Intermediate element for arrangement between battery cells of a battery stack

Abstract

An intermediate element (14) for arrangement between battery cells (1) of a battery stack, comprising a casing (15) and a phase change material (16) arranged within the casing (15) which has a boiling point at a temperature of more than 70°C, is characterized in that the casing (15) provides a receiving space for receiving the phase change material (16) in the gaseous state.

Description

[0001] The invention relates to an intermediate element for arrangement between battery cells of a battery stack. The invention further relates to a battery stack with at least one such intermediate element.

[0002] A battery cell comprises one or, more commonly, several galvanic cells or battery elements arranged within an enclosure, usually in the form of a foil pouch or casing. Each battery element includes two electrodes, a separator positioned between the electrodes for electrical separation, and an electrolyte acting as an ion conductor between the electrodes. The two electrodes of a battery element differ in terms of their active material, making one electrode anodic and the other cathodic (with respect to a discharge of the battery element). Furthermore, a battery cell typically includes two terminals integrated into the enclosure, which are electrically connected to the electrodes on the inside of the enclosure via current collectors.In this configuration, all anodically active electrodes are connected to one of the battery cell poles and the cathodically active electrodes are connected to the other of the battery cell poles.

[0003] Typically, a large number of battery elements, for example in the form of a stacking or winding of the electrodes and separators, are combined in a battery cell to achieve a sufficiently high electrical performance.

[0004] For particularly high performance requirements, such as those placed on a vehicle's traction battery, a large number of individual battery cells are combined in so-called battery stacks in the most space-saving arrangement possible. The battery cells within a battery stack can be connected electrically in series and / or parallel. Often, the battery cells of a battery stack are also mechanically connected to one another.

[0005] Damage to a battery poses a risk of thermal runaway. Thermal runaway is generally defined as the overheating of an exothermic chemical reaction or a technical device due to a self-reinforcing, heat-generating process. In a battery, such thermal runaway can result, in particular, from an internal short circuit caused by damage.

[0006] In battery stacks, it is important to prevent thermal runaway in one battery cell from leading to thermal propagation, i.e., overheating of the other battery cells in the stack in a chain reaction. To achieve this, it is known to place a thermally insulating intermediate element between adjacent battery cells in a battery stack.

[0007] WO 2021 / 014441 A1 discloses a battery stack with intermediate elements arranged between battery cells, which are made of porous materials. The intermediate elements and the battery cells can be impregnated with or surrounded by a coolant having a boiling point in the range of the operating temperatures of the battery cells, so that the coolant evaporates during operation and thereby cools the battery cells.

[0008] CN 113 594 583 A describes a multilayer intermediate element for a battery stack, comprising a centrally located insulating layer, two thermally conductive layers arranged on either side of the insulating layer, and two layers of a phase-change material arranged on the outside of the thermally conductive layers. In the event of thermal runaway in an adjacent battery, the phase-change material is intended to provide additional cooling through a phase transition of the material and the heat energy required for this transition.

[0009] Intermediate elements for battery stacks, which include a phase change material, are also disclosed in CN 104 795 610 A, CN 105 742 755 A, CN 114 094 228 A and US 2012 / 0171523 A1.

[0010] CN 104 467 574 A discloses a battery stack with intermediate elements made of graphite and additional cooling elements made of a phase change material, which are arranged laterally to the individual battery cells.

[0011] The invention is based on the objective of providing an improved intermediate element for a battery stack.

[0012] This problem is solved by an intermediate element according to claim 1. Advantageous embodiments of this intermediate element are the subject of further claims and will become apparent from the following description of the invention.

[0013] An intermediate element according to the invention, which is intended for arrangement between battery cells of a battery stack and is configured and dimensioned accordingly, comprises an (intermediate element) casing and a phase-change material arranged within the casing, which has a boiling point at a temperature of more than 70°C, preferably more than 100°C. The casing further provides a receiving space for receiving the phase-change material in the gaseous state.

