METHOD FOR TESTING AT LEAST ONE BATTERY ELEMENT STACK WITH REGARD TO THE POSITION OF BATTERY ELEMENT LAYERS

Description

[0001] The invention relates to a method for testing at least one stack of several battery elements (battery element stack), each comprising an electrode configured as an anode, an electrode configured as a cathode, and at least one separator as different types of plate-shaped battery element layers, wherein the separator is arranged between the electrodes and wherein the battery element layers have polygonal large areas with at least partially different sizes and are stacked in a stacking direction that is oriented perpendicular to the large areas. Such a battery element stack, which is also referred to as an electrode-separator assembly (ESA), can in particular be provided as a component of a battery.

[0002] In automated battery manufacturing, battery element layers are stacked into battery element stacks using stacking machines. The placement accuracy of the battery element layers, and especially the electrodes, is the key criterion for the process capability of the stacking machines. All edges of the polygonal and, in particular, rectangular battery element layers must be spaced a defined distance apart and within a defined tolerance range. This ensures optimal electrochemical performance of the batteries and prevents short circuits between adjacent electrodes—one serving as the anode and the other as the cathode of the battery cell—due to insufficient stacking accuracy. Such a short circuit could lead to the failure of the affected battery.

[0003] It may be possible to dimension the separator of a battery cell stack larger than the anode, and the anode in turn larger than the cathode, so that an overhang of, for example, 1 millimeter is created between the separator and anode, and between the anode and cathode, respectively, across the entire circumference. This is intended to reliably prevent short circuits between adjacent electrodes due to insufficiently precise stacking, taking into account the placement accuracy of currently used stacking machines. Such an overhang can also prevent reduced chemical performance of the battery cell stacks resulting from inaccurate electrode positioning. However, this tolerance-related oversizing of the anodes and separators increases material consumption during the production of the battery cell stacks, and thus the costs, space requirements, and weight of the battery cell stacks and, consequently, the batteries themselves.It can therefore be advantageous to minimize such tolerance-related oversizing of battery cell layers in battery cell stacks. To prevent short circuits between adjacent electrodes due to insufficiently precise stacking, the placement accuracy of the stacking machines used should be increased and / or quality control during the manufacturing of the battery cell stacks should be improved, so that the production of short-circuited battery cell stacks can be reliably prevented or reliably rejected during manufacturing.

[0004] DE 10 2009 018 079 A1 discloses a test of a battery, in particular under a certain operating condition, by means of electromagnetic radiation, for example X-rays, whereby the relative alignment of the anode and the cathode of at least one battery cell of the battery can also be checked.

[0005] DE 10 2020 112 814 A1 discloses a method for checking batteries, wherein images of a large number of stacked battery cells are captured using radioactive radiation, such as X-rays.

[0006] EP 4 044 306 A1 discloses a method in which the placement of battery elements on battery stacks is checked using optical cameras.

[0007] JP 2018 087740 A shows a method in which a wound battery cell is inspected using X-rays.

[0008] The invention is based on the objective of providing a method for determining the deposition accuracy of the battery element layers of a battery element stack, which is as simple and / or quick to perform as possible while maintaining sufficient accuracy.

[0009] This problem is solved by a method according to claim 1. Preferred embodiments of the method according to the invention are the subject matter of the further claims and / or will become apparent from the following description of the invention.

[0010] According to the invention, a method for testing at least one stack of several battery elements, i.e., a battery element stack, is provided, wherein the battery elements each comprise an electrode configured as an anode, an electrode configured as a cathode, and at least one separator (separating and electrically insulating the anode and the cathode) as different types of plate-shaped (battery element layers, wherein the separator is arranged between the electrodes, and wherein the battery element layers have polygonal and preferably rectangular large areas with at least partially different sizes and are stacked in a stacking direction that is oriented perpendicular to the large areas.The two electrodes of a battery element differ with respect to an included active material, whereby the electrode designed as an anode is anodically effective and the electrode designed as a cathode is cathodically effective (each with reference to a discharge of the battery cell).

