Heat shield

Abstract

The invention relates to a heat shield (1) for use in devices and apparatuses operated with batteries, in particular for electric cars, wherein the heat shield (1) is constructed at least from a layer (4) that absorbs impacts, a heat protection layer (5) made of a highly heat-resistant material, optionally a gas-tight heat distribution layer (8) and a layer (6) with expansion properties, and support plates (7) for each of the layers for shielding.

Description

TECHNICAL FIELD

[0001] The present invention relates to a heat shield for use in electrical devices and apparatuses, which are operated with batteries, nowadays mostly with lithium-ion batteries. In particular, the present invention relates to a heat shield for electric vehicles. BACKGROUND

[0002] Electrically operated vehicles are gaining more and more popularity as an environmentally friendly alternative to conventional vehicles with internal combustion engines.

[0003] For operating electric vehicles, rechargeable lithium-ion batteries (LIB) are now primarily used. For this purpose, a plurality of battery cells are combined into modules and the modules are combined into packs, which are installed into the vehicle.

[0004] One problem is the safe operation of the cells and cell packs. It is generally pursued to keep the battery cells in a temperature range between 15 and 35 °C, which can be achieved by corresponding cooling or heating depending on the operating state of the battery system. In extreme cases due to, for example, overcharging, overheating or short circuits in the cells, a so-called "thermal runaway" can occur, which is an uncontrolled heating up to a fire and explosion of the cell. This is a cascading process in which mutually influencing physical and chemical processes reinforce each other, which leads to a continuous temperature rise in the cell.

[0005] The electrolyte consists of different components, wherein some of these components can have a relatively low boiling point of only 90.5 °C (dimethyl carbonate, DMC) or slightly above 100 °C (ethyl methyl carbonate, EMC: 107.5 °C; methyl butyrate, MB: 102 °C).

[0006] In the battery housing a safety valve is provided, which opens when the cell pressure rises, so that reaction gases, which are formed in the battery cell upon overheating, can be discharged thereby. Together with the hot gases, a stream of particles consisting of solid decomposition products is entrained at high speed. These solid decomposition products are formed due to the melting of the current collector, which is typically made of aluminum, and the decomposition of the electrode coating.

[0007] The pressure relief through the valve opening leads to a gas-particle mixture which can easily be ignited to suddenly release from the monomer at temperatures of currently 400°C to 700°C and at high velocities of up to 400 m / s. Here, depending on the monomer size, the particle flow is up to 100 g in the first minute. The emitted gas usually ignites in the air, so that the temperature can quickly rise up to 800°C to 1400°C in about 30 to 60 seconds. Thereafter, the burnt monomer starts to cool down slowly.

[0008] The extreme heat and high impact velocity of the gas and particle flow constitute a high safety risk and a great challenge for thermal insulation materials.

[0009] It is therefore absolutely necessary for the use of such battery systems in vehicles to protect the battery cover and thus indirectly the passenger compartment from the impact of the extreme high temperatures and particle flow in order to guarantee the safety of the passengers.

[0010] Thermal shields are usually used above the safety valve of the monomer or generally above the monomer, for example as module cover, or directly below it or in combination with the battery cover, the task of which is first to protect the passenger compartment located above the battery system from high thermal loads. The aim is to keep the temperature acting onto the vehicle bottom in case of a "thermal runaway" as low as possible, ideally below 200°C, and to prevent a direct entry of flames. It is also necessary to intercept the impact forces of the particles due to the high impact velocity in order to thereby prevent damage, in particular of the passenger compartment.

[0011] The thermal shield must therefore be able to fulfill at least the following three functions in order to effectively work:

[0012] 1. The thermal shield must be able to absorb the particle impact at temperatures of 700°C to 1400°C.

[0013] 2. The thermal shield must have a high heat resistance of up to 1000°C to 1400°C over at least 120 seconds in the blow-out of the propulsion; and

[0014] 3. The thermal shield must be able to dissipate the high temperatures generated at the blow-out in such a way that the temperature on the side of the thermal shield facing away from the battery, that is to say on the side where the passenger compartment is located in the vehicle, does not exceed 400°C and ideally is able to maintain a value below 200°C.

