Storage battery incorporating a means for heating the cells thereof

Abstract

The invention relates to a storage battery (10) comprising a housing (20) that houses electrochemical cells and a management system (42) for managing the electrochemical cells. According to the invention, the battery comprises, in the housing (20): - at least one heating layer (60) that incorporates an electrical track suitable for being supplied with current by the electrochemical cells so as to heat the electrochemical cells through Joule heating, and - a transistor (80) controlled by the management system, this management system being programmed to carry out pulse-width modulation of the electrical power received by the at least one heating layer.

Description

BATTERY CELLS INCORPORATING A MEANS OF HEATING THEIR 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 specifically to a battery of accumulators comprising, on the one hand, a casing 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 vehicles generally have 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 heavily 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 temperatures, the dynamics of chemical reactions between the cathode and anode of each electrochemical cell are slowed down, which directly impacts the battery's ability to supply or store energy.

[0009] In cold weather, the plan was to use the cooling system to circulate a hot liquid in order to raise the temperature of the electrochemical cells. To achieve this, an electric immersion heater was installed in the battery so that it was immersed in the fluid of this cooling system.

[0010] However, if the fluid is a refrigerant, the use of a An immersion heater would be unsuitable because it could cause a change in the state of the fluid, from liquid to gaseous, which would cause a failure of the system and require a lot of energy.

[0011] Conversely, if the fluid were glycol water, the efficiency would be very low and therefore unsuitable, since 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 within 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 it is not dependent on whether the battery is charging or not.

[0016] Using a transistor, rather than a relay-type controlled switch, allows the electrical track to be powered not in an 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 (in fact, 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 casing houses a cell cooling circuit electrochemical, 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 different features, variants and embodiments of the invention can be combined with each other in various ways as long as they are not incompatible or mutually exclusive. DETAILED DESCRIPTION OF THE INVENTION

[0024] The description that follows, 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] Regarding the attached drawings:

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

[0027] [Fig. 2] is an electrical diagram of various electrical components of the battery of accumulators in Figure 1;

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

[0029] [Fig. 4] is a diagram illustrating a method of controlling, according to the invention, a heating means equipping the battery of accumulators of figure 1.

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

[0031] Here, and preferentially, this traction battery 10 is intended for use within a motor vehicle.

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

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

[0034] As shown in Figure 1, the traction battery 10 has a housing 20 which houses all the other components referenced in this figure.

[0035] This case 20 is formed here 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 case 20 has an overall parallelepiped shape.

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

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

[0039] The traction battery 10 also includes 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 around 3 to 5 V. These cells are then connected in series to reach the voltage level required by the application.

[0042] Here, there are about a 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 external terminals of the traction battery 10 is approximately 400V. In practice, 96 cells are used here. Of course, the number of cells could be higher (around 200, for example) or lower.

[0043] In Figure 1, these electrochemical cells are not visible. However, they are shown to be arranged in several groups of cells called "modules 31". Eight modules 31, each containing twelve electrochemical cells, are shown here. These modules are electrically connected in series to form a pack of modules 31. Each module 31 has a frame that holds the cells together. This frame is open on its underside.

[0044] The 31 modules are distributed here 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 figure 2.

[0047] It includes, in particular, a battery management system, better known by 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. Specifically, 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 42 management system typically fulfills several functions, including: - 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 electrochemical cells, to prevent them from overheating or to allow them to rise rapidly in temperature when they are initially cold.

[0051] The battery 20 includes temperature sensors for this purpose, 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 case 20, based on other parameters (typically based on temperatures measured elsewhere in the case 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] We will therefore consider that the traction battery 10 includes several temperature sensors, some physical and others software.

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

[0057] Preferably, each module 31 will also include 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 greatest temperature gradient between the upper and lower faces of the electrochemical cells from pack 30.

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

[0061] This management system 42 and this calculator 99 are thus programmed to operate together. Hereafter, the term "calculation unit 98" will be used to refer to either one or both 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 includes a thick plate inside which a coolant circulation channel winds.

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

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

[0065] The cooling circuit conduit 50 has outlets at its ends that open out of the housing 20, allowing it to be connected to coolant inlet and outlet hoses. An external pump, separate from the housing 20, is then used to force the coolant to circulate through 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 takes 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 substrate is preferably flexible. For example, it consists of two superimposed plastic films (typically polyethylene terephthalate) sandwiching the electrical trace. These two films are very thin, in this case 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 substrate surface. It has two ends to which an electrical voltage can be applied so that the electrical trace heats up due to the Joule effect.

