An Integrated Free-Standing Flexible Electrode with Holey-Structured 2D Bimetallic Phosphide Nanosheets for Sodium-Ion Batteries

An integrated, free-standing, and binder-free type of flexible anode electrode is fabricated from numerous holey-structured, 2D nickel-based phosphide nanosheets connected with carbon nanotubes. This electrode architecture can not only uniformly disperse the nanosheets throughout the whole electrode to avoid aggregation or detachment, but also provide an ideal sodium ion and electrolyte diffusion and penetration network with high electronic conductivity. Meanwhile, bimetallic phosphide formation by introducing secondary metal species will lead to a synergistic effect to modify the electrochemical properties. Due to the excellent compositional and structural characteristics of this electrode, it delivers superior performance. This designed flexible anode with Ni1.5Co0.5Px nanosheets demonstrates a reversible capacity of 496.4 mAh g(-1) at 0.5 C and a good rate capacity of 276.1 mAh g(-1) at 8 C. Meanwhile, this connected integrated network woven from carbon nanotubes can effectively restrain volumetric expansion and shrinkage, and affect the conversion reaction products formation as well, from large-sized microspheres to film structure, which is primarily credited with the improvement in electrochemical performance. This work may open up a new path for the synthesis of morphology-controlled phosphides and promote the further development of flexible devices.