Study On The Mechanism And Diagnosis Method Of Internal Short Circuit In Lithium-ion Power Battery

In recent years,with the rapid development of the new energy vehicle industry,the safety of lithium-ion power batteries has increasingly attracted the attention of the industry and society.Internal short circuit is a common link under the three inducing factors of thermal runaway of lithium-ion power batteries,and it is also a key common technical problem to improve and enhance the safety of lithium-ion power batteries.Since the internal short circuit can be randomly formed at any time of the life of the lithium-ion power battery,it needs to be diagnosed in time to eliminate its potential safety hazard to new energy vehicles.Therefore,the research on the internal short-circuit mechanism of lithium-ion power batteries and its diagnostic methods has important theoretical significance and engineering application value.In this paper,the research work is carried out on the internal short circuit mechanism and diagnosis method of lithium-ion power battery,the specific research content of the paper is as follows:Firstly,the working principle of lithium-ion battery is introduced,and the formation mechanism and fusing phenomenon of internal short circuit caused by lithium precipitation and lithium dendrite growth in the battery are analyzed.The finite element numerical model of internal short circuit was established by using COMSOL multiphysics simulation software,and the internal changes of the battery were analyzed when the self-induced internal short circuit was formed;By setting the irreversible transformation of the lithium dendrite domain in the finite element numerical model,and simulating the change of the boundary potential of the battery under the fuse phenomenon,the electrical characteristics of the aluminum current collector-anode and cathode-anode types of short circuits are obtained.Secondly,the principle that the equivalent circuit models of the internal short circuit and the external short circuit of the battery are basically the same from the perspective of electrical characteristics.The Thevenin first-order equivalent circuit model is built,the battery parameters were obtained through the battery performance test experiment and the battery equivalent circuit model was verified;On the basis of Thevenin first-order equivalent circuit model,the internal short circuit model is built,and the internal short circuit model is verified by the internal short circuit substitution experiment;On the basis of the internal short circuit model,the parameter effect of the internal short circuit is analyzed based on the principle of the equivalent parameter of the internal short circuit,and the relationship between the terminal voltage sag value and the equivalent short circuit resistance value is obtained.The selfdischarge effect of the internal short circuit is analyzed and the estimation method of the equivalent short circuit resistance is obtained.Furthermore,based on the assumption that the terminal voltages of each battery in the power system are highly consistent,using the electrical characteristics that the terminal voltage of the internal short-circuit battery is quite different from that of the normal battery,three experimental schemes are designed to simulate the different conditions when the battery forms an internal short circuit.The time series correlation algorithm is used to realize the online diagnosis of the battery with internal short circuit,and the advantages and disadvantages of the outlier algorithm and the correlation coefficient algorithm in diagnosing the internal short circuit fault of the battery are compared,and it is found that the two algorithms are only suitable for the diagnosis of severe internal short-circuit faults;By additionally setting the diagnostic range of suspected internal short-circuit faults,the battery cells with the diagnosis results of the two algorithms in this range are marked as suspected internal short-circuit fault battery cells.Finally,in view of the difficulty of diagnosing minor internal short circuits,an internal short circuit fault diagnosis method based on RC model is further proposed.Using the batteries marked as suspected internal short-circuit faults,based on the fault diagnosis principle of the "average + difference" assumption,the normal batteries in the power battery pack are converted into "average batteries".The combined algorithm of least squares method and extended Kalman filter method is used to identify and estimate the battery model parameters and SOC state of the suspected internal short-circuit fault battery and the "average battery" respectively,and realize the internal short-circuit fault diagnosis by comparing the model parameters and the SOC difference.The experimental results show that the algorithm can complete the diagnosis in time for internal short-circuit faults triggered by different degrees of battery,avoiding the risk of internal short-circuit batteries developing into thermal runaway.