A method for detecting internal short circuits in a single lithium-ion battery.

Abstract

This invention provides a method for detecting internal short circuits in a single lithium-ion battery, relating to the field of lithium battery testing. The method uses the relationship between current and time during the first charging cycle of the lithium-ion battery in n0 charge-discharge cycles as a standard vector, and the relationship between current and time during the charging cycle of each subsequent charge-discharge cycle as a comparison vector. The method accumulates all differences between each comparison vector and the standard vector to obtain a cumulative minimum distance. By analyzing the change of the cumulative minimum distance with the number of charge-discharge cycles, it determines whether an internal short circuit has occurred in the lithium-ion battery. This invention discloses a method for detecting internal short circuits in a single lithium-ion battery. This invention can diagnose internal short circuits in a single battery without applying additional load resistance, accurately determining whether a short circuit exists inside the battery, and avoiding misjudgments caused by differences in battery characteristics.

Description

Technical Field

[0001] This invention relates to the field of lithium battery testing, and in particular to a method for detecting internal short circuits in a single lithium-ion battery. Background Technology

[0002] With the rapid development of portable electronic consumer products (3C), electric vehicles, and end-user energy storage devices, the demand for lithium-ion batteries is increasing. Lithium-ion batteries offer advantages such as high energy density, long lifespan, and recyclability. However, certain safety hazards exist during their use, such as thermal failure caused by internal short circuits, hazardous gases produced by battery expansion, and potential chemical reactions. Monitoring these safety performance indicators and failure metrics is crucial for ensuring the safe operation of lithium-ion batteries.

[0003] Internal short circuits in batteries have always been a key concern in lithium battery safety. Once an internal short circuit occurs, a loop current forms at the short circuit point, accompanied by a large amount of heat generation. In severe cases, if heat dissipation is not timely, thermal runaway can occur, leading to a safety accident. However, the development of an internal short circuit during normal battery cycling is a gradual process, starting from nothing and becoming increasingly severe. Therefore, identifying internal short circuits in their early stages is an effective way to prevent battery safety accidents.

[0004] Existing methods for detecting internal short circuits in single-cell lithium-ion batteries mainly include: 1. Diagnosing internal short circuits by comparing the voltage difference before and after the battery has been left to rest with a threshold. However, this method generally requires the battery to be left to rest for more than 24 hours, and the threshold is not uniformly determined. 2. When an internal short circuit occurs, the battery will self-discharge, so the actual SOC and charging capacity of the battery are lower during actual charging. The equivalent OCV can be calculated, and the relationship between OCV and SOC can be used to determine the actual SOC of the current battery to diagnose whether the battery has an internal short circuit. However, this method requires high model accuracy and has low robustness. 3. When an internal short circuit occurs, the battery may experience a melting phenomenon, which will cause a sharp drop in voltage followed by a rebound. This situation occurs less frequently and is not a reliable reference. 4. Diagnosing internal short circuits by identifying changes in battery parameters through an external load. For example, connecting a constant voltage source in parallel to observe changes in current, or connecting an external resistor to observe changes in the battery's ohmic resistance. This method requires high precision in the external load and is not suitable for practical applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for detecting internal short circuits in a single lithium-ion battery, thereby achieving accurate detection of internal short circuits in lithium batteries.

[0006] To achieve the above object, the present invention provides the following technical solution: A method for detecting internal short circuit in a single lithium-ion battery, comprising the following steps: S1: Obtain the calibrated voltage drop K0 of the lithium-ion battery, and confirm the current voltage drop K1 of the lithium-ion battery; S2: When K1 < K0, connect the lithium-ion battery, a switch and a photoresistor in series; S3: After disconnecting the switch and performing n0 charge and discharge cycles on the lithium-ion battery, measure the current voltage drop K2 of the lithium-ion battery, and record the voltage, current and capacity of the lithium-ion battery during the n0 charge and discharge cycles at a frequency f1; S4: Close the switch and perform n1 charge and discharge cycles on the lithium-ion battery, and at the same time change the light source intensity irradiating the photoresistor to change the resistance value of the photoresistor, so that the resistance value of the photoresistor decays exponentially with the number of charge and discharge cycles of the lithium-ion battery, and record the voltage, current and capacity of the lithium-ion battery during the n1 charge and discharge cycles at a frequency f1; S5: After the lithium-ion battery has undergone n1 charge and discharge cycles, measure the current voltage drop K3 of the lithium-ion battery again; S6: When max(K1, K2) < K0 < K3, confirm the relationship between the current and time of the lithium-ion battery during each charging process of the lithium-ion battery; S7: Take the relationship between the current and time of the lithium-ion battery during the first charging process in the n0 charge and discharge cycles of the lithium-ion battery as the standard vector, and take the relationship between the current and time of the lithium-ion battery during the charging process in each of the remaining charge and discharge cycles as the comparison vector, where the magnitude of the current is the y-axis of the standard vector and the comparison vector, and time is the x-axis of the standard vector and the comparison vector; S8: Scale the x-axis of each comparison vector so that the comparison vector is aligned with the standard vector on the x-axis; S9: Calculate the difference from the standard vector on the y-axis at the same interval in the x-axis direction for each comparison vector, and accumulate all the differences between each comparison vector and the standard vector to obtain the cumulative minimum distance. By analyzing the change of the cumulative minimum distance with the number of charge and discharge cycles of the lithium-ion battery, determine whether the lithium-ion battery has an internal short circuit; S10: When it is determined that the lithium-ion battery has an internal short circuit, obtain the cumulative minimum distance when the lithium-ion battery has an internal short circuit and use the cumulative minimum distance at this time as the threshold; S11: Determine whether the cumulative minimum distance of the lithium-ion battery to be detected exceeds the threshold. When the cumulative minimum distance of the lithium-ion battery to be detected exceeds the threshold, determine that the lithium-ion battery to be detected has an internal short circuit.

