Method for evaluating lithium battery aging and internal short circuit failure based on relaxation voltage curve
Patent Information
- Application Number
- CN202311459937.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-01
- Publication Date
- 2026-10-27
- Estimated Expiration
- 2043-11-01
AI Technical Summary
[0004]但是，上述方法中，荷电状态的评估依赖于准确的等效电路模型，还需引入卡尔曼滤波等算法对模型参数进行辨识与更新，这对嵌入式电池管理系统的计算能力提出了要求
本发明提出的基于弛豫电压曲线的锂电池老化与内短路故障的评估方法，仅依赖于电学测量，即可实现老化状态及内短路故障的检测；仅需要以目标函数的形式拟合电池弛豫曲线，通过拟合得到目标函数的参数，依据参数即可辨识电池老化状态及电池的短路故障，有利于在嵌入式管理系统中实现；本专利提出的方法经过实验验证后，目标函数中辨识的参数与老化状态及短路故障都表现出高度关联性。
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Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery fault diagnosis technology, specifically to an assessment method for lithium battery aging and internal short-circuit faults based on relaxation voltage curves. Background Technology
[0002] Due to their high power density and long cycle life, lithium-ion batteries are now widely used in new energy vehicles, consumer electronics, power grids, and user-side energy storage. However, harsh usage scenarios and complex operating conditions can lead to battery aging, manifesting as capacity decay and increased internal resistance. Under extreme conditions, this can even cause safety issues. For example, internal short circuits caused by battery misuse can trigger thermal runaway, resulting in dangerous accidents such as fires and explosions. Therefore, early warning of internal short circuits in batteries is essential to prevent serious fire accidents during use.
[0003] In existing technologies, battery aging and internal short-circuit faults exhibit similar phenomena, both leading to a decrease in battery discharge capacity. The former is due to a reduction in battery cycle capacity, while the latter is due to energy loss from short-circuit loops within the battery. This similarity makes battery performance evaluation difficult. To differentiate between the two, researchers have proposed a fault identification method based on interactive information to detect battery fault characteristics such as capacity and initial state of charge differences, and to establish a fault identification decision tree. However, this interactive information-based evaluation method requires comparing the operating data of other batteries within the module, making it difficult to provide accurate assessments for single-cell applications. To overcome this challenge, some researchers have evaluated battery aging and short-circuit faults by comparing the charging and discharging capacities of a single battery. This method detects the state of charge during charging and discharging to predict the battery's maximum charging and discharging capacities. When battery capacity decreases, both decrease simultaneously; however, when a short-circuit fault occurs, the former will be greater than the latter.
[0004] However, the above methods rely on accurate equivalent circuit models for state of charge assessment, and require the introduction of algorithms such as Kalman filtering to identify and update model parameters, which places demands on the computational capabilities of embedded battery management systems. To date, a simple and effective method for jointly assessing battery aging status and internal short-circuit faults remains lacking. Summary of the Invention
[0005] The purpose of this invention is to provide an evaluation method for lithium battery aging and internal short-circuit faults based on relaxation voltage curves, so as to solve the problems mentioned in the background art.
[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for evaluating lithium battery aging and internal short-circuit faults based on relaxation voltage curves, the method comprising the following steps: Establish the objective function as ; Explain the physical meaning of each parameter in the objective function; Fit the objective function to identify the parameters in the function; The battery aging status and the degree of internal short circuit fault are assessed by the values and trends of the parameters.
[0007] Preferably, the objective function The value represents the battery voltage during the relaxation process, where Assess battery aging. The internal short-circuit fault is evaluated as shown in Equation (1): (1) In equation (1), This indicates the change in battery relaxation voltage with aging status under conditions of no internal short circuit fault. Describe the impact of internal short-circuit faults on battery relaxation voltage.
