Method for monitoring the health status of a battery

Abstract

A method for monitoring the state of health (SOH) of an electric battery, comprising in particular the steps of: Generating (130) a model of a component of an electrical circuit of the battery configured to assess the SOH of the battery based on the surface resistance Rsurf of the battery, the current intensity I applied to the battery, and the temperature T of the battery; Measuring (140) the current intensity I applied to the battery, the temperature T of the battery, and obtaining the surface resistance Rsurf of the battery; and Determining (150) the SOH of the battery by providing the model with the current intensity I applied to the battery, the temperature T of the battery, and the surface resistance Rsurf of the battery. Figure to be published with the abstract: Figure 1.

Description

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

[0001] The technical field of the invention is that of monitoring and managing electric batteries, in particular batteries on board a vehicle, in particular in an aircraft.

[0002] The present invention relates to a method for monitoring the health status of a battery. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various States. In particular, an ambitious standard applies both to new types of aircraft and those currently in circulation, requiring the implementation of technological solutions to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0004] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into consideration the factors impacting all phases of design and development, to obtain less energy-intensive, more environmentally friendly aeronautical components and products 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 using methods and operating virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible to reduce the environmental footprint of its activity.

[0005] This sustained research and development work covers new generations of aircraft engines, the lightening of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and finally aeronautical biofuels.

[0006] In this context, the use and management of electric batteries within aircraft must be optimized. The state of health of a battery, also commonly called SOH for "State of Health" in English can be defined based on the loss of capacity or the gain in resistance of a battery throughout its life. In this application, the state of health SOH is defined by:

[0007] X 100% {'initial

[0008] With: • ^current, the current maximum battery capacity • Initial G, the initial maximum capacity of the battery

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

[0010] For on-board applications, and in particular in an aircraft, it is therefore essential to measure or estimate the state of health of a battery. Known methods make it possible to monitor the state of health of the battery without requiring the battery to be removed from the device on which it is mounted. For example, a first method, disclosed in Maures, M., Capitaine, A., Delétage, JY, Vinassa, JM, & Briat, O. (2020). Lithium-ion battery SoH estimation based on incremental capacity peak tracking at several current levels for online application. Microelectronics Reliability, 114, proposes to use a method called “incremental capacity”, in which the charged or discharged capacity of the battery is derived with respect to the battery voltage. Then, an analysis of the derivative is carried out to identify peaks in order to determine certain characteristics correlated with the state of health of the battery.The main advantage of this method is that it is simple to implement. However, the estimation of the state of health must be carried out under precise conditions. Thus, the estimation of the state of health by this method is only possible during a constant current charge, passing through a voltage range wide enough to obtain peaks whose characteristics are related to the state of health of the battery.

[0011] A second known 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 to estimate the state of health of a battery based on a recursive least squares method with a forgetting factor. This method is very comprehensive because it also allows estimating the state of charge and the state of operation of the battery. However, this method is complex to implement.

[0012] A third known method, disclosed 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 Pro-gnostics and Health Management, ICPHM 2018, discloses that there is a linear correlation between the state of health of a battery and the voltage integral during a portion of a battery's charge. This method is easy to implement, but the validity of the relationship between the state of health of a battery and the voltage integral has only been demonstrated for the type of battery presented in the article. Thus, this method cannot, at present, be used for batteries with different chemistries than that presented in the article.Additionally, this method requires taking into account a very wide range of battery charge states, which is not systematically done depending on the application.

[0013] There is therefore a need to provide a method for determining the state of health of a battery which makes it possible to at least partially resolve the drawbacks of the methods of the prior art. Summary of the invention

[0014] The invention provides a solution to the problems mentioned above, by making it possible to determine a state of health SOH of a battery from the surface resistance R surf of the battery, the intensity I of current applied to the battery and the temperature T of the battery. Indeed, the inventors have, surprisingly, discovered that it was possible to determine the surface resistance R surf of the battery as the parameters. Thus, the invention comprises the generation of a model of an electrical circuit configured to evaluate a state of health SOH of a battery, said model being based on a model of a component of an electrical circuit configured to evaluate a surface resistance of a battery. Then, by providing the model of the component of the electrical circuit configured to evaluate a state of health SOH of a battery, the intensity I of current applied to the battery and the temperature T of the battery, it is possible to obtain the state of health SOH of a battery.

