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

Abstract

A method for testing a stack of multiple battery cells, each comprising an anode, a cathode, and a separator as types of battery cell layers, wherein the separator is arranged between the anode and the cathode. In a first test step, it is checked whether the edges of the battery cell layers are within a first tolerance range, wherein the battery cells to which this applies are determined to be usable battery cells. Several of the usable battery cells are stacked to the battery cell stack. The battery cell stack is irradiated by X-rays. Via the X-rays, positions of those edges of a type of battery cell layers are determined which delimit at least two of the corners of these battery cell layers, checking whether the greatest distance between the equally located edges of each of the battery cell layers of the selected type is within a second tolerance range.

Claims

1. A method for testing at least one stack of at least two battery cells, each of the at least two battery cells comprising an electrode designed as an anode, an electrode designed as a cathode and at least one separator as different types of plate-shaped battery cell layers, the separator being arranged between the electrodes, and the battery cell layers having polygonal large areas of at least partially different sizes and are stacked in a direction perpendicular to the large areas, the method comprising: determining, in a first test step, the positions of the battery cell layers of the still isolated battery cells determined and checking whether edges of the battery cell layers are within a first tolerance range, wherein the battery cells to which this applies are determined to be usable battery cells; stacking several of the usable battery cells to the battery cell stack; irradiating, in a second test step, the battery cell stack via X-rays emitted by an X-ray emitter and detecting the emitted X-rays via an X-ray detector, the X-rays being directed substantially perpendicular with respect to the large areas of the battery cell layers, and via the detected X-rays, the positions of those edges of the type of battery cell layer that delimit at least two of the corners of this battery cell layer are determined and checking whether a greatest distance between equally located edges of all the battery cell layers of the selected type is within a second tolerance range.

2. The method according to claim 1, wherein the battery cell layers are immovably connected to each other.

3. The method according to claim 1, wherein the large areas of the anodes are larger than large areas of the cathodes.

4. The method according to claim 1, wherein the large areas of the separators are larger than large areas of the cathodes and/or the anodes.

5. The method according to claim 1, wherein positions of the edges of the anodes are determined.

6. The method according to claim 1, wherein positions of the battery cell layers of the individual battery cells are determined on the basis of the image of an optical camera system.

7. The method according to claim 6, wherein the image of the camera system is taken in incident light.

8. The method according to claim 5, wherein when the image is taken, the cathode is closer to a camera of the camera system than the anode.

9. The method according to claim 1, wherein the second tolerance range is determined in each case by adjusting a defined output tolerance range based on a distance of the corresponding edges determined in the first test step.

10. The method according to claim 1, wherein the X-ray detector comprises at least two line detectors arranged substantially perpendicular to each other.

11. The method according to claim 10, wherein the battery cell stack is moved relatively at least once in a substantially perpendicular direction by a line-like detection area of each of the line detectors.

12. The method according to claim 1, wherein the multiple usable battery cells are stacked into at least two battery cell stacks, which are substantially simultaneously irradiated by X-rays in the second test step.

13. The method according to claim 1, further comprising; stacking the multiple usable battery cells in a traced order to the at least one battery cell stack; and performing the second test step at least twice in different positions of the battery cell stack relative to the X-ray emitter and by comparing the results of these at least two second test steps, the determined positions of the edges are assigned to the different battery cells.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0025] FIG. 1: shows a stack of battery cells clamped in a work holder;

[0026] FIG. 2: shows a cross-section of a section of the stack of battery cells and the work holder;

[0027] FIG. 3: shows storage areas for the cathodes, anodes and separators of the battery cell stack;

[0028] FIG. 4: shows a single battery cell and a camera system according to an example;

[0029] FIG. 5: shows a single battery cell and a camera system according to an example;

[0030] FIG. 6: shows the stack of battery cells and an X-ray system;

[0031] FIGS. 7 to 11: show different positions of the battery cell stack relative to an X-ray detector of an X-ray system according to an example;

