A battery pack incorporating a means of heating its cells

Abstract

The invention relates to a battery (10) comprising a casing (20) housing electrochemical cells and a cell management system (42). According to the invention, the battery comprises, within the casing (20): - at least one heating layer (60) incorporating an electrical track adapted to be supplied with current by the electrochemical cells so as to heat said electrochemical cells by Joule heating, and - a transistor (80) controlled by the management system, this management system being programmed to modulate the electrical power received by said at least one heating layer in pulse width. Figure for the abstract: Fig. 1

Description

Title of the invention: Accumulator battery incorporating a means of heating its cells Technical field of the invention

[0001] The present invention relates generally to the storage of electrical energy in accumulator batteries.

[0002] It relates more particularly to a battery of accumulators comprising, on the one hand, a case which houses electrochemical cells, and, on the other hand, an electrical management system for the electrochemical cells.

[0003] It also relates to a method of controlling a transistor in a battery of accumulators as mentioned above.

[0004] The invention finds a particularly advantageous application in electric or hybrid powered motor vehicles. State of the art

[0005] Electric or hybrid motor vehicles generally include an electric motor powered by a battery, commonly called a traction battery. Such a traction battery comprises a plurality of electrochemical cells, for example of the Lithium-ion type, connected together to deliver a high voltage.

[0006] These electrochemical cells heat up when they deliver or receive electrical energy. To prevent their temperatures from exceeding a threshold beyond which they could degrade, the traction battery is generally equipped with a cooling circuit through which a fluid circulates.

[0007] It is also known that the capacity of a traction battery to deliver or store electrical energy depends strongly on the temperature of the electrochemical cells, and therefore on the ambient temperature. This capacity is particularly degraded at low temperatures, which can be especially problematic for vehicles used in the coldest geographical areas, where temperatures can reach -40°C.

[0008] In practice, at low temperature, the dynamics of the chemical reactions between the cathode and the anode of each electrochemical cell are slowed down, which directly impacts the battery's ability to supply or store energy.

[0009] When it is cold, it was therefore considered to use the cooling circuit to circulate a hot liquid in order to increase the temperature of the electrochemical cells. For this purpose, an electric immersion heater was installed in the battery so that it was immersed in the fluid of this cooling circuit.

[0010] However, in the case where the fluid was of the refrigerant type, the use of an immersion heater would be unsuitable because it would risk causing a change in the state of the fluid, from the liquid state to the gaseous state, which would cause a failure of the system and require a lot of energy.

[0011] On the contrary, in the case where the fluid was glycol water, the efficiency would prove to be very low and therefore unsuitable, insofar as the thermal inertia of glycol water is high and the volume of water to be heated is several liters. Presentation of the invention

[0012] In order to remedy the aforementioned drawbacks of the prior art, the present invention proposes to heat the traction battery cells differently.

[0013] More specifically, the invention proposes a traction battery as defined in the introduction, which comprises in its casing: - at least one heating layer comprising at least one electrical track adapted to be supplied with current by the electrochemical cells so as to heat said electrochemical cells by Joule effect, and - a transistor, the battery management system being programmed to drive this transistor in such a way as to modulate the electrical power received by said at least one electrical track in pulse width.

[0014] Such an electrical track has very low thermal inertia, which allows the battery cells to heat up very quickly.

[0015] This heating is done using the electrical energy stored in the electrochemical cells of the battery, so that it is not dependent on whether the battery is charging or not.

[0016] The use of a transistor, rather than a controlled relay-type switch, makes it possible to power the electrical track not in an all or nothing (ON / OFF) fashion, but by varying the electrical power received by the track.

[0017] It is indeed very advantageous to precisely control this received electrical power so that the electrical track can heat up at the required power, despite in particular the manufacturing variations of the heating layers (it is observed that from one battery to another, the shapes and electrical resistances of the tracks can vary by more or less 10%).

[0018] As will be detailed later, this control is also advantageous when it comes to preventing the temperature or temperature gradient within the cells from being too high.

[0019] Preferably, said at least one electrical track is made, at least in part, of aluminium.

