Electrical energy storage system for an aircraft, method for manufacturing such a storage system and method for protection against thermal runaway

Abstract

The invention relates to an electrical energy storage system (1) for an aircraft comprising: - at least one electrical energy storage structure (2) comprising a plurality of electrical energy storage cells (3), - a composite structure (10) interposed between and / or surrounding the storage cells, the composite structure forming a stack (11) comprising, along a stacking axis (Z), an outer layer (12) and an inner layer (13), said outer and inner layers being thermally conductive, and a plurality of electrically insulating layers (14) interposed between the outer and inner layers, characterized in that the stack comprises a thermal runaway protection structure (20) comprising at least one protective layer (21) based on carbon fibers comprising at least one layer (22) of carbon nanostructures (CN) oriented along a stacking axis direction,where each protective layer is interposed between two successive layers and / or between one of the electrically insulating layers and the outer layer and / or between one of the electrically insulating layers and the inner layer. Figure for the abbreviation: Figure 2,

Description

Title of the invention: ELECTRICAL ENERGY STORAGE SYSTEM FOR AN AIRCRAFT, METHOD FOR MANUFACTURING SUCH A SYSTEM STORAGE AND PROTECTION METHOD AGAINST THERMAL RUNAWAY Technical field of the invention

[0001] The present invention relates to an electrical energy storage system for an aircraft and to an aircraft comprising such an electrical energy storage system. The invention further relates to a method for manufacturing such an energy storage system. Finally, the invention relates to a method for protecting an electrical energy storage structure against thermal runaway. Technical background

[0002] In an effort to reduce the carbon footprint of air traffic, several technologies exist to electrify aircraft as much as possible, for example by replacing non-electrical equipment with electrical equipment. This is made possible by equipping the aircraft with electrical energy storage structures such as batteries. These electrical energy storage structures allow electrical energy to be stored and distributed according to the needs of the aircraft's electrical equipment.

[0003] An electrical energy storage structure can experience thermal runaway for various reasons that cannot necessarily be prevented by electronic monitoring of the structure. This can occur in the event of a production failure in a storage cell of the storage structure. This thermal runaway can result in the generation of various gases, some toxic, flames, smoke, and violent explosions, and therefore pose safety problems. It must therefore be subject to reliable and rapid detection.

[0004] In addition to improving the detection of thermal runaway, it is of major interest to aeronautical professionals to be able to effectively and quickly protect electrical energy storage structures against thermal runaway, even if these storage structures are still little used as an energy source in this sector.

[0005] In technical fields unrelated to aeronautics, such as the automotive industry, electrical energy storage structures, such as electric batteries, are more widespread. To protect the structures of To protect electrical energy storage against thermal runaway, manufacturers favor the use of materials with high thermal conductivity such as aluminum alloys in the walls of storage structures.

[0006] However, the constraints related to airworthiness, which were identified during the first change management exercises (in English, "Means of Compliance") and which cover this issue, lead to significantly higher survivability requirements for electrical energy storage structures in the aeronautical field compared to the automotive field.

[0007] In this regard, the prior art has proposed compensating for critical failure modes, such as alloy melting that negates the residual mechanical performance of the storage structure during thermal runaway, by using carbon fibers stable up to extreme temperatures (>1500 °C) in the walls of the storage structure. Indeed, even after degradation of the composite matrix, the carbon fibers allow an acceptable level of performance to be maintained.

[0008] However, such a composite structure presents some drawbacks. Indeed, this composite structure exhibits very low thermal conductivity (generally < 1 W / [mK]) in the transverse direction, that is, in a direction corresponding to the thickness of the composite structure. Now, during thermal runaway, significant gas release is frequently observed, stressing the composite structure both mechanically (high overpressure) and thermally. The rates of temperature rise can be extremely high, i.e., several hundred degrees per second, and a cooling circuit cannot protect the composite structure against this thermal runaway phenomenon.

[0009] The storage structure is therefore generally equipped with a ventilation system that significantly reduces the overpressure imposed on the composite structure. This reduction in overpressure is sufficient to allow a composite structure with a degraded composite matrix to maintain its performance. However, a peak in stress still occurs during the rapid increase in pressure and temperature, which impairs the mechanical properties of the composite structure during thermal runaway.

