Defect‐Enriched Heterojunction Coupling Nano‐Scale Polyhedron with Cavity Structure to Promote Rapid and Stable Sodium Storage

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Abstract
Transition Metal‐sulfides are considered as ideal anode materials in sodium‐ion batteries. Nevertheless, the poor cyclic stability and rate performance at high current density impede their development. Therefore, defect‐enriched nano‐scale heterogeneous NiS2/Cu7.2S4 (NCSs) polyhedron with cavity structure are prepared through component regulation. The cavity structure is formed based on Kirkendall effect due to the component difference, tolerating the mechanical stress during the sodium storage process. And the nano‐scale size cuts down the diffusion path of Na+. Moreover, the defective heterojunction induces built‐in electric filed and active sites for sodium adsorption, improving electronic conductivity and boosting reaction kinetics, respectively. Density functional theory (DFT) calculations theoretically verify that heterojunction can improve electronic conductivity and boost charge transfer, further, enhancing the ability of Na+ adsorption. The synergistic effect of structural design and defective heterojunction construction effectively improves the electrochemical performance. Thus, NCSs electrode shows excellent cyclic stability (437.4 mAh g−1 at 10 A g−1 after 10 000 cycles) and rate performance (514.9 and 486.7 mAh g−1 at 5 and 10 A g−1, respectively) at high current densities. When assembled with Na3V2(PO4)3 cathode, the NCSs|| Na3V2(PO4)3 full cell shows a cyclic performance of 128.2 mAh g−1 after 200 cycles at 1 A g−1.

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