Assessments on Nafion Modifications of Lithium-Sulfur Batteries--Effects at Different Cell Positions: Sulfur Cathode, Separator and Lithium Metal Anode

Abstract

The advantages of high specific energy and low cost of sulfur have recently brought rechargeable lithium-sulfur (Li-S) batteries to the spotlight. Yet shuttle effects, mainly caused by polysulfide migration in the electrolyte, remain major technical obstacles to perfect Columbic efficiency and long-term cycle life. Among all the polysulfide trapping methods, the cation-selective Nafion film stands out as a promising physical barrier to the anionic polysulfide species. In this study, a special device has been set up to directly observe the in-operando phenomena of Li-S batteries with various modified components. Effective Nafion modifications of the sulfur cathode, the polypropylene separator (Celgrad 2400) and the lithium (Li) metal anode are compared respectively. A high sulfur-content sulfur/carbon (S/C) nanocomposite with 74 wt% sulfur in the porous carbon (Pearl 2000) matrix is employed as the cathode material. The sulfur cathode is modified by either coating the S/C nanocomposite powder with Nafion or incorporating Nafion into the binder material. Solution casting method is utilized to modify the porous separator and the metallic Li anode surface. The underneath figure shows inhibited polysulfide passage through a Nafion coated separator. The in-operando observations render complementary explanations on the electrochemical performances of batteries with different modified components and give insights to the cell designs of Li-S batteries. Figure 1