Heating layer for rechargeable batteries

Abstract

The invention relates to a heating layer (60) for a storage battery, comprising a support (61) and at least one electrical track (62) carried by the support (61) and adapted to emit heat by Joule heating when supplied with an electric current. According to the invention, the electrical track has at least a first zone (Z1) in which it is adapted to emit more heat than in a second zone (Z2). Figure for the abstract: Fig. 4

Description

Title of the invention: Heating layer for rechargeable batteries Technical field of the invention

[0001] The present invention relates generally to accumulator batteries.

[0002] It relates more particularly to a heating layer for heating electrochemical cells of a battery of accumulators.

[0003] It also relates to a battery of accumulators comprising such a heating layer.

[0004] It also relates to a motor vehicle comprising such a battery of accumulators.

[0005] The invention finds a particularly advantageous application in electric or hybrid powered motor vehicles. State of the art

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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 cooling circuit in contact with the fluid.

[0011] However, in the case where the fluid was of the refrigerant type, the use of an immersion heater would be unsuitable because it would cause a change in the state of the fluid, from the liquid state to the gaseous state, which would cause a failure of the system.

[0012] On the contrary, in the case where the fluid was glycol water, the efficiency would prove to be 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.

[0013] Finally, even if one or the other of these solutions were used, uneven heating of the electrochemical cells would be observed. If one of the cells has a temperature lower than that of all the other cells, it severely limits the overall capacity of the battery to supply or store energy. Presentation of the invention

[0014] In order to remedy the aforementioned drawbacks of the prior art, the present invention proposes to heat the traction battery cells differently.

[0015] More particularly, the invention proposes a heating layer for a battery comprising a support and at least one electrical track which is carried by the support and which is adapted to emit heat by Joule effect when supplied with electric current, the electrical track having at least a first zone in which it is adapted to emit more heat than in a second zone.

[0016] Such an electrical track has very low thermal inertia, which allows the battery cells to heat up very quickly.

[0017] 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.

[0018] However, it is observed that if the electrical track were homogeneous, and therefore designed to emit heat with a homogeneous power per unit area over the entire surface of the support, non-homogeneous heating of the electrochemical cells would be observed.

[0019] Typically, when the cells are distributed into different modules, and are stacked on top of each other within each module, it is observed that the cells located at the ends of the stacks heat up less quickly than those located in the center.

[0020] This is why the present invention proposes an electrical track whose characteristics are different in the first and second zones, so as to be able to heat more the cells which need it most.

[0021] Other advantageous and non-limiting features of the heating layer according to the invention, taken individually or in all technically possible combinations, are as follows: - the electric track is thinner in the first zone than in the second zone; - the electrical track covers the support with a greater density in the first zone than in the second zone; - the electric track is made of different materials in the first zone and in the second zone; - Two initial zones are planned, located on either side of the second zone.

[0022] The invention also relates to a battery of accumulators comprising a case which houses electrochemical cells and, in the case, at least one heating layer as mentioned above.

[0023] Other advantageous and non-limiting features of the accumulator battery according to the invention, taken individually or in all technically possible combinations, are as follows: - at least part of the electrochemical cells are stacked against each other to form a stack, and the first zone is located at at least one of the ends of said stack; - a transistor and an electrochemical cell management system are planned which is programmed to drive the transistor in such a way as to modulate the electrical power received by said at least one electrical track in pulse width; - the housing contains a cooling circuit for the electrochemical cells, and said at least one heating layer is located between said cooling circuit and at least part of said electrochemical cells.

[0024] The invention finally relates to a motor vehicle comprising an electric traction machine, and a battery of accumulators as mentioned above, adapted to supply current to the electric traction machine.

[0025] 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

[0026] 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.

[0027] On the attached drawings:

[0028] [Fig-1] is a schematic exploded perspective view of a battery of accumulators conforming to the invention;

[0029] [Fig.2] is an electrical diagram of various electrical components of the battery of accumulators of the [Fig.l];

[0030] [Fig.3] is a schematic cross-sectional view of part of the battery of accumulators of the [Fig.l];

[0031] [Fig.4] is a schematic top view of a heating layer of the battery of accumulators of the [Fig.l].

[0032] Figure [Fig. 1] shows an exploded view of a battery of accumulators, hereinafter referred to as traction battery 10.

[0033] Here, and preferably, this traction battery 10 is intended to be used within a motor vehicle.

[0034] 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.

[0035] 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.

[0036] As shown in [Fig.1], the traction battery 10 includes a housing 20 which accommodates all the other components referenced in this figure.

[0037] 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.

[0038] 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.

[0039] This case 20 is designed to be hermetically sealed.

