Rapid Identification,Structural Assembly Of Graphene Oxide And Current Collector Application

Graphene oxide(GO)has a wide variety of oxygen-containing functional groups such as hydroxyl,carboxyl and epoxy groups,which are easily dispersed in water and a small amount of organic solvents.As a precursor for the preparation of graphene by chemical oxidation,GO retains the delocalized π conjugated system of graphene fragments,exhibits unique physicochemical properties,and shows great application prospects in the fields of composites,new energy and biomedicine.However,the microscopic dispersion morphology of GO in solution is affected by many factors in practical applications.In addition,the lamellar assembly of GO also has a certain impact on the application of graphene foil.Therefore,this thesis takes GO as a starting point,develops a method based on optical microscope to rapidly identify the micro-dispersion morphology of GO in solution,and realizes the controllable preparation of graphene foil thickness by functionalizing GO and adjusting its lamellar assembly and micro-structure.At the same time,the graphene foil was used as the current collector of the cathode material,and was successfully applied to Li-ion batteries,which provided experimental basis and theoretical basis for the industrial application of GO.The main results of this thesis are as follows:(1)Based on the light absorption of GO sheets,the direct and rapid recognition of the microscopic dispersion morphology(such as unfolding,crimping and agglomeration)of GO in solution was realized by Optical Microscope.The results showed that the factors such as concentration,pH value,ultrasonic treatment time and ionic strength could affect the microscopic dispersion morphology of GO in the solution.When GO is used in the composite,the influence of the micro-dispersion morphology of GO in the precursor solution on the micro-morphology of the composite can also be obtained by Optical Microscopy,which provides guidance for us to prepare composites with uniform morphology.(2)Based on the existence of oxygen-containing functional groups in GO,ethylenediamine-functionalized GO papers were prepared by the reaction of the amino group in ethylenediamine with the epoxy group and carbonyl group in GO.The experimental results showed that the amount of oxygen-containing functional groups of GO foil was reduced,the degree of cross-linking between the GO sheets was increased,the self-assembly between the GO sheets was promoted,and the thickness of graphene foil was regulated during thermal reduction.(3)After high temperature heat treatment,a GF with a thickness of 12 μm was obtained,which had a conductivity of 5800 S cm-1 and a density of 1.80 g cm-3.The problem of electrochemical corrosion of metal current collector was solved by using GF as current collector of cathode material of Li-ion batteries(LIBs).At the same time,GF has a lower density,which can effectively improve the mass energy density of LIBs.When the current density was 0.5 C,the first specific capacitance of NCM523/GF electrode(137.3 mAh g-1)was 44.5%higher than that of NCM523/AF electrode(95.0 mAh g-1).At 5.0 C,the energy density of NCM523/GF electrode was 383.3 Wh kg-1,while that of NCM523/AF electrode was only 33.2 Wh kg-1.Therefore,GF as a current collector can improve the electrochemical performance of LIBs,including rate performance,cycle stability and mass energy density.