Method for estimating the remaining lifetime of an electrochemical element and associated devices

Abstract

Method for estimating the remaining lifespan of an electrochemical element and associated devices. The present invention relates to a method for estimating a parameter relating to the health status of an electrochemical element (12) of a battery (10), the estimation method comprising: - a step of obtaining the values ​​of several physical quantities including: - several measurements of the minimum transient voltage of the electrochemical element (12), the minimum transient voltage being the minimum voltage reached by the electrochemical element (12) when a current pulse having a current intensity is applied to the electrochemical element (12), to obtain an applied current intensity and a set of voltages, - the temperature of the electrochemical element (12), - the usage time of the electrochemical element (12),and - a step of applying a technique to the values ​​obtained to obtain a value for the parameter relating to the health status of the electrochemical element (12). Figure for the abstract: Figure 1,

Description

Title of the invention: Method for estimating the remaining life of an electrochemical element and associated devices

[0001] The present invention relates to a method for estimating a parameter relating to the state of health of at least one electrochemical element of a battery, in particular a primary electrochemical element. The present invention also relates to an associated calculator, management system and battery.

[0002] Typically a battery comprises one or more current accumulators also called electrochemical generators, cells or elements. An accumulator is an electricity production device in which chemical energy is converted into electrical energy. The chemical energy comes from the electrochemically active compounds deposited on at least one face of electrodes arranged in the accumulator. The electrical energy is produced by electrochemical reactions during a discharge of the accumulator. The electrodes, arranged in a container, are electrically connected to current output terminals which ensure electrical continuity between the electrodes and an electrical consumer with which the accumulator is associated.

[0003] In order to increase the electrical power delivered, several sealed accumulators can be combined together to form a battery. Thus, a battery can be divided into modules, each module being composed of one or more accumulators connected together in series and / or in parallel. Thus, a battery can, for example, comprise one or more parallel branches of accumulators connected in series and / or one or more parallel branches of modules connected in series.

[0004] A charging circuit is generally provided to which the battery can be connected to recharge the accumulators.

[0005] Furthermore, an electronic management system comprising measurement sensors and an electronic control circuit, more or less advanced depending on the applications, can be associated with the battery. Such a system makes it possible in particular to organize and control the charging and discharging of the battery, to balance the charging and discharging of the different accumulators of the battery with respect to each other.

[0006] The state of health is information useful to the electronic battery management system to optimize its use and lifespan. The state of health is often referred to by the abbreviation SOH, which refers to the English term for “State of Health”.

[0007] The state of health SOH makes it possible to estimate the aging of the battery between a new state and an end-of-life state, or more generally, between an initial state and a final state.

[0008] In this sense, the state of health SOH defines the ability of the battery to provide a current.

[0009] A technique for determining the SOH state of health is a technique in which the temperature, voltage, and possibly current values ​​of the battery are monitored to determine a value of the SOH state of health from aging laws. Such aging laws are obtained from tests carried out in the laboratory. The application of the aging laws to the monitored values ​​thus gives an estimate of the aging of the battery.

[0010] However, for certain types of battery chemistry, particularly lithium-based, this static type technique assumes homogeneous aging of the battery accumulators and as such does not take into account the phenomenon of the increase in the internal resistance of the battery by the formation of a so-called passivation layer on the surface of the lithium which limits its consumption.

[0011] Passivation is a phenomenon of lithium corrosion which occurs spontaneously in the battery as soon as it comes into contact with the lithium-based electrolyte and continues to varying degrees throughout its discharge. This phenomenon will depend on the conditions of use of the battery (temperature, stresses, etc.). This corrosion reaction gradually creates a protective insulating layer between the lithium and the electrolyte which will prevent the discharge reaction from taking place at its optimal voltage and thus reduce the energy supplied.

[0012] There is a need for a method for estimating a parameter relating to the state of health of an electrochemical element of a battery which makes it possible to better take into account the passivation phenomenon.

