Method for estimating the remaining useful life of an electrochemical element and related device
By measuring the transient minimum voltage and temperature of lithium-based batteries and combining them with machine learning algorithms, the influence of passivation in the health status estimation of lithium-based batteries was resolved, and accurate prediction of battery life was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SAFT CORP
- Filing Date
- 2024-11-06
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies fail to effectively account for the increase in internal resistance caused by passivation when estimating the health status of lithium-based batteries, resulting in a reduction in energy supply.
By measuring the transient minimum voltage, temperature, and usage time of the electrochemical element, voltage polarization is calculated using the k-nearest neighbor algorithm and the random forest algorithm. Combined with interpolation and smoothing operations, the remaining lifetime of the electrochemical element is estimated.
It enables accurate estimation of the health status of lithium-based batteries, and in particular, improves the accuracy of predicting remaining lifespan by detecting changes in the resistance of the passivation layer.
Smart Images
Figure CN122122469A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for estimating parameters related to the health status of at least one electrochemical element of a battery, particularly a primary electrochemical element. The invention also relates to associated calculators, management systems, and batteries. Background Technology
[0002] Typically, a battery comprises one or more current storage units, also known as electrochemical generators, cells, or components. A storage unit is a power generation device in which chemical energy is converted into electrical energy. The chemical energy originates from electrochemically active compounds deposited on at least one surface of electrodes disposed within the storage unit. Electrical energy is generated by electrochemical reactions during the discharge of the storage unit. The electrodes disposed within the container are electrically connected to a current output terminal, which provides electrical continuity between the electrodes and the electrical consumption devices associated with the storage unit.
[0003] To increase the delivered power, several sealed energy storage units can be connected together to form a battery. Therefore, a battery can be divided into multiple modules, each module consisting of one or more energy storage units connected in series and / or in parallel. Thus, a battery can, for example, include one or more parallel branches of energy storage units connected in series and / or one or more parallel branches of modules connected in series.
[0004] A charging circuit is typically provided, which the battery can connect to to recharge the energy storage.
[0005] Furthermore, depending on the application, an electronic management system, including measuring sensors and electronic control circuitry, can be associated with the battery to varying degrees of sophistication. Such a system allows for the organization and control of battery charging and discharging, in particular, to balance the charging and discharging of the battery's different energy storage units relative to each other.
[0006] State of health is useful information for electronic battery management systems to optimize their use and lifespan. State of health is usually specified by the abbreviation SOH, which stands for "State of Health".
[0007] State of Health (SOH) allows for the estimation of battery aging between a new state and the end-of-life state, or more generally, between the initial state and the final state.
[0008] In this sense, the State of Health (SOH) defines the battery's ability to deliver current.
[0009] One technique for determining state of health (SOH) is to monitor the battery's temperature, voltage, and selectable current values to determine the SOH value according to aging laws. These aging laws are obtained from laboratory tests. Therefore, applying the aging laws to the monitored values provides an estimate of battery aging.
[0010] However, for certain types of battery chemistry, especially lithium-based chemistry, this static technology assumes uniform aging of the battery's energy storage and does not adequately account for the phenomenon of increasing the battery's internal resistance by forming a so-called passivation layer on the lithium surface, which limits its consumption.
[0011] Passivation is a phenomenon of lithium corrosion that occurs spontaneously within a battery once it comes into contact with the electrolyte, and its extent continues to vary throughout its discharge process. This phenomenon depends on the cell's operating conditions (temperature, stress, etc.). This corrosion reaction gradually creates an insulating protective layer between the lithium and the electrolyte, which prevents discharge reactions from occurring at their optimal voltage, thus reducing the energy supplied.
[0012] There is a need for a method to estimate parameters related to the health status of the electrochemical elements of a battery, which would allow for better accounting for passivation. Summary of the Invention
[0013] Therefore, this specification describes a method for estimating parameters related to the health state of at least one electrochemical element of a battery, the estimation method being implemented using a calculator and including:
[0014] - Steps for obtaining values of several physical quantities, said physical quantities including:
[0015] - Several measurements of the transient minimum voltage of the at least one electrochemical element, the transient minimum voltage being the minimum voltage reached by the at least one electrochemical element when a current pulse of current intensity is applied to the at least one electrochemical element, to obtain the applied current intensity and a set of voltages.
