Battery comprising at least one stack of electrical cells and an associated elastic play recovery device

Abstract

This electrical energy storage battery (1) comprises at least one stack (7) of electrical cells (6) and a casing having a base (3) on which said stack (7) of battery cells (1) is fixed. The battery (1) comprises at least two compression plates (8) arranged on either side of the stack, means for fixing the compression plates (8) to the base (3), at least one tie rod (12) capable of compressing the compression plates (8) against the cells (6) of the stack (7), and at least one elastic device (15) for compensating for play in the stack in a direction of dimensional variation of the stack. Figure for the abbreviation: [Fig 3]

Description

Title of the invention: Battery comprising at least one stack of electric cells and an associated elastic play recovery device Technical field

[0001] The present invention relates to the storage of electrical energy, in particular in the field of aeronautics. It relates generally to the storage of electrical energy, for applications in which mass is an important issue such as an application in aeronautics. Previous techniques

[0002] Conventionally, in the field of aeronautics, the storage of electrical energy is carried out by means of low voltage Lithium-Ion batteries, typically a voltage lower than 120V.

[0003] The term battery means a set of individual modules each comprising power elements arranged in series and / or in parallel in order to achieve the desired electrical voltage and electrical capacity.

[0004] Modern aircraft have increasing electrical power requirements, which requires batteries to be configured accordingly. Indeed, climate change is a major concern for many legislative and regulatory bodies around the world. Various restrictions on carbon emissions have been, are being, or will be adopted by various states.

[0005] Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

[0006] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. Consequently, the Applicant is constantly working to reduce its climate impact by using methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible, in order to reduce the environmental footprint of its activity.

[0007] This sustained research and development work covers new generations of aircraft engines, the lightening of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to ensure propulsion, and finally aeronautical biofuels.

[0008] In order to provide the electrical power required in the aircraft network while minimizing the weight of the electrical equipment, it is advantageous to increase the voltage of the batteries, for example at 800 V.

[0009] Inside high-voltage batteries, the power elements or electrical cells of the battery are generally grouped into modules, each of which contains a certain number of cells, including mechanical fixing, electrical connection and possibly thermoregulation devices.

[0010] In order to improve the integration of the battery in terms of volume and mass, it is usual to stack the cells within the battery module along a stacking axis.

[0011] However, depending on the chemistry of the cells, it is necessary to take into account of a possible significant variation in the thickness of the cells along the stacking axis during a charge and discharge cycle, otherwise there is a risk of damage to the structure of the cells, or even to the structure that holds them.

[0012] Conventionally, taking into account this risk of dimensional variation involves layers of foam interposed between the cells, along the stacking axis, which allow a certain degree of deformation. Thus, the foam layers follow the swelling and shrinkage of the cells while returning a pressure compatible with the structure of the cells.

[0013] However, the mechanical characteristics of foams sometimes lead to significant pressure increases which require increasing the number of foam layers, and which therefore negatively affect the integration balance in terms of volume and mass. In addition, the mechanical characteristics of foams can vary with their aging which can lead to permanent deformations of the foams. Statement of the invention

[0014] The aim of the invention is therefore to propose an electrical energy storage battery, in particular for an aircraft, whose integration in terms of volume and mass is improved while taking into account the dimensional variation of the electrical cells during the charge and discharge cycles. In particular, a battery module structure is sought which allows a certain variation in the thickness of the cells along their stacking axis without risking damage or loss of mechanical integrity of the cells.

[0015] The subject of the invention is an electrical energy storage battery comprising at least one stack of electrical cells and a housing comprising a base on which the stack of the battery is fixed.

[0016] The battery comprises at least two compression plates arranged on either side of said stack, means for fixing said compression plates to the base, at least one tie rod capable of compressing the compression plates against the cells of the stack, and at least one elastic device for taking up play of stacking in a direction of dimensional variation of the stack.

[0017] Preferably, each elastic device comprises at least one compressed spring between a pair of support pieces substantially perpendicular to the direction of dimensional variation of the stack. Such an elastic device makes it possible to absorb any dimensional variation of the stack by a variation in the length of the compressed spring.

[0018] Advantageously, each support piece comprises a first face and a second face that are flat and opposite, the second face being provided with a reinforcement intended to house one end of the at least one compressed spring. Such a reinforcement facilitates the installation and holding in place of springs on the second face while making it possible to increase the rigidity of the support pieces.

[0019] Preferably, at least one elastic device comprises at least one flat wire wave spring. Such a spring promotes the compactness of the elastic device.

[0020] Advantageously, at least one elastic device comprises at least one spring having an axial direction oriented according to the direction of dimensional variation of the stack.

[0021] For example, at least one elastic device comprises concentric springs around the direction of dimensional variation of the stack. Such a configuration facilitates obtaining the necessary stiffness of the elastic device.