[0011] A body or a section of a body (e.g., in the case of a meandering separator strip, where the sections located between the adjacent electrodes represent plate-shaped separators) is understood to be "plate-shaped" if it has two (outer) large surfaces extending in a longitudinal and a lateral direction of the body, wherein a (maximum) height of the body, which corresponds to the (maximum) distance between the large surfaces, is smaller (in particular, at most 1 / 10 or 1 / 100 or 1 / 100) than the (maximum) length and than the (maximum) width.

[0012] In a first test step of the procedure, the relative position of the battery element layers of the still isolated battery elements is determined and it is checked whether distances of (some or all) edges of the battery element layers are within a first tolerance range, whereby the battery elements for which a positive test has been carried out, i.e. which meet the requirement of the first test step, are identified as usable battery elements.

[0013] Subsequently, several of the usable battery elements are stacked to form the battery element stack. In a second test step, the battery element stack is irradiated with X-rays emitted by an X-ray source and detected by an X-ray detector. The X-ray radiation (i.e., at least one beam, in particular the central beam thereof) is directed perpendicular to the large surfaces of the battery element layers. The battery element stack should be moved relative to the X-ray radiation during this process. Using the detected X-ray radiation, the positions, preferably the poses, of the edges of (only) one type of battery element layer—i.e., the cathodes, separators, or, preferably, anodes—are then determined. It is checked whether the maximum distance between the corresponding edges of all battery element layers of the selected type lies within a second tolerance range.To achieve a sufficiently reliable and accurate test result, at least those edges of the battery cell layer type under consideration are taken into account that define at least two of the corners (defined as the transition between two non-coaxial straight sides of the large area, which need not be tapered) of these battery cell layers. These two corners can, in particular, be diagonally opposite corners.

[0014] In the first inspection step, the individual battery elements are therefore checked with regard to the distances between the edges of their battery element layers, and those battery elements that meet the relevant quality criteria are selected for use in the battery element stack. This significantly simplifies the second inspection step, in which the battery element stack as a whole is inspected. In this step, only the positions, preferably the poses, of the edges of one type of battery element layer, particularly the anodes, need to be determined and checked for an arrangement within the second tolerance range. This enables a simple and rapid inspection of the battery element stack and thus, in particular, advantageous integration into an automated battery manufacturing process.In particular, the combination of the two test steps according to the invention makes it possible to carry out the second test step "in view" of the X-ray radiation, i.e. with the X-ray emitter "looking" at the large areas of the battery element layers and particularly preferably with a central beam of the X-ray radiation perpendicular to these large areas, thereby making it possible to advantageously detect the edges of at least the type of battery element layers under consideration.

[0015] According to a preferred embodiment of a method according to the invention, the battery element layers can be immovably connected to one another, in particular by a material bond, for example by gluing or laminating, already during the first test step. This ensures that the positions of the battery element layers of the individual battery elements determined in the first test step do not change during the subsequent stacking or during the second test step, and therefore the corresponding test results can be taken into account without error during the evaluation in the second test step.Alternatively, changes in the positions of the battery cell layers during stacking and the second test step can be prevented by other measures, such as a temporary fixing device used to secure the battery cell layers. Deformation and, in particular, buckling of the battery cell layers should be avoided during stacking. The fact that the battery cell layers are already bonded together can be advantageous in this regard.

[0016] The battery elements used in a method according to the invention can preferably be configured such that the large areas of the anode are larger than the large areas of the cathodes, and the large areas of the at least one separator are larger than the large areas of the cathode and preferably also larger than the large areas of the anode. This different size of the large areas should result in an all-around overhang of the relatively large battery element layers (separator and anode) relative to the next smaller battery element layer. This allows for the advantageous execution of both test steps, which may be based on the different absorption behavior of these various battery element layers for both visible light and X-rays.These differing absorption behaviors can be attributed to the different materials used to construct the various battery cell layers. The absorption behavior of the cathodes can be highest in both cases (i.e., with visible light and X-rays), while that of the separators can be lowest in both cases.

