Method for monitoring the health status of a battery cell

Abstract

A method (100) for monitoring the SOH (State of Health) of an electrical cell, comprising in particular the steps of: Obtaining (110) a voltage range in which a relationship exists between an average of voltage variations and a capacitance loss of the electrical cell, the relationship being modeled by a function with: Measurement (120) of the constant current applied to the electrical cell and of the temperature of the electrical cell, Measurement (130) of the voltage of the electrical cell, When the measured voltage of the electrical cell is within the voltage range obtained (110), storage (140) of the measured voltage, When the measured current is a constant current of intensity not within the predetermined current intensity range and when a voltage has been stored at a previous time: Calculation (170) of the capacitance loss of the electrical cell using the relationship obtained with the calculated average of the voltage variations,Figure to be published with the abbreviation: Figure 1.

Description

Title of the invention: Method for monitoring the health status of a battery cell. TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of the monitoring and management of electrical cells, in particular electrical cells embedded in a vehicle, especially in an aircraft.

[0002] The present invention relates in particular to a method for monitoring the health status of a battery electrical cell, as well as a method for monitoring the health status of an electric battery. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new types of aircraft and those currently in operation, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change.

[0004] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and whose integration and use in civil aviation have moderate environmental impacts, with the aim of improving the energy efficiency of aircraft. The Applicant is constantly working to reduce its climate impact by employing methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0005] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and finally aviation biofuels.

[0006] In this context, the use and management of electrical cells or batteries within aircraft must be optimized. The state of health (SOH) of a cell or battery can be defined based on the loss of capacity or the gain in resistance of the cell or battery throughout its lifetime. In this application, the SOH is defined as:

[0007] soh ^£^ x1 oo%

[0008] With: • current, the current maximum capacity of the cell or battery • Cinitiale, the initial maximum capacity of the cell or battery

[0009] Depending on the health status of a cell or battery, its use can be modified. For example, in the transportation sector, cells or batteries are usually used up to a threshold health status of between 70% and 80%. This initial use corresponds to what is called the "first life" of a cell or battery. Below this threshold health status, the loss of capacity tends to accelerate, but the cell or battery can continue to be used in so-called "second life" applications, such as "smart grid" type energy networks.

[0010] For embedded applications, particularly in aircraft, it is therefore essential to measure or estimate the health status of a cell or battery. Known methods exist for monitoring battery health without requiring the battery to be removed from the device in which it is installed. One such method, disclosed in Shen, P., Ouyang, M., Lu, L., Li, J., & Feng, X. (2018). The co-estimation of State of Charge, State of Health, and State of Function for lithium-ion batteries in electric vehicles. IEEE Transactions on Vehicular Technology, 67(1), 92-103, proposes estimating battery health based on a recursive least squares method with a forgetting factor. This method is very comprehensive because it also allows for estimating the state of charge and the operating state of the battery. However, this method is complex to implement.

[0011] A second known method, in Zhou, Y., Huang, M., & Pecht, M. (2018, August 27). An Online State of Health Estimation Method for Lithium-ion Batteries Based on Integrated Voltage. 2018 IEEE International Conference on Prognostics and Health Management, ICPHM 2018, reveals that there is a linear correlation between the state of health of a battery and the integral of the voltage during a portion of the battery's charge. However, this method requires taking into account a very wide range of battery charge states (e.g., between 10% charge and 90% charge), which is not systematically done depending on the application. Furthermore, the battery charge state range to be covered to implement this method is not compatible with certain uses.

[0012] There is therefore a need to provide a method for determining the health status of an electrical cell which at least partially resolves the drawbacks of prior art methods. Summary of the invention

[0013] The invention offers a solution to the problems mentioned above, by allowing the determination of a state of health (SOH) of an electrical cell from an analysis of the voltage variation within a certain voltage range of the electrical cell.

