WO2023060394A1

WO2023060394A1 - Battery self-discharge detection method, and circuit and device

Info

Publication number: WO2023060394A1
Application number: PCT/CN2021/123090
Authority: WO
Inventors: 张继君; 王少飞; 魏奕民; 吴兴远; 欧阳楚英
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2021-10-11
Filing date: 2021-10-11
Publication date: 2023-04-20
Also published as: CN116783498A

Abstract

Provided in the present application is a battery self-discharge detection method. The method comprises: forming a first parallel circuit by means of a standard battery cell and a plurality of battery cells to be tested; if the first parallel circuit achieves potential balance, respectively connecting, in series, the standard battery cell and the plurality of battery cells to be tested to ammeters so as to form a second parallel circuit; if the second parallel circuit achieves potential balance, acquiring a read value of each ammeter; acquiring a standard leakage current value of the standard battery cell; and according to the standard leakage current value and the read value of each ammeter, obtaining a leakage current value of each battery cell to be tested. Potential balancing can be quickly realized, thereby improving the efficiency of a battery self-discharge test.

Description

Battery self-discharge detection method, circuit and device

technical field

The present application relates to the field of batteries, in particular to a battery self-discharge detection method, circuit and equipment.

Background technique

Energy conservation and emission reduction is the key to the sustainable development of the automobile industry, and electric vehicles have become an important part of the sustainable development of the automobile industry due to their advantages in energy conservation and environmental protection. For electric vehicles, battery technology is an important factor in its development.

At present, with the further widespread application of lithium-ion batteries, the use of batteries is not limited to the use of a single battery alone, but more and more applications tend to appear in the form of series and parallel battery packs. The inventors of the present application have discovered that the capacity and life of a battery pack are not only related to a single battery, but also related to the consistency of multiple batteries. At present, there is no effective solution for determining the consistency of batteries.

Contents of the invention

In order to solve the problem in the prior art that the battery consistency cannot be effectively determined, the embodiments of the present application provide a battery self-discharge detection method, circuit and device.

On the one hand, the embodiment of the present application proposes a battery self-discharge detection method, including:

The standard battery cell and the first current measuring meter form a first series circuit, and the battery cell to be tested and the first resistor form a second series circuit, and the resistance value of the first current measuring meter is the same as that of the first resistor;

connecting the first series circuit and the second series circuit in parallel to form a first parallel circuit;

If the first parallel circuit reaches potential equilibrium, then replace the first resistor with a second current measuring meter to form a second parallel circuit;

Acquiring the reading value of the first current measuring meter, the reading value of the second current measuring meter and the standard leakage current value of the standard cell;

According to the reading value of the first current measuring meter, the reading value of the second current measuring meter and the standard leakage current value, calculate the leakage current value of the cell under test, wherein the first current measurement The resistance value of the meter and the second current measuring meter are the same.

Through the battery self-discharge detection method proposed in the embodiment of the present application, the reading value of the second current measuring meter of each battery cell to be tested can be quickly obtained, which saves the time for potential equalization of the second parallel circuit, and greatly improves the battery detection. At the same time, by greatly reducing the total line resistance, the influence of temperature changes on the test is reduced, and the accuracy of the test is improved.

In some embodiments, before forming the first series circuit of the standard battery cell and the first current measuring meter, and forming the second series circuit of the battery cell under test and the first resistance, the steps include: forming the second series circuit of the standard battery cell and the battery cell under test Three parallel circuits; determining that the third parallel circuit achieves potential equilibrium.

In this way, since the potential equalization of the third parallel circuit is performed first, when the first parallel circuit is formed, the process of potential equalization of the first parallel circuit will be greatly accelerated, thereby improving the detection efficiency.

In some embodiments, the third parallel circuit achieves potential equalization, including: respectively obtaining the voltage values of the standard cell and the cell to be tested; if the difference between the voltage values is less than the preset first voltage threshold, it is determined that the third parallel circuit has reached potential equilibrium. In this way, it can be quickly determined whether the third parallel circuit has reached potential equilibrium, thereby improving measurement efficiency.

In some embodiments, the third parallel circuit achieves potential equalization, including: after the standard battery cell and the battery cell to be tested form a third parallel circuit, if the operating time of the third parallel circuit exceeds the first duration threshold, it is determined that the third parallel circuit has reached potential equilibrium. Realizing the potential equalization of the third parallel circuit in this way is relatively simple and convenient to implement.

In some embodiments, the first parallel circuit achieves potential equalization, including: obtaining the reading value of the first current measuring meter connected in series with the standard cell, and if the variation of the reading value is less than the preset first current threshold, Then it is determined that the first parallel circuit has reached potential equilibrium. In this way, the state of the first parallel circuit can be quickly obtained, which can greatly improve the measurement efficiency.

In some embodiments, the step of achieving the potential balance of the first parallel circuit includes: determining that the first parallel circuit has reached the potential balance when the operating time of the first parallel circuit exceeds a second duration threshold. Realizing the potential equalization of the first parallel circuit in this way is relatively simple and convenient to implement.

