Cell separator for a battery module with improved thermal behavior and battery module

Abstract

The invention relates to a cell separator (18) for a battery module (10) for arrangement between two battery cells (12) of the battery module (10), wherein the cell separator (18) is formed from a material (M) comprising at least one first material component (M1). At least the at least one first material component (M1) is designed such that a thermal conductivity (λ) of the at least one first material component (M1) decreases with increasing temperature (T), at least in a specific temperature range (ΔT).

Description

The invention relates to a cell separating element for a battery module for arrangement between two battery cells of the battery module, wherein the cell separating element is formed from a material which comprises at least one first material component. Furthermore, the invention also relates to a battery module having such a cell separating element.Batteries for electric vehicles are typically constructed from individual battery cells. These battery cells can be combined to form individual battery modules, for example to form cell stacks, that is to say to form cell stacks having a plurality of battery cells arranged next to one another. In the course of maximum utilization of installation space, battery concepts are developed in which these cells are not combined in separate modules and installed in the housing, but rather are introduced directly into the battery housing in the form of individual cell stacks, which is also referred to as a so-called moduleless concept or cell-to-pack concept.Within the scope of the present invention, however, such a cell stack or cell stack introduced directly into the overall battery housing should also be understood as a battery module.With regard to the fire behavior, in particular in connection with thermal propagation of batteries, legal requirements must be fulfilled. An important contribution provider for satisfying these requirements is the cell intermediate material, which is also referred to in the present case as a cell separation element. The cell intermediate material or cell separating element is, for example, plate-shaped or a planar structure and is introduced between the individual battery cells and, in addition to the influence on the thermal propagation, may also have further tasks.It would be desirable in this case to be able to simultaneously optimize the requirements of the cell separation element for different tasks.DE 20 2018 101 387 U1 describes a vehicle traction battery assembly with a traction battery cell and a container to accommodate the traction battery cell. A thermal plate is also provided that is positioned adjacent to the traction battery cell and that defines a coolant passage such that the traction battery cell is in thermal communication with the coolant flowing through the coolant passage. The container is in this case of multilayer construction and comprises a first polymer layer, a second polymer layer and an aluminum layer which is arranged between the polymer layers.It is an object of the present invention to provide a cell separating element and a battery module which allow the best possible adaptation to different tasks or functions to be fulfilled by the cell separating element.This object is achieved by a cell separating element and a battery module having the features according to the respective independent patent claims. Advantageous embodiments of the invention are the subject matter of the dependent patent claims, the description and the figures.A cell separating element according to the invention for a battery module for arrangement between two battery cells of the battery module is formed from a material which comprises at least one first material component. At least the at least one first material component is designed such that a thermal conductivity of the at least one first material component decreases with increasing temperature at least in a specific temperature range.The invention is based on the finding that the cell separation element can also be used for improved heat dissipation during regular operation of a battery, in particular also without integrated active cooling, i.e. without a coolant being able to flow through it. The surface area between the battery cells is typically relatively large, which is why heat can be effectively exchanged between the cells and the heat capacity of such a battery as a whole can thus be used for cooling. This can be realized by a good thermal conductivity of the cell separation element. However, the requirements for the cell separation element with regard to its task would therefore seem to be contrary in the case of a thermal propagation and its task for increasing the efficiency of the battery cooling, since with regard to a thermal propagation a low thermal conductivity of the cell separation element is useful in order to reduce the heat transfer from cell to cell and thus to lengthen the propagation times. A propagation time is understood here to mean the time duration within which the thermal runaway of a battery cell reaches one or more adjacent cells and from these to further cells, up to possibly all cells of the battery. In the battery cooling in the normal operation of such a battery, on the other hand, a high thermal conductivity of the cell separator is useful in order to be able to effectively use the heat capacity and the thermal mass of the entire battery. The invention is further based on the finding that, however, there are materials which can be used at least as the at least one first material component of the material of the cell