Preparation And Lithium~-/sodium~- Storage Performances Of Ultrasmall Nanodots/rGO Derived From Ldh Precursors/GO

The development of efficient energy storage systems has recently become a research focus in the current energy field with the continuous development of renewable energy technologies.Lithium-ion batteries(LIBs)have been widely used in various energy storage systems due to their high energy density and good cycle life.However,the excessive consumption of lithium resources,insufficient natural abundance,and,increasing cost have limited the application in large-scale energy storage systems.Sodium-ion batteries(SIBs)are expected to be potential for the large-scale energy storage systems due to their rich sodium resources and low cost,as well as relatively stable energy storage capabilities.Therefore,it is of great imprtance to develop high-performance lithium/sodium-ion battery anode materials to further improve battery performances to meet the needs for high-efficiency energy storage systems.Conversion type/alloy type materials are promising anode materials for lithium/sodium ion batteries due to their good energy storage mechanism and higher theoretical capacity.In order to improve the poor cycle performance of conversion-type/alloy-type materials during charging and discharging,the currently used method is to synthesize composite materials combined with carbon materials.However,their electrochemical performances are not still satisfactorry mainly to the aggeagation of active nanomaterials.In this thesis,ultra-small active nanodots/mesoporous reduced graphene oxide composite nanomaterials(SnO2@N-rGO and NiS2@N,S-rGO)are prepared by using hydrothermal synthesis,calcination and slective acid etching treatments.Those two composite materials were well characterized,and electrochemical performances of lithium/sodium ion half-cells were tested.The following two parts are presented in the thesis.(1)SnO2@N-rGO anode nanomaterial:We obtained the CoAlSn-LDH precursor(CoAlSn-LDH/GO)uniformly supported on graphene oxide through the hydrothermal reaction,followed by calcination and selective acid etching.With the help of the CoAlSn-LDH layer plate lattice trapping effect,the ultra-small SnO2 nanodots load on the N-doped mesoporous rGO composite material were obtained.The composite materials were assembled into lithium/sodium ion half-cells for electrochemical performance test:as a lithium ion battery,at 0.1 A g-1,a reversible capacity of 1146.2 mAh g-1 can be obtain at 100 cycles;When used in sodium ion batteries,it can maintain a reversible capacity of 280.1 mAh g-1 even after 200 cycles.Compared with the control N-rGO electrode,the composite negative electrode has greatly enhanced electrochemical performance.The improvement of its electrochemical performance is mainly due to the active material SnO2 nanodots loaded and highly uniformly dispersed.(2)NiS2@N,S-rGO anode nanomaterial:Sodium dodecyl sulfate ion DS-and(NiEDTA)2-ions co-interclated/MgAl-LDH precursor(DS-/NiEDTA2--MgAl-LDH/GO)was uniformly loaded on graphene oxide through hydrothermal reaction,followed by calcination and selective acid etching.The NiS2 nanodots@N,S-rGO exhibited a reversible capacity of 801.2 mAh g-1 at 100 cycles in 0.1 A g-1 when used anode nanomatrials for LIBs.The composite also delivered a reversible capacity of 207.7 mAh g-1 at 200 cycles in 0.1 A g-1.Both values are significantly higher than those of the N,S-rGO electrode without NiS2 nanodots.The excellent electrochemical performance of the composite material is mainly attributed to the low-content active material NiS2 and uniformly dispersion in the N,S co-doped mesoporous reduced graphene oxide(rGO),which is achieved by virtue of the interlayer confinement between the interlayere galleries of LDH host/guest precursors.