A method for detecting short circuit fault in lithium ion battery

Abstract

The application relates to the technical field of battery fault detection, in particular to a lithium ion battery internal short circuit fault detection method; in the method, first, constant voltage testing is carried out at a high SOC, and the short circuit resistance of the battery is calculated; whether the battery is short-circuited is judged according to the short circuit resistance data; if yes, then constant voltage testing is carried out at a low SOC, and the short circuit resistance is calculated; whether the battery is internally short-circuited or externally short-circuited is judged according to whether the short circuit resistance data is the same as the previous short circuit resistance data; if the battery is internally short-circuited and is a single-layer single-body structure battery, then the specific internal short circuit type is judged according to the two short circuit resistance data; through the fault detection method, the internal short circuit type of the fault resistance can be effectively judged.

Description

Technical Field

[0001] This invention relates to the field of battery fault detection technology, and specifically to a method for detecting internal short-circuit faults in lithium-ion batteries. Background Technology

[0002] With the rapid development of the electric vehicle industry, the safety performance of lithium-ion batteries has become a focus of industry attention. Internal short circuits, as one of the typical faults of lithium-ion batteries, can, in severe cases, lead to problems such as thermal runaway, seriously damaging battery reliability and threatening the safe and stable operation of electric vehicles.

[0003] Currently, there is no clear method in the industry for diagnosing internal short-circuit faults based on the expansion characteristics of internally short-circuited batteries.

[0004] The invention patent "Method for Detecting Internal Short Circuit in Lithium-ion Power Battery" published by CN107192914B describes a method that obtains a first fault position based on the battery's state of charge, a second fault position based on the battery's voltage, and a third fault position based on the battery's temperature, thereby obtaining a total fault position. The method then uses the total fault position to determine whether an internal short circuit has occurred in the single cell of the internal short circuit test, thus improving the detection accuracy of internal short circuit detection in lithium-ion power batteries.

[0005] However, the above method detects whether an internal short circuit occurs in a lithium-ion battery based on external characteristics, and cannot determine the type of internal short circuit based on external characteristics. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for detecting internal short-circuit faults in lithium-ion batteries that can determine the type of internal short-circuit fault in a lithium-ion battery.

[0007] To solve the above-mentioned technical problems, the technical solution provided by the present invention is: the method for detecting internal short circuit faults in lithium-ion batteries, comprising the following steps:

[0008] (1) Select the first SOC to perform constant voltage test on the battery under test and calculate the short-circuit resistance of the battery under test. If the short-circuit resistance of the battery under test is less than that of the conventional battery, it is judged that the battery under test has a short circuit; otherwise, it is judged that the battery under test has not a short circuit.

[0009] (2) Select a second SOC lower than the first SOC, and perform a constant voltage test on the battery under test again. Use the external stable current under constant voltage charging as the current internal short circuit current of the battery under test, calculate the short circuit resistance of the battery under test, and compare the short circuit data of the battery under test under the first SOC with the short circuit resistance data under the second SOC. If the two data are the same, it is judged that the battery under test has an external short circuit. If the two data are different, it is judged that the battery under test has an internal short circuit.

[0010] Furthermore, after determining in step (2) that the battery under test has an internal short circuit, if the battery under test is a single-layer structure cell and the short-circuit resistance data of the battery under test at the first SOC is lower than the short-circuit resistance data at the second SOC, it is determined that the battery under test has an internal short circuit between the positive and negative electrode active materials. If the short-circuit resistance data of the battery under test at the first SOC is not lower than the short-circuit resistance data at the second SOC, it is determined that the battery under test has a current collector-current collector internal short circuit or a material-current collector internal short circuit.

[0011] The above scheme can effectively detect internal short-circuit faults in batteries based on their external characteristics and obtain the specific type of internal short-circuit fault. Attached Figure Description

[0012] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0013] Figure 1 The figures show the charging voltage and expansion stress curves of the battery under different pressures in an embodiment of the present invention.

[0014] Figure 2 This is the equivalent circuit model of a normal battery and an internally short-circuited battery in the embodiments of the present invention;

[0015] Figure 3 These are the short-circuit current curves of a normal battery and a faulty battery under different pressures in an embodiment of the present invention.

[0016] Figure 4 These are the short-circuit internal resistance curves of a normal battery and a faulty battery under different pressures in this embodiment of the invention.