[0007] Further, the frequency f1 is 30 ms / time.

[0008] Furthermore, determining whether the lithium-ion battery has an internal short circuit includes: setting a preset change value; determining whether the difference between the cumulative minimum distance of every two adjacent charging and discharging cycles is greater than the preset change value; if the difference is greater than the preset change value, then the lithium-ion battery is determined to have an internal short circuit.

[0009] Further, in step S3, the lithium-ion battery is charged and discharged at a constant current and constant voltage rate of 1C, and the number of charging and discharging cycles of the lithium-ion battery n0 = 5; the charging cut-off current of the lithium-ion battery is 0.05C; and the interval between charging and discharging of the lithium-ion battery in the charging and discharging cycle is 5 minutes.

[0010] Further, in step S4, the lithium-ion battery is charged and discharged at a constant current and constant voltage rate of 1C, and the number of charging and discharging cycles of the lithium-ion battery is n1 = 5; the charging cut-off current of the lithium-ion battery is 0.05C; and the interval between charging and discharging of the lithium-ion battery in the charging and discharging cycle is 5 minutes.

[0011] Furthermore, the resistance of the photoresistor is 10Ω-2000Ω.

[0012] Furthermore, the same interval described in step S9 is 30ms.

[0013] Furthermore, the light source is a variable intensity power supply.

[0014] Analysis shows that the present invention discloses a method for detecting internal short circuits in a single lithium-ion battery. The present invention can diagnose internal short circuits in a single battery without applying additional load resistors, and can accurately determine whether there is a short circuit inside the battery, while also avoiding misjudgments caused by differences in battery characteristics. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0016] Figure 1 An equivalent circuit diagram of an internally short-circuited battery according to an embodiment of the present invention.

[0017] Figure 2 A flowchart of the present invention. Detailed Implementation

[0018] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments. Each example is provided by way of explanation of the present invention and not by way of limitation. In fact, those skilled in the art will appreciate that modifications and variations can be made to the present invention without departing from the scope or spirit thereof. For example, features shown or described as part of one embodiment can be used in another embodiment to yield yet another embodiment. Accordingly, it is intended that the present invention cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0019] In the description of the present invention, the orientation or positional relationships indicated by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", etc. are based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention rather than requiring the present invention to be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention. The terms "connected", "connected to", and "disposed" used in the present invention should be understood in a broad sense. For example, they can be fixedly connected or detachably connected; they can be directly connected or indirectly connected through an intermediate component; they can be connected by wire or radio, or can be connected by a wireless communication signal. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0020] One or more examples of the present invention are shown in the accompanying drawings. The detailed description uses numerical and alphabetical labels to refer to features in the drawings. Similar or like labels in the drawings and the description have been used to refer to similar or like parts of the present invention. As used herein, terms such as "first", "second", "third", and "fourth" can be used interchangeably to distinguish one component from another, and are not intended to indicate the position or importance of individual components.

[0021] As Figure 2 shown, according to an embodiment of the present invention, a method for detecting internal short circuit in a single lithium-ion battery is provided, including the following steps:

[0022] S1: Obtain the calibrated voltage drop K0 of the lithium-ion battery, and confirm the current voltage drop K1 of the lithium-ion battery. In this embodiment, an LCO / graphite system battery with a voltage of 3.0V - 4.45V is used. First, the K value of a fresh battery is tested (using a 48-hour test method, k = (V1 - V2) / t) and recorded as K1. If K1 < K0 (K0 is calibrated by the battery manufacturer), it is considered that there is no internal short circuit in the battery. Then, components such as the battery, switch, and photoresistor (10 - 2000Ω) are assembled and connected as Figure 1 shown.

