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A theoretical framework to explain how interactions between redox mediators (RMs) and electrolyte components impact electron transfer kinetics, thermodynamics, and catalytic efficiency is presented. Specifically focusing on ionic association, 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) is used as a case study to demonstrate these effects. Our analytical equations reveal how the observed redox couple's potential and electron transfer rate constants evolve with Li+ concentration, resulting from different redox activity mechanisms. Experimental validation by cyclic voltammetry measurements shows that DBBQ binds to three Li+ ions in its reduced state and one Li+ ion in its neutral form, leading to a maximum in the electron transfer kinetic constant at around 0.25 M. The framework is extended to account for other phenomena that can play an important role in the redox reaction mechanisms of RMs. The effect of Li+ ion solvation and its association with the supporting salt counteranion on the redox processes is considered, and the role of "free Li+" concentration in determining the electrochemical behaviour is emphasized. The impact of Li+ concentration on oxygen reduction reaction (ORR) catalysis was then explored, again using DBBQ and modelling the effects of the Li+ concentration on electron transfer and catalytic kinetics. We show that even though the observed catalytic rate constant increases with Li+ concentration, the overall catalysis can become more sluggish depending on the electron transfer pathway. Cyclic voltammograms are presented as illustrative examples. The strength of the proposed theoretical framework lies in its adaptability to a wider range of redox mediators and their interactions with the various electrolyte components and redox active molecules such as oxygen. By understanding these effects, we open up new avenues to tune electron transfer and catalytic kinetics and thus improve the energy efficiency and rate capability of Li–O2 batteries. Although exact results may not transfer to different solvents, the predictions of our model will provide a starting point for future studies of similar systems, and the model itself is easily extensible to new chemistries. [ABSTRACT FROM AUTHOR]

This document is a discussion from the journal Faraday Discussions about practical metal-oxygen batteries, specifically focusing on lithium-oxygen batteries. The discussion covers various topics such as the effectiveness of interfacial layers, the influence of porous interlayer structures, charge transport, the use of indium, metal protection layers, and lithium carbonate redox mediators. The authors provide insights and explanations based on their research findings and previous literature. They also address concerns about solvent decomposition, discharge mediators, carbon electrode degradation, and reaction product distribution. The overall tone is informative and respectful, highlighting the challenges and complexities associated with lithium-oxygen batteries and the need for further research. The discussion also includes suggestions for standardizing the reporting and evaluation of lithium-air batteries, emphasizing the importance of detailed information and standardized protocols. [Extracted from the article]

This document is a discussion from the journal Faraday Discussions on the topic of metal anodes and protected interfaces in lithium-oxygen batteries. The participants discuss various aspects of battery performance, including the use of lithium peroxide in the anode, the stability of materials against water and carbon dioxide, the deposition of lithium on copper electrodes, and the impact of depth of discharge and current density. They also discuss the fabrication of pinhole-free LLZO membranes and the use of ceramic electrolytes. The researchers have made observations on metal ion migration, short circuit formation, and the compatibility of LLZO with different liquid electrolytes. They have disclosed their conflicts of interest. [Extracted from the article]

This document is a collection of discussions among researchers about various aspects of oxygen reactions in non-aqueous electrolytes, specifically in the context of lithium-oxygen batteries. The researchers discuss topics such as the purity of electrolyte solutions, the choice of electrode material, the role of different cations, and the effects of impurities on experimental results. They also explore the mechanisms and properties of singlet oxygen and its impact on battery degradation. The researchers provide insights and explanations based on their experiments and calculations, while acknowledging the need for further investigation in some areas. Overall, more research is needed to fully understand the complexities of these reactions and their implications for battery performance. [Extracted from the article]

This document is a discussion from the journal Faraday Discussions about materials for stable metal-oxygen battery cathodes. The discussion covers various topics such as the role of oxygen crossover in creating the solid electrolyte interface, the redox reactions of the iodide/triiodide couple, the effect of electrolyte composition on redox processes, the source of side reactions in the battery, the role of ionic liquids in changing product morphology, and the importance of water content in electrode reactions. The authors also discuss the stability of sodium salts in solvents and the stability of the battery with the addition of an ionic liquid. The document concludes with a discussion on the deposition of lithium superoxide and its dissolution into the electrolyte solution. The text discusses the experimental observations and calculations related to the growth and stabilization of LiO2 discharge products in lithium-oxygen batteries. The authors note that the epitaxial interfacial energy provides sufficient stabilization energy for LiO2 growth. The text also mentions the solubility of LiO2 in electrolytes and addresses questions about strain, template stabilization, and the conductivity of LiIr3 alloy. Experimental evidence for LiO2 and its disproportionation is mentioned, as well as the potential for using single crystal approaches to test these ideas. The text discusses various aspects of lithium-oxygen (Li-O2) and potassium-oxygen (K-O2) battery systems. It mentions the use of Ir nanoparticles to stabilize LiO2 as a discharge product and the lattice [Extracted from the article]

