Iron-cobalt phosphide/nitrogen-doped carbon composite derived from prussian blue analogues as anode materials for sodium-ion batteries

Abstract

Transition metal phosphides (TMPs) are recognized as attractive substitutes for lithium/sodium storage owing to their notable capacity and outstanding safety features. However, they face significant challenges in applications, particularly poor cycling stability and rapid capacity decay. In this study, we report a simple strategy utilizing dopamine-coated Prussian blue analogues as precursors to prepare bimetallic iron‑cobalt phosphide/nitrogen-doped carbon (Fe1-xCoxP/NC) composite materials via a one-step carbothermal phosphorization process. Benefiting from their nanostructured advantages and electronic interactions between Fe and Co sites, Fe0.17Co0.83P/NC, prepared by adjusting and optimizing the ion ratio, exhibits excellent rate capability and cycling performance as an anode material for sodium-ion batteries. It achieves a high specific capacity of 505.6 mAh g−1 at 0.5 A g−1. Even after 1000 cycles at a high current of 1 A g−1, the reversible specific capacity remains at 413.6 mAh g−1. Ex-situ XRD studies confirm that Fe0.17Co0.83P/NC stores Na+ via a conversion mechanism, where the crystalline CoP phase transforms into Na3P phase during the discharging process.