[0023] S2: When K1 < K0, connect the lithium-ion battery, the switch, and the photoresistor in series. The photoresistor and the switch are equivalent to an external resistor. During the cycling process of the battery, there is no internal short circuit inside the battery during the early production process. The internal short circuit of the battery mainly occurs in the middle and late stages of the battery cycle, and there are two main reasons for the occurrence of the internal short circuit: 1. The gas generation caused by the decomposition of the electrolyte damages the structure of the battery, resulting in situations such as diaphragm misalignment and electrode plate movement, causing an internal short circuit; 2. Lithium plating often occurs in the later stage of the battery cell cycle, and the generation of lithium dendrites has the risk of piercing the diaphragm. However, under normal circumstances, the generation of an internal short circuit proceeds relatively slowly and often requires time deposition. At the same time, in the later stage of the cycle, due to the increase in polarization, the capacity accumulation stage occurs during the constant voltage charging stage. In this stage, the current gradually decreases, and the internal short circuit should gradually increase over time. Therefore, the short-circuit current gradually increases. As one increases and the other decreases, the current drop caused by the internal short circuit becomes obvious. In summary, the present invention uses the method of an external resistor to simulate the internal short circuit of the battery. Different from the conventional method of an external internal short circuit, this patent uses an externally connected photosensitive variable resistor to change the resistance value of the external resistor by adjusting the light intensity, so as to simulate the gradually accumulating change of the internal short circuit of the battery during the cycling process. Figure 1 is the equivalent circuit diagram of the battery after connecting the switch and the photoresistor, where: U OCV is the open-circuit voltage, R0 is the ohmic resistance, R c and C are the polarization resistance and the polarization capacitance respectively, U0 is the terminal voltage, LDR is the photoresistor, and LED is the variable light intensity power supply.

[0024] S3: Disconnect the switch and perform n0 charge and discharge cycles on the lithium-ion battery, then measure the current voltage drop K2 of the lithium-ion battery, and record the voltage, current, and capacity of the lithium-ion battery during the n0 charge and discharge cycles at a frequency f1. Without an external resistor, charge at a constant current and constant voltage at a rate of 1C until the current is 0.05C, then set aside for 5 minutes, discharge at a constant current of , then set aside for 5 minutes, and repeat this cycle 5 times. Test the K value of the battery again according to step 1 and record it as K2. Compare K2 with K0 and K1 to determine that there is no obvious difference between the battery after 5 cycles and the initial state.

[0025] S4: Close the switch and perform n1 charge and discharge cycles on the lithium-ion battery. Meanwhile, change the light source intensity irradiating the photoresistor to change its resistance value, such that the resistance value of the photoresistor decays exponentially with the number of charge and discharge cycles of the lithium-ion battery. Record the voltage, current, and capacity of the lithium-ion battery during the n1 charge and discharge cycles at a frequency f1. After opening the switch, under the light source irradiation, make the resistance value of the photoresistor decay exponentially from large to small with the number of cycles. Continue cycling at the previous rate for another 5 weeks. Meanwhile, test the K value again after 5 weeks of cycling (when testing the K value at this time, consider the battery and the external resistor as a virtual battery for testing), denoted as K3. Compare the magnitudes of K3 with K0, K1, and K2 to determine that max(K1, K2) < K0 < K3, and record the data such as voltage, current, and capacity during the cycling process as the data source, with a sampling frequency of 30 ms / measurement;

[0026] S_{5}: Measure the current voltage drop K3 of the lithium-ion battery again after performing n1 charge and discharge cycles on the lithium-ion battery;

[0027] S_{6}: When max(K1, K2) < K0 < K3, confirm the relationship between the current and time of the lithium-ion battery during each charging process of the lithium-ion battery;

[0028] S_{7}: Use the relationship between the current and time of the lithium-ion battery during the first charging process in the n0 charge and discharge cycles of the lithium-ion battery as the standard vector, and use the relationship between the current and time of the lithium-ion battery during the charging process in each of the remaining charge and discharge cycles as the comparison vector. Among them, the magnitude of the current is the y-axis of the standard vector and the comparison vector, and time is the x-axis of the standard vector and the comparison vector;

