Method for producing a battery cell

Abstract

The invention relates to a method for producing a battery cell (2), wherein a battery housing (4) is provided having at least one face (8) comprising a degassing valve (14) with a closed outlet opening (16), and a conductor track (20) extending over the closed outlet opening (16) is produced by applying a metal coating (22) by means of a photolithography method or a passivation method, the conductor track being interrupted or destroyed when the outlet opening (16) is opened.

Description

[0001] Description

[0002] Method for manufacturing a battery cell

[0003] The invention relates to a method for manufacturing a battery cell. The invention further relates to a battery cell with a battery housing which has a degassing valve with a sealed outlet opening on one side of the housing.

[0004] Electrically powered or electromechanically driven motor vehicles, such as electric or hybrid vehicles, generally include an electric motor that drives one or both axles. To supply electrical energy, the electric motor is usually connected to an internal (high-voltage) battery, which serves as an electrical energy storage device.

[0005] In this and the following, the term "electrochemical battery" refers specifically to a so-called secondary battery of a motor vehicle. In such a (secondary) vehicle battery, the chemical energy consumed can be replenished by means of an electrical (re)charging process. These types of vehicle batteries are, for example, designed as electrochemical accumulators, particularly lithium-ion accumulators. To generate or provide a sufficiently high operating voltage, such vehicle batteries typically have at least one battery cell module in which several individual battery cells are connected modularly.

[0006] The battery cells are designed, for example, as electrochemical (thin) film cells.

[0007] Thin-film cells have a layered structure consisting of a cathode layer, an anode layer, and a separator layer sandwiched between them. These components are permeated, for example, by a liquid electrolyte, which creates an ion-conducting bond between the components and thus balances the charge. Typically, several thin-film cells are stacked on top of each other.

[0008] To protect the cell stack (electrode stack) against the ingress of moisture and / or dirt, and conversely to prevent the leakage of chemicals or liquid electrolyte in the event of damage to the battery cell, a battery or cell casing is generally provided as an enclosure or sheath. Such battery casings can be designed, for example, as pouches or as mechanically stable cylindrical or prismatic housings.

[0009] During the operation of lithium-ion cells, decomposition reactions occur within the battery cell, which release gases, i.e., gaseous reaction products. This gas formation or evolution occurs more frequently during charging. The resulting gases accumulate inside the battery casing and cause an increase in internal pressure (overpressure), which can also lead to an increase or expansion of the battery casing and / or other undesirable side reactions.

[0010] Gas-induced overpressure, particularly due to aging gases or thermal runaway, can rise to such an extent that damage (cracks) or complete destruction of the battery or battery housing occurs. In such cases, the battery cell can rupture uncontrollably, i.e., at an unpredictable location, and vent gases in an undirected or uncontrolled manner into the installation space of the battery module or battery system. Such uncontrolled venting of the battery cell in all directions can lead to damage or complete destruction of components in the surrounding installation space. This is particularly critical for components that perform important or safety-related functions. These components must therefore be protected from damage by additional packaging measures.These measures cause additional costs and require more installation space, which consequently reduces the energy density of the battery system.

[0011] For example, an additional pressure relief or degassing valve can be provided on the battery housing, which allows for controlled degassing or pressure reduction of the internal pressure in the event of overpressure. With such a degassing valve, also known as a (cell) valve, it is important to be able to detect when the degassing valve opens (trigger) in order to initiate appropriate safety measures.

[0012] The valve status can be monitored, for example, by measuring the current. For this purpose, an electrical conductor is positioned on the surface of an outlet opening of the degassing valve. During operation, a defined control current flows through the electrical conductor. The conductor is positioned at the outlet opening in such a way that when the degassing valve opens, the conductor is essentially destroyed, thus interrupting the flow of the control current. This allows the activation of the degassing valve to be detected reliably and easily.

[0013] The electrical conductor can be a wire or a sheet and is either embedded in the degassing valve, which complicates installation, or attached to the degassing valve, which, however, causes mechanical stress at the attachment points. The electrical conductor is attached to the degassing valve, for example, by gluing, clamping, or welding. However, such attachments can be mechanically unstable or weaken the cell housing material. Furthermore, they require additional installation space due to the spatial dimensions of the attachment points (e.g., in the case of welds).

