Method and device for determining battery pack self-discharge

Abstract

The present invention provides a method and a device for determining the self-discharge of a battery pack. The method for determining the self-discharge of the battery pack according to the present invention first obtains the discharge capacity C0 of the battery pack at room temperature; then, based on the obtained discharge capacity C0, the battery pack is discharged in stages to obtain the discharge capacity C at each stage. n , and the discharge operations of each stage of the battery pack are carried out at room temperature; after the battery pack is charged, at room temperature, the battery pack is left standing and discharged in stages to obtain the actual discharge capacity C at each stage. m ; finally, based on the discharge capacity C at each stage n and the actual discharge capacity C at each stage m , the self-discharge rate of the battery pack is obtained. In the determination method of the present invention, two groups of discharge capacitance measurement values are detected, and one of the measurement values is obtained after the battery pack is left standing to adapt to the ambient temperature, which can reduce the influence of the temperature rise factor of the battery pack caused by discharge on the capacitance measurement error; with the help of the correction calculation of the two groups of data, it is beneficial to measure the more accurate self-discharge rate of the battery pack.

Description

Technical Field

[0001] The present invention relates to the field of battery testing technology, and in particular to a method for determining self-discharge of a battery pack. In addition, the present invention also relates to a device for determining self-discharge of a battery pack. Background Art

[0002] Due to the advantages of high energy density, long service life and high voltage, lithium-ion batteries have been widely used in the rapidly developing new energy market. However, during the storage process of the battery, the capacity is usually attenuated, a phenomenon called battery self-discharge. Generally speaking, there are two types of self-discharge of lithium-ion batteries: one is the self-discharge caused by the physical micro-short circuit inside the battery, which is generally small and reversible; the other is a chemical reaction, that is, the chemical reaction between the electrolyte and the positive and negative electrodes, which is irreversible. However, no matter which type of self-discharge occurs, it will affect the performance of the battery. If the self-discharge rate of the battery cannot be accurately tested, it will affect the battery system's assessment of its life, and even affect the vehicle's warranty and functional safety.

[0003] Therefore, determining an accurate and reasonable self-discharge test method is of great significance to the performance evaluation of battery systems. Most of the existing self-discharge test methods are formulated in reference to relevant standards. Generally, the battery is first adapted to the environment at room temperature, then standard charged at room temperature, and then standard cycle (standard discharge + standard charge), and the standard discharge capacity C0 is recorded; thereafter, the battery's SOC (state of charge) is adjusted to 50%, and the discharge capacity C1 is recorded; thereafter, the battery is stored at the corresponding temperature (general test conditions are 25℃~45℃) for 720 hours (30 days), adapted to the environment at room temperature, and then standard cycle (standard discharge + standard charge) is performed twice at room temperature, and the standard discharge capacities C2 and C3 are recorded.

[0004] Through the above test method, the self-discharge rate of the battery pack can be obtained as (1-(C1+C2) / C0)*100%, and the capacity recovery rate is C3 / C0. However, with the development of lithium-ion batteries, the types of battery pack structures have become more diverse. During the charging and discharging process of the battery pack, there will definitely be different degrees of temperature rise, and the temperature will affect the performance of the entire battery system. The above method does not take into account the impact of temperature changes during the charging and discharging process, and does not eliminate the error caused by this factor, so the self-discharge rate obtained by the test will be inaccurate.

[0005] However, as an important indicator of battery performance, self-discharge has strict index requirements in battery design verification, product verification and shipment requirements. If self-discharge cannot be accurately tested, it will affect product performance and even affect customer use. Summary of the invention

[0006] In view of this, the present invention aims to provide a method for determining the self-discharge of a battery pack, so as to improve the measurement accuracy of the self-discharge rate of the battery pack.

[0007] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0008] A method for determining self-discharge of a battery pack, the method comprising the following steps:

[0009] Get the discharge capacity C0 of the battery pack at room temperature;

[0010] According to the obtained discharge capacity C0, the battery pack is discharged in stages to obtain the discharge capacity C in each stage. n , the discharge operation of each stage of the battery pack is carried out at room temperature;

[0011] After charging the battery pack, the battery pack is left to stand at room temperature and discharged in stages to obtain the actual discharge capacity C at each stage. m ;

[0012] According to the discharge capacity C at each stage n And the actual discharge capacity C at each stage m , get the self-discharge rate of the battery pack.

[0013] Furthermore, the method further comprises the following steps:

[0014] Get the actual discharge capacity C at each stage m After that, the battery pack is charged, and the battery pack is discharged after the temperature of the battery pack is allowed to stand at room temperature to obtain the discharge capacity C of the battery pack. x ;

[0015] Based on discharge capacity C0 and discharge capacity C x , obtain the capacity recovery rate of the battery pack.

[0016] Furthermore, the capacity recovery rate is C x / C0.