[0010] The present invention proposes a solution to at least part of the problems mentioned above by providing an electrical energy storage system that allows the storage structure to be protected thermally and mechanically from the major phenomenon of thermal runaway. Summary of the invention

[0011] The invention proposes an electrical energy storage system for an aircraft comprising:

[0012] - at least one electrical energy storage structure comprising a plurality of electrical energy storage cells,

[0013] - a composite structure interposed between and / or surrounding the storage cells, the composite structure forming a stack comprising, along a stacking Z-axis:

[0014] > an outer layer and an inner layer, said outer and interiors being thermally conductive,

[0015] > a plurality of electrically insulating layers interposed between the layers exterior and interior

[0016] characterized in that the stacking comprises a thermal runaway protection structure comprising at least one protective layer based on carbon fibers comprising at least one layer of carbon nanostructures oriented along a stacking Z-axis direction, the protective layer or each layer being interposed between two successive electrically insulating layers and / or between one of the electrically insulating layers and the outer layer and / or between one of the electrically insulating layers and the inner layer.

[0017] The invention thus proposes an electrical energy storage system with an improved capacity to maintain its mechanical properties when the storage structure undergoes thermal runaway. Indeed, the carbon fiber-based protective layers of the thermal runaway protection structure each comprise at least one layer of carbon nanostructures oriented along a stacking axis direction, which significantly increases the transverse conductivity, i.e., the thermal conductivity in the thickness direction. This therefore reduces the temperature increase of the composite structure and thus expands its optimal range of mechanical strength. In fact, by protecting the electrical energy storage structure from thermal runaway, the invention also reduces the risk of significant gas release that stresses the composite structure both mechanically and thermally.

[0018] According to various features of the invention which may be taken together or separately: - carbon nanostructures are carbon nanotubes; - the volume fraction of carbon nanotubes in the or each layer of carbon nanotubes relative to the total volume of the or each protective layer is at least 20%, preferably at least 40%, and even more preferably at least 60%; - the average diameter of carbon nanotubes is between 1 nm and 100 nm; - the distance separating the carbon nanotubes in an extension plane of the or each protective layer is between 5 nm and 100 nm; - each protective layer further comprises, on each side of the carbon nanostructure layer, a layer of carbon fibers oriented along a longitudinal axis X and / or a transverse axis Y direction, the longitudinal axis X and the transverse axis Y being orthogonal to the stacking axis Z and orthogonal to each other; - each protective layer has a thickness between 10 pm and 15 pm; - the outer and inner layers are made of carbon fibers pre-impregnated with a first thermoplastic or thermosetting matrix; - the electrically insulating layers are made of glass fibers pre-impregnated with a second thermoplastic or thermosetting matrix; - the first and second thermoplastic or thermosetting matrices are made of the same material, preferably a material chosen from an epoxy and a polyaryletherketone type thermoplastic; - the electrical energy storage structure is an aircraft electric battery.

[0019] The invention relates to an aircraft comprising at least one electrical energy storage system as previously described.

[0020] The invention further relates to a method for manufacturing an electrical energy storage system as previously described, the manufacturing method comprising the following steps:

[0021] 110) successively deposit along a stacking Z axis:

[0022] - a thermally conductive outer layer or an inner layer thermally conductive,

[0023] - at least one protective layer based on carbon fibers comprising at minus a layer of carbon nanostructures oriented along a stacking axis direction,

[0024] - at least one electrically insulating layer and repeat the deposition steps of the protective layer and deposit layer of the electrically insulating layer,

[0025] - at least a second layer of carbon nanostructures,

[0026] - the other of the outer and inner layers,

[0027] 120) heat and 130) consolidate the stack thus obtained so as to obtain a one-piece stacking.