In some embodiments, the calculation of the leakage current value of each battery cell under test according to the reading value of the first current measuring meter, the reading value of the second current measuring meter and the standard leakage current value includes: obtaining and The reading value of the first current measuring meter connected in series with the standard battery cell; the reading value of the first current measuring meter connected in series with the standard battery cell is summed with the standard leakage current value, and subtracted from the The value of the second current measuring table is used to obtain the leakage current value of the cell to be tested.

By obtaining the standard leakage current value of the standard battery cell, combined with the measurement values of each first current measuring meter and each second current measuring meter, the leakage current value of each battery cell to be tested can be accurately calculated, which improves the measurement accuracy and measurement accuracy. s efficiency.

In some embodiments, the method further includes: if the leakage current value of the battery cell under test is greater than a preset allowable leakage current threshold, determining that the self-discharge of the battery cell under test is unqualified.

In this way, cells with abnormal self-discharge can be quickly screened out, avoiding the combination of cells with different leakage current values and affecting battery performance.

On the other hand, the embodiment of the present application also proposes a battery self-discharge detection circuit, including: a standard cell, a cell to be tested, a first resistor, a first current measuring meter, a second current measuring meter, and a first selection switch;

The standard cell and the first current measuring meter form a first series circuit;

One end of the battery cell to be tested is respectively connected to the first resistance and one end of the second current measuring meter through the first selection switch; the resistance values of the first current measuring meter and the second current measuring meter are the same;

When the first selection switch is connected to the first resistor, the cell to be tested and the first resistor form a second series circuit, and the first series circuit and the second series circuit form a first parallel circuit ;

If the first parallel circuit achieves potential balance, the first selection switch disconnects the connection between the cell to be tested and the first resistor, and connects the cell to be tested to the second current measuring meter , the battery cell to be tested and the second current measuring meter form a third series circuit;

The first series circuit and the third series circuit form a second parallel circuit.

Through the battery self-discharge detection circuit proposed in the embodiment of the present application, the reading value of the second current measuring meter of each battery cell to be tested can be quickly obtained, which saves the time for potential equalization of the second parallel circuit, and greatly improves the battery detection. At the same time, by greatly reducing the total line resistance, the influence of temperature changes on the test is reduced, and the accuracy of the test is improved.

On the other hand, the embodiments of the present application also provide a battery self-discharge detection device, including the battery self-discharge detection circuit in the above embodiments.

Description of drawings

The drawings described here are used to provide a further understanding of the application and constitute a part of the application. The schematic embodiments and descriptions of the application are used to explain the application and do not constitute an improper limitation to the application. In the attached picture:

FIG. 1 shows a flowchart of a battery self-discharge detection method proposed in an embodiment of the present application;

Fig. 2 shows a schematic diagram of the connection of the first parallel circuit proposed by the embodiment of the present application;

Fig. 3 shows a schematic diagram of the connection of the second parallel circuit proposed by the embodiment of the present application;

Fig. 4 shows the experimental data diagram of leakage current test temperature proposed by the embodiment of the present application;

Fig. 5 shows the experimental data diagram of the balanced leakage current test proposed in the embodiment of the present application;

FIG. 6 shows a schematic diagram of the connection of the third parallel circuit proposed by the embodiment of the present application;

FIG. 7 shows a structural diagram of a battery self-discharging detection circuit proposed by an embodiment of the present application.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are the Claim some of the examples, not all of them. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of this application.

Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the technical field of this application; the terms used in this application in the description of the application are only to describe specific implementations The purpose of the example is not intended to limit the present application; the terms "comprising" and "having" and any variations thereof in the description and claims of the present application and the description of the above drawings are intended to cover non-exclusive inclusion. The terms "first", "second" and the like in the description and claims of the present application or the above drawings are used to distinguish different objects, rather than to describe a specific sequence or primary-subordinate relationship.

Reference in this application to an "embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearances of this phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are independent or alternative embodiments mutually exclusive of other embodiments. It is understood explicitly and implicitly by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

In the description of this application, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installation", "connection", "connection" and "attachment" should be understood in a broad sense, for example, it may be a fixed connection, It can also be detachably connected or integrally connected; it can be directly connected or indirectly connected through an intermediary, and it can be internal communication between two components. Those of ordinary skill in the art can understand the specific meanings of the above terms in this application according to specific situations.

The term "and/or" in this application is only an association relationship describing associated objects, which means that there may be three relationships, for example, A and/or B, which may mean: A exists alone, A and B exist simultaneously, and A and B exist alone. There are three cases of B. In addition, the character "/" in this application generally indicates that the contextual objects are an "or" relationship.

"Multiple" appearing in this application refers to more than two (including two), similarly, "multiple groups" refers to more than two groups (including two groups), and "multi-piece" refers to more than two (Includes two pieces).