[0014] Such an intermediate element offers particularly improved protection against thermal propagation between adjacent battery cells. This is because the phase change material initially acts as an active cooling agent during the phase change to the gaseous state, as the phase change requires a relatively large amount of thermal energy, which is drawn from the adjacent battery cells. The resulting gaseous phase change material then remains, at least temporarily, within the intermediate element's casing, resulting in particularly effective thermal separation between the battery cells. This is due to the relatively low thermal conductivity that the phase change material can exhibit in its gaseous state compared to its solid and / or liquid state.

[0015] Against this background, it may be advantageous if, as is preferably provided, the intermediate element has two opposing contact sides which are appropriately arranged for contact with each of the battery cells, wherein the phase change material and / or the receiving space extends over at least 50% or at least 70% or at least 90% of the surface area of ​​the contact sides, so that the phase change material, in particular in the gaseous state, can have the largest possible effect on the adjacent battery cells.

[0016] To ensure that the gaseous phase-change material remains within the enclosure, it is preferably provided that the enclosure is gas-tight or has a defined gas permeability. This defined gas permeability can be permanent, for example, due to the defined permeability of a material used to form the enclosure, particularly a film material. However, the defined gas permeability can also be temporary, especially in the case of an open outlet valve, which may be integrated into the enclosure.

[0017] The intermediate element can preferably be designed in the form of a plate, so that its thickness (extension in the direction of the adjacent battery cells or the contact surfaces of the casing provided for contact with the battery cells) corresponds to at most 1 / 10, preferably at most 1 / 25, particularly preferably at most 1 / 50 of the width and length.

[0018] The provision of the receiving space can be achieved by ensuring that a designated free space exists within the enclosure even when the phase change material is not (yet) in a gaseous state. Alternatively or additionally, the receiving space can be provided by the expansion of the enclosure as a result of the phase transition of the phase change material into the gaseous state and the consequent pressure increase within the enclosure. The receiving space can also be created by the compression of another material located within the enclosure due to the pressure increase. The latter two configurations offer the advantage that, in an initial state of the intermediate element where the phase change material is not in the gaseous state, the intermediate element can be designed with minimal dimensions.This can be advantageous with regard to the overall dimensions of a battery stack, which may comprise a large number of battery cells and intermediate elements arranged between them.

[0019] Accordingly, it is preferable that the casing of the intermediate element be designed to be functionally deformable, so that it deforms when used to fulfill a defined function. Besides expansion to provide the receiving space, such functional deformation can also consist of compensating for different distances between adjacent battery cells as well as volume changes of the battery cells during their use. Such volume changes can be reversible during charging and discharging processes or irreversible due to aging processes.

[0020] The invention also relates to a battery stack with several battery cells, each comprising at least one battery element, a battery cell casing surrounding the at least one battery element, and two battery cell poles integrated into the battery cell casing, wherein the battery cells are arranged as a stack. Accordingly, the battery cells are arranged in a row in essentially the same orientation. At least one intermediate element according to the invention is arranged between adjacent battery cells of the battery stack, spatially separating the respective adjacent battery cells and preferably also completely preventing their direct contact.

[0021] Each battery cell comprises at least one battery element, comprising two electrodes, a separator arranged between the electrodes for electrical separation, and an electrolyte acting as an ion conductor between the electrodes. This electrolyte can be liquid or solid and, particularly in the case of a solid electrolyte, can also function as a separator. A first electrode of each battery element is electrically connected to a first battery cell terminal, and a second electrode of each battery element is electrically connected to a second battery cell terminal.

[0022] The battery cell casing can preferably be designed as a housing, in particular as a dimensionally stable housing. A housing is understood to be "dimensionally stable" if, on its own (i.e., without supporting components), it does not deform, at least not due to its own mass, and preferably not to a significant extent, under the forces acting upon it during normal use. This allows for a relatively high mechanical load-bearing capacity of the battery cells. This is particularly true compared to a foil casing ("pouch"), which the battery cells of a battery stack according to the invention can also have. Furthermore, the battery cell casing can be cuboid in shape, which can be advantageous with regard to the installation space required for integrating the battery stack into a system, such as a motor vehicle.

