Laser-assisted stripping of battery packs

Abstract

A laser cutting method for cutting open a battery assembly (10) is provided, wherein the battery assembly (10) comprises a cell assembly (12) and a housing (14) surrounding the cell assembly (12), the housing comprising a first housing shell (142) and a second housing shell (144), wherein the first and the second housing shell (142, 144) are rigidly connected to each other along a connection area (146) on the outer circumference of the housing (14). The method comprises generating, by means of the laser cutting method, a cutting gap in the first housing shell (142) along a predetermined cutting contour (C), wherein the cutting contour (C) extends laterally outside the cell assembly (12) and laterally within a connection area (146). Furthermore, a laser cutting device for implementing the laser cutting method is provided.

Description

Field of the invention

[0001] The present invention relates to the field of batteries, such as those used to power electric motors in electric vehicles. In particular, the present invention relates to a technique for disassembling a battery assembly using laser cutting. State of the art

[0002] The structure of battery arrangements, which are also referred to as battery packs, is roughly simplified below using Fig. 1a. The exploded view according to Fig. 1a shows a battery arrangement 10, in the interior of which a cell arrangement 12 with a plurality of cell modules 122 is arranged as the core, which in turn comprise one or more electrically interconnected battery cells (in Fig. 1a not shown). The battery assembly 10 includes further functional components, such as a controller (also referred to as BMS or Battery Management System), an interface to an electrical consumer, cooling elements, and others, which are shown here only as examples and without their own reference numerals in the figures. The interior of the battery assembly is shielded from the outside by two housing shells 142, 144 that are firmly connected to one another (e.g., screwed and / or glued), which can also be referred to as the upper and lower parts of the tray, and which together form a housing 14 of the battery assembly 10.

[0003] In order to make the components of a battery assembly 10 reusable in a resource-efficient manner after the end of its life cycle, the battery assembly 10 must be at least partially disassembled or dismantled. To disassemble or dismantle a battery assembly 10, one of the first steps is to remove or at least open the housing 14 in order to access the core components of the battery assembly 10—in particular, the battery cells contained in the cell assembly 12, i.e., the valuable active material of the battery assembly 10.

[0004] To date, the housing shells 142, 144 of the housing 14 have generally been disassembled manually by a person. This manual process, which usually requires loosening a screw flange and / or adhesive bonds (and / or other connections such as riveted joints, welded joints, etc.) between the housing shells 142, 144, is very complex and requires that the battery cells inside the battery arrangement 10 are completely discharged in order to rule out the risk of uncontrolled discharge (e.g. electric shock, short circuit, etc.) or thermal runaway of the battery cells during disassembly. In this context, experts also refer to this as deep discharging of the battery cells. The use of (partially) automated screw techniques or the use of machining processes for loosening orSeparating the joints between the housing shells 142, 144, which are generally constructed from aluminum- or iron-based materials, contributes only marginally to increasing the efficiency of disassembling the battery assemblies.

[0005] The present invention is based on the object of improving the state of the art regarding the disassembly of battery assemblies. In particular, it should be possible to open the housing of the battery assembly flexibly and efficiently in an automated process, regardless of the condition and type of connection of the housing shells, without damaging the battery cells. The invention

[0006] The problem underlying the invention is solved by the subject matter of the independent claims. Further possible embodiments of the invention are specified in the subclaims, the description, and the drawings. Features, advantages, and possible embodiments presented in the description for one of the subject matter of the independent claims are to be regarded at least analogously as features, advantages, and possible embodiments of the respective subject matter of the other independent claims, as well as any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the subclaims.