[0016] - The temperature of the at least one electrochemical element,
[0017] - The usage time of the at least one electrochemical element; and
[0018] - The step of applying the technology to the obtained values in order to obtain values of parameters related to the health status of the at least one electrochemical element.
[0019] According to a specific implementation, the estimation method has one or more of the following characteristics, individually or in combination of all technically possible features:
[0020] The technique includes the following operation: applying a first function to the values of usage time, temperature, and applied current intensity to obtain a value representing the presence of voltage polarization of the at least one electrochemical element.
[0021] - The first function is obtained by implementing the k-nearest neighbor algorithm.
[0022] - The first function is obtained by implementing the random forest algorithm.
[0023] - Define a cutoff voltage for an electrochemical element. This technique involves applying a second function to the cutoff voltage and quantities derived from a set of voltages for operation of parameters related to the health status of the electrochemical element.
[0024] - Each transient minimum voltage measurement corresponds to a point on a curve that gives the time evolution of the transient minimum voltage measurement, and the technique includes determining the slope coefficient of the tangent to the curve at that point for each point.
[0025] - The quantity derived from this set of voltages is the sum of the slope coefficients determined at each point.
[0026] - The technique includes an interpolation operation for transient minimum voltage measurement to obtain an interpolation curve, followed by a smoothing operation for the interpolation curve to obtain a curve that gives the time evolution of the transient minimum voltage measurement result.
[0027] - At least one parameter related to health status is the remaining service life of at least one electrochemical element.
[0028] - The battery is a primary battery.
[0029] - The at least one electrochemical element is an electrochemical element of LiSOCl2.
[0030] This specification also describes a calculator configured to estimate parameters related to the health status of at least one electrochemical element of a battery, the calculator being configured to:
[0031] - Obtain the values of several physical quantities, including:
[0032] - Several measurements of the transient minimum voltage of the at least one electrochemical element, the transient minimum voltage being the minimum voltage reached by the at least one electrochemical element when a current pulse of current intensity is applied to the at least one electrochemical element, to obtain the applied current intensity and a set of voltages.
[0033] - The temperature of the at least one electrochemical element,
[0034] - The usage time of the at least one electrochemical element; and
[0035] - Apply the technology to the obtained values in order to obtain values of parameters related to the health status of the at least one electrochemical element.
[0036] This specification also provides a management system for at least one electrochemical element of a battery, said at least one electrochemical element having terminals, the management system comprising:
[0037] - A current generator configured to apply a current pulse of current intensity to the at least one electrochemical element.
[0038] - A voltage sensor configured to measure the transient minimum voltage of the at least one electrochemical element, the transient minimum voltage being the minimum voltage reached by the at least one electrochemical element when a current pulse is applied by the current generator.
[0039] - A temperature sensor configured to measure the temperature of the at least one electrochemical element; and
[0040] - The calculator as described above.
[0041] This manual also describes a battery, including:
[0042] - At least one electrochemical element; and
[0043] - The management system as described above.
[0044] In this specification, the expression "configured as" means indiscriminately "suitable", "suitable for", or "configured as". Attached Figure Description
[0045] The features and advantages of the present invention will become apparent upon reading the following description, which is given by way of non-limiting example only and with reference to the accompanying drawings, wherein:
[0046] Figure 1 This is a schematic diagram of an example battery that includes electrochemical components.
[0047] Figure 2 This indicates that in the presence of a current pulse... Figure 1 The evolution of voltage measured on the battery,
[0048] Figure 3 A flowchart illustrating an example implementation of a method for estimating the remaining lifespan of electrochemical components, and
[0049] Figure 4 The applicant implements the law based on Figure 3 A schematic diagram illustrating an example of experimental results obtained using the flowchart method. Detailed Implementation
[0050] Battery 10 in Figure 1 As shown in the image.