[0013] To this end, the description describes a method for estimating a parameter relating to the state of health of at least one electrochemical element of a battery, the estimation method being implemented by a computer and comprising:

[0014] - a step of obtaining the values ​​of several physical quantities, the quantities physical including:

[0015] - several measurements of the minimum transient voltage of the at least one electrical element electrochemical, the minimum transient voltage being the minimum voltage reached by the at least one electrochemical element when a current pulse having a current intensity is applied to the at least one electrochemical element, to obtain an 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] - a step of applying a technique to the values ​​obtained to obtain a value of the parameter relating to the state of health of at least one electrochemical element.

[0019] According to particular embodiments, the estimation method has one or more of the following characteristics, taken in isolation or according to all the com- technically possible combinations:

[0020] - the technique comprises an operation of applying a first function to the value of the applied current intensity, the temperature and the time of use to obtain a value representative of the presence of a polarization of the voltage of at least one electrochemical element.

[0021] - the first function is obtained by implementing a k plus algorithm close neighbors.

[0022] - the first function is obtained by implementing a forest algorithm random.

[0023] - a cut-off voltage is defined for the electrochemical element, the technique comprising an operation of applying a second function to the cut-off voltage and a quantity derived from the set of voltages for the parameter relating to the state of health of the electrochemical element.

[0024] - each minimum transient voltage measurement corresponds to a point on a curve giving the temporal evolution of the minimum transient voltage measurements, the technique comprising, for each point, an operation of determining a director coefficient of a tangent of the curve at said point.

[0025] - the quantity derived from the set of voltages is a sum of coefficients di rectors determined at each point.

[0026] - the technique comprises an operation of interpolation of the voltage measurements transient minimum to obtain an interpolated curve followed by a smoothing operation of the interpolated curve to obtain the curve giving the time evolution of the transient minimum voltage measurements.

[0027] - the at least one parameter relating to the state of health is the remaining life of the at least one parameter relating to the state of health is the remaining life of the at least one parameter relating to the state of health. less one electrochemical element.

[0028] - the battery is a primary battery.

[0029] - at least one electrochemical element is an electrochemical element of type LiSOCl2.

[0030] The description also describes a calculator capable of estimating a parameter relating to the state of health of at least one electrochemical element of a battery, the calculator being capable of:

[0031] - obtain values ​​of several physical quantities, the physical quantities including:

[0032] - several measurements of the minimum transient voltage of the at least one electrical element electrochemical, the minimum transient voltage being the minimum voltage reached by the at least one electrochemical element when a current pulse having a current intensity is applied to the at least one electrochemical element, to obtain an 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 a technique to the values ​​obtained to obtain a value of the parameter relating to the state of health of at least one electrochemical element.

[0036] The description also proposes a system for managing at least one electrochemical element of a battery, the at least one electrochemical element having terminals, the management system comprising:

[0037] - a current generator capable of applying a current pulse having a current intensity on said at least one electrochemical element,

[0038] - a voltage sensor suitable for measuring the minimum transient voltage of the at least one electrochemical element, the minimum transient 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 capable of measuring the temperature of said at least one electrochemical element, and

[0040] - a calculator as previously described.

[0041] The description also describes a battery comprising:

[0042] - at least one electrochemical element, and

[0043] - a management system as previously described.

[0044] In the present description, the expression “suitable for” means indifferently “adapted for”, “adapted to” or “configured for”.

[0045] Characteristics and advantages of the invention will appear on reading the description which follows, given solely by way of non-limiting example, and made with reference to the appended drawings, in which:

[0046] - [Fig.l] [Fig.l] is a schematic representation of an example of a battery comprising an electrochemical element,

[0047] - [Fig.2] [Fig.2] represents the evolution of the voltage measured on the battery of the [Fig.l] in the presence of a current pulse,

[0048] - [Fig.3] [Fig.3] is a flowchart of an example implementation of a method of estimating the remaining life of the electrochemical element, and

[0049] - [Fig.4] [Fig.4] is a schematic representation of an example of an experimental result rimental obtained by the applicant by implementing processes according to the flowchart in [Fig.3].

[0050] A battery 10 is shown in [Fig.l].

