Gas outlet plate for battery modules

Abstract

The present invention relates to a gas outlet plate (1) having gas outlet flaps (3) with adjustable pressure release as a safety device for a battery module in the event of thermal runaway of a battery cell (6) for discharging the hot gas flow from the cell region of the module, wherein the gas outlet plate (1) has a main plate (2) which is composed of a high temperature-resistant material and in which an arrangement of adjustable gas outlet flaps (3) is inserted, wherein the gas outlet flaps (3) have a free circumference (4), which defines the foldable region, and a bending edge (5), via which the gas outlet flaps (3) are connected to the main plate (2), and open when struck by a hot gas flow, and to the use of the gas outlet plate (1) for producing a battery module, and to a battery module having a gas outlet plate (1).

Description

[0001] Gas outlet plate for battery modules

[0002] The present invention relates to a gas discharge plate as a safety device for battery modules, which, in the event of a thermal failure of a battery cell of the module, ensures safe discharge of a hot gas escaping from the battery cell, which is also enriched with conductive particles in order to prevent it from spreading to neighboring cells and causing a short circuit with the formation of an arc between the battery housing ground and the current-carrying components.

[0003] Furthermore, the present invention relates to a battery module with a gas discharge plate according to the invention and to the use of a gas discharge plate according to the invention for battery modules.

[0004] Rechargeable battery systems are used for electric vehicles, with lithium-ion battery cells being particularly popular these days. Two or more cells are arranged as closely as possible to form a module in a battery cell or module housing and electrically connected to each other. Several battery modules are then combined to form a battery pack and electrically interconnected.

[0005] For operation in vehicles, these battery systems must have very high energy densities, which, however, also pose a high safety risk.

[0006] Safe operation of these battery systems is only possible down to a comparatively low critical temperature. At approximately 80 °C, oxidation processes begin between electrolyte components and components of the battery cell electrodes, leading to progressive heating of the cell and eventual cell damage, even leading to thermal runaway.

[0007] The progressive heat buildup within the cell leads to gas formation, which, with increasing gas pressure, can lead to the cell's explosion. A highly flammable gas escapes from the cell at high pressure, usually igniting immediately upon contact with air and reaching very high temperatures. This very hot gas also carries with it conductive particles, such as graphitic carbon, metallic particles, and other decomposition products of the cell contents.

[0008] In order to reduce the increased cell pressure caused by gas formation, it is known to equip battery cells with venting openings such as a safety valve or a bursting membrane through which the gas can escape into the environment of the battery cell.

[0009] However, even in this case, for the operational safety of the battery cells and, in particular, of any vehicle occupants, it must be ensured that energy transfer to neighboring cells and modules is avoided in order to prevent the spread of thermal runaway or at least to prevent it for as long as possible.

[0010] In particular, it must be prevented that the gas loaded with conductive particles leads to a short circuit between the current-carrying components and the mass of the battery pack and the formation of an arc that can reach temperatures of up to several thousand degrees Celsius.

[0011] For operational safety and to protect vehicle occupants, a suitable protection concept for a battery pack must ensure that no sparks or flames appear outside the battery pack, i.e., become visible, for a period of several minutes after the first sign of thermal runaway of a battery cell is detected. This period until flames become visible outside the battery pack should preferably be no shorter than 5 minutes to meet safety standards.

[0012] This is where the present invention comes in. The present invention relates to a gas discharge plate with adjustable gas outlet flaps having the features of claim 1.

[0013] The subclaims relate to preferred embodiments.

[0014] Furthermore, the present invention relates to a battery cell module with a gas discharge plate according to the invention with adjustable gas outlet flaps and a module housing with a gas discharge plate with adjustable gas outlet flaps, as well as the use of a gas discharge plate according to the invention with adjustable gas outlet flaps for a battery module or module housing.

[0015] The gas discharge plate according to the invention with adjustable gas outlet flaps is formed from a high-temperature-resistant base plate which has gas outlet flaps which are designed to open upon the action of a predetermined gas pressure and to discharge gas from the interior of a battery module.