[0040] In the remainder of the 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.

[0041] The traction battery 10 also comprises a plurality of cells electrochemicals 32;.

[0042] These could typically be lithium-ion type cells, but other variants would be conceivable.

[0043] Each electrochemical cell 32; here presents 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.

[0044] 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.

[0045] In [Fig. 1], these electrochemical cells 32 are not visible. However, it can be seen that they are distributed in several groups of cells called "modules 31". Here, eight modules 31 of twelve electrochemical cells 32 are provided, which are electrically connected to each other in series, so as to form a pack 30 of modules 31.

[0046] As shown in [Fig. 3], each module 31 has a frame 33 which holds the cells together. This frame 33 is open on its lower face. Preferably, it is also open on its upper face. It therefore has four lateral walls which surround the twelve electrochemical cells 32.

[0047] Each electrochemical cell 32 has a thin parallelepiped shape, with a bottom turned towards the base plate 21, an opposite apex from which emerge its two connection terminals, two sides and two main faces.

[0048] Within each module 31, the twelve electrochemical cells 32 are stacked one against the other, main face to main face. They thus form a stack of twelve electrochemical cells 32 (where i is an index from 1 to N, with N here equal to twelve). In the following, the first and last electrochemical cells 32, 32N will be distinguished from the stack of other electrochemical cells. They will hereafter be called the end electrochemical cells 32, 32N.

[0049] As shown in [Fig.1], the modules 31 are here distributed side-by-side, on two separate lines.

[0050] 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 modules 31 of electrochemical cells 32i.

[0051] This electrical circuit 40 is partly shown in [Fig.2].

[0052] It includes, in particular, a battery management system 42, better known as the acronym BMS (from the English "battery management system").

[0053] This management system 42 comprises a processor (CPU), memory, and various input and output interfaces. It typically performs several functions, including: - continuously monitor the individual voltages of each 32i 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 32i electrochemical cells.

[0054] Here, as will be described below, it also ensures the thermal management of the electrochemical cells 32i, to prevent them from overheating or to allow them to rise rapidly in temperature when they are initially too cold.

[0055] The battery accumulator 20 includes for this purpose temperature sensors enabling the determination of temperature values ​​in different areas of the housing 20.

[0056] These could be physical sensors, i.e. sensors positioned in specific areas of the housing 20 to measure the desired temperature values.

[0057] 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 32i, the current that these cells deliver...).

[0058] In practice, here, a single temperature sensor will be provided in each module 31, placed above one of the electrochemical cells 32i, and the management system 42 will be programmed to calculate several temperature values ​​in each module 31.

[0059] Thanks to its interface, the management system 42 can receive higher level instructions from a computer 99 external to the housing 20.

[0060] 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.

[0061] When they deliver or receive current, the electrochemical cells 32 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 comprises a thick plate inside which a conduit for circulating a coolant runs.

[0062] This cooling circuit 50 therefore has a heat exchanger function.

[0063] It is located here on the lower side of the modules 31, against the base plate 21 of the housing 20.

[0064] 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 compressor The housing 20 is then designed to force the circulation of the coolant in the circuit. Alternatively, if the coolant used were not a refrigerant but glycol water, a pump would be used instead of this compressor.

[0065] In the context of the invention, the traction battery 10 comprises at least one heating layer 60.

[0066] The heating layer(s) 60 are interposed here between the cooling circuit 50 and the modules 31.

[0067] The maximum power emitted by the entire assembly of said at least one heating layer 60 is greater than or equal to 1000 Watts. Here it is equal to 3500 Watts.

[0068] Each heating layer 60 is preferably located as close as possible to the modules 31. As shown in [Fig.3], only a thermal interface 59 facilitating heat exchange is provided between the electrochemical cells 32i and each heating layer 60. Here, this thermal interface 59 is in the form of a thermal paste.

[0069] As shown in [Fig.4], each heating layer 60 is in the form of a sheet, and therefore comprises a support 61 and at least one electrical track 62 carried by the support 61.

[0070] The support 61 is made of an electrically insulating material.

[0071] This support 61 is preferably flexible. For example, it is formed of two superimposed plastic films (typically polyethylene terephthalate) sandwiching the electrical track 62. These two films have very small thicknesses, here on the order of a quarter of a millimeter.

[0072] Each electrical track 62 is, on the contrary, made of an electrically conductive material. By "electrical track," we mean a conductive path used to carry electric current. Such a track is therefore devoid of any electronic components.

[0073] Each electrical track 62 winds between these two films so as to cover at least 50% of the surface of the support 61. It has two ends to which it is possible to apply an electrical voltage so that the electrical track heats up by Joule effect.