[0020] Advantageously, the housing accommodates a cooling circuit for the electrochemical cells, and in which said at least one heating layer is located between said cooling circuit and said electrochemical cells.

[0021] The invention also relates to a method of controlling a transistor in a battery of accumulators as mentioned above, according to which the transistor is controlled so that the electric current delivered by the electrochemical cells to said at least one electrical track varies by pulse width modulation.

[0022] Other advantageous and non-limiting features of the process according to the invention, taken individually or in all technically possible combinations, are as follows: - it is planned to measure at least one temperature relative to the temperature of the electrochemical cells, and the transistor is controlled according to the measured temperature; - it is planned to determine a state of charge of the accumulator battery and then to calculate a target heating power as a function of the state of charge and the measured temperature, and the transistor is controlled so that the electrical power received by said at least one heating layer is equal to the target heating power; - each electrochemical cell has a first face located on the side of said at least one heating layer and a second opposite face; - it is planned to acquire a value representative of the temperature of the first face of at least one of the electrochemical cells, and the transistor is controlled so that the acquired value remains less than or equal to a maximum threshold; - it is planned to acquire a first value representing the temperature of the first face of at least one of the electrochemical cells and a second value representing the temperature of the second face of at least one of the electrochemical cells, and the transistor is controlled so that the difference between the first and second values ​​remains less than or equal to a threshold; - it is planned to acquire two representative values ​​of the temperature of the second face of two of the electrochemical cells, and the transistor is controlled so that the difference between the two values ​​remains less than or equal to a threshold; - when the battery is connected to an external charger and is charging, it is planned to determine the maximum electrical power that the charger can deliver, and the transistor is controlled so that the electrical power received by said at least one heating layer remains less than said maximum electrical power; - the transistor is controlled so that the electrical power received by said at least one heating layer is equal to a target heating power.

[0023] Of course, the various features, variants, and embodiments of the invention can be combined with one another in various ways, provided they are not incompatible or mutually exclusive. Detailed description of the invention

[0024] The following description with regard to the attached drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be carried out.

[0025] On the attached drawings:

[0026] [Fig-1] is a schematic exploded perspective view of a battery of accumulators conforming to the invention;

[0027] [Fig.2] is an electrical diagram of various electrical components of the battery of accumulators of the [Fig.l];

[0028] [Fig.3] is a detail view of area III of [Fig.2];

[0029] [Fig.4] is a diagram illustrating a control method according to the invention of a heating means equipping the accumulator battery of the [Fig.l].

[0030] Figure [Fig. 1] shows an exploded view of a battery of accumulators, hereinafter referred to as traction battery 10.

[0031] Here, and preferably, this traction battery 10 is intended to be used within a motor vehicle.

[0032] This motor vehicle could be of any type (truck, bus, airplane, boat). Preferably, it will be a car which conventionally comprises a chassis, wheels of which at least two are driven, and a powertrain adapted to turn the driven wheels.

[0033] The powertrain is preferably purely electric, but alternatively it could be hybrid. In all cases, it comprises at least one electric machine (hereinafter referred to as the electric motor) supplied with current by the traction battery 10. It will be considered in the following that it comprises two separate electric motors.

[0034] As shown in [Fig.1], the traction battery 10 includes a housing 20 which accommodates all the other components referenced in this figure.

[0035] This housing 20 is here formed in several parts. In the illustrated example, it comprises a base plate 21, a frame 22 and a cover 23, fixed to each other.

[0036] The frame 22 has four substantially flat side walls. It has two edges adapted to come to be applied respectively against the base plate 21 and the cover 23, so that the housing 20 has an overall parallelepiped shape.

[0037] This case 20 is designed to be hermetically sealed.

[0038] In the following description, the term "lower" will be used to designate a side or object turned towards the side of the base plate 21, while the term "upper" will be used to designate a side or object turned towards the side of the cover 23.

[0039] The traction battery 10 also comprises a plurality of electrochemical cells.

[0040] These could typically be lithium-ion type cells, but other variants would be conceivable.

[0041] Each electrochemical cell here has a voltage across its terminals of the order of 3 to 5 V. These cells are then connected in series to reach the voltage level required by the application.

