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The need for safe, low cost, high energy and density storage devices is ubiquitous the world over. Satisfying this need requires various energy storage and conversion applications, one of which is the aluminum ion batteries. One problem with expansion in their development and commercialization is the availability of optimized electrolytes. Recently, deep eutectic solvents (DES) have gained attention as electrolytes for energy storage devices. These solvents are similar to ionic liquids, but are generally cheaper and easier to prepare. Additionally, they are known to dissolve metal oxides which plague AIBs operation, and their solubility is dependent on the hydrogen bond donor. Because of their inherent tunability, we studied the effect of AlCl3 concentration (1:1 – 1.7:1 molar ratio), amide type (acetamide (AA), butyramide (BA), propionamide (PA)), viscosity reducing additive type and concentration, on the aluminum ion species and transport in AlCl3:amide DES electrolytes using multi-Nuclear (1H, 27Al) Magnetic Resonance (NMR) and AC Impedance Spectroscopy techniques, as a function of temperature. Below are a few noteworthy observations. Firstly, for both AlCl3:PA and AlCl3:BA DES electrolytes, a maximum in ionic conductivity was observed at the 1.3:1 molar ratio. For AlCl3:AA DES the maximum occurred at the 1.5:1 molar ratio. secondly, the 27Al spectra the 1:1 molar ratio DES electrolytes showed three well resolved peaks at about 101, 88 and 74 ppm, assigned to [AlCl2(amide)2]+, AlCl4 -, and [AlCl2(amide)2]+ respectively. An example of this is shown in Figure 1 for the 1.0:1 (left) AlCl3:PA. With increasing AlCl3 concentration, the narrow well resolved peaks gave way to broadened, asymmetric spectra with two to three visible but not separated peaks. This is also shown in Figure 1 (right) for the 1.3:1 (right) AlCl3:PA. A fourth peak also appeared for DES electrolytes which could be due to free AlCl3:amide species. Figure 1. 27Al variable temperature spectra for 1.0:1 (left) and 1.3:1 (right) AlCl3:Propionamide (PA). Thirdly, like the spectra, the 27Al T1 data for the pure DES electrolytes were very dependent on salt concentration and the species type. For the 1:1 molar ratio electrolyte, the AlCl2(amide)+ species had the longest T1, while the AlCl2(amide)2 +had the shortest. Fourthly, with the inclusion of additives such as propylene carbonate (PC) both the 1H and 27Al T1increased, indicating increasing local ion dynamics possibly through the reduction of bulk viscosity effects and Coulombic interactions. In addition to this, PC also caused additional resolution of the [AlCl2(amide)2]+ species - which was not observed in the pure DES. These results and more will be expounded upon in our presentation. Figure 1

In this work we aimed to determine the ions association and solvation in electrolytes comprised of NaPF6 in binary EC:PC, and ternary 5EC:3PC:2DEC carbonate solvents. We studied their local and bulk transport properties through multi-Nuclear (1H, 19F and 23Na) Magnetic Resonance spin-lattice relaxation time (T1 ) and self-diffusion coefficient (D) measurements. These studies were complemented with ionic conductivity and solution viscosity measurements. Results show several interesting features. Firstly, the Walden Product – which relates the molar conductivity and viscosity through a temperature-dependent constant – showed a dependence on temperature (see Figure 1). This suggested the dissociation of NaPF6 is dependent on temperature and is lower for the less polar electrolytes. Secondly, the sodium ions are preferentially solvated by PC molecules over EC. Thirdly, significant cation-anion association was observed for the less polar electrolytes. Lastly, this association was independent of temperature indicating that the temperature dependence of the Walden Product is primarily due to that of the viscosity. These results can aid in the improvement of ‘beyond lithium ion’ electrolytes for energy storage applications. Figure 1

We performed an extensive study on Nafion 117 membrane imbibed with various concentrations of aqueous ammonium metavanadate (NH4VO3), and vanadyl sulfate (VOSO4), in 2 M H2SO4 over the temperature range of 20–100 °C, using 1H NMR and AC Impedance spectroscopies. The objective was to determine the effect of the tetravalent (VO2+) and pentavalent (VO2+) vanadium ions on the proton transport of Nafion 117.1H NMR chemical shift and linewidth data show greater short-range proton transport for the VO2+ imbibed membranes compared with the VO2+. However, the local environments seem to differ in that while the data for VO2+ imbibed membranes seem to follow more the trends observed for water hydrated Nafion 117, those for the VO2+ followed the trend of its aqueous bulk vanadium solvents, indicating that viscosity plays a larger role for the VO2+ imbibed membranes compared to the VO2+.

