Ultrathin NiO/Ni₃S₂ Heterostructure as Electrocatalyst for Accelerated Polysulfide Conversion in Lithium–Sulfur Batteries

The practical application of Lithium–Sulfur batteries largely depends on highly efficient utilization and conversion of sulfur under the realistic condition of high-sulfur content and low electrolyte/sulfur ratio. Rational design of heterostructure electrocatalysts with abundant active sites and strong interfacial electronic interactions is a promising but still challenging strategy for preventing shuttling of polysulfides in lithium–sulfur batteries. Herein, ultrathin nonlayered NiO/Ni₃S₂ heterostructure nanosheets are developed through topochemical transformation of layered Ni(OH)₂ templates to improve the utilization of sulfur and facilitate stable cycling of batteries. As a multifunction catalyst, NiO/Ni₃S₂ not only enhances the adsorption of polysulfides and shorten the transport path of Li ions and electrons but also promotes the Li₂S formation and transformation, which are verified by both in-situ Raman spectroscopy and electrochemical investigations. Thus, the cell with NiO/Ni₃S₂ as electrocatalyst delivers an area capacity of 4.8 mAh cm⁻² under the high sulfur loading (6 mg cm⁻²) and low electrolyte/sulfur ratio (4.3 μL mg⁻¹). The strategy can be extended to 2D Ni foil, demonstrating its prospects in the construction of electrodes with high gravimetric/volumetric energy densities. The designed electrocatalyst of ultrathin nonlayered heterostructure will shed light on achieving high energy density lithium–sulfur batteries.