A method and system for calculating the self-discharge of lithium-ion batteries

Abstract

This disclosure provides a method and system for calculating the self-discharge of lithium-ion batteries, relating to the field of lithium-ion battery calculation technology. The method includes: acquiring the lithium-ion battery to be tested and determining its basic performance before self-discharge calculation; setting the self-discharge days of the lithium-ion battery to be tested, and placing the lithium-ion battery to be tested in environments with different set temperatures for a set duration of self-discharge; using the self-discharge days as an independent variable and inputting it into a self-discharge voltage change model to obtain the self-discharge voltage of the lithium-ion battery to be tested; wherein, the process of obtaining the self-discharge voltage change model is as follows: performing a self-discharge capacity test on a sample lithium-ion battery, charging and discharging the sample lithium-ion battery three times according to a set current, and calibrating its actual capacity before self-discharge; performing a self-discharge test based on the calibrated actual capacity, placing the sample lithium-ion battery in environments with different set temperatures for a predetermined duration of self-discharge, using the self-discharge days as an independent variable, performing multiple fittings, and finally obtaining the self-discharge voltage change model.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery measurement technology, specifically to a method and system for measuring the self-discharge of lithium-ion batteries. Background Technology

[0002] The statements in this section are merely background information relating to this disclosure and do not necessarily constitute prior art.

[0003] Lithium-ion batteries are among the most widely used batteries today, boasting advantages such as high energy density, long lifespan, and portability, making them widely applicable in mobile electronic devices, electric vehicles, and other fields. However, lithium-ion batteries exhibit self-discharge during long-term storage or use, leading to reduced battery capacity and even rendering them unusable. Therefore, researching the self-discharge mechanism of lithium-ion batteries is of guiding significance for electrode material selection, battery failure analysis, and smart grid management.

[0004] There are many existing methods and tests for lithium-ion battery self-discharge. The paper "Research and Application of Lithium-ion Battery Self-Discharge Detection Technology" addresses the difficulty of quickly and accurately measuring lithium-ion battery self-discharge by proposing its own solution. This solution involves building experimental circuits, programming and debugging hardware and software, and verifying measurement results through extensive experiments, aiming to achieve rapid detection of lithium-ion battery self-discharge. The paper "Mechanism and Measurement Method of Lithium-ion Battery Self-Discharge" reviews the phenomenon of lithium-ion battery self-discharge from three aspects: the generation mechanism, influencing factors, and measurement methods. First, it describes the self-discharge generation mechanism of different structural parts of lithium-ion batteries and introduces improved techniques to reduce self-discharge. Then, it analyzes the influence of battery state of charge (SOC), environmental factors (temperature and humidity), and resting time on battery self-discharge, summarizing the optimal storage scheme for lithium-ion batteries. Finally, it briefly describes various self-discharge measurement methods that have emerged in recent years, analyzes the problems and limitations of each method, and points out the future development direction for rapid measurement of lithium-ion battery self-discharge rates. Patent - A Method for Testing the Self-Discharge of Lithium-ion Batteries. This invention relates to the field of lithium-ion battery testing and discloses a method for testing the magnitude of self-discharge in lithium-ion batteries. This method can test and select lithium-ion batteries in a short time. It utilizes the principle that the battery itself generates a magnetic field due to a micro-short-circuit current during self-discharge, and uses a teslameter or gaussmeter to measure the difference in the intensity of the magnetic field to determine the magnitude of the battery's self-discharge.

[0005] However, the above methods still have the problems of long evaluation cycles or limited evaluation dimensions, which increases the time spent on testing resources and is easily affected by the external test environment, making it impossible to obtain test results efficiently and accurately. Summary of the Invention

[0006] To address the aforementioned issues, this disclosure proposes a method and system for calculating the self-discharge of lithium-ion batteries. By establishing a model for calculating the self-discharge of lithium-ion batteries, the changes in the open-circuit voltage and AC internal resistance of lithium-ion batteries after N days can be obtained quickly and accurately, which is more conducive to judging the changes in the open-circuit voltage and health status of lithium-ion battery cells.

[0007] According to some embodiments, the present disclosure adopts the following technical solutions:

[0008] A method for calculating the self-discharge of a lithium-ion battery includes:

[0009] Obtain the lithium-ion battery to be tested and determine its basic performance before self-discharge calculation;

[0010] Set the self-discharge days of the lithium-ion battery to be tested, and place the lithium-ion battery to be tested in environments with different set temperatures for a set duration of self-discharge.