[0015] Another requirement for the use, for example in electric cars, results from the limited space available. The thermal shield should therefore take up as little space as possible but nevertheless still be able to provide the necessary protection. SUMMARY

[0016] According to the application, this task is solved by a heat shield which consists of a plurality of layers of different materials which, in combination, are able to meet the different requirements for effective burst protection listed above.

[0017] The heat shield according to the application has a first layer made of a heat-resistant elastomer or a fiber composite with an elastomer matrix which can compensate for the impact of colliding particles at high impact speeds via elastic deformation and also prevents mechanical damage to the following layers as a result of the impact of the particles. The first layer is usually the layer closest to the battery cell.

[0018] This is followed by a second layer made of a material with high-temperature resistance which can also withstand temperatures of up to 1400°C for approximately 60 seconds, a third layer made of an intumescent material which has an intumescent or swelling property under the action of heat and constitutes an insulating layer as a result of the swelling which functions as a heat sink.

[0019] As a preferred embodiment, a heat-spreading layer can be provided between the second and third layers which can distribute the heat from the second layer over a larger area and thus heat-loads the intumescent layer over a larger area, whereby the effect of the intumescence can be enhanced.

[0020] Furthermore, in order to improve the stability of the stack, a support layer for each functional layer can be provided as the uppermost layer.

[0021] The length and width of the individual layers depend on the size of the battery device, taking into account the flight path of the gas stream and the particle stream when the gas is ejected from the valve.

[0022] The total thickness of the heat shield-composite and thus the thickness of the individual layers is essentially predetermined by the space available for use. For use in an electric vehicle, a total thickness of no more than 1.5 mm is generally desirable.

[0023] From the total thickness of 1.5 mm to be pursued for the heat shield-composite, the average thickness of the individual layers is 0.3 mm and fluctuates between 0.2 mm and 0.5 mm.

[0024] The thickness of the individual layers is determined by the function thereof in the stack. For example, the thickness of the heat shield layer is in the higher region and the thickness of the heat-spreading layer is in the lower region.

[0025] If desired, the individual layers or individual layers can be sewn to one another in order to, for example, prevent unintentional loosening. It has thus proven advantageous to sew the intumescent layer to the layers arranged below and / or above the intumescent layer in order to prevent loosening as a result of the bulging. As a sewing material, a heat-resistant thread material can be used, as is known from fire protection. An example is an aromatic polyamide filament, as is marketed, for example, under the product name Kevlar® or Nomex®.

[0026] A great advantage of the heat shield-composite stack according to the application is its very good 3D deformability. This means that the shield deforms well and thus can be adapted to the structural requirements and spatial circumstances of the purpose of use or the position of use of the shield. BRIEF DESCRIPTION OF DRAWINGS

[0027] The application is explained in more detail below together with the design and composition of the individual layers, with reference to the drawings, which show examples of embodiments of the heat shield according to the application. In the drawings:

[0028] Figure 1 An arrangement of the heat shield according to the application above a battery module is shown;

[0029] Figure 2 An exploded view of the heat shield in Figure 1 is shown;

[0030] Figure 3 Another design of the heat shield according to the application is shown; and

[0031] Figure 4 A graph showing a comparison of the temperature progression over time on the side of the heat shield facing the battery and on the side of the heat shield facing away from the battery in the event of a battery failure is shown. DETAILED DESCRIPTION

[0032] The impact-absorbing layer is the layer of the heat shield-composite that is closest to the battery device. The impact-absorbing layer is therefore also referred to as the "first" or "lowermost" layer of the stack.

[0033] In the arrangement according to Figure 1 the heat shield 1 is located on the face of the battery module that has the safety valve 3. If the battery pack fails, for example as a result of a fire, the hot gases formed escape together with the likewise formed particles consisting of decomposition products through the ruptured safety valve 3 in the direction of the heat shield 1.

[0034] The gas flow and the particle flow are drawn in Figure 1 by dark, line-shaped smoke rising from the safety valve 3 in the direction of the heat shield 1.

[0035] The heat shield 1 prevents the impact forces of the hot gas stream and the particle stream, which impinge on the lower side of the heat shield 1 at high speed, and at the same time protects the side facing away from the battery, for example the side with the passenger compartment in a vehicle, against high temperatures.

