ELECTROCHEMICAL BATTERY CELL WITH AN INTEGRATED FLAT HEAT PIPE

Abstract

The invention relates to a cell (10) for an electrochemical battery, comprising cathode elements connected to a first electrical terminal (21) and anode elements connected to a second electrical terminal (22), with the cathode and anode elements contained within an internal volume (V1) hermetically sealed by an enclosure, the first and second electrical terminals being arranged outside the internal volume, the cell comprising a pulsed heat pipe (1) with a first portion (11) arranged within the internal volume and a second portion forming a thermal terminal, the second portion (12) being arranged outside the internal volume. Figure 2

Description

Title of the invention: ELECTROCHEMICAL BATTERY CELL COMPRISING AN INTEGRATED FLAT HEAT PIPE

[0001] The invention relates to electrochemical batteries formed as an assembly of several battery cells, and to such an electrochemical cell for an electrochemical battery. The invention relates in particular, but not exclusively, to a lithium-ion type electrochemical battery, otherwise called a lithium-ion type electrochemical accumulator.

[0002] An electrochemical battery cell usually comprises electrochemical elements forming a cathode connected to a first electrical cathode terminal and electrochemical elements forming anode connected to a second electrical anode terminal, the electrochemical elements being contained in an envelope in order to isolate them from the external environment.

[0003] The electrochemical phenomena which occur during the charging and discharging of the battery cell give rise to a release of heat which must be evacuated outside the cell.

[0004] The optimal operation of electrochemical cells in terms of power and aging requires precise thermal management. Indeed, if the internal temperature is too high, the cells age prematurely even without being used in operation. Conversely, if the internal temperature is too low, the cells are unable to provide power because the electrical resistance is excessive.

[0005] Furthermore, the lack of homogeneity within a cell also has the consequence of accelerating aging due to the presence of localized temperature peaks.

[0006] It is known to cool the battery cell from the outside via the walls of the casing. It is also known to add heat drains present partly inside the thermal contact of the electrochemical elements to extract the calories as close as possible to their place of generation.

[0007] Some heat sinks operate on the principle of thermal conduction. Other heat sinks use a two-phase material, for example heat pipes. Conventional tubular heat pipes or thermosiphon-type heat pipes are limited by their geometry and mode of operation, and their application for cooling an electrochemical battery cell leaves something to be desired, particularly from the point of view of the performance of homogenizing the temperature at the heart of the electrochemical cell.

[0008] It should also be noted that in certain circumstances, in cold weather, the drain thermal can also be used to heat the electrochemical cell.

[0009] The inventors therefore sought to further improve the collection of calories inside an electrochemical battery cell and the homogenization of temperatures inside the electrochemical cell.

[0010] Furthermore, for a battery pack formed as an assembly of several cells, it is relevant to have independence of thermal behavior between adjacent cells, in order to prevent an undesirable thermal runaway occurring in one cell from quickly propagating to adjacent and neighboring cells. It is therefore necessary that the proposed solution is suitable for the function of independence of thermal behavior. It is also preferable that the proposed solution allows the electrochemical cell to be heated in the event of a temperature that is too low.

[0011] In view of these objectives, the invention provides an electrochemical battery cell, comprising cathode elements connected to a first electrical terminal and anode elements connected to a second electrical terminal, the cathode elements and the anode elements being contained in an interior volume hermetically delimited by an envelope, the first and second electrical terminals being arranged outside the interior volume, the cell extending generally in a main plane comprising a first direction and a second direction, the cell having a first dimension along the first direction and a second dimension along the second direction, the cell having a third dimension along a third direction perpendicular to the first and second directions, characterized in that the cell comprises at least one pulsed heat pipe comprising a first portion arranged in the interior volume and a second portion forming a thermal terminal,in that the second portion is arranged outside the interior volume, and in that the first portion of the heat pipe is flat and generally extends in the main plane.

[0012] Thanks to these arrangements, the pulsed heat pipe draws calories from the heart of the electrochemical cell and, due to its flat shape, it integrates well with the electrochemical cell, also of flat prismatic shape. An example of an electrochemical cell shape is a flat pocket or pouch with two main dimensions and low thickness, a shape known in the jargon as 'pouch'.

[0013] Advantageously, this makes it possible to obtain good temperature homogeneity throughout the electrochemical cell.

[0014] Furthermore, unlike a thermosiphon, the heat pipe operates regardless of the orientation of the battery cell.