[0015] One aspect of the invention relates to a method for monitoring a state of health SOH of an electric battery comprising the following steps: • Obtaining a first model of a component of an electrical circuit of the battery, the first model being configured to evaluate a surface resistance Rsurf of the battery from an intensity I of current applied to the battery and a temperature T of the battery, the first model further comprising parameters, the parameters comprising: • A resistance of an interphase of the solid electrolyte at a predetermined temperature noted RSEi (Tpre), • An activation energy linked to the interphase of the solid electrolyte noted Ea.SE1, • An exchange current at a predetermined temperature noted I0(Tpre), and • An activation energy linked to the exchange current noted Ea>10, • Determination, for each parameter among the parameters of the first model, of a function characterizing the evolution of said each parameter as a function of an evolution of the state of health of the SOH battery, • Generation of a second model of the component of the electrical circuit of the battery configured to evaluate the state of health of the SOH battery from the surface resistance Rsurf of the battery, the intensity I of current applied to the battery and the temperature T of the battery, the generation of the second model comprising for each parameter of the first model, the integration of the function characterizing the evolution of said each parameter as a function of an evolution of the state of health of the SOH battery, • Measurement of the current intensity I applied to the battery, the temperature T of the battery and obtaining the surface resistance Rsurf of the battery, and • Determination of the state of health of the SOH battery by providing the second model with the current intensity I applied to the battery, the temperature T of the battery and the surface resistance Rsurf of the battery obtained.

[0016] Thanks to the invention, monitoring the state of health of the battery can be carried out easily and directly in an embedded system. Indeed, the method according to the invention can be applied to any operational condition in terms of current and temperature and does not require scanning a wide range of state of charge. Furthermore, the method according to the invention does not require the use of a continuous "observer" component. It can be applied discontinuously, for example at times when updating the state of health of the battery is necessary. For example, the method according to the invention can be implemented during the charging of the battery. Indeed, the charging of the battery is an opportune moment to implement the method according to the invention, because it is possible, during the battery charging, to apply a constant current slot from which it is possible to obtain the surface resistance.

[0017] In addition to the characteristics which have just been mentioned in the preceding paragraph, the monitoring method according to one aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations: • the first model of the battery electrical circuit component is based on the following equation: Rsurf{L 7 ) = 7^ / (25 ° C)exp( -ç- - — ) ) + ._ asinh^_— - 298 ) ) )

[0018] With: * ^sej(^ ° C), a resistance of an interphase of the solid electrolyte at a temperature of 25°C, expressed in ohms noted Q, • E^j, an activation energy linked to the interphase of the solid electrolyte, expressed in electron volts noted eV, • / J25 0 C), an intensity of a battery exchange current at 25°C, expressed in amperes noted A, • an activation energy linked to the intensity of an exchange current of the battery at 25°C, expressed in electronvolts noted eV, • kg, a Boltzmann constant, expressed in electronvolts per kelvin noted eV / K, • R, a universal constant of ideal gases, expressed in joules per mole per kelvin noted J / (mol*K), • F, a Faraday constant, expressed in coulombs per mole noted C / mol, • T, a battery temperature, expressed in kelvin noted K, • I, an intensity of the cell current, expressed in amperes noted A. • The method according to the invention further comprises a modification of the battery usage conditions based on the determined SOH state of health. • Changing battery usage conditions based on the determined SOH state of health includes: • When the determined SOH state of health is below a predetermined state of health threshold value, replace the battery with a new battery, and / or • Suspend battery use upon reaching a maximum temperature, the maximum temperature being determined from the determined SOH state of health, and / or • Charge the battery 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. • the determination, for each parameter among the parameters of the first model, of a function characterizing the evolution of said each parameter as a function of an evolution of the state of health of the SOH battery comprises: • a first electrochemical impedance spectroscopy test consisting of applying to the battery a sinusoidal current wave with a zero average value to the battery and measuring a battery voltage variation, and / or • a second current pulse test consisting of applying current pulses to the battery during charging and discharging. • the generation of the second model of the battery electrical circuit component includes a determination of an equation between the surface resistance Rsurf and the state of health SOH and: • A resolution of the equation, for a set of SOH values, allowing the SOH state of health to be evaluated from the surface resistance Rsurf of the battery, or • Generation of a parameter table allowing the SOH state of health to be directly evaluated from the current intensity I applied to the battery, the battery temperature T and the surface resistance Rsurf of the battery.

