A method for detecting a battery capacity drop-off inflection point
By combining accelerated aging and conventional operating conditions in battery testing, the inflection point of battery capacity drop can be quickly detected, solving the problem of low testing efficiency and enabling battery life prediction and safety risk control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- EVE POWER CO LTD
- Filing Date
- 2023-12-22
- Publication Date
- 2026-07-21
AI Technical Summary
Existing technologies have low efficiency in detecting the inflection point of battery capacity drop, and the detection process takes a lot of time. They cannot effectively predict the causes of battery capacity drop in advance, resulting in shortened battery life and increased safety risks.
The battery is subjected to accelerated aging conditions for charge-discharge cycles to quickly reach the target healthy state. Then, it is switched to normal operating conditions to detect the capacity drop inflection point. By combining accelerated aging conditions and normal operating conditions, the number of charge-discharge cycles is reduced and the detection efficiency is improved.
It shortens the detection cycle for capacity drop inflection points, improves detection efficiency, enables early identification of battery life inflection points, reduces safety risks, and guides risk control during battery design and use.
Smart Images
Figure CN117761560B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of battery technology, and in particular to a method for detecting the inflection point of battery capacity drop. Background Technology
[0002] Predicting the inflection point of battery capacity drop remains a challenge in the industry. Current research attempts to predict lithium plating at the negative electrode by tracking changes in the average charge-discharge voltage caused by the loss of active lithium (Li), thus enabling early prediction of reversible capacity drops in lithium-ion batteries. However, various factors can cause battery capacity drops. Besides negative electrode lithium plating, electrolyte drying out or depletion of electrolyte additives are also common causes, limiting the applicability of this method.
[0003] A significant drop in battery capacity can drastically shorten its lifespan. This capacity drop is often accompanied by a surge in internal resistance, which can easily lead to safety issues. Predicting this capacity drop inflection point in advance can guide battery design during the research and development phase. In actual use, identifying this inflection point early and taking measures to delay or suppress its occurrence is crucial for extending battery lifespan and reducing safety risks.
[0004] When detecting the inflection point of capacity drop, the battery needs to undergo repeated charge and discharge cycles, which takes a lot of time and results in low detection efficiency for the inflection point of capacity drop. Summary of the Invention
[0005] To address the aforementioned issues, this application provides a method for detecting the inflection point of battery capacity drop, which can improve the detection efficiency of the inflection point of battery capacity drop.
[0006] One technical solution adopted in this application is: a method for detecting the inflection point of battery capacity drop, the method comprising: performing charge-discharge cycles on the battery under test under a first operating condition until the battery health state of the battery under test drops to a first set threshold; performing charge-discharge cycles on the battery under test whose battery health state has dropped to the first set threshold under a second operating condition, and determining the capacity drop inflection point of the battery under test during the charge-discharge cycle; wherein, the rate of decrease of battery health state under the first operating condition is greater than the rate of decrease of battery health state under the second operating condition.
[0007] In one embodiment, the battery under test whose battery health status has decreased to a first preset threshold is subjected to charge-discharge cycles under a second operating condition, and the capacity drop inflection point of the battery under test is determined during the charge-discharge cycle. This includes: performing charge-discharge cycles on the battery under test whose battery health status has decreased to the first preset threshold under the second operating condition until the battery health status of the battery under test decreases to a second preset threshold, and determining the capacity drop inflection point of the battery under test during the charge-discharge cycle; wherein the second preset threshold is less than the first preset threshold.
[0008] In one embodiment, the battery under test is charged and discharged in a first operating condition until the battery health status of the battery under test is reduced to a first set threshold. This includes: charging and discharging multiple batteries under test in the first operating condition until the battery health status of the multiple batteries under test is reduced to the first set threshold respectively; wherein the first set thresholds corresponding to the multiple batteries under test are different.
[0009] In one embodiment, a second operating condition is used to perform charge-discharge cycles on a battery under test whose battery health state has decreased to a first preset threshold, until the battery health state of the battery under test decreases to a second preset threshold, and the capacity drop inflection point of the battery under test is determined during the charge-discharge cycle. This includes: performing charge-discharge cycles on multiple batteries under test whose battery health state has decreased to the first preset threshold using the second operating condition, until the battery health state of the multiple batteries under test decreases to the second preset threshold, and determining the capacity drop inflection point of the battery under test during the charge-discharge cycle; wherein the second preset thresholds corresponding to the multiple batteries under test are different.
[0010] In one embodiment, the method further includes: during the charge-discharge cycle of multiple batteries under test using the second operating condition, when one of the batteries under test is determined to have a capacity drop inflection point, stopping the charge-discharge cycle of the remaining batteries under test.
