Simultaneous densification and nitrogen doping of laser-induced graphene by duplicated pyrolysis for supercapacitor applications

Laser pyrolysis of polyimide is a facile and cost-effective method to fabricate high performance supercapacitor electrodes. This study proposes a duplicated laser pyrolysis method to densify pyrolyzed carbon electrodes and hence improve electrochemical performance. The initial laser pyrolysis of polyimide generates a graphene-like carbon, called laser-induced graphene (LIG). This LIG is then coated with an additional polyimide layer, and the second laser pyrolysis is applied, producing densified LIG. Laser power effects on densified LIG morphology and electrochemical characteristics are investigated, confirming remarkable density increase. Increased nitrogen content is also observed, signifying significant nitrogen doping. The densified electrode achieves 49.0 mF cm(-2) specific capacitance at 0.2 mA cm(-2) current density in a standard three-electrode system, approximately 6-fold that for singly pyrolyzed LIG electrodes. A solid-state flexible supercapacitor with densified LIG electrodes is fabricated using a gel electrolyte (PVA-H2SO4), achieving 19.8 mF cm(-2) capacitance at 0.05 mA cm(-2) current density, with outstanding cyclic charge-discharge stability and mechanical flexibility.