In the present application, the battery cells may include lithium-ion secondary batteries, lithium-ion primary batteries, lithium-sulfur batteries, sodium-lithium-ion batteries, sodium-ion batteries, or magnesium-ion batteries, which are not limited in the embodiments of the present application. The battery cell can be in the form of a cylinder, a flat body, a cuboid or other shapes, which is not limited in this embodiment of the present application. Battery cells are generally divided into three types according to packaging methods: cylindrical battery cells, square square battery cells and pouch battery cells, which are not limited in this embodiment of the present application.

At present, with the development of technology, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydraulic, thermal, wind and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric vehicles, as well as military equipment and aerospace and other fields . With the continuous expansion of power battery application fields, its market demand is also constantly expanding.

The applicant found in the research that the capacity and life of the battery are not only related to the battery cell, but also related to the consistency of the battery. The consistency of self-discharge is an important part. The self-discharge of the battery affects the battery cell, The overall performance of the battery module and even the electric cabinet. Therefore, in the production process, it is very important to screen and classify the self-discharge consistency of the battery cells, and how to quickly judge the size of the self-discharge is the key difficulty.

At present, the main self-discharge screening method for lithium-ion batteries is to measure the battery K value (OCV changes with time), that is, to test the voltage drop of the battery per unit time. Although this method can effectively detect the self-discharge rate of the battery, it has a big disadvantage, that is, it takes a long time. This method originated from the self-discharge detection of lithium-ion batteries for portable devices with low capacity. The test time is relatively acceptable. However, as the capacity of the battery cell increases, if it is used for the detection of large batteries such as power lithium-ion batteries, The voltage drop per unit time becomes very small, which is limited by the measurement accuracy of the voltage, so it takes a longer time to measure the self-discharge rate more accurately.

At present, there are still some methods based on leakage current testing, such as constant voltage source-cell method and cell-cell parallel connection method. The main judgment is based on the compensation current at the same time Δt or the change ΔI of the current. As the capacity of the battery cell increases, the ΔI change in a short period of time is small. Considering the actual production line application, the ambient temperature change is an important factor. If the temperature change is superimposed, it may take longer to identify the leak. difference in current changes. At the same time, the current difference measured by this method is a relative value, not the absolute leakage current of the cell, so it is difficult to formulate screening criteria.

Based on the above considerations, the embodiment of the present application proposes a battery self-discharge detection method, circuit and detection equipment, which connects a standard battery cell with a known leakage current value and the battery cell under test, and first uses a resistor instead of an ammeter for potential equalization. After the potential balance is reached, switch the resistance to the current measuring meter for current measurement, and replace the change of the test voltage by the change of the test current. It does not need to stand for a long time, and can detect the leakage of each cell more accurately and intuitively. current situation. At the same time, by reducing the total line resistance, the leakage current with a larger value can be reached more quickly, and the influence of temperature on the measurement accuracy can be effectively avoided.

When implementing the battery self-discharge detection method, circuit and detection equipment proposed in the embodiments of the present application, potential equalization and total line resistance are two factors that have a relatively large impact on the detection results.

Potential balance refers to the voltage balance between the cells. If the voltage between the cells is in an unbalanced state, the current in the line will be too large. If the current in the line is too large, there will be an Larger current charging and discharging will cause the polarization of the battery to increase, causing the polarization current to increase, which will increase the basic current of the test, and the battery will need a longer time to perform depolarization operations to detect the real leakage current. In order to quickly achieve balance, the potentials between the cells should be as balanced as possible to ensure that the initial current is in a low range, which is not enough to cause or minimize the generation of polarization current.

The total line resistance refers to the total resistance value of the entire detection circuit, mainly including the resistance of the connecting sheet, the internal resistance of the cell, the internal resistance of the ammeter, and the resistance of the test line. If the total line resistance is too large, the current value in the line will be low. , if the same balance leakage current is to be achieved, a longer balance time is required. Since the internal resistance of the battery cell and the connecting sheet resistance are much smaller than the internal resistance of the ammeter and the resistance of the test line, the reduction of the total line resistance is mainly to reduce the internal resistance of the ammeter and the resistance of the test line.

Fig. 1 shows the flowchart of the battery self-discharge detection method proposed in the embodiment of the present application, the battery self-discharge detection method mainly includes:

Step 110: form a first series circuit with the standard battery cell and the first current measuring meter, and form a second series circuit with the battery cell to be tested and the first resistor, the first current measuring meter and the first resistor have the same resistance value.

The standard battery cell refers to the battery cell with known leakage current value. The performance of the standard battery cell is relatively stable, and its leakage current value is known, which can be used as a standard for measurement comparison. Usually, the battery cell stored for about 90 days is selected as the standard battery cell. Use the known leakage current value as the standard leakage current value for comparison. Of course, other standards can also be used for the selection of the standard cell, as long as it has a stable standard leakage current value. The number of standard batteries can be one or more, and the number is not limited.