[0042] Here, there are approximately one hundred of these cells, so that each electric motor can develop sufficient torque and power to propel the vehicle for a desired duration. Thus, the voltage at the outer terminals of the traction battery 10 is approximately 400V. In practice, 96 cells are used here. Of course, the number of cells could be greater (approximately 200, for example) or less.

[0043] In [Fig. 1], these electrochemical cells are not visible. However, they can be seen distributed in several groups of cells called "modules 31". Here, eight modules 31 of twelve electrochemical cells are provided, which are electrically connected to each other in series, so as to form a pack 30 of modules 31. Each module 31 has a frame that holds the cells together. This frame is open on its underside.

[0044] The modules 31 are here distributed side-by-side, on two separate lines.

[0045] The traction battery 10 includes an electrical circuit 40, part of which is carried by a plate 41 which is here fixed under the cover 23, above the electrochemical cell modules 31.

[0046] This electrical circuit 40 is partly represented in [Fig.2].

[0047] It includes, in particular, a battery management system 42, better known as the acronym BMS (from the English "battery management system").

[0048] This management system 42 comprises a processor (CPU), memory, and various input and output interfaces. Its memory stores data used in the process described below. In particular, it stores a computer application consisting of computer programs containing instructions whose execution by the processor enables the implementation of the process described below.

[0049] The management system 42 typically performs several functions, including those consisting of: - continuously monitor the individual voltages of each electrochemical cell and the charge and discharge currents, to ensure that all these parameters remain within safe operating ranges, and - balance the voltages between the electrochemical cells.

[0050] Here, as will be described below, it also ensures the thermal management of the electrochemical cells, to prevent them from overheating or to allow them to rise rapidly in temperature when they are initially cold.

[0051] The battery accumulator 20 includes for this purpose temperature sensors enabling the determination of temperature values ​​in different areas of the housing 20.

[0052] These could be physical sensors, i.e. sensors positioned in specific areas of the housing 20 to measure the desired temperature values.

[0053] Alternatively, it could be software sensors, i.e. algorithms programmed or trained to calculate temperature values ​​in specific areas of the housing 20, based on other parameters (typically based on temperatures measured elsewhere in the housing or outside, the voltage of the electrochemical cells, the current that these cells deliver...).

[0054] In practice, here, a single temperature sensor will be provided in each module 31, placed above one of the electrochemical cells, and the management system 42 will be programmed to calculate several temperature values ​​in each module 31.

[0055] It will therefore be considered that the traction battery 10 comprises several temperature sensors, some physical and others software.

[0056] In the following, it will then be considered that in each module 31 there is provided at least one first temperature sensor located under one of the electrochemical cells so that it can measure the value of the temperature of the lower face of this cell.

[0057] Preferably, each module 31 will also be provided with at least one second temperature sensor located above this electrochemical cell so that it can measure the temperature value of the upper face of this cell.

[0058] Preferably, several second temperature sensors will be provided, respectively located above different electrochemical cells of each module 31.

[0059] More generally, it will be considered that it will thus be possible to determine the following values: - the highest temperature among the temperatures of the lower faces of electrochemical cells in pack 30, - the highest temperature among the temperatures of the upper surfaces of electrochemical cells in pack 30, - the lowest temperature among the temperatures of the upper surfaces of electrochemical cells in pack 30, and - the largest temperature gradient between the upper and lower faces of the electrochemical cells in pack 30.

[0060] Thanks to its interface, the management system 42 can receive instructions from a computer 99 external to the housing 20 allowing the implementation of the process described below.

[0061] This management system 42 and this computer 99 are thus programmed to operate together. Hereafter, the term "calculation unit 98" will be used to refer to one and / or the other of these two components.

[0062] When they deliver or receive current, electrochemical cells heat up. To prevent their temperatures from exceeding a threshold beyond which they would risk rapid degradation, a cooling circuit 50 is provided. This cooling circuit 50 here comprises a thick plate inside which a conduit for circulating a coolant runs.

[0063] This cooling circuit 50 therefore has a heat exchanger function.

[0064] It is located here on the lower side of the modules 31, against the base plate 21 of the housing 20.

