Design And Preparation Of New Carbon/metal Oxide Composite Materials And Study Of Their Lithium Storage Performanc

Currently,the low theoretical specific capacity of active electrode materials for commercial lithium ion batteries severely limits their application in large-scale energy storage.Compared with conventional graphite anode materials,metal oxide materials generally have higher lithium storage capacity.In view of the metal oxides in the actual process of the volume change and poor electrical conductivity and other problems,researchers generally adopt methods such as reducing the size of active materials and preparing composite materials to improve lithium storage performance.Taking the above factors into consideration,it is of great significance for the further development of lithium ion batteries to adopt a more optimized material synthesis route to prepare new cathode materials with special structure and metal oxide as the electrochemical active center.In this thesis,the new carbon material as the carrier and nano metal oxide effective composite,respectively from the material selection,preparation,morphology design and crystal structure optimization.Carbon nanotubes and graphene oxide,as well as zinc,iron and tin elements in new carbon materials were selected as research objects.Firstly,the preparation of the material was studied.Graphene and carbon nanotubes were combined with metal oxides respectively to form the composite material,and the lithium storage performance was studied.Then,the morphology of the composite material and the crystal structure of the metal oxide were designed.The carbon nanotubes and graphene were mixed to form a multi-stage carbon material framework,and then the metal oxide was composite.New metal oxide/carbon composite materials greatly reduces the metal oxide materials in the process of charging and discharging pulverization,at the same time new carbon materials limits the aggregation and grow up of certain metals,the use of carbon nanotubes and graphene excellent chemical and physical properties to enhance the stability of metal oxide in lithium ion battery cycle,showed excellent lithium ion storage capacity.Based on the above research strategies,the following four research works are introduced in detail in this thesis:1.The composite of graphene and metal oxide was studied.Based on the interaction between nano Zn O and GO,Zn O nanoparticles were coated with reduced GO framework under mild water phase conditions.Finally,Zn O/RGO composites were prepared with uniformly dispersed nano Zn O on graphene.Compared with pure graphene material or nano-Zn O material,the material shows better cycling performance in the cycle process of lithium battery,and can maintain a reversible specific capacity of 560 m Ah/g after 250cycles at a current density of 500 m A/g.Meanwhile,the interaction mechanism between Zn O nanoparticles and GO was studied,and it was proved that Zn O nanoparticles can be used as an effective catalyst for the deoxidation of small layers of GO.2.The composite of carbon nanotubes and metal oxides was studied.Due to the advantages of high specific capacity,environmental friendliness and natural abundance of ferric oxide,the composite of nano-ferric oxide and supporting carbon material is beneficial to improve the cycling stability and rate capacity.Using low cost and environmentally friendly metal iron as iron source,one-dimensional carbon nanotubes supported heterogeneous iron oxide nanoparticle composites（Fe₂O₃@Fe₃O₄/CNT）were successfully constructed by redox reaction with functionalized carbon nanotubes under hydrothermal conditions.At the same time,the synthesis mechanism of the material was explored,the size and phase of iron oxide nanoparticles were effectively regulated,and the lithium storage performance of Fe₂O₃@Fe₃O₄/CNT material was tested.Under the high current density of 1000 m A/g,the reversible specific capacity of 924 m Ah/g could be maintained after 200 cycles.3.In order to give full play to the advantages of new carbon materials and metal oxides as anode materials for lithium ion batteries,combined with the previous two work,the morphology of composite materials was further designed,and the multistage structure of carbon nanotubes and graphene framework was constructed.Zn O/CNT and Fe OOH/RGO precursors were prepared by redox reactions between graphene oxide and functionalized carbon nanotubes,respectively.Zn O/CNT materials were uniformly loaded nano-Zn O particles by carbon nanotubes,and Fe OOH/RGO materials were graphene-loaded needle-like iron hydroxide.Finally,Zn Fe₂O₄@CNT/RGO composites were synthesized by high temperature solid state reaction.The material forms a structure of carbon nanotubes inserted between graphene layers and loaded with zinc ferrite nanoparticles.Compared with the precursors,the material has better lithium storage performance,with a reversible specific capacity of 1250 m Ah/g after 100 cycles at a low current density of 200 m A/g,and a high reversible specific capacity of 1100 m Ah/g after300 cycles at a high current density of 1000 m A/g.4.On the basis of the current research on cathode materials and the previous research work,the crystal structure of composite materials is further studied.To improve the electrochemical performance of tin-based materials,Zn-Sn O-II nanoribbons doped with zinc were synthesized for the first time in mild aqueous solution to alleviate the volume effect of tin-based materials,and the reaction mechanism was studied.The multistructure carbon nanotubes and graphene-supported Zn-doped tin dioxide composite Zn-Sn O₂/CNT@RGO were constructed through redox reaction by mixing functionalized carbon nanotubes and go to form a carbon framework to inhibit its volume expansion.Compared with the pure tin-based material,the composite showed excellent battery performance,maintaining a reversible specific capacity of 901 m Ah/g after 300 cycles at a high current density of 1000 m A/g.