[0019] A second aspect of the invention relates to a method for determining a surface resistance Rsurf of an electric battery comprising the steps: • Obtaining a first model of a component of an electrical circuit of the battery, the first model being configured to evaluate a surface resistance Rsurf of the battery from an intensity I of current applied to the battery and a temperature T of the battery, the first model further comprising parameters, the parameters comprising: • A resistance of an interphase of the solid electrolyte at a predetermined temperature noted RSEi (Tpre), • An activation energy linked to the interphase of the solid electrolyte noted Ea>SEb • An exchange current at a predetermined temperature noted I0(Tpre), and • An activation energy linked to the exchange current noted Ea>10, • Determination, for each parameter among the parameters of the first model, of a function characterizing the evolution of said each parameter as a function of an evolution of the state of health of the SOH battery, • Generation of a second model of the component of the electrical circuit of the battery configured to evaluate the surface resistance Rsurf of the battery from the intensity I of current applied to the battery, the temperature T of the battery and the state of health of the SOH battery, the generation of the second model comprising for each parameter of the first model, the integration of the function characterizing the evolution of said each parameter as a function of an evolution of the state of health of the SOH battery, • Measurement of the intensity I of current applied to the battery, of the temperature T of the battery and obtaining the SOH health status of the battery, and • Determination of the surface resistance Rsurf of a battery by providing the second model with the current intensity I applied to the battery, the temperature T of the battery and the state of health SOH of the battery measured or obtained.

[0020] A third aspect of the invention relates to a system for managing an electric battery comprising means for implementing the method according to the invention.

[0021] A fourth aspect of the invention relates to an aircraft comprising an electric battery and a battery management system according to the invention.

[0022] A fifth aspect of the invention relates to a computer program comprising instructions which, when the program is executed by a computer, cause the latter to implement a method according to the invention.

[0023] A sixth aspect of the invention relates to a computer-readable data carrier, on which the computer program according to the invention is recorded.

[0024] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0025] The figures are presented for information purposes only and in no way limit the invention. • [Fig.l] shows a block diagram of an example of a method for monitoring a state of health SOH of a battery according to the invention. • [Fig.2] shows a block diagram of an example of a method for monitoring a surface resistance Rsurf of a battery according to the invention. • [Fig.3A], [Fig.3B], [Fig.3C] and [Fig.3D] show an example of the relationship between each of the parameters of the first model and the health status of the SOH battery. • [Fig.4] shows an example of a result from an electrochemical impedance spectroscopy test performed on a battery. • [Fig.5] shows an example of a result of a current pulse test carried out on a battery. • [Fig.6] shows an example of a schematic representation of an electrical circuit. • [Fig.7] shows an example of deducing the state of health SOH of a battery from the surface resistance Rsurf for a battery current I of 2 A and a battery temperature T of 0°C. • Figure 8 shows an example of the evolution of the surface resistance Rsurf as a function of the state of health SOH of a battery for a battery temperature T of 0°C and for current intensities I between 0 and 20 amperes in discharge. • Figure 9 shows an example of the evolution of the surface resistance Rsur / as a function of the state of health SOH of a battery for a fixed current intensity of 2 amperes in discharge for temperatures between -10 and 40°C. DETAILED DESCRIPTION

[0026] The figures are presented for information purposes only and in no way limit the invention.

[0027] [Fig.l] is a block diagram illustrating the steps of an example of the method 100 for monitoring a SOH state of health of a battery. The mandatory steps of the example of the method 100 are indicated by a solid line rectangle and the optional steps are indicated by a dotted line rectangle.