[0065] The cooling circuit conduit 50 has outlets at its ends that open out of the housing 20, through which it is adapted to be connected to coolant inlet and outlet hoses. An external pump, located outside the housing 20, is then provided to force the circulation of the coolant in the circuit.

[0066] In the context of the invention, the traction battery 10 comprises at least one heating layer 60.

[0067] The heating layer(s) 60 are interposed here between the cooling circuit 50 and the modules 31.

[0068] Each heating layer 60 is preferably located as close as possible to the modules 31. Only a thermal interface facilitating heat exchange is provided between the electrochemical cells and each heating layer. Here, this thermal interface is in the form of a thermal paste.

[0069] Each heating layer 60 is in the form of a sheet, and includes a support and an electrical track carried by the support.

[0070] The support is preferably flexible. For example, it is formed of two superimposed plastic films (typically polyethylene terephthalate) that sandwich the electrical trace. These two films have very thin thicknesses, here on the order of a quarter of a millimeter.

[0071] Each electrical trace winds between these two films so as to cover at least 50% of the surface of the substrate. It has two ends at which it is possible to apply an electrical voltage so that the electrical track heats up by Joule effect.

[0072] Each electrical track is preferably made of aluminium.

[0073] Here, since the modules 31 are divided into two sets located at a distance from each other, two separate heating layers 60 are provided, which are connected together (preferably in series). Alternatively, an independent heating layer could be provided under each module.

[0074] It may be foreseen that each heating layer 60 comprises only one single electrical track which winds under several modules, typically under the four modules of the corresponding assembly.

[0075] Alternatively, each heating layer 60 may be provided to have several distinct electrical tracks connected to each other (preferably in series).

[0076] In any case, the electrical track(s) are distributed in such a way as to be able to heat the different electrochemical cells of the modules homogeneously.

[0077] In the following description, for the sake of clarity, it will be assumed that a single electrical track is provided on a single heating layer.

[0078] This electrical track is intended to be supplied with electric current by the electrochemical cells themselves, under the control of the computing unit 98.

[0079] According to the invention, this control is achieved using a transistor 80, in pulse width modulation.

[0080] Pulse width modulation (PWM) is a modulation technique used to vary electrical power without loss due to the Joule effect. It is generally performed at a constant frequency, here on the order of one Hertz.

[0081] The signal generated by transistor 80 and transmitted to electrical track 62 is then characterized by a series of pulses at a constant frequency. The width of each pulse varies according to the electrical power that one wishes to transmit to the electrical track.

[0082] The duty cycle is the proportion of the time during which the pulse is active (in the high state) relative to the total period of the signal.

[0083] The transistor 80 used is of the MOSFET type. It should be noted here that transistors are semiconductor devices that use materials such as silicon to control the current flow. Lacking moving parts, they have a lifespan much longer than that of a relay and a much shorter response time. This is why only a transistor could be used in the context of the invention.

[0084] In [Fig.2], the electrical circuit 40 allowing the electrochemical cells of the pack 30 of modules 31 to be connected to different terminals has been schematically represented.

[0085] Among these terminals, at least one pair of external terminals is provided which emerge from the housing 20. Here, two pairs of external terminals 71, 72 are provided to which the two electric motors can be connected.

[0086] Each pair of outdoor terminals has, like the pack of 30, a positive terminal and a negative terminal.

[0087] The positive terminal of each pair of external terminals 71, 72 is connected to the positive terminal of the pack 30 via a controlled switch 43 (or "relay") and via a protective fuse 44, 45 designed to open the circuit as soon as the current exceeds a safety threshold. Here, a single controlled switch 43 is connected between the positive terminal of the pack 30 and the two positive terminals, and a protective fuse 44, 45 is specific to each of these positive terminals.

[0088] The negative terminal of each pair of external terminals 71, 72 is connected to the negative terminal of the pack 30 via a controlled switch 46 (here a single relay) and via a current sensor 47.

[0089] The electrical circuit 40 also includes other sub-circuits, illustrated in detail in [Fig.3].

