Insulation mat for battery systems

Abstract

The invention relates to an insulating mat (1) for separating adjacent battery cells (2) in a battery system, in particular rectangular battery cells, which consists of an elastically deformable substrate (7) made of a fiber-elastomer composite, the two main faces of which are provided with a given number of ribs (8) running parallel to one another and spaced apart from one another across the main faces of the substrate (7), the rib units on the two main faces being surrounded by an annular frame (10) with gaps (11) between the ribs (8) and the frame (10), the fiber-elastomer composite of the substrate (7) being formed from an elastomeric matrix in which at least one intermediate layer of mineral fibers is embedded, the insulating mat simultaneously being able to compensate for the system-specific volumetric changes of the battery cells due to chemical degradation of the cell components and the cyclic expansion and contraction of the cells during charging and discharging.

Description

[Technical field]

[0001] The present invention relates to an insulating mat for a battery system, in particular a lithium-ion battery system, where the insulating mat is arranged between the individual cells of the battery system, thereby preventing overheating from progressing to adjacent battery cells in the event of failure of the battery cell, for example as a result of overheating of the battery cell. The insulating mat according to the invention can be advantageously used in battery systems such as those used in the field of electric vehicles. [Background technology]

[0002] A battery system is generally made up of a number of individual cells, which allows the required high energy density to be achieved. A certain number of individual cells are then combined into a module, which are then combined into a stack and electrically connected to one another. The resulting battery system is then placed in a hermetically closed housing to protect it from external influences.

[0003] In principle a distinction is made between cylindrical, prismatic and pouch-type battery types: prismatic cells have a rectangular parallelepiped shape with a rigid housing (also called cell cup), whereas pouch-type cells, also called coffee bag-type cells, have a flexible cover made of a sheet. Summary of the Invention [Problem to be solved by the invention]

[0004] The invention particularly relates to battery systems with rechargeable batteries, also called accumulators, so-called secondary batteries. Battery systems frequently used, for example in the field of electric vehicles, are battery systems based on lithium-ion batteries.

[0005] In order to ensure reliable operation of a battery system consisting of multiple single cells, if a cell fire occurs in one battery cell, for example as a result of overheating, it is essential to prevent the cell fire from spreading to adjacent cells to the point of burning out the entire battery system (thermal runaway).

[0006] In the case of a cell fire, temperatures of over 600°C can occur within a matter of seconds. To prevent overheating and the spread of the fire to adjacent cells, measures must be taken to prevent the temperature of the adjacent cells from rising above a critical value.

[0007] The factors that determine this critical temperature value in a lithium-ion battery are, inter alia, the electrolyte or its composition and the activation range of the shutdown separator.

[0008] For lithium-ion batteries, electrolytes are used that have a boiling point of 100 °C and contain easily ignitable components. Therefore, the cell temperature must be kept below the boiling point to avoid pressure buildup in the hermetically closed cell. In the event of extremely high internal cell pressure, a safety valve is opened to allow the gas formed to escape, and under these conditions the highly reactive electrolyte usually ignites immediately. A shutdown separator is a safety measure that blocks the ion migration and interrupts the flow of electric current by blocking the separator's micropores when a critical temperature is exceeded. Shutdown separators are known that are made of a laminate of two polymer sheets, where the polymers have different melting points. For example, a frequently used shutdown separator is made of a polyethylene / polypropylene laminate, with polyethylene having a melting point of 120 °C and polypropylene having a melting point of 170 °C. When the melting point of the polymer sheet with the lower melting point, in this case polyethylene, is exceeded, this polymer sheet melts and blocks the pores of the polymer sheet that melts at a higher temperature, in this case polypropylene.

[0009] From the above it is clear that in order to avoid overheating of the cell and the associated safety risks, the cell temperature must necessarily be kept below 150°C, in particular below 120°C and preferably as far as possible below 100°C.

[0010] It is known to provide thermal insulation between adjacent cells to prevent the adjacent cells from heating above a critical temperature and thus causing a cell fire.

[0011] Besides thermal insulation, further aspects may be taken into consideration for the safe operation of a battery system.

[0012] In other words, it is desirable for the heat insulating means to simultaneously have a function of an electrical insulator that electrically insulates the cells of one module from the potential difference applied to the cells or cell housings.

[0013] Another important aspect in forming lithium-ion battery systems is the system-induced volume change (also known as swelling) of the battery cells, which is caused on the one hand by the continuous cell expansion due to the chemical degradation of the cell components and on the other hand by the cyclic expansion and contraction of the cells during charging and discharging. This system-specific volume change must be taken into account, especially when manufacturing battery systems based on prismatic cells, due to their rigid cell housings. In this case, the volume increase of the cell components leads to an expansion in the central region of the large main surface. In contrast, the edge regions are mechanically stabilized by the corners that connect to the adjacent surfaces.

