| Slot coating is widely used in the production of pole pieces of power lithium batteries due to its advantages such as fast coating speed,less material waste,high coating uniformity,and wide coating width.The application of the power lithium battery in new energy vehicles,however,is faced with the challenge of safety performance,among which the quality and controllability of the negative electrode sheets hugely affect the quality of the power battery pack.Combined with engineering practice,this dissertation analyzed the fluid dynamics characteristics of the internal and external flow field of the slit extrusion coating head and established the model for coating stability prediction and anode plate thickness prediction,with the help of which this dissertation effectively predicted the coating stable state and the thickness of the pole piece,improved the coating quality,and consolidated the theoretical basis for optimizing the production process of slot coating.The specific research contents are as follows:(1)Research on the flow field characteristics of the flow channel in the coating head was conducted.The influence of feed velocity on the flow characteristics of the slurry and the velocity distribution at the outlet of the die were analyzed,and the pressure drop model of the flow channel in the die was established.The influence of different gasket structures and the cavity structure of the leveling chamber on the distribution of the outlet velocity of the coating head was discussed,and the structure optimization of the gasket and the leveling chamber was carried out,both of which effectively improved the consistency of the velocity at the exit of the coating head.(2)Research on the flow field characteristics of the outer flow channel of the coating head was carried out.The dissertation analyzed the initial flow characteristics of the slit-coated power lithium battery negative electrode slurry on the copper foil substrate,set up a theoretical model of pressure drop across the coated beads,and summarized the influence of different process parameters on the coating stability.The mathematical model for critical pressure drop was established afterwards,and the critical pressure drop of the coated beads with four different meniscus shapes on the coated beads was analyzed.By conducting the research above,the dissertation predicted the stable state of coating under different process parameters and showed the slurry flow mechanism in the initial stage of slot coating.(3)Research on the coating thickness of the negative electrode sheet of power lithium battery produced by slot-die coating was completed.Based on the Landau-Levich film equation and the Ruschak model and with the influence of temperature and slurry spreading characteristics on the coating thickness considered,a prediction model with high accuracy for the thickness of the negative electrode sheet was established.The experiment of the production of power lithium battery negative pole pieces by slot coating had been carried out,whose process and resultant statistics were also included in the dissertation.Through the comparative analysis of theoretical calculation value and the thickness measurement value of 40 pole piece samples,the accuracy rate of this thickness prediction model can reach 98.75%. |
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