[0017] Furthermore, the self-discharge rate of the battery pack is (1-actual discharge capacity C m Sum / Each discharge capacity C n sum)*100%.

[0018] Furthermore, the discharge capacity C0 is obtained by the following steps:

[0019] Adapting the battery pack to the environment at room temperature;

[0020] Performing standard discharge at room temperature, and then leaving the battery pack to stand until the temperature of the battery pack reaches room temperature;

[0021] Performing standard charging at room temperature, and then leaving the battery pack to stand until the temperature of the battery pack reaches room temperature;

[0022] Perform standard discharge at room temperature, then leave the battery pack to stand until the temperature of the battery pack reaches room temperature, and obtain the discharge capacity C0 of the battery pack.

[0023] Furthermore, the discharge capacity C at each stage n Including discharge capacity C n1 and discharge capacity C n2 According to the discharge capacity C0, adjust the battery pack SOC to 50% at room temperature to obtain the discharge capacity C of the battery pack at this time n1 Then, the battery pack is left to stand until the temperature of the battery pack reaches room temperature, and then a standard discharge is performed until the battery pack reaches the cut-off voltage, and the discharge capacity C of the battery pack in this process is obtained. n2 .

[0024] Furthermore, after a standard discharge is performed until any cell in the battery pack reaches a cut-off voltage, the discharge capacity C of the battery pack in this process is obtained. n2 .

[0025] Furthermore, the actual discharge capacity C m Including actual discharge capacity C m1 And the actual discharge capacity C m2 , and obtain it through the following steps:

[0026] According to the discharge capacity C0, adjust the battery pack SOC to 50%, and record the actual discharge capacity C of the battery pack at this time. m1 ;

[0027] After storing the battery at the test temperature for T hours, standard discharge is performed at room temperature until the battery pack reaches the cut-off voltage, and the discharge capacity C of the battery pack during this process is obtained. m2 .

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] The method for determining the self-discharge of a battery pack of the present invention obtains two sets of discharge capacitance measurement values ​​through segmented discharge, and one set of measurement values ​​is performed after the battery pack is left to stand to adapt to the temperature of the environment, thereby reducing the influence of the temperature rise factor of the battery pack caused by discharge on the capacitance measurement error; with the help of correction calculation of the two sets of data, it is beneficial to measure a more accurate self-discharge rate of the battery pack, thereby helping to better evaluate the performance of the battery pack.

[0030] In addition, at the end of the test process, the battery pack is charged and discharged after the temperature of the battery pack is left to cool to room temperature. The discharge capacity C can be measured.x , and then the capacity recovery rate of the battery pack is obtained, which helps to further evaluate the performance of the battery pack.

[0031] Another object of the present invention is to provide a device for determining self-discharge of a battery pack, the device comprising:

[0032] Acquisition module (1) obtains the discharge capacity C0 of the battery pack at room temperature and the discharge capacity C at each stage n , and the actual discharge capacity C at each stage m ;

[0033] Calculation module (2), based on the discharge capacity C at each stage n And the actual discharge capacity C at each stage m , get the self-discharge rate of the battery pack.

[0034] Compared with the prior art, the determination device of the present invention provides a system structure architecture for testing the self-discharge performance of a battery pack, which is beneficial to improving the accuracy of measurements such as the self-discharge rate and capacity recovery rate of the battery pack, and quickly obtaining the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0036] Figure 1 A schematic flow chart of the steps of a method for determining battery pack self-discharge according to Embodiment 1 of the present invention;

[0037] Figure 2 A schematic diagram of the system structure of the device for determining the self-discharge of a battery pack according to the second embodiment of the present invention;

[0038] Description of reference numerals:

[0039] 1. Acquisition module; 2. Calculation module. DETAILED DESCRIPTION

[0040] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0041] In the description of the present invention, unless otherwise clearly defined, the terms "installed", "connected", "connected", and "connector" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be internal communication between two elements. The terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in combination with specific circumstances.

[0042] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0043] Embodiment 1

[0044] This embodiment relates to a method for determining the self-discharge of a battery pack. Figure 1 As shown, the method generally comprises the following steps:

[0045] Step 1: Obtain the discharge capacity C0 of the battery pack at room temperature;

[0046] Step 2: Discharge the battery pack in stages according to the obtained discharge capacity C0 to obtain the discharge capacity C0 at each stage. n , the discharge operation of each stage of the battery pack is carried out at room temperature;

[0047] Step 3: After charging the battery pack, the battery pack is left to stand at room temperature and discharged in stages to obtain the actual discharge capacity C at each stage. m ;

[0048] Step 4: Based on the discharge capacity C at each stage n And the actual discharge capacity C at each stage m , get the self-discharge rate of the battery pack.

[0049] Based on the above-mentioned overall measurement idea, this method preferably adopts segmented discharge for the battery pack self-discharge test.

