Covalent bond glued sulfur nanosheet-based cathode integration for long-cycle-life Li-S batteries

High-capacity electrochemical active material-based electrodes for lithium ion batteries (LIBs), such as sulfur (S), always face the collapse of the electrode due to the big volume change during insertion of the lithium (Li) ion and therefore shorten the cycle life of the cells. Herein, a series of design from the viewpoint of both individual components and the entire cathode in lithium-sulfur (Li-S) cell was introduced aiming at addressing the issues of poor conductivity, leakage of intermediate polysulphides, and large volumetric expansion upon insertion of the Li ion. In the designed electrode, polydopamine (PD)-coated S nanosheets (NSs) were used as active materials, carboxylic acid functionalized multiwall carbon nanotube (MWCNT-COOH) as conductive additives, and poly(acrylic acid) (PAA) as binders. Far different from the traditional hydrogen bond and/or van der Waals force linked electrodes, stronger covalent bonds formed by cross-linking of PD/MWCNT-COOH and PD/PAA into amide bonds, respectively, were built throughout the whole electrode to firmly integrate all of the individual components in the electrode together. As a result, the cathode demonstrated excellent cyclic performance with a charge capacity of 640 mAh/g after 500 cycles at a current density of 1 A/g. Besides, the charge capacity decay after 500 cycles is as small as 0.021% per cycle, which represents the best capacity retention so far.