Process Parameter Control Of Liquid Injection And Heat Seal For Liquid Injection Equipment Of Pouch Lithium Battery

The proposed goal of "double carbon" has promoted the rapid development of the new energy lithium battery industry.With flexible size and higher safety,the pouch lithium battery with aluminum plastic film packaging has a broader application prospect.However,at present,the pouch lithium battery still has problems such as poor consistency of liquid injection seal and difficult to ensure the long-term reliability of seal.Therefore,it is of great practical significance to study the production process of pouch lithium battery so that its equipment can meet the increasing technical requirements.Aiming at the automatic vacuum filling line equipment of a certain type of large-size pouch lithium battery,this paper realizes the control of liquid injection accuracy and heat-sealing strength through process research.Details are as follows:The whole process of liquid injection line equipment of pouch lithium battery was analyzed,the structure and performance parameters of the liquid injection and heat seal station that affect battery quality in the equipment were determined.On the basis of the existing production process,combined with the product requirements of pouch lithium battery,the process flow of liquid injection line equipment was designed.The modular design method was adopted to divide the functions of the equipment into sections and the overall layout of the equipment,and the specific production plan were formulated.By analyzing the possible failure forms of pouch lithium battery,the injection precision and heat-sealing strength are the target performance parameters that need to be controlled was clarified.The core structural components in the liquid injection station and heat-sealing station were designed to pave the way for further technological research.The influence of pump process parameters on injection accuracy was studied,and a reference model for judging and controlling injection accuracy based on working pressure was established.Based on the structure and working principle of the liquid injection pump,three controllable process parameters(injection speed,injection needle diameter and height difference between outlet and pump)were selected in the design process of the liquid injection equipment,and the maximum pressure difference in the cavity of the liquid injection pump was introduced as the apparent intermediate quantity.A simple test bench was set up to explore the variation rule of liquid filling accuracy of each process parameter,reveal the relationship between liquid filling accuracy and working pressure,and the corresponding mathematical model was constructed by response surface method.The injection process parameter values of the suggested equipment were given and verified by the actual production data.The mapping relationship between heat-sealing process parameters and heat-sealing strength was proved,and the method of judging and controlling heat-sealing strength was put forward.A 152 μm thick PA/Al/CPP aluminum-plastic composite film was selected to analyze the heat conduction mechanism in the process of heat sealing.The heat conduction model was established and solved.The heat-sealing process was determined as heat-sealing temperature,heat-sealing time and heat-sealing pressure.The single-factor thermal sealing performance test of aluminum plastic film was designed.The maximum tensile load that aluminum plastic film could bear after thermal sealing was tested by universal material testing machine,and that was taken as the standard to measure the strength of hot sealing.The variation rule of heat-sealing strength under different parameters of heat-sealing process was expounded.The orthogonal test was designed for the value of screening heat-sealing process parameters,and the sealing edge thickness after hot sealing was introduced as the apparent intermediate quantity.The influence of heat-sealing pressure was excluded through significance analysis,and it was found that the temperature and time of heat seal had the same mechanism on the sealing edge thickness and heat-sealing strength.A mathematical model of heat-sealing strength about heat-sealing temperature and heat-sealing time was established,and the response curve between sealing edge thickness and heat-sealing strength was fitted.The thermal sealing process parameters of the suggested equipment were given and verified by actual production data.The mathematical model obtained in this research can be used to adjust and control the process parameters according to the requirements of different performance parameters,and can quickly judge whether the target performance is up to the standard according to the size of the apparent intermediate quantity,so as to adjust the process parameters in time,reduce the time of manual trial and error in the later period,and improve the production efficiency of the equipment.