Dual-Mediation pathways promote redox kinetics for High-Loading Lithium-Sulfur batteries under lean electrolyte

The high energy density (2500 Wh kg-1) makes that lithium-sulfur batteries (LSBs) have a great potential in energy storages. However, the practical application of LSBs is severely hampered by several inherent problems, including the sluggish sulfur redox kinetics, the shuttling of lithium polysulfides (LiPSs) and poor electronic conductivity. Although heterogeneous or homogeneous mediators could improve the cycling performance of LSBs to a certain extent, single mediators could not completely promote sulfur conversions, especially under high sulfur loading and lean electrolyte. Herein, dual-mediator systems consist of heterogeneous and homogeneous mediators that are introduced to address the above issues. Density functional theory (DFT) calculations and electrochemical analysis indicate that CoSe nanoparticles embedded in urchin-like nitrogen-doped porous carbon with in-situ growth of CNTs (CoSe@CNTs) as heterogeneous mediators and soluble CoCp2 as homogeneous mediators could effectively accelerate the bidirectional conversion kinetics of liquid LiPSs <-> solid Li2S through the synergistic effect. As a consequence, the cell with dual-mediators delivers a high initial specific capacity of 1005 mAh/g with a low attenuation rate of 0.045 % per cycle at a current density of 1.0C under sulfur loading of 2.8 mg cm-2 after 800cycles. Importantly, it still maintains a high areal capacity of 6.53 mAh cm-2 under lower electrolyte/sulfur ratio (E/S, 4.2 mu L mg -1) and higher sulfur loading of 7.3 mg cm-2 over 100cycles at 0.1C.