Synthesis And Electrochemical Performance Of Carbon Fiber Paper Base Manganese,Cobalt Oxide Air Electrode Materials For Lithium Air Batteries

Lithium air batteries as a new type of battery system,received extensive attention of the scientific workers by its high theoretical energy density(11.14 KWh/kg).Lithium air batteries have high energy density,good cycle reversibility and friendly to environment which shows good application prospect for the development of future energy.The unique of this new type of battery is that the cathode reaction active material is from the air and don’t need to use special container for storage.Thus it can reduce the total mass of the battery and increase the energy density of the battery.But affected by the positive response,the actual energy density of the lithium air batteries can meet is very low.In order to improve the actual energy density of battery,the urgent task is to research and development of high performance of air electrode to improve the comprehensive performance of lithium air batteries.In this paper,we use in-situ electrochemical vapor deposition and electrodeposition method to preparation of high performance lithium air batteries air electrode.The in-situ synthesis method is effective to avoid the use of binder,retained the original collection of fluid and the structure of the catalyst,while reducing the produce side effects because of the binder.We use X-ray diffraction(XRD),scanning electron microscope(SEM),energy spectrum(EDS),transmission electron microscopy(TEM),specific surface area analysis(BET)and X-ray photoelectron spectroscopy(XPS)to characterize the air electrode.And use the constant current charge and discharge,impedance(EIS),cyclic voltammograms(CV)and other methods to test and analysis its electrochemical performance.We have systemly study the morphology,structure and electrochemical performance of air electrode.(1)We use electrochemical deposition methode prepared the MnO2/CP and Co3O4/CP air electrode,respectively.The electrochemical deposition were carried out in manganese acetate(Mn(CH3COO)2),sodium sulfate(Na2SO4)and cobalt sulfate(CoSO4),sodium citrate(Na3C6H5O7·2H2O)solution,respectively.The structure of MnO2 and Co3O4 is similarity and they are all flower-like nanoparticles which are slef-assembled by ultrathin nanosheets.The flower-like nanoparticles are distributing uniformly on the carbon paper,the specific surface area is big,thus leading to more reaction catalytic sites,more discharge product attachment points and more conducive to the battery charge and discharge.But the structure of MnO2 nanoparticles is more regular and the separation between nanosheets is more clearly.The electrochemical performance test of MnO2/CP and Co3O4/CP is made.Under the current density 500 mA/g,the discharge specific capacity of the MnO2/CP and Co3O4/CP air electrode are 5136 mAh/g and 3407 mAh/g,respectively.And under the current density 100 mA/g,limiting the discharge specific capacity 500 mAh/g,the MnO2/CP can circular 125 cycles and the Co3O4/CP can only circular 50 cycles.After contrast and analyze,it was found that the MnO2/CP has more excellent structure and better electrochemical properties than the Co3O4/CP.(2)Using nickel chloride(NiCl26H2O)as catalyst and adopt the method of chemical vapor deposition,we in-situ generate the carbon nanotubes(CNTs)on the carbon fiber paper(CFP)and preparation the CNTs/CFP composite materials.Using the CNTs/CFP as electrode and in Mn(CH3COO)2 and Na2SO4 electrodeposition solution we synthesized the flower-like MnO2 nanoparticles and preparation the MnO2/CNTs/CFP air electrode.The CNTs coated on the surface of CFP uniformly and which cross each other form a three-dimensional structure.The diameter of CNTs is about 20 nm.The nanosheets MnO2 automatically aggregated into a flower-like nanopaticals and evenly coated on the surface of carbon nanotubes.The flower-like MnO2 nanoparticles is around 100 nm and the thickness of MnO2 nanosheets is between 4-7 nm.We made electrochemical performance test of MnO2/CNTs/CFP.The discharge profiles of the MnO2/CNTs/CFP electrode are examined at 100 mA/g,200 mA/g,300 mA/g and 500 mA/g by control the voltage at 2.2V.The discharge capacity is 8723.5 mAh/g,7435.1 mAh/g,6325.3 mAh/g and 5439.8 mAh/g,respectively.The MnO2/CNTs/CFP can circular 20 cycles under the current density 100 mA/g and limit the discharge specific capacity of 500 mAh/g.(3)Using CNTs/CFP as electrode,we prepared Co3O4 nanoparticles in CoSO4 electrodeposition solution by electrochemical deposition method and preparation the Co3O4/CNTs/CFP composite materials.The Co3O4 nanoparticles are uniformly coated on the surface of CNTs.The thickness of single Co3O4 nano-flake is about 4 nm and the total thickness Co3O4 nanoparticles is between 10-15 nm.The diameter of the carbon nanotubes is about 20 nm.The 3D structure of carbon nanotubes increasing the specific surface area of the electrode and provide more attachment sites for the catalyst.The Co3O4 nano-flake can form a three-dimensional network structure which is good for the transportation of electronic and oxygen.And it can help the electrolyte inside into the catalyst and improve the utilization efficiency of the catalyst.The discharge specific capacity is 7196.5 mAh/g under the current density of 200 mA/g.The Co3O4/CNTs/CFP electrode can to circular 40 cycles when limit the capacity of 500 mAh/g and under the current density of 100 mA/g and the discharge voltage is above 2.5 V.When limiting the discharge specific capacity of 1000 mAh/g it can circular 25 cycles.