[0022] Preferably, the support parts are made of an electrically insulating material. Such support parts promote the electrical safety of the battery environment, particularly with respect to leakage currents.

[0023] According to one characteristic, adjacent support pieces corresponding to adjacent stacks each comprise a first hook and a second hook, opposite one another and aligned in a transverse direction, perpendicular to the longitudinal axes of the adjacent stacks, the hooks having complementary U shapes allowing sliding of the first hook of a first support piece through the second hook of a second support piece adjacent to the first and allowing the passage of tie rods through said hooks without hindering the relative translation of the adjacent support pieces in the direction of dimensional variation of the stacks.

[0024] According to another characteristic, the number of tie rods is one greater than the number of cell stacks. This configuration makes it possible to have a reduced number of tie rods and thus to improve integration in terms of mass and volume.

[0025] According to another aspect, the invention relates to an aircraft comprising a battery as described above. Brief description of the drawings

[0026] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0027] [Fig-1] is a schematic perspective view of an energy storage battery electric according to one embodiment of the invention;

[0028] [Fig.2] is a perspective view of the battery of [Fig.l], in which the bell from the case has been removed;

[0029] [Fig.3] is a side view of the battery of [Fig.2]; and

[0030] [Fig.4] is a perspective view of a support piece according to an example of the invention. Detailed description of at least one embodiment

[0031] Figures 1 and 2 illustrate an exemplary embodiment of an electrical energy storage battery according to the invention, designated by the general numerical reference 1.

[0032] The battery 1 comprises a housing 2 comprising a base 3. Preferably, the housing 2 comprises a bell 4, covering the base 3. The housing 2 is intended to ensure the mounting, the connection and the protection of the power elements of the battery 1, visible in [Fig.2] on which the bell has not been shown.

[0033] The housing 2 is provided with means for mechanically fixing the bell to the base, produced for example in the form of screws, bolts or any other fixing means appropriate for the intended use.

[0034] In the embodiment described, the battery 1 is intended to be mounted on board an aircraft, for example in a turbomachine. The battery 1 is used, for example, to selectively deliver electrical energy for the purposes of electric propulsion. It will be noted, however, that the invention also applies, in general, to other fields and environments in which problems of mass management and integration arise (automobile, railway, etc.).

[0035] The base 3 is also equipped with several fixing elements 5 which allow its installation on board an aircraft. It will be noted, however, that the base 3 may be constituted, as a variant, by a structural element supporting the aircraft provided for the integration of the battery.

[0036] As regards the bell 4, this covers all of the elements located inside the housing 2 and represents a physical barrier which separates and protects the interior of the housing 2 and its external environment.

[0037] In the case where the bell 4 is present, this bell is in particular intended to reduce the risk of gas leaks. Preferably, a seal is then implemented between the base 3 and the bell 4 to contain the gases.

[0038] Furthermore, in the event of a thermal runaway type event of the battery 1, the bell 4 provides a function of protecting the external environment of the housing 2 by limiting the impact of this event on the external environment of the housing 2.

[0039] The power elements of the battery 1 comprise electric cells 6. The cells 6 are preferably in flexible packaging format, usually referred to by the English term “pouch”. Alternatively, the electric cells may be prismatic or even cylindrical.

[0040] The electrical cells 6 are grouped into at least one stack 7. In other words, the cells of a stack are arranged next to each other along a longitudinal axis X of the stack ([Fig. 3]). Preferably, the longitudinal axis X of the stack is parallel to the base 3. The longitudinal axis X is preferably parallel to the direction of dimensional variation of the stack.

[0041] The battery 1 comprises at least two opposite compression plates 8, arranged on either side of the stacks 7 of cells 6. The compression plates 8 are here placed in lateral positions, at the ends of the at least one stack 7. Preferably, the number of compression plates is limited to two, i.e. one per side, but it remains possible to provide a greater number of plates 8.

[0042] The compression plates 8 have a rigidity enabling them to meet maximum admissible deformation criteria along the longitudinal axis X of the stack, under the maximum pressure exerted by the cells 6. For example, the rigidity of the plates 8 is such that the maximum deformation is less than 0.1 mm.

[0043] In order to meet the maximum deformation criteria while reducing the mass, the compression plates 8 comprise stiffeners 8a.

[0044] The compression plates 8 are preferably substantially planar and extend orthogonally to the longitudinal axis X of the stack of cells.

[0045] The compression plates 8 are connected by their lower part 9 to the base 3 by fixing means 10.

[0046] In the present example, the compression plates 8 are connected to each other by their upper part 11 by at least one tie rod, preferably by tie rods 12.

[0047] Preferably, the tie rods 12 are installed in a direction parallel to the longitudinal axes X of the stacks 7 and parallel to the base 3.