[0051] In a manner known per se, batteries are typically an arrangement of multiple electrochemical elements; however, for the sake of simplicity, the case with a single electrochemical element is described below. It should be understood that transposition to other arrangements is straightforward.
[0052] The battery 10 includes an electrochemical element 12 and a management system 14 for the electrochemical element 12.
[0053] As previously mentioned, the electrochemical element 12 is a power generation device in which chemical energy is converted into electrical energy.
[0054] Therefore, the electrochemical element 12 delivers current and voltage between the two terminals.
[0055] Based on the example described, battery 10 is a primary battery.
[0056] Preferably, the electrochemical element 12 is a primary lithium electrochemical element with a liquid cathode, such as lithium thionyl chloride (LiSOCl2).
[0057] According to another implementation, a primary electrochemical element with a liquid cathode of type LiSO2 or LiSO2Cl2 can be considered.
[0058] As a variation, a primary lithium-ion electrochemical element with a solid cathode, such as LiMnO2 or LiCF, can be envisioned. X type.
[0059] Of course, these examples are not limiting, and the methods described later can be used for any type of electrochemical element 12, especially electrochemical elements that do not form part of a primary battery.
[0060] The management system 14 is a system configured to manage the electrochemical element 12.
[0061] The management system 14 includes a current generator 16, a voltage sensor 18, a temperature sensor 20, and a calculator 22.
[0062] The current generator 16 is configured to apply a current pulse with a current intensity to the electrochemical element 12.
[0063] Voltage sensor 18 is configured to measure the voltage across the terminals of electrochemical element 12.
[0064] During the current pulse applied by the current generator 16, the voltage of the electrochemical element 12 drops to a minimum and then rises again.
[0065] The corresponding changes are Figure 2 As can be seen, Figure 2 This indicates the change in voltage over time for several different batteries.
[0066] The minimum value is called the transient minimum voltage.
[0067] The minimum value is usually represented as TMV, an abbreviation for "Transient Minimum Voltage".
[0068] In the following text, the term "TMV voltage" will be used to refer to this minimum value.
[0069] The TMV voltage can be obtained within the first 100 milliseconds after the current pulse is applied.
[0070] The TMV voltage corresponds to the ohmic drop caused by the resistance of the passivation layer. However, the value of the TMV voltage also depends on the temperature and the strength of the applied current pulse.
[0071] Voltage sensor 18 is configured to measure the transient minimum voltage (TMV) of electrochemical element 12.
[0072] Temperature sensor 20 is used to measure the temperature of electrochemical element 12 on which the TMV voltage depends.
[0073] The calculator 22 is configured to implement a method for estimating the remaining useful life of the electrochemical element 12.
[0074] Calculator 22 is an electronic circuit designed to process and / or transform data represented by electronic or physical quantities in registers of the calculator and / or memory into other similar data corresponding to physical data in register memory or other types of display devices, transmission devices or storage devices.
[0075] As a specific example, calculator 22 includes single-core or multi-core processors (such as central processing unit (CPU), graphics processing unit (GPU), microcontroller and digital signal processor (DSP)), programmable logic circuits (such as application-specific integrated circuit (ASIC)), field-programmable gate array (FPGA), programmable logic device (PLD) and programmable logic array (PLA), state machine, logic gate and discrete hardware components.
[0076] Now for reference Figure 3 The flowchart describes an example of an implementation of a method for estimating the remaining useful life of electrochemical element 12.
[0077] As the name suggests, the estimation method aims to estimate parameters related to the health status of electrochemical element 12.
[0078] The estimation method includes obtaining step E24 and applying step E26.
[0079] During step E24, calculator 22 obtains several values of several physical quantities.
[0080] according to Figure 3 In this case, the calculator 22 obtains the temperature of the electrochemical element 12, the TMV voltage, and the current intensity of the current pulse applied by the current generator 16.
