Covalent Confinement of Sulfur Copolymers onto Graphene Sheets Affords Ultrastable Lithium–Sulfur Batteries with Fast Cathode Kinetics
2019
Ma, Junpeng | Fan, Jingbiao | Chen, Shang | Yang, Xinyue | Hui, Kwun Nam | Zhang, Hongwen | Bielawski, Christopher W. | Geng, Jianxin
Lithium–sulfur (Li–S) batteries have received significant attention due to the high theoretical specific capacity of sulfur (1675 mA h g–¹). However, the practical applications are often handicapped by sluggish electrochemical kinetics and the “shuttle effect” of electrochemical intermediate polysulfides. Herein, we propose an in-situ copolymerization strategy for covalently confining a sulfur-containing copolymer onto reduced graphene oxide (RGO) to overcome the aforementioned challenges. The copolymerization was performed by heating elemental sulfur and isopropenylphenyl-functionalized RGO to afford a sulfur-containing copolymer, that is, RGO-g-poly(S-r-IDBI), which is featured by a high sulfur content and uniform distribution of the poly(S-r-IDBI) on RGO sheets. The covalent confinement of poly(S-r-IDBI) onto RGO sheets not only enhances the Li⁺ diffusion coefficients by nearly 1 order of magnitude, but also improves the mechanical properties of the cathodes and suppresses the shuttle effect of polysulfides. As a result, the RGO-g-poly(S-r-IDBI) cathode exhibits an enhanced sulfur utilization rate (10% higher than that of an elemental sulfur cathode at 0.1C), an improved rate capacity (688 mA h g–¹ for the RGO-g-poly(S-r-IDBI) cathode vs 400 mA h g–¹ for an elemental sulfur cathode at 1C), and a high cycling stability (a capacity decay of 0.021% per cycle, less than one-tenth of that measured for an elemental sulfur cathode).
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