[0029] S_{8}: Scale the x-axis of each comparison vector to align the comparison vector with the standard vector on the x-axis. During the data analysis stage, mainly use the I-t curve in the constant voltage stage (the curves of the standard vector and the comparison vector in the x-axis and y-axis coordinate system), and perform dynamic time adjustment (Dynamic Time Warping, DTW) on the comparison vector to match the time series of the standard vector, making it consistent with the time series of the standard vector, and obtaining the current difference between the two at the same time;

[0030] S9: For each comparison vector, the difference between it and the standard vector on the y-axis is calculated at the same interval along the x-axis. All differences between each comparison vector and the standard vector are accumulated to obtain the cumulative minimum distance. After the loop ends, the data is exported. First, the current and time data during the constant voltage charging process are extracted. Particle filtering is used to denoise the It curve (the curves of the standard vector and the comparison vector in the x-axis and y-axis coordinate systems). Then, the It data of the first week is used as the standard vector. Using MATLAB, the subsequent loop data is dynamically adjusted to align with the standard vector of the first week, and the cumulative minimum distance with the standard vector is obtained. By analyzing the change of the cumulative minimum distance with the number of charging and discharging cycles of the lithium-ion battery, it is determined whether the lithium-ion battery has an internal short circuit. The sum of the current differences (cumulative minimum distance) is used as the parameter value for judging the standard of internal short circuit in the battery, and the threshold is determined accordingly. By analyzing the change of the cumulative minimum distance with the number of cycles, the threshold for the occurrence of internal short circuit is determined, thereby determining whether an internal short circuit has occurred.

[0031] S10: When it is determined that an internal short circuit has occurred in the lithium-ion battery, obtain the cumulative minimum distance when the internal short circuit has occurred and use the cumulative minimum distance at this time as the threshold.

[0032] S11: Determine whether the cumulative minimum distance of the lithium-ion battery to be tested exceeds the threshold. When the cumulative minimum distance of the lithium-ion battery to be tested exceeds the threshold, it is determined that the lithium-ion battery to be tested has an internal short circuit. After determining the threshold of the lithium-ion battery, it is possible to determine whether the lithium-ion battery to be tested has an internal short circuit based on the threshold.

[0033] Preferably, the frequency f1 is 30 ms / time. A frequency of 30 ms / time can obtain enough values ​​to establish the subsequent It curve.

[0034] Preferably, determining whether an internal short circuit has occurred in the lithium-ion battery includes: setting a preset change value; determining whether the difference between the cumulative minimum distance of two adjacent charging and discharging cycles is greater than the preset change value; if the difference is greater than the preset change value, then the lithium-ion battery is determined to have an internal short circuit. The change in the cumulative minimum distance is observed to determine whether an internal short circuit has occurred in the lithium-ion battery; if the change is too large, it proves that a short circuit exists inside the battery. Preferably, in step S3, the lithium-ion battery is charged and discharged at a constant current and constant voltage rate of 1C, and the number of charging and discharging cycles n0 = 5; the charging cutoff current of the lithium-ion battery is 0.05C; in the charging and discharging cycle of the lithium-ion battery, the interval between charging and discharging is 5 minutes. Charging and discharging at a rate of 1C can maximize the charging and discharging speed while ensuring normal battery operation. The 5-minute interval between charging and discharging can reduce overheating caused by charging and discharging. Typically, 5 cycles n0 are sufficient to obtain a sufficient data sample.

[0035] Preferably, in step S4, the lithium-ion battery is charged and discharged at a constant current and constant voltage rate of 1C, and the number of charging and discharging cycles of the lithium-ion battery is n1 = 5.

[0036] The charging cutoff current for lithium-ion batteries is 0.05C.

[0037] In the charging and discharging cycle of a lithium-ion battery, the interval between charging and discharging is 5 minutes.

[0038] Preferably, the resistance of the photoresistor is 10Ω-2000Ω. The 10Ω-2000Ω range can simulate most loads, and the resistance of the photoresistor is simple to adjust and easy to operate.

[0039] Preferably, the same interval in step S9 is 30ms, and the interval in S9 is the same as the frequency f1, so that the standard vector can be compared with the scaled comparison vector based on the actual point values ​​it collects.

[0040] Preferably, the light source is a variable intensity power supply, typically a variable intensity LED light-emitting device.

