Bridge-bond tailored binuclear Cu spatial proximity steers homogeneous catalysis in Li-S batteries

Metal-organic small molecules have recently emerged as homogeneous catalysts, presenting a new paradigm for catalysis in lithium-sulfur (Li-S) batteries. Precise tailoring of molecular configurations is crucial for elevating their catalytic activity in facilitating the redox reactions in Li-S chemistry. In this study, paired oxygen-bridge and chlorine-bridge bonds are precisely incorporated into a binuclear copper complex (Cu-2-B) to generate a homogeneous catalyst in situ in the electrolyte. This versatile molecular engineering modulation effectively reduces the proximal distance between adjacent copper atoms in the complex molecule from 4.7 to 3.2 Å, leading to an optimized catalyst configuration. Using synchrotron radiation X-ray three-dimensional nano-computed tomography, the Li₂S nucleation and growth at a high-resolution and spatial-distribution level were visualized. It is found that the introduction of an oxygen bridge into Cu-2-B enables the Li₂S deposition that is high in mass, small in size, and uniform in distribution. By combining neutron imaging and small-angle neutron scattering techniques, surface and internal deposited lithium are qualitatively and quantitatively deciphered. It is confirmed that Cu-2-B can guide the lithium stripping/plating behaviors, resulting in a robust lithium working surface and inner architecture. Benefiting from the enhanced homogeneous catalytic effect of the saturated Cu-2-B, the Li-S cell achieves stable cycling over a wide temperature range of 273-328 K. Impressively, the Cu-2-B endows a 1.1-g-sulfur pouch cell with a gravimetric energy density of 345.3 Wh kg^-1, indicating its great potential for future power supply implementations.