[0017] Figure 5 These are the short-circuit current curves of a normal battery and an internally short-circuited battery under different SOCs in embodiments of the present invention.

[0018] Figure 6 The figures show the short-circuit resistance curves of a normal battery and an internally short-circuited battery under different states of charge (SOC) in this embodiment of the invention.

[0019] Figure 7 This is a flowchart of the detection method in an embodiment of the present invention. Detailed Implementation

[0020] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention. In this embodiment, a ten-layer internal short-circuit battery with a capacity of 3.95 Ah is used as an example. A 6 mm hole is made at the center of the fifth separator layer of the battery to serve as a simulated internal short-circuit battery. Internal short-circuit fault tests are performed under three specific initial pressures.

[0021] Test 1:

[0022] Different initial preload forces were applied to normal batteries and batteries with internal short circuits between positive and negative electrode materials, respectively. Then, under the condition of maintaining constant displacement, the batteries were charged with constant current to the cutoff voltage, and the changes in battery expansion force were measured.

[0023] The charging voltage and expansion stress of a normal battery and an internally short-circuited battery under different pressures are as follows: Figure 1 As shown, it can be seen that for both normal and internally short-circuited batteries, the charging voltage is basically the same under different pressures, and the battery expansion stress gradually increases with the increase of SOC. Furthermore, the battery expansion stress is affected by the initial preload, leading to the conclusion that at the same SOC, the greater the initial preload, the greater the battery expansion stress.

[0024] Test 2:

[0025] To determine how the battery short-circuit resistance changes with the contact surface pressure, the internally short-circuited battery can be charged to a fixed state of charge (SOC). Then, different mechanical stresses are applied at the short-circuit location, and the short-circuit current of the internally short-circuited battery under different pressures is obtained using a constant-voltage charging method. The short-circuit resistance of the battery is then calculated based on an equivalent circuit model.

[0026] Taking the first-order equivalent circuit as an example, the equivalent circuit models of a normal battery and an internally short-circuited battery are as follows: Figure 2 As shown. Where U is the battery terminal voltage, I is the external charging / discharging current of the battery, and IC is the external charging / discharging current of the battery. o R is the actual charge and discharge current of the battery. o R is the ohmic internal resistance of the battery. p With C p These represent the battery's polarization internal resistance and polarization capacitance, respectively; OCV is the battery's equilibrium potential; I s With R s These are the battery short-circuit current and short-circuit resistance, respectively.

[0027] Under normal conditions, due to the presence of the separator, the battery short-circuit resistance R s Approaching infinity, the short-circuit current I sIt is almost zero. When the battery is charged to a certain SOC and switches to constant voltage charging, the external charging current I gradually decreases under the influence of depolarization. When the battery depolarization disappears, the external charging current I approaches zero.

[0028] For an internally short-circuited battery, due to the presence of the short-circuit resistance Rs, the battery short-circuit current I... s When the battery is charged to a specific SOC and transitions to constant voltage charging, the charging current I also decreases due to the initial depolarization effect. However, when the battery depolarization effect disappears, due to I... s Due to the presence of the battery, the external charging current I cannot be reduced to zero, and it gradually decreases until I... s The same applies thereafter, and remains constant. Therefore, the external stable current I under constant voltage charging can be used as the battery's current internal short-circuit current I. s .

[0029] Based on a constant terminal voltage U and internal short-circuit current I s Calculate the short-circuit resistance R s :

[0030] ;

[0031] Both the normal battery and the internally short-circuited battery were charged at constant current to the cutoff voltage under different pressures, and then switched to constant voltage charging. The test was stopped once the constant voltage charging current value stabilized. Figure 3 As shown, the current curves of a normal battery and an internally short-circuited battery after constant-voltage charging for a period of time under different pressures are plotted. It can be seen that the constant-voltage charging current of the normal battery eventually falls below 0.1mA over time, while the constant-voltage charging current of the internally short-circuited battery gradually stabilizes within the same time period, and the higher the pressure, the greater the stable value of the battery. This is achieved by using a constant terminal voltage U and the internal short-circuit current I... s ,like Figure 4 As shown, the short-circuit resistance of a normal battery and an internally short-circuited battery at a specific SOC is calculated under different pressures. For the normal battery, the short-circuit resistance is a large, constant resistance that does not change with pressure. The short-circuit resistance of the internally short-circuited battery, however, is significantly smaller and gradually decreases with increasing pressure.