[0028] The invention also relates to a method of protecting at least one electrical energy storage structure against thermal runaway by means of an electrical energy storage system as previously described. Brief description of the figures

[0029] Other objects, features and advantages of the invention will become more apparent in the following description, made with reference to the accompanying figures, in which:

[0030] - Fig. 1 is a very schematic perspective view of a storage system of electrical energy used in an electrical energy storage system according to an embodiment of the invention,

[0031] - Figure 2 schematically illustrates a composite structure for a system of electrical energy storage according to an embodiment of the present invention,

[0032] - Figure 3 illustrates the phenomenon of thermal runaway,

[0033] - Figure 4 illustrates the phenomenon of thermal runaway and its effect on the temperature of the composite structure,

[0034] - Figure 5 schematically illustrates the mechanisms involved in a system of electrical energy storage according to an embodiment of the invention

[0035] - Figure 6 schematically illustrates a detailed view of a protective structure for composite structure as illustrated in [Fig.2],

[0036] - [Fig. 7] is a SEM image of a protective structure as illustrated in the [Fig.6]

[0037] - [Fig.8] is a SEM image of a carbon nanostructure,

[0038] - Figure 9 schematically illustrates carbon nanotubes,

[0039] - Figure 10 schematically illustrates a manufacturing process for a system of electrical energy storage according to an embodiment of the present invention,

[0040] - Figure [Fig. 1 1] schematically and in detail illustrates the process of manufacture as illustrated in [Fig. 10]. Detailed description of the invention

[0041] With reference to [Fig. 1], the invention relates to an electrical energy storage system 1 for an aircraft. [Fig. 1] is a highly simplified schematic view of the storage system 1 according to one embodiment of the invention. Such a system 1 can be electrically connected to one or more electric machines used to distribute electrical energy to the aircraft's distribution networks as part of the aircraft's electric hybrid system.

[0042] The electrical energy storage system 1 according to the invention comprises at least one electrical energy storage structure 2 having a plurality of electrical energy storage cells 3. The term "cells" here refers to any component, module, or element surrounding the electrical energy storage structure 2 that participates directly or indirectly in the storage of electrical energy.

[0043] By way of example, the electrical energy storage structure 2 may be a lithium-ion type electric battery and, in this case, comprise lithium-ion electrical energy storage cells 3. Other types of electric batteries may be considered by those skilled in the art.

[0044] The energy storage structure 2 may further include a housing 5 with an internal compartment 4 configured to receive the electrical energy storage cells 3. In the embodiment illustrated in [Fig. 1], the housing 5 has a parallelepiped shape, although it can have any shape. The compartment 4 may include a plurality of internal walls (not shown) delimiting the storage cells 3. Although in the embodiment illustrated in [Fig. 1] the storage cells 3 are cylindrical, their shape is by no means limited to this representation.

[0045] The electrical energy storage system 1 may comprise a plurality of electrical energy storage structures 2 to meet the aircraft's electrical energy requirements. An electrical energy storage structure 2 may be connected to one or more electrical machines of the aircraft to supply power to the aircraft's distribution networks.

[0046] The electrical energy storage system 1 according to the invention further comprises a composite structure 10 interposed between and / or surrounding the storage cells 3. The composite structure 10 serves to provide mechanical support for the electrical energy storage structure 2 while protecting it from thermal runaway. Where applicable, the casing 5 and the internal walls of the energy storage structure 2 may, in whole or in part, form this composite structure 10. In this case, the composite structure 10 provides protection for the storage cells 3 from the external environment and / or physical separation between the different storage cells 3.

[0047] Depending on the type of storage cell 3, the storage structure 2 may optionally include a cooling circuit. The cooling circuit may be located inside or outside the storage structure 2, depending on the desired thermal performance. This cooling circuit is designed to cover "in-service" cooling requirements, i.e., moderate temperature variations, with the aim of maintaining the storage cells 3 within their optimal temperature range. However, as indicated in the introduction, this cooling circuit standard does not aim to and does not allow the protection of storage structure 2 from a critical failure resulting from thermal runaway.

[0048] The composite structure 10 forms a stack 11 of layers extending along a stacking Z-axis. Its role is to mechanically support the storage structure(s) 2 and to protect the storage structure(s) 2 from thermal runaway. At each point of the composite structure, the stacking Z-axis defines the transverse direction, that is, the direction of the thickness of the composite structure 10. Thus, the orientation of the stacking Z-axis depends on the point of the composite structure 10 that is considered.

