Fe-Doped Ni2P Nanosheet Arrays as Self-supported Anodes for Sodium-Ion Batteries

Conversion-type anode materials, particularly transition metal phosphides (TMPs), are considered to be highly promising candidates for sodium-ion batteries (SIBs) due to their substantial theoretical capacity, which can reach up to 1000 mAh g–1, as well as their cost-effectiveness. But their practical application is constrained by significant changes, including substantial volume changes during charge/discharge cycles and poor reaction kinetics. Addressing these challenges requires precise nanoscale engineering to optimize material structure and functionality. Herein, we present the fabrication of a carbon-coated, Fe-doped nickel phosphide (Fe–Ni2P@C) nanosheet array directly grown on a three-dimensional nickel foam (NF) substrate via a simple hydrothermal and phosphating process. The hierarchical nanosheet array architecture offers several nanoscale advantages: the nanosheets provide abundant active sites for electrochemical reactions and significantly reduce Na+ diffusion distances, while the carbon coating effectively suppresses the volume expansion during cycling. Additionally, Fe doping at the nanoscale introduces phosphorus vacancies and increases the material's intrinsic conductivity and electrochemical reaction kinetics. This synergistic nanoscale design enables the Fe–Ni2P@C nanosheet arrays to function as self-supported anode materials without the need for binders, additives, or additional processing steps. As a result, the material achieves exceptional sodium storage performance, exhibiting a rate capability of 317.16 mAh g–1 at a current density of 2 A g–1 and a reversible capacity of 418.89 mAh g–1 following 500 cycles at a current density of 0.5 A g–1. This study highlights the critical role of nanoscale engineering in overcoming the limitations of TMP-based anodes and provides a facile and scalable approach for developing high-performance, self-supported anode materials for SIBs of the future.