Figure 2 is a schematic diagram of the connection of the battery self-discharge detection circuit proposed by the embodiment of the present application. In the figure, the first current measuring meter A1 is connected to one end of the standard battery S, and is connected in series with the standard battery S, and the first resistor is set at the end of the standard battery S. One end of the cell under test forms a second series circuit with the cell to be tested. As shown in FIG. 2 , each cell to be tested forms a second series circuit with a different first resistor.

In order to achieve potential equilibrium as soon as possible and avoid the generation of polarization current, the resistance value of the first resistor is the same as the resistance value of the first current measuring meter. Smaller connecting wires.

Since the total resistance value of the circuit has a great influence on the potential balance, if the total resistance value of the circuit is too large, the time for potential balance will be too long. In the embodiment of the present application, the resistance value of each first resistor is not greater than 50 milliohms. Under this resistance value, the potential equalization time of the first parallel circuit is greatly shortened, as shown in Table 1, which shows the time required for the circuit to achieve potential equalization when the first resistors with different resistance values are selected.

Table 1

第一电阻阻值The first resistance value	电位均衡时间 Potential equalization time
1毫欧1 milliohm	1.25小时1.25 hours
10毫欧10 milliohms	2.5小时2.5 hours
100毫欧100 milliohms	20小时20 hours
1欧1 euro	150小时150 hours

10 euros

1750 hours

It can be seen from Table 1 that the embodiment of the present application uses the first resistor with a resistance value not greater than 50 milliohms, which can greatly shorten the time for potential equalization.

Step 120: Connect the first series circuit and the second series circuit in parallel to form a first parallel circuit.

Continuing to refer to FIG. 2 , after completing the first series circuit of the first current measuring meter A1 and the standard cell S, and the second series circuit of the cell to be tested and the first resistor, the first series circuit and the plurality of second series circuits The two series circuits are connected in parallel to form a first parallel circuit. In the first parallel circuit, the negative poles of each battery cell to be tested are connected, and the positive poles are respectively connected to the first resistor.

Step 130: If the first parallel circuit reaches potential equilibrium, replace the first resistor with a second current measuring meter to form a second parallel circuit.

After the standard cell, the cell to be tested, the first current measuring meter A1 and the first resistor form the first parallel circuit, it is necessary to perform potential equalization among the cells to reduce the influence of the polarization current. The potential equalization of the first parallel circuit can be carried out by resting the first parallel circuit. For example, after the first parallel circuit is left for 3-5 hours, it is considered that it has reached the potential equalization potential equalization; it can also be judged The reading value variation of the first current measuring meter connected in series with the standard battery cell is used to determine whether the first parallel circuit has reached potential equilibrium.

When the first parallel circuit reaches the potential balance, it is considered that the polarization current between the standard cell and each cell to be tested is the smallest, and the cell is in a stable state, and the first resistor is replaced by the second current measuring meter respectively, forming second parallel circuit.

The second parallel circuit is shown in Figure 3. After the first parallel circuit reaches potential equilibrium, the first current measuring meter A1 connected to the standard cell S remains unchanged, and the first resistor connected in series with each cell to be tested is quickly Replaced by second current measuring gauges A2, A3...A16 etc.

Since the leakage current value of each battery cell is generally relatively small, in order to accurately measure the leakage current value of each battery cell to be tested, both the first current measuring meter and the second current measuring meter need to use high-precision ammeters, for example: you can choose an accuracy of ±1uA current measuring meter. At the same time, the resistance values of the selected first current measuring meters and the second current measuring meters should be consistent, or the difference between the resistance values of the first current measuring meters and the second current measuring meters should be within a certain threshold range to avoid resistance. If the value differs too much, it will affect the measurement accuracy. That is, the resistance values of the first current measuring meter, the second current measuring meter and the first resistor used in the embodiment of the present application must be the same or the resistance difference is within a certain threshold range.

When replacing the first resistor with the second current measuring meter, fast switching is required to avoid potential imbalance of the second parallel circuit caused by too slow switching speed. The above-mentioned switching is carried out after the first parallel circuit reaches potential equilibrium, and the resistance values of the first resistor and the second current measuring meter are the same, therefore, quickly switching the first resistor to the second current measuring meter will not destroy the original The potential equilibrium state of the first parallel circuit, after forming the second parallel circuit, the second parallel circuit can still be in the potential equilibrium state, thereby avoiding the influence of the polarization current on the second parallel circuit.

Step 140: Obtain the reading value of the first current measuring meter, the reading value of the second current measuring meter and the standard leakage current value of the standard cell.

After the first resistor is switched to the second current measuring meter, since the second parallel circuit is still in the potential equalization state, it is not necessary to perform potential equalization on the second parallel circuit, and the first current measuring meter and the second current The measuring meter obtains the current reading value of each series circuit, which saves the time for potential equalization of the second parallel circuit, and greatly improves the efficiency of self-discharge detection of the battery cell.