[0049] With reference to [Fig. 2], the composite structure 10 comprises, along the Z-axis, a thermally conductive outer layer 12, a thermally conductive inner layer 13, and a plurality of electrically insulating layers 14 interposed between the outer and inner layers 12, 13. The outer layer 12 is so named because it represents the layer of the stack 11 furthest from the area to be protected from thermal runaway, i.e., a storage cell 3, a storage structure 2, or something else. Similarly, the inner layer 13 represents the layer of the stack 11 closest to the area to be protected from thermal runaway.

[0050] The thermally conductive outer and inner layers 12, 13 allow the composite structure 10 to dissipate heat, which is particularly useful in the context of the invention since the storage structure 2 must be able to release the heat generated by the high temperatures caused by the thermal runaway phenomenon, as will be seen later. The outer and inner layers 12, 13 play a dual role. In addition to allowing heat dissipation, they have sufficient mechanical strength to ensure the formation of an easily manipulated "sandwich structure." It is referred to as a "sandwich structure" because the electrically insulating layers 14 are interposed between the outer and inner layers 12, 13.

[0051] In this regard, the outer and inner layers 12, 13 can advantageously be made of carbon fibers pre-impregnated with a first thermoplastic or thermosetting matrix. Preferably, the first matrix is ​​made of a material selected from an epoxy and a polyaryletherketone (PAEK) type thermoplastic. These materials exhibit both high thermal conductivity and high mechanical strength. Moreover, they are capable of bonding to a very wide variety of materials and readily impregnate the carbon fibers when they are heated to a temperature above their forming temperature. The type of material chosen can be adapted according to the desired thermal conductivity. This choice is made at the time of design according to the type of storage cells 3 which is equipped with the storage structure 2. In addition, it is advantageous that the carbon fibers used in the outer and inner layers 12, 13 of the composite structure 10 are made from carbon fiber scraps, which allows the valorization of production waste while maintaining intact mechanical performance.

[0052] The electrically insulating layers 14, interposed between the outer and inner layers 12, 13, provide electrical insulation for the composite structure 10. They are preferably made of glass fibers pre-impregnated with a second thermoplastic or thermosetting matrix. Preferably, the second matrix is ​​made of a material selected from an epoxy and a PAEK-type thermoplastic. The advantages of these materials are listed above and are not repeated here. It is advantageous for the first and second thermoplastic and / or thermosetting matrices to be made of the same material. In other words, if the first matrix of the outer and inner layers 12, 13 is made of epoxy, then the second matrix of the electrically insulating layers 14 is also made of epoxy.Indeed, this promotes and simplifies chemical bonding at the interfaces between the outer and inner layers 12, 13 on the one hand and the electrically insulating layers 14 in contact with said outer and inner layers 12, 13, which makes the structural integrity of the composite structure 10 more reliable once consolidated.

[0053] That being said, and as we shall see later, the outer layer 12 is not necessarily in contact with an electrically insulating layer 14. Similarly, the inner layer 13 does not necessarily have to be in contact with an electrically insulating layer 14. Thus, using the same material for the first and second matrices is more advantageous when the outer and inner layers 13 are in contact with one of the electrically insulating layers 14.

[0054] In this regard, it can be specified that the different layers of the stack 11 can advantageously have similar, i.e., identical, dimensions along a longitudinal axis X and along a transverse axis Y, the longitudinal axis X and the transverse axis Y being orthogonal to the stacking axis Z and orthogonal to each other. In other words, each layer is entirely superimposed on the layers to which it is adjacent in the stack 11.

[0055] As indicated above, one of the functions of the composite structure 10 of the system 1 according to the invention is to protect the storage structure or structures 2 from the phenomenon of thermal runaway. In order to better understand the benefit of such protection, the following sections explain thermal runaway.

