A method and system for determining the standardization of a power battery retirement

Abstract

The application provides a power battery retirement standardization judgment method and system, the method comprises the following processes: obtaining capacity data and health state data of the power battery; obtaining a retirement index of the power battery by subtracting the battery capacity of the current charge-discharge cycle from the battery capacity of the last charge-discharge cycle, and dividing the square of the health state of the current charge-discharge cycle by the capacity degradation gradient; when the retirement index is less than a set threshold, the power battery is retired; otherwise, the power battery can continue to operate; the application comprehensively evaluates the battery aging state based on the SOH and the capacity degradation gradient, proposes a brand-new battery retirement index, can comprehensively evaluate each battery monomer according to various real-time states of the battery, and further achieves personalized retirement, which guarantees the safe use of the battery and improves the utilization rate of the battery.

Description

Technical Field

[0001] This invention relates to the field of power battery retirement assessment technology, and in particular to a standardized method and system for determining the retirement of power batteries. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and stable performance, have been widely used in electric vehicle energy supply systems. However, during charge-discharge cycles, the battery's energy storage capacity and state of health (SOH) decrease with each cycle. When this decrease reaches a certain level, phenomena such as a significant drop in battery capacity, electrolyte leakage, and battery bulging may occur. Continued use could lead to numerous safety hazards. Even battery cells of the same type can exhibit different degradation characteristics depending on usage conditions. Therefore, properly retiring batteries not only ensures safe battery use but also maximizes their utilization.

[0004] The aging mechanism of lithium-ion batteries is complex, and capacity degradation is nonlinear and uncertain, making it very difficult to establish accurate aging models. Batteries typically exhibit different degradation characteristics at different stages of capacity degradation, generally divided into two phases: the first phase is characterized by a relatively small change in the capacity degradation gradient and a slow decrease in state of equilibrium (SOH); the second phase sees a gradually increasing capacity degradation gradient and a gradually accelerating rate of SOH decrease. These different degradation characteristics in the two phases result in a nonlinear overall capacity degradation gradient and SOH change in the battery, and differences also exist between different battery cells. Traditionally, power batteries are retired based on 80% SOH. This "one-size-fits-all" approach fails to consider the degradation characteristics of individual battery cells, cannot fully utilize the battery, and cannot ensure safe use, thus having certain limitations. Under actual operating conditions, batteries will exhibit different degradation characteristics due to variations in external operating conditions and internal chemical reaction environments. Battery cells should be retired reasonably based on their own degradation characteristics: when the battery has a high State of Health (SOH) but a large capacity degradation gradient, retiring the battery at 80% SOH cannot guarantee safety, and early retirement can be considered; when the battery has a low SOH but a small capacity degradation gradient, retiring at 80% SOH will not fully utilize the battery, and continued use can be considered, postponing the retirement time. Therefore, how to accurately identify the battery retirement point and accurately assess the battery aging status in real time based on new indicators has become a hot research topic in the field of power battery health management.

[0005] Many scholars have conducted extensive research on battery retirement point identification, but a comprehensive evaluation index for accurate and reasonable retirement of lithium-ion batteries is still lacking. For example, Chinese invention patent CN115166563A proposes a method for power battery state assessment and retirement screening. It performs initial screening based on voltage data and obtains battery capacity and resistance data using standard capacity testing. Specifically, it achieves high-precision and high-reliability data acquisition by charging and discharging the battery. Based on the derivative and second derivative of the battery capacity-voltage curve, it extracts the first and second indicators of the set peak values ​​of the differentiated curve to determine battery type and consistency, achieving a second screening. A third level of screening is performed based on the battery's DC internal resistance. However, this is a time-consuming and energy-wasting process, making large-scale battery retirement difficult. Chinese invention patent CN1096983B calculates the slope inflection point based on the relationship curve between the battery's open-circuit voltage (OCV) and discharge capacity. By comparing the voltage corresponding to the slope inflection point of a certain charge-discharge process with the cutoff voltage, it determines whether the battery should be retired. However, obtaining the OCV requires a long period of rest, resulting in poor economic efficiency. Chinese invention patent CN116125301A proposes a method for assessing the reliability status of lithium batteries. Based on the upper and lower threshold ranges of multiple parameters for safe battery operation, the reliability parameters of each parameter of the current battery within the threshold range are calculated, thereby evaluating the reliability status of the battery and determining whether the battery should be retired. However, this method relies on empirically given parameters and has a certain degree of subjectivity.