[0041] Compared with the prior art, the present invention discloses a method for detecting internal short circuits in a single lithium-ion battery. The present invention can diagnose internal short circuits in a single battery without applying additional load resistors. During the cycling process, the battery's It time curve is continuously updated, and its cumulative minimum distance from the standard time series is also continuously updated. When a certain value is reached, a significant increase occurs, at which point it can be considered that an internal short circuit has occurred in the battery. At the same time, it avoids misjudgment caused by the differences between batteries, that is, the threshold of each single battery is defined based on its own previous characteristics.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for detecting internal short circuits in a single lithium-ion battery, characterized in that, The steps include: S1: Obtain the calibrated voltage drop K0 of the lithium-ion battery, and confirm the current voltage drop K1 of the lithium-ion battery; S2: When K1 < K0, connect the lithium-ion battery, the switch, and the photoresistor in series; S3: After disconnecting the switch and performing n0 charge and discharge cycles on the lithium-ion battery, measure the current voltage drop K2 of the lithium-ion battery, and record the voltage, current, and capacity of the lithium-ion battery during the n0 charge and discharge cycles at a frequency f1; S4: Close the switch and perform n1 charge and discharge cycles on the lithium-ion battery, and at the same time change the light source intensity irradiating the photoresistor to change the resistance value of the photoresistor, so that the resistance value of the photoresistor decays exponentially with the number of charge and discharge cycles of the lithium-ion battery, and record the voltage, current, and capacity of the lithium-ion battery during the n1 charge and discharge cycles at a frequency f1; S5: After the lithium-ion battery has undergone n1 charge and discharge cycles, measure the current voltage drop K3 of the lithium-ion battery again; S6: When max(K1, K2) < K0 < K3, confirm the relationship between the current and time of the lithium-ion battery during each charging process of the lithium-ion battery; S7: Take the relationship between the current and time of the lithium-ion battery during the first charging process in the n0 charge and discharge cycles of the lithium-ion battery as the standard vector, and take the relationship between the current and time of the lithium-ion battery during the charging process in each of the remaining charge and discharge cycles as the comparison vector. Among them, the magnitude of the current is the y-axis of the standard vector and the comparison vector, and time is the x-axis of the standard vector and the comparison vector; S8: Scale the x-axis of each comparison vector so that the comparison vector is aligned with the standard vector on the x-axis; S9: For each comparison vector, calculate the difference from the standard vector on the y-axis at the same interval in the x-axis direction, and accumulate all the differences between each comparison vector and the standard vector to obtain the cumulative minimum distance. By analyzing the change of the cumulative minimum distance with the number of charge and discharge cycles of the lithium-ion battery, judge whether the lithium-ion battery has an internal short circuit; S10: When it is judged that the lithium-ion battery has an internal short circuit, obtain the cumulative minimum distance when the lithium-ion battery has an internal short circuit and take this cumulative minimum distance as the threshold; S11: Judge whether the cumulative minimum distance of the lithium-ion battery to be detected exceeds the threshold. When the cumulative minimum distance of the lithium-ion battery to be detected exceeds the threshold, judge that the lithium-ion battery to be detected has an internal short circuit.

2. The method for detecting internal short circuits in a single lithium-ion battery according to claim 1, characterized in that, The frequency f1 is 30 ms / time.

3. The method for detecting internal short circuits in a single lithium-ion battery according to claim 1, characterized in that, The judgment of whether the lithium-ion battery has an internal short circuit includes: Set a preset change value; Judge whether the difference between the cumulative minimum distances of every two adjacent charge and discharge cycles is greater than the preset change value. When the difference is greater than the preset change value, judge that the lithium-ion battery has an internal short circuit.

4. The method for detecting internal short circuits in a single lithium-ion battery according to claim 1, characterized in that, In step S3, the lithium-ion battery is charged and discharged at a constant current and constant voltage rate of 1C, and the number of charging and discharging cycles of the lithium-ion battery n0 = 5. The charging cutoff current of the lithium-ion battery is 0.05C; In the charging and discharging cycle of the lithium-ion battery, the interval between charging and discharging is 5 minutes.

5. The method for detecting internal short circuits in a single lithium-ion battery according to claim 1, characterized in that, In step S4, the lithium-ion battery is charged and discharged at a constant current and constant voltage rate of 1C, and the number of charging and discharging cycles of the lithium-ion battery is n1 = 5. The charging cutoff current of the lithium-ion battery is 0.05C; In the charging and discharging cycle of the lithium-ion battery, the interval between charging and discharging is 5 minutes.

6. The method for detecting internal short circuits in a single lithium-ion battery according to claim 1, characterized in that, The resistance of the photoresistor is 10Ω-2000Ω.

7. The method for detecting internal short circuits in a single lithium-ion battery according to claim 1, characterized in that, The same interval described in step S9 is 30ms.

8. The method for detecting internal short circuits in a single lithium-ion battery according to claim 1, wherein the light source is a variable intensity power supply.

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