Research On Preparation And Lithium Storage Properties Of LiFePo₄/Multilayer Graphenes Composites

Under the background of the Internet of Everything and Artificial Intelligence,lithium-ion batteries play an important role in human life production.Lithium iron phosphate has become one of the most promising cathode materials due to its large discharge capacity,good cycle performance,low price,environmental friendliness and long service life.However,lithium iron phosphate has a problem of low electron conductivity and poor lithium ion diffusion coefficient,which limits its application.Common modification measures include carbon coating,design of three-dimensional carbon structure or element doping.Different from the traditional modification scheme,this thesis improves the defects of lithium iron phosphate material by growing lithium iron phosphate particles on the surface of multilayer graphene.At the same time,the lithium iron phosphate/multilayer graphene material prepared in this thesis is better tough.The external force influences the process to provide a new idea for the preparation of flexible electrode materials.The main research contents are as follows:(1)Using chemical method to synthesis the iron oxide nanoparticles/multilayer graphene precursor,synthesizing iron oxide nanoparticles and lithium dihydrogen phosphate into lithium iron phosphate precursor by hydrothermal treatment,and finally converting the precursor into iron phosphate by high temperature calcination.Lithium,thereby preparing a composite material of lithium iron phosphate and multilayer graphene.The microstructure of the composites was studied by XRD and SEM,and the electrochemical properties of the composites were studied.The results show that lithium iron phosphate has high crystallinity but uneven particle size.The 0.1 C lithium storage performance based on the total mass of the composite was 35 m Ah/g.(2)The iron oxide nanoparticles/multilayer graphene prepared by the chemical method and the lithium dihydrogen phosphate are mixed and stirred,and the lithium iron phosphate particles are grown in situ on the surface of the multilayer graphene by calcination.The thesis studied the effects of mixing methods,the ratio of iron oxide composites to lithium dioxygen phosphate,heating temperature and other factors on the composites.The best preparation process was obtained: using the grinding and stirring mixing method,the molar ratio of iron oxide to lithium dihydrogen phosphate in the composite material was 1:1.1,the heating rate was 3 °C/min,and the calcination temperature was 650 °C.According to XRDand SEM analysis,the lithium iron phosphate particles prepared in the lithium iron phosphate/multilayer graphene composite have good crystallinity,uniform particle size of about 300 nm and uniform distribution on the surface of the multilayer graphene.Electrochemical tests based on the total weight of the composite showed a reversible specific capacity of 50.1 m Ah/g at a rate of 0.1 C and a reversible specific capacity of 46.7m Ah/g after 100 cycles.The reversible specific capacity at 5C rate is 25.8 m Ah/g.EIS tests show that the composite has good charge transfer resistance and lithium ion diffusion coefficient.