High-efficiency sodium storage of Co_0.85Se/WSe₂ encapsulated in N-doped carbon polyhedron via vacancy and heterojunction engineering

With the advantage of fast charge transfer, heterojunction engineering is identified as a viable method to reinforce the anodes' sodium storage performance. Also, vacancies can effectively strengthen the Na+ adsorption ability and provide extra active sites for Na+ adsorption. However, their synchronous engineering is rarely reported. Herein, a hybrid of Co0.85Se/WSe2 heterostructure with Se vacancies and N-doped carbon polyhedron (CoWSe/NCP) has been fabricated for the first time via a hydrothermal and subsequent selenization strategy. Spherical aberration-corrected transmission electron microscopy confirms the phase interface of the Co0.85Se/WSe2 heterostructure and the existence of Se vacancies. Density functional theory simulations reveal the accelerated charge transfer and enhanced Na+ adsorption ability, which are contributed by the Co0.85Se/WSe2 heterostructure and Se vacancies, respectively. As expected, the CoWSe/NCP anode in sodium-ion battery achieves outstanding rate capability (339.6 mAh g(-1) at 20 A g(-1)), outperforming almost all Co/W-based selenides.