Two-dimensional nitrogen and phosphorus co-doped mesoporous carbon-graphene nanosheets anode for high-performance potassium-ion capacitor

Abstract

Heteroatom-doped carbon materials have high gravimetric potassium-ion storage capability because of their abundant active sites and defects. However, their practical applications toward potassium storage are limited by sluggish reaction kinetics and short cycling life owing to the large ionic radius of K+ and undesirable parasitic reactions. Herein, we report a new strategy that allows for bottom-up patterning of thin N/P co-doped carbon layers with a uniform mesoporous structure on two-dimensional graphene sheets. The highly porous architecture and N/P co-doping properties provide abundant active sites for K+, and the graphene sheets promote charge/electron transfer. This synergistic structure enables excellent K+ storage performance in terms of specific capacity (387.6 mAh g-1 at 0.05 A g-1), rate capability (over 5 A g-1), and cycling stability (70% after 3,000 cycles). As a proof of concept, a potassium-ion capacitor assembled using this carbon anode yields a high energy density of 107 Wh kg-1, a maximum power density of 18.3 kW kg-1, and ultra-long cycling stability over 40,000 cycles.

Revealing the Effect of the Microstructure on Potassium Storage Behavior in a Two-Dimensional Mesoporous Carbon Anode

“…After 10 cycles, the intensity of the C 1s peak reduces, which is mainly associated with SEI formation (Figures S18c,d and S19). Two new peaks at around 293.08 and 295.83 eV appear, which are assigned to the K 2p2/3 and K 2p1/3 signals, respectively, which are largely related to KHCO 3 or RO-COOK derived from SEI. , The whole O 1s peak slightly shifts to a lower binding energy, which provides additional evidence of K-salt, RO-COOK, and RO-K on the surface of 2D-MCM-1100/1500 electrodes (Figure S20). After 1000 cycles, C 1s, O 1s, and K 2p XPS spectra show little change, suggesting the structural stability of 2D-MCM-1100/1500 electrodes and SEI layer.…”

“…Figure S10c,d displays the CV curves at various scan rates ranging from 0.2 to 200 mV s –1 . During the following anodic and cathodic scans, no obvious peaks appear, which is largely due to the combination of multiple charge storage mechanisms with the stepwise extraction of K + from K-intercalated carbon and/or the reversible reactions between K + and surface functional groups. ,,, Figure a and Figure S11 show the galvanostatic charge–discharge (GCD) curves at 0.05 A g –1 of 2D-MCM- x samples. 2D-MCM- x samples show large irreversible capacity during the first cycle, primarily due to the formation of the SEI layer and irreversible side reactions on the surface of the 2D-MCM- x electrode, which is consistent with CVs’ observation.…”

“…The slurry was then homogeneously painted on the current collector (Cu foil) using a blade and dried at 80 °C under vacuum for 6 h. The foil was punched into round electrodes with a diameter of 14 mm. The active mass loading of 2D-MCM on Cu foil was 0.5–0.8 mg. For cathode materials, homemade polyaniline-derived porous carbon (PDPC) was used; more details about the synthesis procedure can be seen in our previous work. , For the PDPC cathode, a mixture was prepared by blending PDPC powder with a conductive filler, carbon black, and binder polytetrafluoroethylene (PTFE) in a mass ratio of 8:1:1. The mixture was rolled to form a film, dried at 120 °C for 12 h, and then cut into a rectangle shape.…”

“…However, the practical use of a graphite anode in PICs is hindered by poor rate capability and short cycling life due to the large volume change (∼61%) and sluggish K + kinetics associated with K + intercalation. ,, To solve the inherent problems of graphite, hard carbons, featuring a highly disordered and less crystalline structure, have been explored. , In addition to the intercalation of K + into the graphitic structure at lower working potential (e.g., <0.5 V vs K + /K), surface-driven capacitive K + storage occurs at the disordered or noncrystalline structure from the higher working potential (e.g., >0.5 V vs K + /K). , The combined mechanisms of K + charge storage typically result in a sloping curve in the electrochemical profile of hard carbon, which enables fast kinetics and good structural integrity, leading to high rate capability and cycling stability . Currently, substantial studies have been conducted to enhance the surface-driven capacitive contribution of hard carbon for pursuing better electrochemical performance by introducing meso/micropores into the carbon matrix, , incorporating heteroatom functional groups on the surface, − and creating large defects on carbon layers. − These modified hard carbons exhibited a high reversible capacity over 300 mAh g –1 and excellent cycling stability. Nonetheless, more capacity arises from the high voltage region, and low initial Coulombic efficiency becomes popular.…”

Exploring nature-behaviour relationship of carbon black materials for potassium-ion battery electrodes

“…In recent years, potassium-ion batteries (PIBs) have strongly emerged as a viable technology for stationary storage [14][15][16][17] . Indeed, potassium (K) possesses some features that place it at the forefront of post-lithium technologies [18][19][20][21] .…”