Measuring battery capacity

Abstract

Battery Capacity Measurement This description relates to a method for measuring the effective capacity of a battery comprising a first measurement (202), during a relaxation phase of said battery, of a first voltage delivered by said battery during use over a duration, said duration being the difference between a first initial instant and a second instant defined as the instant at which a first straight line, tangent at the origin of a curve corresponding to the time evolution of a voltage delivered by said battery during said relaxation phase, reaches a second voltage delivered by said battery when it is relaxed. Figure for the abstract: Fig. 2

Description

Title of the invention: Measuring the capacity of a battery Technical field

[0001] The present description relates generally to accumulator batteries, commonly called batteries, and relates more particularly to Lithium Ferro-Phosphate type batteries. The present description relates more particularly to methods for measuring the effective capacity and aging of such a battery. Prior art

[0002] Accumulator batteries, commonly called batteries, are used very commonly today to power all kinds of electronic devices.

[0003] Among the different types of batteries that exist, lithium batteries are widely used to power small portable electronic objects such as mobile phones, connected objects, electronic cigarettes, etc. Lithium Ferro-Phosphate batteries and Lithium-Cobalt-Oxide batteries are examples of lithium batteries.

[0004] A battery is characterized by different values, including its capacity which indicates the amount of current that a battery can provide over time, and its aging which indicates its degree of degradation.

[0005] It would be desirable to be able to improve, at least in part, at least certain aspects of the methods for measuring the capacity and aging of a battery. Summary of the invention

[0006] There is a need for a method for measuring the capacity of a battery that is simpler to use and consumes less energy.

[0007] There is a need for a method for measuring the aging of a battery that is simpler to use and consumes less energy.

[0008] One embodiment overcomes all or part of the drawbacks of known methods for measuring the capacity of a battery.

[0009] One embodiment provides a method for measuring the capacity of a battery that is simpler to use.

[0010] One embodiment provides a method for measuring the capacity of a battery that consumes less energy.

[0011] One embodiment provides a method for measuring the aging of a battery that is simpler to use.

[0012] One embodiment provides a method for measuring the aging of a battery. consuming less energy.

[0013] One embodiment overcomes all or part of the drawbacks of known methods for measuring the aging of a battery.

[0014] One embodiment provides a method for measuring the effective capacity of a battery comprising a first measurement, during a relaxation phenomenon of said battery, of a first voltage) delivered by said battery in use from a duration, said duration being the difference between a first initial instant and a second instant defined as being the instant at which a first straight line, tangent to the origin of a curve corresponding to the temporal evolution of a voltage delivered by said battery during said relaxation phenomenon, reaches a second voltage delivered by said battery when it is relaxed.

[0015] According to one embodiment, the relaxation phenomenon of said battery is obtained by carrying out a partial charge of said battery until said battery requires an end-of-charge current, the relaxation phenomenon appearing when said partial charge is stopped.

[0016] According to one embodiment, the value of the end of charge current is defined as being equal to the typical capacity of said battery divided by 10 hours.

[0017] According to one embodiment, said partial charge is carried out at constant current and constant voltage.

[0018] According to one embodiment, said effective capacity is given by the following mathematical formula: [Math 3] Ceff = Ctyp - R ( Vr - V ( tr ) ) in which: - Ceff is the effective capacity; - Ctyp represents the typical capacity of said battery; - R represents the resistance of said battery; - Vr represents the voltage delivered by said battery when said battery is relaxed; and - V(tr) represents said first voltage.

[0019] According to one embodiment, the method further comprises a second measurement of said resistance of the battery.

[0020] According to one embodiment, the second measurement is carried out by performing a second discharge of said battery with a first current.

[0021] According to one embodiment, the first current is greater than 500 mA.

[0022] According to one embodiment, the first discharge is the second discharge.

[0023] According to one embodiment, said battery is a Lithium Ferro- type battery. Phosphate.

[0024] Another embodiment provides a method for measuring the aging of a battery comprising the method described above.

