Batteriestack

Abstract

Battery stack with several battery cells (1), each comprising a casing (2) and two battery cell poles (10), wherein the battery cells (1) are arranged as a stack and wherein at least one intermediate element (14) is arranged between adjacent battery cells (1), characterized in that the intermediate element (14) has an insulating material which has a thermal conductivity of at most 0.04 W / m·K at a temperature of 800°C and an exponentially increasing force profile during compression.

Description

[0001] The invention relates to a battery stack with several battery cells.

[0002] A battery is an electrochemical storage device for electrical energy. During discharge, the stored chemical energy is converted into electrical energy through an electrochemical redox reaction. In the context of the invention, batteries are understood to include both so-called primary batteries, which are designed for a single discharge and not for recharging, and so-called secondary batteries or accumulators, which are designed and constructed for multiple charging. Charging a secondary battery represents the electrolytic reversal of the electrochemical redox reaction occurring during discharge, which is realized by applying an electrical voltage.

[0003] A battery cell comprises one or, usually, several galvanic cells or battery elements arranged within an enclosure, usually in the form of a foil enclosure often referred to as a "pouch" or a housing. The battery elements each comprise two electrodes, a separator arranged between the electrodes for electrically separating the electrodes, and an electrolyte serving as an ion conductor between the electrodes. The two electrodes of a battery element differ in terms of the active material they contain, whereby one of the electrodes is anodically active and the other cathodically active (in each case with regard to discharging the battery element). Furthermore, a battery cell usually comprises two battery cell terminals that are integrated into the enclosure and are electrically connected to the electrodes on the inside of the enclosure via so-called current conductors.All anodic electrodes are connected to one of the battery cell poles and the cathodic electrodes are connected to the other of the battery cell poles.

[0004] Typically, a large number of battery elements are combined in a battery cell, for example in the form of a stack or winding of the electrodes and separators, in order to achieve a sufficiently high electrical performance.

[0005] For particularly high performance requirements, such as those for a motor vehicle's traction battery, a large number of individual battery cells are combined in so-called battery stacks. The battery cells of a battery stack can be electrically connected in series and / or parallel. The battery cells of a battery stack are often also mechanically connected to one another.

[0006] If a battery is damaged, there is a risk of what is known as 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 a thermal runaway can result, in particular, from an internal short circuit caused by damage.

[0007] In battery stacks, it is important to prevent thermal runaway of one battery cell from leading to thermal propagation, i.e., overheating of the other battery cells in the battery stack in a chain reaction. For this purpose, it is known to arrange a thermally insulating intermediate element between adjacent battery cells of a battery stack (see US 2022 / 0181716 A1 and US 2022 / 0200080 A1).

[0008] WO 2021 / 142169 A1 describes a thermally protective element for a battery, which can be used, for example, as a separator for the battery.

[0009] The invention is based on the object of providing an improved battery stack.

[0010] This problem is solved by the subject matter of the patent claims.

[0011] A battery stack according to the invention comprises a plurality of battery cells, each having a casing and two battery cell terminals, wherein the battery cells are arranged as a stack. Accordingly, the battery cells are arranged in a row with essentially the same orientation. Between adjacent battery cells, at least one intermediate element is arranged, spatially separating the adjacent battery cells or preventing their direct contact.

[0012] In addition to the casing, which is preferably designed to be gas-tight, and the two battery cell poles, a battery cell of the battery stack also comprises at least one battery element, preferably a plurality of battery elements. The at least one battery element comprises (each) two electrodes, a separator arranged between the electrodes for electrically separating the electrodes, and an electrolyte acting as an ion conductor between the electrodes. This electrolyte can be liquid or solid and, particularly in a solid configuration, can also function as a separator. A first electrode of (each) battery element is electrically connected to a first of the battery cell poles, and a second electrode of (each) battery element is electrically connected to a second of the battery cell poles.

[0013] The enclosure can preferably be designed as a housing, in particular as a dimensionally stable housing (i.e. this one). “Dimensional stable” is understood to mean a housing which, on its own (i.e. without components supporting the housing), does not deform at least due to its own mass and preferably also not to a relevant extent when subjected to forces which act on it during normal use. This makes it possible to achieve a relatively high mechanical load-bearing capacity of the battery cells. This applies in particular in comparison to a film enclosure (“pouch”), which the battery cells of a battery stack according to the invention can also have. Furthermore, the enclosure can be cuboid-shaped, which can be advantageous in terms of the installation space required for integrating the battery stack into a system, such as a motor vehicle.