[0008] Preferably, a second-order equivalent circuit model is established, with two... Parallel Network , The terms (2) and (3) represent the effects of activation polarization and concentration polarization on the relaxation voltage, respectively. The voltage source represents the open-circuit voltage of the battery. The battery relaxation voltage is calculated using equation (2). (2) In the formula It is the battery relaxation voltage without considering short-circuit faults; OCV represents the battery open-circuit voltage. , These represent the activation polarization voltage and concentration polarization voltage, respectively.
[0009] Preferred, relaxation process The voltage response of a parallel network can be considered as the zero-input response of the system, and can be expressed as: (3) According to equation (3), Expressed as (4) In formula (3) , , and These four parameters, along with the open-circuit voltage (OCV), represent the amplitudes of the activation polarization voltage and concentration polarization voltage, and the time constants of the activation polarization and concentration polarization processes, respectively. They all have the potential to serve as indicators for assessing the aging state of batteries.
[0010] Preferably, during the discharge of a lithium battery, a small short-circuit current causes an observable voltage drop, which is expressed as... (5) In formula (5) is a constant, representing the linear relationship between the short-circuit current and the resulting voltage drop; The magnitude of the value is used to reflect the degree of short circuit within the battery. The larger the value, the faster the voltage drop caused by the short-circuit current, meaning the more severe the short-circuit fault, and vice versa.
[0011] Preferred, Among them, OCV, , These parameters serve as indicators for battery aging assessment. As an indicator for evaluating internal short-circuit faults in batteries.
[0012] Compared with the prior art, the beneficial effects of the present invention are: The proposed method for evaluating lithium battery aging and internal short-circuit faults based on relaxation voltage curves relies solely on electrical measurements to detect aging conditions and internal short-circuit faults. It only requires fitting the battery relaxation curve to an objective function, obtaining the parameters of the objective function through fitting, and then identifying the battery aging state and short-circuit faults based on these parameters. This method is advantageous for implementation in embedded management systems. Experimental verification of the proposed method shows a high correlation between the parameters identified in the objective function and aging conditions and short-circuit faults. Attached Figure Description
[0013] Figure 1 This is a schematic diagram illustrating the relationship between aging and relaxation in this invention; Figure 2 This is a schematic diagram illustrating the relationship between short circuit and relaxation in this invention; Figure 3 This is a second-order equivalent circuit model diagram of the present invention; Figure 4 This is a schematic diagram illustrating the relationship between voltage and state of charge in this invention; Figure 5 This is a schematic diagram of the battery testing platform structure of the present invention; Figure 6 This is a schematic diagram of the aging test results of the present invention; Figure 7 This is a schematic diagram illustrating the relationship between the parameters of the present invention and the capacity retention rate; Figure 8This is a schematic diagram of the internal short-circuit test results of the present invention; Figure 9 This is a schematic diagram illustrating the relationship between the parameters of the present invention and the capacity retention rate. Detailed Implementation
[0014] To make the objectives, technical solutions, and advantages of the present invention clear and complete, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only some, not all, embodiments of the present invention, and are merely illustrative of the embodiments of the present invention. They are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0015] Example 1 Please see Figures 1 to 4 This invention provides a technical solution: a method for evaluating lithium battery aging and internal short-circuit faults based on relaxation voltage curves, the method comprising the following steps: 1.1 Relationship between battery aging and relaxation The relaxation process refers to the process by which the battery voltage recovers to its open-circuit voltage after the battery has finished charging and discharging. The difference between the open-circuit voltage and the battery's operating voltage is called the polarization voltage. During the relaxation process, the ohmic polarization voltage, activation polarization voltage, and concentration polarization voltage caused by charging and discharging gradually disappear. The activation polarization and concentration polarization voltages are related to the charge balance at the electrode particle-electrolyte interface and within the electrode, respectively, indicating that voltage relaxation behavior contains direct information about lithium-ion transfer. As the battery ages, its polarization resistance gradually increases, making lithium-ion transfer between the positive and negative electrodes increasingly difficult, and the battery's polarization voltage gradually increases. During the relaxation process, the degree of aging can be judged by observing the relaxation voltage curve. Figure 1 As shown. Figure 1 As the battery polarization voltage gradually increases along the direction of the arrow, the degree of battery aging also deepens.
