A separator-based lithium polysulfide recirculator for high-loading and high-performance Li–S batteries

Lithium–sulfur (Li–S) batteries are promising for the next-generation energy storage devices due to their high theoretical energy density and low cost. However, the shuttle effect and the passive layer between the separator and electrode still affect the cycling stability and coulombic efficiency seriously. Herein, we develop a 10 μm-thick rGO (reduced graphene oxide) and molybdenum phosphide (MoP) composite coating layer on a Celgard separator to improve the electrochemical performance of Li–S batteries. The introduction of such a MoP/rGO coating layer on the separator not only impedes the diffusion of polysulfides to the anode but also improves the sulfur utilization. In particular, the 10 nm MoP nanoparticles are very efficient for the polysulfide adsorption. Compared to the pristine Celgard separator, superior electrochemical performance is obtained in both coin cells and pouch cells with the MoP/rGO coated separator. High areal capacity (∼3 mA h cm−2), good rate performance, and long cycle life (300 cycles) are attained under a sulfur loading of 3.88 mg cm−2. The capacity decay rate is as low as 0.045% per cycle over 300 cycles. In addition, the pouch cells made by the modified separator with a high sulfur loading of 4.6 mg cm−2 achieve good electrochemical performance. At 0.1C, the initial discharge capacity is 1083 mA h g−1, and still remains at 759 mA h g−1 after 120 cycles. The result reveals the potential practical use of this MoP/rGO coated separator for Li–S batteries.