[0014] For typical dimensions of prismatic cells for automotive applications, 236mm long, 115mm high and 32mm thick, when a degraded prismatic cell is charged, the main surfaces may expand by less than 0.2mm to 1mm, which can result in a total expansion of less than 2mm to 10mm in a module, typically containing 10 to 14 individual cells.

[0015] It is therefore desirable that the insulating mat, in addition to thermally and electrically insulating adjacent battery cells, can advantageously compensate for the volumetric expansion of the cells, both the cyclic volume changes during charging and discharging, and the continuous volume increase, over the service life of the cells.

[0016] Additionally, it is desirable for the insulating mat to have minimal weight, install in a space-saving manner, and be inexpensive.

[0017] By thermal insulation it is meant that in the event of a cell fire generating heat of 600°C or more, the heat transferred to adjacent cells within only 30 seconds should be limited to preferably less than 100°C.

[0018] Ensuring compensation for cell volume changes over life requires that the material be elastically deformable and have a sufficiently small compressive strain so that it does not solidify under compressive loads and temperature fluctuations.

[0019] A further consideration is that to assemble a module, the desired number of single cells, typically 12-14, are grouped together in a stack, pressurized with a pre-load force, e.g. 5-19 kN, and fixed based on this pre-load force to obtain a defined stack geometry. The insulating mat must be able to maintain this pre-load over its entire lifespan in order to guarantee the dimensional stability of the module. [Means for solving the problem]

[0020] According to the invention, the problem stated above is solved by an insulating mat comprising an elastically deformable substrate made of a fiber-elastomer composite, on both main faces of which a predefined number of ribs are provided, which run parallel to each other and spaced apart from each other across the substrate's main faces, the ribs on both main faces being offset from each other, the substrate with the ribbed structure being surrounded by an annular frame, the ribs being separated from the frame, preferably likewise made of an elastomeric material.

[0021] By "staggered" the ribs we mean that a rib on one major surface of the substrate extends into a space between two ribs on the other major surface of the substrate. The space between the ribs is preferably wider than the width over which the ribs extend, thereby allowing the ribs to resiliently flex into the space.

[0022] By "separate" it is meant that the ribs are not attached to the frame, i.e., neither the end faces of the ribs nor the outer side faces of each outermost rib are in contact with the frame.

[0023] The dimensioning of the insulating mat according to the invention depends on the respective application: in the form described herein, the insulating mat is specifically designed for use between prismatic cells, although the insulating mat can easily be adapted for use with other types of batteries.

[0024] For use as intermediate insulation for rectangular battery cells, the insulating mat has a substantially rectangular basic shape. The periphery of the insulating mat may be aligned with the periphery of the battery cell in the installed state. Alternatively, the frame or the edges of the frame may protrude beyond the periphery of the battery cell, for example with a long side or a short side or both.

[0025] The elastically deformable substrate has a planar rectangular shape with two main surfaces, each of which is provided with a number of ribs extending across the main surfaces, arranged parallel to and spaced apart from one another, with the ribs of the two main surfaces being offset from one another.

[0026] The substrate with the rib units is surrounded by an annular frame, the insulating mat according to the present invention is disposed between adjacent rectangular battery cells with the major surfaces in contact with each other, and the exposed upper surface of the frame contacts the adjacent battery cell or cells in the installed state.

[0027] In the assembled state, the frame of the insulating mat thus extends along and can be supported on the dimensionally rigid edge of the battery cells, in such a way that pre-loads applied to the battery cells and the frame of the insulating mat when constructing the module can be received and compensated for via the annular frame.

[0028] The frame is desirably only very slightly deformed by the preload and has a correspondingly low compressibility. The compressive strength of the frame can be adjusted in various ways depending on the elasticity of the material, the width of the frame, and the structure of the frame. For example, depending on the compressive modulus of the elastomeric material used to manufacture the frame, the frame height can be selected so that the desired frame thickness is obtained after tightening during module construction.

[0029] Expansion of the main surfaces of the cells due to volume increase due to ageing and charging processes is compensated via ribs associated with the elastically deformable substrate, as described in more detail below.

[0030] When the expansion of one main surface of one battery cell exerts pressure on the ribs of the adjacent insulating mat of the present invention, the ribs are displaced into the intervals between the ribs arranged on the other surface of the substrate, which are located below the respective ribs, due to the deformation of the substrate. For example, when the expansion part contracts and the pressure is released due to discharge, the ribs can return to their initial state again due to the elasticity of the substrate. The elastically deformable substrate on which the ribs are arranged acts as a spring member, and in this case, when a compressive load is applied, it bends elastically, and when the compression is relieved, it springs elastically back to its initial state.