[0090] It thus comprises a sub-circuit 81 connected to the terminals of the controlled switch 43, which includes a relay 82 and a resistor 83 connected in series. This sub-circuit 81 reduces the current surge observed when the vehicle is started. Indeed, if the two controlled switches 43 and 46 were closed simultaneously, the current required to charge all the vehicle's capacitors would be very high and potentially destructive. This sub-circuit 81, thanks to its resistor 83, smooths out the current surge before the controlled switch 43 is closed.

[0091] The electrical circuit 40 also includes a sub-circuit 84 which is connected to the output of the controlled switch 46 (i.e., opposite the pack 30 with respect to this switch) and which includes a fuse 85 and a terminal 74 through which it is adapted to be connected to a DC-DC voltage regulator. Typically, this regulator can be used to supply power to the vehicle's on-board electrical system via the pack 30.

[0092] The electrical circuit 40 also includes a sub-circuit 86 which is connected to the output of the controlled switch 43 and which includes a fuse 87 and a terminal 75 by which it is adapted to be connected to a current charger such as a charging station external to the vehicle.

[0093] In the context of the invention, the electrical circuit 40 includes a sub-circuit 90 specially designed to allow the electrochemical cells of the pack 30 to supply the electrical track of the heating layer 60 with electric current.

[0094] This sub-circuit 90 has a pair of terminals 73 connected respectively to the ends of the electrical track.

[0095] One of these terminals is connected to the output of the controlled switch 43, via a fuse 91, a relay-type controlled switch 93, and a current sensor.

[0096] The other is connected to the output of the controlled switch 46, via a fuse 85 (here that of the sub-circuit 84), a current sensor 94 and the transistor 80.

[0097] It could be envisaged that this sub-circuit 90 would only have one current sensor, but it is preferable to use two separate ones for safety reasons in case of failure of one of them.

[0098] We could also do without the controlled switch 93, but we will prefer to use one in case of failure of the transistor 80.

[0099] We can now describe how the computing unit 98 is programmed to drive this sub-circuit 90.

[0100] The controlled switch 93 is always operated in the closed state, except in the event of a failure, which will not be the subject of this presentation.

[0101] The transistor 80 is controlled between a blocked state (which opens the sub-circuit 90) and a conducting state (which closes the sub-circuit 90), so that it delivers a square wave voltage, i.e. a square wave signal whose value is either equal to 0 V, or equal to the potential at the negative terminal of the pack 30.

[0102] In practice, the computing unit 98 implements the process illustrated in [Fig.4] to control this transistor 80.

[0103] This method is designed to be implemented in loops, at regular time intervals, as soon as the vehicle is woken up (i.e., as soon as the two controlled switches 43, 46 are closed). Hereafter, each loop will be identified by an index i, with i equal to 1 for the first loop following the vehicle's wake-up.

[0104] The first step S0 consists for the computing unit 98 in acquiring (by calculation or by measurement) the temperature values ​​from the sensors, as well as the charge level SOC of the traction battery 10 (expressed as a percentage).

[0105] It can then deduce, by reading a map stored in its memory, the electrical power that the traction battery 10 can deliver and that which it can receive (under load).

[0106] The objective is for these electrical powers to be as high as possible.

[0107] However, when the temperature of the electrochemical cells is low, these electrical powers are reduced.

[0108] Thus, if either of these electrical powers is greater than a threshold (which amounts to: if the average temperature of the electrochemical cells is greater than a threshold, for example between 0 and 10°C), it is considered that no heating of the cells is necessary, and the process stops until the next awakening of the vehicle.

[0109] Otherwise, two cases can be considered.

[0110] Either the process has already been implemented (i > 1) and a target heating power Pcib has already been calculated, in which case its value is retained. Or the process is being looped for the first time since the vehicle was woken up (i = 1), in which case the calculation unit then determines a target heating power Pcib.

[0111] This target heating power Pcib can be defined as the electrical power to be supplied to the electrical track to heat the electrochemical cells of the pack 30 as quickly as possible, expressed in Watts.

[0112] During the first loop (i=l), this target heating power Pcib is defined at the maximum possible value, on the order of several kW.

[0113] The objective is then that the electrical track of the heating layer 60 receives an electrical power equal to the target heating power Pcib.

