Unlocking the structure and anion synergistic modulation of MoSe₂ anode for ultra-stable and high-rate sodium-ion storage

The two-dimensional MoSe₂ possesses a large interlayer spacing (0.65 nm) and a narrow bandgap (1.1 eV), showing potential in sodium-ion storage. However, it faces slow kinetics and volume stress during Na⁺ (de)intercalation process, thereby affecting the cycling stability and lifespan of sodium-ion batteries (SIBs). In this work, a novel approach involving anionic doping and structural design has been proposed, wherein a two-step in-situ selenization and surface thermal annealing doping process is applied to fabricate a novel configuration material of fluorine-doped MoSe₂@nitrogen-doped carbon nanosheets (F-MoSe₂@FNC). The obtained F-MoSe₂@FNC, benefiting from the dual advantages of structure and F-doping, synergistically promotes and accelerates the stable (de)intercalation of Na⁺. Henceforth, F-MoSe₂@FNC demonstrates notable characteristics in terms of reversible specific capacity, boasting a high initial coulombic efficiency of 76.97%, alongside remarkable rate capabilities and cyclic stability. The constructed F-MoSe₂@FNC anode-based half cell manifests exceptional longevity, enduring up to 2550 cycles at 10 A·g⁻¹ with a specific capacity of 322.04 mAh·g⁻¹. Its electrochemical performance surpasses that of MoSe₂@NC and Pure MoSe₂, underscoring the significance of the proposed synergistic modulation. Through comprehensive kinetic analyses, encompassing in-situ electrochemical impedance spectroscopy (EIS), it is elucidated that the F-MoSe₂@FNC electrode showcases elevated pseudo-capacitance and rapid diffusion attributes during charge and discharge processes. Furthermore, the assembled full-cell (F-MoSe₂@FNC//Na₃V₂(PO₄)₃) attains a notable energy density of 166.94 Wh·kg⁻¹. This design provides insights for the optimization of MoSe₂ electrodes and their applications in SIBs.