Supercapacitive Properties of Micropore‐ and Mesopore‐Rich Activated Carbon in Ionic‐Liquid Electrolytes with Various Constituent Ions

Abstract

Ionic‐liquid (IL) electrolytes, characterized by large potential windows, intrinsic ionic conductivity, low environmental hazard, and high safety, are used for micropore‐ and mesopore‐rich activated‐carbon (ACmicro and ACmeso) supercapacitors. IL electrolytes consisting of various cations [1‐ethyl‐3‐methylimidazolium (EMI+), N‐propyl‐N‐methylpyrrolidinium (PMP+), and N‐butyl‐N‐methylpyrrolidinium (BMP+)] and various anions [bis(trifluoromethylsulfonyl)imide (TFSI−), BF4−, and bis(fluorosulfonyl)imide (FSI−)] are investigated. The electrolyte conductivity, viscosity, and ion transport properties at the ACmicro and ACmeso electrodes are studied. In addition, the capacitance, rate capability, and cycling stability of the two types of AC electrodes are systematically examined and post‐mortem material analyses are conducted. The effects of IL composition on the charge–discharge capacitances of the ACmicro electrodes are more pronounced than those for the ACmeso electrodes. The FSI‐based IL electrolytes, for which electrochemical properties are cation dependent, are found to be promising. Incorporating EMI+ with FSI− results in a low electrolyte viscosity and a fast ion transport, giving rise to optimized electrode capacitance and rate capability. Replacing EMI+ with PMP+ increases the cell voltage (to 3.5 V) and maximum energy density (to 42 Wh kg−1) of the ACmicro cell at the cost of cycling stability.

Two Birds with One Stone: Hydrogel-Derived Hierarchical Porous Activated Carbon toward the Capacitive Performance for Symmetric Supercapacitors and Lithium-Ion Capacitors

“…Moreover, the accelerated experiment conducted in the voltage range from 1.35 to 2.7 V (i.e., 50% of the state of discharge) at the current of 5 mA (0.45 A/g) was utilized to explore its cycling stability of the symmetric cell (Figure e). According to the same electrolyte and similar voltage window, our H-HPAC shows reasonable energy (29.1 to 13.7 Wh/kg) and power (116.3 to 833 W/kg) densities, and promising cycling performance (capacitance retention: 76% after 10 000 cycles, and ≥99.5% of Coulombic efficiency), which were comparable with previously reported results (Figure d) and Table . ,− …”

Manipulation of Nitrogen-Heteroatom Configuration for Enhanced Charge-Storage Performance and Reliability of Nanoporous Carbon Electrodes

“…Table shows that the specific capacitances of AC-P, AC-MEL, AC-NH 3 , and AC-NO at 20 A g –1 were 69, 74, 63, and 81 F g –1 , respectively. Among the electrodes, AC-NH 3 showed lower high-rate performance (even worse than that of AC-P), probably because of its lower portion of mesopores, which are beneficial for electrolyte ion transport. , AC-MEL had markedly better rate capability than AC-NH 3 . Besides the greater portion of mesopores, the higher percentage of N-Q (and thus higher conductivity) in AC-MEL is responsible for the improved performance.…”

Ionic Liquids for Supercapacitive Energy Storage: A Mini-Review

“… ,,, The thermal stabilities and electrochemical windows of ILs also can be tuned via multiple couplings of cations and anions to regulate the voltage/temperature ranges of supercapacitor devices . ILs explored in supercapacitors are generally based on the combination of imidazolium/tetraalkylammonium/pyrrolidinium/piperidinium/pyridinium cations and versatile anions covering bis­(trifluoromethane sulfonyl)­imide (TFSI – ), bis­(fluorosulfonyl)­imide (FSI – ), hexafluorophosphate (PF 6 – ), tetrafluoroborate (BF 4 – ), and Cl – . − For instance, Chen’s group developed a model of confined ion packing in micro/mesocylindrical pores for sponge-like carbon electrodes (Figure a), quantitatively revealing the influence of pore textures on the capacitive performance in neat ILs (1-ethyl-3-methylimidazolium tetrafluoroborate EMIMBF 4 and 1-butyl-3-methylimidazolium hexafluorophosphate BMIMPF 6 ). Upon densest surface packing, the double-layer capacitances reached to 290 and 387 F g –1 at 20 and 60 °C, respectively, under 4 V, and thus, an unprecedented large energy capacity of 204 W h kg –1 was delivered in the BMIMPF 6 electrolyte .…”