Magnesium Ion Storage Properties in a Layered (NH4)2V6O16·1.5H2O Nanobelt Cathode Material Activated by Lattice Water

Magnesium ion batteries have attracted increasing attention as a promising energy storage device due to the high safety, high volumetric capacity, and low cost of Mg. However, the strong Coulombic interactions between Mg 2+ ions and cathode materials seriously hinder the electrochemical performance of the batteries. To seek a promising cathode material for magnesium ion batteries, in this work, (NH 4 ) 2 V 6 O 16 ·1.5H 2 O and water-free (NH 4 ) 2 V 6 O 16 materials are synthesized by a one-step hydrothermal method. The effects of NH 4 + and lattice water on the Mg 2+ storage properties in these kinds of layered cathode materials are investigated by experiments and first-principles calculations. Lattice water is demonstrated to be of vital importance for Mg 2+ storage, which not only stabilizes the layered structure of (NH 4 ) 2 V 6 O 16 ·1.5H 2 O but also promotes the transport kinetics of Mg 2+ . Electrochemical experiments of (NH 4 ) 2 V 6 O 16 ·1.5H 2 O show a specific capacity of 100 mA·h·g –1 with an average discharge voltage of 2.16 V vs Mg 2+ /Mg, highlighting the potential of (NH 4 ) 2 V 6 O 16 ·1.5H 2 O as a high-voltage cathode material for magnesium ion batteries.