Abstract: Carbon nanofibers (CNFs) with high specific surface area show great potential for sodium storage as a hard carbon material. Herein, CNFs anchored with Ni nanoparticles (CNFs/Ni) were prepared through chemical vapor deposition and impregnation reduction methods, in situ growing on the three-dimensional porous copper current collector (3DP-Cu). The coupling effect of high-spin state Ni nanoparticles leads to the increase of defect density and the expansion of lattice spacing of CNFs. Meanwhile, the 3DP-Cu ensures a high loading capacity of CNFs and short ion/electron transport channels. As an integral binder-free anode, the 3DP-Cu/CNFs/Ni exhibits excellent electrochemical performance, which demonstrates a high specific capacity with 298.5 mAh g^-1 at 1000 mA g^-1 after 1500 cycles, and a high power density with 200 mAh g^-1 over 1000 cycles at 5000 mA g^-1. Density functional theory calculation results show that the high-spin state Ni regulates the electronic structure of CNFs, which significantly reduces the adsorption energy for Na⁺ (-2.7 Ev) and thus enables high-rate capability. The regulation of the electronic structure of carbon materials by high-spin state metal provides a new strategy for developing high-power carbonaceous anode materials for sodium-ion batteries.

Key words: Carbon nanofibers, Ni nanoparticles, High-spin state, Sodium-ion batteries, Anode materials, Density functional theory calculation