[0023] Preferably, the at least one intermediate element may cover the adjacent surfaces of the battery cell casings to at least 90%, preferably 100%, in order to achieve the most advantageous protective effect.

[0024] According to a preferred embodiment of an intermediate element according to the invention, the casing comprises an outlet valve which, in an open state, connects the receiving chamber (directly or indirectly) to the environment (of the intermediate element) via a gas flow. The outlet valve is further preferably configured such that it opens (automatically) only after at least a partial transition of the phase change material into the gaseous state. For this purpose, the outlet valve can, in particular, be configured such that it opens as a result of a defined input of heat energy, for example, by a melting element of the outlet valve transitioning from a solid state to a liquid or gaseous state, thereby opening a flow path for the gaseous phase change material.Alternatively or additionally, the outlet valve can be designed to open as a result of an interaction with the phase change material in the gaseous state. For example, a valve closure element can be progressively weakened by contact with the phase change material in the gaseous state (e.g., because it dissolves) and thus fail after a defined period, thereby opening a flow path for the gaseous phase change material. Additionally or alternatively, the outlet valve can also be designed to open at a defined opening pressure within the receiving chamber, which is reached as a result of the phase change material transitioning into the gaseous state.Such an outlet valve can be designed in a particularly simple way as a burst valve, which has, for example, a foil-shaped bursting element that is destroyed when the opening pressure is reached, thus opening a flow path for the gaseous phase change material.

[0025] Controlling the pressure that arises within the enclosure due to the transition of the phase change material into the gaseous state can be achieved by appropriately dimensioning the receiving space or enclosure provided for the gaseous phase change material and the elements contained therein.

[0026] An embodiment of an intermediate element according to the invention, featuring an outlet valve, offers the significant advantage that the targeted release of the gaseous phase-change material through the open outlet valve allows for additional cooling of the adjacent battery cells. This cooling is due to the Joule-Thomson effect, which arises from the expansion of the gaseous phase-change material, previously contained under increased pressure within the casing, upon release. To achieve this, the phase-change material should have a positive Joule-Thomson coefficient, so that expansion of the gaseous phase-change material leads to a reduction in its temperature.

[0027] To achieve the best possible protective effect of the intermediate element in this context, it is preferable to design the outlet valve so that it only opens (for example, because the opening pressure is only reached at that point) when at least 50%, 75%, or 90% of the phase change material has transitioned into the gaseous state. This allows for the best possible thermal insulation effect, firstly due to the gaseous phase change material located within the encapsulation, and secondly, the highest possible cooling effect through a relatively large volume of gas being released from the encapsulation into the environment, thereby leading to a correspondingly large pressure drop within the encapsulation.

[0028] Preferably, the phase change material is inert in its gaseous state. This ensures that the gaseous phase change material does not pose a fire hazard. Furthermore, if the inert, gaseous phase change material escapes into the vicinity of the intermediate element, it can reduce the risk of fire by displacing any oxygen that may be present there, thereby achieving a further improved protective effect against thermal propagation in a battery stack according to the invention. Against this background, it can be advantageous if the outlet valve of an intermediate element according to the invention is designed such that the gaseous phase change material is discharged into the immediate vicinity of the intermediate element.In a battery stack according to the invention, the outlet of the outlet valve can be arranged within a battery stack casing that accommodates the battery cells and the intermediate elements. Such a battery stack casing can preferably be designed as a housing, in particular as a gas-tight housing.