The lithium–air battery (LAB) is arguably the battery with the highest energy density, but also a battery with significant challenges to be overcome before it can be used commercially in practical devices. Here, we discuss experimental approaches developed by some of the authors to understand the function and failure of lithium–oxygen batteries. For example, experiments in which nuclear magnetic resonance (NMR) spectroscopy was used to quantify dissolved oxygen concentrations and diffusivity are described. 17O magic angle spinning (MAS) NMR spectra of electrodes extracted from batteries at different states of charge (SOC) allowed the electrolyte decomposition products at each stage to be determined. For instance, the formation of Li2CO3 and LiOH in a dimethoxyethane (DME) solvent and their subsequent removal on charging was followed. Redox mediators have been used to chemically reduce oxygen or to chemically oxidise Li2O2 in order to prevent electrode clogging by insulating compounds, which leads to lower capacities and rapid degradation; the studies of these mediators represent an area where NMR and electron paramagnetic resonance (EPR) studies could play a role in unravelling reaction mechanisms. Finally, recently developed coupled in situ NMR and electrochemical impedance spectroscopy (EIS) are used to characterise the charge transport mechanism in lithium symmetric cells and to distinguish between electronic and ionic transport, demonstrating the formation of transient (soft) shorts in common lithium–oxygen electrolytes. More stable solid electrolyte interphases are formed under an oxygen atmosphere, which helps stabilise the lithium anode on cycling. [ABSTRACT FROM AUTHOR]

In situ subtractively normalized Fourier transform infrared spectroscopy (SNIFTIRS) experiments were performed simultaneously with electrochemical experiments relevant to Li–air battery operation on gold electrodes in two glyme-based electrolytes: diglyme (DG) and tetraglyme (TEGDME), tested under different operational conditions. The results show that TEGDME is intrinsically unstable and decomposes at potentials between 3.6 and 3.9 V vs. Li+/Li even in the absence of oxygen and lithium ions, while DG shows a better stability, and only decomposes at 4.0 V vs. Li+/Li in the presence of oxygen. The addition of water to the DG based electrolyte exacerbates its decomposition, probably due to the promotion of singlet oxygen formation. [ABSTRACT FROM AUTHOR]

Composites of ferromagnetic CoFe2O4 nanoparticles and two conducting polymers (polyethylenedioxythiophene-PEDOT- and polypyrrole-Ppy-) were prepared and characterized. Both syntheses were performed by monomer polymerization in presence of a dispersion of the magnetic nanoparticles, at different monomer: CoFe2O4 molar ratios. For PPy-composites, both the coercive field and the applied field required to reach the maximum magnetization decrease as the polymer content increases. For PEDOT-composites, the remanence ratio increases as the polymer content increases, indicating the presence of interactions related to the amount of polymer present. Electrical conductivity measurements indicate that, for both types of composites, a high polymer content gives rise to high electrical conductivity. These results indicate that the composite properties can be modulated by varying the polymer identity and the monomer: CoFe2O4 molar ratio. [ABSTRACT FROM PUBLISHER]

• A new procedure is proposed to calculate the intrinsic volume of pure salts in WiS solutions. • In the dilute regime (x ≤ 0.1) the volumetric properties are dominated by the water electrostriction. • In the WiS regime (x > 0.1) the molar volume is determined by the hydrated Li+ ion and dehydrated anion, • A WiS structure is formed by a percolating network of anions embedded by Li(H 2 O) n + cations. • Excess viscosity is positive and small at all concentrations, but increases near the solubility limit. The density and viscosity of LiTf, LiTFSI and LiTFSI + LiTf (mole ratio 3:1) aqueous solutions have been measured at temperatures between 25 °C and 55 °C, over a wide range of concentrations covering the Water-in-Salt (WiS) region, where no free water is present in the system. As it was observed in mixtures of ionic liquids with water and mixtures of melted salt hydrates, the molar volumes of these WiS electrolytes are linear functions of the salt mole fraction. We propose a new procedure to calculate the intrinsic volume of the salts in the WiS solutions, corresponding to the volume of the hypothetical supercooled pure salts. The contributions of electrostriction and conformational changes of the anion to the partial molar volume of the WiS are discussed. The presence of Li+ ions in the salts free of water (supercooled salts) produces a large contraction of the Tf− and TFSI− volumes as compared with ionic liquids containing the same anions in contact with bulky cations. In terms of the apparent partial molar volume of water we could identify a dilute regime (x ≤ 0.1) where the volumetric properties are dominated by the water electrostriction, and a WiS regime (x > 0.1), without free-water, where the molar volume is determined by the volumes of the hydrated Li+ ion and the corresponding dehydrated anion, compatible with a proposed WiS structure formed by a percolating network of anions embedded by Li(H 2 O) n + cations. The excess volume of the ternary WiS (LiTf + LiTFSI) is very small at all temperatures and concentrations, while the excess viscosity is positive and small, but increases near the solubility limit. The viscosity of the WiS electrolytes exhibit a normal Arrhenius dependence, but simple extrapolation to the glass transition temperature indicates that the WiS electrolytes behave as fragile fluids. [ABSTRACT FROM AUTHOR]

