Cation vacancy modified bismuth selenide nanosheets toward durable and ultrafast sodium-ion batteries

High-performance metal chalcogenide anodes based on conversion and alloy reaction are promising for the next generation of sodium-ion batteries (SIBs) due to their high theoretical capacity. However, the intrinsic limitations of metal chalcogenides, including inadequate electrical conductivity and suboptimal ion diffusion kinetics, impede high-rate performance and large-scale applicability. Herein, a two-dimensional ultrathin Cu heteroatom-doped Bi₂Se₃ nanosheet with cation vacancies (denoted as DBS) has been developed as an anode for SIBs, exhibiting high capacity and superior rate performance. The electrical conductivity of DBS is enhanced by the contribution of surface topological states and the regulation of electronic structure due to structural defects. Furthermore, the modified crystal structure demonstrates improved ion transport capabilities, elevated Na⁺ adsorption energy, and a greater number of adsorption sites, as substantiated by density functional theory (DFT) calculations. Consequently, the DBS electrode exhibits reduced polarization potential, fast capacitive charge storage and a more comprehensive conversion-alloy reaction, thereby achieving a high specific capacity (528 mA h g^-1 at 0.2 A g^-1), large rate performance (383 mA h g^-1 at 10 A g^-1), and long cycling stability. This superior performance enhances the appealing electrochemical properties of both coin and pouch-type DBS//Na₃V₂(PO₄)₃@C full cells.