Obtain the current reading value of each series circuit by reading the first current measuring meter and the second current measuring meter, for example: the reading value of the current measuring meter connected to the standard cell is _Is , and the current measuring meter connected to the cell to be tested The reading values of are respectively I ₂ , I ₃ , I ₄ ... I ₁₅ .

Since the standard leakage current value is known when selecting a standard cell, it is sufficient to use the standard leakage current value I _s directly.

Step 150: Calculate the leakage current value of the cell to be tested according to the reading value of the first current measuring meter, the reading value of the second current measuring meter and the standard leakage current value.

Since the reading values of the first current measuring meter and each second current measuring meter are obtained when the second parallel circuit is in the potential equilibrium state, the total current value of each series circuit is the same, that is, each to-be-tested The leakage current value of the cell is equal to the sum of the current values measured by the second current measuring meter corresponding to the cell to be tested.

Assuming that the leakage current value of each cell to be tested is I _{2 leakage} , I _{3 leakage} ...I _{15 leakage} , the leakage current value of each cell to be tested can be calculated by the following formula:

I _s +I _{s leak} =I ₂ +I _{2 leak} =I ₃ +I _{3 leak} =...=I ₁₅ +I _{15 leak} ;

Since _{the leakage of I s} is known, I _s , I ₂ , I ₃ , I ₄ _. Display the leakage current value of each cell to be tested: I _{2 leakage} , I _{3 leakage} ...I _{15 leakage} .

Figure 4 shows a schematic diagram of the influence of temperature fluctuations on the measurement results when the battery self-discharge detection method proposed in the embodiment of the present application is used to detect the leakage current. It can be seen from the figure that the method proposed in the embodiment of the present application, After a parallel circuit reaches potential equilibrium, when the temperature changes at ±1°C, ±2°C and ±3°C, the impact on the leakage current value of each battery cell to be tested is very small, which further verifies the self-discharge of the battery provided by this application. The effectiveness of the detection method.

Figure 5 shows the Simulink simulation results of self-discharge detection using the battery self-discharge detection method proposed in this application, simulating batteries with different leakage currents, when the line resistance is fixed, the self-discharge of the battery proposed by the embodiment of the application When the detection method is tested, the change of the balance leakage current and the balance time further verify the feasibility of the test method proposed in the embodiment of the present application.

As can be seen from the above, the battery self-discharge detection method proposed in the embodiment of the present application achieves After the potential is balanced, the first resistor is switched to the second current measuring meter, and the reading value of the second current measuring meter of each cell to be tested can be quickly obtained, which saves the time for potential equalization of the second parallel circuit and greatly improves the At the same time, by greatly reducing the total line resistance, the influence of temperature changes on the test is reduced, and the accuracy of the test is improved.

In some embodiments, in order to achieve a better detection effect and improve the accuracy of detection, the standard cell and the first current measuring meter are formed into a first series circuit, and the cell to be tested and the first resistor are formed into a second series circuit Before, it further includes: forming a third parallel circuit with the standard cell and the cell to be tested; determining that the third parallel circuit has reached potential equilibrium.

As shown in Figure 6, in order to reduce the influence of the polarization current, before the standard cell and the first current measuring meter form the first series circuit, and the test cell and the first resistor form the second series circuit, Firstly, the potential of the standard cell and each cell to be tested is equalized.

FIG. 6 shows a third parallel circuit formed by connecting the standard cell and the cell under test in parallel. The third parallel circuit is used to equalize the potential between the cells to reduce the influence of the polarization current. The potential equalization of the third parallel circuit can be carried out by placing the third parallel circuit at rest. For example, after the third parallel circuit is left standing for 12 hours, it is considered that it has reached the potential equilibrium; it can also be determined by judging the standard voltage. The voltage variation of the core and each cell under test, if the variation is less than a certain threshold, it is considered that it has reached the potential equilibrium. When the third parallel circuit reaches the potential balance, it is considered that the polarization current between the standard battery cell and each battery cell to be tested is the smallest, and the battery cell is in a stable state, and the standard battery cell, the first current measuring meter, and each battery cell to be tested are respectively connected to The battery cell and each first resistor form a first parallel circuit.

In some embodiments, determining whether the third parallel circuit has reached potential equalization includes: respectively obtaining the voltage values of the standard cell and the plurality of cells to be tested; if the difference between the voltage values is less than the preset first voltage threshold, then determine The third parallel circuit achieves potential equalization.

After the standard cell and multiple cells to be tested form a third parallel circuit, it is necessary to perform potential equalization on the third parallel circuit. Potential equalization can greatly reduce the polarization current between the cells and improve the accuracy of detection.

In the embodiment of the present application, it may be determined whether the third parallel circuit has reached potential equilibrium by obtaining the voltage difference between the standard cell and each cell to be tested. The voltage values at both ends of the standard cell and each cell to be tested are measured by a voltmeter, and when the difference between the voltages is less than the preset first voltage threshold, it is determined that the third parallel circuit has reached potential equilibrium.

In this way, it can be quickly determined whether the third parallel circuit has reached potential equilibrium, thereby improving measurement efficiency.

