Kinetic Acceleration of Lithium Polysulfide Conversion via a Copper-Iridium Alloying Catalytic Strategy in Li-S Batteries.

To solve the shuttle effect of soluble lithium polysulfides (LiPSs), a porous N-doped carbon-supported copper-iridium alloy catalyst composite (CuIr/NC) has been synthesized and served as a modified cathode sulfur host for lithium-sulfur batteries (LSBs). The metal-organic framework-derived calcined carbon frameworks build efficient conductive channels for fast ion/electron transport. Furthermore, alloying noble metals Ir with thiophilic metal Cu provides abundant active sites to effectively capture LiPSs and accelerate the catalytic conversion process, originating from modulating the surface electronic structure of the metal Cu by introducing Ir atoms to affect the 3d-orbital distribution. All of the above are strongly supported by a range of characterization studies and density functional theory calculations. Benefiting from the above advantages, the LSBs generally show satisfactory cycling performance. Apart from exhibiting a terrific initial specific capacity of 1288 mA h g-1 at 0.2 C, they can also keep long-term cycling stability under a high current density up to 5 C together with a slow specific capacity decay ratio (0.033%) per cycle after 1000 cycles. In addition, it is worth mentioning that a high areal capacity (4.7 mA h cm-2) with a low E/S ratio (6.2 μL mg-1) could still be accomplished at higher sulfur loading (4.3 mg cm-2).