Research On Step-By-Step Utilization Technology And Thermal Management Of Decommissioned Lithium Battery

With the increasingly serious problems of fossil energy consumption and environmental pollution,countries around the world are seeking solutions.At present,the main means is to vigorously develop clean energy,such as wind power,solar power and so on.However,although new energy can effectively alleviate the fossil energy crisis,its energy output has large randomness and volatility.If the power output is not stabilized by timely and effective frequency modulation and voltage regulation,the grid-connected process will have a greater impact on the power grid,eventually resulting in power paralysis.Therefore,the power transfer storage has become the main solution,so the power storage has emerged as the times require.At present,the main mainstream energy storage technologies include lithium battery energy storage,flow battery energy storage,and super capacitors.Among them,the most mature and efficient technology is lithium battery energy storage.It is widely used in the field of electric vehicles,and the standard for decommissioning electric vehicle power batteries is usually a 20% decrease in battery capacity or a doubling of battery impedance.Although it has reached the decommissioning standard,the decommissioned lithium battery still has about 80% of the remaining capacity,so it still has utilization value.At the same time,the thermal safety of lithium batteries during use is also a current hot spot.Therefore,this topic focuses on the research on the step utilization technology and thermal management of retired lithium batteries.In this paper,two batches of decommissioned lithium batteries were used to study the screening and classification,rate cycle test and thermal management of decommissioned lithium batteries.Firstly,the research status of electric vehicles,cascade utilization technology and thermal management of decommissioned lithium batteries are summarized,and then the performance of the battery is tested and screened through experiments.Based on the performance test results of the battery,this paper uses mathematical methods to classify a batch of retired lithium batteries,and lists three suitable classification methods,that is,the battery module classification method based on maximum available capacity,the classification method based on capacity interval division and the clustering method based on battery feature vector Mahalanobis distance.Taken together,the three methods have their own advantages and disadvantages.For fast classification,the optimal selection is the classification method based on capacity interval segmentation;for the classification method with good economic benefits,the optimal selection is the battery pack classification method based on maximum available capacity and the classification method based on capacity interval segmentation;for comprehensive and accurate classification method,the optimal selection is the clustering method based on Mahalanobis distance of battery pack feature vector.According to the availability and safety of decommissioned lithium battery in different scenarios and the internal heat release and thermal behavior of decommissioned lithium battery under different operating conditions,reasonable battery thermal management measures are also proposed in this paper.The specific method is to first carry out charge-discharge cycle experiments at different rates to observe the change of temperature rise.Then,based on the experimental data and results,by analyzing the structure,working principle,heat generation and heat dissipation mechanism of the lithium-ion battery,based on the heat transfer theory,a three-dimensional thermal model of the battery pack is established,and the battery is subjected to different operating conditions according to the model.The following simulations study the effects of different discharge rates,air convection heat transfer coefficients,cycle times and battery spacing on the battery temperature field and propose reasonable solutions.At the same time,this paper establishes a new battery pack model through simulation,which keeps the cross-sectional area and length of the internal cells unchanged,and changes the cross-sectional shape from rectangular to square,and maintaining the number and gap of the single cells,the thickness of the aluminum shell on the outer surface,Ambient temperature,various heat dissipation coefficients and the rate of heat generation of the battery are unchanged.It is found that the battery model with a square cross section has a smaller surface area and lower overall heat dissipation,and still causes a smaller temperature rise at the same discharge rate.The main reason is that the internal flow channel space of the battery pack increases,which will correspondingly increase the effect of convection and heat transfer inside the battery pack,thus taking away more heat.This discovery has a certain optimization effect on the thermal management of lithium batteries.The heat dissipation structure can be further studied in the future,and it is possible to further optimize it.