[0036] Figure 2 The layer construction of the heat shield 1 shown in Figure 1 The layer construction of the heat shield 1 shown in

[0037] The heat shield 1 is constructed from a plurality of layers made of different materials, which in combination compensate for the impact of the hot gas stream and the particle stream on the one hand and lead the heat away on the other hand, thereby protecting the side of the heat shield 1 facing away from the heat stream against high temperatures on the impact side of the heat shield 1.

[0038] The first layer 4 is made of a high-temperature-resistant elastomer with impact-absorbing properties, which compensates for the impact of the gas stream and the particle stream impinging at high speed by elastic deformation and at the same time can first withstand high thermal loads of up to approximately 400°C to 450°C. The first layer 4 is therefore also referred to as "impact-absorbing layer" according to the invention.

[0039] Examples of suitable elastomers are silicone elastomers, such as fluoro-vinyl-methyl-silicone rubber (FVMQ), methyl-phenyl-silicone rubber (PMQ), methyl-phenyl-vinyl-silicone rubber (PVMQ), methyl-silicone rubber, methyl-vinyl-silicone rubber (VMQ), ethylene-propylene-terpolymer-rubber (EPDM), styrene-butadiene-rubber (SBR), acrylonitrile-butadiene-rubber (NBR), natural rubber (NR), butyl rubber, isobutylene-isoprene-rubber (IIR) and isoprene-rubber (IR).

[0040] As a particularly functional embodiment, mineral fibers can be added to this elastomer layer. Suitable examples are basalt fiber fabrics or silicate fiber fabrics with a weight per unit area of 100 to 600 g / m2.

[0041] The main purpose of the impact-absorbing layer 4 is to intercept the initially very high particle load of the impinging gas stream and the particle stream. This very high load caused by the particle impact initially usually leads to at least partial removal of the layer 4. However, since the particle load is significantly reduced after the first impact, sufficient protection of the further layers by the subsequent thermal protection layer 5 is ensured.

[0042] The subsequent second layer 5 acts as thermal protection against the extreme temperatures during the high-temperature phase of uncontrolled gas ejection. To effectively protect the passenger compartment, this second layer must withstand the peak thermal load of up to 1400°C for approximately 60 seconds. According to the present invention, this second layer 5 is therefore also referred to as a "thermal protection layer."

[0043] Accordingly, the second layer is made of a material having high heat resistance.

[0044] Examples of such high-temperature-resistant materials are mica materials, basalt fiber composites, oxide-ceramic composites, silicate fiber composites.

[0045] In the event that the particles cannot be sufficiently retained by the first layer 4 , the heat protection layer 5 simultaneously protects the subsequent layers from damage due to particle impact.

[0046] As in Figure 2 As shown in FIG, a heat spreading layer 8 is preferably provided between the heat protection layer 5 and the expansion layer 6.

[0047] The heat spreading layer 8 serves to distribute the heat over a larger surface area in order to reduce the thermal load per unit area of ​​the heat shield.

[0048] Advantageously, this layer with high thermal conductivity also has thermal properties that are as anisotropic as possible, so that the heat from the heat spreading layer 8 is introduced into the subsequently arranged layer 6 with expansion properties in a manner distributed over a large area, and the layer 6 with expansion properties can simultaneously expand over a large area and thus form a continuous insulation layer.

[0049] Furthermore, it is advantageous if the heat spreading layer 8 is as airtight as possible in order to thereby support the expansion effect of the layer 6 . The airtightness prevents the swelling gas formed when the expansion layer 6 is activated from escaping through the heat spreading layer 8 and thus no longer being available for swelling of the layer 6 .

[0050] Examples of suitable materials for forming the heat spreading layer 8 with high thermal conductivity and the desired strongly anisotropic thermal properties are, for example, graphite foils, carbon fibers, and ceramic foils based on hexagonal boron nitride (HBN), with graphite foils being particularly preferred.

[0051] The expansion layer 6 is formed from or contains an expanding material. When heated, the layer swells and forms an insulating layer as additional thermal protection.

[0052] It is known to use mineral, carbon or glass nonwovens or felts as thermal insulation layers, which, however, increase the overall thickness of the heat shield and thus its space requirement due to their generally greater layer thickness.

[0053] In contrast thereto, the intumescent material used according to the application can be applied in only a thin layer, which intumescent material swells on demand in the action of heat, for example in such a way that it releases a non-combustible swelling gas, for example nitrogen, carbon dioxide or an ammonium gas.

