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Cation-disordered rock-salt cathodes (DRX) are promising materials that could deliver high capacities (>250 mAh g-1) with Earth abundant elements and materials. However, their electrochemical performances, other than the capacity, should be improved to be competitive cathodes, and many strategies have been introduced to enhance DRXs. Fluorination has been shown to inhibit oxygen loss and increase power density. Nevertheless, fluorinated cation-disordered rock-salts still suffer from rapid material deterioration and low scalability which limit their practical applications. This mini-review highlights the key challenges for the commercialization of fluorinated cation-disordered rock-salts, discusses the underlying reasons behind material failure and proposes future development directions.

Fluorescent species are formed during cycling of lithium ion batteries as a result of electrolyte decomposition due to the instability of the non-aqueous electrolytes and side reactions that occur at the electrode surface. The increase in the background fluorescence due to the presence of these components makes it harder to analyse data due to the spectroscopic overlap of Raman scattering and fluorescence. Herein, Kerr gated Raman spectroscopy was shown to be an effective technique for the isolation of the scattering effect from the fluorescence enabling the collection of the Raman spectra of LiPF6 salt and LiPF6-based organic carbonate electrolyte, without the interference of the fluorescence component. Kerr gated Raman was able to identify POF3 on the LiPF6 particle surface, after the addition of trace water.

Fluorescent species are formed during cycling of lithium ion batteries as a result of electrolyte decomposition due to the instability of the non-aqueous electrolytes and side reactions that occur at the electrode surface. The increase in the background fluorescence due to the presence of these components makes it harder to analyse data due to the spectroscopic overlap of Raman scattering and fluorescence. Herein, Kerr gated Raman spectroscopy was shown to be an effective technique for the isolation of the scattering effect from the fluorescence enabling the collection of the Raman spectra of LiPF6 salt and LiPF6-based organic carbonate electrolyte, without the interference of the fluorescence component. Kerr gated Raman was able to identify POF3 on the LiPF6 particle surface, after the addition of trace water.

V2Se9 displays facile electrochemical insertion of up to 1.6 Mg2+ per unit formula with fast diffusion (coefficients of 10−10–10−12 cm2 s−1) surpassing best-in-class materials like Mo6S8. Detailed structural characterization of synchrotron X-ray diffraction data with ab initio Maximum Entropy Method analysis reveals Mg2+ insertion into octahedral sites within the large vdW space between [V4Se18]∞ chains. Fast rate performance is attributed to low structural perturbation and low diffusion barriers, calculated by bond valence pathway analysis, resulting from the low charge-per-size of anionic selenium. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy reveal that reversible insertion of Mg2+ is facilitated by V5+/V3+ redox. V2Se9 demonstrates that selenides, despite their larger molecular weight, offer potential as fast-rate positive electrode materials for magnesium batteries over well-explored oxides and sulfides. [ABSTRACT FROM AUTHOR]

Lithium nickel oxide (LNO) is an attractive positive electrode active material for lithium ion batteries (LIBs) due to its high reversible specific capacity and absence of cobalt. Nevertheless, it is prone to structural instabilities that lead to rapid capacity fading, safety concerns and shows in average a lower voltage than mixtures with cobalt, limiting its applicability to date. Herein this study introduces the sulfur‐based electrolyte additive, benzo[d][1,3,2]dioxathiole 2,2‐dioxide (DTDPh), to stabilize the LNO electrode and study its effects on interphase compositions by means of complementary electrochemical and spectroscopic techniques. Obtained results demonstrate an improved galvanostatic cycling performance in terms of cycle life and achievable specific discharge capacity that significantly outperform the common film‐forming additive vinylene carbonate (VC). The cycle life is increased from 102 to 147 cycles compared to the baseline electrolyte and the accumulated discharge energy until end of life is increased by 45%. This study furthermore provides strong evidence of a significant cross‐talk and negative interplay between DTDPh and VC when both are present in the electrolyte formulation. Mechanistic consideration based on density functional theory (DFT) calculations suggest the formation of mobile poly(VC) species, which is supported by the results of post mortem analysis of the resulting interphases. [ABSTRACT FROM AUTHOR]

Magnesium batteries attract interest as alternative energy‐storage devices because of elemental abundance and potential for high energy density. Development is limited by the absence of suitable cathodes, associated with poor diffusion kinetics resulting from strong interactions between Mg2+ and the host structure. V2PS10 is reported as a positive electrode material for rechargeable magnesium batteries. Cyclable capacity of 100 mAh g−1 is achieved with fast Mg2+ diffusion of 7.2× ${\times }$ 10−11–4× ${\times }$ 10−14 cm2 s−1. The fast insertion mechanism results from combined cationic redox on the V site and anionic redox on the (S2)2− site; enabled by reversible cleavage of S−S bonds, identified by X‐ray photoelectron and X‐ray absorption spectroscopy. Detailed structural characterisation with maximum entropy method analysis, supported by density functional theory and projected density of states analysis, reveals that the sulphur species involved in anion redox are not connected to the transition metal centres, spatially separating the two redox processes. This facilitates fast and reversible Mg insertion in which the nature of the redox process depends on the cation insertion site, creating a synergy between the occupancy of specific Mg sites and the location of the electrons transferred. [ABSTRACT FROM AUTHOR]

