| With new energy sources such as solar energy,wind energy,tidal energy and other more and more alternatives to traditional energy sources,the storage demand for corresponding new energy sources is also increasing.Electrochemical energy storage has attracted much attention because of its high energy density and power density.Among them,metal-air batteries have attracted people’s attention due to their huge specific energy density and broad application prospects.The mass transfer capacity of the cathode has a greater impact on the actual performance of the metal-air battery,and the actual specific energy density is lower.Aiming at the mass transfer problem of metal-air batteries,the research content of this paper includes three parts: 1.A fast and accurate calculation method of oxygen effective diffusion coefficient;2.The relationship between electrode porous structure and preparation process;3.The influence of porous structure parameters on battery performance.In this paper,a variety of porous carbon electrodes are prepared with different ratios of carbon materials and different solvents.The BET analysis method is used to measure the specific surface area and specific pore volume of different electrodes,and the BJH theory is used to calculate the pore size distribution of the porous electrodes.Among the single carbon materials,the electrode using Vulcan XC 72 R carbon black and isopropanol solvent has the largest specific surface area and specific pore volume,while the electrode using Kejten Black carbon black and isopropanol solvent has the smallest average pore size.The electrode that uses Super P carbon black and Kejten Black carbon black mixed in a 6:4 ratio and anhydrous ethanol solvent has a smaller average pore size than the Kejten Black carbon black isopropanol electrode.In addition,the specific surface area of the electrode mixed with Super P carbon black and Kejten Black carbon black is higher than that of the two single-carbon materials.A transmission X-ray microscope was used to obtain a 2D image stack containing the structure of the porous carbon electrode body,and the three-dimensional structure of the carbon electrode was reconstructed by a self-written program,and the effective diffusion rate of oxygen in the porous electrode was simulated based on the random walk theory.The comparison between the simulation results in the small range of 0.65～0.757 is basically consistent with the results in the reference,which verifies the accuracy of the model and algorithm.This paper studies the effective diffusivity of porous structures in a larger porosity range(0.52～0.9).The lower the porosity,the smaller the effective diffusivity changes with porosity.As the porosity increases,the greater the effective diffusivity change rate..A region with liquid is generated in the porous electrode to simulate the influence of the degree of wettability on the effective diffusivity.At low wettability,the decrease in the effective oxygen diffusion rate is due to the fact that the fine pores are filled so that the oxygen diffusion path is greatly increased.At high wettability,all pore channels are filled with liquid phase,and the effective diffusion rate of oxygen in the porous structure is close to the effective diffusion rate in pure liquid phase.Design a magnesium alloy dissolved oxygen seawater battery,using magnesium alloy as the anode,self-made porous carbon electrode as the cathode,and comparing the discharge performance of different carbon cathodes.Comparing the discharge of a single carbon electrode at a constant current of 1 mA and 10 mA,a higher current requires more oxygen consumption,and the average voltage of a 10 mA current discharge is lower than that of a 1 mA current discharge.The discharge performance of electrodes mixed with two carbon materials was compared by 20 mA constant current discharge.Acetylene Black carbon black-Ketjen Black carbon black 64-isopropanol electrode has a stable discharge voltage with a maximum voltage of 1.0V and a discharge capacity of 100 mA·h. |
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