[0051] In a manner known per se, a battery is generally an arrangement of a plurality of electrochemical elements but for the sake of simplification of the subject, a case with a single electrochemical element is described in the following, knowing that the transposition to other arrangements is immediate.

[0052] The battery 10 comprises an electrochemical element 12 and a management system 14 for the electrochemical element 12.

[0053] As explained previously, an electrochemical element 12 is an electricity generating device in which chemical energy is converted into electrical energy.

[0054] The electrochemical element 12 therefore delivers a current and a voltage between two terminals.

[0055] According to the example described, the battery 10 is a primary battery.

[0056] Preferably, the electrochemical element 12 is a primary lithium electrochemical element with liquid cathode, for example of the lithium thionyl chloride LiSOCl2 type.

[0057] According to another embodiment, primary electrochemical elements with liquid cathode, of the LiSO2 type or of the LiSO2Cl2 type can be considered.

[0058] Alternatively, primary lithium electrochemical elements with solid cathode, for example of the LiMnO2 or LiCFx type, could be considered.

[0059] Of course, these examples are non-limiting and the method described later can be used for any type of electrochemical element 12, and in particular electrochemical elements not forming part of a primary battery.

[0060] The management system 14 is a system suitable for managing the electrochemical element 12.

[0061] The management system 14 comprises a current generator 16, a sensor voltage 18, a temperature sensor 20 and a calculator 22.

[0062] The current generator 16 is capable of applying a current pulse having a current intensity to the electrochemical element 12.

[0063] The voltage sensor 18 is suitable for measuring the voltage across the terminals of the electrochemical element 12.

[0064] When a current pulse is applied by the current generator 16, the voltage of the electrochemical element 12 decreases until it reaches a minimum before rising again.

[0065] The corresponding variation is visible in [Fig.2] which represents the evolution of the voltage as a function of time for several different batteries.

[0066] The minimum is called the minimum transient voltage.

[0067] The minimum is often noted TMV, the acronym referring to the corresponding English name of “Transient Minimum Voltage”.

[0068] In the following, the term “TMV voltage” will be used to designate this minimum.

[0069] The TMV voltage can be obtained within the first hundred milliseconds after the application of the current pulse.

[0070] The TMV voltage corresponds to the ohmic drop generated by the electrical resistance of the passivation layer. The value of the TMV voltage nevertheless depends also on the temperature and the intensity of the applied current pulse.

[0071] The voltage sensor 18 is capable of measuring the minimum transient voltage (TMV) of the electrochemical element 12.

[0072] The temperature sensor 20 is used to measure the temperature of the electrochemical element 12 on which the TMV voltage depends.

[0073] The calculator 22 is capable of implementing a method for estimating the remaining lifetime of the electrochemical element 12.

[0074] The computer 22 is an electronic circuit designed to manipulate and / or transform data represented by electronic or physical quantities in registers of the computer and / or memories into other similar data corresponding to physical data in the memories of registers or other types of display devices, transmission devices or storage devices.

[0075] As specific examples, the computer 22 includes a single-core or multi-core processor (such as a central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, and a digital signal processor (DSP)), a programmable logic circuit, such as an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a programmable logic device (PLD), and programmable logic arrays (PLA), a state machine, a logic gate, and discrete hardware components.

[0076] An example of implementation of the method for estimating the remaining lifetime of the electrochemical element 12 is now described with reference to the flowchart of [Fig.3],

[0077] The estimation method aims, as its name indicates, to estimate a parameter relating to the state of health of the electrochemical element 12.

[0078] The estimation method comprises an obtaining step E24 and an application step E26.

[0079] During the obtaining step E24, the calculator 22 obtains several values ​​of several physical quantities

[0080] According to the case of [Fig.3], the computer 22 obtains the temperature, the TMV voltages of the electrochemical element 12 and the current intensity of the current pulse applied by the current generator 16.

[0081] In the example described, the TMV voltage and temperature measurements come respectively from the voltage sensor 18 and the temperature sensor 20. These values ​​are then measurements.