[0016] 1.2 Relationship between internal short circuit and relaxation In a normal lithium-ion battery, the battery separator allows lithium ions to pass through but not electrons. A healthy separator prevents internal short circuits. However, when the battery is subjected to harsh operating conditions, such as overcharging / discharging, high temperatures, or external impacts, the separator's performance is damaged, reducing its ability to block electrons. A small number of electrons can then pass through the separator, creating a current loop inside the battery and causing an internal short circuit. When an internal short circuit occurs, even if the battery is disconnected from the load (i.e., in a relaxed state), the battery continues to discharge due to the internal current loop, and the battery voltage continues to drop. As the internal short circuit deepens, the internal short-circuit current increases, and the battery voltage drops faster. Figure 2 As shown. Figure 2 In the middle, the degree of internal short circuit fault gradually increases along the direction of the arrow, and the battery voltage drops faster and faster.
[0017] 1.3 Establishing an objective function to achieve joint evaluation of battery aging and internal short circuit As described in Sections 1.1-1.2, both aging conditions and internal short-circuit faults are related to relaxation voltage, which makes it possible to jointly evaluate aging conditions and internal short-circuit faults based on relaxation voltage curves. This patent establishes an objective function, explains the physical meaning of each parameter in the objective function, identifies the parameters in the function by fitting the objective function, and evaluates the battery aging condition and the degree of internal short-circuit fault by the value and trend of the parameters.
[0018] The objective function in this patent It consists of two sums, the value of which represents the battery voltage during the relaxation process, where Used to assess battery aging. It is used to evaluate internal short-circuit faults, as shown in Equation (1).
[0019] (1) In equation (1), This is used to represent the change in battery relaxation voltage with aging under conditions without internal short-circuit faults. As described in Section 1.1, the battery relaxation voltage is related to the polarization process. To quantify the effect of polarization on the relaxation voltage, such as... Figure 3 The second-order equivalent circuit model shown is constructed. Two [circuits] in the figure. Parallel Network , The terms (2) and (3) represent the effects of activation polarization and concentration polarization on the relaxation voltage, respectively, while the voltage source represents the open-circuit voltage of the battery. Therefore, without considering short-circuit faults, the battery relaxation voltage can be calculated using equation (2). (2) In the formula It is the battery relaxation voltage without considering short-circuit faults; OCV represents the battery open-circuit voltage. , These represent the activation polarization voltage and concentration polarization voltage, respectively. According to circuit theory, during the relaxation process... The voltage response of a parallel network can be considered as the zero-input response of the system, and can be expressed as: (3) According to equation (3), It can be expressed as (4) In formula (3) , , and These four parameters, along with the open-circuit voltage (OCV), represent the amplitudes of the activation polarization voltage and concentration polarization voltage, and the time constants of the activation polarization and concentration polarization processes, respectively. They all have the potential to serve as indicators for assessing the aging state of batteries.
[0020] In equation (1), This describes the impact of internal short-circuit faults on battery relaxation voltage. Internal short-circuit faults cause a drop in battery voltage. In the early stages of an internal short circuit, the fault level is low, the short-circuit current is weak, and the resulting polarization voltage is small. Its main impact on battery voltage is reducing the battery's state of charge (SOC), thus lowering the battery voltage. Especially in the low SOC range, the battery voltage drops rapidly with increasing SOC, and at this time, the short-circuit current has the most significant effect on the battery voltage. Figure 4 As shown. Figure 4 The graph shows the voltage variation with state of charge (SOC) during lithium battery discharge. In the low SOC range highlighted in the graph, the battery voltage decreases rapidly and linearly with increasing SOC. This means that even a small short-circuit current can cause an observable voltage drop, which can be expressed as: (5) In formula (5) It is a constant used to represent the linear relationship between the short-circuit current and the resulting voltage drop. The magnitude of the value is used to reflect the degree of short circuit within the battery. The larger the value, the faster the voltage drop caused by the short-circuit current, meaning the more severe the short-circuit fault, and vice versa.
