Advanced separator containing metallic cobalt-molybdenum carbide@ 3D porous carbon for lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries have many good prospects for electrochemical energy storage, but they still face some important challenges, such as lithium polysulfide shuttles, which leads to irreversible loss of active materials. In this work, for the first time, metallic cobalt-molybdenum carbide wrapped within 3D porous carbon, served as a functional layer (MoCo@CHS3) on the separator of high-performance Li-S batteries. The MoCo@CHS3 obtained through the sol-gel method composite renders superior cycling performance and structural stability. Electrochemical performance confirms that the 3D porous framework with large specific surface area and pore volume can reuse the sulfur, improve conductivity, and effectively suppress the shuttling problem on account of the polysulfide capture capability. Additionally, the MoCo@CHS3 electrocatalyst provides multiple adsorption sites to capture polysulfides and promote redox reactions of polysulfides, which limit the shuttle of polysulfides. Consequently, the Li-S battery with MoCo@CHS3-PP coated separator shows an excellent capacity of 1026.7 mAh g−1 at 1 C (sulfur load, 1.9–2.2 mg cm−2), and excellent cycle stability (after 600 cycles, the capacity decay rate was only 0.066%). A high discharge specific capacity of 1022.4 mAh g−1 at 0.2 C is obtained after activation and it remains at 780.7 mAh g−1 after 200 cycles when the sulfur load is 5.0 mg cm−2. The separators modified by MoCo@CHS3 have excellent application prospects in Li-S batteries.