Mg<sub>3</sub>V<sub>4</sub>(PO<sub>4</sub>)<sub>6</sub>: A Potential Cathode Material\nwith High Stability for Aqueous Zinc-Ion\nBatteries

Aqueous zinc-ion batteries (AZIBs) have wide application\nprospects\nin the field of large-scale energy storage systems. The lack of a\nsuitable cathode material is an important factor limiting the development\nof AZIBs. Polyanionic phosphate Mg<sub>3</sub>V<sub>4</sub>(PO<sub>4</sub>)<sub>6</sub> has a stable three-dimensional framework structure\nand open zinc-ion transmission channels, which are conducive to zinc-ion\nstorage. Here, a carbon-coated Mg<sub>3</sub>V<sub>4</sub>(PO<sub>4</sub>)<sub>6</sub>@C cathode material is synthesized, and the zinc-ion\nstorage properties are studied for the first time. Benefiting from\nthe open ion transport channels and fast electron transport paths,\nMg<sub>3</sub>V<sub>4</sub>(PO<sub>4</sub>)<sub>6</sub>@C shows a\nfavorable electrochemical performance. The Mg<sub>3</sub>V<sub>4</sub>(PO<sub>4</sub>)<sub>6</sub>@C cathode delivers a specific capacity\nof 84 mA h·g<sup>–1</sup> at 0.04 A·g<sup>–1</sup> and good cycle stability, with a capacity retention of 85% after\n100 cycles. The electrochemical reaction mechanism is investigated\nby ex situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy.\nThis work deepens our understanding of the proton and zinc-ion storage\nbehavior in Mg<sub>3</sub>V<sub>4</sub>(PO<sub>4</sub>)<sub>6</sub> cathode materials.