Aluminum ion speciation in AlCl3:amide deep eutectic solvents (DES) were explored using variable temperature multi-Nuclear (1H and 27Al) Magnetic Resonance and Electrochemical Impedance Spectroscopies. Focus was on the interplay between the local and bulk interactions on species transport, and the effect of AlCl3 concentration on their dynamics. Acetamide, butyramide and propionamide were chosen and molar ratios of 1:1–1.7:1 of AlCl3:amide were studied. Calculated Walden products show that although the DES electrolytes are ‘subionic,’ they are more conductive than ‘poor ILs’. The ionic conductivity data showed VFT temperature dependences, and calculated fragility values were less than 5 for all three amides and concentrations, indicating high levels of conformational mobility for the aluminum species. 1H chemical shift data showed increased shielding with increasing molar ratios for all three amides indicating an enhancement in the local electron densities, possibly due to an increase in the more shielded cis conformation population. 27Al spectra revealed multiple aluminum species that experienced both intermediate and fast chemical exchanges with increasing AlCl3 concentration. The AlCl2(amide)2+ species population decreased with both increasing temperature and AlCl3 concentration, especially for shorter alkyl chains amides. This suggests it plays a less significant role in the aluminum ion transport at higher AlCl3 concentration. 27Al T1 values for the various species revealed a temperature and concentration dependent plateauing in the T1 of the AlCl2(amide)+ species for molar ratios greater than 1:1. Additionally, with increasing AlCl3 concentration, the merging of the AlCl4− and [AlCl2(amide)2]+ species resulted in its T1 being the shortest and increasing with increasing temperatures, suggesting it experiences greater electric field gradients compared to the other aluminum species.

Mixtures of ionic liquids (ILs) containing single-walled carbon nanotubes (SWCNTs) were prepared and characterized to obtain electrolytes with optimized transport properties for the use in energy storage devices such as supercapacitors. Imidazolium ILs bearing cations with side chains of different functionality coupled with bis(trifluoromethylsulfonyl)amide (NTf2 -) or bis(fluorosulfonyl)amide (FSA-) anions were used in mixtures containing up to 5 wt % SWCNTs. It was determined that the ionic conductivities of all ILs studied can be significantly increased with the addition of single-walled carbon nanotubes when the loading of the nanotubes is above 2 wt %. Moreover, higher conductivities were observed for the ILs containing the NTf2 - anion and 5 wt % SWCNTs. These results can significantly contribute to the development of improved energy storage devices. The work at Brookhaven National Laboratory was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under contract DE-SC0012704. The work at Brooklyn College was supported by the National Science Foundation, Solid State and Materials Chemistry Program, Division of Materials Research, EAGER award #1841398.

Variable temperature ionic conductivity, viscosity and 1H NMR spin-lattice relaxation times, linewidths and chemical shifts measurements were determined for various concentrations of aqueous ammonium metavanadate (NH4VO3) and vanadyl sulfate (VOSO4) over the temperature range of 20–100 °C. Concentration ranges of 0.05–2 M and 0.05–0.2 M were investigated for VOSO4 and NH4VO3 respectively in 2 M H2SO4. Results show ion and proton transport processes that are mediated strongly by increasing solution viscosity, especially in the case of VOSO4. Activation energies calculated from ionic conductivity and solution viscosity show greater energy being needed for translational ion dynamics with increasing concentration for both solutions. Additionally, data suggest that with greater metal ion concentration ion association is more prevalent for the vanadyl ion. The differences between the transport capabilities of the two solution are discussed in terms of the 1H NMR, ionic conductivity and viscosity data.

Binary mixtures of ionic liquids (ILs) were prepared and characterized to obtain ILs with viscosity and conductivity properties optimized for use in energy storage devices such as supercapacitors. The bis(trifluoromethylsulfonyl)amide anion (NTf2 -) was the common anion for both ILs in the mixture. Ethoxyethyl was the common substituent on the solute and solvent, as ether substituents have been shown to produce low viscosity ILs. N-Ethoxyethyl-N-methylpyrrolidinium NTf2 was used as the solvent for all of the IL mixtures. The solutes were either monocationic or dicationic and made up 10% of the binary mixture by weight. We report here on the physical properties of the individual ILs and their binary mixtures.

The need for improved energy storage capability in supercapacitors has prompted the use of ionic liquids as alternatives to acetonitrile based solvents. Despite the advantages of supercapacitors, their use in transportation is not favorable because of the deterioration of organic solvents with increasing temperatures and their high vapor pressures. We report here on the synthesis and characterization of ionic liquids optimized for use in supercapacitors. The cations were designed to bear ether substituents which are known to lower the viscosity of ILs. ILs and binary mixtures of ILs based on pyrrolidinium, imidazolium and dicationic ammonium cations bearing ether substituents and bis(trifluoromethylsulfonyl)amide [NTf2 -] anions have been synthesized, purified and characterized. The halide salts were synthesized by reaction of the amine with 2-bromoethylethylether. They were then converted to the NTf2 salts after purification. The structures of the salts were confirmed using H-1 and C-13 Nuclear Magnetic Resonance spectroscopy. The dicationic ILs were used as the solutes in the binary IL mixyures. The binary IL mixtures have been analyzed for their transport properties using NMR. The work at BNL was supported by the BNL Office of Educational Programs and the DOE Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under contract # DE-AC02-98CH10886.