[0017] Regarding the first test step, it is therefore preferably possible to determine the positions of the battery cell layers of the individual battery cells based on the image from an optical camera system, i.e., by means of a visible light-based image-generating system comprising one or more cameras, which enables a simple and cost-effective execution of the first test step. The image acquisition by a camera of the camera system can preferably be taken from above, i.e., with a "view" of the large surfaces of the battery cell layers, and particularly preferably with the optical axis of the camera of the camera system perpendicular to these large surfaces.This can also be advantageous for carrying out the first test step, because it allows for the capture of the largest possible area of ​​the battery cells, including the edges to be detected, preferably all edges of the battery cell layers completely. Due to the highest absorption of visible light, the cathode of each individual battery cell can be visible in the image, even though, as the smallest of the battery cell layers, it may be completely covered by at least one other battery cell layer. Furthermore, at least the edges of the anode can also be visible in the image. This applies at least when, as is preferably intended, the anode is larger than the cathode.The at least one separator, arranged between the anode and the cathode of each battery element, is preferably larger than at least the cathode (and preferably also larger than the cathode) to achieve sufficient separation of the anode and cathode for the purpose of electrical isolation. Furthermore, this allows the at least one separator to be advantageously visible in the camera system image. The at least one separator is particularly advantageously visible if it is also larger than the anode, which can further improve the separation of the anode and cathode. Although the at least one separator may completely cover the anode or the cathode, depending on the orientation of the battery element relative to the camera, the absorption characteristics of this separator can be so low that this does not prevent the detection of at least the edges of the anode or the cathode.This also applies to one or more additional separators that may be arranged on the otherwise exposed side of the anode or cathode. The arrangement of light sources for the camera system can preferably be such that a first light source is located on the same side as the camera with respect to the individual battery elements (and preferably at approximately the same location), and a second light source is located on the opposite side with respect to the individual battery elements. The execution of the first test step can therefore be based on a combination of incident and transmitted light detection.

[0018] A particularly advantageous image for evaluation can be determined in the first test step if the large areas of the at least one separator are larger than the large areas of the anode and the large areas of the anode are larger than the large areas of the cathode, wherein the image of the camera system is taken from above and the cathode is closer to the camera of the camera system than the anode when the image is taken.

[0019] Preferably, it can be provided that in the second test step the relative positions of the edges of (only) the anodes are determined, which can be particularly advantageous due to the preferably provided average absorption behavior and the average size of the large areas of the anodes.

[0020] According to a preferred embodiment of a method according to the invention, the second tolerance range (i.e., of the various detected edges) can be determined by adjusting, and in particular reducing, a (pre-)defined initial tolerance range based on a distance between the corresponding edges determined in the first inspection step. This allows deviations in the positions of these edges, determined during the first inspection step, to be used to adjust the second tolerance range, thereby achieving a better inspection result in the second inspection step of the method according to the invention.

[0021] In carrying out a method according to the invention, an X-ray detector comprising at least (and preferably exactly) two line detectors oriented perpendicular to each other can preferably be used. Such an X-ray detector advantageously enables the detection of edges with respect to their positions, particularly also by a purely translational movement of the battery element stack relative to the X-ray detector. It is particularly preferred that the battery element stack is moved at least once in a perpendicular direction relative to a line-shaped detection area of ​​each of the line detectors. It can be provided that, as is preferably the case, only the battery element stack, or only the X-ray detector (and then also the X-ray source), or the battery element stack and the X-ray detector (with the X-ray source) are moved.

[0022] An inventive method advantageously enables the simultaneous testing of several, and in particular two, battery element stacks during the second test step. This is particularly advantageous due to the simplified testing of the positions of only one type of battery element layer and the resulting relatively simple, and in particular purely translational, relative movement of the battery element stacks relative to the X-ray radiation. Simultaneous testing of several battery element stacks allows the time required for testing multiple battery element stacks to be kept relatively short.

[0023] A further improvement in the accuracy of the battery element stack test according to the invention can be achieved if the several usable battery elements are stacked in a traceable sequence, i.e., a sequence known after stacking, into the at least one battery element stack, and the second test step is performed at least twice in different positions of the battery element stack relative to the X-ray source. By comparing the results of these at least two second test steps, the determined edge positions are assigned to the different battery elements. This makes it possible, in particular, to determine which of the battery elements in the battery element stack have the greatest distances between the edges under consideration and at what position or height these edges are arranged within the battery element stack.