[0031] In one advantageous configuration, an adjustable pressure can be applied to the cell surfaces via a substrate on which the ribs are arranged, acting as a spring element, so that the cell stack is lightly compressed in addition to the clamping pressure. It has been found that the additional pressure obtainable in this way can have a positive effect on the cycling stability of the cells of the stack.

[0032] The degree of spring-elastic deflection can be controlled by a number of different means which may be used alone or in combination of two or more.

[0033] For example, the degree of spring-elastic deflection can be controlled geometrically by the spacing between the ribs, which is preferably at least 1.5 to 2 times the rib width. The wider the spacing compared to the rib width, the more the substrate-rib structure can deform, i.e., the deeper the ribs, together with the substrate, can be pushed into the spacing.

[0034] Furthermore, the degree of spring-elastic deflection is determined by the composition and material of the substrate. The substrate is made of a fiber-elastomer composite with a matrix of elastomeric plastic (elastomer) and has at least one intermediate layer of fibers (also called fiber interlayer) embedded in the substrate. Besides the required elasticity, the elastomer must have sufficient heat resistance to be able to withstand high temperatures in case of a cell fire.

[0035] Examples of suitable high temperature resistant elastomers are silicone elastomers such as methyl-phenyl-silicone rubber (PMQ), methyl-phenyl-vinyl-silicone rubber (PVMQ), methyl-silicone rubber, methyl-vinyl-silicone rubber (VMQ), fluoro-vinyl-methyl-silicone rubber (FVMQ), ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), natural rubber (NR), butyl rubber, isobutane-isoprene rubber (IIR), and isoprene rubber (IR) and polyurethane (PUR).

[0036] The elasticity of the elastomer is preferably in the range of 20-80, particularly 45-75, and particularly preferably 50-60 Shore A hardness.

[0037] In view of the desired heat resistance, mineral fibres, such as glass fibres, basalt fibres, silica fibres and oxide ceramic fibres, are used in the fibre intermediate sheet. The mineral fibres may be present in the form of a surface structure, such as a woven fabric or a scrim, which may itself be produced from rovings or threads made from these fibres. The fibres are typically in a density of 20 g / m 2 ~200g / m 2 For example, if more than one fibrous interlayer is provided, the weight per unit area of ​​the individual layers may be within the range below or even less.

[0038] The fibers are embedded in the elastomer matrix as reinforcing interlayers. In the case of more than one fiber interlayer, a thin layer of elastomer may be provided between the individual fiber interlayers as a binder.

[0039] One suitable material combination for the substrate is a silicone elastomer with one or two intermediate layers of woven fiberglass cloth.

[0040] Besides the type of elastomer, the deformability of the substrate and therefore the degree of spring-elastic deflection is determined by the orientation of the fibers. The least deformability is shown at 0° / 90° orientation, where there is no or at most only slight spring-elastic deflection. In contrast, the fibers show maximum fiber movement with maximum spring-elastic deflection between the ribs at ±45° orientation. An example of a suitable orientation lying between these values ​​is a 30° / 120° orientation. When spring-elastic deflection occurs, the substrate stretches in the longitudinal direction, where the angle between the fibers decreases, i.e. an interaction occurs between the matrix and the fibers.

[0041] Furthermore, the elasticity can be modified by adding inorganic fillers to the elastomer matrix. In this case, the fillers can take on a purely mechanical function. When the elastomer is deformed, the spacing between the filler particles decreases until they come into contact with each other, thus preventing further deformation of the elastomer. The realization of the blocking effect can be influenced via several parameters, such as the degree of filling, the particle size and shape, the particle size distribution (monomodal, bimodal or trimodal). For example, the particle shape, for example round or sharp, affects the sliding and blocking properties of the particles in the matrix.

[0042] The filler may be essentially of ceramic, carbon-based or metallic nature. However, when selecting the filler, the thermal and electrical properties of the filler should be taken into account with respect to the basic thermal and electrical insulation functions of the insulating mat according to the invention. Therefore, fillers with minimal electrical conductivity, such as ceramic fillers, are preferred.

[0043] In addition to tailoring the mechanical and electrical properties, fillers may be added to improve the thermal behavior of the elastomer.

[0044] For example, a filler that reduces thermal conductivity can be used, which can be a material that forms an insulating air or gas cushion, such as hollow bodies, e.g. glass hollow spheres, or a highly porous material, such as aerogel, aerosil or expanding materials.