[0011] The number of days of self-discharge is used as an independent variable and input into the self-discharge voltage change model to obtain the self-discharge voltage of the lithium-ion battery to be measured.

[0012] The process of obtaining the self-discharge voltage change model is as follows: a self-discharge capacity test is performed on the sample lithium-ion battery. The sample lithium-ion battery is charged and discharged three times according to the set current, and its actual capacity before self-discharge is calibrated. A self-discharge test is performed based on the calibrated actual capacity. The sample lithium-ion battery is placed in an environment with different set temperatures for a predetermined duration of self-discharge. The number of self-discharge days is used as the independent variable, and multiple fittings are performed to finally obtain the self-discharge voltage change model.

[0013] According to some embodiments, the present disclosure adopts the following technical solutions:

[0014] A lithium-ion battery self-discharge measurement system includes:

[0015] The data acquisition module is used to acquire data about the lithium-ion battery to be tested and determine its basic performance before self-discharge calculation.

[0016] The self-discharge calculation module is used to set the self-discharge days of the lithium-ion battery to be tested, and to place the lithium-ion battery to be tested into environments with different set temperatures for a set duration of self-discharge.

[0017] The number of days of self-discharge is used as an independent variable and input into the self-discharge voltage change model to obtain the self-discharge voltage of the lithium-ion battery to be measured.

[0018] The process of obtaining the self-discharge voltage change model is as follows: a self-discharge capacity test is performed on the sample lithium-ion battery. The sample lithium-ion battery is charged and discharged three times according to the set current, and its actual capacity before self-discharge is calibrated. A self-discharge test is performed based on the calibrated actual capacity. The sample lithium-ion battery is placed in an environment with different set temperatures for a predetermined duration of self-discharge. The number of self-discharge days is used as the independent variable, and multiple fittings are performed to finally obtain the self-discharge voltage change model.

[0019] According to some embodiments, the present disclosure adopts the following technical solutions:

[0020] A non-transitory computer-readable storage medium is provided for storing computer instructions, which, when executed by a processor, implement the aforementioned method for calculating the self-discharge of a lithium-ion battery.

[0021] According to some embodiments, the present disclosure adopts the following technical solutions:

[0022] An electronic device includes a processor, a memory, and a computer program; wherein the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device is running, the processor executes the computer program stored in the memory to enable the electronic device to implement the aforementioned method for calculating the self-discharge of a lithium-ion battery.

[0023] Compared with the prior art, the beneficial effects of this disclosure are as follows:

[0024] This disclosure relates to a model for calculating the self-discharge of lithium-ion batteries. By establishing a new model for calculating the self-discharge of lithium-ion batteries, the changes in the open-circuit voltage and AC internal resistance of lithium-ion batteries after N days can be obtained quickly and accurately. This is more conducive to judging the changes in the open-circuit voltage and health status of lithium-ion battery cells, reducing the time occupied by test resources, saving test costs and improving test utilization. Moreover, this invention has the characteristics of high efficiency, cost-effectiveness and higher accuracy.

[0025] This disclosure can reduce the time required for traditional testing, eliminate the need for cumbersome voltage testing, and is unaffected by the experimental environment. It can obtain test results more efficiently and accurately, and the error between the calculated value and the actual test value can be controlled within 1%.

[0026] Compared with existing testing methods, the method for evaluating voltage change models during the self-discharge process of lithium-ion batteries provided in this disclosure can quickly and accurately obtain the battery voltage by simply measuring the number of test days, which is of guiding significance for optimizing the battery development process. Attached Figure Description

[0027] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute an undue limitation of this disclosure.

[0028] Figure 1 This is a flowchart of the measurement method according to an embodiment of the present disclosure; Detailed Implementation

[0029] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0030] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0031] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this disclosure. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0032] Example 1

[0033] One embodiment of this disclosure provides a method for calculating the self-discharge of a lithium-ion battery, including:

[0034] Obtain the lithium-ion battery to be tested and determine its basic performance before self-discharge calculation;

[0035] Set the self-discharge days of the lithium-ion battery to be tested, and place the lithium-ion battery to be tested in environments with different set temperatures for a set duration of self-discharge.

[0036] The number of days of self-discharge is used as an independent variable and input into the self-discharge voltage change model to obtain the self-discharge voltage of the lithium-ion battery to be measured.

