Research On Key Technologies For Manufacturing High Consistency Lithium-ion Batteries

Lithium-ion batteries have become the most reliable power source for new energy vehicle applications due to their advantages of high energy density,high power density,long cycle life and no memory effect.However,for vehicle applications,lithium-ion batteries still have a series of technical problems that restrict the benign development of the industry,such as safety,durability and reliability.In order to meet the requirements of high energy and high power for the whole vehicle lithium-ion batteries need to work in series and in parallel,and their consistency problems may lead to the capacity attenuation,the shortening of cycle life and even the safety problems.The consistency problem of lithium-ion battery is mainly reflected in three aspects: capacity,self-discharge rate and internal resistance.The more the lithium-ion batteries exist in the battery system,the worse the consistency problem presents,which implies that improving the consistency of lithium-ion batteries has become an important subject in promoting the development of new energy vehicle industry.Lithium-ion battery manufacturing is a serial system with multi-process flow,so the deviation of manufacturing process will inevitably lead to the inconsistency of lithium-ion batteries.At present,the relationship between manufacturing process and consistency of lithium-ion batteries has not been analyzed due to the lack of effective process data acquisition methods,and the selection and matching of process parameters still depend on subjective experience.Therefore,the current study was derived from the manufacturing process of lithium-ion batteries and a theoretical model was established,based on the collected process data,to analyze the structure-activity relationship between the manufacturing process and consistency.Subsequently,a data-driven method for consistency prediction and process parameter optimization of lithium-ion batteries was constructed.Finally,the selection and matching of process parameters in the battery design stage were determined.The main contents and achievements are as follows:(1)In terms of the information island problem in lithium-ion battery manufacturing process,an information model of lithium-ion battery intelligent manufacturing workshop was proposed on the basis of analyzing the key technical problems of lithium-ion battery manufacturing process and their influence on consistency.According to the mapping relationship between information model and OPC UA address space,a data communication architecture of lithium-ion battery intelligent manufacturing workshop based on OPC UA was proposed.By the actual project verification,the data in the information model can be circulated and interchanged among all levels of the workshop.The research results could provide a constructive suggestion for the intelligent transformation and upgrading of lithium-ion battery manufacturing industry.(2)Due to the difficulty of data traceability and the lag of product quality control in lithium-ion battery manufacturing process,the correlation logic between process data and consistency was modeled.An information traceability model of data lineage was proposed by applying data lineage to lithium-ion battery manufacturing process,which can dynamically modelize the relationship between the input / output data of the process and the consistency.Based on the information traceability model,a set of process data tracing information platform was developed and applied to the practical engineering project,and the information traceability of 49565 battery samples was realized.Consequently,the research results provide an engineering application method for quality tracing in the lithium-ion battery manufacturing industry.(3)Since the factors affecting the consistency of lithium-ion battery manufacturing process data are difficult to be confirmed,a new structure-activity method of process data and consistency was proposed on the basis of 49565 sample data.Pearson correlation analysis and multiple regression model were adopted to quantify the contribution and the correlation of the process data to the consistency.The results show that the positive electrode areal density,positive electrode compaction density and electrolyte injection quantity have high correlation and contribution to the capacity.The research results could clarify the process improvement direction for the consistency improvement of the lithium-ion battery manufacturing industry.(4)In order to solve the difficulty of determining the threshold of lithium-ion battery manufacturing process parameters,a model for lithium-ion battery capacity prediction and process parameter optimization was proposed by combining BP neural network and particle swarm optimization algorithm.Specifically,the BP neural network was used to establish the nonlinear mapping relationship between process data and the capacity,which was used as the capacity prediction model.Secondly,the process parameter optimization model was established by taking the capacity prediction model as the fitting function of the particle swarm optimization algorithm,so as to solve the process parameter formula when the capacity consistency was optimal.Finally,a set of system integration platform was developed based on the capacity prediction and process parameter optimization model,and then applied to the practical engineering project.The research results could provide capacity prediction for lithium-ion battery manufacturers before large-scale production,and contribute an engineering application method to guide the selection and confirmation of process parameters in the battery design stage.Under the support of National Science and Technology Planning Project(No.2018YFB0104102,No.2019YFA0705103)and Guangzhou Basic and Applied Basic Research Foundation(No.202201011733)research projects,this study has accumulated a wealth of actual production data in the previous R & D process,and has a good research foundation in dealing with the consistency problem,which was an industrial bottleneck.The complex relationship between the manufacturing process and consistency of lithium-ion batteries was analyzed by the theoretical model,and the selection and matching of the process parameters could thus be determined in the battery design stage.Such research results could provide theoretical guidance and engineering-applicable method for improving the consistency of lithium-ion battery.