Impregnation of sulfur into a 2D pyrene-based covalent organic framework for high-rate lithium–sulfur batteries

Abstract

Two-dimensional covalent organic frameworks (2D COFs) have recently attracted increasing attention in energy storage devices. Herein, by loading 70 wt% sulfur into a pyrene-based 2D COF (Py-COF), we succeeded in the construction of lithium–sulfur (Li–S) batteries with high-rate capacity and long-term stability. The Py-COF/S cathode can deliver a reversible capacity of 481.2 mA h g⁻¹ for up to 550 cycles at 5.0C (1C = 1680 mA g⁻¹), which is 73.8% of the initial capacity with a decay rate of 0.048% per cycle. This is a benchmark among all reported COF-based Li–S batteries, and more impressively, even beyond the performances of some porous carbon-based sulfur host electrodes. Specifically, by using commercially available porous carbon BP2000 as the sulfur host under the same conditions, the thus-prepared electrode can only exhibit a reversible capacity of 265 mA h g⁻¹ after 220 cycles at 5.0C, much lower than that of the Py-COF/S electrode. According to cyclic voltammetry analysis, this high performance could be attributed to the fast lithium ion transport in the pores of Py-COF, especially at a high rate. These results clearly demonstrate that it is reasonable to design a 2D COF sulfur host for high performance Li–S batteries.