[0015] It is noted that the surface of the first portion of the pulsed heat pipe can occupy a large part of the surface of the anode and cathode electrochemical elements in the main plane of the electrochemical cell, and the pulsed heat pipe takes calories almost everywhere in the volume of the electrochemical cell.

[0016] Regarding the term "thermal terminal", it designates a member whose function is to exchange calories with another member, here another member extrinsic to the electrochemical cell. The term "thermal terminal" covers both the case of a cooling terminal (evacuation of calories) and the case of a heating terminal (evacuation of frigories).

[0017] According to one aspect, the pulsed heat pipe comprises a plurality of internal channels, extending parallel to each other, each internal channel extending from the first portion to the second portion. Said internal channels transport the two-phase working fluid from the first portion to the second portion and vice versa.

[0018] The internal channels are fluidically connected at their ends at least to their immediate neighbors. The arrangement of the internal channels can form a coil looped back on itself.

[0019] The internal channels have a small transverse dimension, for example between 0.4 millimeters and 1 millimeter.

[0020] According to one aspect, the third dimension may be at least five times smaller than the first dimension and at least five times smaller than the second dimension. The cell thus has a flat form factor, favorable to a stack of cells. In addition, the shape correspondence between the second portion of the heat pipe and the electrochemical elements is favorable to good heat collection and good heat evacuation. For example, seen along the third dimension, the general shape of the first portion of the heat pipe is similar to the general shape of the body of the cell.

[0021] Furthermore, the third dimension can preferably be chosen to be at least ten times smaller than the first dimension and at least ten times smaller than the second dimension. The cell is thus very flat, and a large number of cells can therefore be assembled against each other in a battery pack, in particular with a series electrical connection.

[0022] According to one option, the envelope comprises a front wall and a back wall, their edges being hermetically joined, with further sealing ensured at the location of the passage of the electrical and thermal terminals. Thus, the electrochemical elements inside the interior volume of the cell are isolated from the external environment, in particular from humidity, or from any other chemical component.

[0023] According to an advantageous option, one of the front or back walls is formed by one face of the heat pipe. The pulsed heat pipe thus forms a natural reinforcement for the cell, and the material of the second specific wall forming the envelope is saved. Being rather rigid, the heat pipe forms a solid wall making it possible to avoid buckling of the cell in the event of mechanical stresses coming from adjacent cells.

[0024] According to an advantageous option, the heat pipe is in a middle position along the third direction. In other words, the first portion of the heat pipe is located in the thickness of the electrochemical part of the cathode elements and the anode elements, for example in a middle position of the thickness of the electrochemical cell. This allows for good balancing of the heat extraction. In addition, the heat pipe in the middle position makes it possible to prevent buckling of the cell in the event of mechanical stress exerted by the adjacent cells or in the event of the occurrence of internal overpressure.

[0025] According to one option, the thermal terminal is located on the opposite side with respect to the first and second electrical terminals. It is thus easy to organize on the one hand the electrical connections on the side of the electrical terminals and on the other hand the collection of calories on the thermal terminals, either by a solid collector or by a collector in liquid form as will be seen later.

[0026] According to an alternative option, it may be provided that the thermal terminal exits from a first side parallel to the first direction and that the first and second electrical terminals exit from a second side parallel to the second direction. Here too, in this configuration which can be described as 'orthogonal', it is thus easy to organize on the one hand the electrical connections on the side of the first direction and on the other hand an efficient heat exchange, in particular the collection of calories, on the thermal terminals on the side of the second direction.

[0027] According to one option, two pulsed heat pipes may be provided, one next to the other in the main plane. This configuration may be advantageous for balancing the withdrawal of calories or even ensuring redundancy if one of the pulsed heat pipes were to fail.

[0028] According to one option, it may be provided that each of the two electrical terminals is in contact with the thermal terminal outside the casing. As a result, the pulsed heat pipe cools not only the electrochemical elements, but also directly the connection terminal conductors.

[0029] According to one option, several thermal terminals may be provided, for example two or three, each emerging on a respective side of the electrochemical cell. This provides great flexibility of arrangement for designing this or that type of battery pack.

[0030] The invention also relates to an electrochemical battery comprising a plurality of cells as described above, arranged one after the other and with a thermal insulating separator between two successive cells. The cells are electrically connected in series, in daisy chain mode, which makes it possible to obtain a desired voltage for the battery pack. The thermal insulating separator thermally insulates the adjacent cells to prevent possible propagation of an em- thermal swing from near to near.

[0031] The invention also relates to an electrochemical battery in which the cells are received in a tank filled with dielectric liquid in contact with the thermal terminals of the cells. As a result, efficient cooling is obtained, with very good contact between the dielectric liquid and the parts to be cooled or heated respectively, the exchange of calories can occur in small interstices and in places that are difficult to access for a solid heat pipe.