[0037] The process of obtaining the self-discharge voltage change model is as follows: a self-discharge capacity test is performed on the sample lithium-ion battery. The sample lithium-ion battery is charged and discharged three times according to the set current, and its actual capacity before self-discharge is calibrated. A self-discharge test is performed based on the calibrated actual capacity. The sample lithium-ion battery is placed in an environment with different set temperatures for a predetermined duration of self-discharge. The number of self-discharge days is used as the independent variable, and multiple fittings are performed to finally obtain the self-discharge voltage change model.

[0038] As one example, the health status of an electric vehicle's battery pack comes from the voltage and capacity of the cells. The capacity needs to be measured with specialized equipment, while the cell voltage is monitored by the BMS. The normal operating temperature test is 25°C and 45°C. This disclosure uses the true value taken by the actual BMS and the existing value to fit the formula multiple times, and the difference between the forward and reverse derivations is within 1%.

[0039] Specifically, the calculation process is as follows:

[0040] 1. Let the number of days of self-discharge be the independent variable and the voltage change be the dependent variable, and let x and f(x) be the independent variable and the voltage change be the dependent variable, respectively.

[0041] 2. Record the self-discharge voltage at 25℃ and 45℃, and plot a scatter plot with smooth curves according to the number of days.

[0042] 3. By observing the scatter plot, the trajectory is found to resemble an exponential function.

[0043] 4. The self-discharge voltage function expression is obtained through fitting:

[0044] 25℃ (f(x)=3.30181e) (0.00003)x ); 45℃ (f(x)=3.30091e (0.00003)x )

[0045] 5. Through multiple fitting tests, the voltage change model was finally determined: the self-discharge voltage change model at 25℃ is: 3.30192e -0.00003395x The self-discharge voltage change model at 45℃ is: 3.30109e -0.00009557x .

[0046] By observing certain patterns in existing values, a formula was derived. Initially, the calculation process involved significant errors, but after continuous refinement, the exponential function model formulas for 25℃ and 45℃ were finally obtained.

[0047] The specific implementation process of the self-discharge calculation method for lithium-ion batteries disclosed herein is as follows:

[0048] Step 1: Select six parallel samples of 73Ah lithium iron phosphate batteries and measure their basic performance before self-discharge testing. Batteries #1, #2, and #3 underwent a 25℃ self-discharge test, while batteries #4, #5, and #6 underwent a 45℃ self-discharge test.

[0049] Step 2: Perform a pre-self-discharge capacity test on these lithium batteries. Charge and discharge these lithium-ion batteries three times at a current of 1C to calibrate their actual capacity before self-discharge.

[0050] Step 3: Perform a self-discharge test at 50% SOC as per step 1. Save and record the data after the self-discharge test is completed.

[0051] Step 4: Place the lithium-ion battery in temperatures of 25°C and 45°C respectively for a predetermined period of self-discharge.

[0052] 5. Perform voltage tests every 3 days and record the data.

[0053] Through verification, the test data was processed, and the number of days of self-discharge was used as the independent variable for multiple fitting tests. The final model for the self-discharge voltage change at 25℃ was obtained as: 3.30192e. -0.00003395x The functional expression for f(x) is given by f(x), where x represents the number of days of self-discharge and f(x) corresponds to the battery voltage. The self-discharge voltage change model at 45℃ is: 3.30109e -0.00009557x The functional expression is f(x), where x represents the number of days of self-discharge and f(x) corresponds to the battery voltage.

[0054] As one embodiment, the specific implementation method of self-discharge includes:

[0055] 1. Take six 73Ah square lithium iron phosphate batteries: #1, #2, #3, #4, #5, and #6.

[0056] 2. Let stand for 30 minutes;

[0057] 3. Discharge all 6 batteries to 2V using a constant current of 1C;

[0058] 4. Let stand for 30 minutes;

[0059] 5. Charge all 6 batteries to 3.65V using a 1C constant current and constant voltage method;

[0060] 6. Let stand for 30 minutes;

[0061] 7. Place batteries #1, #2, and #3 at 25°C and test their voltage every 3 days, recording the data.

[0062] 8. Place batteries #4, #5, and #6 at 45°C and test their voltage every 3 days, recording the data.

[0063] 9. Repeat steps 7-8 above for the self-discharge test of the predetermined duration;

[0064] The self-discharge voltage data obtained after testing using the above method were used to calculate the self-discharge voltage at different temperatures. The self-discharge data obtained under each condition are shown in Tables 1, 2, 3, 4, 5, and 6.