[0025] According to one embodiment, the aging of a battery is defined as being the ratio of the effective capacity of the battery to the typical capacity of the battery.

[0026] Another embodiment provides an electronic cigarette adapted to implement the method for measuring a capacity described above.

[0027] Another embodiment provides an electronic cigarette adapted to implement the aging measurement method described above. Brief description of the drawings

[0028] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0029] [Fig.l] represents, very schematically, a Lithium Ferro-Phosphate type battery;

[0030] [Fig.2] represents a block diagram illustrating a mode of implementation of a method for measuring the effective capacity of a battery and a mode of implementation of a method for measuring the aging of a battery;

[0031] [Fig.3] represents a curve illustrating the realization of a step of the methods of [Fig.2]; and

[0032] [Fig.4] represents a curve illustrating the realization of another step of the processes of [Fig.2]; and

[0033] [Fig.5] represents a practical example of use of the battery of [Fig.l]. Description of the embodiments

[0034] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0035] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed.

[0036] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0037] In the following description, when referring to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., are referred to, unless otherwise specified, the orientation of the figures.

[0038] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0039] The embodiments described below relate to the determination of the capacity of a lithium battery, and more particularly of a Lithium Ferro-Phosphate type battery, or lithium-iron-phosphate battery, or lithium ferro-phosphate type battery, and the aging of such a battery. The embodiments relate more particularly to two methods for measuring the capacity and aging of a battery which are easier to implement and consume less energy.

[0040] In the remainder of the description, the capacity of a battery is defined as a value, expressed in Ampere-hours (A / h), indicating the amount of current that a battery can supply over time. The capacity of a battery degrades over time, and the reasons for this degradation are, for example, the weather itself, the use of the battery, the storage conditions of the battery such as temperature and / or humidity, etc.

[0041] The capacity that a battery has at the end of its manufacture is called typical capacity. Finally, the capacity that a battery has at a given time is called effective capacity, current capacity, or real capacity of a battery. The effective capacity of a battery is necessarily lower than the typical capacity of the same battery.

[0042] Furthermore, in the remainder of the description, the aging of a battery, or state of health (State of Health) of a battery, is defined by the ratio of the effective capacity to the typical capacity of this battery. Aging can be expressed as a percentage. Aging makes it possible to evaluate a degree of degradation of a battery.

[0043] [Fig.l] represents, very schematically, a lithium battery of the Lithium Ferro-Phosphate 100 type.

[0044] The battery 100 comprises the structure of a typical Lithium Ferro-Phosphate type battery. The battery 100 comprises two compartments 101 (LiFePO4) and 102 (C) separated by a porous membrane 103.

[0045] The compartment 101 is filled with a crystalline structure of lithium iron phosphate allowing the insertion and deinsertion of lithium atoms. The compartment 101 is crossed by a metal electrode 104, for example made of aluminum, constituting the positive electrode, or cathode, of the battery 100. The electrode 104 is in direct contact with the structure of lithium iron phosphate. The electrode 104 is, in addition, connected to a connection terminal 105 forming the cathode terminal of the battery 100.

[0046] The compartment 102 is filled with a crystalline carbon structure, for example graphite, allowing the insertion and deinsertion of lithium atoms. The compartment 102 is crossed by a metal electrode 106, for example made of copper, constituting the negative electrode, or anode, of the battery 100. The electrode 106 is in direct contact with the carbon structure. The electrode 106 is, in addition, connected to a connection terminal 107 forming the anode terminal of the battery 100.

[0047] The porous membrane 103 is adapted to allow only lithium atoms to pass through. According to one example, the membrane 103 is made of polymer.

[0048] When charging the battery 100, the lithium atoms present in the compartment 101 migrate to the compartment 102, that is to say migrate from the cathode to the anode.

[0049] When the battery 100 is discharged, the lithium atoms present in the compartment 102 migrate towards the compartment 101, that is to say migrate from the anode towards the cathode.