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

[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 can be anticipated that each heating layer 60 will have 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 separate 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, we will assume that a single electrical track is planned on a single heating layer.

[0078] This electrical track is designed to be powered by the electrochemical cells themselves, under the control of 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, in this case 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 the pulse is active (in the high state) relative to the total period of the signal.

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

[0084] Figure 2 schematically represents the electrical circuit 40 which allows the electrochemical cells of the pack 30 of modules 31 to be connected to different terminals.

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

[0086] Each pair of outdoor terminals, like the 30 pack, has 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 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 provided for 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 Figure 3.

[0090] It thus includes a sub-circuit 81 connected to the terminals of the controlled switch 43, which comprises a relay 82 and a resistor 83 connected in series. This sub-circuit 81 reduces the current surge observed when the vehicle is switched on. Indeed, if both 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 power 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 an external charging station for 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] One might expect 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 one of them fails.

[0098] We could also do without the controlled switch 93, but we would prefer to use one in case of failure of 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] Transistor 80 is controlled between a blocked state (which opens sub-circuit 90) and a conducting state (which closes 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 pack 30.

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

[0103] This process is designed to be implemented in loops, at regular time intervals, as soon as the vehicle wakes up (i.e., as soon as the two controlled switches 43 and 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 calculation 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 goal is for these electrical power levels to be as high as possible.

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

[0108] Thus, if either of these electrical powers is above a threshold (which amounts to: if the average temperature of the electrochemical cells is above 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 P has already been calculated C ib, in which case its value is retained. Either the process is looped for the first time since the vehicle was woken up (i=1), in which case the computing unit then determines a target heating power P C ib.

[0111] This target heating power PC ib 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= 1 ), this target heating power P C ib is defined at the maximum possible value, on the order of several kW.

[0113] The objective is then for the electrical track of the heating layer 60 to receive an electrical power equal to the target heating power P C ib.

[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 of different batteries manufactured using the same process, such that the electrical resistances of the tracks can vary by plus or minus 10% from the desired electrical resistance.

[0115] Furthermore, the voltage across the battery pack 30 can change very rapidly, for example during strong vehicle acceleration. It also varies depending on the battery's state of charge (SOC). 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 must be constantly adjusted so that the electrical trace receives electrical power equal to the target heating power P C ib.

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

[0118] It will be considered equal to the ratio between the intensity i C ib of the current required to achieve the target heating power P C ib, and the intensity i ma x maximum that the electrical track can receive.

[0119] The intensity i C ib is calculated here by dividing the target heating power P C ib by the voltage across the terminals of pack 30.

[0120] The intensity i ma x is calculated by dividing the voltage across the terminals of the 30 pack by the actual resistance of the electrical track.

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

[0122] It could be expected that transistor 80 would remain 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 preferentially, steps are planned to adjust 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 So threshold is in the range 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 achieve this, during step S3, a new target heating power P is to be defined. C ib, using a predetermined table. The new duty cycle is then calculated in the same way as above, based on this new target heating power P Cib. 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] Because the electrical track is only in contact 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, then it compares the largest difference with a threshold Si.

[0134] This threshold Si is in the range 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 achieve this, during step S5, a new target heating power P is to be defined. C ib, using a predetermined table. The new duty cycle is then calculated in the same way as above, based on this new target heating power P C ib. Once this new duty cycle has been calculated and applied to transistor 80, step S4 is repeated.

[0138] During an S6 step, 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 S2 threshold is in the range 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 achieve this, during step S7, a new target heating power P is to be defined. Cib, using a predetermined table. The new duty cycle is then calculated in the same way as above, based on this new target heating power P C ib. 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 the 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] Alternatively, the electrical track could be made of any electrically conductive material, typically copper.

Claims

DEMANDS

1. A battery (10) comprising a casing (20) which houses electrochemical cells and an electrochemical cell management system (42), characterized in that it comprises in the casing (20): - at least one heating layer (60) 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 (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 (10) and then to calculate a target heating power (P C (ib) depending at least on the state of charge (SOC) and the measured temperature, and wherein the transistor (80) is driven such that the electrical power received by said at least one heating layer (60) is equal to the target heating power (P C ib) .

7. A control method according to claim 5 or 6, wherein each electrochemical cell has a first face located on the side of said cell. minus a heating layer (60), it is planned to acquire a value representative of the temperature of the first face of at least one of the electrochemical cells, and in which the transistor (80) is driven 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.

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