[0074] Here, as shown in [Fig.1], the modules 31 being 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).

[0075] Each heating layer 60 therefore extends under four modules 31.

[0076] Alternatively, a single heating layer could be provided, or on the contrary a heating layer under each module.

[0077] 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.

[0078] Alternatively, each heating layer 60 may be provided to have several distinct electrical tracks connected to each other (preferably in series).

[0079] In any case, the electrical track(s) are distributed so as to be able to heat the different electrochemical cells 32; of the modules 31 of the pack 30.

[0080] In [Fig.4], a portion of one of the heating layers 60 extending under one of the modules 31 is shown. This portion therefore has a length and width equal to those of this module 61.

[0081] In the following description, the expressions "part of electrical track 62" and "part of support 61" will therefore designate the parts of the electrical track 62 and of the support 61 which extend under the aforementioned module 31.

[0082] Thus, this portion of the electrical track 62 meanders so as to cover at least 50% of the surface of this support portion 61. It could meander in various ways on it. In practice, here it forms back-and-forth loops across the width of the support portion 61, extending along the entire length of this support portion 61.

[0083] Here, the electrical track portion 62 has four ends 63, allowing its connection between two other portions of the electrical track 62 of the heating layer 60.

[0084] According to an essential feature of the invention, the electrical track portion 62 has at least a first zone Z1 in which it is adapted to emit more heat than in a second zone Z2. The objective is that the thermal power per unit area (e.g., per mm2) emitted by the electrical track portion 62 is not identical from one zone to another, and that it has a non-zero value in these zones when it is supplied with a substantially constant electrical power.

[0085] In practice, depending on the configuration of the electrochemical cells 32; in the housing 20, some will naturally be cooled more than others.

[0086] In the example shown in [Fig.3], heat is naturally dissipated more away from the end electrochemical cells 32b 32N which are in contact with the frame 33 (by conduction) than from the other electrochemical cells 322-32n_i since the latter are sandwiched between two hot electronic cells.

[0087] Thus, when the electrical track portion 62 is energized, it becomes necessary to supply more heat to the end electrochemical cells 32i, 32n than the other electrochemical cells 322-32x । so that the temperatures of all these cells remain homogeneous.

[0088] Therefore, in the illustrated example, the electrical track part 62 has two first zones ZI located under the end electrochemical cells 32b 32N, in which it is adapted to emit more heat than in a second central zone Z2, located between the first two zones Zl, under the other electrochemical cells 322-32n_i.

[0089] Here, two types of zone Z1, Z2 are provided within each of which the thermal power emitted per unit area is homogeneous but between which the values ​​of thermal power per unit area differ.

[0090] Of course, alternatively, more types of zones could be provided. Typically, intermediate zones could be provided between zones Z1 and Z2, at which point the electrical track section 62 would emit intermediate heat.

[0091] In order to be able to emit a thermal power per unit area that varies from one zone to another, the electrical track portion 62 has different geometric characteristics or intrinsic properties from one zone to another.

[0092] It can therefore exhibit a thermal resistance or conductivity that varies from one area to another.

[0093] Here, three main embodiments are envisaged to vary the thermal power per unit area emitted by the part of the electric track 62 from one zone to another when this part of the track is traversed by an electric current of equal intensity over its entire length.

[0094] The first mode consists of refining the electrical track section 62 more in the first zone than in the second zone.

[0095] Thus, it can be predicted that the section of track will have a lower width and / or height in each first zone Zl.

[0096] The second embodiment consists of densifying the electric track section more in each first zone Z1 than in the second zone Z2.

[0097] This is the embodiment illustrated in [Fig. 4]. In this embodiment, the gap between two parallel sections of the electrical track is thus smaller in each first zone Z1 than in the second zone Z2. The objective is therefore to ensure that the surface density of the support occupied by the electrical track is greater in each first zone Z1 than in the second zone Z2.

[0098] The third embodiment consists of using different materials to manufacture the electrical track portion in the different zones. For example, the electrical track portion 62 could be made of copper (whose resistivity at 20°C is 17.109 Qm) in the second zone Z2 and in aluminium (whose resistivity at 20°C is 28.109 Qm) in each first zone Zl.

[0099] Of course, these three embodiments are not mutually exclusive. Thus, the first and second embodiments, or the first and third embodiments, or the second and third embodiments, could be used jointly. It would also be possible to use these three embodiments in combination.

[0100] The electrical track 62 is intended to be supplied with electrical current by the electrochemical cells 32i themselves, under the control of the computing unit 98.

