New Insights into the High-Performance Black Phosphorus Anode for Lithium-Ion Batteries

Black phosphorus (BP) is a promising anode material in lithium-ion batteries (LIBs) owing to its high electrical conductivity and capacity. However, the huge volume change of BP during cycling induces rapid capacity fading. In addition, the unclear electrochemical mechanism of BP hinders the development of rational designs and preparation of high-performance BP-based anodes. Here, a high-performance nanostructured BP-graphite-carbon nanotubes composite (BP/G/CNTs) synthesized using ball-milling method is reported. The BP/G/CNTs anode delivers a high initial capacity of 1375 mA h g^-1 at 0.15 A g^-1 and maintains 1031.7 mA h g^-1 after 450 cycles. Excellent high-rate performance is demonstrated with a capacity of 508.1 mA h g^-1 after 3000 cycles at 2 A g^-1 . Moreover, for the first time, direct evidence is provided experimentally to present the electrochemical mechanism of BP anodes with three-step lithiation and delithiation using ex situ X-ray diffraction (XRD), ex situ X-ray absorption spectroscopy (XAS), ex situ X-ray emission spectroscopy, operando XRD, and operando XAS, which reveal the formation of Li₃ P₇ , LiP, and Li₃ P. Furthermore, the study indicates an open-circuit relaxation effect of the electrode with ex situ and operando XAS analyses.