[0014] The invention is based on the objective of providing a particularly suitable method for manufacturing a battery cell. In particular, a reliable and simple application of an electrical conductor to a degassing valve is to be achieved. The invention is further based on the objective of providing a particularly suitable battery cell.

[0015] With regard to the method, the problem is solved according to the invention by the features of claim 1, and with regard to the battery cell by the features of claim 7. Advantageous embodiments and further developments are the subject of the dependent claims. The advantages and embodiments mentioned with regard to the method are also transferable to the battery cell and vice versa.

[0016] The method according to the invention is designed and configured for the production of a battery cell. The battery cell is in particular an electrochemical battery cell, for example a lithium-ion battery cell, preferably with a liquid electrolyte.

[0017] In this method, at least one housing side of a battery housing is provided. The battery housing is, in particular, a cell housing, preferably a prismatic cell housing with an approximately rectangular cell can and a cell lid that closes or covers the cell can. The battery cell is, in particular, designed as a prismatic cell, and the housing side provided in the course of the method is, in particular, a cell lid having the terminals of the battery cell. Alternatively, the entire battery housing can be provided. The housing side of the battery housing has a degassing valve with a closed outlet opening. The degassing valve is thus, in particular, integrated into the housing side.During operation of the battery cell, the degassing valve serves to reduce any overpressure that may occur inside the battery housing by opening the outlet and releasing gas into the environment.

[0018] According to the invention, a conductive track extending across the sealed outlet opening is created by applying a metal coating and using a photolithography or passivation process. The electrically conductive track extends across the outlet opening in a secant or central configuration, such that the track is interrupted or completely destroyed when the outlet opening is opened. The conductive track is particularly well-suited as a (valve opening) sensor conductor for monitoring the degassing valve status. This provides a particularly suitable method for manufacturing a battery cell.

[0019] According to the invention, instead of a conductor wire, a thin layer of metal (for example, copper) is applied to the outlet opening, analogous to the application methods for conductive traces on printed circuit boards (PCBs). This allows for the application of an electrical conductor without the need for welds or adhesives. Furthermore, the application method according to the invention is applicable to both metal and plastic degassing valves, and optionally to their insulating plastic layers.

[0020] The use and combination of the photolithography process and metal coating enables the application of parameters proven effective for circuit board production to the manufacture of the conductive track. In particular, the process according to the invention is thus easily applicable to mass production.

[0021] The application method for a mechanically stable, electrically conductive metal layer, proven in other industries, is thus applied according to the invention for cell vent opening detection on battery housings. There is no weakening of the battery housing or the housing side, and the mechanical and chemical resistance of the conductor track is maintained. Furthermore, in contrast to other fastening methods (e.g., welding), there are essentially no or only very minor dimensional changes (material deposition). Here and in the following, a "photolithography process" or "photolithography" is understood to mean, in particular, a microstructural manufacturing process in which a pattern is created on a surface using light and a photosensitive material (photoresist), which is then used to produce the electrical conductor track.To create the pattern, an exposure or lithography mask (photomask) is used, which transmits or blocks the exposure light in specific areas according to the pattern to be created. This results in the photoresist being exposed differently according to the pattern due to the resulting shadows. During exposure, the chemical composition of the photoresist changes, allowing it to be selectively removed with a developer, depending on the exposure or development state. The remaining photoresist is then used to deposit structured layers of other materials or to create them through etching.

[0022] In this and the following, "metal coating" refers specifically to the application of a thin metal layer to the surface of the housing side or the outlet opening. This metal coating can be applied, for example, by thermal evaporation or electroplating. The thickness of the metal coating is chosen to create a sufficiently mechanically stable conductor track with a low enough ohmic resistance to carry a control current for current-based monitoring of the degassing valve's opening status. The specific stability and / or resistance values ​​considered sufficient, and their exact magnitudes, are initially of secondary importance. These can be determined, for example, from past conductor track data or from relevant tests and trials.

[0023] Optionally, an additional adhesive layer is applied to the surface of the housing side or the outlet opening before the metal coating is applied, in order to improve the adhesion of the metal coating.

