properties. Moreover, the assembly of all-LNPs-based symmetric supercapacitor (SSC) devices was achieved using LF electrolyte and LCA electrodes for the first time, confirming the LF3 electrolyte superior to commercial cellulose separator in capacitive behaviour. This SSC device exhibited a specific capacitance of 122.7 F g^-1 at 0.5 A g^-1 and the maximum energy density of 17.04 W h kg^-1. Furthermore, the incorporation of sodium alginate (SA) significantly enhanced the ionic conductivity of SA/LF3 electrolyte, and the resulting SSC device delivered a higher specific capacitance of 174.5 F g^-1 at 0.5 A g^-1 and the maximum energy and power densities of 24.24 W h kg^-1 and 5023 W kg^-1, respectively. This study proposes a promising approach for sustainable utilization of lignin in energy storage applications.