Preparation And Application In Lithium-sulfur Batteries Of Sulfur Containing Polymers Grafted On Carbon Nanotubes Composites

The huge consumption of fossil energy and the increasingly serious environmental pollution make it an urgent demand for cleaner and more efficient energy storage systems.Traditional lithium ion batteries cannot meet the needs of high capacity density.As an emerging secondary battery system,lithium-sulfur(Li-S)batteries are recognized as the most promising candidates for next-generation high-capacity energy storage systems due to its advantages of high specific capacity,low cost,non-toxicity and environmental friendliness.Therefore,it has become a research hotspot in recent years.Despite these advantages,Li-S batteries still have many drawbacks.For example,the insulating nature of elemental sulfur results in slow redox kinetics and limits the practical discharge capacity.The "shuttle effect" of polysulfide in charge and discharge process leads to poor cycle life and Coulombic efficiency.The structural destruction of electrode can be caused by the volume expansion effect of the sulfur cathode.Considerable efforts have been exploited to combat these limitations,typically by combining sulfur with various materials.However,the practical performance cannot fully satisfy the practical application needs of Li-S batteries.Herein,we proposed a strategy to solve the above-mentioned problems of Li-S batteries by covalently grafting sulfur-containing polymers onto carbon nanotubes(CNTs).First,isopropenyl-modified carbon nanotubes(i.e.CNT-gIDBI)were obtained by covalent surface modification of the CNTs using 4aminobenzoic acid and 3-isopropenyl-?,?-dimethylbenzyl isocyanate(IDBI).Then,the in-situ polymerization of sulfur on the surface of CNTs was realized by the "inverse vulcanization" reaction with element-sulfur,rendering the sulfur copolymer covalently grafted on carbon nanotubes composite(i.e.CNT-gpoly(S-r-IDBI)).Finally,the as-prepared CNT-g-poly(S-r-IDBI)composite were used as the electroactive material for the cathode in Li-S batteries,showing significantly enhanced electrochemical performance.Electrochemical test results demonstrate that CNT-g-poly(S-r-IDBI)cathode shows lower polarization and faster Li+and electron transmission rate,leading to faster redox reaction kinetics.The high discharge specific capacity and excellent rate performance are achieved(initial discharge specific capacity up to 1368 mA h g-1 at 0.05 C and 601 mA h g-1 at 1 C),as well as more stable cycling performance(capacity decay rate is only 0.074%per cycle at 1 C for 500 cycles).The enhancement performance of Li-S batteries is due to the unique structure design of CNT-g-Poly(S-r-IDBI):the sulfur-containing polymers covalently grafted onto the surface of CNTs forming a uniform polymer layer,which is favor of charge transmission and thus speed up the reaction kinetics.Covalently grafting sulfur-containing polymers onto CNTs can greatly suppress the shuttle effect,so the cycling stability of Li-S batteries can be significantly improved.The polymer structure formed by covalent grafting can also withstand a certain volum expansion,which provides a guarantee for maintaining the structural integrity of the electrode.The covalent attachment strategy between the sulfur-containing copolymer and CNTs provides a new insight for the structural design of the cathode for Li-S batteries.