[0024] The invention is explained in more detail below with reference to an embodiment illustrated in the drawings. The drawings show, in simplified representations: Fig. 1: A battery element stack clamped in a workpiece carrier; Fig. 2: A cross-section through a section of the battery element stack and the workpiece carrier; Fig. 3: Storage areas for the cathodes, anodes, and separators of the battery element stack; Fig. 4: A single battery element and a camera system according to a first embodiment; Fig. 5: A single battery element and a camera system according to a second embodiment; Fig. 6: The battery element stack and an X-ray system; Figs. 7 to 11: Various positions of the battery element stack relative to an X-ray detector of an X-ray system according to a first embodiment; Figs. 12 to 16: Various positions of the battery element stack relative to X-ray detectors of an X-ray system according to a second embodiment; Figs. 17 to 22: Various positions of several battery element stacks relative to X-ray detectors of an X-ray system according to a third embodiment; Fig.23: a representation for determining a (second) tolerance range; Fig. 24: a representation of deviations in the positions of adjacent edges of a cathode and an anode of a battery cell; and Fig. 25: geometric relationships in determining the spatial positions of an edge using the X-ray system.

[0025] In the context of battery cell manufacturing, battery element stacks 1, also known as electrode separator assemblies (ESVs), can be manufactured according to the Fig. 2to be manufactured. This involves stacks 1 of several battery elements, which in alternating sequence comprise battery element layers in the form of plate-shaped electrodes 2 (again alternating in configurations and arrangements corresponding to their intended uses as anodes 2a and cathodes 2b of the battery elements) and electrically insulating, plate-shaped separators 3, wherein the electrodes 2 and separators 3 have large rectangular areas. It is intended that the anodes 2a, the cathodes 2b, and the separators 3 have large areas of different sizes in order to avoid short circuits between adjacent anodes 2a and cathodes 2b, as well as excessive losses with regard to the electrical performance of the battery elements, despite inaccuracies in the stacking, which are at least within the relevant tolerance ranges. According to the Fig. 2It may be provided that the cathodes 2b have the smallest large areas and the separators 3 have the largest large areas, resulting in a full-surface overhang (i.e., present with respect to both the widths and lengths of the battery element layers) of the anodes 2a with respect to the cathodes 2b on the one hand and of the separators 3 with respect to the anodes 2a (and thus also the cathodes 2b) on the other hand.

[0026] The plate-shaped separators 3 can also be at least partially sections of a meandering separator strip (not shown). The protruding edge areas of adjacent separators 3 can also be bonded together.

[0027] Following a stacking process, a stack of battery elements 1 is fixed between a lid 4a and a base 4b of a workpiece carrier 4 (see figure). Fig. 1The base 4b of the workpiece carrier 4 may have two centering bores (not visible) which are used for reproducible positioning of the workpiece carrier 4 during the stacking process and during irradiation of the battery element stacks 1 with X-rays, which serves to check for sufficiently accurate stacking of the battery element layers 1, within the framework of a method according to the invention. The geometry of the workpiece carrier 4 shown may differ. A material should be used for the workpiece carrier 4 that does not prevent testing by means of X-rays and preferably also does not significantly hinder or influence it.

[0028] The Fig. 3This shows possible specifications for sufficiently precise stacking of the battery elements, or rather the electrodes 2 and separators 3 that form them, for one of the four corners of the battery element stack. These specifications should be met for all corners. Accordingly, a storage area AA, AK, AS can be provided for each of the anodes 2a, the cathodes 2b, and the separators 3, within which the edges of these different types of battery element layers of all battery elements should lie. In addition, the optimal position SA, SK, SS with respect to the respective width and length is shown for each of the different types of battery element layers, with this optimal position SA, SK, SS being centered within the respective storage area AA, AK, AS.The widths of the storage areas AA, AK, AS can be, for example, 1.0 mm or ±0.5 mm on both sides of the respective optimal position SA, SK, SS.