[0007] According to the invention, a laser cutting method for cutting open a battery arrangement is provided. The battery arrangement has a cell arrangement and a housing or battery housing which surrounds the cell arrangement and forms an enclosure for the battery arrangement. The housing comprises a first housing shell and a second housing shell which are firmly connected to one another along an outer circumference of the housing (for example by a screw, rivet, adhesive and / or welded connection). In a simple embodiment of the battery arrangement, the housing shells can also be referred to as shell halves. The battery arrangement can, for example, have a so-called cell-to-pack battery pack architecture. This means that individual battery cells are directly installed (e.g. foamed) within a battery pack (= battery arrangement). Alternatively, the battery arrangement can also have a so-called cell-to-module orHave a module-to-pack architecture in which several battery cells are packaged in one cell module. If the battery arrangement comprises several cell modules, these are usually electrically connected to one another in order to bundle the capacity of all battery cells. In addition to those mentioned, the battery arrangement can also have other pack architectures. For example, there are so-called cell-to-chassis architectures in which the battery cells are integrated directly into the vehicle structure of a vehicle. In this case, the battery arrangement according to the invention could be regarded as part of the vehicle and the battery housing as part of the vehicle structure. The housing shells or at least one of the housing shells can be made of a metallic material, in particular based on aluminum (in particular 3000 or 5000 series aluminum) or based on iron (in particular stainless steel).The thickness of a metallic housing shell can, for example, range from 0.5 mm to 3 mm. Alternatively, at least one of the housing shells can be made of a plastic or a fiber-reinforced plastic (CFRP). The housing shells preferably have the same or a similar material composition. Examples of battery arrangements according to the present disclosure include various (rechargeable) batteries from the eMobility sector, for example for use in cars, trucks, or commercial vehicles (BEV, PHEV, MHEV, or HEV), in forklifts, eBikes, ships, aircraft, drones, etc., as well as in other areas, for example for building power supply or grid stabilization or in power tools (gardening tools, cordless screwdrivers, etc.).

[0008] According to the invention, a cutting gap is created in the first housing shell along a predetermined cutting contour by means of the laser cutting process, wherein the cutting contour extends laterally outside the cell arrangement and laterally within a connecting region along which the housing shells are connected to one another. The laser cutting process can preferably be carried out using a solid-state laser (in particular a fiber laser (such as from the applicant's TruFiber 500-2000 series) or a disk laser (such as from the TruDisk 2000-8000 or TruDisk 3001-24001 series)) as a single-mode laser or multi-mode laser. The laser power can be, for example, in the range from 500 W to 24 kW, preferably in the range from 2 kW to 8 kW.

[0009] The terms "laterally outside" and "laterally inside" are to be understood as meaning that the cutting contour extends, in a plan view of the battery assembly, between the battery assembly and the connecting area (which may be formed, for example, by a screw flange). The plan view of the battery assembly is taken from a direction (z-direction) perpendicular to an xy-plane of a Cartesian coordinate system, which can be used to describe the spatial dimensions of the battery assembly.

[0010] The design of the cutting contour is intended to ensure that the laser beam used for laser cutting is not directed at the cell arrangement inside the battery assembly, thereby preventing critical damage. At the same time, the connection between the housing shells is circumvented by creating the cut within the connection area in only one housing shell.

[0011] The inventors have recognized that a laser cutting method according to the present invention is suitable for disassembling battery assemblies. This is not a given, because laser cutting involves very high energies and the workpiece being machined is partially heated to very high temperatures. However, for the battery cells of a battery assembly, heat input as low as 60°C can be critical (risk of ignition). It has been shown that laser cutting, due to its flexible application and high degree of automation, can significantly simplify the process of disassembling battery assemblies. Firstly, the speed of disassembly is significantly increased compared to a manual process. By selectively separating only one housing shell, the process is independent of the type and / or quality of the connection between the housing shells (welded joint, screw joint, riveted joint, adhesive joint, etc.).) and offers a high degree of flexibility. Discharging the battery cells is generally not necessary when using a (numerically controlled) laser cutting process according to the invention, since the high precision of the process means that critical damage to or interference with the battery cells inside the battery assembly, which could lead to uncontrolled discharge or thermal runaway of the battery cells, can be ruled out with a high degree of probability. The laser cutting process takes place in a safe environment and is preferably fully automated. This also reduces the risk of injury to people during disassembly of the battery assemblies.

