High-performance sodium-ion anode based on stable phosphorus-carbon bond in black phosphorus-hard carbon nanocomposite

Black phosphorus (BP) is a promising material with a high theoretical specific capacity and high carrier mobility. Nevertheless, the anode volume expansion of BP during charging and discharging represents a significant obstacle to its further development in sodium-ion batteries (SIBs) which reduces their properties in terms of specific capacity and cycling stability. To solve the problem, a series of BP and hard carbon (BP-HC) composites are prepared with different mass ratios (7:3, 5:5, and 4:6) by a simple ball milling method. Various characterization techniques are used to analyze the microstructures and binding conformations of the materials. It is found that a strong interaction between BP and HC through the formation of phosphorus-carbon (P-C) and phosphorusoxygen-carbon (P-O-C) bonds which benefits the electrochemical performance of SIBs. Among the three BP-HC anodes, the BP-HC-46 anode shows the best cycling stability, with a high initial discharge specific capacity of 2448.8 mAh g- 1 at a current density of 0.1 A g- 1 and a reversible capacity of up to 1842.2 mAh g- 1 after 50 cycles with a retention rate of 97.4 % (compared to the second discharge specific capacity of 1890.6 mAh g- 1). This study proposes a straightforward method for synthesizing BP-HC anode composites in SIBs.