[0029] In addition to the various storage areas AA, AK, AS for the different types of battery element layers of all battery elements in a battery element stack 1, a minimum distance dAK, dAS between the different storage areas AA, AK, AS can also be specified to ensure sufficiently accurate stacking. For example, the minimum distance dAK between storage area AA for the anodes 2a and storage area AK for the cathodes 2b, as well as the minimum distance dAS between storage area AA for the anodes 2a and storage area AS for the separators 3, can each be 0.8 mm. The chain comprising these two minimum distances dAK, dAS, and the width of storage area AA for the anodes 2a, thus also results in a minimum distance between storage area AK for the cathodes 2b and storage area AS for the separators 3.

[0030] The method according to the invention enables, through a combination of two test steps, the simplest and fastest possible testing of the battery element stack 1 with regard to sufficiently accurate positions of all battery element layers of the battery element stack 1.

[0031] In a first test step, the positions of the battery cell layers of the still individual battery cells are determined, and it is checked whether all edges of the different types of battery cell layers lie within a first tolerance range. These different first tolerance ranges for the different types of battery cell layers can be used to determine the values ​​in the Fig. 3 The storage areas AA, AK, and AS shown must correspond to these requirements. Those battery elements that meet this requirement are declared suitable for forming a battery element stack 1 and are therefore usable.

[0032] The individual battery elements each comprise an anode 2a, a cathode 2b, and a first separator 3 arranged between the anode 2a and the cathode 2b. Preferably, each individual battery element also comprises a second separator 3 arranged on the side of the cathode 2b or, more preferably, the anode 2a facing away from the first separator 3. Integrating such a second separator 3 into the individual battery elements simplifies their stacking into the battery element stack 1, which follows the first test step as a process step, because the battery elements can then be stacked directly on top of each other without having to insert an additional separator 3 between the previously isolated battery elements.

[0033] The first inspection step is performed using an optical camera system (see below). Fig. 4 and 5) is carried out, by means of which at least one image of the individual battery elements is captured and evaluated. A first light source (not shown) can preferably be arranged on the same side with respect to the individual battery elements as at least one camera 5 of the camera system, and a second light source (not shown) can be arranged on the opposite side with respect to the individual battery elements.

[0034] For the evaluation, the different sizes of the various types of battery cell layers and their differing absorption properties for visible light are utilized. The absorption properties of the separators 3 are so low that the electrode(s) 2 covered by at least one of the separators 3 are translucent through the separators 3. Preferably, the at least one camera 5 of the camera system is positioned closer to the cathode 2b than to the anode 2a when the image is captured. In the described configuration of the individual battery cells, the cathode 2b, which exhibits the strongest absorption properties for visible light, is thus directly visible in the image, while the anode 2a, which has a medium absorption properties for visible light, is translucent through the first separator 3.The corresponding large areas of the different types of battery element layers are recognizable in the image by different dark colors and can therefore be automatically evaluated by an evaluation device 6 of the camera system.

[0035] Provided the detection area 5a of the at least one camera 5 used is large enough, the individual battery elements can be completely captured even without relative movement to this camera 5. However, to achieve a relatively high resolution, it is also possible to move the individual battery elements and the at least one camera 5 relative to each other, with the at least one camera 5 capturing only sections of the battery elements at any given time. A relatively high resolution without relative movement can be achieved by using several cameras 5, each of which can then have a detection area 5a that is smaller than the large areas of the battery element layers. Fig. 5Figure 1 shows an embodiment in which a camera 5 is assigned to each of the four corners of the individual battery elements.

[0036] After the individual battery elements have been tested in the first test step, the battery elements declared usable are stacked in a defined number and optionally in a traceable sequence to form battery element stack 1. To prevent the battery element layers of the individual battery elements from shifting relative to each other, which could distort the result of the first test step, it is preferably provided that the battery element layers of the previously isolated battery elements are already immovably connected to each other, in particular glued, during the execution of the first test step.

