Effect of alkali and halide ion doping on the energy storage characteristics of ionic liquid based supercapacitors

Investigating Molecular Interactions through Computational Modeling, Thermodynamic Analysis, and Acoustic Measurements of LiOTf in Aqueous TEGDME and DME Solutions at Different Temperatures

This study investigates solute-solvent interactions in ternary systems consisting of lithium trifluoromethanesulfonate (LiOTf) as the solute and tetraethylene glycol dimethyl ether (TEGDME) and 1,2-dimethoxyethane (DME) as solvents over a range of temperatures (293.15-313.15 K). A multidisciplinary approach involving computational modeling, thermodynamic analysis, and acoustic measurements was used to elucidate molecular-level dynamics. The positive V ϕ 0 values in the thermodynamic analysis revealed the prevalence of solute-solvent interactions in the investigated ternary (LiOTf + H2O + DME/TEGDME) solutions. Hepler's constant was determined to predict the structure maker/breaker behavior. Cyclic voltammetry analysis showed that TEGDME offers a higher electrochemical window (EW) of 1.36 V in 0.01 TEGDME and 1.40 V in 0.05 TEGDME compared with that of 1.25 V in 0.01 DME and 1.38 V in 0.05 DME, yielding favorable and comparable working EWs. DFT calculations using the B3LYP functional and 6-311++G(d,p) basis set provided insights into the electron-donating and -accepting properties of the molecules, showing higher reactivity for LiOTf. These findings present novel insights into ternary electrolyte systems, which hold the potential for applications in energy storage technologies.

Electric field induced associations in the double layer of salt-in-ionic-liquid electrolytes

Ionic liquids (ILs) are an extremely exciting class of electrolytes for energy storage applications. Upon dissolving alkali metal salts, such as Li or Na based salts, with the same anion as the IL, an intrinsically asymmetric electrolyte can be created for use in batteries, known as a salt-in-ionic liquid (SiIL). These SiILs have been well studied in the bulk, where negative transference numbers of the alkali metal cation have been observed from the formation of small, negatively charged clusters. The properties of these SiILs at electrified interfaces, however, have received little to no attention. Here, we develop a theory for the electrical double layer (EDL) of SiILs where we consistently account for the thermoreversible association of ions into Cayley tree aggregates. The theory predicts that the IL cations first populate the EDL at negative voltages, as they are not strongly bound to the anions. However, at large negative voltages, which are strong enough to break the alkali metal cation-anion associations, these IL cations are exchanged for the alkali metal cation because of their higher charge density. At positive voltages, we find that the SiIL actually becomes more aggregated while screening the electrode charge from the formation of large, negatively charged aggregates. Therefore, in contrast to conventional intuition of associations in the EDL, SiILs appear to become more associated in certain electric fields. We present these theoretical predictions to be verified by molecular dynamics simulations and experimental measurements.

Eco-friendly synthesis of an α-Fe2O3/rGO nanocomposite and its application in high-performance asymmetric supercapacitors

This work presents an innovative and environmentally friendly biological synthesis approach for producing α-Fe2O3 nanoparticles (NPs) and the successful synthesis of α-Fe2O3/reduced graphene oxide (rGO) nanocomposites (NCs). This novel synthesis route utilizes freshly extracted albumin, serving as both a reducing agent and a stabilizing agent, rendering it eco-friendly, cost-effective, and sustainable. A combination of characterization techniques including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and field emission scanning electron microscopy (FE-SEM) was employed to predict and confirm the formation of the as-synthesized α-Fe2O3 NPs and α-Fe2O3/rGO NCs. Transmission electron microscopy (TEM) verified the anisotropic nature of the synthesized nanoparticles. To gain insight into the enhanced capacitance of the α-Fe2O3/rGO NCs, a series of electrochemical tests, namely cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS), and stability assessments, were conducted in a conventional three-electrode configuration. Furthermore, a two-electrode asymmetric supercapacitor (ASC) device was fabricated to assess the practical viability of this material. The α-Fe2O3/rGO NCs exhibited a remarkable potential window of 2 V in an aqueous electrolyte, coupled with exceptional cycling stability. Even after undergoing 10 000 cycles, the capacitive retention exceeded 100%, underlining the promising potential of this material for advanced energy storage applications.

The review of advances in interfacial electrochemistry in Estonia: electrochemical double layer and adsorption studies for the development of electrochemical devices

The electrochemistry nowadays has many faces and challenges. Although the focus has shifted from fundamental electrochemistry to applied electrochemistry, one needs to acknowledge that it is impossible to develop and design novel green energy transition devices without a comprehensive understanding of the electrochemical processes at the electrode and electrolyte interface that define the performance mechanisms. The review gives an overview of the systematic research in the field of electrochemistry in Estonia which reflects on the excellent collaboration between fundamental and applied electrochemistry.

Artificial Solid Electrolyte Interphases for Lithium Metal Electrodes by Wet Processing: The Role of Metal Salt Concentration and Solvent Choice

In this study, the artificial solid electrolyte interphase (SEI) formed on lithium metal when treated in ZnCl₂ solutions is thoroughly investigated. The artificial SEI on lithium metal electrodes substantially decreases the interfacial resistance by ca. 80% and improves cycling stability in comparison to untreated lithium. The presence of a native SEI negatively affects the morphology and interfacial resistance of the artificial SEI. Increasing the ZnCl₂ concentration in tetrahydrofuran (THF) (precursor solution) results in higher homogeneity of the surface morphology. Independent of the ZnCl₂ concentrations, the artificial SEI is composed of C_x, CO, LiCl, Li₂CO₃, ZnCl₂, and Li_xZn_y alloys. ZnCl₂ (1 M) produces the most homogenous surface and additional surface species with carbonyl side groups. Nonetheless, the ZnCl₂ concentration only has a small effect on the interfacial resistance or cycling stability. Using ethyl methyl carbonate (EMC) as the solvent significantly reduces the interfacial resistance to 7 Ω cm², in comparison to 25 Ω cm² for THF. The composition of the artificial SEIs varies depending on the solvent. Either way, the SEI consists of C_x Li_xC, LiCl, Li₂CO₃, ZnCl₂, and LiZn alloys. The THF-based SEI additionally features ether and carbonyl groups, LiZnO, and Zn metal. For the artificial SEI formed with both solvents, the atomic percentage of the LiZn alloy increases close to the Li surface.