[0081] In the described example, the TMV voltage and temperature measurements are obtained from voltage sensor 18 and temperature sensor 20, respectively. These values are then the measurement results.
[0082] However, it is conceivable that these measurement results are obtained by implementing a method for estimating these values, which will be applied to measurements from other types of sensors.
[0083] The current intensity is provided by the set point of the current generator 16.
[0084] In the described example, the TMV voltage measurements are spaced out at one-day intervals, but this interval can vary depending on the desired implementation of the method.
[0085] During step E26, the calculator 22 applies the technique to the value obtained during step E24.
[0086] The mathematical techniques employed enable the determination of the remaining lifespan of the electrochemical element 12.
[0087] according to Figure 3 For example, the technique includes several operations, namely interpolation operation O30, smoothing operation O32, determination operation O34, and two operations applying their respective functions O36 and O38.
[0088] The interpolation O30 and smoothing O32 operations are designed to obtain a curve that gives the time evolution of the TMV voltage measurement results.
[0089] In this curve, each TMV voltage measurement corresponds to a point.
[0090] During interpolation operation O30, calculator 22 uses interpolation techniques applied to TMV voltage measurement to obtain an interpolation curve.
[0091] Any interpolation technique relevant to this context can be conceived that can be used with simple linear interpolation.
[0092] During the smoothing operation O32, the calculator 22 applies a smoothing function to the interpolated curve to reduce its irregularities and singularities.
[0093] Therefore, calculator 22 obtains a curve showing the time evolution of the TMV voltage measurement results.
[0094] Any other technique that could make it possible to obtain the time evolution curve is also conceivable here, and the smoothing operation O32 may be particularly useless in practice.
[0095] Calculator 22 performs a determination operation O34 on the obtained curve.
[0096] During operation O34, calculator 22 determines the slope coefficient of the tangent line to the curve corresponding to each point of the TMV voltage measurement result.
[0097] Therefore, calculator 22 can calculate the time derivative of the curve and determine the slope coefficient as the value of the derivative at that point.
[0098] During operation O34, calculator 22 calculates the quantities derived from the set of TMV voltages, which is the sum of the slope coefficients determined at each point of interest.
[0099] The sum here is the sum of all slope coefficients determined for each measurement point included in the predefined time interval.
[0100] The calculator 22 also applies the first function F1 to the applied current intensity, the set of voltages, temperature and usage time values, using operation O36.
[0101] Therefore, the first function F1 makes it possible to obtain an existence value, which is a value representing the existence of voltage polarization of electrochemical element 12.
[0102] Based on the described example, there exists a value that is equal to 0 or 1.
[0103] This presence value indicates a change in the slope of the TMV voltage, which is a sign of the presence of polarization and therefore a risk of end-of-life.
[0104] In other words, a value of 1 corresponds to an anomaly being detected x days before the voltage of electrochemical element 12 reaches the cutoff voltage.
[0105] The cutoff voltage is the minimum operating voltage of the system that uses energy provided by the electrochemical cell 12.
[0106] This value is sometimes referred to as the threshold voltage. Most commonly, it is specified by the corresponding English name "cut-off voltage" and depends on the use of electrochemical element 12.
[0107] In the example described, the cutoff voltage is 2.5 V.
[0108] The first function F1 is obtained by using a database.
[0109] The applicant conducted experiments to obtain a database that provides the TMV voltage measured between 0 and 100 ms after a current pulse at several moments in the lifetime of the electrochemical element, and this is used for several electrochemical element models, several current intensities, and several temperatures.
[0110] To this end, the applicant conducted corresponding electrical tests using actual electrochemical components. This resulted in the execution of over 200 different tests.
[0111] Then, the first function F1 is learned by utilizing artificial intelligence-generated techniques from the previous database.
[0112] This acquisition mode is usually specified by the term "machine learning," which refers to the corresponding English term "machine learning."
[0113] To perform this learning, the database can be divided into two databases: a learning database and a test database.