[0006] In summary, the traditional standard for battery retirement is 80% SOH. Currently, there is a lack of standardized methods to accurately identify battery retirement points. Most methods are based on a single characteristic or are subjective and have certain limitations. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a standardized method and system for determining the retirement of power batteries. Based on two indicators, State of Health (SOH) and capacity degradation gradient, the invention comprehensively evaluates the aging state of the battery and proposes a novel battery retirement index. This index can comprehensively evaluate each battery cell based on multiple real-time battery conditions, thereby achieving personalized retirement. This approach ensures the safe use of the battery while improving its utilization rate.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] The first aspect of this invention provides a standardized method for determining the retirement of power batteries.

[0010] A standardized method for determining the retirement of power batteries includes the following process:

[0011] Obtain capacity and health status data of the power battery;

[0012] The degradation gradient is obtained by subtracting the battery capacity of the current charge-discharge cycle from the battery capacity of the previous charge-discharge cycle. The retirement index of the power battery is obtained by dividing the square of the health status of the current charge-discharge cycle by the capacity degradation gradient.

[0013] The power battery is decommissioned when the retirement index is lower than the set threshold; otherwise, the power battery can continue to operate.

[0014] As a further limitation of the first aspect of the present invention, the acquisition of the threshold includes:

[0015] Obtain curves of retirement indicators relative to the number of cycles for multiple power batteries of the same model;

[0016] Based on the curve, the distribution of retirement indicators under an X% health state is obtained, and based on the distribution of retirement indicators, a set threshold is obtained.

[0017] As a further limitation of the first aspect of the invention, X% health status means 80% health status.

[0018] As a further limitation of the first aspect of the present invention, the distribution of the decommissioning index conforms to the gamma distribution, and the extreme point of the gamma distribution represents the maximum distribution frequency of the decommissioning index at that value, and the ratio of the shape parameter to the inverse scale parameter of the gamma distribution is used as the set threshold.

[0019] The second aspect of this invention provides a standardized determination system for the retirement of power batteries.

[0020] A standardized system for determining the retirement of power batteries, comprising:

[0021] The data acquisition module is configured to acquire the capacity data and health status data of the power battery.

[0022] The retirement index calculation module is configured to: subtract the battery capacity of the current charge-discharge cycle from the battery capacity of the previous charge-discharge cycle to obtain the degradation gradient, and divide the square of the health status of the current charge-discharge cycle by the capacity degradation gradient to obtain the retirement index of the power battery.

[0023] The power battery is decommissioned when the retirement index is lower than the set threshold; otherwise, the power battery can continue to operate.

[0024] As a further limitation of the second aspect of the present invention, the acquisition of the set threshold includes:

[0025] Obtain curves of retirement indicators relative to the number of cycles for multiple power batteries of the same model;

[0026] Based on the curve, the distribution of retirement indicators under an X% health state is obtained, and based on the distribution of retirement indicators, a set threshold is obtained.

[0027] As a further limitation of the second aspect of the invention, X% health status means 80% health status.

[0028] As a further limitation of the second aspect of the present invention, the distribution of the decommissioning index conforms to the gamma distribution, and the extreme point of the gamma distribution represents the maximum distribution frequency of the decommissioning index at that value, with the ratio of the shape parameter to the inverse scale parameter of the gamma distribution as the set threshold.

[0029] A third aspect of the present invention provides a computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the steps in the standardized determination method for the retirement of power batteries as described in the first aspect of the present invention.

[0030] The fourth aspect of the present invention provides an electronic device, including a memory, a processor, and a program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps in the standardized determination method for the retirement of power batteries as described in the first aspect of the present invention.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] 1. This invention comprehensively evaluates the aging state of batteries based on two indicators: State of Health (SOH) and capacity degradation gradient. It proposes a novel battery retirement index that can comprehensively evaluate each battery cell based on multiple real-time battery conditions, thereby achieving personalized retirement. This ensures the safe use of batteries and improves their utilization rate.