[0050] Specifically, for a fully charged battery pack, firstly, perform environmental adaptation at room temperature, then perform standard discharge at room temperature, and then let the battery pack stand until its temperature approaches room temperature; then, perform standard charge at room temperature, then let the battery pack stand until its temperature reaches room temperature, and then perform standard discharge at room temperature. When the battery pack stands until its temperature reaches room temperature, measure and record the discharge capacity C0. Then, perform the measurement in step 2.

[0051] In step 2, standard charging is performed at room temperature, and then the battery pack is left to stand until the temperature of the battery pack reaches room temperature; then, based on C0, the SOC of the battery pack is adjusted to 50% at room temperature, which is recorded as capacity C1, and then the battery pack is left to stand until the temperature of the battery pack reaches room temperature, and standard discharge is performed again until any cell in the battery pack reaches the cut-off voltage, and the discharge capacity of this process is recorded as C2; the C obtained in this step n Including discharge capacity C n1 and discharge capacity C n2 Among them, C n1 C1, C n2 Then proceed to step 3.

[0052] In step 3, standard charging is performed at room temperature, and then the battery pack is left to stand until the temperature of the battery pack reaches room temperature; then, the SOC of the battery pack is adjusted to 50% at room temperature according to C0, which is recorded as capacity C3; the battery pack is stored for about 720 hours at a corresponding temperature (generally the test condition is 25°C to 45°C) to allow the battery pack to adapt to the environment at room temperature; thereafter, standard discharge is performed at room temperature, which is recorded as discharge capacity C4. The C obtained in this step is m In this step, C m Including actual discharge capacity C m1 And the actual discharge capacity C m2 , the room temperature is 25℃, the battery storage time T is 720; get C m1 is C3; m2 Then proceed to step 4.

[0053] In step 4, the actual discharge capacity C at each stage is obtained. m After that, the battery pack is charged at room temperature, left to stand until the battery pack temperature reaches room temperature, and then discharged to measure the discharge capacity C of the battery pack. x ; The C obtained in this step x is C5.

[0054] In addition, in the specific measurement and acquisition steps for the discharge capacity C0, the following method is preferably used. First, before obtaining the discharge capacity C0, the battery pack needs to be acclimatized at room temperature, then standardly discharged at room temperature, and the battery pack is left standing until the temperature of the battery pack is room temperature; thereafter, standard charged at room temperature, and then the battery pack is left standing until the temperature of the battery pack is room temperature; finally, standard discharged at room temperature, and then the battery pack is left standing until the temperature of the battery pack is room temperature, to obtain the discharge capacity C0 of the battery pack.

[0055] Based on the data obtained from the above tests, the capacity recovery rate of the battery pack can be calculated as C x / C0=C5 / C0; the self-discharge rate of the battery pack is (1-actual discharge capacity C mSum / Each discharge capacity C n The sum of the self-discharge rate is (1-(C3+C4) / (C1+C2))*100%.

[0056] It should be pointed out that the above-mentioned staged measurement of the battery pack can be divided into different stages according to the different proportional values ​​of the state of charge SOC of the battery pack. For example, it can be carried out when the SOC is 50%, or it can be carried out when it is 40%, 60%, etc. The storage time T of the battery is preferably 720 hours, and the T can also be adjusted within a reasonable time range, such as 600 hours, 840 hours, etc. The normal temperature or room temperature mentioned above can be referred to the conventional understanding in chemical technology or engineering; in the actual operation of the present invention, the temperature range can be between 20°C and 30°C, for example, 20°C, 25°C, 28°C or 30°C; generally, the normal temperature or room temperature is 25°C.

[0057] The above test method can be used to obtain the capacity recovery rate and self-discharge rate of the battery pack. Since two sets of discharge capacitance measurement values ​​are obtained through segmented discharge, and one set of measurement values ​​is performed after the battery pack is left to adapt to the temperature of the environment, the influence of the temperature rise of the battery pack caused by discharge on the capacitance measurement error can be reduced; with the help of the correction calculation of the two sets of data, it is helpful to measure the self-discharge rate of the battery pack more accurately. Compared with the existing test method, the measurement results obtained are more accurate, which helps to better evaluate the performance of the battery pack.

[0058] In the method of the present invention, segmented discharge is used to avoid the inconsistent capacity of the battery pack caused by the different temperature rises under full discharge conditions and segmented discharge. By controlling variables, the temperature conditions will not affect the self-discharge rate test results of the entire pack. This method can be used to measure a more accurate self-discharge rate of the battery pack, thereby better evaluating the performance of the battery system.

[0059] In addition, at the end of the test process, the battery pack is charged and discharged after the temperature of the battery pack is left to cool to room temperature. The discharge capacity C can be measured. x , and then the capacity recovery rate of the battery pack is obtained, which helps to further evaluate the performance of the battery pack.