[0024] In a passivation process, the entire surface is first coated with the metal layer, and then only the area where the conductive track is to be formed is passivated to prevent subsequent etching. Passivation can be achieved by covering the conductive track area and then applying a chemical passivation treatment. Preferably, the passivated metal layer exhibits similar electrical properties to the bare metal layer, thus eliminating the need for subsequent removal of the passivation layer. Depending on the design of the covering or the targeted application of the passivation chemical, this enables an alternative process without the use of polymer layers or photolithography.

[0025] In an advantageous embodiment, the housing side and the outlet opening are covered with a protective film, and the photolithography process and the application of the metal coating are carried out on this protective film. The protective film is, in particular, an electrically insulating plastic layer that covers the surface of the housing side and the outlet opening. Specifically, the protective film is designed as a so-called blue film, which is used to protect the battery cell or the housing side from mechanical damage, moisture, and chemical influences, while simultaneously providing insulation between different battery cells or modules. This provides a continuous surface for the application of the metal coating and the photolithography process.

[0026] Depending on the specific photolithography process, the metal coating is applied to the surface of the housing side or the outlet opening either before or after the photolithography process. This depends, among other things, on the type of photoresist used (positive resist, negative resist) and the exposure mask (which areas are transparent / opaque).

[0027] In one possible embodiment, the metal coating is applied prior to the photolithography process. This means that the photoresist is applied to the metal coating and exposed. Preferably, a photoresist and exposure mask are used such that the electrical conductor track remains covered with photoresist after development, with the exposed areas of the metal coating being removable, for example, by an etching process, leaving only the conductor track. In a particularly advantageous embodiment, a (wet) chemical etching process is used. The etching process essentially removes the metal coating (and any adhesive layer present) from the exposed areas completely. Subsequently, the remaining (undeveloped) photoresist is removed from the conductor track.

[0028] For example, the photolithography process uses a positive resist. This means that the exposed areas of the positive resist are chemically altered and removed during development. With positive resists, the already solidified photoresist becomes soluble again for the appropriate developer solutions upon exposure, and after development, only those areas remain that were protected from radiation by the mask.

[0029] Preferably, a negative resist is used in the photolithography process. With a negative resist, the photoresist polymerizes upon exposure to light, so that only the exposed areas remain after development. For example, a monomer coating is used as the negative resist, which, after application, is photoactivated during exposure, for example, using ultraviolet (UV) light, and thus polymerizes into a polymer coating in certain areas. After development, the remaining polymer coating covers the conductive traces.

[0030] In one possible embodiment of the application process, a metal coating is first applied to the surface of the housing side / outlet opening or to the protective film. Preferably, copper, i.e., a copper layer, is applied as the metal coating.

[0031] In a subsequent process layer, a negative lacquer, for example in the form of a monomer layer, is applied to the metal coating as part of the photolithography process.

[0032] The negative resist is then exposed to light using a light source (e.g., a UV lamp) and a photomask, resulting in photoactivated polymerization along the desired conductor path—that is, in the areas where the metal coating is to remain. The unexposed negative resist, i.e., the monomer layer that was not photoactivated to form a polymer layer, is then removed. This is done using a developer or developer solution that removes the unexposed areas of the photoresist.

[0033] The metal coating is then removed from the exposed areas, i.e., the areas where the photoresist has been removed. A wet chemical etching process is preferably used for this purpose. In the case of a copper layer as the metal coating, the housing side is immersed, for example, in a bath of an iron chloride solution, in particular an iron(II) chloride (FeCh) solution. The iron chloride solution removes or etches the areas of the metal coating not covered by the photoresist. Finally, the exposed or polymerized negative resist, i.e., the polymer layer, is removed. For example, the remaining negative resist is removed with a suitable solvent, so that only the conductive trace remains on the surface of the housing side / outlet or on the surface of the protective film.

[0034] The method described above is not limited to copper layers; other metals can also be used to create the metal coating. Instead of a polymer film, the desired conductive area can also be electrochemically passivated. Conductive surfaces or areas can be created analogously not only on the degassing valve but also on other parts of the housing. The etching agent and its molar concentration can vary depending on the metal coating used.