[0101] This control is carried out here using a transistor 80, in pulse width modulation.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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 much longer lifespan than a relay and a much shorter response time.

[0106] Figure 2 shows a schematic representation of the electrical circuit 40 allowing the electrochemical cells 32; from the pack 30 of modules 31 to be connected to different terminals.

[0107] 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.

[0108] Each pair of outdoor terminals has, like the 30 pack, a positive terminal and a negative terminal.

[0109] 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 adapted to open the circuit as soon as the current intensity exceeds a safety threshold. Here, a single controlled switch 43 is provided. connected between the positive terminal of pack 30 and the two positive terminals, and a protection fuse 44, 45 specific to each of these positive terminals.

[0110] 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.

[0111] The electrical circuit 40 also includes other sub-circuits.

[0112] It thus includes a sub-circuit 81 connected to the terminals of the controlled switch 43, which comprises a relay and a resistor 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, smooths out the current surge before the controlled switch 43 is closed.

[0113] 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 and a terminal by 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.

[0114] 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 and a terminal by which it is adapted to be connected to a current charger such as a charging station external to the vehicle.

[0115] In the context of the invention, the electrical circuit 40 includes a sub-circuit 90 specially designed to enable the electrochemical cells 32 of the pack 30 to supply each electrical track 62 of each heating layer 60 with electric current.

[0116] This sub-circuit 90 has a pair of terminals 73 connected to each electrical track 62.

[0117] One of these terminals is connected to the output of the controlled switch 43, via a fuse, a relay-type controlled switch, and a current sensor.

[0118] The other is connected to the output of the controlled switch 46, via a fuse (here that of the sub-circuit 84), a current sensor and the aforementioned transistor.

[0119] It could be envisaged that this subcircuit 90 would have only one current sensor, but it is preferable to use two separate ones for safety reasons in case one of them fails. The controlled switch could also be omitted, but it is preferable to use one in case of failure of transistor 80.

[0120] The present invention is in no way limited to the embodiments described and represented, but a person skilled in the art will be able to make any variation in accordance with the invention.

[0121] Thus, the areas in which the heating layer emits the most heat can be distributed very differently from that illustrated in [Fig.4], taking into account the way in which the electrochemical cells will be housed in the casing.

[0122] By way of example, the cells of the same module could be located at varying distances from each other, with a compressible layer interposed, for instance, between the two cells located closest to the center of the module. In this case, the track could be designed to heat these two cells more effectively, in order to compensate for the heat losses they will experience due to the presence of this compressible layer.

[0123] As another example, it could be foreseen that not all cells will have the same contact area with the heating layer. In this event, the electrical track could be designed to deliver more heat to the cell with the smallest contact area.

Claims

Demands

1. Heating layer (60) of accumulator battery (10) comprising a support (61) and at least one electrical track (62) which is carried by the support (61) and which is adapted to emit heat by Joule effect when supplied with electric current, the electrical track (62) having at least a first zone (Z1) in which it is adapted to emit more heat than in a second zone (Z2).

2. Heating layer (60) according to claim 1, wherein the electrical track (62) is thinner in the first zone (Z1) than in the second zone (Z2).

3. Heating layer (60) according to claim 1 or 2, wherein the electrical track (62) covers the support (61) with a greater density in the first zone (Z1) than in the second zone (Z2).

4. Heating layer (60) according to any one of claims 1 to 3, wherein the electrical track (62) is made of different materials in the first zone (Z1) and in the second zone (Z2).

5. Heating layer (60) according to any one of claims 1 to 4, wherein two first zones (Z1) are provided situated on either side of the second zone (Z2).

6. Accumulator battery (10) comprising a case (20) which houses electrochemical cells (320), characterized in that it comprises in the case (20) at least one heating layer (60) according to any one of claims 1 to 5.

7. Accumulator battery (10) according to claim 6, wherein at least a portion of the electrochemical cells (32,) are stacked against each other to form a stack, and wherein the first zone (Z1) is located at at least one of the ends of said stack.

8. Accumulator battery (10) according to claim 6 or 7, wherein a transistor (80) and an electrochemical cell (32) management system (42) are provided, which is programmed to drive the transistor (80) so as to modulate the electrical power received by said at least one electrical track (62) in pulse width.

9. A battery (10) according to any one of claims 6 to 8, wherein the casing (20) houses a cooling circuit (50) for the electrochemical cells (32), and wherein said at least one

10. A heating layer (60) is located between said cooling circuit (50) and at least a portion of said electrochemical cells (32). A motor vehicle comprising an electric traction machine, characterized in that it comprises a battery of accumulators (10) according to any one of claims 6 to 9, adapted to supply current to the electric traction machine.

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