[0056] Figure 3 illustrates the progression of this phenomenon, which occurs in two phases: a transient phase II (high pressure / high temperature) and a static phase III. These two phases are themselves preceded by a phase I (service phase) because the gas temperature Tgas is equal to the service temperature Tserv and the pressure Within storage structure 2, Pstruct is equal to the service pressure Pserv, which generally corresponds to atmospheric pressure. Tserv and Pserv correspond respectively to the standard operating temperature and pressure of energy storage structure 2.

[0057] Phase II. occurs due to a triggering of the DEG gas evacuation. Following the activation of the DEG gas venting, an initial thermal runaway occurs within one or more cells. A very rapid local chain reaction (lasting a few seconds) takes place, generating almost simultaneously a high temperature, typically between 800°C and over 1500°C depending on the type of storage structure, and a high associated pressure that can reach several tens of bar, depending on the type of storage structure and the available space in the storage cells. This Phase II therefore creates a very high mechanical stress on the composite structure of prior art storage systems. This phase, which lasts at most a few tens of seconds, is generally preceded by a few seconds by a sharp increase in the temperature of the composite structure, thus combining two phenomena that have a negative effect on the composite structure.If the storage structure includes an active evacuation system, it should normally be triggered during this phase.

[0058] Static phase III follows transient phase II. Assuming an exhaust system is present, the pressure reaches a fixed value related to the gas flow rate and the cross-section of the exhaust system. The temperature gradually decreases because the majority of the heat transfer occurring during this phase is a conduction / convection phenomenon of the generated hot gases. When the gases are removed, non-volatile elements (e.g., metals) remain in the module and generate heat by radiation. Thus, the temperature and pressure conditions are significantly lower (a few hundred degrees Celsius and 1-2 bars depending on the type of storage structure) compared to those of phase III, and the structure is generally able to withstand this stress.

[0059] It should be noted that this thermal runaway phenomenon can propagate through several storage structures, for example, through several batteries if the storage system comprises several batteries. These phenomena do not necessarily all occur at the same time and can happen progressively.

[0060] In order to reduce the effect of this thermal runaway phenomenon and with reference to Figures 2 and 6, the storage system 1 according to the invention is characterized in that the stack 11 forming the composite structure 10 comprises a thermal runaway protection structure 20. The protective structure 20 is therefore an integral part of the composite structure 10 and is not separate from it, which allows it, as described below, to effectively protect the or each storage structure 2 and / or each storage cell 3 against thermal runaway.

[0061] According to the invention, the protective structure 20 comprises at least one protective layer 21 made of carbon fibers, including at least one layer 22 of carbon nanostructures oriented along a stacking Z-axis direction. Figures 7 and 8 illustrate SEM images for visualizing such nanostructures. The use of carbon nanostructures in the stacking Z-axis direction allows for intrinsic heat diffusion during the transient phase II HP / HT, which enables the composite structure 10 to maintain its mechanical performance despite the high temperatures generated during this transient phase II. Indeed, the orientation of the carbon nanostructures significantly increases the transverse conductivity, i.e., the thermal conductivity in the direction of the thickness of the composite structure 10.This has the effect of reducing the temperature increase of the composite structure 10 and thus widening its optimal range of mechanical resistance.

[0062] In this respect, and still according to the invention, the protective layer or layers 21 is interposed between two successive electrically insulating layers 14 and / or between one of the electrically insulating layers 14 and the outer layer 12 and / or between one of the electrically insulating layers 14 and the inner layer 13. In other words, the protective layer or layers 21 is located at the interface(s) between the outer and inner layers 12, 13 on the one hand, and the electrically insulating layers 14 on the other. Thus, in addition to the presence of the protective layer or layers 21 in the composite structure 10, the positioning of the protective layer or layers 21 at the interface(s) ensures a balanced distribution of the functions of the composite structure 10 by alternating the different layers. Furthermore, this improves the heat dissipation dynamics during the transient phase IL

[0063] In [Fig. 4], Tgaz (°C - degrees Celsius) and Pstruct (Pa - Pascals) illustrate, respectively, the evolution of the gas temperature and gas pressure during the thermal runaway phenomenon. Furthermore, Tstruct>i (°C) and Pstructja (°C) illustrate, respectively, the temperature evolution of a storage structure not including a protective structure 20 and the temperature evolution of a storage structure 2, according to the invention, including a protective structure 20 during the thermal runaway phenomenon. As illustrated in this figure, the temperature increase of the storage structure 2 is less in the case of the invention compared to a storage structure according to the prior art because the storage structure 2 according to the invention includes a protective structure 20 as described above.