[0035] The battery cell according to the invention is manufactured in particular according to the method described above. The battery cell comprises a battery housing which has a degassing valve with a sealed outlet opening on one side of the housing. A photolithographically produced conductor extends over the sealed outlet opening, which is interrupted or destroyed when the outlet opening is opened. During operation of the battery cell, the conductor is connected to a monitoring unit, whereby a control current flowing through the conductor is detected by the monitoring unit to check the state of the degassing valve. This results in a particularly suitable battery cell.

[0036] An exemplary embodiment is explained in more detail below with reference to a drawing. The drawing shows, in schematic and simplified representations:

[0037] Fig. 1 shows a prismatic battery cell in perspective with a cell cover, and

[0038] Fig. 2 shows a method for manufacturing the battery cell in successive schematic representations with a top view of the cell cover.

[0039] Corresponding parts and sizes are always marked with the same reference symbols in all figures.

[0040] Fig. 1 shows a battery cell 2, which in this embodiment is specifically designed as a prismatic cell. The battery cell 2 has a prismatic battery housing 4 with a cell cup 6 and a cell cover that closes the cell cup. The cell cover forms an end face 8 of the battery housing 4 and is subsequently referred to as such.

[0041] A cell stack or electrode stack (not shown in detail) is inserted into the cell pot 6, which is designed, for example, as a deep-drawn part. A liquid electrolyte is filled into the battery housing 4 or into the cell pot 6 via a filling opening 10 located on the housing side 8, and the filling opening 10 is sealed fluid-tight after filling.

[0042] On the housing side 8, two battery terminals or connection contacts 12 of the battery cell 2 are arranged, which are contacted with the cell stack and via which the battery cell 2 can be electrically connected. A degassing valve 14 with an outlet opening 16 is integrated into the housing side 8 between the connection contacts 12. The outlet opening 16 is closed and only opens when the degassing valve 14 opens due to overpressure inside the battery housing 4.

[0043] In an alternative embodiment not shown, the connection contacts 12 are arranged, for example, on the two short sides of the cell, so that the connection contacts 12 are arranged opposite each other on the battery housing 4.

[0044] The battery housing 4, in particular the housing side 8, is provided, for example, with an enveloping protective film 18 in the form of a blue film. The protective film 18 covers, in particular, the outlet opening 16 of the degassing valve 14. A conductive track 20 is applied to the surface of the protective film 18 as an electrical conductor by photolithography and metal coating.

[0045] The conductor track 20, which is particularly straight, extends at least partially over the outlet opening 16. In other words, the outlet opening 16 is at least partially overlapped by the conductor track 20. Preferably, the conductor track 20 runs secant-like or centrally across the closed outlet opening 16. For example, the conductor track 20 runs along a center line of the outlet opening 16.

[0046] During operation of battery cell 2, conductor track 20 is coupled to a monitoring or sensor unit. The sensor unit applies a control current to conductor track 20 and monitors the flow of this current. In this context, conductor track 20 acts primarily as a valve opening sensor conductor, allowing monitoring of the opening state of the outlet port 16 – and thus the state of the degassing valve 14. When the degassing valve 14 is triggered and the outlet port 16 opens, the conductor track 20 running above it is destroyed, thus interrupting the flow of the control current.

[0047] The following describes in more detail the manufacture of the battery cell 2, in particular the manufacture of the conductor track 20 on the housing side 8 of the battery housing 4, with reference to Fig. 2.

[0048] Figure 2 shows six consecutive illustrations of various process steps of the manufacturing process. Each illustration shows a top view of the housing side 8, with the connection contacts 12 and the filling opening 10 omitted for simplification.

[0049] The process can be carried out on an already assembled battery housing 4. Alternatively, the process is carried out only on the housing side 8 or the cell cover, which is then mounted on the cell pot 6 to form the battery housing 4.

[0050] According to the procedure, in a first process step I, at least the housing side 8 of the battery housing 4 is provided. The housing side 8 can optionally be covered with the protective film 18.

[0051] In a second process step II, a metal coating 22 is applied to the surface of the housing side 8. For example, a copper layer is vapor-deposited onto the surface of the housing side 8 or the protective film 12, so that the outlet opening 14 is covered.

[0052] Subsequently, in a third process step III not shown in detail, a layer of a photoresist, for example a negative resist in the form of a monomer layer, is applied to the metal coating 22 or to the housing side 8.

