Preparation Of Nanosheets Filled Hollow Carbon Sphere And Its Lithium Sulfur Battery Performances

Lithium sulfur battery has higher theoretical specific capacity and higher theoretical specific energy,in addition,sulfur is cheap,non-toxic and environmental friendly.However,there are still many problems hindering its commercial development:The poor conductivity of sulfur and the intermediate during discharge process would lead to the low utilization of active substances.The"shuttle effect"would reduce the specific capacity and decrease the cycle life.The volume expansion is about 80%due to density difference when sulfur is reduced to lithium sulfide would cause the collapse of the cathode structure.The growth of lithium dendrites would rupture the membrane and short-circuit the battery.In view of the above problems,this thesis deals with the design and preparation of hollow carbon sphere filled with porous nanosheets as an efficient sulfur hosts for lithium–sulfur batteries.The main contents are as follows:?1?Preparation of nanosheets filled hollow carbon spheres.A kind of hollow carbon spheres filled with porous carbon nanosheets was prepared by Nitrogen-rich dopamine as carbon source,nano-CaCO₃ with a size of 50-80 nm as a template and functional activator.High levels of nitrogen increase chemical adsorption of polysulfide and the excellent conductivity of carbon materials neutralizes the poor conductivity of sulfur.In addition,the hollow ball filled with porous carbon nanosheets not only has a larger specific surface area?166.85 m²/g?,but also the rich mesoporous structure generated by the activation of CO₂ gas,which is efficient to the physical entrapment of polysulfide and increased the cycle stability of the battery.The electrode with sulfur content 68.12%gain excellent battery performance.The specific capacity of the first cycle at 0.1 C was 1516 mAh/g and maintained a 86.45%capacity at 0.5 C after 250 cycles.?2?The nickel doped nanosheets filled hollow spheres.The weak van der Waals interaction between nonpolar carbon and polar polysulfide species can't effectively suppress the shuttle effect of polysulfide during long-term cycling,which results in the loss of reactive intermediates.In addition,the high nucleation barrier also impedes the efficient interfacial redox activity of sulfur species on carbon.Therefore we used the atomic nickel as an efficient electrocatalyst in sulfur cathodes for super lithium-sulfur batteries.The results show that the hollow ball filled with porous carbon nanosheets material doped with nickel atoms have the best electrochemical properties when the theoretical content of nickel is 9.5%.With a high sulfur content of 70.57%,the Ni@F-HCS/S electrode show a specific capacity of 1491.8mAh/g at 0.1 C,even at the high current density of 2 C,the specific capacity remain 492.2mAh/g after 980 cycles and the average capacity loss was only 0.025%.The structure of the hollow carbon spheres filled with porous carbon nanosheets designed in this thesis has a good electronic transmission channel,it can improve the conductive grid of sulfur electrodes and increase the utilization rate of active materials.Furthermore,Ni@F-HCS material has a larger specific surface area,it can provide more adsorption sites for polysulfide.What's more the metal nickel as efficient sulfur host meet the demand for both sufficient surface reaction and efficient surface conversion.It not only improves the specific capacity of the battery,but also solves the problem of shuttle effect fundamentally.