[0016] In the context of the present invention, “adjustable gas outlet flap” means that the gas outlet flap is only triggered when a predetermined pressure is applied.

[0017] A thermally continuous battery cell is also called a propagating battery cell.

[0018] The gas outlet flaps are partially cut out areas in the base plate, whereby a part of the circumference of the area is detached from the base plate, this part is referred to here as the “free circumference”, and only the remaining part of the circumference is connected to the base plate, this connected part is referred to here as the “kink edge”.

[0019] The free circumference may be separated from the base plate continuously over the entire thickness of the base plate, the separation may also be only partial, for example, the separation of the thickness of the base plate may not completely pass through the base plate, or the base plate may have a perforation along the free circumference.

[0020] The shape of the gas outlet flaps can be selected as needed. They can be round, oval, or square. They must be sufficiently large to ensure the incoming gas flow is safely and completely diverted.

[0021] During normal operation, the base plate and gas outlet flaps form a substantially flat surface. If the pressure acting on a gas outlet flap due to gas escaping from a battery cell exceeds a predetermined value, the gas outlet flap yields to the pressure and folds open along the bent edge, diverting the gas flow from the propagating battery cell. The gas outlet plate according to the invention enables the rapid and immediate discharge of a hot gas flow laden with conductive particles escaping from an overheated cell of a module from the battery module, without causing a short circuit or arcing between current-carrying components and the ground of the battery pack.

[0022] In accordance with safety regulations, the spread to neighboring battery cells and the occurrence of visible flames outside the battery pack can thus be prevented for a sufficiently long period of at least 5 minutes and, in particular, at least 7 minutes and longer.

[0023] With regard to the task, the gas discharge plate with gas outlet flaps according to the invention is made of a high-temperature-resistant material so that safe gas discharge can be ensured without the plate itself catching fire or deforming due to the thermal effects.

[0024] Preferably, the gas discharge plate is formed from a layered structure of high-temperature-resistant fiber composite material, with high-temperature-resistant fibers being used in particular for the layers.

[0025] The gas discharge plate according to the invention can be used equally for modules made of prismatic cells, cylindrical cells (round cells) or pouch cells.

[0026] Due to its structure, the gas discharge plate according to the invention can absorb mechanical loads that arise during assembly of the battery cells, so that it can also be used as a structural component for the module housing.

[0027] For example, the gas discharge plate according to the invention with adjustable gas outlet flaps can be integrated into a module housing depending on the position of the degassing openings on the outer surface of the battery cells.

[0028] For example, if the venting openings are located on the top side of the battery cells of a battery cell arrangement, the gas venting plate according to the invention can be designed as a cover of the module housing. If the venting openings are located in the bottom surface of the battery cells, the gas venting plate can form the mounting surface or the bottom surface of the module housing.

[0029] The gas discharge plate can also be arranged as a component in the module between the area with the degassing openings of the battery cells and the module housing wall.

[0030] To divert a gas stream escaping from a propagating battery cell as quickly as possible from the danger zone, the respective gas outlet flaps should be positioned close to the battery cell vents to ensure that the gas outlet flaps can open as quickly as possible under the combined temperature and pressure load. The gas outlet flaps of the non-propagating cells must remain closed to prevent contact of the non-propagating cells with the electrically conductive particles in the gas in these areas.

[0031] Typically, each battery cell in a module is assigned a gas outlet flap in the gas discharge plate. Very large battery cells with more than one venting opening can be assigned two or more gas outlet flaps if necessary. Depending on the specific application, there may also be fewer gas outlet flaps than battery cells.

[0032] For example, according to one embodiment, for a module of battery cells with venting openings in the base surface, the gas discharge plate can serve as a support surface for the battery cells and simultaneously as the base plate of the module, wherein the gas discharge plate can have a gas outlet flap for each battery cell. The peripheral shape of the gas outlet flaps can expediently be adapted to the shape of the base surface of the battery cell, for example, essentially circular in the case of a round cell or rectangular in the case of a prismatic cell.