[0045] Fillers can also be used that react endothermically at fire temperatures to remove heat energy from the system. These are, for example, materials that ceramify, vitrify or carbonize at flame temperatures, have a cooling effect and remove oxygen, for example materials known as fire protection for plastics in principle. Suitable examples are metal hydroxides or metal oxyhydroxides that, when heated, form a protective ceramic layer with the separation of water, such as aluminum hydroxide (aluminum trihydrate) (ATH) from about 200°C, which reacts to form Al2O3 and water, or magnesium hydroxide from about 300°C, which reacts to form MgO and water. Another example of a suitable filler for removing heat is based on polyphosphates, such as melamine polyphosphate or ammonium polyphosphate, which swell (expand) on the separation of ammonia (NH3) and act to remove oxygen by the reaction of ammonia to nitrogen and water.

[0046] In principle, by varying the filler and the degree of filling, it is possible to advantageously adjust and adapt the material properties precisely. In this case, the degree of filling to be achieved depends to a great extent on the particle size distribution, particle size and surface reactivity of the filler particles. For example, the degree of filling can be up to 60% by weight for particles with a main proportion of particles with a size of 10 to 100 μm, and can be significantly more than 100 volume percent for nanoscale particles. The prerequisite for all fillers is that they do not negatively affect the elastic behavior of the elastomer.

[0047] In one advantageous configuration, if necessary, passages can be provided in the insulating mat according to the invention for the escape of gases formed by the reaction of the filler and the pyrolysis of the elastomer, which can act against the occurrence of overpressure in the area, which is essentially hermetically sealed by the preload between the walls of the battery cells in a module and the insulating mat.

[0048] For this purpose, interruptions can be provided across the ribs and / or outlet openings can be provided in the annular frame. In this case, the formed reaction gas can be distributed over the surface of the substrate along the interruptions and can escape via the outlet openings. It is particularly advantageous if the interruptions have a continuous arrangement. In this case, the interruptions are provided in adjacent ribs in such a way that they extend one another and thus form a continuous passage interrupted by the spacing between the ribs. Due to the continuous arrangement of the interruptions, the gas can be directed to escape.

[0049] As already mentioned, the dimensions of the insulating mat according to the invention and its structure are determined by the specific requirements of use: for use as intermediate insulation in a battery system, e.g. a module, consisting of a number of rectangular battery cells, it is desirable for the insulating mat according to the invention to have a minimum total thickness.

[0050] Preferably, the thickness does not exceed 3 mm in the unloaded state, with a rib height of 0.4-0.5 mm, a rib width in the range of 1.0 mm-3.0 mm, and a spacing between the ribs in the range of 1.5-3 times the rib width, and a frame thickness of 5-10 mm. Advantageously, the total thickness of the insulating mat is 1.5 mm or less, in particular 1 mm or less, under a preload of 5 kN of the battery module.

[0051] It is self-evident that these values ​​are merely exemplary and can be easily changed according to the requirements of the time.

[0052] In one further advantageous configuration, the substrate can additionally be provided with an intermediate layer consisting of an infrared-reflective metal sheet, for example an aluminum sheet. With regard to space-saving requirements, it is desirable for the sheet to be as thin as possible, for example about 0.1 mm.

[0053] The insulating mat according to the invention can be produced by the usual production methods known for producing components made of fiber-reinforced plastics. One example is the casting or pressing method using a mold formed according to the desired structure of the component. That is, for example, the mold can first be filled with a first elastomer layer for forming the rib structure and, optionally, the structure for the annular frame, then with a fiber material for the fiber intermediate layer, and then the mold can be filled with another elastomer material for impregnating the fibers and for forming another rib structure and, optionally, the frame structure.

[0054] The insulating mat provided by the present invention can meet all the requirements desired for practical use, namely: This insulation mat has a material thickness of approximately 1.5 mm, and when the temperature on the high side is 700°C, the temperature on the low side is less than 100°C. The fiber-elastomer composite substrate can be compressed by at least 0.4 mm, which compensates for the expansion of the battery cells due to cell aging and charging cycles. Only small compressive strains are experienced, which ensures the stroke compensation function while maintaining the preload on the cell composite over the entire service life of the battery module. With regard to the desired electrical insulation performance, the dielectric strength can be advantageously adjusted to at least 3 kV. Space requirements can be kept small for the low packaging density desired for battery systems. This insulating mat is easy and inexpensive to manufacture.