A theoretical framework to explain how interactions between redox mediators (RMs) and electrolyte components impact electron transfer kinetics, thermodynamics, and catalytic efficiency is presented. Specifically focusing on ionic association, 2,5-di- tert -butyl-1,4-benzoquinone (DBBQ) is used as a case study to demonstrate these effects. Our analytical equations reveal how the observed redox couple's potential and electron transfer rate constants evolve with Li + concentration, resulting from different redox activity mechanisms. Experimental validation by cyclic voltammetry measurements shows that DBBQ binds to three Li + ions in its reduced state and one Li + ion in its neutral form, leading to a maximum in the electron transfer kinetic constant at around 0.25 M. The framework is extended to account for other phenomena that can play an important role in the redox reaction mechanisms of RMs. The effect of Li + ion solvation and its association with the supporting salt counteranion on the redox processes is considered, and the role of "free Li + " concentration in determining the electrochemical behaviour is emphasized. The impact of Li + concentration on oxygen reduction reaction (ORR) catalysis was then explored, again using DBBQ and modelling the effects of the Li + concentration on electron transfer and catalytic kinetics. We show that even though the observed catalytic rate constant increases with Li + concentration, the overall catalysis can become more sluggish depending on the electron transfer pathway. Cyclic voltammograms are presented as illustrative examples. The strength of the proposed theoretical framework lies in its adaptability to a wider range of redox mediators and their interactions with the various electrolyte components and redox active molecules such as oxygen. By understanding these effects, we open up new avenues to tune electron transfer and catalytic kinetics and thus improve the energy efficiency and rate capability of Li-O 2 batteries. Although exact results may not transfer to different solvents, the predictions of our model will provide a starting point for future studies of similar systems, and the model itself is easily extensible to new chemistries.

The increasing interest in developing safe and sustainable energy storage systems has led to the rapid rise in attention to superconcentrated electrolytes, commonly called water-in-salt (WiS). Several works indicate that the transport properties of these liquid electrolytes are related to the presence of nanodomains, but a detailed characterization of such structure is missing. Here, the structural nano-heterogeneity of lithium WiS electrolytes, comprising lithium trifluoromethanesulfonate (LiTf) and bis(trifluoromethanesulfonyl)imide (LiTFSI) solutions as a function of concentration and temperature, was assessed by resorting to the analysis of small-angle neutron scattering (SANS) patterns. Variations with the concentration of a correlation peak, rather temperature-independent, in a Q range around 3.5-5 nm -1 indicate that these electrolytes are composed of nanometric water-rich channels percolating a 3D dispersing anion-rich network, with differences between Tf and TFSI anions related to their distinct volumes and interactions. Furthermore, a common trend was found for both systems' morphology above a salt volume fraction of ∼0.5. These results imply that the determining factor in the formation of the nanostructure is the salt volume fraction (related to the anion size), rather than its molality. These findings may represent a paradigm shift for designing WiS electrolytes.

In situ subtractively normalized Fourier transform infrared spectroscopy (SNIFTIRS) experiments were performed simultaneously with electrochemical experiments relevant to Li-air battery operation on gold electrodes in two glyme-based electrolytes: diglyme (DG) and tetraglyme (TEGDME), tested under different operational conditions. The results show that TEGDME is intrinsically unstable and decomposes at potentials between 3.6 and 3.9 V vs. Li + /Li even in the absence of oxygen and lithium ions, while DG shows a better stability, and only decomposes at 4.0 V vs. Li + /Li in the presence of oxygen. The addition of water to the DG based electrolyte exacerbates its decomposition, probably due to the promotion of singlet oxygen formation.

Glycol ethers, or glymes, have been recognized as good candidates as solvents for lithium-air batteries because they exhibit relatively good stability in the presence of superoxide radicals. Diglyme (bis(2-methoxy-ethyl)ether), in spite of its low donor number, has been found to promote the solution mechanism for the formation of Li 2 O 2 during the discharge reaction, leading to large deposits, that is, high capacities. It has been suggested that lithium salt association in these types of solvents could be responsible for this behavior. Thus, the knowledge of the speciation and transport behavior of lithium salts in these types of solvents is relevant for the optimization of the lithium-air battery performance. In this work, a comprehensive study of lithium trifluoromethanesulfonate (LiTf) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 1,2-di-methoxyethane (DME) and diglyme, over a wide range of concentrations, have been performed. Consistent ion pairs and triplet ions formation constants have been obtained by resorting to well-known equations that describe the concentration dependence of the molar conductivities in highly associated electrolytes, and we found that the system LiTf/DME would be the best to promote bulky Li 2 O 2 deposits. Unexpected differences are observed for the association constants of LiTf and, to a lesser extent, for LiTFSI, in DME and diglyme, whose dielectric constants are similar. Molecular dynamics (MD) simulations allowed us to rationalize these differences in terms of the competing interactions of the O-sites of the ethers and the SO x groups of the corresponding anions with Li + ion. The limiting Li + diffusivity derived from the fractional Walden rule agrees quite well with those obtained from MD simulations, when solvent viscosity is conveniently rescaled., Competing Interests: The authors declare no competing financial interest.