Core/shell FeSe/carbon nanosheet-assembled microflowers with ultrahigh coulombic-efficiency and rate performance as nonpresodiate anode for sodium-ion battery

Abstract

The microflower-like composites, constructed by two-dimensional core/shell FeSe/carbon nanosheet, are synthesized based on carbon-confined oriented-attachment mechanism. This unique structure can effectively enhance sodium-ion diffusion kinetics, accelerate the electron transfer and inhibit the volume expansion of FeSe kernel. When used as anode materials of sodium ion batteries (SIBs), the composites can deliver a high capacity of 460.2 mA h g−1 with ultrahigh initial Coulombic efficiency (ICE) of 99.8%. Moreover, the composites exhibit excellent rate-performance and super-long cycling stability. The capacity can be as high as 343.8 and 341.3 mA h g−1 at 5 and 10 A g−1. At ultrahigh current density of 30 A g−1, the composites can still deliver a capacity of 183.8 mA h g−1 and maintain a value of ca. 100 mA h g−1 after 10000 cycles. Interestingly, the composites can be directly assembled with Na3V2(PO4)3 into full battery without presodiation. The full battery delivers a capacity of 214.6 mA h g−1 after 140 cycles with a retention of 99.9% at 1 A g−1, showing superior rate and cyclic performances. Accordingly, this work is of great significant for design of non-presodiate anode materials to promote the practical applications of SIBs.