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

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.