Efficient Sodium Storage in Selenium Electrodes Achieved by Selenium Doping and Copper Current Collector Induced Displacement Redox Mechanisms

Selenium (Se), with its high specific volume capacity and high electronic and superior kinetics, is considered a promising electrode material with promising applications. However, the solvation and shuttle effects of polyselenides hinder their further application. The selenium/nitrogen-doped hollow porous carbon spheres (Se/NHPCs) are obtained using the sacrificial template and in situ gas-phase selenization methods. The Se species are doped into carbon matrixes in an adjustable amount to form Se-C(N) bonds during this process. Density functional theory calculations show that the Se-C(N) bond enhances the charge transfer between Na₂Se and carbon matrix and binding energy, which improves rate performance and cycling stability. As expected, Se/NHPCs electrode exhibit high reversible capacity (480 mAh g^–1 at 0.5 A g^–1 after 200 cycles) and rate performance (311 mAh g^–1 at 5 A g^–1) as the anode for sodium-ion batteries. A series of ex situ characterization results show that Cu₂Se produced by copper current collector induction is effective in the adsorption of polyselenides while enhancing the electrode conductivity. Since the lattice structures of Cu₂Se and Na₂Se are similar, this displacement reaction that does not involve lattice reconfiguration provides an effective strategy for the preparation of high-performance and low-cost electrode materials.