Flower-like superstructure of iron phosphide @ carbon nanosheets as an all-in-one anode for ultrahigh-area-capacity sodium-ion batteries

Iron phosphide, which possesses high theoretical capacity and low cost, holds promise for use in sodium-ion batteries. Nevertheless, practical application has been hindered by significant volume expansion during cycling and low electrical conductivity. To address these limitations, a novel three-dimensional flower-like nanosheet structures coated with carbon layers (Fe₂P@C NSs) on iron foam has been constructed via a chemical vapor deposition-like method. This unique 3D flower-like structure serves as a conducive pathway for electrolyte transport and Na⁺ transfer. By combining a carbon layer and a 3D substrate, Fe₂P@C NSs not only accomodates volume expansion and prevents aggregation and pulverization of Fe₂P nanosheets during Na⁺ insertion/extraction, but also establishes a 3D conductive network for charge transfer. Consequently, the migration path of Na⁺ is shortened, enhancing the contact area between the electrode and electrolyte, thus improving reaction kinetics. As a result of these design features, the 3D flower-like Fe₂P@C NSs exhibit an ultra-high surface capacity and remarkable cycling stability (retaining 81 % capacity after 2000 cycles at 5 mA cm^-2) in sodium-ion batteries. The success of this approach suggests that the preparation strategy outlined in this study offers innovative insights for the development of high-performance metal phosphide materials.