Study On The Preparation And Electrochemical Performance Of Flexible Carbon Foam And Its Composities

Carbon foam is a kind of light porous material with three-dimensional cell structure.The unique cell structure endows carbon foam with many excellent properties such as low density,high electrical conductivity,corrosion resistance and high specific surface area.It has been widely used in various fields including catalyst supports,adsorption and electromagnetic shielding,etc.In recent years,benefitting from the excellent electrical conductivity and good mechanical properties,its application in the field of energy storage has drawn extensive attention.Especially,it was wildely utilized to construct composite electrodes for Lithium-ion batteried(LIB).In this work,nitrogen-doped flexible carbon foam(NCF)was successfully prepared by the multi-step heat preservation method,using melamine foam as carbonaceous precursor.Then,the Co₃O₄/carbon foam composite was constructed by solvothermal method,and its electrochemical performance was studied.Lastly,multi-walled carbon nanotubes(MWCNTs)were introduced to further improve their electrical conductivity,and the electrochemical performance of MWCNTs/Co₃O₄/carbon foam composite was investigated.The research results are summarized as follows:(1)Using melamine foam as the precursor,a multi-step heat preservation method was employed to conduct the carbonization treatment for preparing a flexible carbon foam with open-cell architecture.The effects of carbonization temperature,heating rate and holding time on the cell structure,morphology,electrical conductivity and mechanical properties of carbon foam have been systematically studied.Studies showed that as the carbonization temperature and holding time increased,the melamine molecules tended to be arranged in a graphitized structure.When the degree of graphitization of carbon foam increased,and the porosity could reach as high as 96%.The resistance was as low as 30? when the carbonization temperature was 1000?.And when the cyclic strain was loaded to 80%,the compressive strength reached to a maximum value of 50 kPa.Moreover,as the heating rate increased,the degree of graphitization of the carbon foam decreased,while the internal defects and the resistance of sample increased.Especially,the resistance was higher than 2000 ?,and the compressive strength decreased to 36 kPa,but sample still exhibited flexible characteristic.(2)The Co₃O₄/carbon foam composite was prepared by the solvothermal method,and its microstructure,morphology and electrochemical properties were systematically studied.It was demonstrated that Co₃O₄ nanoparticles were successfully grown on the ligaments and ridges of the carbon foam,which was believed to increases the contact area with electrolyte.The unique three-dimensional network structure of carbon foam was advantageous to alleviate the volume expansion of Co₃O₄ nanoparticles in the process of lithium-ion insertion/extraction,and provide a conductive network for the transmission of lithium ions and electrons,naturally lead to the enhancement of the electrochemical performance of Co₃O₄ nanoparticles.The flexible Co₃O₄/carbon foam composite obtained in the experiment retained a specific discharge capacity of 211.9 mA h g^-1 after 200 cycles at a current density of 0.5 A g^-1.(3)In order to further improve the transfer of electrons and the diffusion of lithium ions,MWCNTs/Co₃O₄/carbon foam composites were constructed by introducing highly conductive MWCNTs.The results indicated that the addition of MWCNTs effectively improved the electrical conductivity of the composite material.The composite obtained from the solution with 0.2 mg mL^-1 MWCNTs concentration delivered a reversible capacity of about 480 mA h g^-1 after being circulated for 200 cycles at a current density of 0.5 A g^-1.At the same time,the obtained composite showed excellent rate performance.When the current density was increased from 0.1 A g^-1 to 1 A g^-1,the discharge specific capacity can still reach 376.5 mA h g^-1.