In some embodiments, to determine whether the third parallel circuit has reached the potential balance, it is also possible to make the third parallel circuit run for a time exceeding the first duration threshold after the standard cell and multiple cells to be tested form the third parallel circuit, then Make sure that the third parallel circuit achieves potential equalization.

As an alternative to the above method, in the embodiment of the present application, after the construction of the third parallel circuit is completed, the third parallel circuit is statically placed, and when the static running time of the third parallel circuit exceeds the first duration threshold, the third parallel circuit is determined. Parallel circuits achieve potential equalization. The first duration threshold is generally set to 10-12 hours. Realizing the potential equalization of the third parallel circuit in this way is relatively simple and convenient to implement.

In some embodiments, to determine whether the first parallel circuit has reached the potential balance, it can be obtained by obtaining the reading value of the first current measuring meter connected in series with the standard cell, and if the change in the reading value is less than the preset first current threshold, then the first Parallel circuits achieve potential equalization.

In step 130, after connecting the standard cell in series with the first current measuring meter and the cell under test in series with the first resistor, a first parallel circuit is formed, and the first parallel circuit needs to be placed in a state of potential balance. In the embodiment of the present application, by obtaining the reading value i of the first current measuring meter connected in series with the standard cell, it can be judged whether the change in the reading value of the current measuring meter of the standard cell is less than the preset first current threshold value, which can be determined by judging Whether the reading value of the first current measuring meter connected in series with the standard cell is stable, that is, when di/dt=0, it is considered that the first parallel circuit is in a state of potential equilibrium. If the first parallel circuit has not reached the potential equilibrium state, continue to wait for it to reach the potential equilibrium state.

In this way, the state of the first parallel circuit can be quickly obtained, which can greatly improve the measurement efficiency.

In some embodiments, determining whether the first parallel circuit reaches potential equilibrium may be determined by determining whether the operating time of the first parallel circuit exceeds a second duration threshold, and if so, determining that the first parallel circuit has reached potential equilibrium.

As an alternative to the above method, in the embodiment of the present application, after the construction of the first parallel circuit is completed, the first parallel circuit is placed statically, and when the static running time of the first parallel circuit exceeds the first duration threshold, the first parallel circuit is determined. Parallel circuits achieve potential equalization. The second duration threshold is generally set to 3-5 hours. Realizing the potential equalization of the first parallel circuit in this way is relatively simple and convenient to implement.

In some embodiments, according to the reading value of the first current measuring meter, the reading value of the second current measuring meter and the standard leakage current value, calculating the leakage current value of each battery cell to be tested includes: obtaining the first battery cell connected in series with the standard battery cell The reading value of a current measuring meter; the reading value of the first current measuring meter connected in series with the standard cell and the standard leakage current value are summed, and the value of the second current measuring meter connected in series with the cell to be tested is subtracted to obtain Leakage current value of each cell under test.

In step 150, it is necessary to calculate the leakage current value of each battery cell to be tested according to the standard leakage current value and the reading values of each first current measuring meter and each second current measuring meter, because each first current measuring meter and each second current measuring meter The reading value of the two current measuring meters is obtained when the second parallel circuit is in the potential equilibrium state, therefore, the total current value of each series circuit is the same, that is, the leakage current value of each battery cell to be tested is the same as the current value of the battery cell to be tested. The sum of the current values measured by the current measuring meters corresponding to the measuring cells are all equal.

Since the I _{s leakage} is known, I _s , I ₂ , I ₃ , I _{4 .} . . I ₁₅ are the reading values measured by each first current measuring meter and each second current measuring meter, therefore, The leakage current value of each cell to be tested can be calculated I _{2 leakage} , I _{3 leakage} ...I _{15 leakage} .

In some embodiments, after obtaining the leakage current value of each battery cell to be tested, it is judged whether the leakage current value of the battery cell to be tested is greater than the preset allowable leakage current threshold, and if it is greater, it is determined that the battery cell to be tested is unqualified for self-discharge .

The purpose of measuring the leakage current value of the battery cell is to screen unqualified cells to be tested, and avoid setting cells with large leakage current values together to affect the overall performance of the battery. After the leakage current value is determined, it can be judged whether each cell under test is qualified according to the preset permissible leakage current threshold. The permissible leakage current threshold can be converted to the maximum allowable leakage current value I _max through the monthly self-discharge rate of each battery cell to be tested. If the leakage current value I _{n of the battery cell to be tested is leaked} < I _max , the battery to be tested is considered to be The cell is normal, otherwise the cell is considered to be abnormal.

