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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 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]

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]

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.

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.