[0037] Subsequently, a second test step is carried out in which the battery element stack 1 is irradiated with X-rays, which are emitted by an X-ray source 7 and detected by an X-ray detector 8 (see figure). Fig. 6The X-ray radiation is oriented perpendicularly to the large surfaces of the battery cell layers, with the perpendicular orientation referring to a central beam 9 of the generally conical or cone-shaped X-ray radiation. By evaluating the X-ray radiation detected by the X-ray detector 8, the positions of those (at least three) edges of one type of battery cell layer, in this case the anodes 2a, that define at least two of the corners of these battery cell layers (anodes 2a) are determined. Preferably, the positions of all four edges (at least sectionally) with respect to at least two diagonally opposite corners of the battery cell layers are determined. Based on this, the maximum distance dmax between the corresponding (i.e., equally located) edges of all anodes 2a is determined (see Figure 8). Fig. 6) and also checked whether this respective maximum distance d max lies within a second tolerance range T 2. Due to the advantageous evaluation possible using only the central beam 9 of the X-ray radiation, it is provided that the battery element stack 1 is moved relative to the X-ray radiation for edge detection. The movement and the individual image acquisitions should be synchronized so that a distortion-free image can be combined with the images from the X-ray detector 8.

[0038] The Figs. 7 to 11 This procedure is illustrated. According to the Figs. 7 to 11The battery element stack 1 is moved in a controlled manner through the linear detection areas of two line detectors 10, which together form the X-ray detector 8. The movement of the battery element stack 1 through the detection areas of the line detectors 10 results in an area of ​​detection. The line detectors 10 are arranged perpendicular to each other in a cross shape. The movement of the battery element stack 1 is always perpendicular to the detection area of ​​one of the line detectors 10.

[0039] Instead of line detectors 10, an area detector (not shown) or several area detectors can also be used.

[0040] The positions of all four edges of all anodes 2a are determined. It is not necessary to measure the edges along their entire length. However, measuring as large a section as possible can be advantageous for the result, so that, for example, according to the Figs. 7 and 11 Two different sections of the edges running in the longitudinal directions are determined one after the other, and the corresponding partial results are linked together to determine a single edge path.

[0041] The Figs. 12 to 16 show comparable to the Figs. 7 to 11The four edges of the anodes 2a are detected (section by section), in this case using two X-ray detectors 8, each consisting of two line detectors 10 arranged in a T-shape. These two X-ray detectors 8 can each be combined with an X-ray source (not shown), whereby a central beam of X-ray radiation emitted by the respective X-ray source can be located at the intersection of the T-shaped arrangement of the two line detectors 10. It is also possible, in principle, to use only one T-shaped X-ray detector 8 and thus only one associated X-ray source according to the Figs. 12 to 16 to use.

[0042] The Figs. 17 to 22 show, in turn, comparable to the Figs. 7 to 11The edges of the anodes 2a are detected (section by section), in this case by means of two X-ray detectors 8, each comprising crosswise arranged line detectors 10, two from a plurality (a total of five are shown) of battery cell stacks 1 are detected simultaneously. For a better understanding of the movements of the individual battery cell stacks 1, these are numbered I - V.

[0043] Two line detectors 10 of an X-ray detector 8 can also be arranged in an L-shape.

[0044] If a rotation of the battery element stack is performed between two edge detections, the procedure can also be carried out with a single line detector 10.

[0045] The line detectors can also be designed to be so long that they can capture the entire length of an edge in one pass.

[0046] Point-based measurement may also be sufficient. This applies at least if at least two point-based measurements are taken per edge.

[0047] Distinguishing the edges of the different types of battery cell layers when evaluating the X-rays detected by the X-ray detector 8 is based on the different absorption characteristics that the various types of battery cell layers exhibit for X-rays due to the different materials from which they are made. In particular, it can be provided that the X-rays are essentially not absorbed by the separators 3, are absorbed to a moderate extent by the anodes 2a, and are absorbed to a relatively high extent by the cathodes 2b. This advantageously allows the determination of the greatest distance between the various (equally located) edges of all anodes 2a under consideration.Different dark values ​​are evaluated in a region where these edges are located. Due to the only partially, but simultaneously sufficiently high, absorption of the X-rays by the anodes 2a, the positions of the considered edges of all anodes 2a can be determined, since they can be clearly distinguished. This does not apply only if two or more edges lie exactly and directly on top of each other. Consequently, the positions of the two edges that have the greatest distance d max between them, and thus this distance d max itself, can also be determined (cf. ). Fig. 6This determination of the edges of the anodes 2a is not hindered by the relatively strongly absorbing cathodes 2b due to the relatively small size of their large surfaces (compared to the anodes 2a). The same applies to the separators 3, whose large surfaces are indeed larger than those of the anodes 2a, but which at the same time do not absorb the X-rays to a significant extent and thus do not prevent the edges of the anodes 2a from being detected as a result of sufficiently clear, abrupt changes in the absorption of the detected X-rays.

