Battery comprising at least one stack of electrical cells and associated assembly method

Abstract

The invention relates to an electrical energy storage battery (1) comprising at least one stack (7) of electrical cells (6), a housing comprising a base (3) to which the stack (7) of the battery (1) is attached and a shell covering the base (3). The battery (1) comprises at least two compression plates (8) arranged on either side of the stack (7), means (10) for attaching the plates (8) to the base (3) and at least one tie rod (12) capable of compressing the compression plates against the cells of the stack (7). The base (3) comprises means (13) for the thermal management of the electrical cells (6).

Description

[0001] DESCRIPTION

[0002] TITLE: Battery comprising at least one stack of electric cells and associated assembly method

[0003] Technical field

[0004] 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.

[0005] Previous techniques

[0006] Traditionally, in the aeronautics field, the storage of electrical energy is carried out using low-voltage Lithium-Ion batteries, typically a voltage lower than 120V.

[0007] The term battery means a set of individual modules each comprising power elements arranged in series and / or parallel in order to achieve the desired electrical voltage and electrical capacity.

[0008] Modern aircraft have increasing electrical power requirements, requiring battery configurations accordingly. Indeed, climate change is a major concern for many legislative and regulatory bodies around the world. Various carbon emission restrictions have been, are being, or will be adopted by various states.

[0009] Civil aviation has been mobilizing for several years now to contribute to the fight against climate change.

[0010] 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.

[0011] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction 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.

[0012] In order to provide the required electrical power while minimizing the weight of the electrical equipment, it is interesting to increase the battery voltage, for example to 800 V.

[0013] 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.

[0014] In order to improve the integration of the battery in terms of volume and mass, it is possible to stack the cells.

[0015] Document FR 3 067 859 A1 describes in this regard a battery comprising a stack of a plurality of cells assembled by means of mechanical fixing devices comprising frames or shells into which the cells are inserted. This assembly multiplies the mechanical interfaces and does not allow for optimizing integration in terms of volume and mass. In addition, the presence of rather thermally insulating frames or shells disrupts the heat exchange within the battery, making thermal management of the battery more difficult.

[0016] There are also battery modules comprising stacked cell assemblies, held in compression using four tie rods. The presence of such a large number of tie rods negatively affects the integration balance in terms of volume and mass. Furthermore, the thermal management of such assemblies is not considered. Presentation of the invention

[0017] 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, and whose thermal management is facilitated.

[0018] The subject of the invention, according to a first aspect, is an electrical energy storage battery comprising at least one stack of electrical cells, a housing comprising a base on which said stack of the battery is fixed and a bell covering the base.

[0019] The battery comprises at least two compression plates arranged on either side of said stack, means for fixing said plates to the base, and at least one tie rod capable of compressing the compression plates against the cells of said stack, the number of tie rods being exactly one greater than the number of stacks.

[0020] In addition, the base includes means of thermal management of the electric cells.

[0021] The use of stacked electric cells in such a battery improves integration in terms of volume and mass. Thermal management of the electric cells is facilitated by heat exchange with the base. The use of compression plates on either side of the stack reduces the need to include other mechanical compression elements, such as additional tie rods.

[0022] The use of a number of tie rods exactly one greater than the number of stacks makes it possible to have a smaller number of tie rods compared to the battery modules of the prior art and results in significant mass savings.

[0023] According to a preferred characteristic of the invention, the tie rods are provided only in the upper part of the compression plates. Thus, advantageously, a stack of cells can be held by only two tie rods associated with the compression plates.

[0024] Preferably, each stack of cells comprises at each of its ends a layer of end foam, so that the compression plates are in contact with said layers of end foam of the stacks.

[0025] For example, the battery comprises at least one heat sink disposed on a first external surface of at least one cell of each stack and / or comprises at least one intermediate foam layer disposed on a second external surface of at least one cell of each stack, the second external surface being opposite the first.

[0026] According to one feature, the heat sink comprises at least one layer of graphite and at least one layer of glue.

[0027] Preferably, the heat drain is folded under the cell with which it is in contact, so as to constitute a contact surface of the drain with the base.

[0028] Such a configuration allows to increase the thermal transfers between the base and the cells.

[0029] According to another feature, the battery includes a layer of glue covering the contact surface of the drain with the base.

[0030] For example, the fixing means comprise first and second fixing elements, said first elements being fixed to the base and intended to pass through holes provided on a base of each compression plate, and said second fixing elements cooperating with the first fixing elements to fix the compression plates to the base.