[0032] FIGS. 12 to 16: show different positions of the battery cell stack relative to X-ray detectors of an X-ray system according to an example;

[0033] FIGS. 17 to 22: show different positions of several battery cell stacks relative to X-ray detectors of an X-ray system according to an example;

[0034] FIG. 23: shows a representation to determine a (second) tolerance range;

[0035] FIG. 24: shows a representation of deviations of the positions of adjacent edges of a cathode and an anode of a battery cell; and

[0036] FIG. 25: shows geometrical relationships in the determination of spatial positions of an edge via the X-ray system.

DETAILED DESCRIPTION

[0037] In the context of battery cell production, battery cell stacks 1, also referred to as electrode-separator composites (ESVs), can be produced according to FIG. 2. These are stacks 1 of several battery cells, comprising, in alternating order, battery cell layers in the form of plate-shaped electrodes 2 (again alternating in designs and arrangements corresponding to intended uses as anodes 2a and cathodes 2b of the battery cells) and electrically insulating plate-shaped separators 3, wherein the electrodes 2 and separators 3 have large rectangular areas. It is provided that the anodes 2a, the cathodes 2b and the separators 3 will have different large areas in order to avoid a short circuit between adjacent anodes 2a and cathodes 2b as well as excessive losses with regard to the electrical performance of the battery cells, despite inaccuracies in the stacking that are at least still within appropriate tolerance ranges. According to FIG. 2, it can be provided that the cathodes 2b have the smallest large areas and the separators 3 the largest large areas, resulting in a complete peripheral protrusion (i.e., both in terms of the widths and lengths of the battery cell layers) of anodes 2a with respect to cathodes 2b on the one hand and of separators 3 with respect to anodes 2a (and thus also of cathodes 2b) on the other.

[0038] The plate-shaped separators 3 can also be, at least in part, sections of a meandering separator strip. The protruding edges of adjacent separators 3 may also be glued.

[0039] After a stacking process, a battery cell stack 1 is fixed between a lid 4a and a base 4b of a work holder 4 (see FIG. 1). Two centering holes can be provided in the base 4b of the work holder 4, which are used for reproducible positioning of the work holder 4 during the stacking process as well as during irradiation of the battery cell stacks 1 with X-rays, which serves to test for a sufficiently precise stacking of the battery cell layers 1, within the framework of a method according to the invention. The geometry of the work holder 4 shown may differ. For the work holder 4, a material should be used that does not prevent an inspection by means of X-rays nor preferably obstructs or influences it to a significant extent.

[0040] FIG. 3 shows possible specifications for a sufficiently precise stacking of the battery cells or the electrodes 2 and separators 3 forming them for one of the four corners of the battery cell stack, wherein these specifications should be fulfilled for all corners. Accordingly, a storage area A.sub.A, A.sub.K, A.sub.S may 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 cell layers of all battery cells are to lie. In addition, for each of the different types of battery cell layers, the optimal position S.sub.A, S.sub.K, S.sub.S is shown with regard to the respective width and length, wherein this optimal position S.sub.A, S.sub.K, S.sub.S runs centrally within the respective storage area A.sub.A, A.sub.K, A.sub.S. For example, the widths of the storage areas A.sub.A, A.sub.K, A.sub.S can be 1.0 mm or ?0.5 mm on both sides of the respective optimal position S.sub.A, S.sub.K, S.sub.S. In addition to the different storage areas A.sub.A, A.sub.K, A.sub.S for the different types of battery cell layers of all battery cells of a battery cell stack 1, a minimum distance d.sub.AK, d.sub.AS between the different storage areas A.sub.A, A.sub.K, A.sub.S can also be provided as a specification for sufficiently accurate stacking. For example, the minimum distance d.sub.AK between the storage area A.sub.A for anodes 2a and the storage area A.sub.K for the cathodes 2b, as well as the minimum distance d.sub.AS between the storage area A.sub.A for the anodes 2a and the storage area A.sub.S for the separators 3, can be 0.8 mm each. The chain, which includes these two minimum distances d.sub.AK, d.sub.AS and the width of the storage area A.sub.A for the anodes 2a, thus also results in a minimum distance between the storage area A.sub.K for the cathodes 2b and the storage area A.sub.S for the separators 3.