[0014] According to the invention, the at least one intermediate element comprises an insulating material which, at a temperature of 800°C, has a thermal conductivity of 0.04 W / mK or less and an exponentially increasing force curve upon compression (i.e., upon compressive deformation). The thermal conductivity relates to a relative humidity of 10% and / or can be determined in accordance with DIN EN 12667. Due to the very low thermal conductivity according to the invention, thermal propagation is effectively suppressed in the event of thermal runaway of one of the battery cells of the battery stack. The exponentially increasing force curve upon compression causes a decreasing thermal resistance. Due to high elasticity, this resistance can be increased directly after the strong compression, thus reducing the necessary thickness of the cell intermediate material.

[0015] The intermediate element can preferably be designed in the shape of a plate, so that its thickness (extension in the stacking direction of the battery stack) corresponds to at most 1 / 10, preferably at most 1 / 25, particularly preferably at most 1 / 50 of the width and the length.

[0016] Preferably, the at least one intermediate element can cover the adjacent surfaces of the battery casings by at least 90%, preferably 100%. Furthermore, the at least one intermediate element can preferably be designed to be electrically insulating in order to also realize electrical separation between the adjacent battery cells.

[0017] Furthermore, it can preferably be provided that the compressive stress in the insulating material of the intermediate element is between 0.05 MPa and 2.1 MPa. This applies to the different deformation states of the at least one intermediate element that can occur during the intended use of the battery stack, including in the event of a thermal runaway of one of the batteries. This increases the service life and safety of the battery stack.

[0018] To achieve the properties of the insulation material according to the invention, it can preferably comprise a matrix material (preferably a microporous insulating material) and at least one additive material (preferably a material for increasing elasticity). The matrix material can, in particular, provide the relatively low conductivity according to the invention, while the at least one additive material can influence the matrix material in such a way that the insulation material achieves the force distribution provided for by the invention upon compression.

[0019] The relatively low thermal conductivity of the matrix material can preferably be based at least in part on the fact that the matrix material is porous, in particular with a (total) porosity of at least 10%, preferably of at least 25%, particularly preferably of at least 50%. The matrix material can particularly preferably be microporous (i.e., with an average pore size of less than 2 nm).

[0020] Furthermore, the insulation material and in particular the matrix material thereof can preferably be designed as a nonwoven fabric according to DIN EN ISO 9092.

[0021] According to a preferred embodiment of a battery stack according to the invention, it can be provided that the insulation material has an exponentially decreasing force curve when the load is removed.

[0022] In order to realize advantageous manufacturability and / or good handling of the at least one intermediate element, it can be provided that the insulation material is surrounded by a sheath, for example a film sheath (e.g. made of PET).

[0023] A battery stack according to the invention can advantageously be produced by cutting an intermediate element starting material, which can be supplied in particular continuously and provided, for example, as a roll material, to form the intermediate element and then positioning it between two of the battery cells. This makes it possible to form the battery stack and, in particular, stack the battery cells and the at least one intermediate element relatively quickly. For example, stacking can be performed at a stacking frequency of 3 Hz, so that at least three elements (battery cells and intermediate element(s)) are stacked within one second.

[0024] In a corresponding production of a battery stack according to the invention, in which the insulation material is surrounded by a shell, it can further be provided that a seam is formed in the shell of the (each) intermediate element during or after cutting, in order to preferably completely close the shell. In this case, the seam can be formed, in particular, as a material-to-material connection between sections of the shell. A welded and / or adhesive connection can be provided, in particular, as the material-to-material connection.

[0025] The invention is explained in more detail below with reference to exemplary embodiments illustrated in the drawings. The drawings show, in simplified form: Fig. 1: the production of a battery stack according to the invention; Fig. 2: a battery element stack of a battery cell of the battery stack Fig. 3: a cross-section through an intermediate element of the battery stack; Fig. 4: the thermal conductivity curve versus temperature of an insulating material of the intermediate element; and Fig. 5: the force curve over the deformation path during compression and subsequent unloading of the intermediate element.

