基于电化学阻抗谱的锂离子电池过放电诱发内短路的检测方法

Detection Method of Overdischarge-Induced Internal Short Circuit in Lithium-Ion Batteries Based on Electrochemical Impedance Spectroscopy

锂离子电池内短路(ISC)是电池发生热失控的主要原因,电池内短路尤其是过放电导致的内短路初期产热不明显,电压变化小,很难通过常规的观察电、热特征的方法对其进行检测。随着电池内短路的演化,电池内部结构逐渐发生改变,这些电池内部的变化可以在对电池具有良好表征性的电化学阻抗谱中得到体现。该文分别对不同荷电状态(SOC)、不同温度和不同内短路程度的电池进行电化学阻抗谱的测量和研究,筛选检测电池内短路所需的特征参数。结果表明,电池电化学阻抗谱的欧姆电阻R_o基本不受电池温度(25~45℃)、SOC的影响,但是对电池内短路程度较为敏感。为便于检测,该文选择电化学阻抗谱中参数特性和大小都基本和欧姆电阻一致的1 000 Hz频率阻抗的实部作为特征参数,通过监测电池循环过程中特征参数变化趋势来判断电池是否发生内短路。经实验验证,监测1 000 Hz频率阻抗实部值变化的方法可有效检测出电池过放电诱发的内短路,该方法不影响电池的正常循环使用,限制条件少且准确性高。

Internal short circuit(ISC)in lithium-ion batteries is the main cause of thermal runaway,timely and accurate detection of internal short circuit is of great importance in ensuring personal and property safety.ISC of batteries,especially the one caused by over-discharge,produces insignificant heat and small voltage changes,making it difficult to be detected through conventional observation of electrical and thermal characteristics.As ISC evolves and deepens,the battery's internal structure gradually changes,and these subtle changes can be reflected in electrochemical impedance spectroscopy(EIS),which is a good characterization technique for batteries.However,the current methods for detecting ISC induced by over-discharge based on electrochemical impedance spectroscopy do not consider the strict measurement conditions of electrochemical impedance,and changes in temperature and state of charge(SOC)in actual battery applications can affect the accuracy of detection.Therefore,this paper proposes an EIS-based detection method for ISC induced by over-discharge of lithium-ion batteries which is not affected by temperature(25~45℃)and SOC and can accurately detect internal short circuit induced by the overdischarge of the battery.Firstly,electrochemical impedance spectroscopies of the experimental batteries were measured,and an equivalent circuit model was established based on the characteristics of measured electrochemical impedance spectroscopies.Secondly,the electrochemical impedance spectroscopies of lithium-ion batteries were measured at different temperatures,different SOC and different degrees of ISC,the relevant fitting parameters were obtained by fitting the electrochemical impedance with the equivalent circuit model.Parameters that were sensitive to the degrees of ISC but not affected by battery temperature and SOC were selected as characteristic parameters.Finally,the detection method was designed based on the characteristic parameters,and the validation experiment is completed.The results of experiments show that the Ohmic resistance(Ro)meets the requirements of characteristic parameter:it remains basically unchanged within the temperature range of 25~45℃and SOC range of 0%to 100%,with a numerical variation of less than 0.001Ω,its numerical value also increases significantly with the deepening of the internal short circuit.In the electrochemical impedance spectroscopies of the batteries used in this paper,the real part of the impedance at 1000 Hz and the Ohmic resistance have approximately equal values and the same variation trend.For the convenience of detection,the real part of the impedance at 1000 Hz is selected as the characteristic parameter instead of the Ohmic resistance,and the trend of the characteristic parameter in five battery cycles is used to determine whether the battery has internal short circuit.Through experimental verification,it was found that the real part of impedance at 1000 Hz of the normal battery is relatively stable in five battery cycles,with fluctuations of no more than 0.001Ω,presenting a basically unchanged trend.However,the real part of impedance at 1000 Hz which belongs to the internal short circuit battery increased by more than 0.01Ωin five battery cycles,it shows an increasing trend,and there is a clear distinction from normal batteries,which proves the effectiveness of the method described in this paper.