Study On Evaluation Method Of Aging Degree Of Lithium-ion Battery

In recent years,along with the rapid development of the global economy,water pollution,air pollution and many other problems have plagued humanity.Electric vehicles have a good role in promoting emissions reduction and reducing dependence on primary energy,and have gradually entered people's lives under the needs of the times.The degree of aging of the battery is directly related to the endurance and safety of the electric vehicle.How to correctly evaluate the aging degree of the battery is an important problem for electric vehicles.At present,the general aging degree of the battery is expressed by the capacity attenuation,but this evaluation method can only reflect the change of the battery capacity characteristics,and does not reflect the internal and external characteristics of the battery itself.In view of the fact that different driver's use behavior or different vehicle working conditions will lead to different degrees of battery aging.This paper designs four different aging path battery testing schemes,including normal charging at normal temperature.Discharge aging path,overcharge aging path,over-discharge aging path,overcharge and over-discharge aging path.Four lithium iron phosphate batteries of the same batch with the same manufacturer were selected,and they were subjected to different battery life cycle experiments to study the effects of different aging paths on the battery use characteristics.A test platform was set up according to the purpose of the research,and each battery was subjected to capacity calibration and HPPC test after every 100 battery life cycle experiments.The characteristics of power attenuation,capacity attenuation and the difference between the different aging paths of the battery are explored.The results show that the cycle life of the battery and the power characteristics of the battery are related to the aging path of the battery.Even if the capacity attenuation of the battery is the same,there is a big difference in the power characteristics of the battery under different aging paths.Therefore,it is not perfect to evaluate the cycle life of the battery only from the viewpoint of capacity attenuation.In order to further explore the intrinsic relationship between the internal characteristics of the battery and the aging of the battery,the first-order Thevenin circuit was selected as the equivalent model of the battery,and the model parameters of the battery were identified by the recursive least squares method.Look for the mathematical relationship between battery aging and battery power characteristics and battery model parameters.Based on the above research,this paper starts from the demand of battery use,comprehensively considers the battery capacity attenuation and power attenuation,and establishes a new method to evaluate battery aging.