[0048] Additionally, the length or width of the corresponding anodes 2a can be determined by measuring the distance between two opposite edges of the anode edges exhibiting the distance d max. If these values ​​are also recorded during the first test step, a comparison can lead to a unique assignment to one or more anodes 2a in the battery element stack 1.

[0049] The maximum displaced cathode can also be determined with high contrast, allowing for a direct check of the minimum distance between the anode and cathode.

[0050] The second tolerance range T 2 is determined for each of the considered edges by adjusting a defined initial tolerance range TA based on a distance of the equally located edges of the battery element layers determined in the first test step.

[0051] The Fig. 23 shows the initial tolerance range TA with respect to one of the considered edges of the anodes 2a, where this is a section (with unchanged width) of the storage area AA for the anodes 2a according to the Fig. 4The second tolerance range T2 lies within the initial tolerance range TA, but is smaller at the edges by a deviation k, w in each case. These deviations k, w were determined in the first test step and represent the largest deviation determined for all usable battery elements of a battery element stack 1 between the actual distances of the edges of the cathode 2b and the anode 2a of the battery elements from the optimal distance (i.e., the distance between the optimal positions SA, SK of the edges of the cathode 2b and the anode 2a) d opt in the different directions (k: closer together; w: further apart) (cf. Fig. 24A corresponding adjustment of the initial tolerance range TA to determine the second tolerance range T2 can additionally be carried out using the largest deviation, determined for each of the usable battery elements of a battery element stack 1, between the actual distances of the edges of the at least one separator 3 and the anode 2a of the battery elements from the optimal distance in the various directions. This allows deviations k' and w' to be determined, which also reduce the initial tolerance range TA at its edges. The largest of the reductions k and k' on the one hand, and w and w' on the other, then determine the limits of the second tolerance range T2.

[0052] The Fig. 25This shows how, by utilizing the parallax effect in the second test step, the heights of the considered edges of the anodes 2a within the battery element stack 1 can be determined. An edge, which is recognizable as a point when viewed from the side, is projected onto the detection area of ​​the X-ray detector 8 at a first position P1 and at a second position P2 defined by a central beam plane 11, from which the projection lines PP1 and PP2 are determined. A (reference) coordinate system is preferably located at PP2, with the projection lines running in the z-direction and perpendicular to the x-direction. Due to the known arrangement of the X-ray detector 8 relative to the focal point 12 of the X-ray source 7 and the knowledge of the edge's velocity exclusively in the x-direction, h, x12, b12, and thus also the opening angle α1 in the yx-plane are known. With these known values, the formula can be used to calculate the heights of the edges. y 1 = y 2 = h ∗ 1 − x 12 b 12 The direct distance (y₁, y₂) of the edge from the detection area of ​​the X-ray detector 8 (in the y-direction of the coordinate system) is determined. It can be approximately assumed that this distance does not change (y₁ ≈ y₂).

[0053] As an alternative to using an area detector 13 according to the Fig. 25 At least two line detectors 10 can also be used to enable the spatial location of the considered edge to be determined at least twice. Reference symbol list