[0050] [Fig.2] is a block diagram illustrating an embodiment of a method for measuring the effective capacity of a battery of the type of battery 100 described in relation to [Fig.l], and an embodiment of a method for measuring the aging of such a battery.

[0051] According to one embodiment, the effective capacity Ceff of a battery is given by the following mathematical formula: [Math 1] Ceff = Ctyp-R(Vr-V(tr))in which: - Ctyp represents the typical capacity of the battery; - R represents the resistance of the battery; - Vr represents the voltage delivered by the battery when it is relaxed; and - V(tr) represents the voltage delivered by the battery in use defined below.

[0052] According to one embodiment, the SOH aging of this same battery is given by the following mathematical formula: [Math 2] SOH- C typ

[0053] To calculate the effective capacity Ceff and the aging of the battery, it is necessary to have the typical capacity of the battery available, this is generally data present in the technical data sheet of the battery, it is therefore considered as known here.

[0054] In addition, it is necessary to have available the value of the voltage Vr representing the voltage delivered by the battery when it is relaxed. A Lithium type battery Ferro-Phosphate, like other batteries, exhibits a relaxation phenomenon that occurs after applying a current between the battery terminals, for example to charge it. More specifically, when a current has been sent to the battery, the battery's output voltage varies for a non-zero period, called the relaxation period, before stabilizing. Once the battery's output voltage is stable, the battery is said to be relaxed. The value of the voltage delivered by the battery when it is relaxed is generally data present in the battery's technical data sheet, so it is considered known here. According to another example, a measurement of this relaxation voltage can be carried out as described below.

[0055] More particularly, for a Lithium Ferro-Phosphate type battery, such as the battery 100 described in relation to [Fig.l], exhibits a relaxation phenomenon after each application of a current between its terminals. According to one example, for a battery of this type providing an output voltage of the order of 3.6 V after application of a current, once the relaxation phenomenon has appeared, its output voltage is less than 3.6 V.

[0056] In a step 201 (Meas. R), a measurement of the resistance R of the battery is implemented. For this, the battery is discharged with a relatively high current. According to one example, for a battery having a typical capacity of the order of 0.2 A / h or of the order of 1.6 A / h, a relatively high current is a current of the order of 800 mA. Measurements of the current and voltage delivered by the battery are carried out throughout this discharge. An example of a curve obtained during such a discharge is described in more detail in relation to [Fig. 3].

[0057] A linear regression is carried out from these voltage and current measurements, and the value of the electrical resistance, hereinafter called resistance, of the battery is deduced from the slope of the linear regression line. More details are given in relation to [Fig.3].

[0058] At a step 202 (Meas. tr), a measurement of an instant tr, and of a corresponding duration Dr, is implemented. For this, a relaxation phenomenon is induced in the battery to be tested. The following steps are implemented: - a discharge step; - a step of partial charging of the battery until reaching an end of battery charge current; and - observation of the relaxation phenomenon and measurement of the instant tr.

[0059] According to one example, step 202 may be directly implemented after step 201, and the battery discharging step of step 202 may thus be the discharging step of step 201.

[0060] The battery charging step can be implemented by providing a constant current Itr and a constant voltage to the battery, also called CCCV setting. According to an example, the constant current Itr is between 0.5 and 5 A, for example of the order of 1 A. According to an example, the constant voltage is between 1 and 5 V, for example of the order of 3.6 V.

[0061] Furthermore, according to one embodiment, the end of charge current of the battery is defined as the current supplied to the battery at the end of its charge. In practice, this current is set as being equal to the typical capacity of the battery divided by ten hours.

[0062] Once the charging step is complete, the current and voltage applied to the battery are set to zero, and the voltage delivered by the battery is measured. As soon as the charging is stopped, the voltage delivered by the battery begins to decrease until it reaches a plateau. An example of a curve obtained by this measurement is described in more detail in relation to [Fig. 4]. The plateau reached by the voltage corresponds to the voltage Vr, that is to say the voltage delivered by the battery when it is relaxed. According to one example, a measurement of the voltage Vr can be carried out at this step.

