A quantitative testing method and system for battery capacity loss caused by polarization growth

Abstract

This invention discloses a method and system for quantitatively testing battery capacity loss caused by polarization growth, comprising: performing a constant-capacity test on the aged battery and the corresponding BOL battery under test using a set current rate to obtain discharge curves of the two batteries at different rates; determining the discharge rebound equilibrium voltage of the BOL battery and the aged battery respectively based on the discharge curves; determining whether the aged battery has polarization growth based on the comparison of the discharge rebound equilibrium voltages of the two batteries; and determining the amount of battery capacity loss based on the change in the discharge rebound equilibrium voltage after polarization growth has occurred. The quantitative result is not affected by the initial polarization of the BOL battery, and avoids the complex calculations between different capacity values ​​in the traditional tabulation method.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method and system for quantitatively testing battery capacity loss caused by polarization growth. Background Technology

[0002] During service, battery capacity inevitably declines. The decline mechanisms can be summarized into three categories: polarization growth, loss of active materials, and loss of stored lithium. In battery design, the cycle life (or cycle capacity retention) should meet specific targets: for example, a lithium iron phosphate (LFP) graphite battery should retain more than 80% of its state of charge (SOC) after 2500 cycles at room temperature. However, in the selection of specific electrochemical systems, the cycle life sometimes fails to meet these targets. In such cases, it is necessary to analyze the specific decline mechanism of the battery and make targeted adjustments to the battery materials, formulation, and processes to achieve the expected cycle life target.

[0003] Polarization growth is one of the most common characteristics of batteries, but whether it is the primary cause of capacity decay requires analysis. If polarization growth is the main cause of capacity decay, then improving battery cycle performance can start by reducing the degree of polarization. Therefore, precise quantification of the capacity decay caused by battery polarization growth is necessary.

[0004] To qualitatively and quantitatively analyze the impact of battery polarization changes on battery capacity, a low-rate current is typically used to measure the capacity of a degraded battery. If the battery capacity is essentially recovered under this low-rate current—meaning it approaches the capacity of the battery before degradation (BOL battery, short for Beginning of Life)—then the capacity degradation can be attributed to polarization growth. However, in actual battery capacity degradation analysis, the aforementioned three types are usually combined. Furthermore, batteries on the market are divided into two main categories: power batteries and energy batteries. Because energy batteries have greater initial polarization, the calculated capacity loss and its proportion caused by polarization growth when using a low-rate current for gradation are inaccurate. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a quantitative testing method and system for battery capacity loss caused by polarization growth. Based on discharge curves under different currents and the principle of rebound equilibrium potential, quantitative results can be directly obtained without being affected by the initial polarization of BOL batteries. At the same time, it avoids the complex calculations between different capacity values ​​using traditional tabulation methods.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for quantitatively testing battery capacity loss caused by polarization growth, comprising:

[0008] The aged battery and the corresponding BOL battery to be tested were subjected to constant capacity test with a set current rate to obtain the discharge curves of the two batteries at different rates.

[0009] The discharge rebound equilibrium voltage of BOL battery and aged battery is determined according to their respective discharge curves. The polarization growth of aged battery is determined by comparing the discharge rebound equilibrium voltage of the two batteries. After polarization growth occurs, the battery capacity loss is determined by the change in discharge rebound equilibrium voltage.

[0010] As an alternative implementation method, a constant-capacity test is performed on aged batteries and BOL batteries at a first rate current and a second rate current. The first rate current is a minimum value and much smaller than the second rate current. The discharge curve at the first rate current is used as the ideal non-polarization curve.

[0011] As an alternative implementation, a perpendicular line is drawn from the end of the discharge curve at the second rate current, intersecting the discharge curve at the first rate current at a point, and the vertical coordinate of this point is the discharge rebound balance voltage.

[0012] As an alternative implementation, after polarization growth occurs, the battery capacity loss is: the difference on the horizontal axis between the intersection of the discharge curves of the aged battery and the BOL battery at the first rate current is the capacity loss caused by polarization growth.

[0013] As an alternative implementation, after polarization growth occurs, the difference on the vertical axis between the intersection of the discharge curves at the first rate current and the discharge curves at the aging battery and the BOL battery is the voltage drop caused by polarization growth.

[0014] As an alternative implementation, the different current ratios are 1C and 0.01 to 0.1C, and the discharge curve at the 0.01 to 0.1C current is taken as the ideal polarization-free curve.

