Synthesis Of Carbon-based Composite Loaded With NiS₂ For Modified Separator Of Lithium-Sulfur Batteries

Lithium sulfur(Li-S)batteries are expected to be the next-generation energy-storage system batteries due to its high theoretical energy density(2600 Wh kg-1),low cost and environmental friendliness.However,the commercialization of Li-S batteries have been constrained by some key issues,the most severe ones are the shuttle effect of the lithium poly sulfides(Li2Sx,4<x<8)and lithium dendrite growth,which result in faster battery capacity decay,inferior cycle stability and serious safety issues.The separator serves as an important part and its property has a crucial impact on the electrochemical performance of lithium-sulfur batteries.Aiming to address the above issues,two novel modified separators were designed and prepared.Their effects on inhibiting lithium polysulfides(LiPSs)shuttle and improving readox kinetics have been investigated in this dissertation.NiS2 nanospheres with uniform particle size were successfully prepared by hydrothermal method,and then loaded on nitrogen-doped reduced graphene oxide(N-rGO)to obtain the NiS2@N-rGO composite serving as the coating layer of separator for Li-S battery.Physical characterizations show that the NiS2 content of the as-prepared composite is 15%,the cell equipped with the NiS2@N-rGO modified separator manifests the ultralow capacity decay of 0.0578%at 2 C after 1000 cycles.The improved performance of cell originates from the synergistic catalysis of NiS2 and N-rGO,which could promote the fast and efficient conversion of LiPSs to Li2S2/Li2S.Taking the inherent defects of rGO with strong ?-? stacking and low polarity into account,the lithiated CNTs serving as mechanical underpinning were introduced to obtain an interlacing 3D structure rGO/CNTs-Li,and NiS2 nanospheres as chemosorbent/catalyst were infixed into the carbon-based 3D structure to attain the NiS2@rGO/CNTs-Li composite.The rGO/CNTs-Li can serves as the conductive skeleton to facilitate the fast electron/ion transfer,the binding energy between NiS2 and LiPSs were calculated by density functional theory(DFT)calculations to further reveal the chemical adsorption of NiS2@rGO/CNTs-Li in improving the cycling performance of lithium-sulfur batteries.The cell with the NiS2@rGO/CNTs-Li modified separator exhibits excellent long-term cycling stability up to 600 cycles with a low decay rate of 0.071%at 2.0 C.