separation element and which have the property of reducing their thermal conductivity with increasing temperature, at least in a specific temperature range. Thus, a cell separation element can be advantageously provided which has a higher thermal conductivity at low temperatures than at high temperatures. If a battery cell adjoining the cell separating element undergoes thermal runaway, the temperature of the cell separating element also rises accordingly, which correspondingly leads to a lowering of its thermal conductivity. The cell separating element can thus advantageously contribute to an increase in the efficiency of the cooling of the battery during normal operation of a battery, while in the case of a thermal propagation of a cell of a battery through the cell separating element a thermal barrier between the battery cells can be ensured.As described at the beginning, a cell separating element can be a planar structure or plate-shaped component. In principle, the cell separating element can be configured as desired with regard to its geometry, but is preferably configured as rectangular. It is also preferred that the cell separation element is designed as a solid body. It should therefore not have any hollow spaces with defined material recesses. However, the material itself can be designed, for example, as a foam material and can be correspondingly porous. Pores of this type should therefore not be understood as the aforementioned cavities, as should, for example, fillers optionally contained in the material, which comprise particles with gas and / or air inclusions.The cell separating element is furthermore preferably used in a battery module having prismatic battery cells or pouch cells. Such battery cells may be arranged in a cell stack. That is, such a cell stack may comprise a plurality of battery cells which are arranged side by side with their sides facing one another in a stacking direction. Between each two battery cells arranged with respect to one another, a cell separating element according to the invention or a cell separating element according to one embodiment of the invention can be arranged. The cell separating element can be designed for planar contact with the adjoining battery cell, in particular prismatic battery cells or pouch cells. The cell separating element preferably comprises two mutually opposite outer sides which, when the cell separating element is arranged as intended in a cell stack or in a battery module, face the battery cells adjacent to the cell separating element in and / or counter to the stack direction and are optionally in contact, in particular in planar contact, with the side surfaces of these adjacent battery cells. These outer sides are preferably planar.The fact that at least the at least one first material component of the material of the cell separation element is constituted as described above is to be understood in this case as meaning that the material of the cell separation element can also comprise one or more further material components, for example a second material component which exhibits the same behavior, that is to say the thermal conductivity of which decreases with increasing temperature in the specific temperature range. In particular, the material of which the cell separation element is made can be constituted as a whole such that its thermal conductivity decreases with increasing temperature in the specific temperature range. In addition, the at least first material component may be the only material component of the material of the cell separation element that has such a property. In addition, the at least first material component can be the only material component of the material of the cell separation element, i.e. the material consists of the first material component.Due to the fact that at least the at least one first material component has such a property, it can be achieved that the thermal conductivity of the cell separating element as a whole decreases with increasing temperature in the specific temperature range, even if the material of the cell separating element comprises further material components which do not have such a property.The thermal conductivity can also be referred to as a thermal conductivity or thermal conductivity coefficient and is in particular a material property of the at least one first material component. The same also applies to the material as a whole or optional further material components.The determined temperature range may include, for example, a normal operating temperature range, which may also be referred to as a first temperature range and which is specified for the battery module, and an abnormal temperature range, which may also be referred to as a second temperature range and which is different from the normal operating temperature range and which is above the normal operating temperature range. A boundary between the normal temperature range and the abnormal temperature range is preferably above 60° C. and below 300° C., for example.The cell separation element thus enables both effective battery cooling and an increase in the propagation times. The cell separation element, in particular at least the first material component, can be designed such that it has a high thermal conductivity in a first temperature range, namely the normal operating temperature range, of the usual battery operation, which ranges up to 70° Celsius, for example, and has a very low thermal conductivity in a second temperature range, which is relevant for thermal propagation and can also be referred to as an abnormal temperature range, for example from 300° Celsius onwards. Thus, the above-mentioned