[0054] Intumescent materials, as the intumescent material can also be used according to the application, are generally known from fire protection. Examples are intumescent graphite, layered silicates based on aluminosilicate-clay minerals, for example clay minerals of the Illit group, etc.

[0055] These intumescent materials are generally embedded in a polymer matrix, which carbonizes or vitrifies under the action of the high temperatures occurring and forms a hard surface as quickly as possible. Examples of polymer materials for the matrix are acrylic resins, epoxy resins, melamine resins, ethylene-vinyl-acetate, etc.

[0056] The composite material consisting of intumescent material and matrix material can be processed into thin layers, for which current techniques can be used, for example screen printing, blade coating, application of thin films, etc.

[0057] According to a particular design variant, the intumescent composite material consisting of intumescent material and matrix material can be introduced into a support structure. By this the mechanical stiffness can be improved. Furthermore a greater layer thickness and thus a greater swelling action can be obtained if required.

[0058] The support structure is an open or closed cavity structure. Examples are honeycomb structures and open-cell resin-reinforced nonwovens and felts, etc., wherein the geometry of the honeycomb can be selected as required.

[0059] The effect of intumescence can also be obtained by using resin systems and their thermal decomposition. For this primarily silicon resins, elastomers, epoxy resins, etc. can be used.

[0060] The combination of the heat shield layer 5, the gas-tight heat spreading layer 8 and the intumescent layer 6 has proved to be particularly advantageous. As explained above, the gas-tightness of the layer 8 prevents the swelling gas formed on activation of the layer 6 from escaping, wherein the heat shield layer 5 protects the heat spreading layer 8 against the influence of the gas-tightness by the gas flow and the particles of the particle flow.

[0061] Additionally, the intumescent layer 6 can be stitched with layers arranged below and / or above the intumescent layer in order to avoid the layer 6 from loosening due to the swelling gas formed. For example in the embodiment shown in Figure 2 the layer 6 can be stitched with the heat spreading layer 8 and / or the subsequent support plate 7. As stitching material the above-mentioned aramid fibers can be used.

[0062] The support plate 7 forms the closed structure of the upper part of the heat shield-composite stack 1 according to the application, which mechanically supports the other layers.

[0063] The support plate 7 can be a glass-fiber composite, a carbon-fiber composite, a basalt-fiber composite, an SMC (Sheet Moulding Compound) composite or a mica-based plate. Mechanically loadable plastics with sufficiently high heat resistance can also be used for the support plate 7.

[0064] Additionally, the heat shield-composite stack 1 according to the application can also be sheathed for further mechanical stability with thin layers made of glass wool or other materials with corresponding mechanical and thermal loadability.

[0065] Fillers can be added to the impact-absorbing elastomer layer 4 as required in order to adjust the material properties in a targeted manner.

[0066] Adjusting the material properties of the polymer by adding fillers and selecting the appropriate degree of filling is known to the person skilled in the art.

[0067] Fillers can be used with which the heat dissipation and heat resistance in the layer 4 can be improved. Examples are graphite, hexagonal boron nitride (HBN), silicon carbide (SIC), aluminum hydroxide (ATH), metal particles, carbon-fiber fabric, C-chopped fibers, C-ground fibers, etc.

[0068] Fillers can be added which support the carbonization, vitrification and expansion of the layer 4 in the high-temperature range, such as aluminum hydroxide (ATH), magnesium hydroxide (MGH, Mg(OH)2), red phosphorus, oxides such as borax (Na2[B4O5(OH)4] x 8H2O), antimony oxide (Sb2O3), expanded graphite, clay minerals of the illite group, etc.

[0069] According to another design variant, heat-spreading fillers can be provided in the impact-absorbing first layer 4. The heat-spreading fillers support the thermal distribution of the hot gas and particle flows over the entire area of the first layer 4 and thus achieve a reduction in the thermal load, in particular in the locations where the hot gas and particle flows first impinge.

[0070] An example of the design variant of adding heat-spreading fillers to the layer 4 is shown in Figure 3 , in which the heat-spreading fillers 9 are shown in a hexagonal pattern, which are provided distributed over the area. As in the design variant according to Figure 2 , this is followed by the high-temperature-resistant layer 5, the heat-spreading layer 8, the expansion layer 6 and the support plate 7.