[0029] According to a preferred embodiment of an intermediate element according to the invention, the phase-change material can have a melting point at a temperature above 55°C, preferably above 70°C. This allows the phase-change material to be in a solid state at the typical operating temperature of the adjacent battery cells and to transition into a liquid state at unusually high temperatures. With a further increase in temperature, it then transitions into a gaseous state, so that a total of two phase changes of the phase-change material can occur, which can be accompanied by a correspondingly large cooling effect from the phase-change material.

[0030] A phase change material that can exhibit at least some of the described properties can be or comprise an inorganic, eutectic, water-based mixture. A suitable phase change material is, for example, the product SP58 from Rubitherm Technologies GmbH, Berlin, Germany.

[0031] An intermediate element according to the invention preferably has two opposing contact surfaces, each designed and configured for contact with one of the battery cells, wherein the intermediate element is functionally deformable, in particular elastically deformable, at least with respect to the distance between the contact surfaces. This allows the intermediate element to compensate for different distances between the adjacent battery cells as well as for expansions of the battery cells during their use. In addition to the casing, the phase-change material itself can exhibit such functional deformability. This is particularly true if it is in a liquid state at the normal operating temperature of the adjacent battery cells.Alternatively or additionally, the intermediate element can also comprise a deformation element, preferably arranged within the covering, in particular in the form of a deformation layer, which can be made of a correspondingly easily deformable material, for example a foam.

[0032] According to an advantageous embodiment, the phase-change material of an intermediate element according to the invention can form a continuous layer within the encapsulation. It is also possible, if desired, for the intermediate element within the encapsulation to comprise exclusively the phase-change material. Furthermore, the phase-change material can be incorporated in the form of particles within a matrix of another material, thereby enabling particularly advantageous properties for the intermediate element. The other material can, for example, be a material exhibiting particularly advantageous deformation properties.

[0033] An intermediate element according to the invention is preferably designed to be electrically insulating in order to achieve electrical separation between the adjacent battery cells. The electrical insulation effect relates in particular to the casing of the intermediate element, but preferably also to the materials incorporated therein.

[0034] The invention is explained in more detail below with reference to embodiments illustrated in the drawings. The drawings show, in simplified form: Fig. 1: a battery stack according to the invention, Fig. 2: a battery element stack of a battery cell of the battery stack, Fig. 3: a filling element for an intermediate element according to the invention in a first embodiment and Fig. 4: a filling element for an intermediate element according to the invention in a second embodiment.

[0035] The one in Fig. The battery stack shown comprises a plurality of battery cells 1 arranged as a stack.

[0036] The battery cells 1 each comprise a battery cell casing 2, which has a cuboid shape. The battery cells 1 are stacked over the large sides 3 of the battery cell casings 2, such that these large sides 3 each run perpendicular to a stacking direction 11, while the smaller longitudinal and end faces 4, 5 of the battery cell casings 2 are aligned parallel to the stacking direction 11.

[0037] The battery cells 1 each comprise a plurality of battery elements arranged within the battery cell casing 2. The battery elements, or the components forming them, can be in the form of a battery element stack 6. Such a battery element stack 6 can be arranged according to the Fig. The battery cell stack 6 comprises plate-shaped electrodes 7 and electrically insulating, plate-shaped separators 8 arranged in alternating sequence. Within the cell stack 6, the electrodes 7 alternately function as first electrodes 7a, which act as anodes during discharge of the battery cells 1, and as second electrodes 7b, which act as cathodes during discharge of the battery cells 1. The separators 8 can simultaneously contain a solid electrolyte for the battery elements. Alternatively, a liquid electrolyte, in particular, can be arranged within the battery cell casing 2. The plate-shaped electrodes 7 and separators 8 have a (very flat) cuboid shape, which, in conjunction with the stacking arrangement, also results in a cuboid shape for the battery element stack 6.