[0032] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which: - [Fig.l] schematically illustrates in front view an example of an electrochemical battery cell according to the present invention; - [Fig.2] schematically illustrates in profile view the electro battery cell chemical of [Fig.l]; - [Fig.3] schematically illustrates an electrochemical battery pack comprising a plurality of cells according to the present invention, in front view; - [Fig.4] schematically illustrates the electrochemical battery pack of [Fig.3] , in profile view; - [Fig.5] schematically illustrates in detail the ends of the cell of [Fig.l] with the electrical terminals and the thermal terminal; - [Fig.6] schematically illustrates an example of a pulsed heat pipe; - [Fig.7] schematically illustrates a first variant of battery cell electrochemical; - [Fig.8] schematically illustrates a second variant of battery cell electrochemical; - [Fig.9] schematically illustrates, for a third variant, the ends of the electrochemical battery cell; - [Fig. 10] schematically illustrates a view of one end of a fourth variant of the electrochemical battery cell.

[0033] An electrochemical battery cell 10 is schematically illustrated in Figures 1, 2 and 5. The electrochemical battery cell 10 comprises cathode elements 41 and anode elements 42.

[0034] Between the cathode elements 41 and the anode elements 42 are arranged one or more separating membranes making it possible to electrically isolate the cathode elements and the anode elements. At the same time, the separating membranes allow electrons to pass between the cathode and the anode or vice versa.

[0035] According to an alternative, an electrolyte in the form of a gel or liquid may be provided allowing the electrons to pass between the cathode and the anode or vice versa, the cathode elements and anode elements not being in direct contact.

[0036] A basic stack formed by a cathode element, a separating membrane and an anode element may be provided. This basic stack may be repeated N times, with a separating membrane interposed between two adjacent stacks.

[0037] The cathode and anode elements are in the form of thin layers. The number of layers of electrochemical elements and membranes can range from one to several.

[0038] All the cathode elements 41 are connected by an electrical connection element to a first electrical terminal 21, conventionally designated the positive terminal. All the anode elements 42 are connected by another electrical connection element to a second electrical terminal 22 conventionally designated the negative terminal.

[0039] The cathode elements and the anode elements are contained in an interior volume VI hermetically delimited by an envelope 3.

[0040] The envelope 3 contains the cathode elements 41 and the anode elements 42.

[0041] The first and second electrical terminals are arranged outside the interior volume VL

[0042] A Cartesian reference XYZ is defined in the space in which the examples of cells presented in the figures are placed.

[0043] The cell 10 generally extends in a main plane denoted XY which comprises a first direction X and a second direction Y. The third direction denoted Z is perpendicular to the first and second directions.

[0044] The cell has a first dimension LX along the first direction X and a second dimension LY along the second direction Y. The cell has a third dimension E2 along the third direction Z.

[0045] The second dimension LY is called length, the first dimension LX is called width, the third dimension is called thickness E2.

[0046] The third dimension E2 is at least five times smaller than the first dimension LX and at least five times smaller than the second dimension LY.

[0047] E2 can be between 4 mm and 12 mm. LY can be between 10 cm and 30 cm. LX can be between 5 cm and 45 cm. Of course, the principle of the present invention works whatever the dimensions LX and LY.

[0048] According to one option, the third dimension E2 is at least ten times smaller than the first dimension LX and at least ten times smaller than the second dimension LY. Of course, the principle of the present invention works regardless of the form factor.

[0049] In other words, the electrochemical cell 10 has a flat prismatic shape, with a homogeneous or even constant thickness over the width and length of the body of the cell.

[0050] According to the first embodiment presented, the envelope 3 comprises a front wall 31 and a back wall 32. According to the first exemplary embodiment, the front and back walls are substantially symmetrical with respect to the XY plane.

[0051] The front wall and the back wall are connected to each other at their edge by a weld zone 33. This weld zone forms a hermetic barrier. Instead of a weld, in the junction zone, structural bonding may be provided. Any other means of hermetic assembly may of course be used within the scope of the present invention.

[0052] At the location of the passage of the connecting elements of the electrical terminals 21, 22, a stuffing box function is provided to achieve the watertight closure of the interior volume in this zone.

[0053]

[0054] Advantageously according to the present invention, provision is made for the addition of a pulsed heat pipe in the electrochemical system of the cell.

