Magnesium Storage Performance and Mechanism of 2D‐Ultrathin Nanosheet‐Assembled Spinel MgIn2S4 Cathode for High‐Temperature Mg Batteries

Magnesium batteries have the potential to be a next generation battery with large capability and high safety, owing to the high abundance, great volumetric energy density, and reversible dendrite‐free capability of Mg anodes. However, the lack of a stable high‐voltage electrolyte, and the sluggish Mg‐ion diffusion in lattices and through interfaces limit the practical uses of Mg batteries. Herein, a spinel MgIn2S4 microflower‐like material assembled by 2D‐ultrathin (≈5.0 nm) nanosheets is reported and first used as a cathode material for high‐temperature Mg batteries with an ionic liquid electrolyte. The nonflammable ionic liquid electrolyte ensure the safety under high temperatures. As prepared MgIn2S4 exhibits wide‐temperature‐range adaptability (50–150 °C), ultrahigh capacity (≈500 mAh g−1 under 1.2 V vs Mg/Mg2+), fast Mg2+ diffusibility (≈2.0 × 10−8 cm2 s−1), and excellent cyclability (without capacity decay after 450 cycles). These excellent electrochemical properties are due to the fast kinetics of magnesium by the 2D nanosheets spinel structure and safe high‐temperature operation environment. From ex situ X‐ray diffraction and transmission electron microscopy measurements, a conversion reaction of the Mg2+ storage mechanism is found. The excellent performance and superior security make it promising in high‐temperature batteries for practical applications. A spinel MgIn2S4 microflower‐like material assembled by 2D‐ultrathin (≈5.0 nm) nanosheets is first used as the cathode material for high‐temperature Mg batteries with an ionic liquid electrolyte. As prepared MgIn2S4 exhibits wide‐temperature‐range adaptability, ultrahigh capacity, fast Mg2+ diffusibility, and excellent cyclability. The excellent performance and superior security make it promising in high‐temperature batteries for practical applications.