Pseudocapacitance-boosted ultrafast Na storage in a pie-like FeS@C nanohybrid as an advanced anode material for sodium-ion full batteries

In order to develop promising anode materials for sodium-ion batteries (SIBs), a novel pie-like FeS@C (P-FeS@C) nanohybrid, in which all ultrasmall FeS nanocrystals (NCs) are completely embedded into the carbon network and sealed by a protective carbon shell, has been prepared. The unique pie-like structure can effectively speed up the kinetics of electrode reactions, while the carbon shell stabilizes the FeS NCs inside. Studies show that the electrochemical reaction processes of P-FeS@C electrodes are dominated by the pseudocapacitive behavior, leading to an ultrafast Na+-insertion/extraction reaction. Hence, the prepared P-FeS@C nanohybrid exhibits superior Na-storage properties especially high rate capability in half cells. For example, it can deliver reversible capacities of 555.1 mA h g(-1) at 0.2 A g(-1) over 150 cycles and about 60.4 mA h g(-1). at 80 A g(-1) (an ultrahigh current density even higher than that of the capacitor test). Furthermore, an advanced P FeS@C/iNa(3)V(2) (PO4)(2)O2F full cell has been assembled out, which delivers a stable specific capacity of 441.2 mA h g(-1) after 80 cycles at 0.5 A g(-1) with a capacity retention of 91.8%.