[0048] Advantageously, the number of tie rods 12 is reduced compared to solutions used conventionally in which the tie rods are present both in the lower part and in the upper part of the compression plates. The tie rods 12 are here preferably only arranged in the upper part 11 of the compression plates 8. Thus, a single stack of cells could be held by only two tie rods. Alternatively, a single tie rod 12 could be arranged only in the upper part 11 of the compression plates 8 to reduce even more the number of tie rods.

[0049] This results in a total number of tie rods 12 that is one more than the number of stacks 7. In the example illustrated in [Fig.2], four tie rods 12 are present for three stacks 7, i.e. one more than the number of stacks. This reduction in the number of tie rods allows for better integration in terms of mass and volume.

[0050] The base 3 is capable of providing a thermal management functionality and is associated for this purpose with thermal management means. The thermal management means may in particular comprise at least one heat exchanger 13, provided with pipes, inside which a heat transfer fluid circulates. The heat transfer fluid is for example a coolant. The heat exchanger 13 has for example a serpentine shape. The base 3 is advantageously made of thermally conductive material, in particular of metallic material.

[0051] The heat exchanger 13 is for example integrated into the base 3, which optimizes the thermal path between the cells and the fluid, by reducing the thermal resistances linked to the passages between components. Alternatively, the heat exchanger can be installed in heat exchange relation with the base 3, preferably with an external face of the base 3, that is to say with the face opposite an internal face which accommodates the cells 6. The heat exchanger 13 is then for example glued against a face of the base 3.

[0052] The base 3 is in heat exchange relationship with the electrical cells 6 and can consequently bring and maintain the cells 6 at optimal operating temperatures.

[0053] The battery 1 preferably comprises at least one intermediate wall 14 fixed to the base 3, oriented parallel to the electric cells 6 and arranged inside each stack 7. [Fig. 1] illustrates a single intermediate wall 14 arranged in a central zone of the base 3, corresponding approximately to the middle of the base 3. Alternatively, it remains possible to provide several intermediate walls, arranged at regular intervals of each stack. Preferably, the intermediate walls 14 extend over the majority of the width of the base 3.

[0054] The presence of intermediate walls 14 helps to stiffen the stacks 7 and has the effect of limiting deformations in a direction normal to the base 3. The presence of intermediate walls 14 helps to ensure good resistance to vibrations of the battery 1. However, it also remains possible to provide no intermediate walls 14.

[0055] The battery 1 comprises at least one elastic device 15 ([Fig.3]) for taking up play in a stack 7 in a direction of dimensional variation of the stack during electrical charging or discharging of the cells 6 of the stack 7. Preferably, at least one elastic device 15 is associated with each stack 7 to ensure elastic support for each stack 7 in the direction of dimensional variation of the stack. Generally, the direction of dimensional variation of a stack is in the direction of the thickness of the cells 6 which form the stack, i.e. parallel to the longitudinal axis X.

[0056] Thus, each elastic device 15 elastically supports the stack 7 with which it is associated. In other words, each elastic device 15 deforms elastically and provides an elastic compressive force to an associated stack, the compressive force preferably being exerted over the entire amplitude of dimensional variation of the stack. Being in an elastic domain, no residual deformation of the elastic device is formed.

[0057] The same references correspond to the same elements from one figure to another.

[0058] In the example illustrated in [Fig.3], the battery 1 comprises two devices of elastic support 15 arranged inside the stack 7. It remains possible to adjust the position and the number of the devices 15, without departing from the scope of the invention. For example, when the battery 1 does not comprise an intermediate wall 14, the device 15 can be provided in a central zone of the base 3, corresponding approximately to the middle of the base 3. It should be noted that a median position of the device 15 within a segment of a stack 7 whose ends are kept fixed has the advantage of minimizing the maximum displacements of the internal components of the battery 1 induced by the electrical charging and discharging of the cells 6. The maximum value of the induced displacements can also be reduced by distributing several devices 15 associated with any segment of a stack 7 whose ends are kept fixed.In an embodiment not shown, it is also possible to add foam layers between the cells 6 of a stack 7. These foam layers provide a thermal insulation function and have an elasticity capable of compensating for the dimensional variations of the cells 6 during their operation, while returning a pressure compatible with the admissible limits of the cells 6.

[0059] The elastic device 15 comprises at least one compressed spring 16 between a pair of support pieces 17 substantially perpendicular to the direction of dimensional variation of the stack. The support pieces 17 are sufficiently rigid to distribute the compressive force of the spring into a uniform pressure acting on the cells of the stack. The support pieces may be provided with reinforcements so as to increase their rigidity while optimizing their mass.

[0060] As illustrated in [Fig.4], each support piece 17 comprises a first face 18 and a second face 19 which are flat and opposite. The second face 19 is provided with a reinforcement 20 intended to house one end of the at least one compressed spring 16. preferably, the support parts 17 are made of an electrically insulating material.