[0055] In the following, the cell insulating mat according to the invention will be explained in more detail on the basis of the attached drawing, which shows diagrammatically one embodiment of the insulating mat according to the invention suitable for prismatic battery cells. [Brief description of the drawings]

[0056] [Figure 1] FIG. 1 shows an arrangement of four rectangular battery cells with an insulating mat according to the present invention placed between them. [Diagram 2] FIG. 2 is a side view showing a prismatic battery cell in an expanded state. [Diagram 3] FIG. 1 is a top view of an insulating mat according to the present invention. [Figure 4] FIG. 4 is a side view of the insulating mat according to the present invention shown in FIG. 3, viewed from above. [Figure 5a] 5 is a longitudinal section through the ribs and frame of the insulating mat according to the invention shown in FIG. 4 in an unloaded state; [Figure 5b] FIG. 5b shows the diagram shown in FIG. 5a under a compressive load. [Figure 6] FIG. 2 shows a schematic exploded view of an insulating mat according to the invention without the frame. [Figure 7] FIG. 2 shows a schematic diagram of a substrate with staggered ribs in a loaded (elastically deflected) state. [Figure 8a] FIG. 1 shows a top view of the basic structure of a substrate according to the present invention made of a fiber-elastomer composite in an unloaded state. [Figure 8b] FIG. 8b shows the structure shown in FIG. 8a in a loaded (spring-elastically deflected) state. [Figure 9a] FIG. 1 is a schematic diagram showing one embodiment of the basic structure of a substrate made of a fiber-elastomer composite mixed with a filler in an unloaded state. [Figure 9b] FIG. 9b shows a schematic diagram of the structure shown in FIG. 9a in a loaded (spring-elastically deflected) state. [Figure 10] FIG. 2 is a schematic plan view of a heat insulating mat according to the present invention with one embodiment of a channel structure for gas outflow. [Figure 11] 1 is a graph showing the results of heat transfer measurements on samples made according to the present invention. [Figure 12] 1 is a graph showing spring characteristic curves for samples made according to the present invention as a function of rib spacing. [Figure 13] 1 is a graph showing the spring characteristic curves of samples produced according to the present invention as a function of the hardness (Shore A) of the silicone elastomer. [Figure 14] 1 is a graph showing a comparison of the deformation behavior of samples produced according to the present invention as a function of rib spacing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] FIG. 1 shows a battery unit with four prismatic battery cells 2 according to the prior art, where between each two adjacent cells 2 there is provided an insulating mat 1 according to the invention.

[0058] The internal structure of the battery cell 2 is airtightly enclosed by a rigid rectangular or prismatic cell housing, which has two connection terminals 3, 4 and a safety valve 5 on one narrow side.

[0059] The safety valve 5 opens when the pressure inside the cell exceeds a critical value due to reactive gases formed as a result of the temperature increase, allowing the gases to escape and preventing the cell from exploding.

[0060] 2 shows a prismatic battery cell 2 in which the main surface 6 of the cell housing has expanded. This deformation occurs substantially only in the central region of the main surface 6, because the edges of the cell housing through the corners to the adjacent smaller side surfaces are mechanically stable and do not deform during normal operation.

[0061] 3 is a top view of the insulating mat 1 according to the invention, in which the rib arrangement of the insulating mat according to the invention can be clearly seen, with a base plate 7 and a number of ribs 8 which run parallel to one another and at a distance 9 from one another across the base plate 7, where the distance 9 is wider than the width of the ribs 8. The rib unit is surrounded by an annular frame 10 from which the ribs 8 are separated, i.e. they are not in contact with the frame 10. Neither the end faces of the ribs 8 nor the sides of the ribs lying on the outside are connected to the frame 10, so that a gap 11 exists between the end faces of the ribs 8 and the frame 10.

[0062] The frame 10 here has a flat exposed upper surface with which it contacts the annular edge of the battery cell in the installed state, and since the frame 10 is wider than the ribs 8 in the illustrated configuration, the frame 10 has a higher deformation resistance than the ribs. In the installed and loaded state, the frame 10 is able to compensate for the preload, which does not affect the ribs.

[0063] 4 shows an oblique front view of the insulating mat 1 according to the invention. In the figure, the arrangement of the ribs 8 on the upper main surface of the substrate 7 as well as the annular frame 10 extending around the upper and lower rib units between which the substrate 7 is arranged are clearly visible. The substrate 7 has an intermediate layer 12 made of a fibrous material.

[0064] 5a and 5b show a longitudinal section along the rib 8 and the annular frame 10 in an unloaded state (FIG. 5a) and in a loaded state when the frame 10 is pressurized by a preload during assembly of the battery module. In the unloaded state, the height of the frame 10 is greater than the height of the rib 8. Between the end face of the rib 8 and the frame 10 there is a gap 11 which continues to surround the entire rib unit.

[0065] 5b shows a state when a compressive load is applied by a preload applied to the battery module during assembly. The preload compresses the height of the frame 10, and the height of the frame 10 and the height of the rib 8 become uniform. Even when a compressive load is applied to the frame 10, the gap 11 remains, so that the rib 8 is separated from the annular frame 10 even when a compressive load is applied to the frame 10.

[0066] The desired deformation resistance can be set via the width of the frame, where the deformation resistance increases with width, and furthermore, the deformation resistance can be adapted by the choice of material, the degree of crosslinking of the elastomer, the compressibility, etc.