[0064] Figure 5 schematically illustrates the improvement provided by the invention. In Figure 5, the arrows at the top represent the heat flow that is dissipated from a prior art composite structure, while the arrows at the bottom represent the heat flow that is dissipated from the composite structure 10 of the invention. Transverse conduction is significantly improved in the composite structure 10 of the system 1 according to the invention.

[0065] Let us now return to [Fig. 2]. In the illustrated embodiment, the stack 11 comprises successively, i.e., in this order, from bottom to top, the thermally conductive outer layer 12, a first protective layer 21, a first electrically insulating layer 14, a second protective layer 21, a second electrically insulating layer 14, a third protective layer 21, and the inner layer 13. This arrangement can be denoted 12 / 21 / 14 / 21 / 14 / 21 / 13 with reference to the order in which the layers are found. The stack 11 could be made without the second protective layer 21, namely the protective layer 21 in the center of the stack 11. A 12 / 14 / 21 / 14 / 13 arrangement can be considered for protection against thermal runaway. This allows the goal of the invention to be achieved with a limited number of layers.The stacking could include a higher number of electrically insulating layers 14 and protective layers 21. Other arrangements can be considered, such as an arrangement 12 / 21 / 14 / 21 / 14 / 21 / 14 / 21 / 13, which allows the thickness of the stacking 11 to be increased compared to the embodiment illustrated in [Fig.2] without increasing the individual thickness of each layer.

[0066] Other arrangements can be considered, for example, to reinforce the mechanical strength of the composite structure 10. It is possible to add an inner reinforcing layer (not shown) to stiffen the composite structure 10. This is very advantageous when the stack 11 comprises more than eight layers. However, a reinforcing layer can be used when the stack comprises fewer than eight layers but is very thin. The reinforcing layer can be made of glass fibers and thus have good mechanical strength. When the stack 11 comprises an even number of layers, it can be considered to place the reinforcing layer in a central position. When the stack 11 comprises an odd number of layers, it is preferable to place the reinforcing layer on the side of the central layer that is closest to the inner layer 13.

[0067] According to a particular embodiment illustrated in Figures 6 and 7, the protective layer or layers 21 may further comprise, on each side of the layer 22 of NC carbon nanostructures, a layer 23 of carbon fibers oriented along a longitudinal axis X and / or a transverse axis Y. Preferably, these The 23 layers of carbon fibers are arranged in fabric plies, enhancing the mechanical strength of the protective layer(s) 21 and the composite structure 10 as a whole. In addition to reinforcing each protective layer 21, the 23 carbon fiber layers also protect the NC carbon nanostructures. The 23 fiber layers may be pre-impregnated or unimpregnated.

[0068] In a preferred embodiment, the protective layer or layers 21 have a thickness of between 10 µm and 15 µm. The thickness of the protective layer or layers 21 is comparable to those of the other layers of the composite structure 10, such that the composite structure 10 has a thickness, along the stacking Z-axis, of between 100 µm and 200 µm. Such a thickness facilitates the consolidation and hardening of the composite structure 10 during the manufacturing process of the storage system 1. Furthermore, it helps to control the mass of the storage system 1 and therefore of the aircraft in which the storage system 1 is intended to be implemented.

[0069] The NC carbon nanostructures can consist of nanotubes, nanofibers, nanowires, or other nanostructures. However, it is preferable for the nanostructures to consist of carbon nanotubes because carbon nanotubes, due to their geometry, exhibit high transverse conductivity compared to other NC carbon nanostructures ([Fig. 9]). Carbon nanotubes are therefore more effective at protecting the storage structure 2 against thermal runaway.