[0033] 2. This invention abandons the traditional "one-size-fits-all" retirement judgment method that uses 80% SOH as the battery life. It can reasonably and accurately retire the battery according to the degradation characteristics of individual battery cells, calculate the retirement index of the power battery in real time, and the calculation method is simple and robust. It provides an important reference for the residual value assessment and tiered utilization of retired batteries.

[0034] 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

[0035] 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.

[0036] Figure 1 This is a flowchart of the standardized identification process for lithium-ion battery retirement points provided in Embodiment 1 of the present invention;

[0037] Figure 2 This is a schematic diagram of the capacity degradation curve of 124 LFP cells provided in Embodiment 1 of the present invention;

[0038] Figure 3 This is a schematic diagram of the IoD variation curve of 124 batteries with the number of cycles provided in Embodiment 1 of the present invention;

[0039] Figure 4 This is a schematic diagram of the IoD distribution of 124 cells with 80% SOH provided in Embodiment 1 of the present invention;

[0040] Figure 5 This is a schematic diagram of the battery degradation curve and standard retirement point with BDC=1 as the standard provided in Embodiment 1 of the present invention;

[0041] Figure 6 This is a schematic diagram illustrating the proportion of battery life extension or reduction provided in Embodiment 1 of the present invention. Detailed Implementation

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

[0043] 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.

[0044] 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, 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.

[0045] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0046] Example 1:

[0047] like Figure 1 As shown, Embodiment 1 of the present invention provides a standardized method for personalized battery retirement to achieve efficient use of power batteries. The standardized identification method for battery retirement points is as follows: The battery degradation state is comprehensively evaluated and the battery health status is determined based on two indicators: battery capacity degradation gradient and battery health status. The degradation gradient ▽C is obtained by subtracting the capacity of the current charge / discharge cycle from the capacity of the previous charge / discharge cycle, based on the battery capacity degradation curve. i The SOH of the current charge / discharge cycle i The square of C divided by the capacity decay gradient ▽C iA new evaluation metric, the Index of Decommissioning (IoD), can be obtained, allowing for the identification of a suitable IoD threshold. thr And according to IoD thr The standard defines the end point of battery life, i.e. the retirement point, and the specific calculation formula is shown in Equation (1).

[0048]

[0049] In the formula, ▽C in the denominator represents the amount of discharge capacity decay after each cycle. ▽C increases with the number of cycles. SOH in the numerator decreases with the number of cycles, but to maintain a rate of change similar to ▽C, SOH is taken as... 2 In summary, IoD gradually decreases with increasing cycle count and can reflect the aging state of the battery from multiple perspectives.

[0050] The specific steps are as follows:

[0051] (1) Perform three standard capacity tests on the lithium-ion battery and take the average of the three measurements as the rated capacity of the battery.

[0052] (2) Conduct cyclic charge and discharge experiments on the battery, and obtain data such as battery capacity, current, voltage and temperature corresponding to each charge and discharge cycle, and preprocess the collected data;

[0053] (3) When the usable capacity of the battery is less than 60% of the rated capacity, stop the charge-discharge cycle test and record the number of cycles at this time;

[0054] (4) Denoise the original data, plot the capacity decay curve with the number of cycles, and then smooth the curve.

[0055] (5) Calculate the SOH and capacity decay gradient for each cycle based on the capacity decay curve, and further obtain the IoD curve;

[0056] (6) Based on the IoD curve, the IoD distribution at 80% SOH was obtained, and the threshold IoD was further derived. thr and through IoD thr The relationship with capacity, and the standardization of battery retirement point identification.

[0057] In this embodiment, 80% SOH is preferred. This is defined according to the current general standard. It is possible that the ratio will change as battery technology develops in the future. For example, it may become lower than 80% (such as 75% or 60%, etc.). Here, we only take 80% as an example and will not elaborate further.