[0067] As a result, in an assembled module in which an insulating mat 1 according to the invention is placed between two battery cells 2, the frame 10 is loaded with a preload, while the ribs 8 remain substantially unloaded.

[0068] FIG. 6 shows an exploded view of one embodiment of an insulating mat 1 according to the invention, with the annular frame 10 omitted for clarity of construction.

[0069] It can be seen that a plurality of ribs 8 are arranged on the major surfaces of the substrate 7, where each major surface has a plurality of ribs 8 arranged parallel to one another and spaced 9 apart from one another, the ribs 8 extending transversely across the major surfaces.

[0070] In this case, the spacing 9 between the ribs 8 on the main surface is larger than the width of the rib 8 , and preferably the spacing 9 is at least 1.5 to 2 times the width of the rib 8 .

[0071] The ribs of both main faces are arranged offset with respect to one another, with a rib 8 of one main face running along a gap 9 of the other main face.

[0072] The substrate 7 is made of an elastomeric material with an intermediate layer 12 made of mineral fibres.

[0073] If one or two further intermediate layers 12 made of fiber material are provided according to a further embodiment, an additional elastomeric material may be provided between the two intermediate layers made of fiber material as a binder.

[0074] The same elastomeric material can be used for the manufacture of the substrate 7 with the intermediate layer 12 of textile material and for the ribs 8, in which case the ribs 8 can be moulded as an integral part of the substrate 7. The frame 10 can also be made from the same elastomeric material and can be moulded with the substrate 7 as an integral part.

[0075] As shown in FIG. 7, as the expansion portion of the main surface (not shown here) of the battery cell increases, pressure is applied to the ribs 8, and the ribs 8, together with the substrate 7 located underneath, are pushed into the spaces 9 between the ribs 8 that are offset on the main surface located opposite the substrate 7.

[0076] In this resiliently deflected state, the substrate 7 forms a zigzag extension with curved sections that alternately project upwards or downwards into each of the spaces 9. When the compressive load is reduced, for example in the course of discharging the battery cell, these deformations correspondingly return to their original state due to the elasticity of the substrate 7.

[0077] The degree of deformation is substantially determined by the width of the gap 9 and the deformability of the substrate 7, which is influenced in particular by the hardness (elasticity) of the elastomer and the orientation of the fibers, as shown, for example, in Figures 8a, 8b and 9a, 9b.

[0078] Figures 8a, 8b and 9a, 9b respectively show plan views of a substrate 7 with a textile intermediate layer 12, the internal structure of which is illustrated diagrammatically, in an unloaded state (Figures 8a and 9a) and in a spring-elastically deflected state (Figures 8b and 9b).

[0079] The fibers in the fiber interlayer 12 have an orientation of ±45°, so that fibers with different signs cross at a 90° angle 14a. The elastomeric matrix 13 in which the fibers are embedded is shown as a grey surface. Also shown extending across this surface are the ribs 8. The edges running left and right along the ribs 8 indicate the spacing 9 between the staggered ribs 8 on the underside of the substrate 7 below.

[0080] In the unloaded state shown here, fibers with different signs cross at a 90° angle 14a.

[0081] As shown in Fig. 8b, when pressure is applied to the insulating mat 1, causing a spring-elastic deflection of the ribs 8, the fiber-matrix composite of the substrate 7 decreases in width (indicated by the arrows at the top and bottom edges of the figure) and lengthens (indicated by the arrows pointing left or right), so that the crossing angle 14b between the fibers decreases, here to 60°.

[0082] The deformation proceeds similarly when pressure is applied to the ribs 8 of a substrate made of an elastomeric material doped with filler particles 15 and resiliently deflected, as shown in Fig. 9a in an unloaded state and in Fig. 9b in a resiliently deflected state. Again, there is a ±45° orientation of the fibers in the fiber interlayer 12 with a 90° cross angle 14a. In this example, filler particles 15 of different sizes were used.

[0083] When compressed due to pressure from the expansion of an adjacent battery cell (not shown), the substrate 7 lengthens (left and right arrows) and the width of the substrate 7 decreases (up and down arrows). At the same time, the crossing angle 14b of the fibers with different signs decreases to 60°.

[0084] Unlike in Figures 8a and 8b, here the degree of deformation is additionally controlled by the filler particles 15, because the compression reduces the spacing between the particles 15. As soon as the spacing is reduced to the point where the particles 15 come into contact and catch on each other, further deformation stops, because the fibres can no longer move past each other.

[0085] FIG. 10 is a plan view of an insulating mat 1 according to the invention having parallel arranged ribs 8, an annular frame 10 and gaps 11 between the ribs 8 and the annular frame 10, where the ribs 8 have a structure consisting of interruptions 16 extending substantially across the ribs 8.