The embodiment of the present application also proposes a battery self-discharge detection circuit. As shown in FIG. , the second current measuring meter A2, A3...A16 and the first selection switch K1, K2...K16; the standard cell S and the first current measuring meter A1 form the first series circuit; One end of the battery cell D is connected to the first resistance R and one end of the second current measuring meter A2 respectively through the first selection switch K; the resistance values of the first current measuring meter A1 and the second current measuring meter A2 are the same; the first When the selection switch K is connected to the first resistor R, the cell D to be tested and the first resistor R form a second series circuit, and the first series circuit and the second series circuit form a first parallel circuit; if the first parallel circuit reaches potential equilibrium, The first selection switch K disconnects the connection between the cell D to be tested and the first resistor R, and connects the cell D to be tested to the second current measuring meter A2, and the cell D to be tested and the second current measuring meter A2 form a third A series circuit; the first series circuit and the third series circuit form a second parallel circuit.

The standard cell S refers to the cell with known leakage current value. The performance of the standard cell is relatively stable, and its leakage current value is known, which can be used as a standard for measurement comparison. Usually, the cell that has been stored for about 90 days is selected as the standard cell. , taking the known leakage current value as the standard leakage current value for comparison. Of course, other standards can also be used for the selection of the standard cell, as long as it has a stable standard leakage current value.

The first current measuring meter A1 and the second current measuring meter A2 are current measuring meters with the same resistance value, generally high-precision ammeters, for example, a current measuring meter with an accuracy of ±1uA can be selected. At the same time, the resistance values of the selected first current measuring meters and the second current measuring meters should be consistent, or the resistance difference between the first current measuring meters and the second current measuring meters should be within a certain threshold range, so as to avoid the The resistance value difference of the current measuring meter is too large, which affects the measurement accuracy. At the same time, since the total resistance value of the circuit has a great influence on the potential equalization, if the total resistance value of the circuit is too large, the time for potential equalization will be too long. The resistance value of the resistance value is not more than 50 milliohms. Under this resistance value, the potential equalization time of the second parallel circuit is greatly shortened. As shown in Table 1, it shows that the current measuring meter with different resistance values is selected, and the circuit reaches potential equalization. the time required.

The control switch K1 is a single-pole two-throw switch, which is respectively connected to the first current measuring meter and the positive and negative poles of the battery cell, and is used to control the access of the first current measuring meter. The control switches K2, K3...K16 are single-pole three-throw switches, which are respectively connected to the first resistor, the second current measuring meter, and the positive and negative poles of the battery cell, and are used to respectively switch the first resistor to The second current measuring meter, alternatively, short the first resistor or the second current measuring meter. Of course, the control switches K1, K2...K16 can also use other types of switches, such as single-pole single-throw switches, and multiple single-pole single-throw switches can be set, respectively connected to the first resistor, the second current measuring meter, etc. , is not limited here.

As shown in Figure 7, the standard cell S is connected in parallel with multiple cells D2, D3...D16 to be tested, and current measuring meters A2, A3..... are connected in series at one end of each cell to be tested. .A16, the first resistors R2, R3...R16 are respectively connected to the two ends of the control switch K at both ends of the first current measuring meter and the second current measuring meter, K1 is set at both ends of A1, K2 is set at both ends of A2 and R2..., K16 is set at both ends of A16 and R16.

It can be known from the above circuit structure that when the leakage current of each battery cell to be tested is detected by the battery self-discharge detection circuit, each control switch K1, K2, ..., K16 is first contacted with the contact point 1, when When the control switch is placed at the contact point 1, each current measuring meter and the first resistor are directly short-circuited, and the positive and negative poles of each cell are connected to form a third parallel circuit.

When the third parallel circuit reaches the potential equilibrium state, turn on the control switch K1, and at the same time place each control switch K2, ..., K16 on the contact point 2, then each first resistor is connected in series with each cell to be tested , forming a first parallel circuit.

When the first parallel circuit reaches the potential equilibrium state, the control switches K1, K2...K16 are placed on the contact point 3, and the current measuring meters A1, A2, A3...A16 are connected with the standard electric current The cells and the cells to be tested are connected in series to form a second parallel circuit.

When the second parallel circuit reaches the potential equilibrium state, read the reading values of each current measuring meter A1, A2, A3...A16 respectively, and obtain the standard leakage current value of the standard cell at the same time, which will be compared with the standard current value The reading value of the current measuring meter connected in series with the cells is summed with the standard leakage current value, and the value of the current measuring meter connected in series with each cell to be tested is subtracted to obtain the leakage current value of each cell to be tested.

The battery self-discharge test circuit proposed in the embodiment of the present application is connected to the standard battery cell, after the first parallel circuit composed of the standard battery cell, the first current measuring meter, the battery cell to be tested and the first resistor reaches the potential balance, Switching the first resistor to the second current measuring meter can quickly obtain the reading value of the second current measuring meter of each cell to be tested, which saves the time for potential equalization of the second parallel circuit and greatly improves the efficiency of cell detection. At the same time, by greatly reducing the total line resistance, the influence of temperature changes on the test is reduced, and the accuracy of the test is improved.