[0032] Under different initial preload forces, normal batteries and batteries with internal short circuits between the positive and negative electrode active materials were charged to different states of charge (SOC) using a constant current, and then switched to constant voltage charging. The experiment was stopped when the constant voltage charging current value stabilized. The short-circuit current of the normal battery and the battery with internal short circuits at different SOCs was extracted, such as... Figure 5 and 6 As shown, the battery short-circuit resistance under the corresponding SOC is calculated according to the above formula.

[0033] As can be seen, under different initial preloads, the short-circuit resistance of the internally short-circuited battery changes significantly with SOC. Based on this characteristic, the type of short circuit can be distinguished as internal or external. Furthermore, for single-layer cells, the influence of battery expansion characteristics on different types of internal short circuits shows that with increasing SOC, the contact surface pressure between the positive and negative electrode active materials in the short-circuit region increases, while the contact surface pressure decreases for other types of internal short circuits. Therefore, the short-circuit resistance of batteries experiencing material-to-material internal short circuits shows an opposite trend to that of batteries experiencing current collector-to-current collector or material-to-current collector internal short circuits, based on this characteristic, effectively distinguishing between material-to-material internal short circuits and other types of internal short circuits.

[0034] In summary, such as Figure 7 As shown, the lithium-ion battery internal short-circuit fault detection method of the present invention includes the following steps:

[0035] (1) Select the first SOC to perform constant voltage test on the battery under test and calculate the short-circuit resistance of the battery under test. If the short-circuit resistance of the battery under test is less than that of the conventional battery, it is judged that the battery under test has a short circuit; otherwise, it is judged that the battery under test has not a short circuit.

[0036] (2) Select a second SOC lower than the first SOC, perform a constant voltage test on the battery under test again, and take the external stable current under constant voltage charging as the current internal short circuit current of the battery under test, calculate the short circuit resistance of the battery under test, compare the short circuit data of the battery under test under the first SOC with the short circuit resistance data under the second SOC, if the two data are basically the same, it is judged that the battery under test has an external short circuit, if the two data are different, it is judged that the battery under test has an internal short circuit;

[0037] After determining in step (2) that the battery under test has an internal short circuit, if the battery under test is a single-layer structure cell and the short circuit resistance data of the battery under test under the first SOC is lower than the short circuit resistance data under the second SOC, it is determined that the battery under test has an internal short circuit between the positive and negative electrode active materials. If the short circuit resistance data of the battery under test under the first SOC is not lower than the short circuit resistance data under the second SOC, it is determined that the battery under test has a current collector-current collector internal short circuit or a material-current collector internal short circuit.

[0038] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for detecting internal short-circuit faults in lithium-ion batteries, characterized in that, Includes the following steps: (1) Select the first SOC to perform a constant voltage test on the battery under test and calculate the short-circuit resistance of the battery under test. If the short-circuit resistance of the battery under test is less than that of a conventional battery, it is determined that the battery under test has a short circuit; otherwise, it is determined that the battery under test has not a short circuit. Specifically, the constant voltage test involves charging the battery with a constant current until the cutoff voltage is reached, and then switching to constant voltage charging. The test is stopped once the constant voltage charging current value stabilizes. (2) Select a second SOC lower than the first SOC, perform a constant voltage test on the battery under test again, and take the external stable current under constant voltage charging as the current internal short circuit current of the battery under test. Calculate the short circuit resistance of the battery under test, compare the short circuit resistance data of the battery under test under the first SOC with the short circuit resistance data under the second SOC. If the two data are the same, it is determined that the battery under test has an external short circuit. If the two data are different, it is determined that the battery under test has an internal short circuit.

2. The method for detecting internal short circuit faults in lithium-ion batteries according to claim 1, characterized in that, After determining in step (2) that the battery under test has an internal short circuit, if the battery under test is a single-layer structure cell and the short-circuit resistance data of the battery under test under the first SOC is lower than the short-circuit resistance data under the second SOC, then it is determined that the battery under test has an internal short circuit between the positive and negative electrode active materials. If the short-circuit resistance data of the battery under test under the first SOC is not lower than the short-circuit resistance data under the second SOC, then it is determined that the battery under test has a current collector-current collector internal short circuit or a material-current collector internal short circuit.

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