Fabrication of porous carbon nanofibril/MnO₂ composite aerogels from TEMPO-oxidized cellulose nanofibrils for high-performance supercapacitors

Supercapacitors have played a key role in energy storage field due to their fast charge-discharge processes and long cycle life. Here, 2,2,6,6-tetramethylpiperidine-1-oxylradical (TEMPO)-oxidized cellulose nanofibrils were carbonized to fabricate carbon nanofibrils (CTOCN). CTOCN/manganese dioxide (MnO₂) composite aerogels were then obtained via a simple hydrothermal method, through which MnO₂ strongly attached to the surface of CTOCN, thus maintaining the highly porous 3-dimensional (3D) structure. CTOCN/MnO₂ with MnO₂ content of 20.8 wt% exhibited the most outstanding electrochemical performance. It possessed a maximum specific capacitance of 171.1 F g⁻¹ at 0.5 A g⁻¹ and could still remain 98.4% of the initial value after 5000 cycles at 3 A g⁻¹. Moreover, an asymmetric supercapacitor using the CTOCN/MnO₂ composite as positive electrode and activated carbon (AC) as negative electrode was assembled. The assembled supercapacitor delivered an energy density of 8.6 W h kg⁻¹ at a power density of 619.2 W kg⁻¹, and could still remain 4.13 W h kg⁻¹ at a power density of 6.8 kW kg⁻¹. Additionally, it possessed an excellent cycle life with 99.4% retention of the first cycle after 4500 cycles at 3 A g⁻¹, suggesting an available method for designing a promising electrode material for supercapacitors.