Abstract:

Activated carbons are widely used as the electrode material for supercapacitors owing to its large surface area, good electric conductivity, and outstanding electrochemical stability. Improving the electric conductivity of activated carbon is crucial for promoting its electrochemical energy storage, but hard to achieve because well-developed pores usually break the continuous conductive network. To solve this problem, researchers have developed several methods, such as selection of highly-conjugated carbon precursors, high-temperature post-treatment, compositing with highly conductive nanocarbons, and local catalytic graphitization. However, these methods generally suffer from high cost, low efficiency, and sacrifice of specific surface area. Herein, we propose a selective chemical etching strategy to prepare activated carbon with both high surface area and electric conductivity using a mixture of pitch and polyacrylonitrile (PAN) as the precursor. Through systematic investigation of the activation behavior of pure pitch, pure PAN, and the composite precursors, we demonstrate that the PAN-derived carbon contains amorphous and crystallized components. During activation, the amorphous carbon is primarily etched away due to its high reactivity, leading to the in-situ formation of less-defective carbon as the entire conductive network. The optimized sample shows a surface area of 2773 m²·g⁻¹ and 2.6 times increased electric conductivity of 912 S·m⁻¹, outperforming most of the reported activated carbons. Furthermore, the strong cross-linking between pitch and PAN molecules through pre-oxidation leads to a higher activated carbon yield of 58% than the pure pitch-derived activated carbon (34%). The optimized cross-linking structure also allows the activator K⁺ to be adsorbed more easily in the carbon precursor, which enhances the activation efficiency. As a result, the embedded PAN simultaneously construct conductive network and promote activation efficiency, leading to the integration of high electric conductivity and surface area of the activated carbon. For aqueous supercapacitor application, at the high electrode mass loading of 10 mg·cm⁻², the optimized material shows remarkable areal capacitance (2.8 F·cm⁻² at 1 A·g⁻¹) and good rate performance (41% retention at 50 A·g⁻¹). The corresponding device shows high energy densities (10.9 Wh·kg⁻¹) and remarkable cycle stability (100% retention after 50000 cycles). The reason is that good electric conductivity enables high surface area utilization, significantly improved electric double-layer formation and ion transport kinetics. This work demonstrates the significant potential of highly conductive activated carbon for practical applications, and provides novel insights into the design of conductive activated carbon for advanced energy storage.

Key words: Activated carbon, Electric conductivity, Surface area, Supercapacitor, Chemical etching