A Negative Surface Energy Design to Enable Hair Assembled Micron‐Particle Oxide Cathode Toward Long‐Life Mg Metal Batteries

ABSTRACT Vanadium pentoxide (V 2 O 5 ) cathode, with a high theoretical specific capacity, high operating voltage, and an adjustable layered structure, exhibits significant potential in magnesium metal batteries (MMBs). Nevertheless, the strong coulombic attraction between high charge‐radius ratio Mg ions and anionic framework of cathode host, usually results in a high reaction polarization and inferior Mg 2+ ‐de/intercalation kinetics. Herein, we propose an aliovalent‐anion doping strategy to prepare the trace Br‐doped V 2 O 5 (VOBr) cathode featured by hair‐assembled micron‐particles, achieving the improvement in electrochemical kinetics and intercalation pseudocapacitance toward MMBs. Br‐doping enables to diminish the surface energy of (0 0 1) plane of VOBr to a negative value of −0.32 J m −2 and stabilizes a large interlayer spacing of 12.91 Å. Br‐doping also regulates the electronic structure of VOBr with a narrow bandgap, compensating for the poor ion‐electron conductivity of conventional V 2 O 5 . Furthermore, the use of high‐polarity methyl tributyl ammonium chloride additive allows for the regulation of the coordination structure of Mg 2+ , thus enhancing the interfacial reaction kinetics and rechargeable capacity. The VOBr||Mg full cells present a superior reversible capacity of 197.7 mAh g −1 over 100 cycles at 100 mA g −1 as well as outstanding long‐term cyclic stability over 1000 cycles at 500 mA g −1 .