Material structure and chemical bond effect on the electrochemical performance of black phosphorus-graphite composite anodes

Black phosphorus (BP) is a little-studied but promising next-generation anode material for high-energy density Li-ion and Na-ion batteries. To understand the relationship between material property and electrochemical performance, black phosphorus-graphite (BP-G) composite materials are synthesized with two different BP-G molar ratios. This study demonstrates that the crystal structure and PC bond of BP-G composites are affected by the BP-G molar ratio, which are directly correlated to cycle stability and the lithiation/delithiation process. BP0.9G1 shows a medium-range ordered structure, retaining some features of BP and having fewer or weaker PC bonds. In contrast, BP0.3G1 has an amorphous-like structure with robust PC bonds, which is helpful in withstanding the large volume change upon lithiation or delithiation. As a result, fracture and pulverization of particles, which are clearly seen in BP0.9G1 electrode, are scarcely observed in the cycled BP0.3G1 electrode. The possibility of mechanical failure in the BP-based electrode induced by BP's hydrophilic nature and the formation of Cu3P is also discussed. This work not only contributes to improving the current understanding of phosphorus-based anodes, but also provides direct evidence of fracture and pulverization of BP particles during cycling.