Raman and FTIR Spectroscopic Studies of 1-Ethyl-3-methylimidazolium Trifluoromethylsulfonate, its Mixtures with Water and the Solvation of Zinc Ions

Recent advances in zinc-ion dehydration strategies for optimized Zn-metal batteries

Aqueous Zn-metal batteries have attracted increasing interest for large-scale energy storage owing to their outstanding merits in terms of safety, cost and production. However, they constantly suffer from inadequate energy density and poor cycling stability due to the presence of zinc ions in the fully hydrated solvation state. Thus, designing the dehydrated solvation structure of zinc ions can effectively address the current drawbacks of aqueous Zn-metal batteries. In this case, considering the lack of studies focused on strategies for the dehydration of zinc ions, herein, we present a systematic and comprehensive review to deepen the understanding of zinc-ion solvation regulation. Two fundamental design principles of component regulation and pre-desolvation are summarized in terms of solvation environment formation and interfacial desolvation behavior. Subsequently, specific strategy based distinct principles are carefully discussed, including preparation methods, working mechanisms, analysis approaches and performance improvements. Finally, we present a general summary of the issues addressed using zinc-ion dehydration strategies, and four critical aspects to promote zinc-ion solvation regulation are presented as an outlook, involving updating (de)solvation theories, revealing interfacial evolution, enhancing analysis techniques and developing functional materials. We believe that this review will not only stimulate more creativity in optimizing aqueous electrolytes but also provide valuable insights into designing other battery systems.

Ethanol as Solvent Additives with Competitive Effect for High-Stable Aqueous Zinc Batteries

Aqueous zinc-ion batteries are emerging as promising sustainable energy-storage devices. However, their cyclic stability is still a great challenge due to the inevitable parasitic reaction and dendrite growth induced by water. Herein, a cosolvent strategy based on competitive effect is proposed to address the aforementioned challenges. Ethanol with a higher Gutmann donor number demonstrates lower polarity and better wettability on the Zn surface compared with water, which endows ethanol with the ability of minimizing water activity by weakening H bonds and preferentially adsorbing on the Zn electrode. The above competitive advantages synergistically contribute to inhibiting the decomposition of free water and dendrite growth. Besides, an organic-inorganic hybrid solid-electrolyte interphase layer is in situ built based on ethanol additives, where organic matrix suppresses water corrosion while inorganic fillers promote fast Zn2+ diffusion. Consequently, the electrolyte with ethanol additives boosts a high reversibility of Zn deposition, long-term durability, as well as superior Zn2+ diffusibility in both Zn half-cells (Zn||Cu and Zn||Zn batteries) and Zn full cells (Zn||PTCDA and Zn||VO2 batteries). This work sheds light on a universal strategy to design a high-reversible and dendrite-free Zn anode for stable aqueous batteries.

Empowering Zn Electrode Current Capability Along Interfacial Stability by Optimizing Intrinsic Safe Organic Electrolytes

Metallic Zn is one of the most promising anodes, but its practical application has been hindered by dendritic growth and serious interfacial reactions in conventional electrolytes. Herein, ionic liquids are adopted to prepare intrinsically safe electrolytes via combining with TEP or TMP solvents. With this synergy effect, the blends of TEP/TMP with an IL fraction of ≈25 wt% are found to be promising electrolytes, with ionic conductivities comparable to those of standard phosphate-based electrolytes while electrochemical stabilities are considerably improved; over 1000 h at 2.0 mA cm^-2 and ≈350 h at 5.0 mA cm^-2 with a large areal capacity of 10 mAh cm^-2 . The use of functionalized IL turns out to be a key factor in enhancing the Zn²⁺ transport due to the interaction of Zn²⁺ ions with IL-zincophilic sites resulting in reduced interfacial resistance between the electrodes and electrolyte upon cycling leading to spongy-like highly porous, homogeneous, and dendrite-free zinc as an anode material.

Ionogels Derived from Fluorinated Ionic Liquids to Enhance Aqueous Drug Solubility for Local Drug Administration

Gelatin is a popular biopolymer for biomedical applications due to its harmless impact with a negligible inflammatory response in the host organism. Gelatin interacts with soluble molecules in aqueous media as ionic counterparts such as ionic liquids (ILs) to be used as cosolvents to generate the so-called Ionogels. The perfluorinated IL (FIL), 1-ethyl-3-methylpyridinium perfluorobutanesulfonate, has been selected as co-hydrosolvent for fish gelatin due to its low cytotoxicity and hydrophobicity aprotic polar structure to improve the drug aqueous solubility. A series of FIL/water emulsions with different FIL content and their corresponding shark gelatin/FIL Ionogel has been designed to enhance the drug solubility whilst retaining the mechanical structure and their nanostructure was probed by simultaneous SAXS/WAXS, FTIR and Raman spectroscopy, DSC and rheological experiments. Likewise, the FIL assisted the solubility of the antitumoural Doxorubicin whilst retaining the performing mechanical properties of the drug delivery system network for the drug storage as well as the local administration by a syringe. In addition, the different controlled release mechanisms of two different antitumoral such as Doxorubicin and Mithramycin from two different Ionogels formulations were compared to previous gelatin hydrogels which proved the key structure correlation required to attain specific therapeutic dosages.