[0082] Nevertheless, it could be envisaged that these measurements are obtained by implementing a method for estimating these values ​​which would be applied to measurements from other types of sensors.

[0083] The current intensity is provided by the setpoint of the current generator 16.

[0084] In the example described, the TMV voltage measurements are spaced by a time interval of one day but this interval can be varied according to the desired implementations of the method.

[0085] During the application step E26, the calculator 22 applies a technique to the values ​​obtained during the obtaining step E24.

[0086] The mathematical technique used makes it possible to obtain the remaining lifetime of the electrochemical element 12.

[0087] According to the example of [Fig.3], the technique comprises several operations, namely an interpolation operation 030, a smoothing operation 032, a determination operation 034 and two operations of application of a respective function 036 and 038.

[0088] The interpolation 030 and smoothing 032 operations aim to obtain a curve giving the temporal evolution of the TMV voltage measurements.

[0089] In this curve, each TMV voltage measurement corresponds to a point.

[0090] During the interpolation operation 030, the computer 22 uses an interpolation technique applied to the TMV voltage measurements to obtain an interpolated curve.

[0091] Any interpolation technique relevant in this context is conceivable, a simple linear interpolation can be used.

[0092] During the smoothing operation 032, the computer 22 applies a smoothing function to the interpolated curve in order to reduce its irregularities and singularities.

[0093] The calculator 22 thus obtains the curve giving the temporal evolution of the TMV voltage measurements.

[0094] Any other technique for obtaining the time evolution curve is also conceivable here, the smoothing operation 032 may in particular not be useful in practice.

[0095] The calculator 22 implements the determination operation 034 on the curve obtained.

[0096] During the determination operation 034, the calculator 22 determines a direction coefficient of a tangent of the curve for each point corresponding to a TMV voltage measurement.

[0097] For this, the calculator 22 can calculate the time derivative of the curve and determine the slope coefficient as being the value of the derivative at this point.

[0098] During the determination operation 034, the calculator 22 calculates a quantity derived from the set of TMV voltages which is here the sum of director coefficients determined at each point of interest.

[0099] The sum here is the sum of all the slope coefficients determined for each measurement point included in a predefined time interval.

[0100] The calculator 22 also implements an application operation 036 of a first function Fl on the value of the applied current intensity, the set of voltages, the temperature and the time of use.

[0101] The first function Fl thus makes it possible to obtain a presence value, the presence value being a value representative of the presence of a polarization of the voltage of the electrochemical element 12.

[0102] The presence value is, according to the example described, equal to 0 or 1.

[0103] This presence value indicates a variation 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 presence value equal to 1 corresponds to the detection of an anomaly x days before the voltage of the electrochemical element 12 reaches the cut-off voltage.

[0105] The cut-off voltage is the minimum operating voltage for the system using the energy supplied by the electrochemical element 12.

[0106] This value is sometimes also called threshold voltage. Most often, this value is designated by the corresponding English term “cut-off voltage” and depends on the use of the electrochemical element 12.

[0107] In the example described, the cut-off voltage is equal to 2.5 V.

[0108] The first function Fl is obtained through the use of a database.

[0109] The applicant carried out experiments to obtain a database giving the TMV voltage measured between 0 and 100 ms after the current pulse at several times in the life of an electrochemical element and this for several models of electrochemical element, several current intensities and several temperatures.

[0110] For this, the applicant carried out the corresponding electrical tests with real electrochemical elements. This led to carrying out more than 200 different tests.

[0111] The first function Fl is then learned by a technique derived from artificial intelligence using the previous database.

[0112] Such a method of obtaining is often designated by the term machine learning, referring to the corresponding English term “machine learning”.

[0113] To perform such training, the database can be separated into two databases, a training database and a test database.

[0114] The split between the training database and the test database depends on the applications, but a split of 80%-20% is usual.

[0115] In this example, the first function Fl is obtained by implementing a random forest algorithm.

[0116] Such a technique is more often designated by the acronym RF which refers to the de- corresponding English name of "random forest".

[0117] In such a technique, the random forest algorithm is used to fix a model whose learning aims to determine the free parameters.

