Numerical Simulation And Technology Foundation For Efficient Slot Coating Of Lithium-ion Battery Electrode

Slot coating is the core manufacturing process of lithium-ion battery electrode,which directly determines the capacity,cycle life,and other performance of the battery.With the rapidly demand of lithium-ion power batteries,higher efficiency of slot coating is required.Not only are the coating width and coating speed increased,but both sides of the electrode need to be coated simultaneously.Wide-width,high-speed,and simultaneous double-sided coating have brought a series of challenges: the coating uniformity for the wide-width coating is difficult to guarantee,the coating bead easily loses stability and causes coating defect for the high-speed coating,the coating stability of the simultaneous double-sided coating is poor,and the component tends to migrate during the rapid suspension drying.In this dissertation,the numerical simulation and technology foundation for efficient slot coating of lithium-ion battery electrode have been researched.A simulation model of the flow field in the slot die and a die structural optimization method were proposed,which improved the uniformity of wide-width coating.Firstly,the relationship between cathode and anode slurry viscosities and shear rate were fitted,and a simulation model of the flow field inside the slot die was established.The key factor impacting the uniformity of the wide-width coating,according to the analysis of the flow field uniformity in the die,was the difference in viscosity and pressure generated by the shear rate difference in the width direction.Furthermore,a response surface model and optimization method between the wide-width coating uniformity and the structural parameters of the die was established,and the wide-width uniformity was improved from96.24% to 99.88%.An evolution model of multiphase flow and coating bead in the external flow field of the slot die was established,which revealed the formation mechanism of trailing and missing defects in the high-speed intermittent coating,and an optimization method of the die lip structure was proposed.According to the analysis of the coating bead forming process,it was found that there existed three trailing length regions and minimum coating thickness regions related to the capillary number.The trailing defect was closely related to the rupture process of the coating bead,while the missing defect was closely related to the dynamic contact line of the upstream meniscus.The trailing defect could be effectively controlled by locating the capillary number in the trailing length stable region.The proposed downstream die lip increased the maximum coating speed by more than 25%.A simultaneous double-sided coating process based on the contacted die was developed to enhance the stability of simultaneous double-sided coating.The simultaneous doublesided coating process using the contacted slot die for the second side coating was proposed.To calculate the frequency response of the coating thickness variation to the gap fluctuation,the electrode vibration model and the coating stability frequency response model were established.The gap fluctuation amplitude based on the contacted die was found to be two orders of magnitude smaller than that of the traditional non-contact die,and the stability of double-sided coating was high below the critical vibration frequency.Simultaneous doublesided coating experiments with various coating thicknesses and coating speeds were carried out.The standard deviations of coating thickness were all less than 2.5 μm,indicating that the simultaneous double-sided coating process based on the contacted die was extremely stable.A solvent evaporation model of the electrode in the suspension drying process was established to investigate the controlled mechanism of solvent evaporation,and a rapid and uniform staged drying process was proposed.A coupling model of the suspension drying field and the solvent evaporation of the capillary porous electrode was established.It was found that the electrode solvent evaporation can be divided into three drying stages: the preheating drying stage,the constant-rate drying stage,and the reduced-rate drying stage.The preheating stage was controlled by the electrode temperature,while the constant-rate stage and the reduced-rate stage were controlled by the surface heat transfer and internal mass transfer,respectively.A staged drying process was proposed,in which low drying temperature is used in the constant-rate stage,and high drying temperature is used in the preheating and reduced-rate stages.The staged drying process increased the drying efficiency on the premise of suppressing component migration.Based on the above analysis,the wide-width,high-speed,double-sided slot coating die and coating process were optimally designed.The application verification was carried out on the double-sided coating equipment.The research in this dissertation has significance guideline for the research and development of lithium-ion battery electrode manufacturing process and equipment.