Co2P nanoparticles encapsulated in 3D porous N-doped carbon nanosheet networks as an anode for high-performance sodium-ion batteries

Transition metal phosphides (e.g. Co2P) have received tremendous attention as alternative anodes for sodium-ion batteries (SIBs) because of their high specific capacity. However, the severe capacity fading and short cycle life resulting from the large volume variation upon the repeated cycling process greatly hinder their practical applications. Herein, we report a facile approach to encapsulate Co2P nanoparticles (NPs) in 3D porous N-doped carbon nanosheet networks (3D-PNC) as an anode for SIBs, using a cobalt nitrate-induced polyvinylpyrrolidone (PVP)-blowing method combined with an in situ phosphidation process. Benefiting from the synergistic effect of carbon nanosheet networks, N-doping and nanosized Co2P particles associated with the unique 3D porous architecture, the 3D-PNC encapsulated Co2P (denoted as Co2P-3D PNC) composite can not only avoid the direct contact between encapsulated Co2P and electrolyte and maintain the surface/interface stabilization, but also accommodate the volume variation of Co2P NPs. Additionally, significant advantages could be achieved in the electrode, including sufficient active sites, promoted ionic and electronic transport and reduced ionic diffusion distance. Substantially, the resultant Co2P-3D PNC electrode suggests impressive Na-storage performance with a high initial discharge capacity of 827 mA h g(-1) at 50 mA g(-1), enhanced cycling stability and long cycle life of 271 mA h g(-1) after 700 cycles at 500 mA g(-1), and an improved rate capability of 179 mA h g(-1) at 3000 mA g(-1). The excellent Na-storage performance, together with the novel synthesis route, ensures the resulting Co2P-3D PNC composite to be a highly attractive anode material for SIBs.