Breaking the Spin Blockade: Ferromagnetic NiF ₂ Electrocatalyst with Exchange‐Upgraded d‐π Coupling for Electrocatalytic Sulfur Conversion

ABSTRACT The spin‐state engineering of transition‐metal catalysts plays a decisive role in enhancing electrocatalytic activity in lithium‐sulfur batteries. While high/low‐spin transitions are accessible for 3 d 4 ‐3 d 7 ions in octahedral fields, Ni 2+ (3 d 8 ) has long been considered spin‐inert under such coordination. Herein, we demonstrate that ferromagnetic NiF 2 effectively circumvents this limitation through exchange‐mediated spin alignment. In contrast to antiferromagnetic NiO, the parallel spin ordering in NiF 2 generates a permanent magnetic moment and upshifts the d‐band center, thereby promoting the injection of spin‐polarized electrons into the antibonding π* orbital of S─S bonds in lithium polysulfides. This strong d‐π coupling significantly reduces the S─S bond order and facilitates sulfur reaction kinetics. As a result, Li‐S batteries with the NiF 2 catalyst deliver an initial capacity of 842.7 mAh g −1 at 1 C and exhibit exceptional cycling stability, with a capacity increase to 941.6 mAh g −1 after 500 cycles. Moreover, a high areal capacity of 7.2 mAh cm −2 is achieved under elevated sulfur loading (8 mg cm −2 ). This work breaks the conventional spin blockade in Ni 2+ catalysts and offers a strategic approach to spin‐level electrocatalyst design for efficient sulfur redox reactions.