Asymmetric cobalt sites induced low-spin state for enhanced redox kinetics in lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries have drawn widespread attention for their exceptionally high theoretical energy density, yet their progress remains impeded by sluggish reaction kinetics and the notorious polysulfide-shuttle effect. Herein, we strategically construct a well-defined MXene-interwoven CoO/Mo2C heterostructure uniformly anchored on electrospun carbon nanofibers (MX-CoO/Mo2C@CNFs) through an innovative electrospinning-MXene hybridization approach, serving as an advanced freestanding cathode for Li–S batteries. The introduced Co–O–Mo linkages disrupt native Co–O–Co chains at the interface, lowering crystal field symmetry, thereby reducing cobalt’s spin state and decreasing eg orbital occupancy. Theoretical calculations reveal that Mo2C incorporation asymmetrically redistributes electron density, modulating the d-p orbital hybridization of CoO with sulfur intermediates to accelerate charge transfer and optimize adsorption energetics. Employing Li2S6 as the sulfur source, in situ Raman spectroscopy reveals the preferential disproportionation of Li2S6 into Li2S4 and Li2S8 during discharge, while the low-spin cobalt centers effectively mitigate polysulfide permeation through strong chemisorption. Consequently, the electrode delivers an exceptional initial capacity of 1267.9 mAh g−1 at 0.2 C and maintains 787.7 mAh g−1 after 300 cycles at 1 C with an ultralow capacity decay rate of merely 0.062% per cycle. The design of asymmetric coordination-induced low-spin state establishes a new paradigm for efficient electrocatalysis in Li–S batteries.