apparently contrary requirements for the cell separation element can be met simultaneously.According to a further advantageous embodiment of the invention, at least the at least one first material component is designed such that the thermal conductivity of the at least one first material component decreases continuously and / or strictly monotonically with increasing temperature at least in the specific temperature range. In particular, the first material component should preferably be designed such that the reduction in the thermal conductivity does not change abruptly with increasing temperature, in particular in the sense of a non-continuously differentiable profile of the thermal conductivity as a function of the temperature. An abrupt change in the thermal conductivity as the temperature rises is also not required here, since in particular a relatively large temperature interval can lie between the normal temperature range and the abnormal temperature range in the case of a thermal propagation, wherein no particularly low thermal conductivity is yet required in this temperature interval to provide a thermal barrier. In addition, the temperatures typically rise very rapidly in the case of a thermal runaway of a battery cell, with the result that the change in the thermal conductivity of the cell separating element as a result of the rapid temperature rise also takes place very rapidly in the event of a continuously falling change in the thermal conductivity, and therefore a low thermal conductivity is achieved very rapidly.According to a further advantageous embodiment of the invention, at least the at least one first material component is designed such that its thermal conductivity in the determined temperature range decreases with increasing temperature as a result of a phase transition of the material component, for example as a result of melting and / or softening. The first material component can undergo a phase transition by melting and / or softening, for example. The first material component changes from a solid state to a softened and / or liquid state. In the liquid state, the first material component can still have a high viscosity, in particular a very viscous consistency. For example, the first material component can also only soften strongly during the phase transition without liquifying. It is preferred that the first material component is designed such that it does not flow out of this intermediate space when arranged between two battery cells of a battery module as intended. Nevertheless, such a phase transition can ensure that the heat conducting properties of the material component change. Thus, a material can be advantageously selected as the first material component, which material has a phase transition temperature in the temperature range of interest between the first and second temperature ranges defined above. In this context, a glass transition temperature, for example for amorphous polymers, should also be understood in particular as such a phase transition temperature. In other words, the material component does not necessarily have to change its aggregate state when performing the phase transition. For example, the material component can also only change its internal structure.The glass transition or softening temperature is the temperature at which a corresponding substance, for example glass or plastic, has the greatest change in deformation capability. A glass is a solidified liquid. Glasses are formed, for example, by the inorganic glasses understood in the context of the present invention, such as the window glass, but also by organic glasses, such as amorphous plastics. This so-called glass transition separates the underlying brittle energy-elastic region (=glass region) from the overlying soft entropy-elastic region (=gum-elastic region). The transition to the flow region of the amorphous plastic is smooth.Partially crystalline plastics have both a glass transition temperature below which the amorphous phase 'freezes' and a melting temperature at which the crystalline phase dissolves. The melting temperature clearly separates the entropy-elastic region from the flow region. In contrast, crystalline plastics have only one melting temperature.According to a further advantageous embodiment of the invention, the first material component constitutes a polymer or comprises a polymer. The use of a polymer or polymer material as the first material component has numerous advantages. On the one hand, there are polymers which have exactly the above-described properties, i.e. reduce their thermal conductivity with increasing temperature. Such a polymer can soften and / or melt with increasing temperature, for example, and thereby change its internal structure. The change in internal structure causes not only the softening and / or melting of the polymer but also the change in its thermal conductivity. The polymer material or the first material component can comprise, for example, an amorphous plastic. A further great advantage of using such a polymer as the first material component is, moreover, that the polymer can advantageously be combined with further components or elements as further constituents of the material of the cell separation element in order to equip the cell separation element with further advantageous properties. In particular, a polymer material can simultaneously also be used as a matrix, in particular a plastic matrix, in order to accommodate further elements or particles in order to modify the properties of the cell separation element in the desired manner.Therefore, it represents a further very advantageous embodiment of the invention if the