[0012] Compared to conventional dismantling methods, the laser cutting method according to the invention offers the following additional advantages: • The disassembly or opening of the battery housing takes place in a cutting process, which can remove either at least two screw connections (or rivet connections) or a continuous joint connection (glued, welded) in one process step; • Several joining and packing variants of a battery arrangement can be processed on one system without changing tools; • There is no dependence on the condition of the joint between the housing shells. This condition can be affected by environmental influences over years of use. Therefore, precise knowledge of the battery pack's deterioration is generally not necessary; • The process can be fully automated without manual intervention; • Using the flexible, laser-supported (3D) process, battery packs of different designs can be cut open on one system; • The fact that only one half of the housing shell has to be cut (or split open) increases productivity during disassembly; • Compared to other thermal cutting processes (e.g. plasma cutting), laser cutting involves a considerably lower heat input into the workpiece; • In contrast to machining processes (e.g. milling), no chips are produced that could contaminate the interior of the battery assembly; • No foreign substances are introduced, e.g. through coolants (especially cooling lubricants) or other operating materials that must be used in other processes.

[0013] According to a preferred variant of the laser cutting process, an optical axis of the laser beam used for the laser cutting process has a distance from the cell arrangement of at least 0.5 mm, preferably of at least 1 mm, at all times during the laser cutting process (i.e. when the laser beam is switched on). In other words, the laser beam used for cutting always has the specified minimum distance from the cell arrangement or from the battery cells arranged therein. In this way, critical heat input by laser radiation during the cutting process can be significantly minimized. The heat input is particularly critical when a battery cell, or a region of a battery cell, is heated to a temperature of 60 °C or higher, or (particularly critical) 100 °C or higher.

[0014] According to one variant, the laser cutting process can be implemented as a laser fusion cutting process. In this case, an inert cutting gas can be used to expel the melt and to shield the process zone from unwanted reactions with the surrounding atmosphere (especially with atmospheric oxygen). In particular, nitrogen can be used as the inert cutting gas. The use of an inert cutting gas can also prevent the risk of ignition of adjacent plastics (e.g., foams or plastic components) inside the battery assembly.

[0015] According to an alternative variant, the laser cutting process can be implemented as a laser flame cutting process, using oxygen or an oxygen-containing gas mixture as the cutting gas. This process variant can be particularly advantageous when cutting a ferrous housing shell, especially with a relatively thick wall.

[0016] When implemented as a laser melting or laser flame cutting process, the laser cutting process is carried out using a laser cutting system, which preferably has a fixed optics system, by means of which the laser beam, together with the cutting gas jet, is directed onto the first housing shell via a cutting nozzle. Furthermore, a laser beam having a central core beam and an annular beam surrounding the core beam can be used to carry out the process. This beam shape can be implemented using the known so-called 2-in-1 technology, in which the laser beam is guided into the processing optics via a 2-in-1 optical fiber, enabling both an increase in cutting speed and an improvement in the cut edges.

[0017] For example, a nozzle with an inner contour similar to a Laval nozzle can be used as a cutting nozzle. Using a Laval nozzle as a cutting nozzle allows for comparatively larger working distances with comparatively lower cutting gas consumption.

[0018] According to a variant of the laser cutting method, the processing beam, comprising a laser beam and a cutting gas jet, can be directed at the first housing shell at an angle to a surface of the first housing shell, in particular to the xy plane along which the cell arrangement is arranged, such that the laser beam is directed in the beam propagation direction in a direction away (opposite the z direction) from the cell arrangement. The angle to the xy plane can be in a range between 90° (vertical beam incidence - simple arrangement that can be implemented without a pivoting laser cutting head) and (inclusive) 45°. Due to the oblique arrangement of the processing beam, the melt that is expelled downwards from the cutting gap during laser fusion cutting or laser flame cutting can be kept away from the cell arrangement. Contamination (orContamination of the important, central components of the battery assembly, in particular contamination (and heating) of the cell assembly by the expelled cutting slag, can thus be avoided.