[0114] The distribution between the learning and testing databases depends on the application, but it is typically 80%–20%.
[0115] In this example, the first function F1 is obtained by implementing the random forest algorithm.
[0116] This technology is more often specified by the acronym RF, which stands for the English name "random forest".
[0117] In this technique, the random forest algorithm is used to set up a model whose learning is aimed at determining the free parameters.
[0118] According to another example, the first function F1 is obtained by implementing the "k nearest neighbor" algorithm.
[0119] This technology is typically designated by the acronym KNN, which stands for the English name "k-nearest neighbor".
[0120] In the presence of a non-zero value, calculator 22 then applies the second function F2 to the cutoff voltage and the amount derived from the set of TMV voltages.
[0121] As mentioned earlier, the derived quantity here is the sum of the slope coefficients determined at each point within a predetermined time interval.
[0122] Here, this involves, for example, considering only the points where the value is equal to 1 in the described case.
[0123] Calculator 22 outputs the remaining lifetime.
[0124] Therefore, the second function F2 allows the measured value of the derived quantity to be compared with the cutoff voltage in order to obtain the service life.
[0125] The second function F2 calculates the intersection between the derived value and the cutoff voltage.
[0126] The intersection is, for example, a linear regression.
[0127] Similarly, the second function F2 is obtained by using a technique similar to that used for the first function F1 and the previous database.
[0128] Examples of the experimental results obtained are in Figure 4 The diagram is used to represent this.
[0129] Curve C1 corresponds to the curve obtained after the smoothing operation O30, curve C2 corresponds to the cutoff voltage at 2.5 V (left scale), and curve C3 corresponds to the existence value obtained after the first function F1 in the case of implementing the KNN algorithm (right scale).
[0130] For the random forest algorithm, curve C3 will be the same.
[0131] Both technologies provide similar information, indicating a remaining service life of 40 days.
[0132] Further experiments showed that the battery had a remaining lifespan of 39 days, indicating that the method had very good accuracy.
[0133] Although this did not appear Figure 4 The results show that, however, additional tests allow the applicant to demonstrate that the random forest algorithm used for the first function F1 can achieve slightly improved performance.
[0134] The results are shown in the table below:
[0135]
[0136] In this table, recall is defined as the number of true positives. The number of true positives and the number of false negatives The ratio between the sums is mathematically written as:
[0137]
[0138] Precision corresponds to the number of false positives Rather than the number of false negatives The same ratio leads to the following mathematical formula:
[0139]
[0140] The F1 score is derived from recall and precision using the following formula:
[0141]
[0142] An F1 score greater than 0.9 is a sign of a good level of accuracy.
[0143] Therefore, the analysis of the results in this table shows that the use of both techniques can achieve very good performance, with each value greater than 0.9.
[0144] A comparison of the two techniques shows a slight advantage of the model generated by the random forest algorithm.
[0145] Therefore, this method can detect significant changes in the temporal evolution of the TMV voltage and quantify its impact on the remaining lifetime of the electrochemical element 12 by repeatedly measuring the TMV voltage during the operation of the electrochemical element 12.
[0146] Other implementation plans may also be considered.
[0147] In particular, this method can be used to predict another parameter related to the health status of electrochemical element 12, such as the percentage change in resistance.
[0148] It is also possible to imagine that, in addition to reference Figure 3 Other operations besides those described.
[0149] For example, according to one implementation, the result can be calculated using two techniques (e.g., as here, using KNN and RF techniques) and the average of them can be taken.
[0150] It is also conceivable to combine the two functions F1 and F2 by using a function that takes the obtained value as input and performs all operations to output only the remaining lifetime, without outputting the existing value according to this example.
[0151] Alternatively, we can envision using other mathematical techniques, such as neural networks.
[0152] According to the specific implementation plan, the first function F1 is only applied to the values of the applied current intensity, temperature, and usage time.
[0153] Furthermore, the order of operations presented in the described examples may be different, and some operations may be performed simultaneously.