[0070] In this regard, the geometry of the carbon nanotubes can be adapted to enhance the performance of the protective layer(s) 21. The average diameter of the NC carbon nanotubes is advantageously between 1 nm and 100 nm. This range of values ​​promotes the protective effect of the protective layer(s) 21. The diameter of the NC carbon nanotubes can also be adapted according to the type of storage cell 3 and / or storage structure 2 that one wishes to protect from thermal runaway. Similarly, the distance separating the NC carbon nanotubes in an extension plane of the protective layer(s) 21, i.e., along the longitudinal axis X and / or the transverse axis Y, is between 5 nm and 100 nm, which promotes the protective effect of the protective layer(s) 21.The distance separating the NC carbon nanotubes can also be adapted according to the type of storage cell 3 and / or storage structure 2 that one wishes to protect from thermal runaway.

[0071] Furthermore, the volume fraction of NC carbon nanotubes in the or each layer 22 of NC carbon nanotubes relative to the total volume of the or each protective layer 21 is at least 20%, preferably at least 40%, and even more preferably at least 60%, which improves the protection provided by the protective structure 20 against thermal runaway.

[0072] At this stage, it should be noted that the invention also relates to an aircraft comprising a storage system 1 as previously described.

[0073] In addition, the invention also relates to a method of protecting at least one electrical energy storage structure 2 against thermal runaway by means of an electrical energy storage system 1 as previously described.

[0074] With reference to Figures 10 and 11, the invention further relates to a method 100 for manufacturing an electrical energy storage system 1 as previously described. In Figures 10 and 11, optional steps are indicated by dashed boxes.

[0075] The manufacturing process 100 comprises a first step 110 consisting of successively depositing along a stacking Z-axis:

[0076] - 111 an outer layer 12 thermally conductive or an inner layer 13 thermally conductive

[0077] - 112 at least one protective layer 21 based on carbon fibers comprising at minus a layer 22 of NC carbon nanostructure oriented along a Z-axis stacking direction,

[0078] - 113 at least one electrically insulating layer 14,

[0079] - optionally 1135, repeat steps 112 and 113,

[0080] - 114 at least a second protective layer 21,

[0081] - 115 the other of the outer and inner layers 12, 13,

[0082] At the end of step 110, a provisional stack of several layers is obtained as previously described. The layers are initially "non-agglomerated" because they are not bonded to each other, for example by means of a binder. However, this does not preclude each layer of the provisional stack considered in isolation, or any of the inner layers considered in isolation, from itself being formed of several agglomerated layers (as is the case, for example, with the protective layer 21). The first step 110 of the manufacturing process 100 of the invention, called the layer deposition step, is therefore likely to vary depending on the nature, number, and arrangement of the layers of the stack 11 to be produced.

[0083] The optional step 1135 can be repeated several times, in particular up to three times.

[0084] Then, in a second step 120 and a third step 130 of the process according to the invention, respectively, the provisional stack is heated 120 and consolidated 130 so as to obtain a monolithic stack 11. The consolidation step 130 may include cooling the composite structure 10. If a binder is used to improve the chemical cohesion between the layers, it may then be heated the temporary stacking up to a temperature greater than or equal to the melting point of the material from which the binder is made. That being said, if any of the outer and inner layers 12, 13, of the electrically insulating layer(s) 14 and protective layer(s) 21 are made of a thermoplastic or thermosetting material, the temporary stacking can then be heated up to a temperature greater than or equal to the melting point(s) of said material(s).

[0085] Following heating steps 120 and consolidation steps 130, the stack formed during deposition step 110 has thus "disappeared," the resulting composite structure 10 being made of a single-piece stack 11. The stack is said to be "single-piece" because the different layers of which it is formed are bonded together, that is to say, the layers form only one piece.

[0086] The heating steps 120 and consolidation steps 130 can advantageously be carried out under pressure. The pressure allows control of the given structure of the composite structure 10.

[0087] The manufacturing process 100 of the system according to the invention may optionally include an additional cooling step 140 of the composite structure 10, for example, to improve its rigidity (for possible transport and use). Thus, during this additional cooling step, the hardness of the composite structure 10 can increase.

[0088] The configurations shown in the cited figures are only possible examples, by no means limiting, of the invention which on the contrary encompasses the variants of designs within the reach of the person skilled in the art.

