Electronic Spin Alignment within Homologous NiS2/NiSe2 Heterostructures to Promote Sulfur Redox Kinetics in Lithium-Sulfur Batteries.

The catalytic activation of the Li-S reaction is fundamental to maximizing the capacity and stability of Li-S batteries (LSBs) by blocking the migration of lithium polysulfides (LiPSs) and enhancing sulfur utilization. Current research on Li-S catalysts mainly focuses on the optimization of the energy levels to promote adsorption and catalytic conversion of LiPSs, while frequently overlooking the electronic spin state influence on charge transfer and orbital interactions. Here, hollow NiS2/NiSe2 heterostructures encapsulated in a nitrogen-doped carbon matrix (NiS2/NiSe2@NC) are synthesized and used as a catalytic additive in sulfur cathodes. The NiS2/NiSe2 heterostructure promotes the spin splitting of the 3d orbital, driving the Ni3+ transformation from low to high spin, and thereby generating additional unpaired electrons. The high spin configuration orbit of NiS2/NiSe2@NC raises the electronic energy level and activates the electronic state. X-ray absorption near-edge structure, extended X-ray absorption fine structure spectra, and density functional theory results show that the activated electronic state accelerates the charge transfer and the regulated d-band center optimizes the adsorption energy, lowering the reaction energy barrier of the LiPSs conversion rate-determining step. In situ X-ray diffraction analyses further reveal that the spin polarization associated with the formed heterostructures can accelerate the sulfur conversion kinetics. Benefiting from these characteristics, LSBs based on NiS2/NiSe2@NC/S cathodes exhibit high initial capacity (1458 mAh·g-1 at 0.1C), excellent rate capability (572 mAh·g-1 at 5C), and stable cycling with an average capacity decay rate of only 0.025% per cycle at 1C during 500 cycles. Even at a high sulfur loading (6.2 mg·cm-2), a high initial capacity of 1173 mAh·g-1 (7.27 mAh·cm-2) is measured at 0.1C, and 1058 mAh·g-1 is retained after 300 cycles. This work not only provides an effective strategy for improving the electrochemical performance of LSBs but also shows new insights into the role of spin polarization in the field of electrocatalysis. This article is protected by copyright. All rights reserved.