| Since the 21st century,economic development and social progress continue to promote human's demand for energy.Lithium-ion batteris(LIBs)have been widely used in many fields because of its advantages such as light weight,small size,high voltage,high specific energy,wide operating temperature range,specific power,long storage time,no memory effect,and no pollution.While the successful fabrication of LIBs depends strongly on the choice of nanomaterials with outstanding lithium storage properties.However,current LIBs have low theoretical capacity,serious volume effect,bad cycling performance and other shortcomings,which heavily limit their commercial applications.Therefore,the best effective way to solve this problem is to increase the conductivity of electrode substrate.In this thesis,different kinds of transition metal oxide and sulfide doped three dimensional(3D)macroporous graphene composite were prepared as cathodic materials of LIBs by one-step hydrothermal method.The lithium storage properties of the composite materials were studied in detail.The detailed study are as following:(1)Using cobalt acetate as cobalt source,lithium hydroxide as precipitant,water as solvent,and 3D macroporous graphene as template material,cobalt monoxide(CoO)/3D macroporous graphene composite materials were prepared by simple stirring and high temperature calcination.These composite materials was characterized with scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD)analysis,and X-ray photoelectron microscopy(XPS),and directly applied to the negative electrode material of LIBs.The electrochemical test indicates that electrical capacity of the resultant LIBs can remain at 1160 mAh g-1 when the current density is 100 mA g-1 and the cycle charge and discharge are 100 cycles,suggesting good cycle stability and excellent reversibility.When the current density increased to 4800 mA g-1,its capacitance still maintained at 200 mAh g-1,showing better rate performance.(2)The sea urchin bismuth sulfide(Bi2S3)/3D macroporous graphene composite material was prepared by the simple hydrothermal method using bismuth nitrate as bismuth source,sulfur urea as sulfur source,trimellitic acid as binder,cetyltrimethylammonium bromide as surfactant,secondary distilled water as solvent,and 3D macroporous graphene as template material.The SEM,TEM,and XRD characterizations show that the prepared Bi2S3 has uniform morphology and has successfully been loaded into the pores structure of 3D macroporous graphene.Compared with single Bi2S3,the Bi2S3/3D macroporous graphene composite greatly improve the cycle performance of LIBs.The Bi2S3/macroporous graphene based LIBs have a first discharge specific capacity of 469 mAh g-1 at a current density of 200 mA g-1 and then keep at 415 mAh g-1.Compared with single Bi2S3,the electrical capacity of resultant LIBs increased by 72.9%,indicating the great improvement of the electrochemical performance of LIBs.(3)The 3D molybdenum disulfide(MoS2)microspheres were firstly synthesized by controlling the conditions of hydrothermal synthesis,and then MoS2/3Dmacroporous graphene composite materials were prepared as an ideal cathodic composite material of LIBs by one-step hydrothermal method.The composite materials were characterized with SEM,TEM,XRD,and XPS techniques.By the effective combination of high capacity of MoS2 and good structural stability of graphene,both the performance and conductivity of the single MoS2 material and the theoretical capacity of the single carbon material can be improved obviously.At a current density of 5.0 A g-1 and constant-current charged and discharged of 1000 cycles,MoS2/3Dmacroporous graphene based LIBs maintain a relatively high specific capacity of 215 mAh g-1,showing better rate performance and cycle stability. |
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