Synthesis and physicochemical characterization of room temperature ionic liquids and their application in sodium ion batteries

Structurally flexible pyrrolidinium- and morpholinium-based ionic liquid electrolytes

Ion transport measures and details as well as physico-chemical and electrochemical properties are presented for a small set of structurally flexible pyrrolidinium (Pyrr) and morpholinium (Morph) cation-based ionic liquids (ILs), all with oligoether phosphate-based anions. All have high thermal stabilities, low glass transition temperatures, and wide electrochemical stability windows, but rather moderate ionic conductivities, where both the anions and the cations of the Pyrr-based ILs diffuse faster than those of the Morph-based ILs. Overall, the Pyrr-based ILs show significantly more promise as high-temperature supercapacitor electrolytes, rendering a specific capacitance of 164 F g^-1 at 1 mV s^-1, a power density of 609 W kg^-1 and a specific energy density of 27 W h kg^-1 at 90 °C in a symmetric graphite supercapacitor.

Physical Properties and Low-Frequency Polarizability Anisotropy and Dipole Responses of Phosphonium Bis(fluorosulfonyl)amide Ionic Liquids with Pentyl, Ethoxyethyl, or 2-(Ethylthio)ethyl Group

This study compared the physical properties, e.g., glass transition temperature, melting point, viscosity, density, surface tension, and electrical conductivity, and the low-frequency spectra under 200 cm^-1 of three synthesized ionic liquids (ILs), triethylpentylphosphonium bis(fluorosulfonyl)amide ([P₂₂₂₅][NF₂]), ethoxyethyltriethylphosphonium bis(fluorosulfonyl)amide ([P_222(2O2)][NF₂]), and triethyl[2-(ethylthio)ethyl]phosphonium bis(fluorosulfonyl)amide ([P_222(2S2)][NF₂]), at various temperatures using femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES) and terahertz time-domain spectroscopy (THz-TDS). The [P_222(2S2)][NF₂] had the highest viscosity and glass transition temperature, whereas the [P_222(2O2)][NF₂] had the lowest. Among the three ILs, the [P_222(2S2)][NF₂] had the highest density and surface tension, and the [P_222(2O2)][NF₂] had the highest electrical conductivity. The RIKES and THz-TDS spectral line shapes for the three ILs varied significantly. For the [P₂₂₂₅][NF₂], molecular dynamics simulations successfully reproduced the line shapes of the experimental spectra and indicated that the RIKES spectrum was mainly due to the cation and cross-term and their rotational motions, whereas the THz-TDS spectrum was mainly due to the anion and its translational motion. This shows that it is desirable to utilize both fs-RIKES and THz-TDS methods to reveal molecular motions at the low-frequency domain. The [P_222(2S2)][NF₂] had higher frequency peaks and broader bands in the low-frequency spectra via fs-RIKES and THz-TDS than those for the [P₂₂₂₅][NF₂] and [P_222(2O2)][NF₂].

Supramolecular Thixotropic Ionogel Electrolyte for Sodium Batteries

Owing to the potential of sodium as an alternative to lithium as charge carrier, increasing attention has been focused on the development of high-performance electrolytes for Na batteries in recent years. In this regard, gel-type electrolytes, which combine the outstanding ionic conductivity of liquid electrolytes and the safety of solid electrolytes, demonstrate immense application prospects. However, most gel electrolytes not only need a number of specific techniques for molding, but also typically suffer from breakage, leading to a short service life and severe safety issues. In this study, a supramolecular thixotropic ionogel electrolyte is proposed to address these problems. This thixotropic electrolyte is formed by the supramolecular self-assembly of D-gluconic acetal-based gelator (B8) in an ionic liquid solution of a Na salt, which exhibits moldability, a high ionic conductivity, and a rapid self-healing property. The ionogel electrolyte is chemically stable to Na and exhibits a good Na⁺ transference number. In addition, the self-assembly mechanism of B8 and thixotropic mechanism of ionogel are investigated. The safe, low-cost and multifunctional ionogel electrolyte developed herein supports the development of future high-performance Na batteries.

Recent Advance in Ionic-Liquid-Based Electrolytes for Rechargeable Metal-Ion Batteries

From basic research to industry process, battery energy storage systems have played a great role in the informatization, mobility, and intellectualization of modern human society. Some potential systems such as Li, Na, K, Mg, Zn, and Al secondary batteries have attracted much attention to maintain social progress and sustainable development. As one of the components in batteries, electrolytes play an important role in the upgrade and breakthrough of battery technology. Since room-temperature ionic liquids (ILs) feature high conductivity, nonflammability, nonvolatility, high thermal stability, and wide electrochemical window, they have been widely applied in various battery systems and show great potential in improving battery stability, kinetics performance, energy density, service life, and safety. Thus, it is a right time to summarize these progresses. In this review, the composition and classification of various ILs and their recent applications as electrolytes in diverse metal-ion batteries (Li, Na, K, Mg, Zn, Al) are outlined to enhance the battery performances.

The effects of the position of the ether oxygen atom in pyrrolidinium-based room temperature ionic liquids on their physicochemical properties

A joint computational and experimental approach uncovered that the position effect of the ether oxygen atom in pyrrolidinium-based room temperature ionic liquids on the physicochemical properties.

Molecular design of ionic liquids as novel non-metal catalysts for the acetylene hydrochlorination reaction

Theoretical prediction of catalytic performance is crucial for the rational design of novel catalysts. In this study, density functional theory (DFT) simulations were carried out to predict the catalytic performance of four ionic liquids (ILs) used as novel non-metal catalysts in the acetylene hydrochlorination reaction, and the obtained catalytic performances were verified via our experimental tests; moreover, both the theoretical and experimental results showed that the catalytic performance of the four IL catalysts followed the order tetraphenylphosphonium bromide (TPPB) > tetraphenylphosphonium chloride (TPPC) > butyltriphenylphosphonium bromide (BuTPPB) ≫ tetraphenylphosphonium tetrafluoroborate (TPPT), and the 15%TPPB/SAC catalyst exhibited efficient catalytic performance when compared with the recently reported non-metal catalysts for the acetylene hydrochlorination reaction. Furthermore, the catalytic mechanisms of the four ILs with different cations and anions were revealed via theoretical Mulliken, partial density of states (PDOS) and electron density difference (EDD) analyses combined with the experimental XPS and XRD characterizations. The results showed that the effects of the anions on the catalytic activity were much significant than those of the cations. A good IL non-metal catalyst for acetylene hydrochlorination would mainly donate electrons to Cl to activate the H-Cl bond, and then, the electrons would be donated back to the IL catalyst in the transition state. This study provides new insights into the design of efficient nonmercuric catalysts for the acetylene hydrochlorination reaction.