[0033] Generally, the area of ​​the gas outlet flap is smaller than the base area of ​​the battery cell, but at least sufficiently large to fully encompass the venting opening and thus any escaping gas flow. A key feature of the present invention is the determination and adjustment of the opening pressure of the gas outlet flaps. The opening pressure must be adapted to the trigger pressure of the venting openings of the battery cells. In particular, it must be selected sufficiently low to ensure rapid and safe discharge of the gas flow from a propagating cell.

[0034] If the opening pressure is too high, the flap will only open with a delay when needed, or even not at all. If it is too low, there is a risk that the gas outlet flap will open prematurely, e.g., due to external influences during module manufacturing. Alternatively, the pressure of the gas escaping from one cell could also cause neighboring gas outlet flaps to open when needed, posing a risk of contamination of neighboring cells with electrically conductive particles in the gas stream.

[0035] The vents of commercially available lithium-ion battery cells typically open at a pressure between 0.4 and 13 bar. The pressure at which the opening occurs is influenced by numerous factors, such as cell size, cell chemistry, state of charge, cell geometry, the design of the battery cell's vents, and the basic cell design.

[0036] According to the invention, the opening pressure of the gas outlet flaps is precisely adjusted in accordance with these requirements, whereby the opening pressure is influenced in particular by the length of the bending edge and the thickness of the base plate as well as the size of the area of ​​the gas outlet flap exposed to gas and the material composition of the base plate.

[0037] In the case of a gas outlet flap with a circular plan, the length of the kink edge is the distance between the two end points of the circle segment representing the flap area, ie the free circumference defines a circle segment forming the flap area, as shown below, for example, in Figure 1.

[0038] To determine and adjust a defined opening pressure of a gas discharge plate according to the invention with gas outlet flaps, in particular for designing the dimensions, including the geometry of the bending edge and the length, a simple test was developed using a bending strip and a weight. The bending strip is made of the same material as used for a gas discharge plate and has the same thickness. The test is explained below with reference to Figure 5 using the example of a gas outlet flap with a circular basic shape.

[0039] With a circle diameter of 43.5 mm, based on a trigger pressure of a degassing opening of 0.4 bar, a pressure of 0.04 MPa acts on the circular area, which corresponds to a force of 59.4 N and thus a weight of 6 kg.

[0040] The determination of the opening pressure can be carried out on this basis, for example, using a balance such as a spring balance, on appropriately manufactured bending strips, whereby the weight is determined at which a bending strip with a predetermined width corresponding to a bending edge and a length corresponding to the extension of the foldable area of ​​the flap bends from the bending edge to the opposite end of the free circumference.

[0041] Analogously, the test can be used to determine and set the trigger pressure for gas outlet valves with a basic shape other than a circular shape.

[0042] The gas vent plate according to the invention is made of a high-temperature-resistant material to ensure safe venting of the hot gas without the gas vent plate itself catching fire or deforming due to thermal effects. The gas vent plate expediently has a temperature resistance of at least 600°C, and preferably higher, up to at least 1400°C, and is itself electrically non-conductive.

[0043] Preferably, the gas discharge plate is formed from a layered structure of fiber composite layers. High-temperature-resistant fibers are used for the fiber composite layers.

[0044] In particular, mineral fibers such as basalt fibers, glass fibers, silicate fibers, and oxide-ceramic fibers can be used. The fibers can be in the form of a fabric such as a woven or nonwoven fabric, whereby the fabrics themselves can be made from rovings or yarns made from these fibers.

[0045] According to one embodiment, the fiber orientation can be bidirectional, e.g., in particular, 0790°. However, the fiber orientation can vary as needed, e.g., it can also be multidirectional, such as 0790745°, etc.

[0046] The plastics used as matrix materials also exhibit high temperature resistance. Examples include silicone resins, especially silicone resins with a high SiO content, especially an SiO content of 50 to 90%, and particularly preferably 75% and higher.

