Physicochemical characterization of AlCl3-urea ionic liquid analogs: Speciation, conductivity, and electrochemical stability

Deep eutectics and analogues as electrolytes in batteries

“…213 Replacing U with AA Chu et al assembled a reversible room-temperature Al-S device using Al foil as the anode and 50 wt% sulfur encapsulated in the ordered mesoporous carbon CMK-3 as the cathode. 212 Raman and 27 Al NMR spectroscopies were used to identify the electrolyte composition, confirming the coexistence of AlCl 4 − and Al 2 Cl 7 − when the AlCl3 to AA molar ratio is 1.3. The battery exhibited an initial capacity above 1500 mA h g −1 at a current density of 100 mA g −1 , and a capacity retention of 500 mA h g −1 for 60 cycles, with a good rate performance and long cycle life.…”

“…25 As an example, the typical HBA choline is currently produced in a megaton per annum basis as a nutritional supplement for livestock, while the typical HBD urea has a global production rate of ~190 million tons per annum and is commonly used in commercial fertilizers. 5,27 As a whole, archetypal DESs like ChCl:U or ChCl:glycerol (G), are comparable in cost to typical organic solvents such as acetonitrile or N,N-dimethylformamide. 7 Another strength of DESs is that the constituents are generally biodegradable and their toxicological properties are well characterized.…”

“…198 Aiming at improving the performances of the AlCl3:U-based battery proposed by Angell et al, while operating at ambient temperature, alternative cathode materials based on natural graphite (NG) flakes obtained by ultrasonication or graphene nanoplatelets (GNP) were proposed. 27,199 Appreciable specific capacities and CEs were obtained both at low current densities (for instance, capacity of 50 mAh g -1 with 96% CE across 1000 cycles at 600 mA g -1 with NG and AlCl3:U 1.3:1, 199 or capacity of 74 mAh g -1 with 78% CE at 100 mA g -1 with GNP and AlCl3:U 1.4:1 27 ) and at a high current density of 1000 mA g -1 (capacity of ~32 mAh g -1 with ~98% CE with NG and AlCl3:U 1.3:1, 199 and capacity of 40 mAh g -1 with 93% CE with GNP and AlCl3:U 1.4:1 27 ).…”

“…At room temperature, only compositions with mole ratio of AlCl3 to U in the range 1.0-1.5 are clear liquids, and beyond 1.5 molar, AlCl3 white solids are formed due to supersaturation. 27 The reactions occurring in the AlCl3:U system are: 27,191,198 ( high concentrations, the acidity of the electrolyte increases, which may lead to the corrosion of the anode (i.e. aluminum foil) and fast capacity decay of the battery, compromising the battery performance.…”

Fundamental Insights into Electrical and Transport Properties of Chloroaluminate Ionic Liquids for Aluminum-Ion Batteries

“…In determining the ion self-diffusion coefficient, electrochemical techniques and nuclear magnetic resonance (NMR) are commonly utilized. − However, neither method provides a comprehensive evaluation of the diffusion coefficient of all ionic species across various r values. For instance, diffusion coefficients determined electrochemically are those of electroactive species involved in diffusion-controlled processes (Al 2 Cl 7 – ), while the diffusion coefficients of ions such as X + and AlCl 4 – cannot be determined. , On the other hand, NMR-based techniques have been employed to study the properties of various speciation in chloroaluminate ILs. , In determining the diffusion coefficient of ionic species, the fast chemical exchange (relative to NMR measurement time scale) between chloroaluminate anions leads to difficulties in distinguishing their corresponding signals in Lewis acidic chloroaluminate IL and IL analogs. , For this reason, only r = 1 and 2 compositions that contain a single type of cation and anion have been utilized in determining ion diffusion coefficients using NMR-based techniques. , …”