[0058] This invention utilizes existing publicly available experimental datasets to verify the feasibility and effectiveness of the proposed method. A lithium iron phosphate (LFP) battery with a rated capacity of 1.1 Ah and a nominal voltage of 3.3 V was cyclically charged and discharged in a forced convection temperature-controlled chamber at 30°C. The dataset contains 124 batteries. The state of harmonics (SOH) of all batteries as a function of the number of charge-discharge cycles is shown below. Figure 2 As shown. Figure 2 The horizontal line represents 80% SOH. Traditionally, this line is used as the standard for battery retirement. Figure 2 It is evident that traditional methods only consider State of Health (SOH) and do not take into account the combined effects of SOH and capacity degradation gradient. When a battery has a high SOH but also a large capacity degradation gradient, retiring it at 80% SOH would compromise battery safety; conversely, when a battery has a low SOH but a small capacity degradation gradient, retiring it at 80% SOH would result in the battery not being fully utilized.

[0059] To address this issue, the battery retirement coefficient is calculated according to equation (1). To avoid IoD tending to infinity, the single capacity degradation gradient is limited to 0.02 Ah / cycle, and the results are as follows. Figure 3 As shown. By Figure 3 It can be seen that the IoD of a single battery cell gradually decreases, with a larger change in the early stages of degradation, and a gradual decrease in both the range and rate of change in the later stages. Overall battery pack analysis shows that the shorter the battery life, the smaller the range of IoD change and the faster the rate at which it approaches zero; conversely, the longer the battery life, the larger the range of IoD change and the slower the rate at which it approaches zero. This reflects, to some extent, the degradation characteristics of the battery pack and the aging state of individual battery cells. Further analysis of the IoD distribution of the battery pack at 80% SOH is also possible. Figure 4 As shown.

[0060] Depend on Figure 4 Analysis shows that under 80% SOH conditions, IoD conforms to the Gamma distribution, as shown in equation (2).

[0061]

[0062] In the formula, α is the shape parameter and β is the inverse scale parameter. Calculations yield α = 8.56 and β = 8.33. The extreme point conforming to the Gamma distribution represents the maximum IoD distribution frequency at that value, where some batteries are decommissioned. Calculations yield... Using IoD=1 as the standard for battery retirement, if the battery's IoD value is less than 1 at this point, retirement can be considered; if the battery's IoD value is still greater than 1, it can continue to be used. Based on this, a battery capacity degradation curve is plotted, and the battery retirement point is determined. Figure 5 As shown, the lifespan of 124 batteries was extended or shortened under standard retirement methods, for example... Figure 6 As shown.

[0063] Depend on Figure 5 and Figure 6 Analysis shows that most batteries degrade inconsistently. Therefore, IoD=1 is selected as the battery retirement threshold, and this threshold is used as the battery retirement standard. Figure 5 The center mark indicates the standardized battery retirement point, and the black horizontal line indicates the battery retirement point defined by 80% SOH. Figure 6 The diagram shows the percentage distribution of battery life extension or reduction under the method described in this invention compared to the traditional 80% SOH retirement method. It can be seen that a very small number of batteries have a lifespan reduction of about 60% and an extension of about 40%, while the lifespan of most batteries is reduced by -10% to extended by 20%.

[0064] This invention no longer uses 80% State of Health (SOH) as the retirement point, but instead comprehensively assesses the battery retirement point based on its health status and capacity degradation gradient. For batteries with a rapid and significant lifespan degradation, even with a high SOH, early retirement is recommended to ensure battery safety. Conversely, for batteries with a slower lifespan degradation rate and a longer cycle life, the later degradation is approximately linear. Even with a low SOH, the slow degradation rate allows for continued use for a period before retirement, improving battery capacity utilization. Therefore, the standardized lifespan end-of-life identification method proposed in this invention overcomes the bottleneck of using 80% SOH as the traditional lifespan end-of-life approach, enabling more rational battery utilization and ensuring battery safety.

[0065] Example 2:

[0066] Embodiment 2 of the present invention provides a standardized determination system for the retirement of power batteries, comprising:

[0067] The data acquisition module is configured to acquire the capacity data and health status data of the power battery.