[0065] Table 1 Self-discharge data of sample #1 at 25℃

[0066]

[0067]

[0068] Table 2 Self-discharge data of sample #2 at 25℃

[0069] Days / d Actual voltage Simulation model calculates voltage changes Voltage variation error 3 3.30175 3.30158 -0.00510％ 6 3.30135 3.30125 -0.00317％ 9 3.30082 3.30091 0.00269％ 12 3.30046 3.30057 0.00342％ 15 3.30017 3.30024 0.00202％ 18 3.29993 3.29990 -0.00090％ 21 3.29968 3.29956 -0.00351％ 24 3.29930 3.29923 -0.00218％ 27 3.29908 3.29889 -0.00569％ 30 3.29887 3.29856 -0.00951％

[0070] Table 3 Self-discharge data of sample #3 at 25℃

[0071] Days / d Actual voltage Simulation model calculates voltage changes Voltage variation error 3 3.30173 3.30158 -0.00450％ 6 3.30129 3.30125 -0.00136％ 9 3.30081 3.30091 0.00300％ 12 3.30045 3.30057 0.00372％ 15 3.30015 3.30024 0.00262％ 18 3.29988 3.29990 0.00062％ 21 3.29963 3.29956 -0.00199％ 24 3.29921 3.29923 0.00055％ 27 3.29898 3.29889 -0.00266％ 30 3.29869 3.29856 -0.00406％

[0072] Table 4 Self-discharge data of sample #4 at 45℃

[0073]

[0074]

[0075] Table 5 Self-discharge data of sample #5 at 45℃

[0076] Days / d Actual voltage Simulation model calculates voltage changes Voltage variation error 3 3.30089 3.30078 -0.00346％ 6 3.30035 3.30046 0.00335％ 9 3.29997 3.30015 0.00531％ 12 3.29982 3.29983 0.00029％ 15 3.29969 3.29951 -0.00532％ 18 3.29928 3.29920 -0.00245％ 21 3.29887 3.29888 0.00042％ 24 3.29861 3.29857 -0.00126％ 27 3.29815 3.29825 0.00313％ 30 3.29802 3.29794 -0.00249％

[0077] Table 6 Self-discharge data of sample #6 at 45℃

[0078]

[0079]

[0080] Based on the fitting results, the final self-discharge voltage variation model at 25℃ can be obtained as: 3.30192e -0.00003395x Where x represents the number of days of self-discharge, and f(x) is the corresponding battery voltage. The self-discharge voltage change model at 45℃ is: 3.30109e -0.00009557x The functional expression is f(x), where x represents the number of days of self-discharge and f(x) corresponds to the battery voltage.

[0081] First, a voltage change model is obtained based on self-discharge at different temperatures. Then, the voltage can be obtained by substituting the variable number of days into x, and the error can be controlled within 1%.

[0082] Example 2

[0083] One embodiment of this disclosure provides a lithium-ion battery self-discharge measurement system, comprising:

[0084] The data acquisition module is used to acquire data about the lithium-ion battery to be tested and determine its basic performance before self-discharge calculation.

[0085] The self-discharge calculation module is used to set the self-discharge days of the lithium-ion battery to be tested, and to place the lithium-ion battery to be tested into environments with different set temperatures for a set duration of self-discharge.

[0086] The number of days of self-discharge is used as an independent variable and input into the self-discharge voltage change model to obtain the self-discharge voltage of the lithium-ion battery to be measured.

[0087] The process of obtaining the self-discharge voltage change model is as follows: a self-discharge capacity test is performed on the sample lithium-ion battery. The sample lithium-ion battery is charged and discharged three times according to the set current, and its actual capacity before self-discharge is calibrated. A self-discharge test is performed based on the calibrated actual capacity. The sample lithium-ion battery is placed in an environment with different set temperatures for a predetermined duration of self-discharge. The number of self-discharge days is used as the independent variable, and multiple fittings are performed to finally obtain the self-discharge voltage change model.

[0088] Example 3

[0089] One embodiment of this disclosure provides a non-transitory computer-readable storage medium for storing computer instructions, which, when executed by a processor, implement the aforementioned method for calculating the self-discharge of a lithium-ion battery.

[0090] Example 4

[0091] One embodiment of this disclosure provides an electronic device, including: a processor, a memory, and a computer program; wherein the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device is running, the processor executes the computer program stored in the memory to enable the electronic device to implement the lithium-ion battery self-discharge calculation method.