material comprises at least one filler different from the first material component. This is particularly advantageous if the first material component is a plastic material, in particular a polymer material. The polymeric material may serve as a matrix for such a filler. A combination of a polymer matrix with at least one filler is also referred to as a compound, in particular a plastic compound. The filler is preferably present in particulate form or in powder form. The filler can thus advantageously be mixed with the corresponding polymer material during the production of the cell separation element. In particular, the material can also comprise a plurality of different fillers, which can be combined with the first material component as a matrix.It is particularly advantageous here if the filler has a higher thermal conductivity than the first material component in the specific temperature range. In particular, the filler can be designed such that it has a higher thermal conductivity at any temperature than the first material component at the same temperature. By means of such a filler, it is possible to provide a particularly high thermal conductivity of the material of the cell separation element, especially in the normal operating temperature range, as a result of which the cell separation element can increase the cooling efficiency of the battery module even more efficiently.According to a further advantageous embodiment of the invention, the filler comprises a ceramic, in particular ceramic particles. The ceramic particles may be provided in the form of a ceramic powder, for example. Pure plastics typically have a very low (average) thermal conductivity, in particular of less than 1 watt per meter and kelvin. Ceramics, on the other hand, have a very high thermal conductivity, for example up to 400 watts per meter and kelvin. With a plastic compound comprising a plastic matrix and powdered ceramics, particularly high thermal conductivities can be achieved, for example, depending on the filler and filler content, a thermal conductivity of the material of the cell separation element of, for example, up to 50 watts per meter and kelvin. Particularly high thermal conductivities are possible here with boron nitrite as filler. This too can be present in the form of a powder or in the form of particles. The thermal conductivity of plastics changes abruptly at phase transitions, in particular also (relatively). Sudden need not necessarily be understood to mean a step-like, abrupt change, but rather, for example, merely a change with a greater gradient in the temperature range around this transition temperature than in other temperature ranges, in particular within the specific temperature range. The phase transition from solid to liquid and / or the glass transition can be used in the case of a thermal event of a cell in order to make the heat transfer between the cells more difficult and to increase the time of a thermal propagation.According to a further advantageous embodiment of the invention, the first material component is a phase change material or the first material component comprises a phase change material which, in the specific temperature range under a specific normal pressure, which can be defined at 1.013 bar, for example, carries out a phase transition, in particular from solid to liquid, when a specific limit temperature is exceeded, which is in particular at least 150° Celsius.Such a phase change material may also be referred to as a phase composite material (PCM) and / or PCM material. Such a phase change material absorbs significantly more energy than conventional materials during a phase change, for example from solid to liquid, without increasing its actual temperature in the process. This energy is also referred to as latent heat. Phase change materials are therefore also referred to as latent heat accumulators. For suitability as a cell separation element, it is advantageous if the thermal conductivity in the solid aggregate state of the phase change material is as high as possible, that is to say the thermal conductivity of the material of the cell separation element as a whole. This can be made possible, for example, by a highly compacted graphite structure which is infiltrated with the phase change material. In other words, the material of the cell separation element can comprise a phase change material infiltrated with highly compacted graphite structures, wherein the phase change material represents the first material component and the graphite structures, for example, represent a further second material component of the material. The phase change temperature is preferably so high that it is not reached during regular battery operation. It is therefore preferably above the above-defined normal operating temperature range or the first temperature range. The phase change material is preferably designed or the material of the cell separation element as a whole such that the phase change temperature is only reached in the case of a thermal event of a cell, in particular of a cell adjoining the cell separation element. Therefore, it is very advantageous if the phase change temperature is at least 550° Celsius or above.Furthermore, the invention also relates to a battery module having a cell separating element according to the invention or one of its embodiments. Furthermore, it is advantageous if the battery module comprises at least two battery cells, wherein the cell separating element is arranged in an intermediate space between the two battery cells, in particular adjacent to the two battery cells. The battery module can be designed, for example, as already described