Patent Application
20240201270
The present invention relates to a method for real-time determination of the service life of an electrochemical cell of a battery. It finds an application in the field of primary-type batteries.
The determination of the remaining life (or the remaining capacity, or the state of charge) of a primary cell or battery, such as a battery comprising one or more electrochemical cells of the primary lithium type, for example of the lithium thionyl chloride type (LiSOCl2), is a particularly important problem in many applications that use this type of cell or battery, in order to anticipate the replacement of a discharged battery.
Solutions for determining the remaining service life of a battery are known, which consist in performing a measurement of the voltage across the battery and using a characteristic curve of the no-load voltage of this battery as a function of its state of charge. However, such solutions are not suitable for application to lithium thionyl chloride electrochemical cells, because in this case the no-load voltage is constant throughout the life of the battery and drops only at the very end of battery life. Applying such a solution therefore is equivalent to generating an alarm indicating to the user that the battery must be replaced, at the very end of service life of the battery, and therefore without actual possibility of anticipating replacement of the battery.
Other solutions for determining the remaining life of a primary cell, particularly of the LiSOCl2 type, are also known, which also involve measuring the voltage across the battery, and then analyzing the voltage response to making a demand on the battery. However, this method is complex because it is based on a very fast data acquisition frequency as well as a very precise estimation of the state of passivation of the battery. In the absence of a sufficiently rapid frequency and a sufficiently accurate estimate, the result may be false. Moreover, the conditions under which the demand is made of the battery (current, temperature . . . ) must be reproducible so that results are comparable. This method is therefore difficult to implement.
It is also known from document CN103592605, a method for determining the remaining capacity of a primary cell of the LiSOCl2 type from a measurement of current and temperature. However, this method is based on a calculation of capacity loss by a coulometric method (calculation of the Amps-hours discharged) as well as taking account of calendar self-discharge (as a function of temperature only). This method is nevertheless not satisfactory because it does not take the specificities of each application into account.
More generally, the known methods are based on the use of theoretical usage profiles. However, if the usage differs from what is expected, the estimate is false with the consequences of either no longer having energy available to perform an operation if the usage has been under-estimated, or the premature replacement of a battery if the usage has been over-estimated.
Thus, the aim of the invention is to solve in particular the aforementioned problems, by providing a method for determining in real time the service life of an electrochemical cell of a primary battery which is accurate, and which takes into account the specificities of each application.
The invention therefore provides, in a first aspect, a method for real-time determination of the service life of an electrochemical cell of a primary battery as a function of a determined application, the method comprising:
Depending upon applications, the background current can represent the majority consumption of a primary battery. This background current corresponds to the permanent consumption of the electronics of the application in question: leakage current of each of the electronic components of the system (for example: consumption of a microcontroller in standby mode).
In some embodiments, the method further comprises one or more of the following features, taken alone or in all technically possible combinations:
The invention also provides, according to a second aspect, a computer program product comprising instructions which, when said program is executed by a computer, cause said computer to carry out the above method, from measuring at least one value for current supplied by the electrochemical cell and at least one temperature value of the electrochemical cell in the determined application.
The invention also provides, according to a third aspect, a system for managing a device or installation comprising a battery, said battery comprising at least one electrochemical cell, the system comprising;
The invention also provides, according to a fourth aspect, a battery comprising at least one electrochemical cell. The battery further includes means for measuring at least one value for current supplied by the electrochemical cell and at least one temperature value of the electrochemical cell in a determined application of said electrochemical cell, and electronic computing means programmed to carry out the above method from the measurement of at least one value for current supplied by the electrochemical cell and at least one temperature value of the electrochemical cell in the determined application
Preferably, said at least one electrochemical cell is of the LiSOCl2 type.
Thus, the method of the invention makes it possible to determine the total service life and the remaining life of a primary battery, taking into account the specificities of the application in which the battery is used, therefore with higher accuracy.
Indeed, the maximum capacity, known as nominal capacity, is not a constant theoretical value, it differs depending on the application. However, unlike the solutions of the prior art, the method of the invention makes it possible to recalibrate 10 this maximum capacity depending upon the use.
Furthermore, the method of the invention takes into account:
It should not be forgotten that, depending on the application, background current can represent the majority consumption of a primary battery. This background current corresponds to the permanent consumption of the electronics of the application in question: leakage current of each of the electronic components of the system (for example: consumption of a microcontroller in standby mode).
The features and advantages of the invention will become apparent upon reading the description which will follow, given solely by way of example, and non-limiting, with reference to the following appended drawings.
Various embodiments of the method of the invention are presented hereinafter, with reference to
The method for real-time determination of the service life of an electrochemical cell of a primary battery, such as an electrochemical cell of the LiSOC2 type, comprises a measurement step 1 and a step of calculating total service life 4.
Measuring step 1 makes it possible to measure at least one value of a current I supplied by the electrochemical cell (step 11) and at least one temperature value T of the electrochemical cell (step 13), in a determined application.
The total service life calculation step 4 makes it possible to calculate availability time of the electrochemical cell starting from a determined initial time, as a function of the one or more current value(s) I and the one or more temperature value(s) T measured during measurement step 1, as a function of a determined value of capacity of the electrochemical cell, of cut-off voltage Vc for the determined application, and of background current If for the determined application.
