Pore-structure regulation and heteroatom doping of activated carbon for supercapacitors with excellent rate performance and power density

Abstract

Activated carbon (AC) has attracted tremendous research interest as an electrode material for supercapacitors owing to its high specific surface area, high porosity, and low cost. However, AC-based supercapacitors suffer from limited rate performance and low power density, which mainly arise from their inherently low electrical conductivity and sluggish ion dynamics in the micropores. Here, we propose a simple yet effective strategy to address the aforementioned issue by nitrogen/fluorine doping and enlarging the micropore size. During the treatment, the decomposition products of NH₄F react with the carbon atoms to dope the AC with nitrogen/fluorine and simultaneously enlarge the pores by etching. The treated AC shows a higher specific surface area of 1826 m² g⁻¹ (by ~ 15%), more micropores with a diameter around 0.93 nm (by ~ 33%), better wettability (contact angle decreased from 120° to 45°), and excellent electrical conductivity (96 S m⁻¹) compared with untreated AC (39 S m⁻¹). The as-fabricated supercapacitors demonstrate excellent specific capacitance (26 F g⁻¹ at 1 A g⁻¹), significantly reduced electrical resistance (by ~ 50%), and improved rate performance (from 46.21 to 64.39% at current densities of 1 to 20 A g⁻¹). Moreover, the treated AC-based supercapacitor achieves a maximum energy density of 25 Wh kg⁻¹ at 1000 W kg⁻¹ and a maximum power density of 10,875 W kg⁻¹ at 15 Wh kg⁻¹, which clearly outperforms pristine AC-based supercapacitors. This synergistic treatment strategy provides an effective way to improve the rate performance and power density of AC-based supercapacitors.