[0053] In a fourth process step IV, which is also not shown in detail, the negative resist is exposed using a light source (e.g. UV lamp) and a photomask in such a way that photoactivated polymerization takes place along the desired conductor path, and the remaining areas of the photoresist are not exposed.

[0054] The unexposed negative resist, i.e. the monomer layer which was not photoactivated to form a polymer layer 24, is removed in a fifth process step V by means of a developer or a developer solution, so that only the polymer layer 24 remains on the metal coating 22.

[0055] In a sixth process step VI, the areas of the metal coating 22 not covered by the polymer layer 24 are removed. For this purpose, a wet chemical etching process is used, for example. In the case of a copper layer as the metal coating 22, the housing side 8 is immersed, for example, in an iron(III) chloride solution to remove the exposed copper areas. The areas covered by the polymer layer 24 are protected from the etching process, so that the conductor track 20 is etched out of the metal coating 22.

[0056] In a final seventh process step VII, the polymer layer 24 is removed, thus exposing the conductive track 20. For example, the polymer layer 24 is removed with a suitable solvent, so that only the conductive track 20 remains on the surface of the housing side 8 or on the surface of the protective film 12.

[0057] The claimed invention is not limited to the embodiments described above. Rather, other variants of the invention can also be derived by a person skilled in the art within the scope of the disclosed claims without departing from the subject matter of the claimed invention. In particular, all individual features described in connection with the various embodiments can also be combined in other ways within the scope of the disclosed claims without departing from the subject matter of the claimed invention.

[0058] Thus, a positive resist can be used instead of a negative resist with a suitably adapted photomask. Furthermore, the photolithography process can be carried out first, followed by the application of a metal coating 22, so that the metal coating 22 is applied to the surface along the conductor track and subsequently removed from the housing side 8 in a lift-off process along with the undeveloped photoresist.

[0059] It is also conceivable that the degassing valve 14 and the outlet opening 16 are integrated not into the cell lid but into the cell housing 6, for example in a base of the cell housing 6, so that the above method is carried out analogously with the base of the cell housing 6 as the housing side 8. Furthermore, the method according to the invention is not limited to prismatic battery housings 4, but can also be carried out analogously with other housing shapes, such as cylindrical cells or pouch cells.

[0060] Reference symbol list

[0061] Battery cell, battery casing, cell pot

[0062] 8 Case side

[0063] 10 Filling opening

[0064] 12 connection contacts

[0065] 14 Degassing valve

[0066] 16 Outlet opening

[0067] 18 protective films

[0068] 20 conductor tracks

[0069] 22 Metal coating

[0070] 24 polymer layer

[0071] I, H, III, IV, V, VI, VII Procedure step

Claims

Patent claims 1. Method for manufacturing a battery cell (2), - wherein at least one housing side (8) of a battery housing (4) which has a degassing valve (14) with a closed outlet opening (16) is provided, and - wherein a conductor track (20) extending over the closed outlet opening (16) is created by applying a metal coating (22) and a photolithography or passivation process, which is interrupted or destroyed when the outlet opening (16) is opened.

2. Method according to claim 1, characterized in that the housing side (8) and the outlet opening (16) are covered with a protective film (12), wherein the photolithography process and the application of the metal coating (22) on the protective film (12) are carried out.

3. Method according to claim 1 or 2, characterized in that the metal coating (22) is applied before the photolithography process.

4. Method according to claim 3, characterized in that a chemical etching process is carried out after the photolithography process.

5. Method according to one of claims 1 to 4, characterized in that a negative varnish is used in the photolithography process.

6. Method according to any one of claims 1 to 5, characterized in that, - that a metal coating (22) is applied, - that a negative lacquer is applied to the metal coating (22), - that the negative varnish is exposed along a path of the conductor track (20), - that the unexposed negative varnish is removed, - that the metal coating (22) is removed in the exposed areas, and - that the exposed negative varnish is removed.

7. Battery cell (2) comprising a battery housing (4) which has a degassing valve (14) with a closed outlet opening (16) on one side (8) of the housing, wherein a photolithographically produced conductor track (20) extends over the closed outlet opening (16), which is interrupted or destroyed when the outlet opening (16) is opened.

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