[0019] According to a further alternative, the laser cutting process can also be implemented as a laser sublimation cutting process. In laser sublimation cutting, the workpiece material is vaporized, resulting in no or only minimal melt, which is expelled from the cutting gap due to the vapor pressure in the cutting gap. Consequently, no (or only minimal) contamination is created inside the battery assembly.

[0020] The laser cutting method according to the invention can further comprise optical observation of the laser cutting process to detect the actual course of the cutting gap. Furthermore, the method can comprise readjusting cutting parameters of the laser cutting process if the course of the cutting gap deviates from the specified cutting contour by at least a predetermined minimum value, in order to align the cutting gap and cutting contour. By compensating for the detected tolerances, the precision of the cutting process can be increased. As a result, scrap can be reduced.

[0021] According to a further preferred variant, the cutting gap created during the laser cutting process is a closed cutting gap, such that a cutout part of the first housing shell is completely separated from a surrounding residual part of the housing shell. In other words, the cutting contour can be a closed contour. Alternatively, the cutting contour or the cutting gap can also be open (for example, a substantially U-shaped cutting contour), such that the cutout part remains connected to the residual part of the housing shell after the cutting process has been carried out. The contour can also be a closed contour, wherein the laser cutting parameters are set such that a microjoint or a nanojoint remains in the resulting cutting gap at at least one point along the cutting contour, which holds the cutout part in the surrounding residual part.Technologies for creating microjoints or nanojoints during laser cutting were already introduced and publicly documented by the applicant several years ago. The cut can also be divided into several subsegments to simplify subsequent removal of the cutout. For example, additional openings can be introduced into the cutout or adjacent to the cutout in the remaining part to simplify intervention when removing the cutout.

[0022] Furthermore, the laser cutting process can comprise the following steps: measuring, during the laser cutting process, a distance between a cutting nozzle used for the laser cutting process and the surface of the first housing shell; and adjusting, based on the measured distance, preset cutting parameters of the cutting process. By measuring and, if necessary, adjusting the working distance of the cutting nozzle (e.g., capacitively, using an OCT measurement method, or using laser triangulation), the contour accuracy and thus the precision during laser cutting can be increased.

[0023] According to the invention, a device for laser cutting a battery assembly is also provided. The device comprises at least: a workpiece support for supporting the battery assembly during the cutting process; a laser beam source for providing a laser beam; a laser processing head for focusing the laser beam toward the battery assembly; and a control unit configured to control the device to perform a laser cutting method according to one of the variants described above. If the laser cutting method is implemented as a laser melting or laser flame cutting method, the device further comprises at least one corresponding cutting gas supply. In particular, the device can be configured as a 3D laser cutting system, by means of which the processing head can be guided not only vertically (cf. 2D laser flatbed system) but also obliquely. Examples of implementation

[0024] The following description of preferred embodiments, in conjunction with the drawings, serves to explain the invention in more detail.

[0025] They show: Fig. 1a A battery arrangement in an exploded view; Fig. 1b Schematically a section of a battery arrangement in which two housing shells of the battery housing are connected to each other by a screw connection; Fig. 2a Schematically a plan view of a battery arrangement to illustrate a laser cutting method according to the invention; and Fig. 2b Schematically a sectional view of the battery arrangement according to Fig. 2a.

[0026] Identical or functionally equivalent elements are provided with the same reference numerals in the figures.

[0027] The battery arrangement according to Fig. 1a has already been described above in connection with the prior art. Reference is made to the corresponding description passage.

[0028] Fig. Figure 1b schematically shows an enlarged section at the edge of the battery housing 14. In this edge region, the first (upper) housing shell 142 and the second (lower) housing shell 144 are connected to one another by a screw connection in a connecting region 146. In the first housing shell 142, a possible positioning of a laser cut according to a laser cutting method according to the invention is indicated by a line. Fig. 2a and Fig. 2b, the laser cutting method according to the invention is described in more detail below.