[0047] Silicone resins with a SiO content of at least 80% have proven particularly suitable. According to one embodiment, silicone / phenolic resin blends, silicone / epoxy blends, or other suitable resin blends can be used to improve or adjust the properties.

[0048] Di- and / or trifunctional polysiloxanes can be used as silicone resin, preferably with methyl and / or phenyl substituents.

[0049] An example of a suitable silicone resin is a methylsilicone resin sold under the trademark SILRES® MK by Wacker.

[0050] The individual layers of the gas discharge plate can have different fibers and / or different fiber orientations.

[0051] For example, a layered structure can consist of one or two cover layers made of a first fiber composite material with—as needed—one or more intermediate layers made of a second fiber composite material. The layers of different fiber composite materials can be arranged alternately.

[0052] The thickness of each layer should be as thick as necessary, but as thin as possible.

[0053] The overall thickness of the gas discharge plate should be as small as possible to achieve the desired space savings; preferably, the overall thickness should not exceed 1.5 mm. A thickness of 1 mm or less is preferred to accommodate the desired compact, space-saving design of battery assemblies.

[0054] Preferably, the thickness should be selected so that the gas discharge plate has sufficient mechanical stability, for example, to support the battery cells until the battery assembly has been encased, for example, with a sealing foam. If necessary, a support foil can also be used, as described in more detail below.

[0055] According to one embodiment, a thin foil can be applied to the side of the gas outlet plate facing away from the battery cells. This foil serves to mechanically stabilize the gas outlet plate and prevent premature opening of the gas outlet flaps due to the application of force during module production.

[0056] For example, depending on the application, the spaces between the joined battery cells can be filled with an expanding foam mass for stabilization and electrical insulation. The resulting expansion pressure can be sufficient to force open the gas outlet flaps. According to one embodiment of the invention, the film prevents unintentional premature opening.

[0057] In addition, the film seals the dividing line along the free circumference between the gas outlet flaps and the base plate so that no moisture can penetrate.

[0058] Suitable films must have low tear strength and low elongation at break to ensure they fail quickly under pressure if necessary, allowing the gas outlet flaps to open safely. A low melting point of the films is also advantageous, as the opening of the gas outlet flaps is thermally supported by the melting of the film.

[0059] Self-adhesive films are particularly advantageous because they can be applied without much effort.

[0060] Examples of suitable self-adhesive films are the electrical adhesive tapes from SynFlex, sold under the product name SynTape®. SynTape® F / X.50, with its aramid paper backing and acrylate-based adhesive, is particularly suitable in terms of its low thickness, tensile strength, and elongation at break. It features a total thickness of 0.05 mm, a tensile strength of 35 N / 10 mm, and an elongation at break of 5%. However, depending on the specific application, films with different thicknesses and different tensile strength and elongation values ​​can be used.

[0061] The present invention is explained in more detail below using an example of a gas discharge plate for round cells with reference to the attached figures, which show an embodiment for an application of the gas discharge plate according to the invention with adjustable gas outlet flaps.

[0062] It shows

[0063] Figure 1 is a plan view of an inventive

[0064] Gas discharge plate with an arrangement of adjustable gas outlet flaps in the area of ​​the installation surfaces for battery cells,

[0065] Figure 2 is a plan view of an inventive

[0066] Gas discharge plate with adjustable gas outlet flaps,

[0067] Figure 3 shows a longitudinal section along line A according to Figure 2;

[0068] Figure 4 shows a longitudinal section along line A according to Figure 2 with

[0069] round cells;

[0070] Figures 5a and 5b show a schematic representation of the determination of the length of a bending edge and the bending strip test for determining the release pressure; and

[0071] Figure 6 is a plan view of the underside of the gas discharge plate according to Figure 1 with a cover film. Figure 1 shows a plan view of a gas discharge plate 1 according to the invention, comprising a base plate 2 and an arrangement of adjustable gas outlet flaps 3 for an array of round cells. The arrangement is hexagonal in shape to achieve the densest possible packing for the round cells. It is understood that, in principle, any other suitable arrangement is also possible.