[0041] By means of a combination of two test steps, the method according to the invention enables the simplest and fastest possible inspection of the battery cell stack 1 with regard to sufficiently precise layers of all battery cell layers of the battery cell stack 1.

[0042] In a first test step, the layers of the battery cell layers of the still isolated battery cells are determined and it is checked whether all of the edges of the different types of the battery cell layers are within a first tolerance range. These different first tolerance ranges for the different types of battery cell layers can correspond to the storage areas A.sub.A, A.sub.K, A.sub.S shown in FIG. 3. Those battery cells for which this requirement is fulfilled are declared suitable for the formation of a battery cell stack 1 and thus as usable.

[0043] The individual battery cells each comprise an anode 2a, a cathode 2b and a first separator 3, which is located between the anode 2a and the cathode 2b. Preferably, each of the individual battery cells also includes a second separator 3, which is located on the side of the cathode 2b or, preferably, anode 2a, facing away from the first separator 3. By integrating such a second separator 3 into the individual battery cells, their stacking to the battery cell stack 1, which follows the first test step as a method step, can be simplified, because the battery cells can be stacked directly on top of each other without having to additionally insert a separator 3 between the previously separated battery cells.

[0044] The first test step is carried out using an optical camera system (see FIGS. 4 and 5), by means of which at least one image of the individual battery cells is taken and evaluated. A first light source can preferably be arranged on the same side with respect to the individual battery cells as at least one camera 5 of the camera system and a second light source on the opposite side with respect to the individual battery cells.

[0045] On the one hand, the different sizes of the different types of battery cell layers and on the other hand, their different absorption behavior for visible light are exploited for the evaluation. The absorption behavior of the separators 3 is so low that the electrode(s) 2 that is/are covered by at least one of the separators 3 is translucent and can be seen through the separators 3. Preferably, it is provided that at least one camera 5 of the camera system is closer to the cathode 2b than to the anode 2a when taking the image. In the picture, the cathode 2b, which has the strongest absorption behavior for visible light, is directly recognizable in the described structure of the individual battery cells, and the anode 2a, which has a medium absorption behavior for visible light, is visible translucent through the first separator 3. The corresponding large areas of the different types of battery cell layers are recognizable by different dark colorations in the image and can therefore be automatically evaluated by an evaluation device 6 of the camera system.

[0046] As long as the detection range 5a of the at least one camera 5 used is large enough, the individual battery cells can also be completely captured without relative movement to this camera 5. In order to achieve a relatively high resolution, however, it may also be provided to move the individual battery cells and at least one camera 5 relative to each other, wherein only sections of the battery cells are captured by the at least one camera 5. A relatively large resolution without relative motion can be achieved by using several cameras 5, each of which can then have a detection range 5a that is smaller than the large areas of the battery cell layers. FIG. 5 shows an embodiment in this respect in which a camera 5 is assigned to each of the four corners of the individual battery cells.

[0047] After testing the individual battery cells in the first test step, the battery cells declared as usable are stacked in a defined number and optionally in a traced sequence to the battery cell stack 1. In order to prevent the battery cell layers of the individual battery cells from shifting in relation to each other, which could falsify the result of the first test step, it may be preferably provided that the battery cell layers of the previously isolated battery cells are already immovably connected to each other, in particular glued, during the execution of the first test step.