Some embodiments of the present application also propose a battery self-discharge detection device, including the battery self-discharge detection circuit in the above embodiments. The battery self-discharge detection circuit includes: a standard cell S, a cell D to be tested, a first resistor R, The first current measuring meter A1, the second current measuring meter A2, A3...A16 and the first selection switch K1, K2...K16; the standard cell S is composed of the first current measuring meter A1 The first series circuit; one end of the cell D to be tested is connected to the first resistance R and one end of the second current measuring meter A2 through the first selection switch K; the first current measuring meter A1 and the second current measuring meter A2 The resistance values are the same; when the first selection switch K is connected to the first resistor R, the cell D to be tested and the first resistor R form a second series circuit, and the first series circuit and the second series circuit form a first parallel circuit; if the first The parallel circuit achieves potential balance, the first selection switch K disconnects the connection between the cell D to be tested and the first resistor R, connects the cell D to be tested to the second current measuring meter A2, and the cell D to be tested is connected to the second current measuring meter A2. The measuring meter A2 forms a third series circuit; the first series circuit and the third series circuit form a second parallel circuit.

The battery self-discharge detection device proposed in the embodiment of the present application can quickly realize potential equalization, improve the efficiency of battery self-discharge test, and at the same time, by greatly reducing the total line resistance, the influence of temperature changes on the test is reduced. Improved test accuracy.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, rather than limiting them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some of the technical features, but these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

A battery self-discharge detection method, characterized in that, comprising:

The standard battery cell and the first current measuring meter form a first series circuit, and the battery cell to be tested and the first resistor form a second series circuit, and the resistance value of the first current measuring meter is the same as that of the first resistor;

connecting the first series circuit and the second series circuit in parallel to form a first parallel circuit;

If the first parallel circuit reaches potential equilibrium, then replace the first resistor with a second current measuring meter to form a second parallel circuit;

Acquiring the reading value of the first current measuring meter, the reading value of the second current measuring meter and the standard leakage current value of the standard cell;

According to the reading value of the first current measuring meter, the reading value of the second current measuring meter and the standard leakage current value, calculate the leakage current value of the cell under test, wherein the first current measurement The resistance value of the meter and the second current measuring meter are the same.
The method according to claim 1, characterized in that, before forming the standard cell and the first current measuring meter into the first series circuit, and the cell under test and the first resistance forming the second series circuit, further comprising:

The standard cell and the cell to be tested form a third parallel circuit;

It is determined that the third parallel circuit achieves potential equalization.
The method according to claim 2, wherein the third parallel circuit to achieve potential equalization comprises:

Obtaining the voltage values of the standard cell and the cell to be tested respectively;

If the difference between the voltage values is smaller than the preset first voltage threshold, it is determined that the third parallel circuit has reached potential equilibrium.
The method according to claim 2, wherein the third parallel circuit to achieve potential equalization comprises:

After the standard cell and the cell to be tested form a third parallel circuit, if the running time of the third parallel circuit exceeds a first duration threshold, it is determined that the third parallel circuit has reached potential equilibrium.
The method according to claim 3 or 4, wherein the first parallel circuit to achieve potential equalization comprises:

Acquiring the reading value of the first current measuring meter connected in series with the standard battery cell, and if the variation of the reading value is smaller than the preset first current threshold, it is determined that the first parallel circuit has reached potential equilibrium.
The method according to claim 3 or 4, wherein the first parallel circuit to achieve potential equalization comprises:

When the running time of the first parallel circuit exceeds the second duration threshold, it is determined that the first parallel circuit has reached potential equilibrium.
The method according to any one of claims 1-6, characterized in that, according to the reading value of the first current measuring meter, the reading value of the second current measuring meter and the standard leakage current value, calculate the The leakage current value of the battery cell, including:

Obtain the reading value of the first current measuring meter connected in series with the standard cell;

summing the reading value of the first current measuring meter connected in series with the standard cell and the standard leakage current value, and subtracting the value of the second current measuring meter connected in series with the cell to be tested to obtain the The leakage current value of the cell.
The method of claim 7, further comprising:

If the leakage current value of the battery cell under test is greater than the preset permissible leakage current threshold, it is determined that the self-discharge of the battery cell under test is unqualified.
A battery self-discharge detection circuit, characterized in that it includes: a standard cell, a cell to be tested, a first resistor, a first current measuring meter, a second current measuring meter, and a first selection switch;

The standard cell and the first current measuring meter form a first series circuit;

One end of the battery cell to be tested is respectively connected to the first resistance and one end of the second current measuring meter through the first selection switch; the resistance values of the first current measuring meter and the second current measuring meter are the same;

When the first selection switch is connected to the first resistor, the cell to be tested and the first resistor form a second series circuit, and the first series circuit and the second series circuit form a first parallel circuit ;

If the first parallel circuit achieves potential balance, the first selection switch disconnects the connection between the cell to be tested and the first resistor, and connects the cell to be tested to the second current measuring meter , the battery cell to be tested and the second current measuring meter form a third series circuit;

The first series circuit and the third series circuit form a second parallel circuit.
A battery self-discharge detection device, characterized in that it comprises the battery self-discharge detection circuit according to claim 9.