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

Abstract

The catalytic activation of the Li-S reaction is fundamental to maximize the capacity and stability of Li-S batteries (LSBs). Current research on Li-S catalysts mainly focuses on optimizing the energy levels to promote adsorption and catalytic conversion, 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. This high spin configuration raises the electronic energy level and activates the electronic state. This accelerates the charge transfer and optimizes the adsorption energy, lowering the reaction energy barrier of the polysulfides conversion. 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 high sulfur loadings (6.2 mg·cm⁻²), high initial capacities of 1173 mAh·g⁻¹ (7.27 mAh·cm⁻²) are measured at 0.1C, and 1058 mAh·g⁻¹ is retained after 300 cycles.

Keywords: hollow particle; homologous heterostructure; lithium polysulfides; lithium‐sulfur battery; nickel selenide; nickel sulfide; spin state.