[0021] In summary, the established objective function is: Among them, OCV, , These parameters can be used as indicators for battery aging assessment. As an indicator for evaluating internal short-circuit faults in batteries.
[0022] Example 2 Based on Example 1, the experiment is described as follows: The battery testing platform includes the following components, such as... Figure 5 As shown: (1) Power battery tester (CT-4008-20V10A-NA), used for battery charging and discharging. The device has 8 charging and discharging channels. The voltage range of each channel is 20V, the maximum charging and discharging current is 10A, and the measurement accuracy of voltage and current is 0.1%FS; (2) Host computer software, which communicates with the power battery tester and is used to collect the voltage and current during the battery charging and discharging process and control the battery charging and discharging strategy; (3) Lithium iron phosphate battery, the specific parameters are shown in Table 1.
[0023] Table 1. Test Battery Parameters
[0024] To verify the proposed method's ability to assess battery aging, batteries in different aging states need to be obtained. This patent accelerates battery aging through high-rate charge-discharge cycles. The tested battery is charged at 6C (9A) constant current and constant voltage to the upper limit cutoff voltage of 3.65V, left to rest for 10 minutes, then discharged at 6C (9A) constant current to the lower limit cutoff voltage of 2.5V and left to rest for 10 minutes. This charge-discharge process is repeated 15 times. Then, the charge-discharge rate is adjusted to 1C (1.5A), and the battery capacity is calibrated by 5 charge-discharge cycles. The above 20 charge-discharge cycles constitute one cycle. This cycle is repeated multiple times until the battery capacity decreases to 80% of the initial capacity. The specific steps are shown in Table 2.
[0025] Table 2. Battery Aging Test Protocol
[0026] To verify the proposed method's ability to assess battery short-circuit faults, different degrees of short-circuit faults need to be applied to healthy batteries. In this patent, different degrees of short-circuit faults are simulated by connecting external resistors (5Ω, 10Ω, 20Ω, 30Ω, 50Ω, 100Ω, 200Ω) between the positive and negative terminals of the battery. The battery with the external resistor is discharged at a constant current of 1C (1.5A) to the lower cutoff voltage of 2.5V and then left to stand for 10 minutes. If the battery voltage drops below the safe voltage (2V) during the standing period, the standing period is stopped and the charging phase begins. The battery is charged at a constant current of 1C (1.5A) and constant voltage to the upper cutoff voltage of 3.65V and then left to stand for 10 minutes. This process is repeated multiple times to reduce measurement errors. The specific steps are shown in Table 3.
[0027] Table 3. Battery Short Circuit Test Procedure
[0028] The experimental results are as follows: During the accelerated aging test, the relaxation curve of the tested battery is as follows: Figure 6As shown in the figure, each relaxation curve represents the average voltage of five relaxation cycles during capacity calibration. The battery capacity corresponding to each relaxation curve gradually decreases along the direction of the arrows in the figure. Accelerated aging experiments were conducted on multiple cells to obtain batteries in different aging states. The least squares method was used to fit each relaxation curve of different cells to the objective function, obtaining the parameter variation law in the objective function under different aging states, as shown in the figure. Figure 7 As shown. Figure 7 The capacity retention rate on the horizontal axis refers to the ratio of the battery capacity under current aging conditions to the battery capacity under initial conditions. It is used to measure the aging state of the battery. The lower the capacity retention rate, the more severe the battery aging. Figure 7 (a)-(d) respectively show the four battery cells , OCV and Changes with aging. Among them... , OCV originates from Used to assess battery aging status. Origin This is used to assess the severity of a battery short-circuit fault. As can be seen from the figure, , Both OCV and other parameters can effectively reflect the degree of battery aging. The value remained at an extremely low level throughout the aging process, correctly assessing that the tested battery had no internal short circuit fault. , Both OCV and OCV can reflect the aging state of a battery. To select the parameter most relevant to the aging state, this patent uses the Pearson correlation coefficient to measure it. , The correlation between OCV and battery capacity retention rate: the absolute values of the correlation coefficients of these three factors are 0.6717, 0.8658 and 0.9183, respectively. The absolute value of the Pearson correlation coefficient is between 0 and 1. The closer the value is to 1, the stronger the correlation and the more helpful it is for aging status assessment. Therefore, OCV is chosen to assess battery aging status.
