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The magnesium chalcogenide spinel MgSc2Se4 with high Mg‐ion room‐temperature conductivity has recently attracted interest as solid electrolyte for magnesium ion batteries. Its ionic/electronic mixed‐conducting nature and the influence of the spinel composition on the conductivity and Mg2+ migration barrier are yet not well understood. Here, results from a combined experimental and computational study on four MgB2Se4 spinels (B = Sc, Y, Er, Tm) are presented. The room‐temperature ionic conductivities (σion = 2 × 10−5–7 × 10–5 S cm−1) of the spinels are accurately measured, as electron transport is effectively suppressed by purely Mg‐ion conducting electrode interlayers. Using the same approach, reversible Mg plating/stripping as well as good electrochemical stability are achieved. Driven by the good accordance of the computationally and experimentally obtained Mg2+ migration barriers Ea(th) and Ea, respectively, further periodic density functional calculations are performed on the MgB2Se4 spinel system, revealing the role of trigonal distortion on the migration path geometry and Ea(th). These findings provide deeper understanding how to reach small Mg2+ migration barriers Ea in the MgB2Se4 spinels. [ABSTRACT FROM AUTHOR]

Secondary batteries using multivalent cations as ionic charge carriers have attracted increasing attention in recent years due to the high theoretical energy density provided by multi‐electron redox reactions. However, the high charge density of these cations inevitably leads to sluggish kinetics of ion migration at room temperature, which poses a challenge for the development of solid‐state batteries using multivalent ions. Here, a magnesium ion conducting hybrid solid electrolyte (HSE) is prepared, consisting of a new NASICON‐structured material, Mg0.5Sn2(PO4)3, and a small amount of magnesium ionic liquid. The HSE shows superior room‐temperature ionic conductivity of 1.11 × 10−4 S cm−1 and an activation energy of 0.36 eV. Due to the good compatibility of the HSE with the magnesium metal anode, symmetric MgǀHSEǀMg cells show stable magnesium plating and stripping behavior at room temperature. Using in situ electrochemical scanning electron microscopy measurements, the room temperature growth‐induced fracture of the HSE is observed, giving unequivocal evidence for magnesium deposition. These results may serve as a starting point for understanding the magnesium deposition mechanism on solid electrolytes in solid‐state batteries. [ABSTRACT FROM AUTHOR]

Magnesium batteries offer promising potential as next‐generation sustainable energy‐storage solutions due to the high theoretical capacity of the magnesium metal anode. Facilitating dendrite‐free operation of metal anodes necessitates the development of solid electrolytes with high magnesium‐ion conductivity. While the chalcogenide spinel MgSc2Se4 is predicted to exhibit high magnesium ion mobility, unequivocal experimental evidence for magnesium ion conduction beyond short‐range motion is still missing. This study confirms magnesium‐ion transport in MgSc2Se4 through two independent electrochemical methods: electrochemical deposition of magnesium metal and reversible magnesium plating/stripping cycling. To overcome the difficulty of measuring the ionic conductivity of the mixed conducting MgSc2Se4 spinel, a pure ion conducting interlayer is employed in a symmetric transference cell. This approach effectively suppresses the electron transport, allowing accurate characterization of the ionic conductivity. The experimental results confirm a low migration barrier of (386 ± 24) meV for magnesium ion transport in MgSc2Se4 and demonstrate one of the best performances at room temperature among the reported inorganic magnesium solid electrolytes. The findings open a new door for exploring additional mixed magnesium ion conductors and highlight the potential of magnesium chalcogenide spinels as a promising class of magnesium solid electrolytes. [ABSTRACT FROM AUTHOR]