[0055] The pulsed heat pipe comprises a first portion 11 arranged in the interior volume and a second portion 12 arranged outside the interior volume VL. The first portion of the heat pipe is flat and generally extends in the main plane XY, preferably in accordance with the geometry of the layers of cathode and anode elements.

[0056] The second portion 12 forms a thermal terminal for the electrochemical cell. This thermal terminal is in the form of a plate. Both sides of this plate can be used for thermal exchanges.

[0057] The second portion 12 emerges from the interior volume VI and projects from the hermetic junction zone by a projection distance of between 1 and 5 cm. Here, in the illustrated case, the length of the plate is dictated by the width LX of the cell.

[0058] It should be noted that the second portion 12 can be curved, or even bent at 90°, so as to reduce the overall size and / or to conform to a heat collector of any type.

[0059] The heat pipe may have a generally parallelepiped shape with a small thickness El, namely between 0.3 millimeters and 1 millimeter. However, the principle of the present invention works regardless of the form factor and regardless of the thickness EL.

[0060] [Fig.6] illustrates the operating principle of the pulsed heat pipe 1. The system is filled with a working fluid which, due to the capillary dimensions, is arbitrarily distributed into a succession of vapor pockets and liquid plugs. This is a passive cooling system, i.e. one that operates without external energy other than the thermal power it dissipates.

[0061] The pulsed heat pipe 1 comprises a plurality of internal channels 6. The internal channels extend along a longitudinal direction W of the pulsed heat pipe. At a first longitudinal end, there is a first heat exchange zone 61 which can be either the cold source or the hot source of the heat pipe. At the second end, opposite in the longitudinal direction W, there is a second heat exchange zone 62 which plays the opposite role to the first zone 61.

[0062] The working fluid may be methanol, acetone, carbon dioxide, without excluding another fluid.

[0063] It is preferable to choose a dielectric fluid, for example from known refrigerating fluids or refrigerants.

[0064] The cross-section of the internal channels is small, typically less than 1mm2.

[0065] The internal channels 6 together form a fluid circuit of closed and predetermined volume in which a fluid in two-phase phase is trapped under normal conditions of use of the heat pipe (temperature and pressure).

[0066] In the example illustrated, the arrangement of the internal channels 6 is formed as a serpentine which is looped back by a transverse collector 64. With the exception of the end channels, each internal channel is connected to its neighbor by a U-shaped connector marked 63.

[0067] Liquid plugs 60 form inside the internal channels 6. When a heat source is applied to the zone called the evaporator and a cold source to a second zone, called the condenser, a chaotic movement of the liquid plugs 60 and vapor pockets appears.

[0068] At the evaporator zone, the phenomena of nucleation, boiling and growth of bubbles generate an increase in pressure which will cause the bubble / plug trains to move. This phenomenon is aided by a depression induced by the recession of the vapor pockets in the condenser zone (condensation of the vapor).

[0069] In practice, to produce a pulsed heat pipe of the type described above, it is possible to use a grooved extruded metal profile, the grooves forming the internal channels, ribs forming walls between the adjacent channels. The end returns are formed by locally removing the rib separating two adjacent grooves.

[0070] In addition, the pulsed heat pipe has a structural rigidity which reinforces the front and back walls of the envelope to avoid or at least minimize buckling of the elements of the electrochemical cell under the effect of mechanical stress or overpressure which may appear inside the envelope.

[0071] The pulsed heat pipe is a passive system, without a pump or other driving element.

[0072] The pulsed heat pipe being reversible, it can also heat the interior volume VI of the cell. All that is required is that the internal temperature of the cell is lower than the temperature of the collector which contacts the thermal terminals (or of the liquid which bathes the thermal terminals).

[0073] In Figures 3 and 4, an electrochemical battery pack 9 is shown comprising a plurality of cells 10.

[0074] The cells are arranged one after the other in the third direction Z. A thermal insulating separator 8 is interposed between two successive cells. This thermal insulator makes it possible to ensure independence of thermal behavior between two adjacent cells. The thermal conduction resistance provided by this thermal insulating separator 8 is quite high, and therefore a runaway (known by the English term 'thermal runaway') between adjacent cells is avoided.

[0075] The cathode 21 and anode 22 terminals are offset in the first direction X as seen in [Fig.3] and offset in the second direction Y as seen in [Fig.4]. Connection jumpers 92 allow the '+' terminal of one cell to be connected to the terminal of the neighboring cell.

[0076] In the example illustrated, the electrochemical battery 9 is contained in a tank 90. ​​In this tank, a dielectric liquid 7 is placed in which at least the thermal terminals 12 of the cells are immersed. The dielectric liquid 7 collects the calories on all the thermal terminals and discharges them into an extrinsic cold source.