[0038] The battery elements further comprise current collectors 9, each of which is electrically connected to one of the electrodes 7, with first current collectors 9a belonging to the first electrodes 7a and second current collectors 9b belonging to the second electrodes 7b. The various (first and second) current collectors 9 are each connected to a battery cell terminal 10. All first current collectors 9a are connected to a first of the battery cell terminals 10, and all second current collectors 9a are connected to a second of the battery cell terminals 10. The battery cell terminals 10 are each integrated into one of the end faces 5 of the battery cell casing 2 such that a section thereof within the battery cell casing 2 is available for connection with the current collectors 9 of the respective assigned electrodes 7.A further section of the battery cell terminals 10, which is arranged outside the battery cell casing 2, is provided for contact with battery cell terminals 10 of other battery cells 1 or with battery stack terminals (not shown) of the battery stack.

[0039] The current collectors 9 are integrally designed with the electrodes 7, in that a planar substrate 12 made of an electrically conductive material, for example a metal foil, is coated on both sides in a section that forms part of the electrode 7 with an anodically or cathodically active material 13, while an uncoated section of the substrate 12 constitutes the current collector 9 belonging to the respective electrode 7. The substrate 12 of the first electrodes 7a may preferably consist of copper and / or nickel and / or aluminum, while the substrate 12 of the second electrodes 7b may preferably be made of aluminum.

[0040] The battery stack according to the Fig. The assembly further comprises plate-shaped intermediate elements 14, with one intermediate element 14 being arranged between each pair of battery cells 1. The intermediate elements 14, whose large sides are at least as large as the large sides 3 of the battery cell casings 2 of the battery cells 1, act as thermal insulators and, through a defined deformability, prevent high local surface pressures, which can protect the battery cell casings 2 and the battery element stacks 6 of the battery cells 1 from damage. Furthermore, in an electrically insulating configuration, the intermediate elements 14 can prevent an electrical short circuit between the battery cells 1.

[0041] According to the invention, the intermediate elements 14 comprise an (intermediate element) covering 15 and a filling element 18 arranged within the covering 15 (see Figure 1). Fig. 3 and Fig. 4), which can, for example, consist of a single layer or of several layers stacked in the stacking direction 11 of the battery stack. The filler element 18 consists at least partially of a phase-change material 16 that has a melting point above an upper limit of a temperature range within which the operating temperatures of the battery cells 1 lie during normal operation (normal operating temperature range). The phase-change material 16 is therefore in the solid phase during normal operation of the battery cells 1.

[0042] In the event of thermal runaway of at least one of the battery cells 1, its temperature can rise to a value significantly above the normal operating temperature range, leading to a corresponding heating of the intermediate element(s) 14 adjacent to this battery cell 1. This initially causes the melting point of the phase change material 16 to be reached, which is thereby transitioned from the solid to the liquid phase. In doing so, it absorbs a considerable amount of thermal energy, which is extracted particularly from the adjacent battery cells 1 and thus also from the thermally runaway battery cell 1, thereby cooling it and thus inhibiting thermal runaway. Further heating of the phase change material 16 of an intermediate element 14 adjacent to the thermally runaway battery cell 1 subsequently also reaches the boiling point of the phase change material 16, which then transitions from the liquid to the gaseous phase.This also requires a considerable amount of thermal energy, which in turn is drawn from the adjacent battery cells 1.

[0043] The resulting gaseous phase change material 16 initially remains within the casing of the affected intermediate element(s) 14, which provides a suitable receiving space for this purpose. Since the gaseous phase change material 16 has a significantly lower thermal conductivity than in the solid and liquid states, the transition from the liquid to the gaseous phase not only cools the affected intermediate element 14 and thus the adjacent battery cells 1, but also provides increased thermal insulation for the battery cells 1 separated by the affected intermediate element 14, thereby preventing or at least delaying thermal propagation.

