Vanadium oxide gels are appealing cathode materials as they offer multiple electron redox processes leading to high cation‐storage capacities. Moreover, they are able to intercalate different ionic and molecular species. Apart from low electronic conductivity, one of the main factors hindering the use of highly porous V2O5 gels is the difficulty in preserving their unique morphology, made up of an entangled network of thin ribbons, during conventional laminated electrode preparation. In this study, we tune the V2O5 synthesis conditions and use an innovative and green binder system (polyacrylic acid and ethanol) to obtain electrodes with a morphology optimized for ion intercalation. The electrochemical performance of such electrodes, tested against lithium and sodium anodes, are shown to be excellent.

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This review aims to address the status of transition metal‐based cathode materials for Mg2+ and Ca2+‐based multivalent‐ion batteries on a critical standpoint, providing a comprehensive overview. Multivalent‐based ions battery (MIB) technologies are among the most promising post‐lithium electrochemical energy storage devices currently studied, but they still fall short in several aspects due to their early stage of research. In addition, difficult experimental conditions related to the electrolyte systems and the cathode materials require an additional quote of care when performing experiments. In this review, a global approach is undertaken, from an introduction to electrolytes to the studied insertion parameters that allow a fast (de)insertion of multivalent ions. Then, the currently studied structural classes of cathode materials and a critical comment on data reporting, which are among the focal points of the actual state‐of‐the‐art research, are thoroughly discussed.

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Mn dissolution is the main drawback of LiMn2O4 cathodes, leading to capacity fading and anode poisoning. It is well known that improved capacity/cycling performances have been obtained by the Al2O3 coating. It is less clear what is the effect of the coating from the point of view of the fundamental processes occurring within the active material and on the interface with the active material, especially during the first cycle, when a dynamical interaction at a high voltage with an electrolyte and a binder leads to the formation of a passivation layer. We present here the close comparison of coated and uncoated electrodes’ X-ray absorption analysis at the interface during the measurements of several charged/discharged states of the electrode. The Al2O3 coating is significantly effective for stopping the high voltage instability of the battery, especially, when the Mn–O couple reacts with organic species, limiting Mn capture and the electrolyte reaction with the oxide surface. In the low-voltage discharge, on the other hand, more complex structure/electronic modifications occur. The presence of the coating limits disproportionation, preventing a general corrosion with dissolution of the Mn2+ species, and hence improves the electrode performance. From the structural point of view, the signatures of the transformations and a reversible modification of the surface character of the nanoparticles from a spinel to a defective phase are observed, while no charge transfer between the coating and manganese oxide is found. The role of nonthermodynamic interphase formation by means of proton transfer is enhanced for the coated oxide particles.

It is well known that the Al2O3 coating of the LiMn2O4 cathodes leads to improvement of the performance of these electrodes. However, the effect of the coating on the fundamental processes occurring on the interface with the active material which results in the formation of the solid permeable interphase is yet to be investigated. These effects should be more pronounced in the first cycle when a dynamic interaction of the active material at high voltage with the electrolyte and binder leads to the formation of this passivation layer. Here, we present a detailed investigation of the solid permeable interphase formation in alumina-coated and uncoated LiMn2O4 electrodes using X-ray absorption spectroscopy and analysis on the electrodes at the predesigned charging/discharging states. We demonstrate that the alumina coating leads to modification of the solid permeable layer and its dynamics. We also discuss the possible influences of interface modifications via coating on the battery performance.

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