Cucurbit[6]uril‐Derived Nitrogen‐Doped Hierarchical Porous Carbon Confined in Graphene Network for Potassium‐Ion Hybrid Capacitors

Abstract

Potassium-ion hybrid capacitors (PIHCs) have attracted tremendous attention because their energy density is comparable to that of lithium-ion batteries, whose power density and cyclability are similar to those of supercapacitors. Herein, a pomegranate-like graphene-confined cucurbit[6]uril-derived nitrogen-doped carbon (CBC@G) with ultra-high nitrogen-doping level (15.5 at%) and unique supermesopore-macropores interconnected graphene network is synthesized. The carbonization mechanism of cucurbit[6]uril is verified by an in situ TG-IR technology. In a K half-cell configuration, CBC@G anode demonstrates a superior reversible capacity (349.1 mA h g −1 at 0.1 C) as well as outstanding rate capability and cyclability. Moreover, systematic in situ/ex situ characterizations, and theory calculations are carried out to reveal the origin of the superior electrochemical performances of CBC@G. Consequently, PIHCs constructed with CBC@G anode and KOH-activated cucurbit[6]uril-derived nitrogen-doped carbon cathode demonstrate ultra-high energy/power density (172 Wh kg −1 /22 kW kg −1) and extraordinary cyclability (81.5% capacity retention for 5000 cycles at 5 A g −1). This work opens up a new application field for cucurbit[6]uril and provides an alternative avenue for the exploitation of high-performance PIHCs.

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

“…As reported, the pseudocapacitance contributed by pyridinic‐N is more reversible than that contributed by pyrrolic‐N, and the pyridinic‐N is energetically more compatible with K + adsorption than other nitrogenous species, such as pyrrolic‐N and quaternary‐N. [ 21,23 ] Therefore, the regulation of N‐doping type from pyrrole to pyridine through appropriate annealing treatment can improve the K + storage capacity of N‐GQD@ASC‐500, which is proved by the subsequent performance test results.…”

“…N‐GQD@ASC‐500 exhibits a large diffusion resistance at initial stage of discharge, which is due to the absence of fast‐ionic conductor film between the electrode surface and electrolyte. [ 23,40 ] The diffusion resistance decreases gradually with the increase of discharge depth, and then it increases slowly at charge stage. This phenomenon is attributed to the K + insertion, which is conducive to the ionic conductivity.…”

What Is the Right Carbon for Practical Anode in Alkali Metal Ion Batteries?

“…Nongraphitic carbons have also been explored as alternatives to graphite, which could relieve the severe volume change that occurs during potassium storage. [104][105][106][107][108] Similar to its lithium and sodium counterparts, soft carbons also give sloping potential profiles in PIBs and are different from graphite. However, they have been reported to have a superior cycling ability than graphite.…”

Application of 2D Materials to Potassium‐Ion Hybrid Capacitors

“…A pomegranate-like graphene-confined cucurbit [6]uril-derived nitrogendoped carbon (CBC@G) with a high nitrogen doping level (15.5 at %) and a unique supermesopore-macropore interconnected graphene network was prepared by freeze-drying and a carbonization approach and used as anode material for PICs. [44] The CBC@G electrode was reported to achieve an outstanding reversible capacity (349.1 mAh g À 1 at 0.1 C) and a superior rate capability and cyclability for potassium-ion storage. The system's in situ and ex situ characterization and DFT calculations also confirm this finding.…”