Zn Electrochemistry in 1‐Ethyl‐3‐Methylimidazolium and N‐Butyl‐N‐Methylpyrrolidinium Dicyanamides: Promising New Rechargeable Zn Battery Electrolytes

Abstract

We have studied both 1‐ethyl‐3‐methylimidazolium (C2mim) and N‐butyl‐N‐methylpyrrolidinium (C4mpyr) dicyanamide (dca) ionic liquids (ILs) containing 3 wt % H2O and 9 mol % Zn(dca)2 salt for their ability to support Zn0/2+ electrochemistry in the context of a rechargeable Zn battery. Despite the similarities of the two IL electrolyte systems [identical H2O and Zn(dca)2 contents], the system based on [C2mim] supported much higher current densities for Zn electrochemistry at greatly reduced overpotentials [−0.23 V vs. Zn pseudo‐reference, 32 mA cm−2 (red) and 61 mA cm−2 (ox)] compared to the [C4mpyr]‐based electrolyte [−0.84 V vs. Zn pseudo‐reference, 8 mA cm−2 (red) and 15 mA cm−2 (ox)]. The overpotential for Zn deposition is reduced by 0.13 V on Zn metal surfaces compared to glassy carbon (GC), regardless of the electrolyte used. The morphologies of the Zn deposits on both GC and Zn surfaces were also studied. The Zn surfaces promote a deposition that displays a smooth morphology, resulting from an instantaneous nucleation mechanism demonstrated by chronoamperometric experiments. Finally, both [C2mim] and [C4mpyr] electrolytes were tested in symmetrical Zn|Zn cells, where it was determined that the [C2mim] system could sustain over 90 cycles at 0.1 mA cm−2, whereas the [C4mpyr] based system could only achieve 15 cycles at the more modest current density of 0.05 mA cm−2.

Rechargeable Zn/PEDOT Battery with an Imidazolium‐Based Ionic Liquid as the Electrolyte

“…The electrochemical cycling of Zn 2+ in [C 2 mim][dca] has been thoroughly explored in our previous work . Figure shows the observed cyclic voltammetry of a 10 mol % solution of Zn(dca) 2 in [C 2 mim][dca], which was found to support exceptionally high currents of Zn plating (45 mA cm −2 ) and stripping (75 mA cm −2 ) on a GC substrate.…”

Voltammetric Study and Electrodeposition of Zinc in Hydrophobic Room-Temperature Ionic Liquid 1-Butyl-1-methylpyrrolidinium Bis((trifluoromethyl)sulfonyl)imide ([BMP][TFSI]): A Comparison between Chloride and TFSI Salts of Zinc

“…Moreover, if aprotic ILs are used, hydrogen evolution, which is usually encountered in the electrodeposition of active metals such as Zn in aqueous solutions, can be significantly suppressed, leading to a more controllable surface morphology and higher current efficiency. Zn has been successfully electrodeposited from the traditional Lewis acidic ILs, 7-10 the air-and water-stable ILs, 3,[11][12][13][14][15][16][17][18][19] To search a common source of Zn ions and a suitable IL for the electrodeposition of Zn metal, however, is still important.The hydrophobic RTIL 1-butyl-1-methylpyrrolidinium bis ((trifluoromethyl)sulfonyl)imide ([BMP][TFSI]) has been widely used for the study of metal and alloy electrodeposition in view of various advantages, such as wide electrochemical window, wide temperature range as a liquid, relatively high conductivity, low viscosity, high hydrophobicity, and so on. Nevertheless, a problem is always encountered when this IL is used for electrodeposition; that is the poor solubility of common metal salts, such as metal chlorides.…”

“…Moreover, if aprotic ILs are used, hydrogen evolution, which is usually encountered in the electrodeposition of active metals such as Zn in aqueous solutions, can be significantly suppressed, leading to a more controllable surface morphology and higher current efficiency. Zn has been successfully electrodeposited from the traditional Lewis acidic ILs, 7-10 the air-and water-stable ILs, 3,[11][12][13][14][15][16][17][18][19] To search a common source of Zn ions and a suitable IL for the electrodeposition of Zn metal, however, is still important.…”

The electrochemical cycling and electrodeposition of lead from 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquid

“…For this reason, 3D instantaneous nucleation and growth is often preferred to progressive nucleation in the search for rechargeable battery electrolytes. [18] As can be seen in Figure 5, the deposition of Pb films from [C2mim][NTf2] + 50 mM Pb(NTf2)2 leads to a mechanism that most resembles progressive type nucleation on all WE materials, in agreement with the results published by Katayama et al [17]. While this may be expected in the case of Cu, Pt and Pt, the fact that performing the deposition on a Pb substrate does not cause a shift of the curve to one more closely represented by the instantaneous mechanism is of note.…”

“…[18] Apart from the peak reduction and oxidation currents, another vital property of rechargeable battery electrolytes is the ability to repeatedly cycle the metal through a large number of deposition/dissolution cycles over the battery life. To evaluate this ability, the effect of numerous CV cycles on an appropriate current collector (Cu) is shown in Figure 4.…”