[0011] In one embodiment, the first set threshold corresponding to the plurality of batteries under test decreases sequentially based on a preset difference, the second set threshold corresponding to the plurality of batteries under test decreases sequentially based on a preset difference, and the difference between the first set threshold and the second set threshold corresponding to the plurality of batteries under test is the same.
[0012] In one embodiment, a first set threshold is less than or equal to 95% and greater than or equal to 85%, and a second set threshold is less than or equal to 90% and greater than or equal to 80%.
[0013] In one embodiment, the ambient temperature corresponding to the first operating condition is greater than the ambient temperature corresponding to the second operating condition.
[0014] In one embodiment, the charging current corresponding to the first operating condition is greater than the charging current corresponding to the second operating condition; and / or the discharging current corresponding to the first operating condition is greater than the discharging current corresponding to the second operating condition.
[0015] In one embodiment, the charging cutoff voltage corresponding to the first operating condition is greater than the charging cutoff voltage corresponding to the second operating condition; and / or the discharging cutoff voltage corresponding to the first operating condition is less than the discharging cutoff voltage corresponding to the second operating condition.
[0016] The capacity drop inflection point detection method provided in this application includes: performing charge-discharge cycles on the battery under test under a first operating condition until the battery health state of the battery under test decreases to a first set threshold; performing charge-discharge cycles on the battery under test whose battery health state has decreased to the first set threshold under a second operating condition, and determining the capacity drop inflection point of the battery under test during the charge-discharge cycle; wherein, the rate of decrease in battery health state under the first operating condition is greater than the rate of decrease in battery health state under the second operating condition. Through the above method, by using accelerated aging operating conditions to perform charge-discharge cycles on the battery under test to quickly bring it to the required battery health state, and then using conventional operating conditions to perform charge-discharge cycles on the battery under test to detect the capacity drop inflection point, the number of battery charge-discharge cycles can be reduced, the capacity drop inflection point detection cycle can be shortened, and the capacity drop inflection point detection efficiency can be improved. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 This is a flowchart illustrating an embodiment of the battery capacity drop inflection point detection method provided in this application;
[0019] Figure 2 This is a flowchart illustrating another embodiment of the battery capacity drop inflection point detection method provided in this application;
[0020] Figure 3 This is a flowchart illustrating another embodiment of the battery capacity drop inflection point detection method provided in this application;
[0021] Figure 4 This is a comparative diagram showing the inflection point of capacity drop under normal operating conditions and the inflection point of capacity drop after accelerated aging. Detailed Implementation
[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0023] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.
[0024] "A and / or B" includes the following three combinations: A only, B only, and a combination of A and B.
[0025] The use of "applies to" or "configured to" in this application implies open and inclusive language, which does not exclude the applicability to or configuration to devices performing additional tasks or steps. Additionally, the use of "based on" implies openness and inclusivity, because processes, steps, calculations, or other actions "based on" one or more of the stated conditions or values may in practice be based on additional conditions or values beyond those stated.
[0026] In this application, the term "exemplary" is used to mean "used as an example, illustration, or description." Any embodiment described as "exemplary" in this application is not necessarily to be construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to make and use this application. Details are set forth in the following description for purposes of explanation. It should be understood that those skilled in the art will recognize that this application can be made without using these specific details. In other instances, well-known structures and processes are not described in detail to avoid obscuring the description of this application with unnecessary detail. Therefore, this application is not intended to be limited to the embodiments shown, but is consistent with the broadest scope of the principles and features disclosed in this application.
[0027] See Figure 1 , Figure 1 This is a flowchart illustrating an embodiment of the battery capacity drop inflection point detection method provided in this application. The method includes:
[0028] Step S11: Perform charge and discharge cycles on the battery under test using the first operating condition until the battery health status of the battery under test decreases to the first set threshold.
[0029] Here, operating condition refers to the sum of environmental parameters and charge / discharge parameters during the battery charge / discharge cycle. Optionally, operating condition may include ambient temperature, charging current, discharging current, charging cut-off voltage, discharging cut-off voltage, etc.
[0030] Battery state of health (SOH) reflects the battery's healthy lifespan, including its charge, energy, and charge / discharge power. Accurate assessment of battery health provides a comprehensive understanding of the battery's current condition. Generally, SOH is expressed as the ratio of the battery's current maximum capacity to its rated capacity.
[0031] Step S12: Use the second operating condition to perform charge and discharge cycles on the battery under test whose battery health status has dropped to the first set threshold, and determine the inflection point of the capacity drop of the battery under test during the charge and discharge cycle.
