An advanced high-rate capability sodium-ion anode: Few-layered NbSe₂ with a mechanism of parallel running...

The unique superconductivity and charge density wave transition characteristics of NbSe₂ make it worthy of exploring its electrochemical performance and potential applications in the field of batteries. Herein, the bulk NbSe₂ was successfully exfoliated into few-layered NbSe₂ nanostructures by wet grinding exfoliation approach, which solved the issues of its long activation period and poor cycle stability. The strong Nb-Se bond in the plane and weak van der Waals force between the adjacent layers could render the fast Na⁺ diffusion, provide abundant reaction sites and multi-directional migration paths, thus accelerate the ionic conductivity. The theoretical calculations verified the high Na⁺ adsorption tendency between the NbSe₂ interlayers stemming from the continuous region of charge accumulation. Thanks to the unique electronic and two-dimensional few-layered structures, the exfoliated NbSe₂ exhibited a high cyclic stability with a capacity of 502 mA h g^-1 over 2800 cycles at 10 A/g. In addition, the reaction mechanism was studied by in-situ X-ray diffraction and other tests, indicating a reaction mechanism containing of simultaneous intercalation (NbSe₂↔Na_xNbSe₂↔NaNbSe₂↔Na_1+xNbSe₂) and conversion processes in NbSe₂. This parallelly running mechanism not only alleviates the volume change but also ensures a high specific capacity. Additionally, different lattice planes of the NaNbSe₂ intermediate in the intercalation process experience varying degrees of contraction and expanding in d-spacing due to the influence of Coulombic force.