Development of high-performance flexible electrodes from lignin-derived carbon nanospheres and reduced graphene oxide for supercapacitors

Flexible supercapacitors combine the advantages of conventional supercapacitors, including excellent mechanical properties, stretchability, and bendability, making them crucial components in wearable electronic devices. Herein, nitrogen and phosphorus co-doped lignin-derived carbon nanosphere (NPCS)/reduced graphene oxide (rGO) flexible electrode materials were synthesized through vacuum filtration and reduction methods. With increasing mass ratio of carbon nanospheres, the electrochemical performance of the electrode gradually improved, reaching an outstanding capacitance of 174.6   F   g −1 for a 1:1 ratio of NPCS to rGO at 1   A   g −1 . Additionally, the electrode maintained stable performance even after bending at different angles. The electrode, assembled into a symmetric supercapacitor with a 6   M KOH electrolyte, exhibited an outstanding capacitance of 130.5   F   g −1 at 1   A   g −1 and exceptional cycle stability, retaining 98.05% of its original capacitance after 5000 cycles at 5   A   g −1 . At a power density of 49.52   W/Kg, the electrode exhibited an energy density of 5.03   Wh/Kg. Moreover, the electrode maintained an excellent capacitance of 143.0   F   g −1 in an acidic electrolyte (1   M H 2 SO 4 ) at 1   A   g −1 . However, the electrode exhibited reduced capacitance in a neutral electrolyte (1   M Na 2 SO 4 ) but achieved a significantly higher energy density of 22.3   Wh/kg. The flexible electrode material exhibited adaptability to different acid–base conditions and maintained good flexibility, highlighting its significant potential for development in flexible supercapacitors.