[0032] Among them, the rate of decrease in battery health under the first operating condition is greater than the rate of decrease in battery health under the second operating condition.
[0033] Understandably, the second operating condition is one that meets the normal operating environment of the battery and is under normal aging conditions, while the first operating condition meets the special operating environment of the battery and is under special operating conditions that accelerates battery aging.
[0034] Specifically, through extensive testing and analysis, it has been found that there is no memory effect during battery cycling. That is, after aging the battery to the same SOH state under different operating conditions (temperature, charging current, discharging current, charging cut-off voltage, discharging cut-off voltage, and DOD (Depth of discharge) can all vary), and then cycling under the same operating conditions, the degradation rate is consistent. Based on this, accelerated aging cycle experiments can be conducted under high temperature and high rate conditions in the early stage, and then switched to the required predicted operating conditions. The capacity degradation rate of the predicted operating conditions can be obtained. By using offline methods to determine whether it will drop significantly, the inflection point of capacity drop under that operating condition can be predicted in advance.
[0035] In an optional embodiment, the following experimental group was used for detection:
[0036] Table 1:
[0037] Operating condition phase First Working Condition Second working condition
[0038] Optionally, in one embodiment, the first set threshold S1 is less than or equal to 95% and greater than or equal to 85%.
[0039] In another optional embodiment, step S12 may include: performing charge-discharge cycles on the battery under test using a second operating condition until the battery health status of the battery under test decreases to a second preset threshold, and determining the capacity drop inflection point of the battery under test during the charge-discharge cycle; wherein the second preset threshold is less than the first preset threshold. Specifically, the following experimental group is used for testing:
[0040] Table 2:
[0041] Operating condition phase First Working Condition Second working condition
[0042] Optionally, the first set thresholds corresponding to multiple batteries under test decrease sequentially based on a preset difference, and the second set thresholds corresponding to multiple batteries under test decrease sequentially based on a preset difference, wherein the difference between the first set thresholds and the second set thresholds corresponding to multiple batteries under test is the same. In one embodiment, the first set threshold S1 is less than or equal to 95% and greater than or equal to 85%, and the second set threshold S2 is less than or equal to 90% and greater than or equal to 80%.
[0043] Optionally, the capacity of the battery under test can be detected in real time during the charge-discharge cycle under the set operating conditions. For example, in one charge-discharge cycle, the current SOH value is determined based on the capacity after full charge and the rated capacity; for example, in the second operating condition, the capacity change is detected in real time based on each charge-discharge cycle, and whether a capacity drop inflection point occurs is detected.
[0044] Specifically, when detecting the inflection point of capacity drop, the capacity of the battery under test can be measured during the discharge process of each charge-discharge cycle. For example, the discharge current can be sampled at a set frequency, and the corresponding capacity can be calculated based on the discharge current and discharge time. When the difference between two or more adjacent capacity changes (reflected as the slope in the capacity-time graph) is greater than a set threshold, it can be considered that a capacity drop inflection point has occurred.
[0045] Understandably, based on extensive testing and analysis, regardless of the battery's initial operating conditions, the SOH value difference at the capacity drop inflection point is very small. Alternatively, in conjunction with the above embodiments, regardless of the first operating condition, using a conventional second operating condition for charge-discharge cycles results in a very small difference in the SOH value at the capacity drop inflection point. Therefore, this embodiment employs a special operating condition in the first operating condition that accelerates battery aging. This reduces the number of charge-discharge cycles, allowing the battery to quickly reach the desired battery health state (i.e., the first set threshold), thus shortening the overall battery capacity drop inflection point detection time.
[0046] The capacity drop inflection point detection method provided in this embodiment includes: performing charge-discharge cycles on the battery under test under a first operating condition until the battery health state of the battery under test decreases to a first set threshold; performing charge-discharge cycles on the battery under test whose battery health state has decreased to the first set threshold under a second operating condition, and determining the capacity drop inflection point of the battery under test during the charge-discharge cycle; wherein, the rate of decrease in battery health state under the first operating condition is greater than the rate of decrease in battery health state under the second operating condition. Through the above method, by using accelerated aging operating conditions to perform charge-discharge cycles on the battery under test to quickly bring it to the required battery health state, and then using conventional operating conditions to perform charge-discharge cycles on the battery under test to detect the capacity drop inflection point, the number of battery charge-discharge cycles can be reduced, the capacity drop inflection point detection cycle can be shortened, and the capacity drop inflection point detection efficiency can be improved.