[0026] The Fig. Figure 1 shows one possible way of producing a battery stack according to the invention. The battery stack comprises a plurality of battery cells 1 arranged as a stack.

[0027] The battery cells 1 each comprise a casing 2, which has an approximately cuboid shape. The battery cells 1 are stacked over the large sides 3 of the casings 2, so that these large sides 3 each run perpendicular to the stacking direction, while the smaller longitudinal and end sides 4, 5 of the casings 2 are aligned parallel to the stacking direction 11.

[0028] The battery cells 1 each further comprise a plurality of battery elements arranged within the casing 2. The battery elements or the components forming them can be in the form of a battery element stack 6.

[0029] The battery element stack 6 comprises according to the Fig. 2, in alternating sequence, plate-shaped electrodes 7 and electrically insulating, plate-shaped separators 8. The electrodes 7 are in turn present in the cell stack 6 alternately as first electrodes 7a, which function as anodes when the battery cells 1 are discharged, and as second electrodes 7b, which function as cathodes when the battery cells 1 are discharged. The separators 8 can simultaneously also be a solid electrolyte of the battery elements. Alternatively, a particularly liquid electrolyte can be arranged within the casing 2. The plate-shaped electrodes 7 and separators 8 have a (very flat) cuboid shape, which, in conjunction with the stacking, also results in a cuboid shape of the battery element stack 6.

[0030] The battery elements further comprise current conductors 9, each of which is electrically conductively connected to one of the electrodes 7, with first current conductors 9a belonging to the first electrodes 7a and second current conductors 9b belonging to the second electrodes 7b. The various (first and second) current conductors 9 are each connected to a battery cell pole 10. All first current conductors 9a are connected to a first (10a) of the battery cell poles 10, and all second current conductors 10a are connected to a second (10b) of the battery cell poles 10. The battery cell poles 10 are each integrated into one of the end faces 5 of the casing 2 in such a way that a section thereof is available within the casing 2 for connection to the current conductors 9 of the respectively assigned electrodes 7.A further section of the battery cell poles 10, which is arranged outside the casing 2, is provided for contacting with battery cell poles 10 of other battery cells 1 or with battery stack poles (not shown) of the battery stack.

[0031] The current collectors 9 are configured integrally with the electrodes 7 in that a flat substrate 12 made of an electrically conductive material, for example a metal foil, is coated on both sides with an anodically or cathodically active material 13 in a section that is part of the electrode 7, while an uncoated section of the substrate 12 represents the current collector 9 belonging to the respective electrode 7. The substrate 12 of the first electrodes 7a can preferably be made of copper and / or nickel and / or aluminum, while the substrate 12 of the second electrodes 7b can preferably be made of aluminum.

[0032] The battery stack according to the Fig. 1 further comprises plate-shaped intermediate elements 14, wherein one intermediate element 14 is arranged between each two of the battery cells 1. The intermediate elements 14, whose large sides are approximately the same size as the large sides 3 of the casings 2 of the battery cells 1, have a thermally insulating effect and, through defined deformability, prevent high local surface pressures, which in particular protects the casings 2 and the battery element stacks 6 of the battery cells 1 from damage. Furthermore, the intermediate elements 14, with an electrically insulating design, can prevent an electrical short circuit between the battery cells 1.

[0033] According to the Fig. 3, each of the intermediate elements 14 comprises an insulating material 15 that is completely surrounded by a sheath 16 made of a foil material. The sheath 16 is formed from two foil layers that are integrally joined, for example, welded or glued, at a circumferential seam 22. The insulating material 15 can comprise a microporous matrix material and at least one additive material.

[0034] The Fig. 4 shows the temperature-dependent curve of the thermal conductivity λ of the insulation material 15. The thermal conductivity λ of the insulation material 15 increases with temperature T, but is not more than 0.04 W / m·K even at a temperature of 800°C. The insulation material 15 thus has a significant thermally insulating effect, whereby thermal propagation in the event of a thermal runaway of one of the battery cells 1 can be correspondingly well suppressed.

