Preparation Of Carbon Nanomaterials And Their Applications In Lithium-sulfur Batteries And Lithium Ion Batteries

Graphene(G)and graphene oxides(GOs)are important carbon material,which has special structure and excellent property and is applied to energy technology,physical chemistry,biological medicine material.It is of great significant to improve the performance of lithium ion battery(LIBs)and cathode material of lithium-sulfur battery(Li-S)by using porous structure carbon materials to prepare anode material of LIBs and composite cathode material of Li-S.In this dissertation,firstly,we reviewed the structure,property and preparation methods of GOs and G as well as the research situation of carbon materials were applied to electrode material of LIBs and Li-S.Based on the above reviews,with the purpose of efficiently and reliably preparing high quality few-layered GOs and G as well as improving the electrochemical performance of carbon material applying to anode material of Li-ion and cathode material of Li-S.On the one hand,the variation of functional groups content and interlamellar spacing of graphite oxide(GO)were studied by designed different oxidation parameters.Then,the GOs and reduced graphene(rGO)were prepared by exfoliated the GO in ultrasonic and thermal exfoliated method,the exfoliation paramerers were studied to efficiently and reliably prepare few-layed GOs and rGO.Finally,the appropriate parameters are confirmed to prepare few-layered GOs and rGO.On the other hand,the nanoporous carbon microsphere was prepared and applied to anode material of LIBs,nanoporous carbon microsphere is used to matrix of sulfur to prepare cathode material of Li-S,the electrochemical performance of LIBs and Li-S was studied.Based on the above studies,combined the advantages of GOs,G and porous carbon application in cathode material of Li-S,the hierarchical architecture composite material of mesoporous carbon wraps graphene was prepared and used to matrix of sulfur to prepare cathode material of Li-S,the performance of Li-S was discussed.The main specific research of dissertation is summarized as follow:1).In the oxidation of GO,using IR and XRD to study the influence of the ratio of potassium permanganate to graphite,oxidation time and oxidation temperature to content of functional groups and interlamellar spacing of GO,when chosing the ratio of potassium permanganate to graphite is 5 and oxidation in 45 ? for 8 h to prepare GO,the interlamellar spacing of GO reached 0.97 nm,the GO contains large number of functional groups,based on above oxidation conditions,the GO is highly oxidized.Through the characterization of structure and morphology of GOs and rGO prepared in different ultrasonic conditions and exfoliation temperature,we confirmed that using ultrasonic power in 150-200 W to ultrasonic treatment 3-5 h can efficiently prepare few-layer GOs;when thermal exfoliated temperature exceed 750 ? can efficiently prepare few-layer rGO.The few-layered rGO was further reduced in Ar/H2(85:15,v/v)atmosphere at 800 ? for 4 h to prepare highly reduced graphene(H-rGO).H-rGO with the content of carbon atom and oxygen atom are 97.2%and 2.8%respectively.After optimizing the conditions of oxidation and exfoliation make using Hummers method to prepare few-layered GOs and rGO are more efficient and reliable.2).Rresorcinol-Formaldehyde spheres were synthesized at room temperature,which was carbonized in inert atmosphere to prepare carbon microsphere and the carbon microsphere was activated by CO2 atmosphere to prepare nanoporous carbon microsphere(NCM).Carbon microsphere and NCM were used to anode materials of LIBs,which shows excellent electrochemical performance.At current density of 210 mA g-1,the carbon microsphere showed the initial discharge carpacity of 482.4 mAh g-1,NCM showed the initial discharge carpacity of 2575.9 mAh g-1,which mained 429.4 mAh g-1 and 1000.0 mAh g-1 after 50 cycles,the initial discharge capacity of NCM is 5.4 times of carbon microsphere,after 50 cycles,the discharge capacity of NCM is 2.3 times of carbon microsphere.Porous structure plays an important role to improve the carpacity of carbon-based anode material of LIBs.3).The NCM prepared in 2)was used to matrix material of sulfur to disperse and attach sulfur,when the sulfur content of cathode material is 53.5%.the cathode material shows relative high discharge capacity.At current of 0.1C,the initial discharge capacity of cathode material is 1274.0 mAh g-1,maintained 776.4 mAh g-1 after 50 cycles.At higher current density of 1C,the cathode materia shows the initial discharge capacity of 830.3 mAh g-1,reversible capacity retention is over 78%after 50 cycles,and the coulombic efficiency is close to to 100%.4).Combined the advantages of graphene and porous carbon,using the prepared condition of 1)to prepare few-layed GOs as basal material,through template method and sol-gel coating method to prepare mesoporous carbon wraps graphene(MC@G)composites,which was used to matrix material of sulfur to prepare composite cathode material of Li-S.The cathode material demonstrated excellent discharge capacity at low current density.At current density of 0.1 C the initial discharge capacity is 1158 mAh g-1;At current density of 0.5C,the initial discharge capacity is 1131.26 mAh g-1,at higher current of 1C,the initial discharge capacity is 600.3 mAh g-1.The cathode material shows the average discharge capacity are 1009.9 mAh g-1,737.3 mAh g-1,664.4 mAh g-1,492.8 mAh g-1 during 10 cycles at current density at 0.1C,0.5C,1C and 2C.