Multidimensional nanobox structural carbon nanofibers with dual confined effect for boosting storage performance and electrochemical kinetics of alkali metal ion batteries

Nanobox structural Fe7S8/MoS2 carbon nanofibers (NB Fe7S8/MoS2-CNFs) are synthesized by the process of electrospinning-sulfuration-hydrothermal, which construct a multidimensional structure with 0D nanoparticles, 1D nanofibers, 2D nanosheets and 3D cross-link networks. NB Fe7S8/MoS2-CNFs display the special dual confined effects, which are the space and interface confinement, respectively. Benefiting from the advantage of multidimensional structure, NB Fe7S8/MoS2-CNFs exhibit remarkable potassium storage capability and stable long cycle (~204.5 mA h g−1 at 1 A g−1 after 500 cycles). The structure evolution of NB Fe7S8/MoS2-CNFs in potassium ion batteries (PIBs) are explored by ex-situ methods, which confirm that dual confined effect can alleviate the volume expansion effectively. Integrating the merits of multidimensional structure and dual confined effects, NB Fe7S8/MoS2-CNFs anode also manifests an outstanding reversibility and long cyclic stability of lithium-ion batteries (LIBs) (~772 mA h g−1 at 1 A g−1 after 500 cycles) and sodium-ion batteries (SIBs) (~368.3 mA h g−1 at 1 A g−1 after 500 cycles). Additionally, the kinetic properties have been studied, which explain the different ion migration laws of alkali metal ion batteries. The density function theory (DFT) calculation further verifies that heterogeneous interfaces can greatly reduce the migration energy barrier. Therefore, this work provides a strategy of dual confined effect to understand the mechanism and kinetics of alkali metal ion batteries.