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

Abstract 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.