[0028] The monitoring method 100 can be implemented by a computer or by a processor. For example, the control method 100 can be implemented by a processor included in a management system for a battery of an on-board system such as an aircraft. The management system preferably has the structure of a calculator (in this case an on-board calculator), and / or a computer. It comprises an electronic circuit (in one or more parts) equipped with at least one non-volatile type memory, and a processor for executing logical operations. It can also comprise one or more other memories, of the random access memory (RAM) type or of another type, and one or more other processors.

[0029] By "computer-implemented" is meant that the steps, or substantially all of the steps, are executed by at least one computer or processor or other similar system. Thus, steps are performed by the computer, possibly fully automatically, or semi-automatically. In examples, the triggering of at least some of the steps of the method may be performed by user-computer interaction. The level of user-computer interaction required may depend on the intended level of automation and balanced against the need to implement the user's wishes. In examples, this level may be user-defined and / or predefined.

[0030] A typical example of a computer implementation of a method is to execute the method with a system adapted for this purpose. The system may comprise a processor coupled to a memory and a graphical user interface (GUI), a computer program comprising instructions for implementing the method being stored in the memory. The memory may also store a database. The memory is any hardware adapted for such storage, possibly comprising several distinct physical parts.

[0031] A first step 110 of the method 100 consists of obtaining a first model of a component of an electrical circuit of the battery. This first model makes it possible to calculate a surface resistance Rsurf of the battery from a current intensity I applied to the battery and a battery temperature T. The current intensity I applied to the battery is expressed in Amperes. The battery temperature T is expressed in Kelvin. This first model also includes four parameters.

[0032] The first parameter of the first model of the component of the electrical circuit of the battery is the resistance of an interphase of the solid electrolyte at a predetermined temperature denoted Rsei (Tpre). The interphase of the solid electrolyte, commonly called "Solid Electrolyte Interphase" in English, is a passivation layer present between the negative electrode and the electrolyte of the battery. The resistance of the interphase of the solid electrolyte RSEi is expressed in ohms. Preferably, the predetermined temperature is between 0°C and 30°C. In the remainder of the application, for the sake of simplification, we will use 25°C as the predetermined temperature. It can be noted that the first model of the component of the electrical circuit is all the more precise as the temperature T of the battery is close to said predetermined temperature.

[0033] The second parameter of the first model of the component of the electrical circuit of the battery is the activation energy linked to the interphase of the solid electrolyte denoted Ea>SEi. The activation energy linked to the interphase of the solid electrolyte Ea>SEi is expressed in electron volts.

[0034] The third parameter of the first model of the battery electrical circuit component is the exchange current at the predetermined temperature denoted Io(Tpre). This parameter is expressed in amperes. This parameter makes it possible to measure the level of oxidation and reduction reactions taking place in the battery for the predetermined temperature. Thus, a high exchange current reflects a level of oxidation and reduction reactions in the battery which is also high, therefore an efficient charge transfer. The predetermined temperature of the third parameter is the same as for the first parameter.

[0035] The fourth parameter of the first model of the component of the electrical circuit of the battery is the activation energy linked to the exchange current Eal0 which is expressed in electron volts.

[0036] In a variant of the invention, the first model of the component of the electrical circuit of the battery is based on the following equation: 100371 T) - RSE, (25 • C)«p(^(| -) ) (l'S ) ) ) (1)

[0038] With: * ^sei( 25 0 G), a resistance of an interphase of the solid electrolyte of a battery at a temperature of 25°C, expressed in ohms noted Q, • Ea,SEJ, an activation energy linked to the interphase of the solid electrolyte of a

[0039]

[0040]