[0014] One aspect of the invention relates to a method for monitoring the SOH (State of Health) of an electrical cell, comprising the steps of: • Obtaining a voltage range in which, for a predetermined current intensity applied to the electrical cell and a predetermined temperature, a relationship exists between an average voltage variation AU and a capacitance loss Qloss of the electrical cell, the relationship being modeled by a function f with: Q lOSS \ / • Measurement of the constant current applied to the electrical cell and the temperature of the electrical cell, • When the measured current is a constant current with an intensity within the predetermined range of current intensities and when the measured temperature is within the predetermined temperature range: • Measurement of the voltage of the electrical cell, • When the measured voltage of the electrical cell is within the obtained voltage range, the measured voltage is stored. • When the measured current is a constant current of intensity not within the predetermined range of current intensities and when a voltage has been stored at a previous time: • Calculation, for each stored voltage, of a voltage variation AU, • Calculation of an average of the calculated voltage variations AU, • Calculation of the capacitance loss Qloss of the electrical cell in using the relationship obtained with the average of the calculated voltage variations AU, • Determination of the SOH health status of the electrical cell using an equation defining the relationship between the SOH health status of the electrical cell and the loss of electrical cell capacity.

[0015] Thanks to the invention, monitoring the health status of the electrical cell can be easily and directly performed in an embedded system. Indeed, the implementation of the method according to the invention is economical in terms of computing resources and does not require a complete discharge and / or charge of the electrical cell. The method of the invention makes it possible to obtain an estimate of the electrical cell's health status by scanning a relatively narrow range of the cell's charge states. Furthermore, the method according to the invention can be implemented during a charging or discharging period of the electrical cell, as long as the current applied to the electrical cell remains constant.

[0016] In addition to the characteristics mentioned in the preceding paragraph, the monitoring method according to one aspect of the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations: • The process further includes modifying the operating conditions of the electrical cell according to the determined SOH health status, • The modification of the conditions of use of the electrical cell includes: • When the determined SOH (State of Health) is below a predetermined health threshold value, replace the electrical cell with an electrical cell, and / or • Discontinue use of the electrical cell if a maximum temperature is reached, the maximum temperature being determined from the determined SOH health status, and / or • Charge the electrical cell at a current intensity less than or equal to a maximum current intensity, the maximum current intensity being determined from the determined SOH health state. • Obtaining the voltage range involves sub-steps of: • Aging of a set of calibration electrical cells similar to the electrical cell, the aging of each calibration electrical cell being carried out under different aging conditions, • Measurement, for each aged calibration electrical cell, of a voltage variation with the constant current applied to the electrical cell within the predetermined current intensity range and with the electrical cell temperature within the predetermined temperature range, and • Identification, based on measurements of voltage variation, of the voltage range in which, for the predetermined current intensity range and the predetermined temperature range, a relationship exists between the capacitance loss of the electrical cell and the average voltage variation, and • Definition of the function modeling the relationship between the capacitance loss of the electrical cell and the average voltage variation, and • the voltage range obtained has an amplitude between 2.7 and 2.8 volts and / or corresponds to a range of a cell charge state having an amplitude between 17 and 50%.

[0017] A second aspect of the invention relates to a method for monitoring the state of health (SOH) of an electric battery in which: • The electric battery comprises electrical cells, • The SOH (State of Health) of the electrical cells in the electric battery are determined using the method according to the invention, • the monitoring process includes a step of calculating the SOH health status of the electric battery, said health status being equal to the minimum SOH health status among the determined SOH health statuses of the electric cells of the electric battery.

[0018] A third aspect of the invention relates to an electrical cell management system comprising means for implementing the method according to the invention.

[0019] A fourth aspect of the invention relates to an aircraft comprising an electrical cell and an electrical cell management system according to the invention.

[0020] A fifth aspect of the invention relates to a computer program comprising instructions which, when the program is executed by a computer, lead the computer to implement a process according to the invention.

[0021] A sixth aspect of the invention relates to a computer-readable data carrier on which the computer program according to the invention is recorded.

