Novel Mg7V4O16(OH)2·H2O and Mg3(VO4)2: preparation, characterization, and performance as lithium-ion anode materials

Mg 7 V 4 O 16 (OH) 2 ·H 2 O was prepared by improving the hydrothermal conditions and Mg 3 (VO 4 ) 2 was obtained by heat treatment of Mg 7 V 4 O 16 (OH) 2 ·H 2 O at 700 °C. XRD shows a phase transition from a hexagonal structure to an orthogonal structure, which is confirmed by the HRTEM results. Mg 3 (VO 4 ) 2 keeps overall pencil-shaped SEM morphology with Mg 7 V 4 O 16 (OH) 2 ·H 2 O but shows a lot of spaces due to the loss of hydroxyl groups and crystal water in the structure during heat treatment. Mg 3 (VO 4 ) 2 enjoys a narrower band gap in comparison with Mg 7 V 4 O 16 (OH) 2 ·H 2 O. The space in Mg 3 (VO 4 ) 2 microstructure and its narrower band gap improve the transmission efficiency of Li + , reaching a stabile capacity of 151 mAh/g after cycling 100 times at a current density of 100 mA/g.