[0072] In the illustrated embodiment, the gas outlet flaps 3 essentially have a circular shape with a free circumference 4 that describes a circular arc, wherein the connecting line between the two end points of the free circumference 4 defines the bending edge 5 of the gas outlet flap 3, along which the gas outlet flap 3 opens when necessary.

[0073] The gas outlet flaps 3 are oriented in the same direction, with the bend edges 5 aligned parallel to each other.

[0074] However, the alignment of the bend edges 5 and orientation of the gas outlet flaps can be selected depending on the requirements of the individual application.

[0075] In the figure, each gas outlet flap 3 corresponds to a mounting surface for a round cell (not shown).

[0076] Figure 2 shows a top view of a gas outlet plate similar to Figure 1, with round cells 6 indicated in the bottom row of the figure on the three right-hand gas outlet flaps 3. The bottom surface of the round cells 6 has a slightly larger diameter than the gas outlet flaps 3, as indicated in the middle illustration of the gas outlet flaps 3 with round cell 6, and completely covers the gas outlet flaps 3.

[0077] Figures 3 and 4 show a longitudinal section through the lower row of gas outlet flaps 3 along line A in Figure 2. Figure 3 shows the section without round cells 6 and Figure 4 with round cells 6.

[0078] In Figure 3, all gas outlet flaps 3 in the row are closed, and base plate 2 and gas outlet flaps 3 form a single plane. Figure 4 shows a failure scenario with a propagating cell 7, in which a hot gas stream 8 exits through a vent opening in the base of the round cell 7, and the pressure of the gas stream 8 causes the underlying gas outlet flap 3 to open. The gas stream 8 is diverted through the open gas outlet flap 3 from the installation area of ​​the battery cells 7, for example, from a module housing.Since the gas outlet flaps 3 of the non-propagating cells remain closed, there is no contact between the gas flow 8 and in particular the electrically conductive particles located in the gas flow 8 and the battery cells or other electrically conductive components, so that a spread of the thermal runaway of the propagating cell 7 to further cells 6 and in particular a short circuit and formation of an arc are reliably prevented.

[0079] Figures 5a and 5b schematically show the determination and adjustment of the opening pressure of the adjustable gas outlet flaps 3 according to the invention using the example of gas outlet flaps 3 with a circular basic shape.

[0080] The hinged part of the gas outlet flap 3 is a circular segment or circular section of a circle with a diameter d (43.50 mm in the figure). The free circumference 4, i.e., the area separated from the base plate 1 or at least partially separated, defines a circular arc, with the folded edge 5 being the connecting line between the endpoints of the circular arc, i.e., the chord of the circle.

[0081] In other words, and as shown in Figure 5a, the length of the folding edge 5 results from the distance between the endpoints of the circular arc defined by the free circumference 4 and the tangent that lies at the full diameter of the circle and is closest to the folding edge (on the right in the figure). The length of the folding edge is the distance between the two intersection points with the tangent. The maximum extent of the foldable area is the distance between the folding edge and the tangent at the full diameter of the free circumference 4 (on the left in the figure).

[0082] In Figure 5b, the situation from Figure 5a is transferred to a bending strip test in order to determine, for a given material composition, the pressure at which a bending edge of a given length bends and thus opens in the case of a gas outlet flap as shown in Figure 5a.

[0083] Horizontally, Figure 5b shows different widths for the bending edge, while vertically the corresponding distance of the bending edge from the tangent at the free circumference 4 is shown. This provides a measure of the remaining area, in this case a circular area, which can open due to gas pressure.

[0084] Figure 6 shows a gas vent plate 1 with adjustable gas outlet flaps 3 and a film 9 applied thereto. The film 9 is applied to the side of the gas vent plate 1 opposite the side with the battery cells. The film 9 serves primarily to seal and prevent moisture from entering the battery side. It can therefore be designed to be very thin. Furthermore, the film 9 can also support mechanical stability.

[0085] To ensure that the film 9 does not impede the opening of the affected gas outlet flaps 3 in the event of a battery cell failure, it should have low elongation at break and low tear strength. It should preferably tear as quickly as possible upon application of pressure, with as little elongation as possible.