[0118] According to another example, the first function Fl is obtained by implementing a k nearest neighbors algorithm.

[0119] Such a technique is more often designated by the acronym KNN which refers to the corresponding English term “k-nearest neighbor”.

[0120] In the presence of a non-zero presence value, the computer 22 then applies a second function F2 to the cut-off voltage and a quantity derived from the set of TMV voltages.

[0121] As indicated previously, the derived quantity is here the sum of the direction coefficients determined at each point over a predefined time interval.

[0122] This involves taking into account, for example, only the points for which the presence value is equal to 1 in the case described.

[0123] The calculator 22 obtains the remaining lifetime as output.

[0124] The second function F2 therefore makes it possible to compare the measured value of the derived quantity with the cut-off voltage, to obtain the lifetime.

[0125] The second function F2 performs a crossover between the value of the derived quantity and the cut-off voltage.

[0126] This crossover is, for example, a linear regression.

[0127] Here again, the second function F2 is obtained by using techniques similar to those of the first function Fl and the previous database.

[0128] An example of the experimental result obtained is shown schematically in [Fig.4],

[0129] Curve C1 corresponds to the curve obtained after the smoothing operation 030, curve C2 to a cut-off voltage at 2.5 V (scale on the left) and curve C3 to the presence value obtained after implementation of the first function Fl for the case of a KNN algorithm (scale on the right).

[0130] Curve C3 would be identical for the case of a random forest algorithm.

[0131] Both techniques give similar information that the lifetime remaining is 40 days.

[0132] The rest of the experiment shows that the remaining life for this battery was 39 days, which shows the very good precision of the method described.

[0133] Although this does not appear in the result of [Fig.4], additional tests have enabled the applicant to demonstrate that the case of the random forest algorithm for the first function Fl makes it possible to obtain slightly improved performance.

[0134] The results obtained are given in the following table:

[0135]

[0136]

[0137]

[0138]

[0139]

[0140]

[0141]

[0142]

[0143]

[0144]

[0145]

[0146]

[0147] [Tables 1] Prediction (in days) Threshold voltage (in V) Technique Recall Precision Fl score 40 2.5 RF 0.99 1 0.99 40 2.5 KNN 0.97 0.93 0.95 60 2.5 RF 0.97 0.99 0.98 60 2.5 KNN 0.97 0.93 0.95 90 2.5 RF 0.97 0.99 0.98 90 2.5 KNN 0.93 0.92 0.93 In this table, recall is defined as the ratio between the number of true positives Ntruepositive and the sum of the number of true positives and the number of false negatives Nfalse negative cc which is written mathematically as: Reminder - - N cr jv vrœ positive true positive '1 Tt Accuracy corresponds to the same ratio with the number of false positives false positive to the ''cu of the number of false negatives Nfalse negative ■> which leads to the following mathematical formulation: Accuracy = true false paùtif The FL score is deduced from recall and precision using the following formula: nRap ixl Precision r 1 score — 2-™—-------— Recall + Precision A value greater than 0.9 for the Fl score indicates a good level of accuracy. It is thus clear from the analysis of the results in this table that the use of both techniques allows very good performances to be obtained, each value being greater than 0.9. Comparison of the two techniques shows a slight superiority of the model resulting from the random forest algorithm. The method thus makes it possible, from repeated measurements of TMV voltage during operation of the electrochemical element 12, to detect a significant change in the temporal evolution of the TMV voltage and to quantify the consequences on the remaining lifetime of the electrochemical element 12. Other embodiments can also be considered. In particular, the method could be used to predict another parameter related to the health status of the electrochemical element 12, such as a percentage variation of resistance.

[0148] Other operations than those described with reference to [Fig.3] could also be envisaged.

[0149] For example, according to one embodiment, the results could be calculated according to two techniques (for example, as here, according to the KNN and RF techniques) and averaged.

[0150] It could also be envisaged to merge the two functions F1 and F2 by using a function taking the acquired values ​​as input and carrying out all the operations to output only the remaining lifetime, the presence value not being given as output according to this example.

