| Lithium-sulfur（Li-S）batteries are one of great candidates for next-generation energy storage because of their high energy density and high theoretical specific capacity.However,the application of Li–S batteries is still challenged by the following problems: the low electrical conductivity of sulfur and lithium sulfide,large volume change during polysulfide conversion and the shuttle effect of intermediate lithium polysulfides.Modification of the sulfur cathode can effectively solve the problems above.To suppressing the shuttle effect,a series of sulfurbased materials have been prepared,making full use of the physical or chemical properties to reduce the dissolution and shuttle of polysulfides and realize the improvement of electrochemical performances.The main research contents and results are as follows:1)Hollow porous carbon spheres（HPCS）were prepared by the template method and used as sulfur host.According to the results,the high conductivity of HPCSs improves the conductivity of the system.The hollow porous structure of HPCSs can provide space ensure the high sulfur load（80.5%）and effectivly relieve the volume expansion during cycling.The structure can also physically limit the dissolution and shuttle of polysulfides.The initial capacity of HPCSs/S electrode is 1320.8 m Ah g-1 at 0.05 C.However,the physical confinement ability of nonpolar HPCSs to limit polysulfides is so weak that the average capacity decay rate per cycle of the cathode is up to 0.209% after 500 cycles at 1 C.2)The m-Ti3C2 and d-Ti3C2 was prepared by etching Ti3 Al C2 with lithium fluoride and hydrochloric acid,and used as a sulfur host.According to the results,the two-dimensional material characteristics and polar surface of d-Ti3C2 can chemisorb lithium polysulfides,showing better cycling stability than HPCSs/S positive electrode.The d-Ti3C2 has a higer specific surface area（20.0 m2 g-1）and sulfur load（71.2%）than that of m-Ti3C2,which can provide more chemical adsorption sites,enhance the adsorption of lithium polysulfides and suppress the shuttle effect.The initial capacity of d-Ti3C2/S electrode is 1147.1 m Ah g-1 at 0.05 C while d-Ti3C2 is easy to collapse during cycling.After 500 cycles at 1 C,the average capacity decay of d-Ti3C2/S electroderate is 0.137% per cycle.3)HPCSs@d-Ti3C2 composite was synthesized by electrostatic self-assembly and used as sulfur host.According to the results,HPCSs@d-Ti3C2 has a sandwich-like structure,d-Ti3C2 nanosheets construct a cross-link conductive network skeleton,HPCSs are fixed closely on double sides of the skeleton.d-Ti3C2 can inhibit the reunion of HPCSs,while HPCSs can prevent d-Ti3C2 from collapsing during cycling,ensuring the structural stability.HPCSs@d-Ti3C2 has large specific surface area（177.0 m2g-1）and sulfur load（76.5%）.The polar d-Ti3C2 can chemisorb polysulfides and cooperate with the physical limitation of HPCSs to suppress the shuttle effect and volume change during cycling,improving the cycling stability of lithium-sulfur batteries.The initial capacity of HPCSs@d-Ti3C2/S electrode is as high as 1397.5 m Ah g-1 at 0.05 C,and the average capacity decay rate per cycle is as low as 0.069% after 500 cycles at 1 C.The HPCSs@d-Ti3C2/S electrode exhibits satisfying sulfur utilization rate,rate performance and cycling stability with physical and chemical synergistic adsorption effect. |