Claims

Demands

1. An electrical energy storage system (1) for an aircraft comprising: - at least one electrical energy storage structure (2) comprising a plurality of electrical energy storage cells (3), - a composite structure (10) interposed between and / or surrounding the storage cells (3), the composite structure (10) forming a stack (11) comprising, along a stacking axis (Z),: > an outer layer (12) and an inner layer (13), said outer and inner layers (12, 13) being thermally conductive, > a plurality of electrically insulating layers (14) interposed between the outer and inner layers (12, 13),characterized in that the stack (11) comprises a thermal runaway protection structure (20) having at least one protective layer (21) based on carbon fibers comprising at least one layer (22) of carbon nanostructures (CN) oriented along a stacking axis (Z) direction, the protective layer or layers (21) being interposed between two successive electrically insulating layers (14) and / or between one of the electrically insulating layers (14) and the outer layer (12) and / or between one of the electrically insulating layers (14) and the inner layer (13).

2. Electrical energy storage system (1) according to claim 1, wherein the carbon nanostructures (NC) are carbon nanotubes.

3. Electrical energy storage system (1) according to claim 2, wherein the volume fraction of carbon nanotubes (NC) of the or each layer (21) of carbon nanotubes (NC) relative to the total volume of the or each protective layer (21) is at least 20%, preferably at least 40%, and even more preferably at least 60%.

4. Electrical energy storage system (1) according to any one of claims 2 to 3, wherein the average diameter of the carbon nanotubes (NC) is between 1 nm and 100 nm.

5. Electrical energy storage system (1) according to any one of claims 2 to 4, wherein the distance separating the carbon nanotubes (NC) in an extension plane of the or each protective layer (21) is between 5 nm and 100 nm.

6. An electrical energy storage system (1) according to any one of claims 1 to 5, wherein the protective layer or layers (21) further comprise, on each side of the carbon nanostructure (NC) layer (22), a layer (23) of carbon fibers oriented along a longitudinal (X) and / or transverse (Y) axis, the longitudinal (X) and transverse (Y) axes being orthogonal to the stacking (Z) axis and orthogonal to each other.

7. CUA. Electrical energy storage system (1) according to any one of claims 1 to 6, wherein the or each protective layer (21) has a thickness between 10 pm and 15 pm.

8. Electrical energy storage system (1) according to any one of claims 1 to 7, wherein the outer and inner layers (12, 13) are made of carbon fibers pre-impregnated with a first thermoplastic or thermosetting matrix.

9. Electrical energy storage system (1) according to any one of claims 1 to 8, wherein the electrically insulating layers (14) are made of glass fibers pre-impregnated with a second thermoplastic or thermosetting matrix.

10. Electrical energy storage system (1) according to claim 9 when it depends on claim 8, wherein the first and second thermoplastic or thermosetting matrices are made of the same material, preferably a material selected from an epoxy and a polyaryletherketone (PAEK) type thermoplastic.

11. Electrical energy storage system (1) according to any one of claims 1 to 10, wherein the electrical energy storage structure (2) is an aircraft electric battery.

12. A method (100) for manufacturing an electrical energy storage system (1) according to any one of claims 1 to 11, the manufacturing method (100) comprising the following steps: - depositing (110) successively along a stacking axis (Z): - (111) a thermally conductive outer layer (12) or a thermally conductive inner layer (13), - (112) at least one protective layer (21) based on carbon fibers comprising at least one layer (22) of carbon nanostructures (NC) oriented along a stacking axis direction (Z), - (113) at least one electrically insulating layer (14), - optionally (1135), repeat steps (112) and (113), - (114) at least one second protective layer (21), - (115) the other of the outer and inner layers (12, 13), (120) heat and (130) consolidate the stack (11) thus obtained so as to obtain a monobloc stack (11).

13. Method of protecting at least one electrical energy storage structure (2) against thermal runaway by means of an electrical energy storage system (1) according to any one of claims 1 to 11.

14. Aircraft comprising at least one electrical energy storage system (1) according to any one of claims 1 to 11.