Nanocellulose/nitrogen and fluorine co-doped graphene composite hydrogels for high-performance supercapacitors

Three-dimensional graphene materials have been studied as typical supercapacitors electrode materials by virtue of their ultra-high specific surface area and good ion transport capacity. However, improvement of the poor volumetric electrochemical performance of these graphene materials has been required although they have high gravimetric energy density. In this work, nanocellulose/nitrogen and fluorine co-doped graphene composite hydrogels (NC-NFGHs) were prepared through a convenient hydrothermal approach utilizing ammonium fluoride as the heteroatom source. Nanocellulose (NC) and high concentration of graphene oxide (GO) were utilized to adjust the structure of NC-NFGHs and increase their packing density. Subsequently, the aqueous symmetric supercapacitor based on NC-NFGH-80 exhibits remarkable gravimetric (286.6 F·g⁻¹) and volumetric (421.3 F·cm⁻³) specific capacitance at 0.3 A·g⁻¹, good rate performance, and remarkable cycle stability up to 10,000 cycles. Besides, the all-solid-state flexible symmetric supercapacitors (ASSC) fabricated by NC-NFGH-80 also delivered a large specific capacitance of 117.1 F·g⁻¹ at 0.3 A·g⁻¹ and long service life over 10,000 cycles at 10 A·g⁻¹. This compact porous structure and heteroatom co-doped graphene material supply a favorable strategy for high-performance supercapacitors.