Hydrogen bonds-triggered differential extraction efficiencies for bifenthrin by three polymeric ionic liquids with varying anions based on FT-IR spectroscopy

Herein, we fabricated three imidazolium-based polymeric ionic liquids (PILs) with different anions (P[VEIM]BF4, P[VEIM]PF6 and P[VEIM]Br), and analyzed their differential extraction efficiencies for bifenthrin through H-bonding induced effects. Three PILs all presented an irregular block structure with rough surface and lower specific-surface area (SSA, 11.2-18.7 m2 g-1) than carbon-based nanomaterials. They formed hydrogen bonds with free-water molecules in the lattice of PILs, including C2,4,5-H⋯O-H, Br⋯H-O-H⋯Br, O-H⋯Br, C2,4,5-H⋯F-P, P-F⋯H-O-H⋯F-P, C2,4,5-H⋯F-B and B-F⋯H-O-H⋯F-B. After extraction, the O-H stretching-vibration peak was prominently intensified, whereas the C-H bond varied slightly concomitant with reduced B-F and P-F vibration. Theoretically, the C-H vibration should become more intense in the C4,5-H⋯H2O and C2-H⋯H2O bonds after extraction in contrast to before extraction. These contrary spectral changes demonstrated that the hydrogen bonds between cations in the PILs and free-water molecules were broken after extraction, yielding the H-bonding occurrence between bifenthrin and H-O-H in the lattice. As a time indicator for the free-water binding and releasing process, the highest slope for the plot of I t /I 0 against time implied that the shortest time was required for P[VEIM]PF6 to reach an adsorption equilibrium. Overall, the strong hydrophobicity, small SSA and electrostatic-repulsion force for P[VEIM]PF6 are all not conducive to its efficient adsorption. Beyond our anticipation, P[VEIM]PF6 provided the highest extraction recovery for bifenthrin up to 92.4% among three PILs. Therefore, these data lead us to posit that the above high efficiency results from the strongest H-bonding effect between P[VEIM]PF6 and bifenthrin. These findings promote our deep understanding of PILs-triggered differential efficiency through a H-bonding induced effect.

Electrochemical Synthesis of Battery Electrode Materials from Ionic Liquids

Electrode materials as well as the electrolytes play a decisive role in batteries determining their performance, safety, and lifetime. In the last two decades, different types of batteries have evolved. A lot of work has been done on lithium ion batteries due to their technical importance in consumer electronics, however, the development of post-lithium systems has become a focus in recent years. This chapter gives an overview of various battery materials, primarily focusing on development of electrode materials in ionic liquids via electrochemical route and using ionic liquids as battery electrolyte components.

On the coordination of Zn2+ ion in Tf2N− based ionic liquids: structural and dynamic properties depending on the nature of the organic cation

The Zn²⁺ coordination structure changes when the Zn(Tf₂N)₂ salt is dissolved in ionic liquids resulting in more favorable interactions among solvent cations and anions.

Copper(II) Chloro Complex Formation Thermodynamics and Structure in Ionic Liquid, 1-Butyl-3-Methylimidazolium Trifluoromethanesulfonate

Metal ions in ionic liquids are laid under an unprecedented reaction field. In order to assess the reaction thermodynamics of metal ions in such a situation, Cu²⁺-chloro complex formation was examined with spectroscopic and calorimetric titrations in an ionic liquid, 1-buthyl-3-methylimidazolium trifluoromethanesulfonate (C₄mimTfO). In addition, the effect of the structure of the solvated complexes on the complexation mechanism was investigated with the aid of DFT calculations. Chloro complexation successively proceeded and finally provided a [CuCl₄]^2- species, which is also the final product in conventional molecular solvents. Their stability constants were comparable to those in molecular solvents. Interestingly, in spite of the charged solvent in the ionic liquid, the entropy profile of the complexation resembled that in the conventional molecular liquids. This indicates that the entropy gain of the released solvent species from the complexes is the main driving force of the chloro complexation in the ionic liquid. In contrast, unlike the major molecular solvents, the total coordination number of Cu²⁺ is saturated to 4 in the ionic liquid, and the Cl^- complexation tends to be accompanied by a 1:1 exchange of the solvent TfO^- from the complex. In addition, this ligand exchange was almost athermal. This possibly indicates that the coordination number is dominated by the electrostatic hindrance among the ligands including the solvent ions in the primary coordination sphere.

