While α-V2O5 has traditionally been considered as a promising oxide to reversibly intercalate high levels of Mg2+ at high potential, recent reports indicate that previously observed electrochemical activity is dominated by intercalation of H+ rather than Mg2+, even in moderately dry nonaqueous electrolytes. Consequently, the inherent functionality of oxides to intercalate Mg2+ remains in question. By conducting electrochemistry in a chemically and anodically stable ionic liquid electrolyte, we report that, at 110 °C, layered α-V2O5 is indeed capable of reversibly intercalating 1 mol Mg2+ per unit formula, to accumulate capacities above 280 mAh g–1. Multimodal characterization confirmed intercalation of Mg2+ by probing the elemental, redox, and morphological changes undergone by the oxide. After cycling at 110 °C, the electrochemical activity at room temperature was significantly enhanced. The results renew prospects for functional Mg rechargeable batteries surpassing the levels of energy density of current Li-ion batteries.

The energy density of rechargeable batteries utilizing metals as anodes surpasses that of Li ion batteries, which employ carbon instead. Among possible metals, magnesium represents a potential alternative to the conventional choice, lithium, in terms of storage density, safety, stability, and cost. However, a major obstacle for metal-based batteries is the identification of electrolytes that show reversible deposition/dissolution of the metal anode and support reversible intercalation of ions into a cathode. Traditional Grignard-based Mg electrolytes are excellent with respect to the reversible deposition of Mg, but their limited anodic stability and compatibility with oxide cathodes hinder their applicability in Mg batteries with higher voltage. Non-Grignard electrolytes, which consist of ethereal solutions of magnesium(II) bis(trifluoromethanesulfonyl)imide (Mg(TFSI)), remain fairly stable near the potential of Mg deposition. The slight reactivity of these electrolytes toward Mg metal can be remedied by the addition of surface-protecting agents, such as MgCl. Hence, ethereal solutions of Mg(TFSI) salt with MgCl as an additive have been suggested as a representative non-Grignard Mg electrolyte. In this work, the degradation mechanisms of a Mg metal anode in the TFSI-based electrolyte were studied using a current density of 1 mA cm and an areal capacity of ∼0.4 mAh cm, which is close to those used in practical applications. The degradation mechanisms identified include the corrosion of Mg metal, which causes the loss of electronic pathways and mechanical integrity, the nonuniform deposition of Mg, and the decomposition of TFSI anions. This study not only represents an assessment of the behavior of Mg metal anodes at practical current density and areal capacity but also details the outcomes of interfacial passivation, which was detected by simple cyclic voltammetry experiments. This study also points out the absolute absence of any passivation at the electrode-electrolyte interface for the premise of developing electrolytes compatible with a metal anode.

Mg migration in oxide spinels is impeded by strong affinity between divalent Mg and oxygen, suggesting a necessity of exploring new chemistry of solid lattices for functional Mg-ion electrode materials. Cationic mobility with a suitable activation energy in Cr spinels is evidenced by theoretical and experimental results, while redox potentials of V are appropriate to operate with currently limited candidates of nonaqueous electrolytes. By controlling the structure, composition, and complexity, a largely solid-solution MgCrVO4 spinel was synthesized, which, unlike nanocomposites, can bring together the advantages of each transition metal in the lattice. The spinel was successfully synthesized by a simple solid-state reaction with minor inactive Cr- or V-rich components, which was confirmed via 25Mg MAS NMR and high-resolution X-ray diffraction analyses. A thermally and anodically stable Mg­(TPFA)2/triglyme electrolyte was utilized for high-temperature electrochemistry and lowering kinetic barriers at and across interfaces so as to observe intercalation behavior of Mg in the designed lattice. Multimodal characterization confirmed an apparent bulk demagnesiation from MgCrVO4 with partial reversibility by probing evolution of the local and long-range structure as well as vanadium and chromium electronic states within the lattice. Characterization experiments also provided a direct evidence for (de)­intercalation reactions that occurred without any major competitive conversion reactions or insertion of protons into the lattice, except for the formation of a surface rock salt phase upon charge. These findings in Mg-ion activity expand opportunities to design Mg spinel oxide materials while highlighting the need to identify the origins of reversibility challenges due to, but not limited to, phase stability, particularly for the charged states, barriers at the interface, electrolyte stabilities, and desolvation phenomena, collectively hindering practical use as cathode materials.

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electrochemical reactions. [1][2][3][4][5][6][7][8][9][10][11] In particular, molybdenum disulfide (MoS 2 ) and a few members of transition metal dichalcogenides (TMDCs) in contact with ionic-liquid (IL) electrolyte have recently shown a great promise to overcome fundamental electronic and thermokinetic limitations for CO 2 reduction reaction, as well as the oxygen reduction and evolution reactions (ORR/OER). [7][8][9][10] These studies have been conducted on a limited number of TMDCs, and the majority of other TMDCs with a wide range of electronic and potentially catalytic properties have not been investigated. In this study, we report synthesis and characterization of a wide range of TMDCs including sulfides, selenides, and tellurides of group V and VI transition metals and study their electrochemical performance in aprotic medium with Li salts. We employ a wide suite of characterization techniques, such as scanning transmission electron microscopy (STEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), dynamic light scattering (DLS), and atomic forceThe optimization of traditional electrocatalysts has reached a point where progress is impeded by fundamental physical factors including inherent scaling relations among thermokinetic characteristics of different elementary reaction steps, non-Nernstian behavior, and electronic structure of the catalyst. This indicates that the currently utilized classes of electrocatalysts may not be adequate for future needs. This study reports on synthesis and characterization of a new class of materials based on 2D transition metal dichalcogenides including sulfides, selenides, and tellurides of group V and VI transition metals that exhibit excellent catalytic performance for both oxygen reduction and evolution reactions in an aprotic medium with Li salts. The reaction rates are much higher for these materials than previously reported catalysts for these reactions. The reasons for the high activity are found to be the metal edges with adiabatic electron transfer capability and a cocatalyst effect involving an ionic-liquid electrolyte. These new materials are expected to have high activity for other core electrocatalytic reactions and open the way for advances in energy storage and catalysis. ElectrocatalystsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.