[0022] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0023] The figures are presented for illustrative purposes only and are not in any way limiting to the invention. • Fig. 1 shows a block diagram of an example of a method for monitoring the SOH health status of an electrical cell according to the invention. • Fig. 2 shows a block diagram of an example of the step of obtaining a voltage range of the method of monitoring a state of health (SOH) of an electrical cell according to the invention. • Fig. 3 is a graph illustrating an example of the variation of the voltage of an electrical cell as a function of the voltage of the electrical cell during a charging of the electrical cell. • Fig. 4 is a graph illustrating an example of the capacitance loss of an electrical cell as a function of an average of the voltage variation of the electrical cell. DETAILED DESCRIPTION

[0024] The figures are presented for illustrative purposes only and are in no way limiting of the invention.

[0025] Figure 1 is a block diagram illustrating the steps of an example of method 100 for monitoring the SOH (Significant Health) of an electrical cell. The mandatory steps of the example of method 100 are indicated by a solid rectangle and the optional steps are indicated by a dashed rectangle.

[0026] The method 100 can be implemented by a computer, a processor, or a microprocessor. For example, the method 100 can be implemented by a microprocessor included in a management system for one or more electrical cells, or for a battery, for example, a battery in an embedded system such as an aircraft. The management system preferably has the structure of a computer (in this case, an onboard computer) and / or a computer. It comprises an electronic circuit (in one or more parts) equipped with at least one non-volatile memory and a processor for executing logical operations. It may also include one or more other memories, of the random access memory (RAM) type or another type, and one or more other processors. The management system may also include measurement means: • the current applied to the electrical cell(s) or battery, • the temperature of the electrical cell(s) or the battery, and • the voltage of the electrical cell(s).

[0027] It can be noted that the current applied to the electrical cell(s) can be obtained by considering it as an average value calculable from the measured current of the battery comprising the electrical cell(s). For example, the current applied to the electrical cell(s) can be obtained by performing:

[0028] j _ I battery 1 Cells- Nallu[e,

[0029] With: • ^Cells, the current applied to the cell(s), • Battery current, the current applied to the battery including the cell(s), and

[0030] Cells, the number of cells, in parallel, included in the battery.

[0031] Alternatively, the current applied to the electrical cell(s) can also can be obtained using an algorithm that estimates the current dispersion in the battery.

[0032] It is also possible to note that the temperature of the electrical cell(s) can be considered as the temperature of the battery comprising the electrical cell(s)

[0033] By "computer-implemented," it is meant that the steps, or virtually all of the steps, are executed by at least one computer or processor or other similar system. Thus, steps are carried out by the computer, possibly in a fully automatic or semi-automatic manner. In some examples, the triggering of at least some of the steps of the process can be achieved through user-computer interaction. The level of user-computer interaction required may depend on the intended level of automation and be balanced against the need to implement the user's requirements. In some examples, this level may be defined by the user and / or predefined.

[0034] A typical example of computer implementation of a process consists of executing the process with a system adapted for this purpose. The system may include a processor coupled with memory and a graphical user interface (GUI), with a computer program comprising instructions for implementing the process being stored in memory. The memory may also store a database. Memory is any hardware adapted for such storage, possibly comprising several distinct physical parts.

[0035] In one example, method 100 can be implemented during the charging or discharging of the electric cell, provided that a constant current is applied to the electric cell. Charging the electric cell is a particularly opportune time to implement method 100 because it is possible to control the current flowing through the battery containing the electric cell(s). For example, it is possible to apply a constant current pulse from which the surface resistance can be obtained. During the discharge of the electric cell, the electric cell powers a third-party device that draws a certain power, and the current is generally variable. However, for applications in which the discharge current can be constant, method 100 can also be implemented during the discharge of the electric cell.