[0031] Preferably, the first fixing elements fixed to the base comprise at least one stud.

[0032] Preferably, said stud passes through a hole provided at the base of the compression plate, and oriented in the direction of lateral movement of the compression plate. Preferably, the second fixing elements comprise at least one nut.

[0033] Advantageously, the base comprises adjustment means capable of imposing a lateral displacement on a compression plate so as to move said compression plate closer to or further away from the middle of the base, when said lateral displacement is respectively increased or reduced.

[0034] Such adjustment means allow perfect control of the relative distance between the compression plates.

[0035] Preferably, the adjustment means comprise at least one cam capable of cooperating with a base of the compression plate.

[0036] Advantageously, the battery comprises a protective wall fixed to the compression walls and arranged between the cells and the bell, so as to protect the bell in the event of thermal runaway of the cells.

[0037] For example, the battery comprises at least one intermediate wall fixed to the base, oriented parallel to the electric cells and arranged inside each stack.

[0038] According to another aspect, the invention relates to a method for mounting a battery as described above, comprising the following steps: placing a first compression plate, placing at least one stack of electric cells against the first plate, placing a second compression plate opposite the first plate, and arranged in contact with the stacks of cells, pressurizing the two compression plates against the stacks, gradually bringing the two compression plates together, after the plates have been brought together, fixing the compression plates to the base and installing the tie rods, and tensioning the tie rods. According to another aspect, the invention relates to an aircraft comprising at least one electrical energy storage battery comprising at least one stack of electric cells, the battery being as defined above according to the first aspect.

[0039] Brief description of the drawings

[0040] 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:

[0041] [Fig 1] is a schematic perspective view of an electrical energy storage battery according to one embodiment of the invention;

[0042] [Fig 2] is a perspective view of the battery of Fig. 1, in which the housing bell has been removed;

[0043] [Fig 3] is a side view of the battery of Figure 2;

[0044] [Fig 4] is a perspective view of a detail of the connection between a compression plate and the base of the battery of Figure 2;

[0045] [Fig 5] is a partial perspective view of a battery according to one embodiment of the invention; and

[0046] [Fig 6] is a flowchart of a method of mounting a battery according to one embodiment of the invention.

[0047] Detailed description of at least one embodiment

[0048] 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.

[0049] The battery 1 comprises a housing 2 comprising a base 3 and a bell 4. The housing 2 is intended to ensure the mounting, connection and protection of the power elements of the battery 1, visible in figure 2 in which the bell has not been shown.

[0050] 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. In the embodiment described, the battery 1 is intended to be carried on board an aircraft. 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.

[0051] 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.

[0052] As regards the bell 4, this covers all 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.

[0053] The bell 4 is intended in particular to reduce the risk of gas leaks. Preferably, a seal is implemented between the base 3 and the bell 4 to contain the gases.

[0054] 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.

[0055] The power elements of the battery 1 comprise electric cells 6. The cells 6 are preferably of prismatic format with flexible packaging, usually designated by the Anglo-Saxon term “pouch”.

[0056] 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 (figure 3). Preferably, the longitudinal axis X of the stack is parallel to the base 3.

[0057] The battery 1 comprises at least two opposing 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.

[0058] 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.

[0059] In order to meet the maximum deformation criteria while reducing the mass, the compression plates 8 include stiffeners 8a.

[0060] The compression plates 8 are preferably substantially planar and extend orthogonally to the longitudinal axis X of the stack of cells.

[0061] The compression plates 8 are connected by their lower part 9 to the base 3 by fixing means 10.

[0062] 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.

[0063] 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.

[0064] Advantageously, the number of tie rods 12 is reduced compared to conventionally used solutions 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 further reduce the number of tie rods.

[0065] 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 Figure 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.

[0066] 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.

[0067] 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.

[0068] The base 3 is in heat exchange relationship with the electrical cells 6 and can therefore bring and maintain the cells 6 at optimal operating temperatures.

[0069] 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. Figure 2 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.

[0070] 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. With reference to FIG. 3, each stack 7 comprises at each of its ends 7a, 7b a layer of end foam 15.

[0071] Each cell 6 comprises a first external surface SI and a second external surface S2 opposite the first.

