In situ composition of Thienothiophene-based covalent organic framework on carbon nanotube as a host for high performance Li-S batteries

Lithium-sulfur batteries (LSBs) is a promising secondary battery system with high energy density and environment-friendly characteristics, however, the severe "shuttle effect" and poor conductivity usually lead to short service life and low initial capacity. Carbon Nanotubes (CNTs) with excellent conductivity and large quantity of cavities are promising host materials, whereas, the weak interaction between CNTs and polysulfides usually leads to serious shuttle effect in charge/discharge processes. Herein, thienothiophene-based covalent organic framework is uniformly wrapped on the outer surface of CNTs to form a nanocomposite TT-BOST@CNT. It is observed that the coexistence of the electron-rich S, O and the electron-deficient B atoms enables the effective adsorption of both Li+ and Sx2- in lithium polysulfides (LiPSs). Studies reveal that the B, O and S atoms endow the nanocomposite with good catalysis ability, whereby, conversion of the insoluble long-chain polysulfides to the soluble short-chain polysulfides is accelerated. Consequently, the TT-BOST@CNT/S cathode displays outstanding electrochemical performance, with a high discharge specific capacity of 1545 mAh g-1 at 0.2 C and a small attenuation rate of 0.035% per cycle in 1000 cycles at 1 C.