[0151] Alternatively, it could also be considered to use other mathematical techniques such as neural networks.

[0152] According to a specific embodiment, the first function Fl is applied only to the value of the applied current intensity, the temperature and the time of use.

[0153] Furthermore, the order of operations presented in the example described could be different, certain operations being able to be implemented simultaneously.

[0154] In each case, the method makes it possible to obtain a good estimate of the state of health of at least one electrochemical element 12 of a battery 10.

Claims

Claims

1. Method for estimating a parameter relating to the state of health of at least one electrochemical element (12) of a battery (10), the estimation method being implemented by a computer (22) and comprising: - a step of obtaining the values ​​of several physical quantities, the physical quantities comprising: - several measurements of the minimum transient voltage of the at least one electrochemical element (12), the minimum transient voltage being the minimum voltage reached by the at least one electrochemical element (12) when a current pulse having a current intensity is applied to the at least one electrochemical element (12), to obtain an 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),and - a step of applying a technique to the values ​​obtained to obtain a value of the parameter relating to the state of health of the at least one electrochemical element (12).,

2. Estimation method according to claim 1, in which the technique comprises an operation of applying a first function to the value of the applied current intensity, the set of voltages, the temperature and the time of use to obtain a value representative of the presence of a polarization of the voltage of the at least one electrochemical element (12).

3. Estimation method according to claim 2, wherein the first function is obtained by implementing a k nearest neighbors algorithm.

4. An estimation method according to claim 2, wherein the first function is obtained by implementing a random forest algorithm.

5. Estimation method according to any one of claims 2 to 4, in which a cut-off voltage is defined for the at least one electrochemical element (12), the technique comprising an operation of applying a second function to the cut-off voltage and a quantity derived from the set of voltages for the parameter relating to the state of health of the at least one electrochemical element (12).

6. Estimation method according to any one of claims 1 to 5, in which each minimum transient voltage measurement corresponds to a point on a curve giving the temporal evolution of the minimum transient voltage measurements, the technique comprising, for each point, an operation of determining a slope coefficient of a tangent of the curve at said point.

7. Estimation method according to claims 5 and 6, in which the quantity derived from the set of voltages is a sum of direction coefficients determined at each point.

8. Estimation method according to claim 6 or 7, in which the technique comprises an operation of interpolation of the minimum transient voltage measurements to obtain an interpolated curve followed by an operation of smoothing the interpolated curve to obtain the curve giving the temporal evolution of the minimum transient voltage measurements.

9. Estimation method according to any one of claims 1 to 8, wherein the at least one parameter relating to the state of health is the remaining life of the at least one electrochemical element (12).

10. An estimation method according to any one of claims 1 to 9, wherein the battery (10) is a primary battery.

11. An estimation method according to any one of claims 1 to 10, wherein at least one electrochemical element (12) is a lithium thionyl chloride (LiSOCl2) type electrochemical element.

12. A calculator (22) capable of estimating a parameter relating to the state of health of at least one electrochemical element (12) of a battery (10), the calculator (22) being capable of: - obtaining values ​​of several physical quantities, the physical quantities comprising: - several measurements of the minimum transient voltage of the at least one electrochemical element (12), the minimum transient voltage being the minimum voltage reached by the at least one electrochemical element (12) when a current pulse having a current intensity is applied to the at least one electrochemical element (12), to obtain an 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), and - applying a technique to the values ​​obtained to obtain a value of the parameter relating to the state of health of the at least one element electrochemical (12).

13. Management system (14) of at least one electrochemical element (12) of a battery (10), the at least one electrochemical element (12) having terminals, the management system (14) comprising: - a current generator (16) capable of applying a current pulse having a current intensity to said at least one electrochemical element (12), - a voltage sensor (18) capable of measuring the minimum transient voltage of the at least one electrochemical element (12), the minimum transient 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) capable of measuring the temperature of said at least one electrochemical element (12), and - a calculator (22) according to claim 12.

14. Battery (10) comprising: - at least one electrochemical element (12), and - a management system (14) according to claim 13.

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