Se-Deficient MoSe₂/Cu₂Se_x Heterostructure for Fast Sodium Storage

In the pursuit of advancing energy storage devices, synchronous improvement of the power and energy density is crucial. However, the sluggish migration kinetics for metal selenides in sodium ion batteries (SIBs) hinder their practical application. To overcome this challenge, we have developed a MoSe 2 /Cu 2 Se x heterostructure with Se vacancies (MSe/CSe) through a self-assembly and postselenylation process. As an anode in SIBs, MSe/CSe exhibits exceptional electrochemical characteristics, with a first sodiation capacity of 479.8 mA h g –1 at 0.2 A g –1 and an upper initial Coulombic efficiency (ICE) of 87.7%. Furthermore, the MSe/CSe electrode displays impressive capacities of 342.3 and 337.5 mA h g –1 at 5.0 and 10.0 A g –1, respectively. In situ experiments were conducted to investigate the Na + storage mechanism behind these superior electrochemical properties. Our results reveal that the defective heterogeneous interface in MSe/CSe, which modulates its physicochemical characteristics, facilitates ultrafast Na + storage with both diffusion- and adsorption-governed behaviors, leading to the observed high ICE and outstanding performance.