[0036] It is worth noting that the method 100 can be carried out in two distinct steps. The first step consists of calibrating a health estimator for a battery cell. This calibration involves, in particular, specifying the values ​​of the coefficients to be determined according to the different use cases of the estimator, such as use of the estimator under load, use of the estimator under discharge, the current intensity during the use of the estimator. This first step includes the implementation of step 110. Then, at a time other than the implementation of step 110, it is possible to use this calibrated estimator as many times as necessary by implementing the other steps of process 100.

[0037] A first step 110 of the process 100 comprises obtaining a voltage range in which a relationship exists between: • an average of voltage variations AU, expressed in millivolts, and • a loss of capacity of the electrical cell expressed as a percentage of the initial maximum capacity Cinitiale of the electrical cell.

[0038] The average voltage variation AU can be calculated with a predetermined time step or by calculating the derivative of the voltage at each predetermined time step.

[0039] Fig. 3 is an example of the average of the variations of a voltage of an electrical cell, expressed in millivolts and represented by the vertical axis on Fig. 3, as a function of the voltage of the electrical cell, expressed in volts and represented by the horizontal axis on Fig. 3, during three charging cycles of the electrical cell of 1 Coulomb at a temperature of 25 °C.

[0040] The relationship is further modeled by a function f defined by: 100411

[0042] Furthermore, the voltage range is obtained for a predetermined current intensity applied to the electrical cell and a predetermined temperature of the electrical cell.

[0043] In one example, the predetermined current intensity applied to the electrical cell is between 0.125 and 3.75 ampere hours and preferably between 2.45 and 2.55 ampere hours.

[0044] In another example, consistent with the previous examples, the predetermined temperature of the electrical cell is between 0 and 50 degrees Celsius and preferably between 24 and 26 degrees Celsius.

[0045] In an example, consistent with the previous examples, the voltage range obtained 110 has an amplitude between 3.7 and 3.8 volts.

[0046] In an example consistent with the preceding examples, the voltage range obtained 110 corresponds to a range of cell charge state with an amplitude between 17 and 50%. Furthermore, it can be noted that at the beginning of its life, i.e., for a health state of 100%, the amplitude can be between 31 and 50%, and that at the end of the electrical cell's life, i.e., for a health state of 80%, the amplitude can be between 17 and 32%.

[0047] In one example, consistent with the preceding examples, the predetermined time step that can be used to determine the average of voltage variations AU is between 1 and 60 seconds, for example 5 or 60 seconds.

[0048] The term “obtaining” means, in this application, receiving and / or measuring and / or calculating.

[0049] In an example consistent with the preceding examples, step 110 comprises 4 substeps. Figure 2 illustrates a block diagram of step 110 comprising 4 substeps labeled 111 to 114.

[0050] The first substep 111 involves the aging of a set of calibration electrical cells. The set of calibration electrical cells is obtained prior to step 111. Furthermore, the calibration electrical cells are similar to the electrical cell. The term "similar" means that the calibration electrical cells have open-circuit voltage, internal impedance, capacitance, and chemical characteristics identical to those of the electrical cell whose health is monitored by process 100. The set of calibration electrical cells may comprise between 10 and 100 calibration electrical cells. The aging of each calibration electrical cell is carried out under different aging conditions.

[0051] In an example consistent with the preceding examples, at least one electrical calibration cell is aged by being subjected to electrical stress, whether charging or discharging. This aging is called cycling aging. For this type of aging, the aging conditions can vary depending on the ambient temperature, the charging and / or discharging current, the average state of charge during the cycles, and the depth of discharge on each cycle.

[0052] The second substep 112 comprises measuring a voltage for each aged calibration electrical cell. This measurement 112 must be carried out under conditions similar to those of steps 130 and 140. Thus, when the voltage 112 is measured, for example, over several minutes, with a predetermined time step, the same predetermined time step as in step 110 must be used. Furthermore, the voltage 112 is measured with a constant current applied to the electrical cell within the predetermined current range and with the electrical cell temperature within the predetermined temperature range. From the voltage measurement taken for each predetermined time step, it is then possible to calculate the voltage variation using two consecutive voltage measurements.