[0041] battery, expressed in electronvolts noted eV, • 0 C), an intensity of an exchange current of the battery at 25°C linked to the battery charge transfer, expressed in amperes noted A, • Eaj0, an activation energy linked to the intensity of an exchange current of the battery at 25°C, and therefore also linked to the charge transfer of the battery, expressed in electronvolts noted eV, • k^, the Boltzmann constant, expressed in electronvolts per kelvin noted eV / K, • R, the universal constant of ideal gases, expressed in joules per mole per kelvin noted J / (mol*K), • F, the Faraday constant, expressed in coulombs per mole noted C / mol, • T, a battery temperature, expressed in kelvin noted K, • / , a cell current intensity, expressed in amperes noted A. This equation is disclosed in Damay N., Mbeya KM, Friedrich G., and Forgez C., “Separation of the charge transfers and solid electrolyte interphase contributions to a battery voltage by modeling their non-linearities regarding current and temperature,” Journal of Power Sources, vol. 516, p. 230617, 12 2021. It models the surface resistance of a battery as a function of a battery current and battery temperature. A second step 120 of the method 100 consists in determining, for the four parameters of the first model, a function characterizing the evolution of said each parameter as a function of an evolution of the state of health of the SOH battery. Figures 3A to 3D show an example of evolution for each parameter of the first electrical model as a function of the SOH state of health of the battery. Figure 3A shows an example of relationship between the resistance of the interphase of the solid electrolyte of a battery at a temperature of 25°C RSE] (25 0 C) and the state of health of the SOH battery. Figure 3B shows an example of relationship between the activation energy linked to the interphase of the solid electrolyte of a battery E^ei and the state of health of the SOH battery. Figure 3C shows an example of the relationship between the zero-current charge transfer resistance of a battery denoted RctQ( T ) and the state of health of the SOH battery.Figure 3D shows an example of the relationship between the activation energy related to the intensity of a battery exchange current at 25°C Eajn and the state of health of the battery SOH. Regarding Figure 3C, it should be noted that it is possible to obtain the intensity of a battery exchange current at 25°C from the zero-current charge transfer resistance of a battery Rct0( T). For example, it is possible to use the following equation: . <2)

[0042] With: • R, the universal constant of ideal gases, expressed in joules per mole per kelvin noted J / (mol*K), • T, a battery temperature, expressed in kelvin noted K, and • F, the Faraday constant, expressed in coulombs per mole noted C / mol.

[0043] The inventors have therefore shown that each of the parameters could be modeled as a function of the state of health of the battery with a function. In this example, a linear form function can be used. Thus, in each of Figures 3A to 3D, the square of the linear correlation coefficient noted R2 is indicated. For example, the square of the linear correlation coefficient R2 for [Fig.3A] is 0.99811. For another type of cell, it is possible that these parameters vary differently as a function of the state of health SOH of the battery: quadratically for example.

[0044] In one example, compatible with the variant of the invention, the determination 120, for each parameter of the first model, of a function characterizing the evolution of said each parameter as a function of an evolution of the state of health of the SOH battery comprises two tests.

[0045] The first test is an electrochemical impedance spectroscopy test. The electrochemical impedance spectroscopy test consists of applying a sinusoidal current wave with a zero average value to the battery and measuring a voltage variation of the battery. From this test, it is possible to identify a series resistance Rs, which is independent of the current, as well as the surface resistance Rsurf of the battery for a quasi-zero current, i.e. the sinusoidal current average is zero or almost zero. The series resistance Rs represents all purely resistive contributions, such as the electrolyte, current collectors and contact resistances of the battery. An example of a result of an electrochemical impedance spectroscopy test is shown in [Fig. 4]. [Fig.4] has as its abscissa axis the real component of the impedance expressed in milliohms, and as its ordinate axis the imaginary component, in negative, of the impedance expressed in milliohms.

[0046] The second test is a current pulse test consisting of applying current pulses to the battery during charging and discharging. This test makes it possible to extract information on the impedance of the battery by analyzing its voltage response. From this test, we identify a cell voltage at equilibrium Uoc, the surface resistance Rsurf of the battery for currents other than zero, a time constant linked to surface phenomena noted rsurf and an impedance noted Zdiff. The cell voltage at equilibrium Uoc is a voltage source representing the open-circuit voltage, commonly noted OCV for the English "Open-Circuit Voltage". The surface resistance Rsurf is linked to the voltage drop between the surface of the active material and the electrolyte, due to the charge transfer and the interphase of the electrolyte. The time constant related to surface phenomena rsurf is equal to the product between the surface resistance Rsurf and the surface capacitance, also called double layer capacitance Csurf. This time constant is related to surface phenomena that are associated with charge transfer, double layers and the interphase of the electrolyte. This time constant related to surface phenomena rsurf represents a fast dynamic, generally less than 1 second. The impedance Zdiff is an impedance related to the diffusion phenomena of lithium ions in the electrolyte and lithium atoms in the two electrodes. This impedance has a slow dynamic, generally of the order of several minutes. An example of a result of a current pulse test is illustrated in [Fig.5]. [Fig.5] has as its x-axis the time expressed in seconds.For easier reading, part of the abscissa axis is hidden; thus, some durations are indicated in seconds (noted s) and others in minutes (noted min). The ordinate axis on the left corresponds to the battery current level, expressed in C-rate, i.e. a charge and / or discharge current in amperes (A) divided by the capacity in ampere-hours (Ah). The ordinate axis on the right corresponds to the battery voltage expressed in volts.