[0072] In the embodiment illustrated in Figure 3, the first external surface S1 of each cell 6 is in contact with a heat sink 16 and the second external surface S2 is in contact with a foam layer 17, 15. Alternatively, it remains possible for only certain cells 6 of a given stack to be in contact with a heat sink and / or a foam layer 17, 15, or even for the cells 6 to be in contact with neither a drain nor a foam layer 17. Here, the stack comprises two end foam layers 15 and a plurality of intermediate foam layers 17. The foam layers 15, 17 provide a thermal insulation function and have an elasticity capable of compensating for dimensional variations of the cells 6 during their operation, while returning a pressure compatible with the permissible limits of the cells 6.

[0073] The foam layers 15, 17 may in particular comprise reinforcing fibers, an aerogel, a neoprene, and / or a thermoplastic.

[0074] The number of foam layers 17 required to compensate for the dimensional variation of the cells 6 depends on the type of cells used. Thus, depending on the chemistry of the cells 6, it is possible to drastically reduce the number of foam layers 17, or even eliminate them.

[0075] The heat sink 16 comprises at least one layer of graphite and at least one layer of glue. The graphite layer of the heat sink 16 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.

[0076] In a particular embodiment, the heat drain 16 comprises a metal layer, for example made of aluminum or copper, associated with a layer of glue and a layer of graphite. Each heat drain 16 comprises a main part 16a and an end part 16b. The main part 16a 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 16a of the heat drains 16 are parallel to the surfaces SI, S2. The main part 16a is in contact with the surface SI of the associated cell 6 and the end part 16b is folded under the associated cell 6 so as to constitute a contact surface 16c of the drain 16 with the base 3.

[0077] Preferably, a layer of glue covers the contact surface 16c of the drain 16 with the base 3, in order to reduce the risk of relative displacement between the drains and the base.

[0078] The fixing means 10 of the compression plates 8 comprise first fixing elements 18 and second fixing elements 19. The first fixing elements 18 are fixed to the base 3. They are intended to pass through holes provided on a base 20 of each compression plate 8 and cooperate with the second fixing elements 19 to fix the compression plates 8 to the base 3. The first fixing elements 18 may in particular be studs, threaded rods or bolts. The second fixing elements 19 may be nuts.

[0079] In the embodiment illustrated in Figure 4, the base 3 is provided with adjustment means 21 capable of imposing a lateral displacement D on at least one compression plate 8. The lateral displacement is imposed here by a rotation R of a cam 22 whose profile is in contact with the plate 8 and which presses on it. The profile of the cam 22 can for example press on the edge of the base 20. The position of the plate 8 can be adjusted as a function of the rotation R of the cam, so as to bring the compression plate 8 closer to or further away from the middle of the base 3 when the lateral displacement D imposed by the rotation R is respectively increased or reduced.

[0080] In this embodiment, each first fixing element 18 passes through an oblong hole 23 provided on the base 20 and oriented in the direction of lateral movement D to allow this movement. The use of such adjustment means 22 makes it possible to guard against possible negative consequences of manufacturing tolerances. It thus becomes possible to precisely adjust the longitudinal distance between the compression plates 8, and to allow better control of the pressure exerted on the stacks 7 of the cells 6.

[0081] Thus, thanks on the one hand to the presence of the two compression plates 8 on the sides, and on the other hand to the precise mechanical fixing of the compression plates 8 on the base 3 using the fixing means 10 (comprising for example studs as described above), the base 3 participates in the compression of the cells 6 and in their maintenance in the stack 7.

[0082] With reference to figure 5, according to a possible variant, the battery is provided with a protective wall 24 fixed on the compression walls 8 and arranged between the electric cells of the battery and the bell 4, so as to protect the bell 4 in the event of thermal runaway of the cells.

[0083] The protective wall 24 is supported vertically by the base 3 and rests laterally on bosses 25 provided on the base 3.

[0084] The protective wall 24 can further be fixed to the intermediate walls 14.

[0085] Figure 6 is a flowchart of a method of mounting a battery 1 according to a possible exemplary embodiment of the invention.

[0086] The method begins with a step 26 of placing a first compression wall 8 at a first predetermined height.

[0087] In the following step 27, at least one stack 7 of electric cells 6 is placed against the first plate 8. Each stack 7 is preferably installed at a second predetermined dimension, different from the first, so that the edge intended to be in contact with the base 3 is further from the center of the stack than the edge of the base 20 also intended to be in contact with the base 3. This difference between the first dimension and the second dimension is called "negative clearance". Alternatively, a flexible seal can be provided under each cell 6, also creating a negative clearance. A second compression plate 8 opposite the first and arranged in contact with the stacks 7 of cells 6 is then placed (step 28). The second compression plate is placed at the same first dimension as the first compression plate 8.