[0114] The electrical track could then be shaped so that, when the battery is charged, a 100% duty cycle allows such electrical power to be transmitted to the heating layer. However, disparities are observed between the heating layers 60 of different batteries manufactured using the same process, such that the electrical resistances of the electrical tracks can vary by plus or minus 10% from the desired electrical resistance.

[0115] Furthermore, the voltage across the terminals of the pack 30 can vary very rapidly, for example during strong vehicle acceleration. It also varies depending on the state of charge (SOC) of the battery. Typically, the voltage range between the terminals of each pair of outer terminals 71, 72 can vary from approximately 240V to 400V.

[0116] These are the reasons why the duty cycle used to drive transistor 80 will have to be constantly adjusted so that the electrical trace receives electrical power equal to the target heating power Pcib.

[0117] This duty cycle will in practice be calculated as follows depending on the target heating power Pcib.

[0118] It will be considered equal to the ratio between the intensity icib of the current required to achieve the target heating power Pcib, and the maximum intensity imax that the electrical track can receive.

[0119] The intensity icib is calculated here by dividing the target heating power Pcib by the voltage across the pack 30.

[0120] The current imax is calculated by dividing the voltage across the terminals of the pack 30 by the actual resistance of the electrical track.

[0121] Once this duty cycle has been calculated, the calculation unit 98 drives the transistor 80 according to this duty cycle, so that heating begins.

[0122] It could be foreseen that transistor 80 remains driven in this way until the temperature of the electrochemical cells is sufficient. In this case, the ratio cyclic should be adjusted in a loop, in order to take into account the voltage variations across the terminals of the 30 pack.

[0123] But here and preferably, steps are provided for adjusting this duty cycle to avoid any overheating of the electrochemical cells.

[0124] Thus, during a step S2, the computing unit 98 compares the temperature of at least one of the lower faces of the electrochemical cells with a threshold So.

[0125] In practice, it determines the highest temperature among the temperatures of the lower faces of the electrochemical cells, and it compares it with the threshold So.

[0126] This threshold So is in the order of 50 to 70°C.

[0127] The objective is to ensure that the temperature of the ends of the electrochemical cells in contact with the heating layers 60 is never too high.

[0128] If the temperature does not exceed this threshold So, the process continues in a step S4.

[0129] Otherwise, if the temperature exceeds this threshold So, the duty cycle is reduced.

[0130] To this end, during step S3, a new target heating power Pcib is defined using a predetermined table. The new duty cycle is then calculated in the same way as above, based on this new target heating power Pcib. Once this new duty cycle has been calculated and applied to transistor 80, step S2 is repeated.

[0131] During step S4, the computing unit 98 determines a temperature difference between the lower and upper faces of at least one of the electrochemical cells.

[0132] Indeed, since the electrical track is in contact only with the underside of the electrochemical cells, heating will generate a potentially significant temperature gradient within the cells, and therefore a temperature difference between the underside and the opposite side of the cells. This temperature difference can damage the electrochemical cells. This is why it is controlled.

[0133] In practice, the computing unit 98 determines the temperature differences between the lower and upper surfaces of each of the cells, and then compares the largest difference with a threshold Sp

[0134] This threshold Si is in the order of 20 to 40°C.

[0135] If this difference does not exceed this threshold Si, the process continues in a step S6.

[0136] Otherwise, the duty cycle is reduced.

[0137] To this end, during step S5, a new target heating power Pcib is defined using a predetermined table. The new duty cycle is then calculated in the same way as above, based on this new target heating power Pcib. Once this new duty cycle has been calculated and applied to transistor 80, step S4 is repeated.

[0138] During a step S6, the computing unit 98 determines a temperature difference between the upper faces of at least two of the electrochemical cells.

[0139] Indeed, when heating the electrochemical cells, it is observed that the temperature is not perfectly homogeneous between all the cells, in particular because those located in the middle of each module 31 lose less heat than those located at the ends of the cells.

[0140] In practice, the computing unit 98 determines the temperature differences between the upper surfaces of the cells, then it compares the largest difference with a threshold S2.

[0141] This threshold S2 is in the order of 5 to 15°C.