[0086] These interruptions 16 and outlet openings 17, 18 are used to guide out reaction gases that may arise, in particular due to phase transitions and decomposition of the filler, when overheated. The resulting gas phase, together with the gas phase resulting from the thermal decomposition of the elastomer, can create very high gas pressures in the area between the cell walls and the substrate 7, sealed by the frame 10. To reduce this pressure, it may be advantageous to incorporate interruptions 16 and outlet openings 17, 18 into the insulating mat 1 as venting aids, as shown by way of example in FIG. 10.

[0087] The interruptions 16 are formed here as a continuous structure in successive ribs 8. In this case, the interruptions 16 in the ribs located to the left or right of one rib 8 form a continuation of the interruptions 16 in the ribs 8 located between these interruptions 16. As a result, a continuous passage for the gas discharge is obtained. In the example shown in FIG. 10, the interruptions 16 each run diagonally starting from the center of the substrate in the direction of the four corners, resulting in an expanded X shape in the overall view. In addition, outlet openings 17, 18 for the discharge of the reaction gas from the intermediate spatial region between the cell wall and the insulating mat 1 are provided on the short sides of the annular frame 10.

[0088] The heat insulating effect and strain characteristics of the heat insulating mat of the present invention were investigated, and the results are shown in the graphs of Figs.

[0089] For the preparation of the samples, the silicone elastomers used were commercially available two-component liquid silicones that crosslink at room temperature and have different hardnesses according to Shore A. The product data and manufacturers are listed in Table 1.

[0090] [Table 1]

[0091] The results of heat transfer measurements on an exemplary cellular insulation mat are shown in Figure 11. The study was carried out at a heat transfer measurement level when a pressure of 1.9 bar was applied to simulate the expansion process. The sample pieces were each 163 g / m 2 The sample was fabricated from ELANTAS silicone elastomer SK85L7, Shore A45, containing two layers of woven E-glass fiber with a weight per unit area of ​​1.0 g / m. The dimensions of the sample piece were 235 mm x 113.5 mm x 2.0 mm, corresponding to the dimensions of a typical rectangular cell. The rib height was 0.4 mm, the rib width was 1.0 mm, and the rib spacing was 2.0 mm.

[0092] For the measurement, the sample was first kept at 50°C for 5 minutes for uniform temperature distribution, and the pressure was adjusted during this time. It was then heated to 700°C within 200 seconds (without post-adjustment of pressure). The temperature rise on the front and back sides was measured using a pyrometer. The results confirmed that even after the front side temperature increased from 50°C to 700°C, the back side temperature was only less than 100°C. Thus, the back side temperature was clearly within the range required for practical use.

[0093] 12 and 13 show stress strain curves with spring characteristic lines of several typical material samples for a cellular insulating mat according to the present invention.

[0094] The dimensions of the sample pieces were 40 mm × 40 mm, with a rib height of 0.4 mm, a rib width of 2 mm, and a total thickness of the sample of 2 mm. The thickness of the fiber interlayer was 0.8-0.9 mm.

[0095] In this case, FIG. 12 shows the spring properties as a function of rib spacing under otherwise identical conditions, and FIG. 13 shows the change in spring properties as a function of the hardness of the silicone elastomer with woven glass fiber cloth under otherwise identical conditions.

[0096] The test shown in FIG. 12 involved a test piece having a Shore A hardness of 45 and a weight per unit area of ​​25 g / m 2 Sample pieces were used that consisted of silicone elastomer ADDV-42 with a fibrous interlayer consisting of woven E-glass fiber cloth in a linen weave format with an orientation of + / - 45° at 100°.

[0097] For the tests shown in Figure 13, the rib spacing of the material samples was uniformly 2 mm. Each of the textile interlayers had a weight per unit area of ​​80 g / m 2 The E-glass fiber woven fabric was in the form of a linen weave with a 0° / 90° orientation at 100° C. All samples exhibited nearly uniform properties up to a strain of 40%, with curves 7 and 8 having the smallest increase for samples made of SK85 L7-45 and QSil 550, with Shore A hardnesses of 45 and 55, respectively.

[0098] The deformation characteristics under preload and full load for samples of different total thickness as a function of rib spacing are shown in Figure 14. The dimensions of the sample pieces are similar to those described above for the tests shown in Figures 12 and 13, but the rib spacing was varied. For the material structure, a weight per unit area of ​​80 g / m2 was used. 2The silicone elastomer SK85 L7-45 described in Table 1 was used, which contains two fibrous interlayers consisting of woven E-glass fiber cloth in a linen weave style with an orientation of + / - 45° at 100°. The initial thickness of the individual samples without compression load varies from 1.860 mm to 1.530 mm. The samples were subjected to a compression load of 0.186 N / mm. 2 Preload of 1.115N / mm 2 The specimens were subjected to a maximum surface pressure of 1.4 mm and the degree of deformation was measured. In this case, the preload strength corresponded to the commonly used preload strength of 5 kN. What we wanted to investigate was the change in deformation under preload around a target thickness of 1.4 mm, which is typically targeted today for applications using prismatic battery cells.