[0068] The retirement index calculation module is configured to: subtract the battery capacity of the current charge-discharge cycle from the battery capacity of the previous charge-discharge cycle to obtain the degradation gradient, and divide the square of the health status of the current charge-discharge cycle by the capacity degradation gradient to obtain the retirement index of the power battery.

[0069] The power battery is decommissioned when the retirement index is lower than the set threshold; otherwise, the power battery can continue to operate.

[0070] The working methods of each module of the system are the same as those of the standardized determination method for the retirement of power batteries provided in Example 1, and will not be repeated here.

[0071] Example 3:

[0072] Embodiment 3 of the present invention provides a computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the steps in the standardized determination method for the retirement of power batteries as described in Embodiment 1 of the present invention.

[0073] Example 4:

[0074] Embodiment 4 of the present invention provides an electronic device, including a memory, a processor, and a program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps in the standardized determination method for the retirement of power batteries as described in Embodiment 1 of the present invention.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A standardized method for determining the retirement of power batteries, characterized in that, The process includes the following: Obtain capacity and health status data of the power battery; The capacity degradation gradient is obtained by subtracting the battery capacity of the current charge-discharge cycle from the battery capacity of the previous charge-discharge cycle. The retirement index of the power battery is obtained by dividing the square of the health status of the current charge-discharge cycle by the capacity degradation gradient. The power battery is retired when the retirement target is lower than the set threshold. Otherwise, the power battery can continue to operate.

2. The standardized determination method for the retirement of power batteries as described in claim 1, characterized in that, The acquisition of the threshold setting includes: Obtain curves of retirement indicators relative to the number of cycles for multiple power batteries of the same model; Based on the curves of battery retirement indicators relative to the number of cycles and the curves of battery health status changing with the number of charge-discharge cycles, the distribution of retirement indicators at the X% health state is obtained, and a set threshold is obtained based on the distribution of retirement indicators.

3. The standardized determination method for the retirement of power batteries as described in claim 2, characterized in that, X% health status is 80% health status.

4. The standardized determination method for the retirement of power batteries as described in claim 2, characterized in that, The distribution of retirement indicators conforms to a gamma distribution. The extreme points of the gamma distribution represent the maximum distribution frequency of retirement indicators under X% health conditions. The threshold is set by the ratio of the shape parameter to the inverse scaling parameter of the gamma distribution.

5. A standardized system for determining the retirement of power batteries, characterized in that, include: The data acquisition module is configured to acquire the capacity data and health status data of the power battery. The retirement index calculation module is configured to: subtract the battery capacity of the current charge-discharge cycle from the battery capacity of the previous charge-discharge cycle to obtain the capacity degradation gradient, and divide the square of the health status of the current charge-discharge cycle by the capacity degradation gradient to obtain the retirement index of the power battery. The power battery is retired when the retirement target is lower than the set threshold. Otherwise, the power battery can continue to operate.

6. The standardized determination system for the retirement of power batteries as described in claim 5, characterized in that, The acquisition of the threshold setting includes: Obtain curves of retirement indicators relative to the number of cycles for multiple power batteries of the same model; Based on the curves of battery retirement indicators relative to the number of cycles and the curves of battery health status changing with the number of charge-discharge cycles, the distribution of retirement indicators at the X% health state is obtained, and a set threshold is obtained based on the distribution of retirement indicators.

7. The standardized determination system for the retirement of power batteries as described in claim 6, characterized in that, X% health status is 80% health status.

8. The standardized determination system for the retirement of power batteries as described in claim 6, characterized in that, The distribution of retirement indicators conforms to a gamma distribution. The extreme points of the gamma distribution represent the maximum distribution frequency of retirement indicators under X% health conditions. The threshold is set by the ratio of the shape parameter to the inverse scaling parameter of the gamma distribution.

9. A computer-readable storage medium having a program stored thereon, characterized in that, When executed by the processor, the program implements the steps in the standardized determination method for the retirement of power batteries as described in any one of claims 1-4.

10. An electronic device comprising a memory, a processor, and a program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the standardized determination method for the retirement of power batteries as described in any one of claims 1-4.

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