[0086] Example

[0087] A gas discharge plate with gas outlet flaps for round cells according to the invention was manufactured, whereby the opening load of the gas outlet flaps was set to 6 kg.

[0088] The gas discharge plate consisted of a 4-layer fiber composite material with an upper and lower cover layer made of a composite of a basalt fabric with a surface weight of 420 g / m 2 and two intermediate layers of silica fabric with a basis weight of 300 g / m 2 The matrix material was a silicone resin, SILRES® MK from Wacker.

[0089] The total thickness of the gas discharge plate was 1.3 mm. The thickness of the basalt fiber composite layers was 0.35 mm each, and the thickness of the silicate fiber composite layers was 0.3 mm each.

[0090] Gas outlet flaps were incorporated into the base plate made of fiber composite material, in the shape of a circular segment of a circle with a diameter of 43.5 cm and a chord forming the bending edge with a length of 39 mm.

[0091] A bending strip test as shown in Figure 5b showed that the resulting gas outlet flap opens reliably under a load of 6 kg.

[0092] 1 Gas outlet plate 2 Base plate

[0093] 3 Gas outlet flap

[0094] 4 free scope

[0095] 5 Bend edge 6 Round cell

[0096] 7 propagating round cell

[0097] 8 Gas flow

[0098] 9 Slide

Claims

Claims 1. Gas discharge plate (1) with an adjustable gas outlet flap (3) for discharging a hot gas flow (8) emerging from a venting opening of a propagating battery cell (7) from the cell region of the battery module, wherein the gas discharge plate (1) has a base plate (2) into which an arrangement of adjustable gas outlet flaps (3) is inserted, wherein the base plate (2) is made of a high-temperature-resistant material having a temperature resistance of at least 600°C, wherein the gas outlet flaps (3) have a free circumference (4) defining the foldable region, and a bent edge (5) via which the gas outlet flaps (3) are connected to the base plate (2), wherein the adjustable gas outlet flaps (3) are designed to open under pressure upon impact of a gas flow (8) and to discharge the gas flow (8) from the cell region of the battery module.

2. Gas discharge plate (1) with adjustable gas outlet flaps (3) according to claim 1, wherein the basic shape of the gas outlet flaps (3) is round, oval or rectangular.

3. Gas discharge plate (1) according to claim 1 or 2, wherein the gas discharge plate (1) is designed as a mounting area for battery cells with a degassing opening in the bottom surface for a battery module.

4. Gas discharge plate (1) according to one of the preceding claims, wherein each battery cell (6) is assigned at least one gas outlet flap (3).

5. Gas discharge plate (1) according to one of the preceding claims, wherein on the side of the gas discharge plate (1) facing away from the battery cell arrangement, a film (9) is applied, which is designed to tear when a gas outlet flap (3) is opened.

6. Use of a gas discharge plate (1) with adjustable gas outlet flap (3) according to one of claims 1 to 5, as a safety device for a battery module.

7. Use according to claim 6, wherein the gas discharge plate (1) is a component of the housing wall of the battery module and is arranged on the side of the housing which, in the finished state, is opposite the degassing openings of the battery cells.

8. Battery module with a gas discharge plate (1) with adjustable gas outlet flaps (3) according to one of claims 1 to 5, wherein the battery module comprises an arrangement of at least two battery cells (6) with venting openings and a housing for receiving the battery cells (6), wherein the gas discharge plate (1) with gas outlet flaps (3) is arranged opposite the venting openings of the battery cells (6).

9. Battery module according to claim 8, wherein the gas discharge plate (1) forms the bottom surface or the top surface or the lid of a battery module.

10. Battery module according to one of claims 8 or 9, with battery cells (6) which are selected from cylindrical or prismatic cells or pouch cells.

11. Battery module according to one of claims 8 to 10, for battery cells (6) with degassing openings in the bottom surface, wherein the gas discharge plate (1) forms the mounting surface for the battery cells (6).

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