[0063] Furthermore, in step 202, the instant tr is measured. The instant tr is the instant at which the tangent at the origin of the temporal evolution of the voltage delivered by the battery, during the relaxation phenomenon, reaches the value of the voltage Vr. In other words, the instant tr is the instant at which this tangent crosses the horizontal line defined by the equation y = Vr. The determination of the instant tr is described in more detail in relation to [Fig.4].

[0064] From the measurement of the instant tr, a measurement of a duration Dr corresponding to the difference between the instant tr and an initial instant corresponding to the start of the relaxation phenomenon is deduced.

[0065] Steps 201 and 202 are battery characterization steps. They can both be implemented as soon as the battery is manufactured. The values ​​that they allow to be calculated are, in theory, independent of the aging of the battery.

[0066] In a step 203 (Meas. V(tr)), a measurement of the voltage V(tr) is implemented. The voltage V(tr) is the value of the voltage delivered by the battery when it is in use. In other words, as soon as a device using the battery is put into operation and begins to be powered by the battery, a measurement of the voltage delivered by the battery is carried out at the end of the duration Dr, corresponding to the duration of the instant tr. In other words, when the device starts to operate, an initial instant is defined, and as soon as the instant tr is reached, the voltage delivered by the battery is measured, this voltage being the voltage V(tr). This step can be implemented at any use of the battery or the electronic device comprising the battery.

[0067] The voltage V(tr) is dependent on the aging of the battery, this step therefore provides a value characteristic of the state of health of the battery.

[0068] In a step 204 (C), subsequent to steps 201 to 203, the determination of the effective capacity of the battery is implemented using the values ​​collected in steps 201 to 203. More particularly, the equation Math 1 defined previously is used to calculate the value of the effective capacity Ceff.

[0069] At a step 205 (SOH), subsequent to step 204, the determination of the aging is implemented using the value of the effective capacity collected at step 204. More particularly, the equation Math 2 defined previously is used to calculate the value of the aging.

[0070] Thus, the mode of implementation of the method for measuring the effective capacity of the battery comprises steps 201 to 204, and the mode of implementation of the method for measuring the aging of the battery comprises steps 201 to 205.

[0071] An advantage of these embodiments is that it is easy to use. In addition, it can be implemented by an on-board device associated with a battery, without requiring a large expenditure of energy. Indeed, the charging carried out in step 202 is only carried out until the end-of-charge current of the battery is reached, and not the typical capacity of the battery. According to one example, such a charge can be any charge of the battery implemented during its use. In other words, step 202 can take advantage of a charge of the battery to be implemented.

[0072] [Fig. 3] is a graph representing a curve 301 obtained during the measurement step 201 described in relation to [Fig. 2].

[0073] Curve 301 represents a linear regression of the value of the voltage delivered by the battery as a function of the value of the current delivered by this battery during the discharge implemented in step 201. According to one example, to obtain curve 301 a circuit, such as a processor, a microprocessor, a controller, or a microcontroller, performs current and voltage measurements. According to one example, curve 301 is obtained by a Gas Gauge type gauge making it possible to monitor a single battery cell. These measurements can be performed in a synchronized or non-synchronized manner. According to a practical example, the current values ​​are recorded every 500 ms and the voltage values ​​are recorded every 4 s.

[0074] The value of the electrical resistance of the battery is obtained by determining the slope coefficient of line 301 and using Ohm's law.

[0075] [Fig.4] is a graph representing curves 401 to 403 obtained during the measurement step 203 described in relation to [Fig.2].

[0076] Curve 401 represents the temporal evolution of the voltage delivered by the battery during the relaxation phenomenon induced during step 202. According to one example, the voltage value measurements are measured every 1 to 5 s, for example every 3 s.

[0077] Curve 402, or straight line 402, is the tangent to the origin of curve 401, that is to say the tangent at the point of curve 401 having abscissa 0.

[0078] Curve 403, or straight line 403, is a horizontal straight line having as its ordinate the voltage Vr delivered by the battery when it is relaxed.

