Superior sodium storage in phosphorus@porous multichannel flexible freestanding carbon nanofibers

Red phosphorus has been regarded as an attractive candidate anode for sodium-ion batteries (NIBs) because it has a high Na-ion storage capacity of similar to 2600 mA h g(-1). However, red phosphorus shows dramatic capacity decay and poor cycle stability resulting from its huge volume changes during sodiation/desodiation process and poor electronic conductivity. In this work, we encapsulated red phosphorus in porous multichannel carbon nanofibers (denoted as phosphorus@PMCNFs) as flexible anodes for NIBs. It shows excellent rate capability capacity (500 mA h g(-1) at 10 A g(-1)) and ultralong cycle life (700 mA h g(-1) at 2 A g(-1) after 920 cycles), calculated based on the composite mass. The improved sodium storage performance is ascribed to the special core/shell structure of phosphorus@PMCNFs. The novel structure of the obtained materials (i.e. nanosized phosphorus, porous structure, highly conductive self-supported interconnected nanofibers) displays synergistic functions: reducing diffusion barrier of both ions and electrons, accommodating the volume variation during sodiation/desodiation process and improving mechanical strength to realize free-standing electrodes, leading to outstanding rate capability and cycling performance.