Large-scale preparation of black phosphorus by molten salt method for energy storage

• Black phosphorus is prepared at large scale by reducing PCl 5 with metallic Al in melt AlCl 3 at 270 °C. • Through gradient centrifugation, gram-scale black phophorus quantum dots can be obtained. • The as-prepared black phosphorus used as anode for lithium ion battery exhibits a high specific capacity of 1610 mAh g −1 with cycle life up to 1000 cycles. Black phosphorus (BP) is a new layered material in concept, which has attracted great interest due to its fascinating optical and electrochemical properties. Here, we report the large scale synthesis of BP (20 g) by reducing PCl 5 with metallic Al in melt AlCl 3 at 300 °C. X-ray diffraction indicates the orthorhombic structure of BP and Raman spectrum shows that there is no obvious impurities. BP samples consist of micron-sized clusters of about 2 µm aggregated by flake-like nanoparticles with 20–100 nm. When used as anode materials for lithium ion battery, it exhibits a high specific capacity of 1610 m Ah g −1 at a current density of 0.1C, and cycle life up to 1000 cycles at a current density of 5C. In addition, through gradient centrifugation of as-prepared BP samples, gram-scale BP quantum dots can be obtained.