Calculation of the total service life of the electrochemical cell, implemented in step 4, makes it possible to calculate availability time of the electrochemical cell starting from the determined initial time using the following formula:
C×Kp×R/(Imoy+Iad)
In this formula:
The cutoff coefficient Kp of the electrochemical cell (step 43) is a function of firstly maximum current Imax drawn by the determined application (obtained in step 41) and secondly cut-off voltage (Vc) for the determined application.
The value of Kp can be obtained from a table associating cutoff coefficient values Kp with pairs of values representing maximum current Imax and cutoff voltage Vc.
The average value of the current Imoy drawn by the determined application (step 42) is obtained from one or more value(s) of the current I supplied by the electrochemical cell. It includes the value for background current If of the determined application.
For the implementation of step 42, the time that has elapsed since the previous implementation of the method, previously determined in step 12, can be used in the context of the main measurement step 1.
The value for the background current If can be obtained, for example by measurement. If the value for current measured is less than the known value for the background current, it is considered that the value for current measured is equal to the value for background current If. Another method could be to permanently add an estimated value for background current to the measured value for current of the electrochemical cell. Alternatively, this value may be a parameterizable constant for the method.
Efficiency in terms of capacity R of the electrochemical cell (step 44) is a function of firstly, the average value Imoy or of the maximum value Imax of the current drawn by the determined application and secondly of the temperature of the electrochemical cell in the determined application.
A value for efficiency in terms of capacity R can be obtained, for example, from a table associating values of efficiency in terms of capacity R with pairs of values representing mean current Imoy or maximum current Imax and temperature T.
The value of self-discharge current Iad of the electrochemical cell (step 45) is a function of firstly the average value of current Imoy drawn by the determined application and secondly the temperature of the electrochemical cell in the determined application.
Just like for efficiency in terms of capacity R, values for self-discharge current can be obtained, for example from a table associating self-discharge current values Iad with mean current Imoy and temperature T value parings.
Once these different values have been obtained, calculation of the service life of the electrochemical cell using the formula previously indicated is carried out (step 46).
In the particular embodiments shown in
In this step of storing the profile 2, the value for maximum current Imax is stored (step 21) and a value for average current Imoy is stored (step 22). Furthermore, the temperature value or values T measured in measurement step 1 are also stored (step 23).
More specifically, step 23 implements storage of the one or more temperature value(s) T in a table in association with durations of exposure to that temperature. These exposure times correspond to durations during which exposure to the respective temperatures T has occurred.
For the implementation of steps 22 and 23, the time elapsed since the previous implementation of the method, previously determined in step 12 in the context of the main measurement step 1, can be used.
Preferably, the temperature values T are grouped together by temperature thresholds T Thus, the table in question associates durations of exposure with temperature thresholds T.
In the particular embodiment shown in
In the context of the implementation of the method of the invention by a computer programmed to this effect (see explanations below), the particular embodiment presented above makes it possible to separate the activities of measurement (step 1) from the profile storage activity (step 2) with little consumption in terms of calculation overhead, for continuous storage of useful data related to the profile, from service life calculation part (step 4) which has a much higher calculation overhead, to just do service life calculation from time to time.
Provision may be made for storage of the time that has elapsed since the determined initial time. The remaining service life of the electrochemical cell can then be obtained by subtracting the elapsed time from the service life calculated during service life calculation step 4.
The state of charge of the electrochemical cell can also be calculated by dividing the remaining service life previously calculated by the service life calculated during service life calculation step 4.
In the method of the invention, the determined value of capacity used can correspond to the nominal capacity of the electrochemical cell. The determined initial time then corresponds to the time production of the electrochemical cell finished.
Alternatively, the determined value of capacity used in the method corresponds to the nominal capacity of the electrochemical cell minus a loss of capacity during a determined period. The determined initial time then corresponds to the time at which the electrochemical cell is put into use for the first time and is determined to be the time production ended plus the duration of the determined period. This determined period may, for example, correspond to a storage period, between the production of the electrochemical cell and the actual commissioning thereof.
The method of the invention can be implemented by a computer. It is then stored as instructions of a computer program product. When the program is executed by the computer in question, the instructions of the program cause the computer to carry out the method of the invention, from the measurement of at least one value for current/supplied by the electrochemical cell and at least one temperature value T of the electrochemical cell, in the determined application.
The method of the invention can also be implemented by a system for managing a device or an installation comprising a battery with at least one electrochemical cell.
Such a system conventionally comprises electronic or computer computing means. It further comprises measurement means.
The calculation electronics or computational means are programmed to implement the method of the invention, from measurement, by the measurement means, of at least one value for current I supplied by the electrochemical cell and at least one temperature value T of the electrochemical cell in the determined application.
It is also possible to provide for the battery to include its own measurement means, and its own electronic calculation means. These electronic calculation means are then programmed to implement the method of the invention, from measurement, by these measurement means, of at least one value for current I supplied by the electrochemical cell and at least one temperature value T of the electrochemical cell in the determined application.
The method disclosed in the invention is applicable to all liquid-cathode primary lithium-type electrochemistries, for example of the LiSOCl2 type and is also potentially applicable to solid-cathode primary lithium electrochemistries, for example of the LiMnO2 or LiCFx type.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002869 | Mar 2020 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/056201 | 3/11/2021 | WO |