[0048] This is followed by a second test step, in which the battery cell stack 1 is irradiated by means of X-rays, which are detected by an X-ray detector 8 emitted by an X-ray emitter 7 (see FIG. 6). It is provided that the X-ray radiation is oriented perpendicular to the large areas of the battery cell layers, wherein the vertical orientation refers to a central beam 9 of the basically conical or cone-shaped X-rays. By evaluating the X-rays detected by the X-ray detector 8, the positions of those (at least three) edges of a type of battery cell layer, in this case the anodes 2a, are determined, which delimit at least two of the corners of these battery cell layers (anodes 2a). Preferably, it is provided that the layers of all four edges (at least in sections) are determined with respect to at least two diagonally opposite corners of the battery cell layers. Based on this, the greatest distance d.sub.max, which exists between the corresponding (i.e., equal) edges of all anodes 2a, is determined (see FIG. 6) and it is also checked whether this respective greatest distance d.sub.max lies within a second tolerance range T.sub.2. Due to the advantageous evaluability only by the central beam 9 of the X-rays, it is provided that the battery cell stack 1 is moved relative to the X-ray radiation for the detection of the edges. The movement and the individual images should be synchronized so that a distortion-free image can be combined with the images of the X-ray detector 8.

[0049] FIGS. 7 to 11 illustrate this procedure. According to FIGS. 7 to 11, the battery cell stack 1 is moved in a targeted manner by linear detection areas of two line detectors 10, which in combination represent the X-ray detector 8. By moving the battery cell stack 1 through the detection areas of the line detectors 10, a flat detection area is obtained. The line detectors 10 are arranged perpendicular to each other and in a cross shape. The movement of the battery cell stack 1 is perpendicular to the detection area of one of the line detectors 10.

[0050] Instead of line detectors 10, one area detector or several area detectors can also be used.

[0051] The positions of all four edges of all anodes 2a are determined. It is not necessary to capture the edges along their entire length. However, capturing as large a section of it as possible can have a beneficial effect on the detection result, so that, for example, according to 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 course.

[0052] FIGS. 12 to 16 show a detection of the four edges (section-by-section) of the anodes 2a, similar to FIGS. 7 to 11, wherein in this case two X-ray detectors 8 are used, each consisting of two line detectors 10, which are arranged in a T-shape. These two X-ray detectors 8 can each be combined with one X-ray emitter, wherein a central beam of X-ray radiation emitted by the respective X-ray emitter may be arranged at the intersection of the T-shaped arrangement of each of the two line detectors 10. In principle, it is also possible to use only one T-shaped X-ray detector 8 and thus only one assigned X-ray emitter according to FIGS. 12 to 16.

[0053] FIGS. 17 to 22 show a similar detection of the edges (in sections) of the anodes 2a, similar to FIGS. 7 to 11, wherein in this case by means of two X-ray detectors 8, each of which comprises crosswise arrayed line detectors 10, two of a plurality (a total of five are shown) of battery cell stacks 1 are simultaneously detected. For a better understanding of the movements of the individual battery cell stacks 1, these are numbered I-V.

[0054] Two line detectors 10 of an X-ray detector 8 can also be arranged in an L-shape.

[0055] If a rotation of the battery cell stack is performed between two acquisitions of edges, the method can also be performed with a single line detector 10.

[0056] The line detectors can also be designed to be so long that they can capture the entire length of an edge in one pass.

[0057] Point detection may also be sufficient. This applies at least if at least two point acquisitions are carried out per edge.