[0015] As an alternative implementation, if the discharge rebound equilibrium voltages of the two are the same, it indicates that no polarization growth has occurred; otherwise, polarization growth has occurred.

[0016] Secondly, the present invention provides a quantitative testing system for battery capacity loss caused by polarization growth, comprising:

[0017] The discharge curve plotting module is configured to perform constant-capacity tests on the aged battery to be tested and the corresponding BOL battery using a set current rate, and obtain the discharge curves of the two batteries at different rates.

[0018] The capacity loss quantification module is configured to determine the discharge rebound balance voltage of BOL batteries and aged batteries respectively based on their discharge curves, determine whether the aged battery has polarization growth based on the comparison of the discharge rebound balance voltages of the two, and determine the amount of battery capacity loss based on the change of discharge rebound balance voltage after polarization growth occurs.

[0019] Thirdly, the present invention provides an electronic device including a memory and a processor, and computer instructions stored in the memory and running on the processor, wherein the computer instructions, when executed by the processor, perform the method described in the first aspect.

[0020] Fourthly, the present invention provides a computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the method described in the first aspect.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention proposes a quantitative testing method and system for battery capacity loss caused by polarization growth. It targets the quantitative measurement of capacity loss caused by battery polarization growth. Based on the 1C and 0.01-0.1C discharge curves of the battery before and after cycling, the method plots them on the same plane. According to the principle of rebound equilibrium potential, the quantitative results can be directly read from the discharge curve graph. The method is simple and highly operable, avoiding the complex calculations of traditional tabulation methods between different capacity values. The quantitative results are not affected by the initial polarization of the BOL battery, and accurately and singularly judge the impact of polarization growth on capacity decay.

[0023] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 This is a flowchart of a method for quantitatively testing battery capacity loss caused by polarization growth, provided in Embodiment 1 of the present invention.

[0026] Figure 2 The discharge curves at 0.04C and 1C for the BOL battery and the aged battery provided in Embodiment 1 of the present invention are shown.

[0027] Figure 3 The discharge curve is a verification example provided in Embodiment 1 of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. 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 invention pertains.

[0030] 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 scope of exemplary embodiments according to the invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well. Furthermore, it should be understood that the terms “comprising” and “including”, and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or apparatus.

[0031] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0032] Example 1

[0033] This embodiment proposes a quantitative testing method for battery capacity loss caused by polarization growth, such as... Figure 1 As shown, it includes:

[0034] The aged battery and the corresponding BOL battery to be tested were subjected to constant capacity test with a set current rate to obtain the discharge curves of the two batteries at different rates.

[0035] The discharge rebound equilibrium voltage of BOL battery and aged battery is determined according to their respective discharge curves. The polarization growth of aged battery is determined by comparing the discharge rebound equilibrium voltage of the two batteries. After polarization growth occurs, the battery capacity loss is determined by the change in discharge rebound equilibrium voltage.

[0036] In this embodiment, BOL batteries and batteries that have been cycled or aged (hereinafter referred to as aged batteries) from the same batch were obtained; BOL and aged batteries were subjected to constant capacity tests using 1C and 0.04C currents to obtain discharge curves of the two batteries at 1C and 0.04C currents.

[0037] In this figure, the VQ (Q stands for Capacity) discharge curves of BOL batteries at 1C and 0.04C currents are placed in the same graph, and the VQ discharge curves of aged batteries at 1C and 0.04C currents are also placed in the same graph. Figure 2 As shown.

[0038] In this embodiment, the discharge curve at a current of 0.04C is taken as the ideal non-polarized curve.

[0039] Therefore, in the discharge curve diagram of the BOL battery, a perpendicular line is drawn from the end of the discharge curve at 1C current, intersecting the discharge curve at 0.04C current at point N. The vertical coordinate of point N is the discharge rebound equilibrium voltage at which the BOL battery cuts off discharge at 1C current, denoted as V. balance .

[0040] Similarly, in the discharge curve of an aged battery, draw a perpendicular line from the end of the discharge curve at 1C current, intersecting the discharge curve at 0.04C current at point O. The vertical coordinate of point O is the discharge rebound equilibrium voltage at which the aged battery cuts off discharge at 1C current, denoted as V'. balance .

