摘要:
结合锂离子电池容量衰减主要机制,建立了基于动态参数响应的电化学热耦合模型,研究磷酸铁锂电池循环寿命及电池内部的电化学行为.模型采用恒流恒压充放电制度对电池进行循环充放电仿真计算.结果显示:800次循环后,电池容量衰减率约为6.35％,电池内部固体电解质界面膜阻抗增大了15.6 mΩ·m-2.分别探讨了充放电倍率、负极活性物质颗粒粒径、负极固相体积分数对电池循环寿命的影响.研究表明:400次循环后,相较于1C (C表示充放电倍率)倍率下的容量衰减率3.31％,2C,3C,4C容量衰减率分别达到3.93％,4.69％和5.04％;负极活性颗粒粒径为2和10 μ.m时对应容量衰减率分别为2.89％,3.87％,差值接近1％;固相体积分数在[0.5,0.6]区间内能保持最好的电池循环稳定性和寿命发挥.
Abstract:
It is one of the important issues for electric vehicle to utilize power batteries which have long lifetime and excellent performance.For optimizing electrochemical performance and lifetime of the lithium ion battery,an electrochemicalthermal model based on dynamic response is developed by COMSOL MULTIPHYSICS.The modeling theory is the reaction mechanism of lithium iron phosphate battery which also includes a parasitic reaction occurring in the constant current and constant voltage charging process.The model consists of three parts:electro-chemical model,thermal model and capacity fade model.A series of temperature-dependent parameters and lithium ion concentration-dependent paramneters relevant to the reaction rate and Li+ transport are employed in this model.Comparing with the results of the experimental test,the model shows high accuracy and reliability.The capacity losses and electrochemical behaviors of the battery in cyclic processes with different rates are investigated.The results show that when the battery is cycled at a rate of 1C,the capacity fading rate is about 6.35％,meanwhile the solid electrolyte interface membrane impedance of the battery is increased by 15.6 mΩ.m-2 after 800 time cycle.In the charge process,the side reaction rate within the anode shows a decreasing trend along the direction from the cooper current collector to separator,which is consistent with the lithium concentration in the anode.Besides,the effects of charge/discharge rate,negative active material particle radius and negative solid volume fraction on the battery cycle life are also discussed respectively.Compared with the fading rate of 3.31％ after 400 time cycle with 1C rate,the capacity fading rates for 2C,3C,4C reach to 3.93％,4.69％ and 5.04％ respectively.When the average particle radii of the anode are 2 m and 10 m,corresponding capacity fading rates are 2.89％ and 3.87％,showing a difference of nearly 1％.The study for solid voluine fraction demonstrates that the battery with a solid volume fraction varying in a range of [0.5,0.6] will keep a longest battery life.These results show that the model has great potential to optimize the design of the battery.
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