[0088] The method continues with a step 29 of pressurizing the two compression plates 8 against the stacks of cells, using pressurizing means. The pressurizing means may in particular be hydraulic cylinders, preferably controllable in movement.

[0089] During the next bringing together step 30, the two compression walls 8 are gradually brought together by controlling the pressurization means. Control is preferably carried out by movement to ensure perfect control of the relative position of the compression plates 8.

[0090] When the two compression plates 8 have been brought together, the method continues with a step 31 of fixing the compression plates to the base 3, followed by a step 32 of installing the tie rods 12. Alternatively, step 32 of installing the tie rods 12 can be carried out before step 31 of fixing the plates 8 to the base 3.

[0091] It should be noted that, when assembling the base 3 and the compression plates 8, the negative clearance between the stacks 7 and the compression plates 8 results in additional pressure between the stacks 7 and the base 3. This additional pressure improves the heat exchange coefficient between the stacks 7 and the base 3.

[0092] When the battery is equipped with heat drains 16, the method may comprise an optional step of placing a layer of glue on the contact surfaces 16b of the heat drains 16 with the base 3. The layer of glue and the additional pressure between the stacks 7 and the base 3 generated by the negative clearance described previously participate in maintaining contact between the heat drains 16 and the base 3.

[0093] The method ends with tensioning the tie rods 12 (step 33). The tensioning of the tie rods can be carried out by removing or deactivating the pressurizing means used during the previous pressurizing and bringing together steps. In addition, the tension of the tie rods 12 could be increased, for example using active anchors. The tension forces of the tie rods 12 are balanced by the compression forces acting on the compression plates 8.

Claims

CLAIMS 1. Battery (1) for storing electrical energy comprising at least one stack (7) of electrical cells (6), a housing (2) comprising a base (3) on which said stack (7) of the battery (1) is fixed and a bell (4) covering the base (3), 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), and at least one tie rod (12) capable of compressing the compression plates (8) against the cells (6) of said stack (7), the base (3) comprising means for thermal management of the electrical cells (6), the number of tie rods (12) being exactly one greater than the number of stacks (7).

2. Battery according to claim 1, in which each stack (7) of cells comprises at each of its ends (7a, 7b) a layer (15) of end foam, so that the plates (8) of compression are in contact with said layers (15) of end foam of the stacks.

3. Battery according to claim 1 or 2, comprising at least one heat sink (16) arranged on a first external surface (SI) of at least one cell (6) of each stack (7) and / or comprising at least one intermediate layer (17) of foam arranged on a second external surface (S2) of at least one cell (6) of each stack (7), the second external surface (S2) being opposite the first (SI).

4. Battery according to claim 3, wherein said heat drain (16) comprises at least one layer of graphite and at least one layer of glue.

5. Battery according to claim 3 or 4, in which said heat drain (16) is folded under the cell (6) with which it is in contact, so as to constitute a contact surface (16c) of the drain (16) with the base (3).

6. Battery according to any one of claims 1 to 5, in which the fixing means (10) comprise first (18) and second (19) fixing elements, said first elements being fixed on the base (3) and intended to pass through holes provided on a base (20) of each compression plate (8), said second (19) fixing elements cooperating with the first (18) fixing elements to fix the compression plates (8) to the base (3).

7. Battery according to claim 6, in which the base (3) comprises adjustment means (22) capable of imposing a lateral displacement (D) on at least one compression plate (8), so as to bring said compression plate (8) closer to or further away from the middle of the base (3), when said lateral displacement (D) is respectively increased or reduced.

8. Battery according to any one of claims 1 to 7, comprising a protective wall (24) fixed on the compression plates (8) and arranged between the cells and the bell, so as to protect the bell in the event of thermal runaway of the cells.

9. Method for mounting a battery according to any one of claims 1 to 8 comprising the following steps: placing a first compression plate (8), placing at least one stack (7) of electric cells (6) against the first plate (8), placing a second compression plate (8) opposite the first plate, and arranged in contact with the stacks (7) of cells (6), pressurizing the two compression plates (8) against the stacks (7), gradually bringing the two compression plates (8) together, after bringing the plates (8) together, fixing the compression plates (8) to the base (3) and installing the tie rods (12), and tensioning the tie rods (12).

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