[0092] This disclosure is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create a machine for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0093] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0094] While the specific embodiments of this disclosure have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of this disclosure. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of this disclosure are still within the scope of protection of this disclosure.

Claims

1. A method for calculating the self-discharge of a lithium-ion battery, characterized in that, include: Obtain the lithium-ion battery to be tested and determine its performance before self-discharge calculation; Set the self-discharge days of the lithium-ion battery to be tested, and place the lithium-ion battery to be tested in environments with different set temperatures for a set duration of self-discharge. The number of days of self-discharge is used as an independent variable and input into the self-discharge voltage change model to obtain the self-discharge voltage of the lithium-ion battery to be measured. The process of obtaining the self-discharge voltage change model is as follows: a self-discharge capacity test is performed on the sample lithium-ion battery. The sample lithium-ion battery is charged and discharged three times according to the set current, and its actual capacity before self-discharge is calibrated. A self-discharge test is performed based on the calibrated actual capacity. The sample lithium-ion battery is placed in an environment with different set temperatures for a predetermined duration of self-discharge. The number of self-discharge days is used as the independent variable, and multiple fittings are performed to finally obtain the self-discharge voltage change model. Battery Management System (BMS) is used to monitor the battery cells. By processing the test data and using the self-discharge days as the independent variable, the actual BMS measurements are fitted multiple times with existing values ​​to obtain a self-discharge voltage variation model, controlling the difference within 1%. The self-discharge voltage variation model is an exponential function model formula for 25℃ and 45℃. The 25℃ self-discharge voltage variation model is as follows: 3.30192e -0.00003395x Where x represents the number of days of self-discharge, and f(x) corresponds to the battery voltage; the self-discharge voltage change model at 45℃ is: 3.30109 e -0.00009557 x The functional expression is f(x), where x represents the number of days of self-discharge and f(x) corresponds to the battery voltage.

2. The method for calculating the self-discharge of a lithium-ion battery as described in claim 1, characterized in that, Multiple lithium-ion battery samples were classified, with half undergoing self-discharge testing at 25°C and the other half undergoing self-discharge testing at 45°C.

3. The method for calculating the self-discharge of a lithium-ion battery as described in claim 1, characterized in that, Before self-discharge, the sample lithium-ion batteries were subjected to a pre-self-discharge capacity test. The sample lithium-ion batteries were charged and discharged three times at a current of 1C, and their actual capacity before self-discharge was calibrated.

4. The method for calculating the self-discharge of a lithium-ion battery as described in claim 1, characterized in that, The self-discharge test was performed by charging the battery to 50% SOC using a 1C0 method. After the self-discharge test was completed, the data was saved and recorded. The sample lithium-ion batteries were then placed in temperatures of 25°C and 45°C for a predetermined duration of self-discharge.

5. A lithium-ion battery self-discharge calculation system, used to execute the lithium-ion battery self-discharge calculation method as described in any one of claims 1-4, characterized in that, include: The data acquisition module is used to acquire data about the lithium-ion battery to be tested and determine its performance before self-discharge calculation. The self-discharge calculation module is used to set the self-discharge days of the lithium-ion battery to be tested, and to place the lithium-ion battery to be tested into environments with different set temperatures for a set duration of self-discharge. The number of days of self-discharge is used as an independent variable and input into the self-discharge voltage change model to obtain the self-discharge voltage of the lithium-ion battery to be measured. The process of obtaining the self-discharge voltage change model is as follows: a self-discharge capacity test is performed on the sample lithium-ion battery. The sample lithium-ion battery is charged and discharged three times according to the set current, and its actual capacity before self-discharge is calibrated. A self-discharge test is performed based on the calibrated actual capacity. The sample lithium-ion battery is placed in an environment with different set temperatures for a predetermined duration of self-discharge. The number of self-discharge days is used as the independent variable, and multiple fittings are performed to finally obtain the self-discharge voltage change model.

6. A non-transitory computer-readable storage medium, characterized in that, The non-transitory computer-readable storage medium is used to store computer instructions, which, when executed by a processor, implement a method for calculating the self-discharge of a lithium-ion battery as described in any one of claims 1-4.

7. An electronic device, characterized in that, include: The device includes a processor, a memory, and a computer program; wherein the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device is running, the processor executes the computer program stored in the memory to enable the electronic device to perform a method for calculating the self-discharge of a lithium-ion battery as described in any one of claims 1-4.

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