[0053] The third substep 113 comprises identifying the voltage range in which a relationship exists between the capacitance loss of the electrical cell and the average voltage variation of the electrical cell. This identification This is performed using measurements from substep 112. Thus, this relationship holds true for current intensity within the predetermined current intensity range and for electrical cell temperature within the predetermined temperature range. The existence of a relationship between the electrical cell capacitance loss and the average voltage variation means that there is a dependence between these two variables. In other words, the electrical cell capacitance loss and the average voltage variation are correlated over this voltage range, and it is therefore possible to model this relationship as a function.

[0054] Figure 4 is a graph showing an example of the capacitance loss of an electrical cell, expressed as a percentage of the initial maximum capacitance of the electrical cell and corresponding to the vertical axis in Figure 4, as a function of an average voltage variation of the electrical cell, expressed in volts and corresponding to the horizontal axis in Figure 4. Each point on the graph represents a measurement of the capacitance loss of an electrical cell for a given average voltage variation of the electrical cell. Furthermore, each measurement was performed on a calibration cell that had been aged under a specific set of aging conditions. In Figure 4, it is thus possible to observe a clear relationship between the capacitance loss of the electrical cell and the average voltage variation up to a capacitance loss of approximately 20%.It is also possible to observe that the relationship begins to disperse between 20 and 25% capacity loss and becomes very dispersed beyond 25% capacity loss.

[0055] The fourth substep 114 comprises the definition of the function modeling the relationship between the capacitance loss of the electrical cell and the average voltage variation of the electrical cell. This definition includes choosing the type of function, for example, linear or polynomial, as well as defining the function's coefficients. This function definition is, of course, dependent on the type of electrical cell whose health is being monitored with process 100. The function's coefficients can be defined using a standard optimization algorithm such as the least squares method. As a reminder, the calibration electrical cells are similar to the electrical cell; therefore, the function defined for these calibration electrical cells is valid for the electrical cell whose health is being monitored with process 100.In this example, a function f can be used to express the equation q — in the form of: .

[0056] ( AU ) = max (k^ ln(k2 - ( AU - k^ ))+^, 0 )

[0057] With: * ^los^ Expressed as a percentage of the initial capacity, and • k^ k2, ky k^ coefficients to be identified.

[0058] It is worth noting that it is necessary to specify two cases depending on the result of the difference between AU and ^3. When ( ■> 0 then the equation can be written in the form described previously. When (AU - U) < 0, so the equation can be: (AU) = 0 in order to avoid obtaining a complex number as a result.

[0059] In this example, there are therefore four coefficients to identify for a given current intensity. Furthermore, in this example, only the maximum value between the logarithmic equation and zero is retained because the electrical capacitance of the electrical cell cannot increase with age. However, some electrical cells can gain a small amount of electrical capacitance during the first few cycles before subsequently beginning to lose it. Thus, for these electrical cells, it is necessary to use a function f to model this capacitance gain during aging.

[0060] It is worth noting that the aging conditions used are independent of the calibration conditions. In other words, the method 100 can be used even if the aging conditions of the electrical cell whose health is being monitored are different from the aging conditions of the calibration electrical cells. At the end of step 110, a function f modeling the relationship between the average voltage variation AU and the capacitance loss Qloss of the electrical cell is thus obtained. Steps 120 to 180 will allow the determination, under real-world conditions, of the health status SOH of the electrical cell using this function f. The second step 120 of the method 100 includes measuring the constant current applied to the electrical cell and measuring the temperature of the electrical cell.These two measurements are used to test whether the current conditions are valid in order to use the function obtained in step 110. The first condition is that the constant current applied to the electrical cell is within the predetermined current intensity range. The second condition is that the temperature of the electrical cell is within the predetermined temperature range. When these two conditions are met, steps 130 and 140 are implemented.

