Engineering Metal Electron Spin Polarization to Regulate p-Band Center of Se for Enhanced Sodium-Ion Storage

Sluggish ion diffusion of large sodium ions is one of the main drawbacks challenging the development of metal selenides-based anode materials for sodium-ion batteries (SIBs). A spin-state regulating strategy is first proposed in this work to lift the p-band center (ɛ_p) of Se for a fast Na⁺ transfer kinetic in (Co,Cu)Se₂. By utilizing the electron transfer from Cu to Co, the π-symmetry t_2g of Co is fully occupied to decrease the spin polarization. The resultant electron repulsion between Co and Se weakens Co–Se bond to lift the ɛ_p of Se. The enhanced sodium adsorption energy effectively accelerates the ion transfer at the active material–electrolyte interface. As a result, the (Co,Cu)Se₂/NC electrode exhibits an superior sodium storage performance with a capacity of 445 mAh g⁻¹ at 0.2 A g⁻¹, 312 mAh g⁻¹ at 50 A g⁻¹, and 363 mAh g⁻¹ after 10 000 cycles at 10.0 A g⁻¹. The insight into the working mechanism of regulating spin-state of metals to lift the p-band center of Se can provide guidelines for the development of both metal selenides-based anode material and high-performance SIBs.