[0047] See Figure 2 , Figure 2 This is a flowchart illustrating another embodiment of the battery capacity drop inflection point detection method provided in this application. The method includes:
[0048] Step S21: Perform charge-discharge cycles on multiple batteries under test using the first operating condition until the battery health status of multiple batteries under test is reduced to the first set threshold.
[0049] Among them, the first set thresholds for multiple batteries under test are different.
[0050] The number of batteries to be tested can be determined according to actual needs; for example, the number of batteries to be tested can be 3.
[0051] The different set thresholds can be determined based on the empirical SOH value corresponding to the inflection point of battery capacity drop. For example, based on the empirical SOH value of 87% corresponding to the inflection point of battery capacity drop, taking three batteries to be tested as an example, the first set thresholds of these batteries to be tested can be set to 95%, 90%, and 85%, or 90%, 85%, and 80%, respectively. In addition, the interval can also be adjusted, for example, it can be set to 90%, 87.5%, and 85%.
[0052] Step S22: Using the second operating condition, charge and discharge cycles are performed on multiple batteries under test whose battery health status has dropped to the first set threshold until the battery health status of multiple batteries under test drops to the second set threshold, and the capacity drop inflection point of the batteries under test is determined during the charge and discharge cycle.
[0053] Among them, the second set thresholds are different for multiple batteries under test.
[0054] Among them, the rate of decrease in battery health under the first operating condition is greater than the rate of decrease in battery health under the second operating condition.
[0055] In step S22, the multiple different second set thresholds can be determined based on the multiple first set thresholds in step S21. For example, if the detection range of the second working condition is 5%, then 5% can be subtracted from the multiple set thresholds in step S21 in sequence.
[0056] In an optional embodiment, the following experimental group was used for detection:
[0057] Table 3:
[0058]
[0059] Specifically,
[0060] The first battery under test is charged and discharged under the first operating condition until the battery health status of the first battery under test drops to 95%; the first battery under test is charged and discharged under the second operating condition until the battery health status of the first battery under test drops to 90%, and the inflection point of the capacity drop of the battery under test is determined during the charge and discharge cycle.
[0061] The second battery under test is charged and discharged under the first operating condition until its battery health status drops to 90%; the second battery under test is charged and discharged under the second operating condition until its battery health status drops to 85%, and the inflection point of capacity drop of the battery under test is determined during the charge and discharge cycle.
[0062] The third battery under test is charged and discharged under the first operating condition until its battery health status drops to 85%. The third battery under test is charged and discharged under the second operating condition until its battery health status drops to 80%. The inflection point of the battery's capacity drop is determined during the charge and discharge cycle.
[0063] Alternatively, in one embodiment, as Figure 3 As shown, Figure 3 This is a flowchart illustrating another embodiment of the battery capacity drop inflection point detection method provided in this application. Step S22 may further include:
[0064] Step S23: During the charge-discharge cycle of multiple batteries under test using the second operating condition, when one of the batteries under test is determined to have a capacity drop inflection point, the charge-discharge cycle of the remaining batteries under test is stopped.
[0065] In one embodiment, taking Table 3 as an example, when battery 1 is accelerated to 95% SOH under the first operating condition, the battery 1 is subjected to a normal charge-discharge cycle under the second operating condition. At this time, batteries 2 and 3 are still accelerated under the first operating condition. If a capacity drop inflection point is detected in battery 1 during this stage, it is not necessary to continue testing batteries 2 and 3, and the testing of batteries 2 and 3 can be stopped.
[0066] In another embodiment, taking Table 3 as an example, when battery 1 is accelerated to 95% SOH under the first operating condition, it is then subjected to a normal charge-discharge cycle under the second operating condition. At this time, batteries 2 and 3 are still undergoing accelerated aging under the first operating condition. During this stage, no capacity drop inflection point is detected in battery 1. When battery 2 is accelerated to 90% SOH under the first operating condition, it is then subjected to a normal charge-discharge cycle under the second operating condition. At this time, battery 3 is still undergoing accelerated aging under the first operating condition. If a capacity drop inflection point is detected in battery 2 during this stage, further testing of battery 3 is unnecessary, and testing of battery 3 can be stopped.
[0067] By using the above method, multiple batteries under test are used as control groups, and different accelerated aging stages are set for each. On the one hand, this can accelerate the detection of the inflection point of battery capacity drop. On the other hand, using multiple batteries allows for simultaneous detection of multiple different SOH ranges without knowing the approximate SOH range. Furthermore, once the capacity drop inflection point of one battery is determined, the testing of other batteries can be stopped, which can also save time.
