High-energy hybrid electrochemical capacitor operating down to −40 °C with aqueous redox electrolyte based on choline salts

Immobilization of Polyiodide Redox Species in Porous Carbon for Battery-Like Electrodes in Eco-Friendly Hybrid Electrochemical Capacitors

“…In order to simultaneously obtain a large potential window and high cell capacitance, redox species are mixed with a supporting aqueous electrolyte of near neutral pH [15,21,22,23,24]. The redox active species that work better in the presence of a supporting electrolyte are iodide salts mixed with aqueous lithium sulfate (Li 2 SO 4 ) [15], aqueous choline chloride or choline nitrate-based supporting electrolyte [24]. The hybrid cells based on these bi-functional electrolytes exhibit nearly twice the capacitance compared to their symmetric counterparts and large potential windows of 1.5–1.6 V.…”

“…Among the various hybrid ECs using redox-active aqueous electrolytes, the iodide-based one is probably the most suitable owing to the redox potential being very close to the equilibrium potential of the cell [25], which drives the battery-like positive electrode to work at a constant potential, while the negative electrode stores charge mainly in the electric double-layer (EDL). So far, hybrid ECs using either potassium iodide (KI) [14,26,27], Li 2 SO 4 + KI [15], MnSO 4 + KI [22] or choline nitrate + choline iodide-based electrolytes [24] have been proposed, and in all these systems, the potential of the positive electrode is nearly constant, while the negative electrode works in a large potential range using more than 90% of the cell potential window. Although the advantageous confinement of polyiodides inside the carbon pores of positive electrode prevents its self-discharge [28], the shuttling of iodine to the negative electrode cannot be fully prevented which affects the cycle-life of the hybrid cell [29].…”

Methods of Assessing Degradation of Supercapacitors by Using Various Measurement Techniques

“…They were made by technology based on aqueous electrolyte. The used samples of supercapacitors in measurements were presented in more detail in [35]. Subsequently, the manufactured supercapacitors were subject to forming and preliminary measurements in order to determine their electrical parameters: C and R ESR .…”

Less Water, Naked Choline, and Solid Iodine for Superior Ecofriendly Hybrid Energy Storage

“…Performance of ACC iodinated /ACC pristine hybrid supercapacitor in 25 mol kg À1 water-in-choline chloride electrolyte: a) galvanostatic charge/discharge curves at 0.2 A g À1 up to 1.6 V and b) capacitance and energy efficiency calculated from these charge/discharge curves at 0.2 A g À1 , c) capacitance and energy efficiency evolution during galvanostatic charge/discharge for 20 000 cycles at 1.0 A g À1 , d) voltage versus capacity curves, e) charge/discharge curves at 1 A g À1 obtained after every 1000 cycles during long-term cycling tests (1000th cycle ¼ red curve, 20 000th cycle ¼ blue curve), f ) capacitance versus frequency showing the time constant (τ) for hybrid supercapacitor, g) schematic model where less free-water blocks the polyiodide shuttling h,i) galvanostatic charge/discharge and cyclic voltammetry curves up to 1.6 V for ACC iodinated /ACC pristine hybrid supercapacitor in 25 mol kg À1 water-in-choline chloride. organic electrolyte-based supercapacitors working up to 2.7 V. [35,36] Symmetric charge/discharge at high currents up to 4 A g c À1 (Figure S8, Supporting Information) is possible due to the highly reversible iodide/iodine redox process enabling the hybrid supercapacitor device to exhibit a time constant τ ¼ 32.87 s which is in the desired range for high power applications. A constant capacitance over a long period of cycling also shows that the redox reaction after iodine electrodeposition in the carbon electrode is chemically reversible.…”