High-capacity, fast-charging and long-life magnesium/black phosphorous composite negative electrode for non-aqueous magnesium battery

Secondary non-aqueous magnesium-based batteries are a promising candidate for post-lithium-ion battery technologies. However, the uneven Mg plating behavior at the negative electrode leads to high overpotential and short cycle life. Here, to circumvent these issues, we report the preparation of a magnesium/black phosphorus (Mg@BP) composite and its use as a negative electrode for non-aqueous magnesium-based batteries. Via in situ and ex situ physicochemical measurements, we demonstrate that Mg ions are initially intercalated in black phosphorus two-dimensional structures, forming chemically stable Mg_xP intermediates. After the formation of the intermediates, Mg electrodeposition reaction became the predominant. When tested in the asymmetric coin cell configuration, the Mg@BP composite electrode allowed stable stripping/plating performances for 1600 h (800 cycles), a cumulative capacity of 3200 mAh cm⁻², and a Coulombic efficiency of 99.98%. Assembly and testing of the Mg@BP | |nano-CuS coin cell enabled a discharge capacity of 398 mAh g⁻¹ and an average cell discharge potential of about 1.15 V at a specific current of 560 mA g⁻¹ with a low decay rate of 0.016% per cycle for 225 cycles at 25 °C.