[0068] Further reading Figure 4 , Figure 4This diagram compares the capacity drop inflection point under normal operating conditions with that after accelerated aging. The left curve represents the "capacity-cycle count" curve when the capacity drop inflection point occurs under accelerated aging conditions combined with normal operating conditions, while the right curve represents the "capacity-cycle count" curve when the capacity drop inflection point occurs under normal operating conditions. The solid line represents the capacity change before the capacity drop inflection point, and the dashed line represents the capacity change after the capacity drop inflection point. The diagram shows that after accelerating the battery to the set SOH value and then switching to normal operating conditions for cycling, the predicted inflection point SOH value is <0.5%, compared to the value predicted by continuous cycling under normal operating conditions throughout the entire process. This demonstrates the effectiveness of the above-mentioned method for detecting the battery capacity drop inflection point.
[0069] The display screen provided in the embodiments of this application has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.
Claims
1. A method for detecting the inflection point of battery capacity drop, characterized in that, The method for detecting the inflection point of battery capacity drop includes: The battery under test is charged and discharged under the first operating condition until the battery health status of the battery under test is reduced to a first set threshold. The second operating condition is used to perform charge-discharge cycles on the battery under test when the battery health status drops to the first set threshold, and the capacity drop inflection point of the battery under test is determined during the charge-discharge cycle. In this case, the rate of decrease in battery health under the first operating condition is greater than the rate of decrease in battery health under the second operating condition.
2. The method for detecting the inflection point of battery capacity drop according to claim 1, characterized in that, The step of performing charge-discharge cycles on the battery under test when its health status drops to the first set threshold under the second operating condition, and determining the capacity drop inflection point of the battery under test during the charge-discharge cycle, includes: The battery under test, whose battery health status has dropped to the first set threshold, is subjected to charge-discharge cycles under the second operating condition until the battery health status of the battery under test drops to the second set threshold, and the capacity drop inflection point of the battery under test is determined during the charge-discharge cycle. Wherein, the second set threshold is less than the first set threshold.
3. The method for detecting the inflection point of battery capacity drop according to claim 2, characterized in that, The step of performing charge-discharge cycles on the battery under test under a first operating condition until the battery health status of the battery under test decreases to a first preset threshold includes: The first operating condition is used to charge and discharge multiple batteries under test until the battery health status of multiple batteries under test is reduced to a first set threshold. Among them, the first set thresholds corresponding to multiple batteries under test are different.
4. The method for detecting the inflection point of battery capacity drop according to claim 3, characterized in that, The step of performing charge-discharge cycles on the battery under test when its battery health status drops to the first preset threshold under the second operating condition, until the battery health status of the battery under test drops to the second preset threshold, and determining the capacity drop inflection point of the battery under test during the charge-discharge cycle, includes: The second operating condition is used to perform charge-discharge cycles on multiple batteries under test whose battery health status has dropped to the first set threshold until the battery health status of multiple batteries under test drops to the second set threshold, and the capacity drop inflection point of the batteries under test is determined during the charge-discharge cycle. The second set thresholds for the multiple batteries under test are different.
5. The method for detecting the inflection point of battery capacity drop according to claim 4, characterized in that, The method further includes: During the charge-discharge cycle of multiple batteries under test using the second operating condition, when one of the batteries under test determines a capacity drop inflection point, the charge-discharge cycle of the remaining batteries under test is stopped.
6. The method for detecting the inflection point of battery capacity drop according to claim 4, characterized in that, The first set threshold corresponding to the plurality of batteries under test decreases sequentially based on a preset difference, and the second set threshold corresponding to the plurality of batteries under test decreases sequentially based on a preset difference, and the difference between the first set threshold and the second set threshold corresponding to the plurality of batteries under test is the same.
7. The method for detecting the inflection point of battery capacity drop according to claim 2, characterized in that, The first set threshold is less than or equal to 95% and greater than or equal to 85%, and the second set threshold is less than or equal to 90% and greater than or equal to 80%.
8. The method for detecting the inflection point of battery capacity drop according to any one of claims 1-7, characterized in that, The ambient temperature corresponding to the first operating condition is higher than the ambient temperature corresponding to the second operating condition.
9. The method for detecting the inflection point of battery capacity drop according to any one of claims 1-7, characterized in that, The charging current corresponding to the first operating condition is greater than the charging current corresponding to the second operating condition; and / or The discharge current corresponding to the first operating condition is greater than the discharge current corresponding to the second operating condition.
10. The method for detecting the inflection point of battery capacity drop according to any one of claims 1-7, characterized in that, The charging cutoff voltage under the first operating condition is greater than the charging cutoff voltage under the second operating condition; and / or The discharge cutoff voltage corresponding to the first operating condition is less than the discharge cutoff voltage corresponding to the second operating condition.