[0054] 1 Battery cell stack / Electrode-separator assembly (ESA) 2 Electrode 2a Anode 2b Cathode 3 Separator 4 Workpiece carrier 4a Cover of the workpiece carrier 4b Base of the workpiece carrier 5 Camera 5a Camera detection area 6 Evaluation device 7 X-ray tube 8 X-ray detector 9 Central beam of the X-ray radiation 10 Line detector 11 Central beam plane 12 Focus point of the X-ray tube 13 Area detector AA Storage area for the anodes AK Storage area for the cathodes AS Storage area for the separators SA Optimal position of an edge of an anode SK Optimal position of a cathode edge SS Optimal position of a separator edge d AK Minimum distance between the edges of an anode and a cathode of a battery cell d AS Minimum distance between the edges of an anode and a separator of a battery cell d max Greatest distance between equally located edges of all anodes d opt Distance between the optimal Positions of the edges of the cathode and anode of the battery cellsT2 second tolerance range TA initial tolerance range k largest converging deviation of the distances of the edges of the anodes and cathodes largest diverging deviation of the distances of the edges of the anodes and cathodes k' largest converging deviation of the distances of the edges of the anodes and separators largest diverging deviation of the distances of the edges of the anodes and separators h distance of the focal point of the X-ray source to the detection area of ​​the X-ray detector P1 first position of an edge P2 second position of the edge PP1 projection line to P1 PP2 projection line to P2 x12 distance between P1 and P2 b12 distance between PP1 and PP2 y1 distance of the edge to the detection area of ​​the X-ray detector at P1 y2 distance of the edge to the detection area of ​​the X-ray detector at P2 α1 opening angle

Claims

1. Method for checking at least one stack (1) of several battery elements which each comprise an electrode (2) designed as an anode (2a), an electrode (2) designed as a cathode (2b) and at least one separator (3) as different types of plate-like battery element layers, wherein the separator (3) is arranged between the electrodes (2) and wherein the battery element layers have large polygonal surfaces of at least partly different sizes and are stacked in a stacking direction which is oriented perpendicularly to the large surfaces, wherein • in a first checking step, the positions of the battery element layers of the still separated battery elements are determined and in the process a check is made as to whether edges of the battery element layers each lie within a first tolerance range, wherein the battery elements to which this applies are determined to be usable battery elements, • several of the usable battery elements are stacked to form the battery element stack (1), • in a second checking step, the battery element stack (1) is irradiated by means of X-ray radiation which is emitted by an X-ray radiator (7) and detected by an X-ray detector (8), wherein the X-ray radiation is oriented perpendicularly with respect to the large surfaces of the battery element layers, and the positions of those edges of one type of battery element layers which delimit at least two of the corners of these battery element layers are determined by means of the detected X-ray radiation, wherein a check is made as to whether the greatest distance between the respectively aligned edges of all of the battery element layers of the selected type lies within a second tolerance range (T2).

2. Method according to Claim 1, characterized in that the battery element layers are immovably connected to each other.

3. Method according to Claim 1 or 2, characterized in that the large surfaces of the anodes (2a) are larger than the large surfaces of the cathodes (2b).

4. Method according to any of the preceding claims, characterized in that the large surfaces of the separators (3) are larger than the large surfaces of the cathodes (2b) and / or the anodes (2a).

5. Method according to any of the preceding claims, characterized in that the positions of the edges of the anodes (2a) are determined.

6. Method according to any of the preceding claims, characterized in that the positions of the battery element layers of the separated battery elements are determined based on the image from an optical camera system.

7. Method according to Claim 6, characterized in that the image from the camera system is captured in incident light.

8. Method according to Claim 5, characterized in that, when the image is captured, the cathode (2b) is closer to a camera (5) of the camera system than the anode (2a).

9. Method according to any of the preceding claims, characterized in that the second tolerance range (T2) is determined in each case by way of a defined output tolerance range (TA) being adapted based on a distance between the corresponding edges determined in the first checking step.

10. Method according to any of the preceding claims, characterized in that the X-ray detector (8) comprises at least two line detectors (10), which are oriented perpendicularly to each other.

11. Method according to Claim 10, characterized in that the battery element stack (1) is moved in a relative manner at least once in a vertical direction through a cell-like detection region of each of the line detectors (10).

12. Method according to any of the preceding claims, characterized in that the several usable battery elements are stacked to form at least two battery element stacks (1), which are simultaneously irradiated by means of the X-ray radiation in the second checking step.

13. Method according to any of the preceding claims, characterized in that • the several usable battery elements are stacked in a reconstructed order to form the at least one battery element stack (1) and • the second checking step is carried out at least twice in different positions of the battery element stack (1) relative to the X-ray radiator and, by comparing the results of these at least two second checking steps, the determined positions of the edges are assigned to the various battery elements.