Space and interface confinement effect of necklace-box structural FeS2/WS2 carbon nanofibers to enhance Na+ storage performance and electrochemical kinetics

Abstract Necklace-box structural FeS2/WS2 carbon nano-composite fibers (NB FeS2/WS2-CNFs) are fabricated by electrospinning-sulfuration-hydrothermal process. NB FeS2/WS2-CNFs exhibit the spatial confined structure, which is able to restrain volume expansion effectively in the process of Na+ intercalation/deintercalation and improve the cycling stability and rate performance. NB FeS2/WS2-CNFs exhibit remarkable initial coulombic efficiency (ICE = 87.0%) and stable long cycle (~422.6 mA h g−1 at 0.5 A g−1 after 500 cycles) for sodium storage capability. The heterojunction interface between FeS2 and WS2 can alleviate the damage of the micro-crystal plane and enhance electrochemical kinetic process. The structure evolution and mechanism of sodium storage are explored by ex-situ methods, which further confirm the spatial and interface confinement effect distinctly. In addition, the electrochemical kinetic properties of lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are compared, thereby revealing the energy storage mechanism and different ion migration modes of the three batteries. This work provides a guide for the synthesis of bimetallic compounds based on the spatial confinement and heterojunction interface confined strategy that efficiently improves energy storage performance of electrode material.