We report on the origin of the surface structural disordering in graphite anodes induced by lithium intercalation and deintercalation processes. Average Raman spectra of graphitic anodes reveal that cycling at potentials that correspond to low lithium concentrations in LixC (0 ≤ x < 0.16) is responsible for most of the structural damage observed at the graphite surface. The extent of surface structural disorder in graphite is significantly reduced for the anodes that were cycled at potentials where stage-1 and stage-2 compounds (x > 0.33) are present. Electrochemical impedance spectra show larger interfacial impedance for the electrodes that were fully delithiated during cycling as compared to electrodes that were cycled at lower potentials (U < 0.15 V vs. Li/Li+). Steep Li+ surface-bulk concentration gradients at the surface of graphite during early stages of intercalation processes, and the inherent increase of the LixC d-spacing tend to induce local stresses at the edges of graphene layers, and lead to the breakage of C-C bonds. The exposed graphite edge sites react with the electrolyte to (re)form the SEI layer, which leads to gradual degradation of the graphite anode, and causes reversible capacity loss in a lithium-ion battery.

Graphitic carbon is currently considered the state-of-the-art material for the negative electrode in lithium ion cells, mainly due to its high reversibility and low operating potential. However, carbon anodes exhibit mediocre charge/discharge rate performance, which contributes to severe transport-induced surface structural damage upon prolonged cycling and limits the lifetime of the cell. Lithium bulk diffusion in graphitic carbon is not yet completely understood, partly due to the complexity of measuring bulk transport properties in finite-sized nonisotropic particles. To solve this problem for graphite, we use the Devanathan-Stachurski electrochemical methodology combined with ab initio computations to deconvolute and quantify the mechanism of lithium ion diffusion in highly oriented pyrolytic graphite (HOPG). The results reveal inherent high lithium ion diffusivity in the direction parallel to the graphene plane (∼10-7-10-6 cm2 s-1), as compared to sluggish lithium ion transport along grain boundaries (∼10 -11 cm2 s-1), indicating the possibility of rational design of carbonaceous materials and composite electrodes with very high rate capability. © 2010 American Chemical Society.

Ensuring the stability of the electrode and electrolyte in Li–O2 batteries and achieving a comprehensive understanding of parasitic side reaction management during cycling are key issues for the progress of this promising energy storage technology. Conditions that favour formation of either Li2O2 or Li2CO3 in Li–O2 cells on carbon-based electrodes were investigated. Operando Raman microscopy measurements and ex situ Raman and X-ray photoelectron spectroscopy (XPS) analyses were performed for Li–O2 systems using Li[ClO4]/DMSO as the electrolyte and carbon paper (CP) and carbon paper with carbon nanotubes (CPCNT) as electrodes. Using CP electrodes (either treated or untreated with O2 plasma), the major discharge product formed was Li2O2. In contrast, for CPCNT electrodes, the formation of Li2CO3 as the main discharge product was observed at lower capacities, then significant formation of Li2O2 proceeded at higher discharge capacities. XPS highlighted that the surface chemistry of the CPCNT electrode comprised fluorine and a variety of iron species, which could be linked to the promotion of Li2CO3 formation. Furthermore, it was observed that when Li2CO3 is the main discharge product, the active sites of functional groups on carbon surfaces that favour carbonate formation become coated/passivated. Consequently, the dominant reaction pathway then alters, leading to the growth of Li2O2 over the surface. These outcomes emphasized the important role in cycling stability of the active sites on carbon electrodes, arising from the synthesis process or possible contaminants. [ABSTRACT FROM AUTHOR]

The Faraday Discussion on rechargeable non-aqueous metal–oxygen batteries is summarised. The remarks paper highlights the specific science contributions made in the vital areas of oxygen reduction and evolution reaction mechanisms in non-aqueous electrolytes; material developments for stable metal–oxygen battery cathodes; achieving stable metal anodes and protected interfaces; and, finally, contributions concerning the progress towards practical metal–oxygen batteries. Key conclusions associated with these papers will be highlighted in an order such that readers can identify papers that they would like to explore in more detail. [ABSTRACT FROM AUTHOR]

The effect of Group 1 alkali-metal cations (Na+, K+, and Cs+) on the oxygen reduction and evolution reactions (ORR and OER) using dimethyl sulfoxide (DMSO)-based electrolytes was investigated. Cyclic voltammetry (CV) utilising different Pt-electrode surfaces (polycrystalline Pt, Pt(111) and Pt(100)) was undertaken to investigate the influence of surface structure upon the ORR and OER. For K+ and Cs+, negligible variation in the CV response (in contrast to Na+) was observed using Pt(111), Pt(100) and Pt(poly) electrodes, consistent with a weak surface-metal/superoxide complex interaction. Indeed, changes in the half-wave potentials (E1/2) and relative intensities of the redox peaks corresponding to superoxy (O2−) and peroxy (O22−) ion formation were consistent with a solution-mediated mechanism for larger cations, such as Cs+. Support for this finding was obtained via in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). During the ORR and in the presence of Cs+, O2− and weakly adsorbed caesium superoxide (CsO2) species were detected. Because DMSO was found to strongly interact with the surface at potentials associated with the ORR, CsO2 was readily displaced at more negative potentials via increased solvent adsorption at the surface. This finding highlights the important impact of the solvent during ORR/OER reactions. [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]