[0041] If the polarization of the aged battery does not increase relative to the BOL battery, the discharge rebound equilibrium voltage at the discharge cutoff point under 1C current remains unchanged, i.e., V' balance =V balance ,exist Figure 2 In the middle, V' balance The discharge curve at a current of 0.04C intersects at point P, and the length of the line segment MN = TP;

[0042] If V' balance ≠V balance ,Right now Figure 2 When a moderately aged battery discharges to its cutoff point at 1C current, the discharge rebound equilibrium voltage reaches point O. The voltage at point O is not equal to V'. balance This indicates that the polarization of the aging battery has increased.

[0043] Therefore, the voltage drop ΔV caused by polarization growth is the projection of the OP segment on the vertical axis, and the capacity loss caused by polarization growth is the projection of the OP segment on the horizontal axis. The capacity loss caused by polarization growth of the battery is quantitatively completed after cycling.

[0044] In this embodiment, taking the determination of the battery capacity loss caused by polarization growth after 1000 cycles of 1C / 1C in a ternary-graphite soft-pack battery as an example, we obtain one BOL battery with a 1C rated capacity of 3.73Ah and one aged battery after 1000 cycles of 1C / 1C.

[0045] Two batteries were fully charged and discharged three times at 0.04C and 1C in a 2.8-4.4V environment at 25℃. The discharge curve of the third cycle was used to plot the VQ graph, and the 0.04C and 1C curves of the same battery were plotted on the same graph.

[0046] Place the VQ diagrams of the two batteries on the same plane, such as... Figure 3As shown, the 1C capacity of the aged battery after 1000 cycles is reduced compared to that of the BOL battery, and the capacity difference between 1C and 0.04C is widened.

[0047] In the discharge curve of a BOL battery, a perpendicular line is drawn from the end of the 1C discharge, intersecting the 0.04C discharge curve at a point. The vertical coordinate of this point is the 1C discharge rebound equilibrium voltage, denoted as V. balance .

[0048] Assuming the battery polarization remains unchanged after 1000 cycles compared to the BOL battery, the 1C discharge rebound equilibrium voltage V' of the aged battery can be derived. balance =V balance ,See Figure 3 V in balance and V' balance The horizontal dashed line intersects the 0.04C discharge curve of the aged battery at point P.

[0049] In fact, the 1C discharge rebound equilibrium potential of an aged battery is Figure 3 The ordinate value of point O clearly shows that the above assumption is not valid, that is, the polarization of the battery increased after 1000 cycles.

[0050] Therefore, the voltage drop caused by polarization growth is the projection of the OP segment on the vertical axis, and the capacity loss caused by polarization growth is the projection of the OP segment on the horizontal axis. Thus, the capacity loss caused by polarization growth is 3.424 - 3.264 = 0.159 Ah.

[0051] The battery after 1000 cycles is designated as the MOL battery. The discharge capacities of the BOL battery, MOL 0.04C, and 1C are then entered into Table 1.

[0052] Table 1. Capacity Loss of MOL Batteries Compared to BOL Batteries

[0053]

[0054] The reversible capacity loss of the MOL battery is calculated by the difference between its 0.04C and 1C capacities; the reversible capacity loss of the BOL battery is calculated by the difference between its 0.04C and 1C capacities; the capacity loss caused by polarization growth is obtained by the difference between the reversible capacity losses of the MOL and BOL batteries; thus, the proportion of capacity loss caused by polarization growth in the 1C capacity loss is obtained. As shown in Table 1, the proportion of polarization growth capacity loss obtained by the traditional tabular conversion method is 20.4%, which is lower than the 34.3% proportion obtained by the graphical method in this embodiment, indicating that the accuracy of the result obtained by the traditional tabular conversion method is not high.

[0055] This embodiment addresses the quantitative analysis of capacity loss caused by battery polarization growth. It plots the 1C and 0.04C discharge curves of the battery before and after cycling on the same plane. Based on the principle of rebound equilibrium potential (potential = voltage), the quantitative results can be directly read from the discharge curve graph. The method is simple and highly operable, avoiding the complex calculations between different capacity values ​​in the traditional tabulation method. The quantitative results are not affected by the initial polarization of the BOL battery. Furthermore, the influence of polarization growth on capacity decay (proportion) can be further obtained by plotting and derivation, saving the complicated process of calculating the absolute polarization of the MOL.

[0056] Example 2

[0057] This embodiment provides a quantitative testing system for battery capacity loss caused by polarization growth, including:

[0058] The discharge curve plotting module is configured to perform constant-capacity tests on the aged battery to be tested and the corresponding BOL battery using a set current rate, and obtain the discharge curves of the two batteries at different rates.