[0058] A differentiation of the edges of the different types of battery cell layers in the evaluation of the X-rays detected by the X-ray detector 8 is in turn based on different absorption behaviors that the different types of battery cell layers have for X-rays due to the different materials from which they are formed. In particular, it may be provided that the X-rays are essentially not absorbed by the separators 3 but absorbed by the anodes 2a to a medium extent and by the cathodes 2b to a relatively high extent. This makes it advantageous to determine the greatest distance between the different (identical) edges of all anodes 2a. Different dark values in an area in which these edges lie are evaluated, wherein the positions of the observed edges of all anodes 2a can be determined due to the only partially but simultaneously sufficiently high absorption of the X-ray radiation by the anodes 2a, since a clear distinction can be made between them. This only does not apply if two or more edges are exactly and directly on top of each other. Consequently, the positions of those two edges that have the greatest distance d.sub.max to each other and thus this distance d.sub.max itself can be determined (cf. FIG. 6). This determination with regard to the edges of the anodes 2a is not prevented by the relatively highly absorbent cathodes 2b due to their relatively small size (as compared to the anodes 2a) of their large areas. The same applies to the separators 3, whose large areas are larger than those of the anodes 2a, but which at the same time essentially do not absorb the X-rays and thus do not prevent the edges of the anodes 2a from being detected as a result of sufficiently clearly recognizable, erratic changes in the absorption of the detected X-rays.

[0059] In addition, the length or width of the associated anodes 2a can be determined by the distance of two opposing edges of the anode edges having the distance d.sub.max. If these values are also recorded during the first test step, a comparison can lead to a clear assignment to one or more anodes 2a in the battery cell stack 1.

[0060] The maximum displaced cathode can also be determined with a high contrast, so that a direct check of the minimum distance between the anode and the cathode can be performed.

[0061] The second tolerance range T.sub.2 is determined for each of the edges under consideration by adjusting a defined output tolerance range T.sub.A based on a distance of the equally located edges of the battery cell layers determined in the first test step. FIG. 23 shows the output tolerance range T.sub.A with respect to one of the considered edges of the anodes 2a, wherein this is a section (with unchanged width) of the storage area A.sub.A for the anodes 2a according to FIG. 4. The second tolerance range T.sub.2 is within the first tolerance range T.sub.A, but is smaller on the edge side by one deviation k, w. These deviations k, w were determined in the first test step and represent the largest deviation between the actual distances of the edges of the cathode 2b and the anode 2a of the battery cells determined for all usable battery cells of a battery cell stack 1 from the optimal distance (i.e., the distance between the optimal positions S.sub.A, S.sub.K of the edges of the cathode 2b and the anode 2a) d.sub.opt in the different directions (k: closer to each other; w: further apart from each other) (cf. FIG. 24). A corresponding adjustment of the output tolerance range T.sub.A to determine the second tolerance range T.sub.2 can also be made using the largest deviation between the actual distances of the edges of the at least one separator 3 and the anode 2a of the battery cells from the optimal distance in the different directions determined for all usable battery cells of a battery cell stack 1. This makes it possible to determine deviations k and w, which also reduce the output tolerance range T.sub.A on the edge side. 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 T.sub.2.

[0062] FIG. 25 shows how the heights of the observed edges of the anodes 2a within the battery cell stack 1 can be determined by exploiting the parallax effect in the second test step. An edge, which can be seen as a point when viewed exactly from the side, is projected onto the detection area of the X-ray detector 8 at a first position P.sub.1 and at a second position P.sub.2 defined by a central beam plane 11, from which the projection lines PP.sub.1 and PP.sub.2 are determined. A (reference-) coordinate system is preferably located in PP.sub.2, wherein the projection lines run in the z-direction and perpendicular to the x-direction. Due to the known arrangement of the X-ray detector 8 relative to the focus point 12 of the X-ray emitter 7 and the knowledge of the speed of movement of the edge in only the x-direction, h, x.sub.12, b.sub.12 and thus also the opening angle ?.sub.1 in the yx plane are known. With these known quantities, the formula:

[00001]$y_1=y_2=h*\left(1-\frac{x_{12}}{b_{12}}\right)$

[0063] can be used to determine the direct distance (y.sub.1, y.sub.2) of the edge from the detection area of the X-ray detector 8 (in the y-direction of the coordinate system). It can be roughly assumed that this distance does not change (y.sub.1?y.sub.2).

[0064] As an alternative to the use of an area detector 13 according to FIG. 25, at least two line detectors 10 can also be used to enable the detection of the spatial position of the observed edge at least twice.

[0065] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.