Synergistic design of a N, O co-doped honeycomb carbon electrode and an ionogel electrolyte enabling all-solid-state supercapacitors with an ultrahigh energy density

Abstract

Significantly boosting the energy densities of supercapacitors without compromising their power densities is of paramount importance for practical applications, but still faces great challenges. Herein, we report an ultrahigh-energy-density solid-state supercapacitor enabled by synergistical design of a N, O co-doped honeycomb porous carbon (HPC) electrode and an ionogel electrolyte. HPC is synthesized through the co-assembly of melamine/formaldehyde with silica spheres, and shows an ultrahigh surface area (2379 m² g⁻¹) coupled with a 3D interconnected macro-, meso- and microporous structure, and high-level redox-active N/O dopants (6.90 and 10.17 wt%). Benefiting from such merits, the HPC electrode yields an extremely high capacitance of 533 F g⁻¹ at 0.5 A g⁻¹ in an alkaline electrolyte, together with superior cycling stability with 92.1% capacitance retention after 20 000 cycles at 5 A g⁻¹. HPC assembled supercapacitors deliver energy outputs of 12.8 and 26.6 W h kg⁻¹ using KOH and Na₂SO₄ electrolytes, respectively. More attractively, a HPC-fabricated all-solid-state symmetric device based on the use of a well-designed, polymer-gel supported ionic liquid electrolyte achieves an ultrahigh energy density of 94.1 W h kg⁻¹, which is the highest value among those of previously reported supercapacitors of the same type, and an excellent cycling stability (91.5% retention over 10 000 cycles). This study highlights promising prospects of developing solid-state energy storage systems of high energy-power supply.