[0029] Battery short-circuit test results are as follows Figure 8 As shown in the figure, the resistance values decrease sequentially along the direction of the arrows, representing a gradual increase in the degree of short circuit. The objective function is used for fitting. Figure 8 The relaxation curve in the figure yields the parameters. The trend of short-circuit resistance variation is as follows Figure 9 As shown. Figure 9 The horizontal axis in the middle represents the increasing short-circuit resistance from left to right, and the parameters... It decreases monotonically as the short-circuit resistance increases, which can effectively assess internal short-circuit faults.
[0030] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for evaluating lithium battery aging and internal short-circuit faults based on relaxation voltage curves, characterized in that: The method includes the following steps: Establish the objective function as ; Explain the physical meaning of each parameter in the objective function, where... , , and These represent the amplitudes of the activation polarization voltage and concentration polarization voltage, and the time constants of the activation polarization and concentration polarization processes, respectively. OCV represents the cell open-circuit voltage. The value represents the battery voltage during the relaxation process; Fit the objective function to identify the parameters in the function; The battery aging condition and internal short-circuit fault severity are assessed by the numerical values and trends of parameters, including OCV. , These parameters serve as indicators for battery aging assessment. As an indicator for evaluating internal short-circuit faults in batteries.
2. The method for evaluating lithium battery aging and internal short-circuit faults based on relaxation voltage curves according to claim 1, characterized in that: objective function The value represents the battery voltage during the relaxation process, where Assess battery aging. The internal short-circuit fault is evaluated as shown in Equation (1): (1) In equation (1), This indicates the change in battery relaxation voltage with aging status under conditions of no internal short circuit fault. Describe the impact of internal short-circuit faults on battery relaxation voltage.
3. The method for evaluating lithium battery aging and internal short-circuit faults based on relaxation voltage curves according to claim 1, characterized in that: Establish a second-order equivalent circuit model, two Parallel Network , The terms (2) and (3) represent the effects of activation polarization and concentration polarization on the relaxation voltage, respectively. The voltage source represents the open-circuit voltage of the battery. The battery relaxation voltage is calculated using equation (2). (2) In the formula It is the battery relaxation voltage without considering short-circuit faults; OCV represents the battery open-circuit voltage. , These represent the activation polarization voltage and concentration polarization voltage, respectively.
4. The method for evaluating lithium battery aging and internal short-circuit faults based on relaxation voltage curves according to claim 3, characterized in that: Relaxation process The voltage response of a parallel network is considered as the zero-input response of the system and is expressed as: (3) According to equation (3), Expressed as (4) In formula (3) , , and These represent the amplitudes of the activation polarization voltage and concentration polarization voltage, and the time constants of the activation polarization and concentration polarization processes, respectively.
5. The method for evaluating lithium battery aging and internal short-circuit faults based on relaxation voltage curves according to claim 1, characterized in that: During the discharge process of a lithium battery, a small short-circuit current causes an observable voltage drop, which is expressed as: (5) In formula (5) is a constant, representing the linear relationship between the short-circuit current and the resulting voltage drop; The magnitude of the value is used to reflect the degree of short circuit within the battery. The larger the value, the faster the voltage drop caused by the short-circuit current, meaning the more severe the short-circuit fault, and vice versa.