[0044] Since the gaseous phase change material 14 has a significantly larger specific volume than the liquid phase change material 14, the phase change from liquid to gaseous also leads to an increase in pressure within the casing 15 of the affected intermediate element 14. This is used to open an outlet valve 17 of the intermediate element 14, designed as a pressure relief valve, specifically a burst valve, as soon as a large proportion of the phase change material 16 has transitioned into the gaseous phase. This allows the gaseous phase change material 16, which is under overpressure within the casing 15, to be discharged via the outlet valve 17 into the environment of the intermediate element 14. As a result of the Joule-Thomson effect, this leads to a cooling of the intermediate element 14 and thus also to a cooling of the adjacent battery cells 1, including the thermally continuous battery cell 14.Furthermore, the gaseous phase change material 16 released into the environment is inert, so that it would have a fire-retardant effect on a fire possibly originating from the thermally through battery cell 1.

[0045] The Fig. 3 and Fig. Figure 4 schematically shows various possibilities for forming a filling element 18 of an intermediate element 14 according to the invention. In the filling element 18 according to the Fig. 3. Particles of the phase-change material 16 are integrated into a matrix of another material 19, for example, a silicone or polyurethane foam. The filling element 18 according to the Fig. In contrast, 4 consists exclusively of the phase change material 16. Reference symbol list 1 battery cell 2 battery cell casing 3 Large side of the battery cell casing 4 Long side of the battery cell casing 5. Front side of the battery cell casing 6 battery element stacks 7 electrode 7a first electrode 7b second electrode 8 Separator 9 current collectors 9a first current collector 9b second current collector 10 battery cell pole 11 Stacking direction 12 Substrat 13 Active material 14 Intermediate element 15 (intermediate element) encasing 16 Phase change material 17 Exhaust valve 18 Filling element 19 other materials QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2021 / 014441 A1

[0007] CN 113 594 583 A

[0008] CN 104 795 610 A

[0009] CN 105 742 755 A

[0009] CN 114 094 228 A

[0009] US 2012 / 0171523 A1

[0009] CN 104 467 574 A

[0010]

Claims

[1] Intermediate element (14) for arrangement between battery cells (1) of a battery stack, comprising a casing (15) and a phase change material (16) arranged within the casing (15) which has a boiling point at a temperature above 70°C, characterized by , that the casing (15) provides a receiving space for receiving the phase change material (16) in the gaseous state. [2] Intermediate element (14) according to claim 1, characterized by , that the casing (15) comprises an outlet valve (17) which, in the open state, connects the receiving chamber to the environment in a gas-carrying manner, wherein the outlet valve (17) is designed such that it opens only after at least a partial transition of the phase change material (16) into the gaseous state. [3] Intermediate element (14) according to claim 2, characterized bya design of the outlet valve (17) such that it opens as a result of a defined heat energy input and / or as a result of an interaction with the phase change material (16) in the gaseous state and / or at an opening pressure within the receiving space which is reached as a result of the transition of the phase change material (16) into the gaseous state. [4] Intermediate element (14) according to claim 3, characterized by , that the outlet valve (17) only opens when at least 50% or 75% or 90% of the phase change material (16) has transitioned into the gaseous state. [5] Intermediate element (14) according to any one of the preceding claims, characterized by that the phase change material (16) is inert in the gaseous state. [6] Intermediate element (14) according to any one of the preceding claims, characterized by , that the phase change material (16) has a positive Joule-Thomsen coefficient in the gaseous state. [7] Intermediate element (14) according to any one of the preceding claims, characterized by , that the phase change material (16) has a melting point at a temperature of more than 55°C. [8] Intermediate element (14) according to any one of the preceding claims, characterized by , that the phase change material (16) is or comprises an inorganic, eutectic water-based mixture. [9] Intermediate element (14) according to any one of the preceding claims, characterized by two opposing contact sides for attachment to each of the battery cells (1), wherein the intermediate element (14) is functionally deformable at least with respect to the distance between the contact sides. [10] Intermediate element (14) according to any one of the preceding claims, characterized bytwo opposing contact sides for attachment to each of the battery cells (1), wherein the phase change material (16) and / or the receiving space extends over at least 50% or at least 70% or at least 90% of the surface area of ​​the contact sides.

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