[0061] The third step 130 involves measuring the voltage of the electrical cell. This voltage measurement verifies whether the third validity condition for using the function obtained in step 110 is met. The third condition is that the measured voltage of the electrical cell is within the voltage range obtained in step 110.

[0062] When the third validity condition is met, the fourth step 140 of storing the measured voltage is implemented. Storage can be performed at each predetermined time step.

[0063] The following steps are implemented when the third validity condition is no longer met but a voltage was measured during the previous time step. For example, during charging of the electric cell, these steps are implemented when the measured voltage becomes greater than an upper terminal Usupi, i.e., the measured voltage was less than or equal to the upper terminal USUp at the previous time step, within the voltage range obtained in step 110. In another example, during discharging of the electric cell, these steps are implemented when the measured voltage becomes less than a lower terminal Uinf, i.e., the measured voltage was equal to or greater than the lower terminal Ujnf at the previous time step, within the voltage range obtained in step 110.

[0064] The fifth step 150 comprises calculating, for each stored voltage, a voltage change AU for the corresponding time step. This calculation can, for example, be performed by taking the difference between the voltage stored for the time step T and the voltage stored for the preceding time T1. Alternatively, this calculation can be performed immediately after storing the voltage measured in step 140, so that both the measured voltage and the calculated voltage change are recorded.

[0065] The sixth step 160 includes calculating an average of the voltage variations AU calculated in step 150. For example, during charging of the electrical cell, when the cell exceeds the upper voltage USUp, step 160 includes the calculation:

[0066] . r Ato AU — n

[0067] With n, the number of time steps for which a voltage was stored in step 140.

[0068] During a discharge of the electrical cell, when the cell exceeds the upper voltage U^f, step 160 may include the same calculation of the average of the voltage variations A U-

[0069] The seventh step 170 includes the calculation of the capacitance of the electrical cell using the relationship obtained with the average of the voltage variations AU calculated in step 160.

[0070] The eighth step 180 comprises determining the SOH (state of health) of the electrical cell. The equation as defined below may be used:

[0071] SOH{ AU) = lQ0%-QloJ AU)

[0072] This equation defines the relationship between the state of health SOH of the electrical cell and the loss of capacity Qj of the electrical cell.

[0073] The optional ninth step 190 includes modifying the operating conditions of the electric cell based on the state of health (SOH) determined in step 180. For example, when the determined SOH 180 is below a predetermined SOH value, for example, 70% or 80%, modifying the operating conditions of the electric cell may involve replacing the electric cell with a new one. Modifying the operating conditions of the electric cell may require modifying the operating conditions of the battery containing the electric cell. The electric cell, or the battery containing the electric cell, whose determined SOH is below a predetermined SOH value may, for example, be used in so-called second-life applications.In a second example, modifying the operating conditions of the electrical cell could involve interrupting its use when a maximum temperature is reached, the maximum temperature being determined from the determined state of health (SOH). In a third example, modifying the operating conditions of the electrical cell could involve charging the electrical cell at a current intensity less than or equal to a maximum current intensity, the maximum current intensity being determined from the determined state of health (SOH).

[0074] It is also possible to note that the method for determining the state of health SOH of an electric cell can be used as an input for methods of determining other parameters of the electric cell such as, for example, the state of charge SOC of the electric cell, the state of energy SOE of the electric cell or the state of power SOP of the electric cell.

[0075] Another aspect of the invention relates to a method for monitoring the state of health (SOH) of an electric battery. The SOH of an electric battery can be deduced from the SOH of the individual cells composing the battery. Thus, in a first example, it is possible to determine the SOH of all the battery cells using method 100. Then, it is possible to consider the SOH of the battery as equal to the minimum SOH of the individual cells previously determined. In a second example, it is possible to determine the SOH of the battery cells having an extreme temperature, i.e., minimum or maximum, among all the battery cells, and / or an extreme voltage, i.e.minimum or maximum among all the battery's electrical cells, using method 100. In a third example, it is possible to determine the SOH (State of Health) of the battery's electrical cells from a number of cells selected according to other criteria. For example, it is possible to determine the SOH. battery cells equipped with a thermocouple. Then, for all the aforementioned examples, it is possible to consider that the state of health (SOH) of the battery is equal to the minimum SOH among the previously determined SOH states of the battery cells.