[0029] Fig. Figure 2a shows a battery assembly 10 in a plan view, wherein the drawing plane in the plan view corresponds to the xy plane of a Cartesian coordinate system. The battery assembly 10 has a cell assembly 12 with a plurality of cell modules 122, which in turn accommodate a plurality of battery cells (not shown in the figures). In other words, the illustrated battery assembly 10 has a cell-to-module or module-to-pack battery architecture. The cell assembly 10, together with further (in the Fig. 2a and Fig. 2b not shown) battery components (see example Fig. 1a) is surrounded by a housing 14. The housing 14 comprises a first housing shell 142 and a second housing shell 144, which are firmly connected to one another along a connecting region 146 on the outer circumference of the housing 14—here, for example, by means of a screw connection. It is understood that, in addition to screw connections, other connection types, such as riveted connections, adhesive connections, welded connections, or even combinations of several connection types, are also possible. According to the invention, the first (in this case the upper) housing shell 142 is cut open along a cutting contour C using a laser beam (e.g., in a laser fusion cutting process).

[0030] As can be clearly seen in the plan view, the cutting contour C (here as a closed cutting contour C) extends laterally outside the cell arrangement 12 and laterally inside the connection area 146. In this way, the first housing shell 142 is separated without the screws 148 of the screw connection having to be loosened and without the cell arrangement 12 being critically heated by the laser beam L.

[0031] Fig. 2b shows a cross section through the battery arrangement 10 according to Fig. 2a along section line AA. Also in Fig. 2b it is clearly visible that the laser beam L impinges on the first housing shell 142 in a region laterally (i.e. in the x and / or y direction) between the connecting region 146 and the cell arrangement 12. The optical axis a Lof the laser beam L at any time during the laser cutting process (while the laser beam is switched on) a minimum distance of at least 0.5 mm, preferably of at least 1 mm, from the nearest cell module 122 or from the nearest battery cell (in the case of a cell-to-pack battery architecture). Fig. 2b shows a highly schematic representation of a laser cutting head 20 of a laser cutting machine or system, by means of which the laser beam L, optionally together with a cutting gas jet, is directed onto the first housing shell 142 of the battery housing 14.

[0032] The following list contains already mentioned, as well as further features and processing parameters that may be relevant for a laser cutting method according to the invention for cutting open a battery housing 14 of a battery assembly 10: • The first housing shell 142, preferably both housing shells 142, 144 consist of a sheet material with a thickness in the range of 0.5 mm to 3 mm, in particular based on aluminum (3000 or 5000 aluminum) or based on iron (in particular stainless steel); • A single-mode laser (e.g. from the applicant's TruFiber series 500-2000) or a multi-mode laser (e.g. from the TruDisk series 2000-8000 or 3001-24001) is used as the laser beam source for the laser cutting process, preferably with a laser power in the range of 2 kW to 8 kW; • Preferably, to carry out the laser cutting process, a fixed optics can be used which is moved over the workpiece (ie the first housing shell 142), with the use of cutting gas (conventional laser cutting), with cutting nozzle and preferably using inert cutting gas to expel the melt; • A scanner optics can also be used for remote cutting, whereby a high intensity is selected in order to drive the resulting molten material of the first housing shell 142 (by means of steam pressure) out of the resulting cutting gap by (partial) evaporation (corresponds to the principle of sublimation cutting); • The laser beam L used for the laser cutting process can have a beam parameter product in the range from 0.38 mm*mrad to 16 mm*mrad, in particular of at most 0.6 mm*mrad (single mode) or of at most 6 mm*mrad (multi-mode), preferably of 4 mm*mrad; • A beam diameter of the laser beam L on the workpiece (i.e. on the surface of the first housing shell 142) can be in the range from 50 µm to 500 µm, in particular in the range from 30 µm to 70 µm (single mode) and / or (single spot or n-in-1) in the range from 100 µm to 300 µm (multi-mode); • Preferably, an infrared laser with a wavelength in the range of 800 nm to 1200 nm can be used as the laser for the laser cutting process, in particular with a wavelength of 1030 nm or 1070 nm; • Alternatively, a VIS laser can be used for the laser cutting process, in particular with a wavelength of 515 nm (green spectral range); • The laser power used for laser cutting can be in the range of 0.5 kW to 24 kW, especially in the range of 2 kW to 8 kW • A cutting feed in the laser cutting process can be in the range of 10 m / min to 80 m / min (depending on the material thickness), in particular in the range of 20 m / min to 60 m / min; • Preferably, a cutting optics with cutting nozzle and cutting gas and with an image ratio of 1:1 to 5:1, in particular of 1.5:1 to 2:1, can be used for the laser cutting process; • Alternatively, a scanner optics (for example the scanner optics designated PFO33-2 by the applicant) with an image ratio of 1:1 to 5:1, in particular of 1.5:1 to 2:1, can be used; • A camera-based sensor (see the applicant's VisionLine product) can be used to control the position during the laser cutting process; • The first housing shell 142 can also be prepared for the cutting process, for example, by appropriate cleaning processes (e.g., laser cleaning; grinding or other mechanical cleaning; chemical cleaning; etc.). This allows surface contaminants to be removed before the laser cutting process, and process reliability during the cutting process can be increased.