[0035] Furthermore, the insulation material 15 of the intermediate elements 14 is characterized by an advantageous deformation behavior, as shown in the Fig. 5 is shown qualitatively. Accordingly, the course of the compressive stress σ in the insulation material 15 during compression (upper curve in the Fig. 5) and also with a relief (lower curve in the Fig. 5) or the resulting expansion, respectively, exponentially, whereby the exponential factor is smaller during compression than during unloading. During compression, the compressive stress σ in the insulation material 15 increases relatively uniformly (in comparison to unloading) over the deformation path x, so that even with relatively large deformation paths, the increase in compressive stress is relatively small. When the insulation material is unloaded, however, the compressive stress σ decreases relatively quickly, or rather, relatively sharply in an initial section of the reduction in the deformation path, and is already almost zero when the remaining deformation path is more than three-quarters.

[0036] When manufacturing the battery stack according to the Fig.1, the battery cells 1 and the intermediate elements 14 are provided for stacking in an alternating arrangement, wherein, to form the intermediate elements 14, a section of a continuously fed intermediate element starting material 17 is cut to size, then placed on the upper side of the battery cell 1 lying on top in the stack to be formed, and subsequently a further battery cell 1 is positioned on this intermediate element 14. Cutting of the sections of the intermediate element starting material 17 can be carried out by means of a corresponding punching device 18, wherein a punching tool 19, which forms cutting edges 20 on at least two parallel sides, is movable so that the cutting edges 20, in cooperation with the boundary of an opening of a die 21 of the punching device 18, can sever the intermediate element starting material and thereby cut it to size.

[0037] In addition, it can be provided that during the cutting or after the cutting and before the additional battery cell 1 is placed on top, the respective casing 16 of the intermediate elements 14 is closed by forming at least one materially bonded seam 22. LIST OF REFERENCE SYMBOLS 1 battery cell 2 Battery cell casing 3 Large side of the envelope 4 Long side of the wrapper 5 Front side of the casing 6 battery element stacks 7 Electrode 7a first electrode 7b second electrode 8 Separator 9 current arresters 9a first current collector 9b second current conductor 10 Battery cell terminal 10a first battery cell terminal 10b second battery cell terminal 11 Stacking direction 12 Substrat 13 Active material 14 Intermediate element 15 Insulation material 16 Shell of the intermediate element 17 Intermediate element starting material 18 Punching device 19 Punching tool 20 Cutting edge of the punching tool 21 Die of the punching device 22 Seam of the shell λ thermal conductivity T Temperature of the insulation material σ compressive stress x Deformation path QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] US 2022 / 0181716 A1

[0007] US 2022 / 0200080 A1

[0007] WO 2021 / 142169 A1

[0008]

Claims

[1] Battery stack with a plurality of battery cells (1), each comprising a casing (2) and two battery cell poles (10), wherein the battery cells (1) are arranged as a stack and wherein at least one intermediate element (14) is arranged between adjacent battery cells (1), characterized by that the intermediate element (14) has an insulating material (15) which has a thermal conductivity of maximum 0.04 W / m·K at a temperature of 800°C and an exponentially increasing force curve during compression. [2] Battery stack according to claim 1, characterized by that the compressive stress (σ) in the insulation material (15) is between 0.05 MPa and 2.1 MPa. [3] Battery stack according to claim 1 or 2, characterized by that the insulation material (15) comprises a matrix material and at least one additive material. [4] Battery stack according to claim 3, characterized by that the matrix material is microporous. [5] Battery stack according to one of the preceding claims, characterized by that the insulation material (15) has an exponentially decreasing force curve when the load is removed. [6] Battery stack according to claim 5, characterized by that the exponential factor is smaller during compression than during unloading. [7] Battery stack according to one of the preceding claims, characterized by that the insulating material (15) is surrounded by a sheath (16). [8] Method for producing a battery stack according to one of the preceding claims, characterized by that an intermediate element starting material (17) is cut to form the intermediate element (14) and then positioned between two of the battery cells (1). [9] Method according to claim 8 for producing a battery stack according to claim 7, characterized by that a seam (22) of the casing (16) is formed during or after cutting. [10] Method according to claim 9, characterized by that the seam (22) is formed as a material connection between sections of the casing (16).

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