Sulfur impregnated in a mesoporous covalent organic framework for high performance lithium–sulfur batteries

Abstract

Undesirable cycling performance has been considered as the main bottleneck that has hindered the practical application of lithium–sulfur (Li–S) batteries, which mainly results from soluble polysulfides shuttling between the anode and the cathode (so-called shuttle effect). To solve this problem effectively, a covalent organic framework (COF), Azo-COF, with a regular pore distribution of 2.6 nm was prepared as the host for sulfur. Such small mesopores can not only confine the sulfur well in the nanopores but also supply Li⁺ with one-dimension (1D) transmission channels. Benefiting from this concept, even without a LiNO₃ additive, the Li–S battery assembly with a S/Azo-COF cathode presented a high stable capacity of 741 mA h g⁻¹ after 100 cycles while delivering a high initial discharge capacity of nearly 1536 mA h g⁻¹ at 0.1C (1C = 1672 mA g⁻¹). Additionally, when the capacity rate (C-rate) was increased to 2C, a high discharge capacity of 770 mA h g⁻¹ can be still achieved after 20 cycles, proving excellent C-rate performance.