[0077] [Fig.7] shows a variant configuration of the electrochemical cell. According to this variant, the second portion 12 of the pulsed heat pipe exits on the long side on the right, while the electrical edges exit on the short side at the top.

[0078] In other words, in general, the thermal terminal exits from a first side parallel to the first direction and the first and second electrical terminals exit from a second side parallel to the second direction.

[0079] In addition, in an embodiment not shown in the figures, there may be several thermal terminals, for example two or three, each emerging respectively on one side of the electrochemical cell.

[0080] [Fig.8] shows another variant of the configuration of the electrochemical cell. Two pulsed heat pipes are arranged next to each other in the main plane. The first heat pipe 1 is on the left with the thermal terminal 12 below and the second heat pipe 101 is on the right with the thermal terminal 112 below. Both thermal terminals are in contact with the cold source of the system.

[0081] In another variant not shown in the figures, two heat pipes could be arranged in parallel, one facing the other throughout the thickness, eg two first portions in the thickness E1 of the heat pipe. Layers of electrochemical elements are interposed between the two heat pipes. Depending on the thickness of the heat pipe, two heat pipes, or more than two, could thus be stacked to obtain the calories throughout the thickness.

[0082] [Fig.9] shows another variant configuration of the electrochemical cell. According to this variant, the front wall of the casing is formed by the heat pipe 1 itself. The heat pipe 1 comprises an external face 14 and an internal face 15. It is the external face 14 which acts as an envelope.

[0083] The dorsal face 32 is made of an aluminum wall as in the previous case.

[0084] More generally, it is understood that one of the walls, front or back, can be formed by the heat pipe 1 itself, in particular one face of the heat pipe, the one located on the outside.

[0085] The hermetic joint between the back face 32 and the internal face 15 of the heat pipe is produced by welding, structural bonding or other equivalent technique.

[0086] [Fig. 10] shows another variant configuration of the electrochemical cell, in which the electrical terminals 21, 22 are in thermal contact with the thermal terminal 12 outside the interior volume VL.

[0087] Of course, in this case, it is necessary to provide an insulating coating at the interface between each of the electrical terminals and the thermal terminal.

Claims

Claims

1. An electrochemical battery cell (10), comprising cathode elements connected to a first electrical terminal (21) and anode elements connected to a second electrical terminal (22), the cathode elements and the anode elements being contained in an interior volume (VI) hermetically delimited by an envelope (3), the first and second electrical terminals being arranged outside the interior volume, the cell extending generally in a main plane (XY) comprising a first direction (X) and a second direction (Y), the cell having a first dimension (LX) along the first direction and a second dimension (LY) along the second direction, the cell having a third dimension (E2) along a third direction (Z) perpendicular to the first and second directions,characterized in that the cell comprises at least one pulsed heat pipe (1) comprising a first portion (11) arranged in the interior volume and a second portion (12) forming a thermal terminal, in that the second portion (12) is arranged outside the interior volume, and in that the first portion of the heat pipe is flat and generally extends in the main plane (XY).,

2. Cell according to claim 1, characterized in that the pulsed heat pipe comprises a plurality of internal channels (6), extending parallel to each other, each internal channel extending from the first portion (11) to the second portion (12).

3. Cell according to any one of claims 1 to 2, characterized in that the third dimension (E2) is at least five times smaller than the first dimension (LX) and at least five times smaller than the second dimension (LY).

4. Cell according to any one of claims 1 to 3, characterized in that the envelope comprises a front wall (31) and a back wall (32), their edges being hermetically joined, with additional sealing at the location of the passage of the electrical and thermal terminals.

5. Cell according to claim 4, characterized in that one of the front or back walls is formed by a face of the heat pipe.

6. Cell according to claim 4, characterized in that the heat pipe is in the middle position in the third direction (Z).

7. Cell according to any one of claims 1 to 6, characterized in that the thermal terminal is on the opposite side from the first and second electrical terminals.

8. Cell according to any one of claims 1 to 7, characterized in that the thermal terminal exits from a first side parallel to the first direction and the first and second electrical terminals exit from a second side parallel to the second direction.

9. Electrochemical battery (9) comprising a plurality of cells (10) according to any one of claims 1 to 8, arranged one after the other and comprising a thermal insulating separator (8) between two successive cells.

10. Electrochemical battery (9) according to claim 9, characterized in that the cells (10) are received in a tank (90) filled with dielectric liquid (7) in contact with the thermal terminals of the cells.

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