[0154] In each case, the method makes it possible to obtain a good estimate of the health status of at least one electrochemical element 12 of the battery 10.
Claims
1. A method for estimating parameters related to the health status of at least one electrochemical element (12) of a battery (10), said estimation method being implemented by a calculator (22) and comprising the following steps: - Steps for obtaining values of several physical quantities, said physical quantities including: - Several measurements of the transient minimum voltage of the at least one electrochemical element (12), which is the minimum voltage reached by the at least one electrochemical element (12) when a current pulse of current intensity is applied to the at least one electrochemical element (12), to obtain the applied current intensity and a set of voltages. - The temperature of at least one electrochemical element (12), - The usage time of at least one electrochemical element (12); and - The step of applying the technology to the obtained values in order to obtain the values of parameters related to the health status of the at least one electrochemical element (12).
2. The estimation method according to claim 1, wherein, The technique includes the following operation: applying a first function to the usage time, the temperature, the set of voltages, and the applied current intensity to obtain a value representing the presence of polarization of the voltage of the at least one electrochemical element (12).
3. The estimation method according to claim 2, wherein, The first function is obtained by implementing the k-nearest neighbor algorithm.
4. The estimation method according to claim 2, wherein, The first function is obtained by implementing the random forest algorithm.
5. The estimation method according to any one of claims 2 to 4, wherein, The technique of defining a cutoff voltage for the at least one electrochemical element (12) includes applying a second function to the cutoff voltage and a quantity derived from the set of voltages for operation of the parameters related to the health status of the at least one electrochemical element (12).
6. The estimation method according to any one of claims 1 to 5, wherein, Each transient minimum voltage measurement result corresponds to a point on a curve that gives the time evolution of the transient minimum voltage measurement result, and the technique includes: for each point, determining the slope coefficient of the tangent of the curve at that point.
7. The estimation method according to claims 5 and 6, wherein, The quantity derived from the set of voltages is the sum of the slope coefficients determined at each point.
8. The estimation method according to claim 6 or 7, wherein, The technique includes: an interpolation operation on the transient minimum voltage measurement result to obtain an interpolation curve, followed by a smoothing operation on the interpolation curve to obtain the curve giving the time evolution of the transient minimum voltage measurement result.
9. The estimation method according to any one of claims 1 to 8, wherein, The at least one parameter associated with the health status is the remaining service life of the at least one electrochemical element (12).
10. The estimation method according to any one of claims 1 to 9, wherein, The battery (10) is a primary battery.
11. The estimation method according to any one of claims 1 to 10, wherein, At least one electrochemical element (12) is a lithium thionyl chloride type electrochemical element, wherein the lithium thionyl chloride type is LiSOCl2.
12. A calculator (22) configured to estimate parameters related to the health status of at least one electrochemical element (12) of a battery (10), said calculator (22) being configured to: - Obtain the values of several physical quantities, including: - Several measurements of the transient minimum voltage of the at least one electrochemical element (12), which is the minimum voltage reached by the at least one electrochemical element (12) when a current pulse of current intensity is applied to the at least one electrochemical element (12), to obtain the applied current intensity and a set of voltages. - The temperature of the at least one electrochemical element (12), - The usage time of the at least one electrochemical element (12); as well as - Apply the technology to the obtained values in order to obtain values of parameters related to the health status of the at least one electrochemical element (12).
13. A management system (14) for at least one electrochemical element (12) of a battery (10), said at least one electrochemical element (12) having terminals, said management system (14) comprising: - A current generator (16) configured to apply a current pulse having a current intensity to the at least one electrochemical element (12). - Voltage sensor (18) configured to measure the transient minimum voltage of the at least one electrochemical element (12), the transient minimum voltage being the minimum voltage reached by the at least one electrochemical element (12) when a current pulse is applied by the current generator (16); - A temperature sensor (20) configured to: measure the temperature of the at least one electrochemical element (12); and - The calculator (22) according to claim 12.
14. A battery (10) comprising: - At least one electrochemical element (12); as well as - The management system (14) according to claim 13.