[0071] Example

[0072] The temperature progression of the heat shield according to the application has been measured and the progression on the side closest to the battery device (impact absorbing layer 4) is compared with the progression on the side farthest from the battery device (support plate 7).

[0073] The construction of the heat shield-composite stack is as follows in the order from the lowermost layer 4 up to the uppermost layer 7:

[0074] Impact absorbing layer 4: fiber composite consisting of basalt fiber fabric with a unit area weight of 400 g / m2and an elastomer matrix (Shore A 25 / 40), thickness 0.3 mm;

[0075] Thermal protection layer 5: fiber composite consisting of silicon fiber fabric with a unit area weight of 300 g / m2and an elastomer matrix, thickness 0.3 mm;

[0076] Thermal spreading layer 8: graphite film, thickness 0.2 mm;

[0077] Inflating layer 6: thickness 0.4 mm, made of an elastomer material which decomposes at temperatures of around 300°C;

[0078] Support plate 7: thickness 0.3 mm;

[0079] Here, layer 6 and layer 8 are sewn to each other in the X direction and the Y direction with aramid threads in such a way that areas of 50 mm x 50 mm size are produced.

[0080] The sewing prevents the thermal spreading layer 8 and the support plate 7 from partially detaching due to the formed bulging gas.

[0081] The results are shown in the diagram in Figure 4 .

[0082] The temperature on the side with the impact absorbing layer 4 (front temperature) significantly exceeds 1000°C even after 120 seconds, while the temperature on the back side (support plate 7) is only 340°C.

[0083] This result shows that with the heat shield-composite stack according to the application, in the case of a "thermal runaway" with an initial temperature of 1200°C, the temperature on the back side of the heat shield can be kept in the order of magnitude of only 340°C even over a period of 120 seconds and thus a significant protection on this side, for example on the passenger compartment of a vehicle, can be guaranteed.

[0084] List of reference signs

[0085] 1 heat shield

[0086] 2 battery

[0087] 3 rupture valve or safety valve

[0088] 4 first layer absorbing the impact

[0089] 5 high-temperature resistant layer (heat shield)

[0090] 6 intumescent layer (insulation layer)

[0091] 7 support plate

[0092] 8 heat spreading layer

[0093] 9 filler for heat spreading

Claims

1. A heat shield (1) for a battery (2) to protect the surroundings from heat and shock damage in the event of battery failure, in, The heat shield (1) has the following layer structure in the order closer to the battery side: a first layer (4) based on a heat-resistant elastomer for absorbing impact; a second layer (5) made of a high-temperature resistant material as heat protection, the high-temperature resistant material being selected from mica materials, basalt fiber composite materials, oxide ceramic composite materials, and silicate fiber composite materials; a third layer (6) with expansion properties for forming a heat insulation structure; and a support plate (7); The heat shield (1) additionally comprises a heat spreading layer (8) between the second layer (5) and a third layer (6) having expansion properties.

2. The thermal shield according to claim 1, wherein The layer stack is encased in a casing made of a mechanically and thermally load-bearing material.

3. The thermal shield according to claim 2, wherein: The cover is formed of glass wool.

4. The thermal shield according to any one of claims 1 to 3, wherein: The first layer (4) contains fillers for improving heat dissipation and / or heat resistance, fillers for supporting carbonization, vitrification and / or expansion, and / or fillers for heat distribution (9).

5. The thermal shield according to any one of claims 1 to 3, wherein The third layer (6) having expansion properties is formed by a support structure comprising a material that expands.

6. The thermal shield according to any one of claims 1 to 3, wherein At least the third layer (6) with expansion properties is sewn to a layer arranged below and / or above the third layer with expansion properties.

7. The thermal shield according to any one of claims 1 to 3, wherein: The heat spreading layer (8) is airtight.

8. The thermal shield according to any one of claims 1 to 3, wherein The heat spreading layer (8) is made of a material having anisotropic thermal properties. 9 . Use of the heat shield according to claim 1 in a battery-operated device as protection against hot gas and particle flows present in the battery in the event of a failure.

10. The use according to claim 9, wherein: The battery-operated device is an electric vehicle.

11. The use according to claim 9 or 10, wherein: The battery is a lithium-ion battery.

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