[0061] Preferably, the elastic device 15 comprises at least one flat wire wave spring, so as to optimize the dimensions of the device 15. Alternatively, other spring systems may be used. For example, it is possible to use a stack of washers, such as a stack of Belleville washers. Of course, it remains possible to use only round wire helical springs.

[0062] Preferably, the springs 16 have an axial direction oriented according to the direction of dimensional variation of the associated stacks, so as to optimize the support force.

[0063] In an example not illustrated, it is possible to use a plurality of concentric springs 16 around the direction of dimensional variation of the stack of cells, within the same elastic device 15, for example two concentric springs, in order to facilitate obtaining the necessary stiffness.

[0064] With reference to [Fig.3], each cell 6 comprises a first external surface SI and a second external surface S2 opposite the first surface.

[0065] In the embodiment illustrated in [Fig. 3], the first external surface SI of each cell 6 is in contact with a heat drain 23. As a variant, it remains possible that only certain cells 6 of a given stack are in contact with a heat drain, or even that the cells 6 are not in contact with any drain.

[0066] The heat drain 23 preferably comprises at least one layer of graphite and at least one layer of glue. The graphite layer of the heat drain 23 is placed in contact with the external SI surface of the associated cell 6 in order to maximize the heat transfer capacity between the drain and the associated cell.

[0067] In a particular embodiment, the heat drain 23 comprises a metallic layer, for example made of aluminum or copper, associated with a layer of glue and a layer of graphite.

[0068] Each heat drain 23 preferably comprises a main part 23a and an end part 23b. The main part 23a is oriented in a direction perpendicular to a longitudinal axis X of the stack which is normal to the surfaces SI, S2 of the cells 6. In other words, the main parts 23a of the heat drains 23 are parallel to the surfaces SI, S2. The main part 23a is in contact with the surface SI of the associated cell 6 and the end part 23b is folded under the associated cell 6 so as to constitute a contact surface 23c of the drain 23 with the base 3.

[0069] The fixing means 10 of the compression plates 8 preferably comprise first fixing elements 24 and second fixing elements 25. The first fixing elements 24 are fixed to the base 3. They are intended to pass through holes provided on a base 26 of each compression plate 8 and cooperate with the second fixing elements 25 for fixing the compression plates 8 to the base 3. The first fixing elements 24 may in particular be studs, threaded rods or bolts. The second fixing elements 25 may be nuts.

Claims

Claims

1. Battery (1) for storing electrical energy comprising at least one stack (7) of electrical cells (6) and a housing (2) comprising a base (3) on which said stack (7) of the battery (1) is fixed, the battery being characterized in that it comprises at least two compression plates (8) arranged on either side of said stack, means (10) for fixing said compression plates (8) to the base (3), at least one tie rod (12) capable of compressing the compression plates (8) against the cells (6) of said stack (7), and at least one elastic device (15) for taking up play in the stack in a direction of dimensional variation of said stack.

2. Battery according to claim 1, wherein each elastic device (15) comprises at least one compressed spring (16) between a pair of support pieces (17) substantially perpendicular to said direction of dimensional variation of said stack.

3. Battery according to claim 2, in which each support piece (17) comprises a first face (18) and a second face (19) which are flat and opposite, the second face (19) being provided with a reinforcement (20) intended to house one end of the at least one compressed spring (16).

4. A battery according to any one of claims 1 to 3, wherein at least one elastic device (15) comprises at least one flat wire wave spring.

5. Battery according to any one of claims 1 to 4, in which at least one elastic device (15) comprises at least one spring (16) having an axial direction oriented according to said direction of dimensional variation of said stack.

6. Battery according to any one of claims 1 to 5, in which at least one elastic device (15) comprises springs (16) concentric around the direction of dimensional variation of the stack.

7. Battery according to any one of the preceding claims 1 to 6, in which the support parts (17) are made of an electrically insulating material.

8. A battery according to any one of the preceding claims 2 to 7, wherein adjacent support pieces (17) corresponding to adjacent stacks (7) each comprise a first hook (21) and a second hook (22), opposite each other and aligned in a transverse direction, perpendicular to the longitudinal axes (X) of the adjacent stacks (7), said hooks (21, 22) having complementary U shapes allowing sliding of the first hook (21) of a first support piece through the second hook (22) of a second support piece adjacent to the first and allowing the passage of tie rods (12) through said hooks (21, 22) without hindering the relative translation of the adjacent support pieces in the direction of dimensional variation of said stacks.

9. Battery according to any one of the preceding claims 1 to 8, in which the number of tie rods (12) is one greater than the number of stacks (7) of cells.

10. An aircraft comprising a battery according to any one of claims 1 to 9.

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