[0142] If this difference does not exceed this threshold S2, the process continues in a step S8. Otherwise, the duty cycle is reduced.

[0143] To this end, during step S7, a new target heating power Pcib is defined using a predetermined table. The new duty cycle is then calculated in the same way as above, based on this new target heating power Pcib. Once this new duty cycle has been calculated and applied to transistor 80, step S6 is repeated.

[0144] Step S8 corresponds to the end of the process steps. In other words, when step S8 is reached, the process can be repeated from step S0.

[0145] The present invention is in no way limited to the embodiment described and represented, but a person skilled in the art will be able to make any variation in accordance with the invention.

[0146] Typically, when charging electrochemical cells on a charging station, the temperature of pack 30 may be low.

[0147] In this scenario, the electrical circuit can be powered to heat the electrochemical cells. However, the electrical power consumed to heat the electrochemical cells must never exceed the electrical power that the charging station can deliver. Otherwise, the user's battery would discharge while it is supposed to be charging. To avoid this, the duty cycle can be calculated in the same way as described above, with a target heating power that will always be set to remain less than or equal to the electrical power that the charging station can deliver.

[0148] According to one variant of the invention, the management system could be located outside the housing.

[0149] As a further alternative, the electrical track could be made of any electrically conductive material, typically copper.

Claims

Demands

1. Accumulator battery (10) comprising a case (20) which houses electrochemical cells and an electrochemical cell management system (42), characterized in that it comprises in the case (20): - at least one heating layer (60) which includes at least one electrical track adapted to be supplied with current by the electrochemical cells so as to heat said electrochemical cells by Joule effect, and - a transistor (80), the management system (42) being programmed to drive the transistor (80) so as to modulate the electrical power received by said at least one electrical track in pulse width.

2. Accumulator battery (10) according to claim 1, wherein said at least one electrical track is made, at least in part, of aluminium.

3. Accumulator battery (10) according to claim 1 or 2, wherein the casing (20) houses a cooling circuit (50) for the electrochemical cells, and wherein said at least one heating layer (60) is located between said cooling circuit (50) and said electrochemical cells.

4. A method for driving a transistor in a battery of accumulators (10) according to any one of claims 1 to 3, wherein the transistor (80) is driven so that the electric current delivered by the electrochemical cells to said at least one electrical track varies by pulse width modulation.

5. A control method according to claim 4, wherein it is provided to measure at least one temperature relative to the temperature of the electrochemical cells, and wherein the transistor (80) is controlled as a function of the measured temperature.

6. A control method according to claim 5, wherein it is provided to determine a state of charge (SOC) of the battery of accumulators (10) and then to calculate a target heating power (Pcib) as a function of at least the state of charge (SOC) and the measured temperature, and wherein the transistor (80) is driven so that the electrical power received by said at least one heating layer (60) is equal to the target heating power (Pcib).

7. A control method according to claim 5 or 6, wherein each electrochemical cell having a first face located on the side of said at least one heating layer (60), it is provided to acquire a value representative of the temperature of the first face of at least one of the electrochemical cells, and wherein the transistor (80) is controlled so that the acquired value remains less than or equal to a maximum threshold.

8. A control method according to any one of claims 5 to 7, wherein each electrochemical cell having a first face located on the side of said at least one heating layer (60) and a second opposite face, it is provided to acquire a first value representative of the temperature of the first face of at least one of the electrochemical cells and a second value representative of the temperature of the second face of at least one of the electrochemical cells, and wherein the transistor (80) is controlled so that the difference between the first and second values ​​remains less than or equal to a threshold.

9. A control method according to any one of claims 5 to 8, wherein each electrochemical cell having a first face located on the side of said at least one heating layer (60) and a second opposite face, it is provided to acquire two values ​​representative of the temperature of the second face of two of the electrochemical cells, and wherein the transistor (80) is controlled so that the difference between the two values ​​remains less than or equal to a threshold.

10. A control method according to any one of claims 4 to 9, wherein, when the battery (10) is connected to an external charger and is charging, it is provided to determine the maximum electrical power that the charger can deliver, and the transistor (80) is controlled so that the electrical power received by said at least one heating layer (60) remains less than said maximum electrical power.