[0047] Thus these tests make it possible to identify all the parameters of a schematic representation of an electrical circuit as illustrated in Figure 6. To identify the parameters RSEj(Tpre), EaSEï, 7o(Tpre) and Eaj0, it is possible to use an optimization algorithm making it possible to adjust an equation to the values ​​of Rsurf identified from the electrochemical impedance spectroscopy and current pulse tests.

[0048] A third step 130 of the method 100 consists of generating a second model of the component of the electrical circuit of the battery. This second model is configured to evaluate the state of health of the SOH battery from the surface resistance Rsurf of the battery, the intensity I of current applied to the battery and the temperature T of the battery. In order to generate this second model of the component of the electrical circuit, each function characterizing the evolution of each of the four parameters of the first model as a function of an evolution of the state of health of the SOH battery is integrated into the second model. For example, in the variant of the invention, it is possible to integrate into equation (1), the function characterizing the evolution of each of the four parameters of the first model as a function of an evolution of the state of health of the SOH battery is integrated into the second model to obtain:

[0049] (LA)]] (3)

[0050] As illustrated in Figure 3B, the activation energy linked to the interphase of the solid electrolyte EclSE] of a battery varies little depending on the state of health SOH of the battery. Thus, in equation (3), the integration of this parameter Eo^ei was not carried out. However, it should be noted that for another type of battery, the activation energy linked to the interphase of the solid electrolyte Ea^EI could vary significantly. The variation of the other three parameters is almost linear, so the following relationship was used for these three parameters in equation (3):

[0051] X„ud = X^fMSOH -1) + 1) (4)

[0052] In one example, compatible with the previous examples, the generation 130 of the second model of the component of the electrical circuit of the battery further comprises a determination of an equation between the surface resistance Rsurf and the state of health SOH. Then, two options are possible. The first option consists of solving this equation for a set of SOH values, thus making it possible to evaluate the state of health SOH from a surface resistance Rsurf. For example, [Fig.8] shows an example of evolution of the surface resistance Rsurf as a function of the state of health SOH of a battery for a battery temperature T of 0°C and for current intensities I between 0 and 20 amperes in discharge. Similarly, [Fig.9] shows an example of evolution of the surface resistance Rsurf as a function of the state of health SOH of a battery for a current intensity of 2 amperes in discharge for temperatures between -10 and 40°C.Alternatively to solving this equation, the second option is to generate a table of parameters allowing the SOH state of health to be directly evaluated from the current intensity I applied to the battery, the temperature T of the battery and the surface resistance Rsurf of the battery.

[0053] This example, regardless of the option chosen, thus makes it possible to use a second model of the electrical circuit component based on an equation such as equation (3). Indeed, this equation cannot be inverted. Thus, the state of health SOH cannot be expressed directly as a function of the current intensity I applied to the battery, the temperature T of the battery and the surface resistance Rsurf of the battery. In this case, it is necessary to solve the equation of the surface resistance Rsurf for the current intensity I and the temperature T measured so as to obtain an equation of the surface resistance Rsur f as a function of the state of health SOH only.According to the first option, this simplified equation can be solved for a number of SOH states of health, thus creating a table of SOH states of health as a function of the surface resistance Rsurf, to then interpolate the already known surface resistance value Rsur f and obtain the desired SOH state of health. This approach is for example illustrated in Figure 7. Thus, Figure 7 illustrates the curve corresponding to Rsurf = / (2 A, 0 ° C, SOH\ i.e. the surface resistance Rsurf of a battery for a measured current of 2 amperes and a measured temperature of 0 ° C. Thus, for a surface resistance Rsurf of 70 mΩ identified for example using embedded algorithms, an interpolation of the curve . Rsurf — f(2 A, 0 °C, S OH) allows to evaluate the SOH state of health of the battery at 0.9055. This means that the current capacity of the battery is equal to 90.55% of its initial capacity, i.e. in new condition. According to the second option, it is also possible to use the equation Rsurf = f(I, T, SOH) to generate a parameter table that can be stored in the embedded system. This table allows to directly interpolate the measured values ​​of I and T and the estimated value of SOH, instead of solving the equation for I and T. The choice of implementing the first or the second option may depend on the system's computing capacity and its storage capacity. Thus, for a system mainly limited in system computing capacity, the second option is the most suitable while for a system mainly limited in storage capacity, the first option is to be preferred.

