Synergistic Action Of Nano-carbon Materials And Metal Compounds And Their Application In Lithium-sulfur Batteries

Lithium-sulfur batteries are considered as one of the most valuable and promising energy storage devices because of their high theoretical specific capacity(1675 mAh·g^-1)and theoretical specific energy(2600 Wh·kg^-1).Its cathode active material,sulfur,has the advantages of large storage capacity,low price and environmental friendliness.However,due to a series of problems,such as poor conductivity of sulfur and its discharge end products,and“shuttle effect”caused by lithium polysulfides soluble in electrolyte,the capacity of lithium-sulfur batteries decays rapidly and the rate performance is poor,which seriously hinders the further development and application of lithium-sulfur batteries.In order to improve the electrical conductivity of sulfur cathode and mitigate the“shuttle effect”of lithium polysulfides,the composite of nano-carbon materials and metal oxygen?sulfur?compounds was designed as the carrier of sulfur.The synergistic effect of carbon materials and metal oxygen?sulfur?compounds was used to improve the energy storage performance of lithium-sulfur batteries.The main research contents are as follows:?1?The synergistic effect of SnS₂ and CNTs was designed to improve the energy storage performance of lithium sulfur batteries.Among them,SnS₂ chemical adsorption on lithium polysulfide can effectively alleviate the“shuttle effect”of lithium polysulfides,and the conductive network constructed by CNTs can improve the conductivity of the whole cathode.SnS₂/CNTs composite cathode material was prepared by one-step hydrothermal method and then melted with S to prepare SnS₂/CNTs/S composite cathode material.The results show that in SnS₂/CNTs/S,CNTs are interwoven outside the SnS₂ nanosheets,partially inserted in SnS₂,and S is evenly loaded on SnS₂/CNTs.At 0.1C,the initial discharge capacity was 1308.6 mAh·g^-1.After 100 cycles,the capacity was maintained at1002.3 mAh·g^-1,and the capacity retention rate was 76.6%.?2?The synergistic effect of molybdenum disulfide?MoS₂?and reduced graphene oxide?rGO?was designed to improve the electrochemical performance of lithium-sulfur batteries.Among them,the chemical adsorption of MoS₂ on lithium polysulfide can effectively alleviate the“shuttle effect”of lithium polysulfides,and the conductive network composed of rGO can improve the conductivity of sulfur cathode.MoS₂@rGO composite was prepared by in situ growth of MoS₂ on graphene oxide?GO?by hydrothermal method.MoS₂@rGO/S composite cathode material was prepared by melting MoS₂@rGO/S with S.The results show that in the prepared material MoS₂@rGO/S,MoS₂ grows uniformly on the rGO chip and S distributes uniformly in the material MoS₂@rGO.At 0.1C,the first initial capacity is 1243.3mAh·g^-1.After 200 cycles at 0.5C,the discharge capacity is 848.4 mAh·g^-1,with an average capacity decay rate of 0.09%.?3?The synergistic effects of SnO₂,rGO and CNTs were designed to further improve the electrochemical performance of lithium sulfur batteries.Among them,SnO₂ can limit the“shuttle effect”of lithium polysulfides by chemical adsorption,and the conductive network composed of rGO and CNTs can improve the conductive power of the cathode.SnO₂@rGO was synthesized by in situ hydrothermal method combined with high temperature treatment.CNTs were introduced by mechanical ball milling and then fused with S to prepare SnO₂@rGO/CNTs/S composite cathode material.The results show that the SnO₂@rGO/CNTs/S nanoparticles are uniformly distributed on the rGO lamellae,and CNTs are interpenetrated in the prepared SnO₂@rGO/CNTs.S is uniformly loaded on the SnO₂@rGO/CNTs.At 0.1C,the initial discharge capacity is 1205.4 mAh·g^-1.After 50 cycles,the capacity is maintained at 958.6 mAh·g^-1,and the capacity retention rate is 79.5%.?4?The synergistic effects of MoS₂,rGO and CNTS were designed to further improve the electrochemical performance of lithium-sulfur batteries.Among them,MoS₂ restricts the“shuttle effect”of lithium polysulfide by chemical adsorption,and the three-dimensional conductive network composed of rGO and CNTs improves the conductivity of sulfur cathode.With the help of hexadecyl trimethyl ammonium bromide?CTAB?,a three-dimensional framework was constructed by the Coulomb interaction between the positively charged CNTs and the negatively charged GO.MoS₂@rGO/CNTs composites were prepared by hydrothermal method,and the positive MoS₂@rGO/CNTs/S was prepared by compounding them with S.The results show that in the prepared MoS₂@rGO/CNTs/S material,the interweaving between rGO and CNTs constitutes a three-dimensional network.MoS₂ is evenly distributed in the network,and S is evenly distributed in the surface and hole of the material MoS₂@rGO/CNTs.At 0.1C,the initial discharge capacity is 1417.8 mAh·g^-1?At0.5C,the initial discharge capacity is 1167.3 mAh·g^-1,the discharge capacity is 962.7mAh·g^-1 after 200 cycles.