[0076] Unless otherwise specified, the same element appearing on different figures has a unique reference.

Claims

Demands

1. A method (100) for monitoring the SOH (Significant Health) of an electrical cell, comprising the steps of: - Obtaining (110) a voltage range in which, for a predetermined current intensity applied to the electrical cell and a predetermined temperature, a relationship exists between an average voltage variation AU and a capacitance loss Qj of the electrical cell, the relationship being modeled by a function f with: - Measurement (120) of the constant current applied to the electrical cell and of the temperature of the electrical cell, - When the measured current is a constant current with an intensity within the predetermined range of current intensities and when the measured temperature is within the predetermined temperature range: • Measurement (130) of the voltage of the electrical cell • When the measured voltage of the electrical cell is within the obtained voltage range (110), storage (140) of the measured voltage, When the measured current is a constant current of intensity not within the predetermined range of current intensities and when a voltage has been stored at a previous time: • Calculation (150), for each stored voltage, of a variation of voltage AV, • Calculation (160) of an average of the calculated AU voltage variations (150), • Calculation (170) of the capacitance loss of the electrical cell using the relationship obtained with 1 a average of the voltage variations AU calculated • Determination (180) of the SOH health status of the electrical cell using a defining equation

2.

3.

4. nt the relationship between the SOH health state of the electrical cell and the loss of electrical cell capacity. Method (100) according to claim 1, further comprising a modification (190) of the conditions of use of the electric cell according to the determined SOH health status (180). Method (100) according to claim 2 wherein the modification (190) of the operating conditions of the electrical cell comprises: - When the determined SOH (180) health status is below a predetermined health status threshold value, replace the electrical cell with an electrical cell, and / or - Interrupt the use of the electrical cell if a maximum temperature is reached, the maximum temperature being determined from the determined SOH health status (180), and / or - Charge the electrical cell at a current intensity less than or equal to a maximum current intensity, the maximum current intensity being determined from the determined SOH health state (180). A method (100) according to any one of the preceding claims, wherein obtaining (110) the voltage range comprises substeps of: - Aging (111) of a set of calibration electrical cells similar to the electrical cell, the aging of each calibration electrical cell being carried out under different aging conditions, - Measurement (112), for each aged calibration electrical cell, of a voltage variation with the constant current applied to the electrical cell within the predetermined current intensity range and with the temperature of the electrical cell within the predetermined temperature range, and - Identification (113), from the measurements (112) of the voltage variation, of the voltage range in which, for the predetermined current intensity range and the predetermined temperature range, the relationship exists between the loss of the capacitance of the electrical cell and the average of the voltage variations, and - Definition (114) of the function modeling the relationship between the loss of capacitance of the electrical cell and the average of the voltage variations.

5. A method (100) according to any one of the preceding claims, wherein the resulting voltage range (110) has an amplitude between 2.7 and 2.8 volts and / or corresponds to a cell charge state range having an amplitude between 17 and 50%

6. / V. Method for monitoring the SOH health status of an electric battery wherein: - the electric battery comprises electric cells, - the SOH health statuses of the electric cells of the electric battery are determined with the method (100) according to any one of the preceding claims, - the monitoring method includes a step of calculating the SOH health status of the electric battery, said health status being equal to the minimum SOH health status among the SOH health statuses of the electric cells of the electric battery determined.

7. Electrical cell management system comprising means for implementing the method according to any one of claims 1 to 5.

8. Aircraft comprising an electrical cell and an electrical cell management system according to the preceding claim.

9. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out a method according to any one of claims 1 to 6.

10. A computer-readable data carrier on which the computer program according to claim 9 is recorded.

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