[0079] As described previously, the instant tr is defined as being the abscissa of the point of intersection between the lines 402 and 403.

[0080] [Fig. 5] represents a practical example of application of such methods. More particularly, [Fig. 5] represents an electronic cigarette 500.

[0081] The electronic cigarette 500 is composed of a case 501 in which a cigarette holder 502 is inserted.

[0082] The case 501 comprises a battery having a large storage capacity, such as, for example, a lithium-ion battery of the lithium-cobalt-oxide type. The case 501 has the function of serving as a wireless charger for the cigarette holder 502. The case may further comprise a display screen, such as, for example, a set of light-emitting diodes.

[0083] The cigarette holder 502 is adapted to comprise and to be powered by a battery of the type of battery 100 described in relation to [Fig.l]. The cigarette holder 502 rather uses a battery of this type for safety reasons. Indeed, Lithium-Ferro-Phosphate type batteries have a less significant technical runaway phenomenon than other Lithium-ion type batteries. In addition, Lithium-Ferro-Phosphate type batteries have a shorter charging time than other batteries. This shorter charging time is due to a greater current absorption capacity of a Lithium-Ferro-Phosphate battery, such a battery can be charged up to five times its typical capacity without premature aging.

[0084] The cigarette holder 502 may, in addition, comprise an electronic module associated with its battery. This module may be adapted to implement the modes of implementation of the measurement methods described in relation to [Fig.2]. According to one example, this module may be a processor, a microprocessor, a controller, or a microcontroller. According to another example, this module may be a gauge of the Gas Gauge type.

[0085] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. In particular, other electronic devices are suitable for implementing the embodiments of the methods described in connection with [Fig. 2].

[0086] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.

Claims

Claims

1. Method for measuring the effective capacity (Ceff) of a battery (100) comprising a first measurement (202), during a relaxation phenomenon of said battery (100), of a first voltage (V(tr)) delivered by said battery (100) in use from a duration (Dr), said duration (Dr) being the difference between a first initial instant and a second instant (tr) defined as being the instant at which a first straight line (402), tangent to the origin of a curve (401) corresponding to the temporal evolution of a voltage delivered by said battery (100) during said relaxation phenomenon, reaches a second voltage (Vr) delivered by said battery (100) when it is relaxed, in which the relaxation phenomenon of said battery (100) is obtained by carrying out a partial charge of said battery until said battery (100) requires an end-of-charge current,the relaxation phenomenon appearing when said partial charge is stopped, which the value of the end of charge current is defined as being equal to the typical capacity of said battery divided by 10 hours, and said effective capacity (Ceff) is given by the following mathematical formula: [Math 3] Cef f = Ctyp - R ( Vr - V ( tr ) ) in which: - Ceff is the effective capacity; - Ctyp represents the typical capacity (Ctyp) of said battery (100); - R represents the resistance (R) of said battery (100); - Vr represents the voltage delivered by said battery (100) when said battery (100) is relaxed; and - V(tr) represents said first voltage.,

2. A method according to claim 1, wherein said partial charging is carried out at constant current and constant voltage.

3. Method according to claim 1 or 2, further comprising a second measurement of said resistance (R) of the battery (100).

4. A method according to claim 3, wherein the second measurement (201) is performed by performing a second discharge of said battery (100) with a first current.

5. The method of claim 4, wherein the first current is greater than 500 mA.

6. The method of claim 5, wherein the first discharge is the second discharge.

7. A method according to any one of claims 1 to 6, wherein said battery (100) is a Lithium Ferro-Phosphate type battery (100).

8. A method of measuring the aging of a battery (100) comprising the method according to any one of claims 1 to 7.

9. The method of claim 8, wherein the aging of a battery (100) is defined as the ratio of the effective capacity (Ceff) of the battery (100) to the typical capacity of the battery (100).

10. Electronic cigarette adapted to implement the method according to any one of claims 1 to 7.

11. Electronic cigarette adapted to implement the method according to claim 8 or 9.

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