[0060] Embodiment 2

[0061] This embodiment relates to a device for determining self-discharge of a battery pack. Figure 2 An exemplary system configuration of the determination device is shown.

[0062] The determination device includes an acquisition module 1 and a calculation module 2. The acquisition module 1 is used to obtain the discharge capacity C0 of the battery pack at room temperature, the discharge capacity C n , and the actual discharge capacity C at each stage mThe calculation module 2 is used to calculate the discharge capacity C at each stage. n And the actual discharge capacity C at each stage m , get the self-discharge rate of the battery pack.

[0063] The acquisition module 1 can be a set of inspection instruments for measuring the discharge point capacitance of a battery pack. Referring to the method for determining the self-discharge of a battery pack provided in the first embodiment, the battery pack is inspected in each step to obtain C0, C n , C m and C x and other measurement data; and transmit them to the calculation module 2 through line communication or other means. The calculation module 2 can be a manually operated calculator, or a computer with a calculation program set according to the calculation formula provided by the present invention. The calculation module 2 can quickly complete the calculation of the measurement results, so as to conveniently obtain the performance indicators such as the self-discharge rate and capacity recovery rate of the battery.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining self-discharge of a battery pack, characterized in that: The method comprises the following steps: Get the discharge capacity C0 of the battery pack at room temperature; According to the obtained discharge capacity C0, the battery pack is discharged in stages to obtain the discharge capacity C in each stage. n The discharge operation of the battery pack at each stage is carried out at room temperature; the discharge capacity C at each stage n Including discharge capacity C n1 and discharge capacity C n2 According to the discharge capacity C0, adjust the battery pack SOC to 40% to 60% at room temperature to obtain the discharge capacity C of the battery pack at this time n1 Then, the battery pack is left to stand until the temperature of the battery pack reaches room temperature, and then a standard discharge is performed until the battery pack reaches the cut-off voltage, and the discharge capacity C of the battery pack in this process is obtained. n2 ; After charging the battery pack, the battery pack is left to stand at room temperature and discharged in stages to obtain the actual discharge capacity C at each stage. m ; Actual discharge capacity C m Including actual discharge capacity C m1 And the actual discharge capacity C m2 , and obtain it through the following steps: According to the discharge capacity C0, adjust the battery pack SOC to 40% to 60%, and record the actual discharge capacity C0 of the battery pack at this time. m1 ; After storing the battery at the test temperature for T hours, standard discharge is performed at room temperature until the battery pack reaches the cut-off voltage, and the discharge capacity C of the battery pack during this process is obtained. m2 ; According to the discharge capacity C at each stage n And the actual discharge capacity C at each stage m , get the self-discharge rate of the battery pack.

2. The method for determining the self-discharge of a battery pack according to claim 1, characterized in that: The following steps are also included: Get the actual discharge capacity C at each stage m After that, the battery pack is charged, and the battery pack is discharged after the temperature of the battery pack is allowed to stand at room temperature to obtain the discharge capacity C of the battery pack. x ; Based on discharge capacity C0 and discharge capacity C x , obtain the capacity recovery rate of the battery pack.

3. The method for determining the self-discharge of a battery pack according to claim 2, characterized in that: The capacity recovery rate is C x / C0.

4. The method for determining the self-discharge of a battery pack according to claim 1, characterized in that: The self-discharge rate of the battery pack is (1-actual discharge capacity C m Sum / Each discharge capacity C n sum)*100%.

5. The method for determining the self-discharge of a battery pack according to any one of claims 1 to 4, characterized in that: The discharge capacity C0 is obtained by the following steps: Adapting the battery pack to the environment at room temperature; Performing standard discharge at room temperature, and then leaving the battery pack to stand until the temperature of the battery pack reaches room temperature; Performing standard charging at room temperature, and then leaving the battery pack to stand until the temperature of the battery pack reaches room temperature; Perform standard discharge at room temperature, then leave the battery pack to stand until the temperature of the battery pack reaches room temperature, and obtain the discharge capacity C0 of the battery pack.

6. The method for determining the self-discharge of a battery pack according to any one of claims 1 to 4, characterized in that: After the standard discharge is performed until any single cell in the battery pack reaches the cut-off voltage, the discharge capacity C of the battery pack in this process is obtained. n2 .

7. A device for determining battery pack self-discharge, characterized in that: The determination device is provided based on the method for determining the self-discharge of the battery pack according to any one of claims 1 to 6, and the determination device comprises: Acquisition module (1) obtains the discharge capacity C0 of the battery pack at room temperature and the discharge capacity C at each stage n , and the actual discharge capacity C at each stage m ; Calculation module (2), based on the discharge capacity C at each stage n And the actual discharge capacity C at each stage m , get the self-discharge rate of the battery pack.

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