Application of 2D Materials to Potassium‐Ion Hybrid Capacitors

Abstract

Metal‐ion hybrid supercapacitors (MICs) are a new type of electrochemical energy storage (EES) device, consisting of a battery‐type electrode and a supercapacitor (SC)‐type electrode. Exhibiting the advantages of both batteries and SCs (e. g., good energy density, excellent power density and long cycle life), these advanced energy storage devices have considerable commercial application prospects. Among MICs, potassium‐ion hybrid supercapacitors (PICs) have several further advantages, including abundancy of resources, low standard electrode potential, and low cost. PICs are regarded as potential substitutes for lithium‐ or sodium‐ion hybrid supercapacitors. However, the practical applications of PICs remain limited, owing to the imbalance of kinetics and capacity between the electrodes, the slow ion/electron diffusion rate, and the poor electrode structural stability. Recently, 2D materials with distinct structures and fascinating features have elicited widespread attention for application in PICs, thus achieving significant enhancements, ranging from charge storage capacity to reaction kinetics. This Review discusses research progress in 2D materials for PICs. Firstly, the energy storage principle and development requirements of MICs are introduced. The pivotal advantages and significant roles of 2D materials in the fabrication of PICs are then discussed in detail. Lastly, the challenges and prospects of the application of 2D materials to high‐performance PICs are presented.

Recent Advances in Layered Metal‐Oxide Cathodes for Application in Potassium‐Ion Batteries

“…Numerous different MICs have been reported in the literature including the lithium-ion (LIC), sodium-ion (NIC), potassium-ion (KIC) and zinc-ion capacitors (ZIC), among others. [116][117][118][119] Comte et al reported the first hybrid KIC using graphite (battery type) as the anode, activated carbon (capacitor type) as the cathode and a 0.8 m KPF 6 EC:DMC electrolyte. [120] During the charging process, the K + ions are intercalated into the anode while the PF 6 − anions in the electrolyte are adsorbed on the cathode surface, forming an electric double layer.…”

Expanded Graphite-Based Materials for Supercapacitors: A Review

“…Li-ion capacitors (LICs) are made up of a capacitor-type cathode, one battery-type anode, and one appropriate electrolyte [ 15 , 69 , 70 , 71 , 72 , 73 , 74 ]. They rely on the surface reaction of the cathode and the lithiation/electrolysis of the anode to achieve energy storage and conversion [ 14 , 16 , 17 , 18 ]. Owning to the higher power density together with the longer cycle life than those of Li-ion batteries, as well as higher energy density than that of supercapacitors, LICs are regarded to be one of the most prospective electrochemical energy storage devices.…”

“…When compared to rechargeable batteries, supercapacitors exhibit quicker charging and discharging (supercapacitors: 1–10 s vs. battery: 0.5–5 h), higher power density (supercapacitors: 500–10,000 W kg −1 vs. battery < 1000 W kg −1 ), remarkable longer life (supercapacitors > 500,000 h vs. battery: 500–1000 h), together with safer operation [ 2 , 11 , 12 , 13 ]. However, the low energy density of supercapacitors (supercapacitors: 1–10 W h kg −1 vs. battery: 10–100 W h kg −1 ) is a major challenge to the further development of supercapacitors [ 2 , 11 , 14 , 15 , 16 , 17 , 18 ]. To overcome this, most studies have focused on developing high-performance supercapacitor electrode materials.…”

“…Asymmetric supercapacitors combine two electrode materials with a good potential window [ 23 , 24 ]. As a new type of supercapacitor, hybrid supercapacitors are composed of battery-type negatives (electrochemical insertion or conversion) and capacitive positives (physical adsorption) and have many characteristics of supercapacitors [ 14 , 15 , 16 , 17 , 18 ].…”

Superior Rate Mesoporous Carbon Sphere Array Composite via Intercalation and Conversion Coupling Mechanisms for Potassium‐Ion Capacitors

“…Nowadays, many types of anode materials, such as carbonaceous materials, [ 4 ] transition‐metal oxides/sulfides, [ 5 ] 2D materials, [ 6 ] metal chalcogenides‐based materials [ 7 ] and organic materials [ 8 ] have been developed for potassium‐ion batteries (KIBs) or KICs. Especially, nanostructured carbon materials such as carbon nanotube, [ 9 ] graphite materials, [ 10 ] porous carbon, [ 11 ] and hollow carbon nanospheres [ 12 ] have been extensively studied as promising anodes for KIBs or KICs owing to their safety, low toxicity, and chemical stability.…”