Claims

[1] Laser cutting method for cutting open a battery assembly (10), wherein the battery assembly (10) has a cell assembly (12) and a housing (14) surrounding the cell assembly (12), which housing comprises a first housing shell (142) and a second housing shell (144), wherein the first and second housing shells (142, 144) are firmly connected to one another along a connecting region (146) on the outer circumference of the housing (14), the method comprising: Creating, by means of the laser cutting process, a cutting gap in the first housing shell (142) along a predetermined cutting contour (C), wherein the cutting contour (C) extends laterally outside the cell arrangement (12) and laterally within a connecting region (146). [2] Method according to claim 1, wherein the optical axis (a L) of the laser beam (L) used for the laser cutting process has a distance from the cell arrangement (12) of at least 0.5 mm, preferably of at least 1 mm, at any time during the laser cutting process. [3] Method according to one of the preceding claims, wherein the method is implemented as a method for laser melt cutting using an inert cutting gas, preferably nitrogen. [4] A method according to claim 1 or 2, wherein the method is implemented as a method for laser cutting using oxygen or an oxygen-containing gas mixture as the cutting gas. [5] Method according to claim 3 or 4, wherein a Laval nozzle is used as the cutting nozzle for the laser cutting process. [6] The method according to claim 1 or 2, wherein the method is implemented as a laser sublimation cutting method. [7] Method according to one of the preceding claims, further comprising: Optical observation of the laser cutting process to detect the actual course of the cutting gap; and Readjustment of cutting parameters of the laser cutting process if the course of the cutting gap deviates from the specified cutting contour (C) by at least a specified minimum value in order to bring the cutting gap and cutting contour into line. [8] Method according to one of the preceding claims, wherein the cutting gap is a closed cutting gap, so that a cutout part of the first housing shell (142) is completely separated from a surrounding remaining part of the housing shell (142). [9] Method according to one of the preceding claims, further comprising: Measuring, during the laser cutting process, a distance between a cutting nozzle used for the laser cutting process and the surface of the first housing shell (142); and Adjusting preset cutting parameters of the cutting process based on the measured distance. [10] Apparatus for laser cutting a battery assembly (10), comprising at least: A workpiece support for supporting the battery assembly (10) during the cutting process; A laser beam source for providing a laser beam; A laser processing head for focusing the laser beam toward the battery assembly; and A control unit configured to control the device for carrying out a laser cutting method according to one of claims 1 to 9.

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