Interfacial Nanostructure and Asymmetric Electrowetting of Ionic Liquids

In this work, the interfacial nanostructure and electrowetting of ionic liquids having the same 1-ethyl-3-methylimidazolium cation ([EMIm]⁺) but different anions such as bis(trifluoromethylsulfonyl)imide (TFSI^-), trifluoromethylsulfonate (TfO^-), methylsulfonate (OMs^-), acetate (OAc^-), bis(fluorosulfonyl)imide (FSI^-), dicyanamide (DCA^-), and tris(pentafluorethyl)trifluorphosphat (FAP^-) on bare metallic electrodes were investigated. In the investigated voltammetric potential regime, the contact angle versus voltage curve is asymmetric with respect to surface polarity. The electrowetting of the ILs occurs at negative potentials but does not occur at positive potentials. In situ atomic force microscopy (AFM) shows that the IL adopts a multilayered structure at the solid/IL interface, and a cation-rich layer is present in the innermost layer during cathodic polarization. The cations can change their orientation and propagate ahead of the three-phase contact line by diffusion, leading to further spreading on the negatively charged surface. The formation of such a surface layer is also evidenced by X-ray photoelectron spectroscopy. Such a surface diffusion mechanism does not occur during anodic polarization, where anions are enriched. In addition, the influence of substrate, water, and dissolved zinc salts on the electrowetting of ILs was studied. Our findings provide valuable insights for the interfacial nanostructure and the electrowetting of ILs.

Suppressing the dendritic growth of zinc in an ionic liquid containing cationic and anionic zinc complexes for battery applications

Metallic zinc is a promising negative electrode for high energy rechargeable batteries due to its abundance, low-cost and non-toxic nature. However, the formation of dendritic zinc and low Columbic efficiency in aqueous alkaline solutions during charge/discharge processes remain a great challenge. Here we demonstrate that the dendritic growth of zinc can be effectively suppressed in an ionic liquid electrolyte containing highly concentrated cationic and anionic zinc complexes obtained by dissolving zinc oxide and zinc trifluoromethylsulfonate in a protic ionic liquid, 1-ethylimidazolium trifluoromethylsulfonate. The presence of both cationic and anionic zinc complexes alters the interfacial structure at the electrode/electrolyte interface and influences the nucleation and growth of zinc, leading to compact, homogeneous and dendrite-free zinc coatings. This study also provides insights into the development of highly concentrated metal salts in ionic liquids as electrolytes to deposit dendrite-free zinc as an anode material for energy storage applications.

Electrodeposition of zinc nanoplates from an ionic liquid composed of 1-butylpyrrolidine and ZnCl2: electrochemical, in situ AFM and spectroscopic studies

Electrodeposition of Zn nanoplates from an ionic liquid composed of cationic and anionic zinc-chloro complexes as constituent ions.

Tuning the electronic environment of zinc ions with a ligand for dendrite-free zinc deposition in an ionic liquid

Dendrite-free zinc was obtained by tuning the electronic environment of zinc ions and the interfacial structure at the interface with a ligand.

A Prussian Blue/Zinc Secondary Battery with a Bio-Ionic Liquid-Water Mixture as Electrolyte

The development of rechargeable zinc ion batteries with high capacity and high cycling stability is a great challenge in aqueous solution due to hydrogen evolution and dendritic growth of zinc. In this study, we present a zinc ion secondary battery, comprising a metallic zinc anode, a bio-ionic liquid-water electrolyte, and a nanostructured prussian blue analogue (PBA) cathode. Both the Zn anode and the PBA cathode exhibit good compatibility with the bio-ionic liquid-water electrolyte, which enables the electrochemical deposition/dissolution of zinc at the zinc anode, and reversible insertion/extraction of Zn(2+) ions at the PBA cathode. The cell exhibits a well-defined discharge voltage plateau of ∼1.1 V with a specific capacity of about 120 mAh g(-1) at a current of 10 mA g(-1) (∼0.1 C). The Zn anode shows great reversibility, and dendrite-free Zn deposits were obtained after 100 deposition/dissolution cycles. The integration of an environmentally friendly PBA cathode, a nontoxic and low-cost Zn anode, and a biodegradable ionic liquid-water electrolyte provides new perspective to develop rechargeable zinc ion batteries for various applications in electric energy storage.

Solid–solid phase transition study of ε-CL-20/binder composites

The comparison of solid–solid phase transition (ε → γ polymorph) of CL-20 and Cl-20/composites revealed by DSC curves.

Electrochemical and spectroscopic study of Zn(ii) coordination and Zn electrodeposition in three ionic liquids with the trifluoromethylsulfonate anion, different imidazolium ions and their mixtures with water

In this paper we report on the use of three ionic liquids, [MIm]TfO, [EMIm]TfO and [EMMIm]TfO containing Zn(TfO)₂ and their mixtures with water as electrolytes for zinc electrodeposition.