[0099] The best results in this case were seen in samples with 2mm rib spacing and samples with 1.5mm or 2.5mm rib spacing, with preload thicknesses only slightly above the desired value of 1.4mm.

[0100] The present invention relates to an insulating mat 1 for separating adjacent battery cells 2, in particular rectangular battery cells, in a battery system, which consists of an elastically deformable substrate 7 made of a fiber-elastomer composite, the two main faces of which are provided with a certain number of ribs 8, which run parallel to and spaced apart from one another across the main faces of the substrate 7, the rib units on the two main faces being surrounded by an annular frame 10, with a gap 11 being present between the ribs 8 and the frame 10, the fiber-elastomer composite of the substrate 7 being formed from an elastomeric matrix in which at least one intermediate layer of mineral fibers is embedded, the insulating mat simultaneously being able to compensate for the system-specific volumetric changes of the battery cells due to chemical degradation of the cell components and cyclic expansion and contraction of the cells during charging and discharging. [Explanation of symbols]

[0101] 1. Insulation mat 2 Battery Cells 3,4 Connection terminals 5 Thermal relief valve 6. Expanded main surface of battery cell 7 Substrate 8. Ribs 9 Spacing (between two ribs) 10 Circular Frame 11 Gap (between rib and frame) 12 Fiber middle layer 13 Elastomer Matrix 14a,b Intersection angle 15 Filler particles 16 Interruption 17, 18 Exit opening in frame 10

Claims

1. A heat insulation mat (1) for separating adjacent battery cells (2) in a battery system in particular, comprising an elastically deformable substrate (7) made of a fiber - elastomer composite, wherein a predetermined number of ribs (8) are provided on two main surfaces of the substrate (7), extending parallel to each other and spaced apart from each other across the main surfaces of the substrate (7), the rib units of the two main surfaces are surrounded by an annular frame (10), and a gap (11) exists between the rib (8) and the frame (10), the fiber - elastomer composite of the substrate (7) is formed from an elastomer matrix containing at least one intermediate layer made of mineral fibers, heat insulation mat (1).

2. The heat insulation mat (1) according to claim 1, wherein the elastomer material is selected from styrene - butadiene rubber (SBR), acrylonitrile - butadiene rubber (NBR), natural rubber (NR), butyl rubber, isobutane - isoprene rubber (IIR), isoprene rubber (IR), and polyurethane (PUR) among silicone elastomers.

3. The heat insulation mat (1) according to claim 2, wherein the elastomer is selected from silicone elastomers and polyurethane.

4. The heat insulation mat (1) according to any one of claims 1 to 3, wherein the mineral fibers for the intermediate layer are selected from glass fibers, basalt fibers, silica fibers, and oxide ceramic fibers.

5. In a state where no compressive load is applied, the height of the annular frame (10) is higher than the height of the rib (8), and the deformation resistance of the annular frame (10) is greater than the deformation resistance of the rib (8). The heat insulation mat (1) according to claim 1.

6. The heat insulation mat (1) according to claim 5, wherein the width of the annular frame (10) is larger than the width of the rib (8).

7. The heat insulation mat (1) according to claim 1, wherein the width of the gap (9) between two adjacent ribs (8) is at least 1.5 to 2 times the width of the rib (8).

8. The heat insulation mat (1) according to claim 1, wherein the rib (8) and the annular frame (10) are formed from an elastomer material.

9. The heat-insulating mat (1) according to claim 8, wherein the rib (8) or both the rib (8) and the annular frame (10) are formed of the same elastomer material as the substrate.

10. The heat-insulating mat (1) according to claim 1, wherein the substrate (7) has two or more intermediate layers (12) made of mineral fibers.

11. The heat-insulating mat (1) according to claim 10, wherein an elastomer material is provided as a binder between the two intermediate layers (12) made of mineral fibers.

12. The heat-insulating mat (1) according to claim 1, wherein a metal sheet that reflects infrared rays is provided on the substrate (7).

13. The heat-insulating mat (1) according to claim 1, wherein the substrate (7), the rib (8), and the annular frame (10) are integral parts.

14. The heat-insulating mat (1) according to claim 1, wherein an interruption portion (16) crossing the rib (8) is provided and / or at least one outlet opening (17, 18) for discharging reaction gas is provided in the annular frame (10).

15. Use of the heat-insulating mat according to claim 1 for a battery system provided with prismatic battery cells.

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