[0054] A fourth step 140 of the method 100 consists of measuring the intensity I of current applied to the battery, the temperature T of the battery and obtaining the surface resistance Rsurf of the battery. To obtain the surface resistance Rsurf of the battery, it is possible to use a known technique of the state of the art which can be implemented via embedded algorithms. This step 140 can be carried out during use of the battery, in particular during charging of the battery.

[0055] A fifth step 150 of the method 100 consists of determining the state of health of the SOH battery by providing to the second model of the component of the electrical circuit of the battery the intensity I of current applied to the battery, the temperature T of the battery and the surface resistance Rsurf of the battery measured or obtained in step 140.

[0056] In one example, compatible with the preceding examples, a sixth optional step 160 of the method 100 consists of modifying the conditions of use of the battery as a function of the SOH state of health determined in step 150. For example, when the determined SOH state of health is lower than a predetermined SOH state of health value, for example 70 or 80%, the modification of the conditions of use of the battery may consist of replacing the battery with a new battery. The battery whose determined SOH state of health is lower than a predetermined SOH state of health value may for example be used in so-called second-life applications. In a second example, the modification of the conditions of use of the battery may consist of interrupting use of the battery in the event that a maximum temperature is reached, the maximum temperature being determined from the determined SOH state of health.In a third example, modifying the battery operating conditions may involve charging the battery 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.

[0057] Another aspect of the invention relates to a method 200 for determining a surface resistance Rsurf of a battery. [Fig.2] is a block diagram illustrating the steps of an example of the method 200. The mandatory steps of the example of the method 200 are indicated by a solid rectangle and the optional steps are indicated by a dotted rectangle.

[0058] A first step 210 and a second step 220 of the method 200 are preferably identical respectively to steps 110 and 120 of the method 100.

[0059] A third step 230 of the method 200 consists of generating a second model of the component of the electrical circuit of the battery configured to evaluate the surface resistance Rsurf of the battery from the intensity I of current applied to the battery, the temperature T of the battery and the state of health of the SOH battery. The generation of the second model comprises, for each parameter of the first model, the integration of the function characterizing the evolution of said each parameter as a function of an evolution of the state of health of the SOH battery. Thus, in one example, the second electrical model of the method 200 can be based on the preceding equation (3).

[0060] A fourth step 240 of the method 200 consists of measuring the intensity I of current applied to the battery, the temperature T of the battery and obtaining the state of health SOH of the battery. To obtain the state of health SOH of the battery, it is possible to use a technique known from the state of the art.

[0061] A fifth step 250 of the method 200 consists of determining the surface resistance Rsurf of the battery by providing the second model with the intensity I of current applied to the battery, the temperature T of the battery and the state of health of the battery SOH obtained in step 240.

[0062] Thus, the method 200 can be used to directly calculate the surface resistance Rsurf of the battery from a known state of health. The method can be implemented by computer or by a processor, for example included in a battery management system. The method 200 is particularly interesting because, among all the parameters of the electrical model of the battery, the surface resistance Rsurf of the battery is the one that changes the most with the aging of the battery and which must be updated as a priority. Moreover, the update alone of said surface resistance can be sufficient for a first estimation of the new impedance of the battery.

[0063] A sixth optional step 260 of the method 200 consists of modifying the conditions of use of the battery as a function of the surface resistance Rsurf of the battery determined in step 250, for example in a similar manner to step 160 previously described in relation to the method illustrated in [Fig.l].

