Nitrogen‐Doped Accordion‐Like Soft Carbon Anodes with Exposed Hierarchical Pores for Advanced Potassium‐Ion Hybrid Capacitors

Abstract

Soft carbon (SC) is a promising anode material for potassium‐ion hybrid capacitors (PIHCs), but there are limited K+ storage sites in common SC due to a skin‐like carbon film covering on the surface. To address this issue, a simple oxidization method to completely remove the skin‐like carbon film is reported and a novel accordion‐like architecture of SC (ASC) is constructed with a hierarchical porous framework composed of micropores, mesopores, and macropores, all of which can be exposed to K+ electrolytes for enhanced energy storage. Importantly, this exposed structure facilitates pseudocapacitance modification by electro‐deposition of highly electrochemically active nitrogen‐doped graphene quantum dots (N‐GQDs) to enhance kinetic performance and additional K+ storage. After annealing treatment to regulate N‐doping type, the accordion‐like N‐GQD@ASC‐500 exhibits excellent reversible capacity of 360 mAh g−1 as well as superior rate capability and cycle stability. Kinetic, in situ Raman/electrochemical impedance spectroscopy analysis, and density functional theory calculation elucidate the K+ storage mechanism. As expected, the PIHC assembled with N‐GQD@ASC‐500 anode and porous carbon cathode delivers an ultrahigh energy/power density (171 Wh kg−1 and 20 000 W kg−1) with long cycle life. This work suggests that ASC is a promising anode material for designing of high‐performance PIHCs.

Interconnected 3D carbon network with enhanced reaction kinetics and architecture stability for advanced potassium-ion hybrid capacitors

“…The peak current (i) obeys a power law relationship with the scan rate (v), according to the formula i = av b . 14,36 Among them, a and b are adjustable parameters. Especially, the b value can be confirmed from the slope of the linear plot of ln(i) against ln(v).…”

“…where k 1 and k 2 are constant values, and k 1 v and k 2 v 1/2 correspond to the capacitive-controlled and diffusion-controlled process, 14 respectively. The NPC electrode shows a 78.4% capacitive contribution from the total capacity at the scan rate of 2 mV s À1 (Fig.…”

“…[11][12][13] Generally, battery-type anodes and capacitor-type cathodes are regarded as key configurations for determining the excellent electrochemical performance of PIHCs, and the charging/ discharging process involves cation intercalation/deintercalation into/from the anode side and anion adsorption/desorption at the cathode side. 11,13,14 Nevertheless, as we all know, intercalation/deintercalation behaviors occurring at the anode is usually more sluggish in comparison with the adsorption/ desorption process lying in the cathode. Furthermore, the anode materials directly affect the rate capability, as well as the cycling stability of the PIHC devices.…”

“…This is mainly because the nitrogen atom possesses a smaller size and is more electronegative than the carbon atom. 14 As a result, the electrical conductivity and fast reaction kinetics of carbon anodes are further improved.…”

Carbonaceous Anode Materials for Non-aqueous Sodium- and Potassium-Ion Hybrid Capacitors

“…44 N-doped graphene quantum dots (N-GQDs) have been used to decorate accordion-like SC (ASC). 132 The composite contained rich functional groups, abundant active sites, and a hierarchical porous framework. The composite acted as "ion-buffering reservoirs" to generate abundant ion transport pathways, resulting in excellent reversible capacity and cycle stability (Figure 11b).…”