Synergetic electronic spin modulation and asymmetric orbital hybridization at the CoSe2/Fe3Se4 interface inducing a robust SEI for enhanced sodium ion storage.

Transition metal selenides (TMSes) are recognized as promising anode materials for sodium-ion batteries (SIBs) owing to their ideal capacity and low cost, but their practical application suffers from crucial issues of inferior cycling stability and sluggish reaction kinetics. Herein, we design a magnetic CoSe2/Fe3Se4 (CFSE) heterostructure to simultaneously regulate orbital and spin features, aiming to systematically reveal their synergistic effect on sodium-ion storage. The orbital spin splitting of the CFSE heterostructure drives the Co2+ spin state transition from low to high, which improves the adsorption energy and lowers the diffusion energy barrier of sodium ions. Meanwhile, Co-Se-Fe asymmetric orbital hybridization promotes a charge transfer pathway at the interface and ensures the directional migration of ions, thereby inhibiting irreversible structural variations and tailoring an ultrathin and robust SEI film during battery operation. As a result, the as-prepared CFSE electrodes achieve a high reversible capacity of 395.8 mAh g-1 at 2.0 A g-1 over 1200 cycles and deliver an excellent rate capability of 364.4 mAh g-1 at 10.0 A g-1. This work provides an in-depth understanding of the spin-orbit modulation mechanism and inspiration for developing advanced conversion-type anodes.