Iron phosphides nanocrystals encapsulated with hierarchical nitrogen doped carbon networks as high-performance anodes for sodium ion batteries

Abstract

Exploiting a facile and effective approach to alleviate huge volume expansion and improve the slow dynamics of conversion-based transition metal phosphides (TMPs) anodes for sodium ion batteries (SIBs) is of great significance but challenging. Herein, a protective etching strategy is developed to construct the iron phosphides nanocrystals encapsulated with hierarchical nitrogen doped carbon networks (FexP@NC). This strategy utilizes phytic acid (PA) and polyvinyl pyrrolidone (PVP) as the etchant and protectant for pretreating the Fe-based metal-organic frameworks. Under the unique synergetic protective etching process, the obtained FexP@NC sample shows optimized nano-sized iron phosphides heterostructures, flexible and rigid nitrogen doped carbon protective networks with high electrical conductivity and high surface area, which are conducive to enhancing the structural stability and sodium ion storage dynamics. As expected, when employed the FexP@NC sample as an anode for SIBs, it delivers remarkable electrochemical performances, including a high discharge capacity of 468.8 mAh g−1 at 0.1 A g−1, rapid rate capability of 272.1 mAh g−1 at 5.0 A g−1, and long cycling stability. This strategy opens up a new approach for designed high-performance TMPs based anodes for SIBs.