[0059] The capacity loss quantification module is configured to determine the discharge rebound balance voltage of BOL batteries and aged batteries respectively based on their discharge curves, determine whether the aged battery has polarization growth based on the comparison of the discharge rebound balance voltages of the two, and determine the amount of battery capacity loss based on the change of discharge rebound balance voltage after polarization growth occurs.

[0060] It should be noted that the above modules correspond to the steps described in Embodiment 1, and the examples and application scenarios implemented by the above modules and the corresponding steps are the same, but are not limited to the content disclosed in Embodiment 1. It should also be noted that the above modules, as part of the system, can be executed in a computer system such as a set of computer-executable instructions.

[0061] In further embodiments, the following is also provided:

[0062] An electronic device includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor, wherein the computer instructions, when executed by the processor, perform the method described in Embodiment 1. For brevity, further details are omitted here.

[0063] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0064] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0065] A computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the method described in Embodiment 1.

[0066] The method in Example 1 can be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules within the processor. The software modules can reside in readily available storage media in the field, such as random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, or registers. This storage medium is located in memory, and the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method. To avoid repetition, a detailed description is not provided here.

[0067] Those skilled in the art will recognize that the units and algorithm steps described in conjunction with the embodiments herein can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0068] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. 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 the present invention are still within the scope of protection of the present invention.

Claims

1. A method for quantitatively testing battery capacity loss caused by polarization growth, characterized in that, include: The aged battery and the corresponding BOL battery to be tested were subjected to constant capacity test with a set current rate to obtain the discharge curves of the two batteries at different rates. The discharge rebound equilibrium voltage of BOL battery and aged battery is determined according to their respective discharge curves. The polarization growth of aged battery is determined by comparing the discharge rebound equilibrium voltage of the two batteries. After the polarization growth occurs, the battery capacity loss is determined by the change in discharge rebound equilibrium voltage. Among them, for aged batteries and BOL batteries, constant capacity tests were conducted at the first rate current and the second rate current. The first rate current was a minimum value and much smaller than the second rate current. The discharge curve at the first rate current was used as the ideal non-polarization curve. Below the discharge curve, draw a perpendicular line from the end of the discharge curve at the second rate current, intersecting the discharge curve at the first rate current at a point. The ordinate value of this point is the discharge rebound equilibrium voltage. After polarization growth occurs, the battery capacity loss is: in the discharge curves of aged batteries and BOL batteries, the difference on the horizontal axis between the intersection of the discharge curves at the first rate current is the capacity loss caused by polarization growth.

2. The method for quantitatively testing battery capacity loss caused by polarization growth as described in claim 1, characterized in that, After polarization growth occurs, the difference on the vertical axis between the intersection of the discharge curves at the first rate current in the discharge curves of aged batteries and BOL batteries is the voltage drop caused by polarization growth.

3. The method for quantitatively testing battery capacity loss caused by polarization growth as described in claim 1, characterized in that, The different currents were 1C and 0.04C, and the discharge curve at 0.04C was taken as the ideal non-polarization curve.

4. The method for quantitatively testing battery capacity loss caused by polarization growth as described in claim 1, characterized in that, If the discharge rebound equilibrium voltages of the two are the same, it indicates that no polarization growth has occurred; otherwise, polarization growth has occurred.

5. A quantitative testing system for battery capacity loss caused by polarization growth, characterized in that, The method for quantitatively testing battery capacity loss caused by polarization growth as described in any one of claims 1-4 includes: The discharge curve plotting module is configured to perform constant-capacity tests on the aged battery to be tested and the corresponding BOL battery using a set current rate, and obtain the discharge curves of the two batteries at different rates. The capacity loss quantification module is configured to determine the discharge rebound balance voltage of BOL batteries and aged batteries respectively based on their discharge curves, determine whether the aged battery has polarization growth based on the comparison of the discharge rebound balance voltages of the two, and determine the amount of battery capacity loss based on the change of discharge rebound balance voltage after polarization growth occurs.

6. An electronic device, characterized in that, It includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor, which, when executed by the processor, perform the method according to any one of claims 1-4.

7. A computer-readable storage medium, characterized in that, Used to store computer instructions, which, when executed by a processor, perform the method described in any one of claims 1-4.

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