above and / or at the outset. The battery module may include a cell stack having a plurality of battery cells. The battery cells can be designed as prismatic cells or pouch cells. In particular, the battery cells can be lithium-ion cells. Between each two battery cells arranged adjacent to one another in the stacking direction, a cell separating element according to the invention or a cell separating element according to an exemplary embodiment of the invention can be located.The advantages described for the cell separating element according to the invention and its embodiments apply in the same way to the battery module according to the invention.According to a further advantageous embodiment of the invention, the cell separation element, in particular the first material component, is designed such that it remains in the intermediate space for each temperature in the defined temperature range. In other words, the first material component or the material as a whole should remain in the intermediate space even at very high temperatures within the temperature range and also in the case of a phase transition, in particular melting of the first material component. This can be achieved, for example, by a first material component which softens and / or melts at high temperatures, but has a high viscosity, e.g., even in the melted state. Alternatively or additionally, this can also be achieved by a first material component which, in the melted and / or softened state, is so viscous that it cannot escape from the intermediate space through slits or gaps or the like.Furthermore, the invention also relates to a battery having a battery module according to the invention or one of its embodiments. The battery can be designed, for example, as a high-voltage battery, in particular for a motor vehicle. Such a battery can also comprise a plurality of battery modules according to exemplary embodiments of the invention and / or battery modules according to the invention.Furthermore, the invention also relates to a motor vehicle having a cell separation element according to the invention or one of its embodiments. Furthermore, the invention also relates to a motor vehicle having a battery module according to the invention or one of its embodiments or having a battery according to the invention or one of its embodiments.The motor vehicle according to the invention is preferably designed as a motor vehicle, in particular as a passenger car or truck, or as a passenger bus or motorcycle.The invention also includes developments of the battery module according to the invention, of the battery according to the invention and of the motor vehicle according to the invention, which have features as have already been described in connection with the developments of the cell separation element according to the invention. For this reason, the corresponding developments of the battery module according to the invention, of the battery according to the invention and of the motor vehicle according to the invention are not described again here.The invention also includes the combinations of the features of the described embodiments. The invention therefore also comprises implementations which each have a combination of the features of a plurality of the described embodiments, provided that the embodiments have not been described as mutually exclusive.Exemplary embodiments of the invention are described below. The following shows: FIG. 1 shows a schematic illustration of a battery module according to an exemplary embodiment of the invention, and FIG. 2 shows a graphical representation of the thermal conductivity of a cell separation element as a function of temperature according to an exemplary embodiment of the invention.The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that are to be considered independently of one another and that also develop the invention independently of one another. Therefore, the disclosure is intended to include combinations of the features of the embodiments other than those illustrated. Furthermore, the described embodiments can also be supplemented by further features of the invention that have already been described.In the figures, identical reference numerals designate functionally identical elements.FIG. 1 shows a schematic illustration of a battery module 10 according to an exemplary embodiment of the invention. The battery module 10 includes a plurality of battery cells 12, for example prismatic battery cells. The battery module 10 includes a cell stack 14 having the plurality of battery cells 12. The battery cells 12 are arranged next to one another in a stacking direction S and face one another with their sides 12 ahaving the greatest area. Between each two battery cells 12 arranged adjacent to one another there is an intermediate space 16, in which a cell separating element 18 according to an exemplary embodiment of the invention is arranged in each case. The cell separation element 18 is formed from a material M which comprises a first material component M 1, for example a polymer material which in the present example acts as a polymer matrix, and a second material component M 2. The second material component M 2 may be provided, for example, in the form of a filler F, for example in the form of a ceramic powder or in the form of ceramic particles embedded in the plastic matrix M 1. The material M of the cell separating element 18 now has particularly advantageous properties with regard to its thermal conductivity λ, as is explained in more detail below with reference to FIG. 2.FIG. 2 shows a schematic and graphical representation of the thermal conductivity λ of the material M and / or of the first material component M 1 as a function of the temperature T. The material M or the material component M 1 is designed in such a way that the thermal conductivity λ decreases, in particular continuously, with increasing temperature at least within a specific temperature interval ΔT, wherein this decrease does not have to be constant. The determined temperature range ΔT includes, in the present example, a first temperature range ΔT 1 corresponding to a normal operating temperature range of the battery module 10. In addition, the temperature range ΔT includes a second temperature range ΔT 2 representing an abnormal temperature range. Furthermore, a limit temperature TG is shown, which is located between the first and second temperature ranges Δt 1, Δt 2. This can be a limit temperature assigned to the material M or to the first material component M 1 and / or a glass transition temperature. Precisely in the region of this limit temperature TG, the decrease in the thermal conductivity λ of the material M or of the first material component M 1 with increasing temperature T is particularly severe.A compound of polymers is particularly suitable as material, i.e. as material M, on account of its advantageous properties. A material mixture of plastic and one or more fillers F is referred to as compound. To greatly increase the thermal conductivity λ, suitable fillers are, for example, fillers F with high thermal conductivity, which are also preferably not electrically conductive.In principle, fillers F with high thermal conductivity are preferred in order to establish a high thermal conductivity λ in the compound as well, especially in the normal operating temperature range ΔT 1. The significantly lower thermal conductivity λ in the case of thermal runaway of a battery cell 12, in particular of a battery cell 12 adjoining the cell separating element 18 in the second temperature range ΔT 2, can be generated, for example, by a melting process of the polymer M 1.Thus, the cell separating element 18 advantageously makes it possible to provide effective battery cooling in the normal operating temperature range ΔT 1, and also very high propagation times in the case of thermal runaway of a battery cell 12 can be provided due to the low thermal conductivity λ in the second temperature range ΔT 2.In particular, the examples show how an optimized cell intermediate material in the form of a cell separating element of traction batteries can be provided by the invention with regard to thermal propagation and battery cooling.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 20 2018 101 387 U1

[0006]

Claims

Cell separating element (18) for a battery module (10) for arrangement between two battery cells (12) of the battery module (10), wherein the cell separating element (18) is formed from a material (M) which comprises at least one first material component (M1), characterized in that at least the at least one first material component (M1) is designed such that a thermal conductivity (λ) of the at least one first material component (M1) decreases with increasing temperature (T) at least in a specific temperature range (ΔT).Cell separating element (18) according to Claim 1, characterized in that at least the at least one first material component (M1) is designed such that the thermal conductivity (λ) of the at least one first material component (M1) decreases continuously and / or strictly monotonically with increasing temperature (T) at least in the determined temperature range (ΔT).Cell separating element (18) according to one of the preceding claims, characterized in that at least the at least one first material component (M1) is designed such that its thermal conductivity (λ) in the determined temperature range (ΔT) decreases with increasing temperature (T) as a result of a phase transition of the material component (M1), in particular as a result of melting.Cell separation element (18) according to one of the preceding claims, characterized in that the first material component (M1) comprises or represents a polymer.Cell separating element (18) according to one of the preceding claims, characterized in that the material (M) comprises a filler (F) different from the first material component (M1).Cell separating element (18) according to one of the preceding claims, characterized in that the filler has a higher thermal conductivity than the first material component (M1) in the specific temperature range (ΔT).Cell separating element (18) according to one of the preceding claims, characterized in that the filler (F) comprises a ceramic, in particular ceramic particles.Cell separation element (18) according to one of the preceding claims, characterized in that the first material component (M1) is a phase change material which, in the specific temperature range (ΔT) under a specific normal pressure, carries out a phase transition when a specific limit temperature (TG) is exceeded, which is in particular at least 150° Celsius.Battery module (10) having a cell separating element (18) according to one of the preceding claims, characterized in that the battery module (10) comprises at least two battery cells (12), wherein the cell separating element (18) is arranged in an intermediate space (16) between the two battery cells (12), in particular adjacent to the two battery cells (12).Battery module (10) according to Claim 9, characterized in that the cell separating element (18), in particular the first material component (M1), is designed such that it remains in the interspace (16) for each temperature (T) in the determined temperature range (ΔT).

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