[0064] Unless otherwise specified, the same element appearing in different figures has a single reference.

Claims

1. Claims Method (100) for monitoring a state of health SOH of an electric battery, comprising steps of: - Obtaining (110) a first model of a component of an electrical circuit of the battery, the first model being configured to evaluate a surface resistance Rsurf of the battery from an intensity I of current applied to the battery and a temperature T of the battery, the first model comprising parameters of the battery, the parameters comprising: • A resistance of an interphase of the solid electrolyte at a predetermined temperature noted RSEi (Tpre), • An activation energy linked to the interphase of the solid electrolyte noted EaSEi, • An exchange current at a predetermined temperature noted I0(Tpre), and • An activation energy linked to the exchange current noted Ea>10, - Determination (120), for each parameter among the parameters of the first model, of a function characterizing the evolution of said each parameter as a function of an evolution of the state of health of the SOH battery, - Generation (130) of a second model of the component of the electrical circuit of the battery configured to evaluate the state of health of the SOH battery from the surface resistance Rsurf of the battery, the intensity I of current applied to the battery and the temperature T of the battery, the generation of the second model comprising, for each parameter of the first model, the integration of the function characterizing the evolution of said each parameter as a function of an evolution of the state of health of the SOH battery, - Measurement (140) of the intensity I of current applied to the battery, of the temperature T of the battery and obtaining the surface resistance Rsurf of the battery, and - Determination (150) of the state of health of the SOH battery in providing the second model with the intensity I of current applied to the battery, the temperature T of the battery and the surface resistance Rsurf of the battery obtained (140).

2. Method (100) according to claim 1 wherein the first model of the component of the electrical circuit of the battery is based on the following equation: With: - Rsei( 25 ° C ) , a resistance of an interphase of the solid electrolyte at a temperature of 25 ° C, expressed in ohms noted Q, - E^ei, an activation energy linked to the interphase of the solid electrolyte, expressed in electronvolts noted eV, - ^( / 25 0 C), an intensity of an exchange current of the battery at 25 ° C, expressed in amperes noted A, - an activation energy linked to the intensity of an exchange current of the battery at 25 ° C, expressed in electronvolts noted eV, - kB, a Boltzmann constant, expressed in electronvolts per kelvin noted eV / K, - R, a universal constant of ideal gases, expressed in joules per mole per kelvin noted J / (mol*K), - F, a Faraday constant, expressed in coulombs per mole noted C / mol, - T, a battery temperature,expressed in kelvin noted K, - I, an intensity of the cell current, expressed in amperes noted A.,

3. A method (100) according to any preceding claim, further comprising modifying (160) the battery usage conditions based on the determined SOH state of health (150).

4. The method (100) of claim 3 wherein modifying (160) the battery usage conditions comprises: When the determined SOH health status (150) is lower than a predetermined health status threshold value, replace the battery with a new battery, and / or - Interrupt battery use when a maximum temperature is reached, the maximum temperature being determined from the determined SOH state of health (150), and / or - Charge the battery 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 (150).

5. Method (100) according to any one of the preceding claims, in which the determination (120), for each parameter among the parameters of the first model, of a function characterizing the evolution of said each parameter as a function of an evolution of the state of health of the SOH battery comprises: - a first electrochemical impedance spectroscopy test consisting of applying to the battery a sinusoidal current wave with a zero average value at the battery and measuring a variation in battery voltage, and / or - a second current pulse test consisting of applying current pulses to the battery during charging and discharging.

6. Method (100) according to any one of the preceding claims, wherein the generation (130) of the second model of the component of the electrical circuit of the battery comprises a determination of an equation between the surface resistance Rsurf and the state of health SOH and: - A resolution of the equation, for a set of SOH values, allowing the SOH state of health to be evaluated from the surface resistance Rsurf of the battery, and / or - Generation of a parameter table allowing the SOH state of health to be directly evaluated from the current intensity I applied to the battery, the battery temperature T and the surface resistance Rsurf of the battery.

7. System for managing an electric battery comprising means for implementing the method according to one of the preceding claims.

8. Aircraft comprising an electric battery and a battery 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 implement a method according to any one of claims 1 to 6.

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

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