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Magnesium (Mg) metal secondary batteries have attracted much attention for their high safety and high energy density characteristics. However, the significant issues of the cathode/electrolyte interphase (CEI) in Mg batteries are still being ignored. In this work, a significant CEI layer on the typical Mo6S8 cathode surface has been unprecedentedly constructed through the oxidation of the chloride‐free magnesium tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)4]2) salt under a proper charge cut‐off voltage condition. The CEI has been identified to contain BxOy effective species originating from the oxidation of [B(hfip)4]− anion. It is confirmed that the BxOy species is beneficial to the desolvation of solvated Mg2+, speeding up the interfacial Mg2+ transfer kinetics, thereby improving the Mg2+‐storage capability of Mo6S8 host. The firstly reported CEI in Mg batteries will give deeper insights into the interface issues in multivalent electrochemical systems. [ABSTRACT FROM AUTHOR]

Chalcogenides have been viewed as important conversion‐type Mg2+‐storage cathodes to fulfill the high volumetric energy density promise of magnesium (Mg) batteries. However, the low initial Columbic efficiency and the rapid capacity degradation remain challenges for the chalcogenide cathodes, as the clear Mg2+‐storage mechanism has yet to be clarified. Herein, we illustrate that the charge storage mechanism of the Cu2−xSe cathode is a reversible displacement reaction along with a polyselenide (PSe) mediated solution process of anion‐compensation. The unique anion redox improves charge storage, while the dissolution of PSe also leads to performance degradation. To address this issue, we introduce Mo6S8 into the Cu2−xSe cathode to immobilize PSe, which significantly improves performance, especially the reversible capacity (from 140 mAh g−1 to 220 mAh g−1). This work provides inspiration for the modification of the Mg2+‐storage cathode, which is a milestone for high‐performance Mg batteries. [ABSTRACT FROM AUTHOR]

Solid‐state zinc (Zn) batteries offer a new candidate for emerging applications sensitive to volume, safety and cost. However, current solid polymeric or ceramic electrolyte structures remain poorly conductive for the divalent Zn2+, especially at room temperature. Constructing a heterogeneous interface which allows Zn2+ percolation is a viable option, but this is rarely involved in multivalent systems. Herein, we construct a solid Zn2+‐ion conductor by inducing crystallization of tailored eutectic liquids formed by organic Zn salts and bipolar ligands. High‐entropy eutectic‐networks weaken the ion‐association and form interfacial Zn2+‐percolated channels on the nucleator surfaces, resulting in a solid crystal with exceptional selectivity for Zn2+ transport (tZn2+ =0.64) and appreciable Zn2+ conductivity (σZn2+ =3.78×10−5 S cm−1 at 30 °C, over 2 orders of magnitude higher than conventional polymers), and finally enabling practical ambient‐temperature Zn/V2O5 metal solid cells. This design principle leveraged by the eutectic solidification affords new insights on the multivalent solid electrochemistry suffering from slow ion migration. [ABSTRACT FROM AUTHOR]