MANUFACTURING PROCESS FOR BUTTON CELLS AND BUTTON CELL

Description

[0001] The invention described below relates to a method for producing a button cell and a button cell that can be produced according to the method.

[0002] A particularly well-known embodiment of an electrochemical cell is the button cell. A button cell typically has a cylindrical casing whose height is smaller than its diameter and which encloses a positive and a negative electrode.

[0003] The casing of button cells typically consists of two metal parts, between which an electrically insulating sealing element is arranged. One of the casing parts is electrically connected to the positive electrode and is therefore positively polarized. The other casing part is electrically connected to the negative electrode and is therefore negatively polarized. The sealing element is designed to prevent electrical contact between the oppositely polarized casing parts. Furthermore, it is designed to prevent the escape of liquid or moisture from or into the casing.

[0004] The housing can contain various electrochemical systems. Button cells based on zinc / air, zinc / MnO2, and nickel / zinc are very common. Secondary systems, such as those based on nickel / metal hydride, nickel / cadmium, or lithium, are also very common.

[0005] The sealing elements used to manufacture button cells are traditionally manufactured using injection molding, for example, from polyamides. However, the injection molding tools required for this are very expensive. Furthermore, it is very difficult to produce sealing elements with wall thicknesses of 0.1 mm or less using an injection molding process. The thicker the wall thickness of a sealing element, the more volume it occupies and the more it impairs the efficient utilization of a button cell's capacity.

[0006] DE 196 47 593 A1, owned by the applicant, discloses the use of a sealing element produced by deep drawing from a film. A cup-shaped molded part is drawn from a heated film using a drawing die and a forming punch under vacuum. The bottom area of ​​the deep-drawn molded part is then punched out using a cutting punch and a cutting bush. Depending on the selected process parameters, this process can produce sealing elements with wall thicknesses well below 0.1 mm.

[0007] A button cell with such a sealing element offers significant advantages in terms of achievable capacity utilization compared to button cells with sealing elements made of injection-molded parts. Nevertheless, the pursuit of ever-thinner sealing elements is limited for another reason. The thinner the sealing elements used, the more difficult they are to process. Processing requires sufficient mechanical strength. This is often no longer possible with thicknesses < 0.1 mm.

[0008] From EP 2258010 B1 of the applicant, it is known to coat button cell housing parts in the sealing area with parylenes, ormocers, or plastics. However, the PVD processes described proved to be very expensive and complex. Furthermore, masking was necessary to avoid unwanted coatings. Problems also arose with housing parts that, in contrast to a double-walled edge formed by folding, as used, for example, in the Figures 1 and 2 of JP 2002-373711 A, are completely single-walled and have a terminal cut edge. While sealing elements produced by injection molding are able to shield such cut edges well, the coatings formed by the coating processes described in EP 2258010 B1 were relatively easily damaged by the cut edge, leading to undesirable gassing effects.

[0009] EP 2 230 704 A1 discloses a button cell comprising a housing comprising a cell can, a cell lid, and a seal that insulates the cell can and the cell lid from each other. The housing has an electrically conductive coating and / or an electrically non-conductive coating on its exterior. This coating can be a thin polymer film formed by applying and subsequently curing a polymer precursor.

[0010] The object of the present invention was to provide improved button cells with sealing elements that are as thin as possible, taking into account the problems described.

[0011] To solve this problem, the invention proposes a method having the features recited in claim 1 and a button cell having the features recited in claim 4. Further developments of the invention are the subject of subclaims.

[0012] The button cells according to the invention that can be produced according to the method according to the invention are characterized by the following features: a. A housing with an interior in which a positive electrode, a negative electrode and a separator are arranged. b. The housing comprises a cup-shaped, metallic first housing part and a cup-shaped, metallic second housing part as well as an electrically insulating sealing element between the housing parts. c. The housing parts each comprise a circular base, a hollow cylindrical shell, a circumferential transition region connecting the base and the shell, and an opening edge defining a circular opening. d. The bases and shells each have an inner side facing into the interior and an outer side facing in the opposite direction, and the opening edges each lie in a plane aligned parallel to the respective base.

[0013] The first and second housing parts are preferably made of metallic materials such as nickel-plated steel or sheet metal. Trimetal, for example, with the sequence nickel, steel, and copper (from outside to inside), is also particularly suitable.

[0014] Preferably, the circular bases of the first and second housing parts are planar or at least substantially planar. Particularly preferably, the bases form an angle Θ of 90° ± 3°, particularly preferably 90° ± 1°, with the hollow cylindrical shells of the housing parts.

[0015] The transition areas connecting the bases and the shells preferably comprise the parts of the first and second housing parts that lie outside the plane of the bases and are not yet part of the respective hollow cylindrical shell. The transition areas can be rounded independently of one another, for example, shoulder-shaped, or can also have the shape of a sharp edge.

[0016] The bases of the first and second housing sections are aligned parallel to each other in the button cell. The distance between the outer sides of the bases defines the height of the button cell.

[0017] It is preferred that the hollow cylindrical shell of the housing parts is axially limited on one side by the transition areas to the bottoms and on the other side by the opening edge.

[0018] In preferred embodiments, the hollow cylindrical shells and the mutually parallel bases dominate the shape of the button cell, the housing of which accordingly preferably has a cylindrical or at least a substantially cylindrical geometry.

[0019] It is preferred that, during assembly of the button cell, the first housing part is inserted into the second housing part with the opening edge first until the opening edge rests on the bottom of the second housing part or a support ring. The connecting line through the center of the bottom of the second housing part and the center of its circular opening defines the axis (axial direction) along which the first housing part is inserted into the second housing part.

[0020] To seal the button cell, the edge of the second housing part can be bent radially inward after the first housing part has been inserted. This process is commonly referred to as flanging.

[0021] The button cell according to the invention is preferably a zinc / air cell, a silver oxide / zinc cell, a zinc / manganese dioxide cell (also known as an alkaline manganese cell), a mercury oxide / zinc cell, a nickel / iron cell (Edison accumulator), a nickel / metal hydride cell, a nickel / zinc cell, or a nickel / cadmium cell. Accordingly, the negative electrode is preferably a zinc electrode, an iron electrode, a metal hydride electrode, or a cadmium electrode. The positive electrode is preferably an air cathode, a silver oxide cathode, a manganese dioxide cathode, a mercury oxide cathode, or a nickel oxyhydroxide cathode.

[0022] Alternatively, the button cell according to the invention can also be a lithium cell, i.e. a cell that comprises at least one lithium-intercalating electrode.

[0023] The separator can be, for example, a porous plastic film or a plastic fleece.

[0024] The electrodes and separator are typically impregnated with an aqueous, alkaline electrolyte, such as potassium hydroxide or sodium hydroxide. However, if the button cell according to the invention is a lithium cell, the electrolyte is typically an organic solvent, usually a mixture of organic carbonates, mixed with a lithium conducting salt.

[0025] Preferably, the electrodes and the separator are positioned in the housing parts before the second housing part is inserted into the first housing part. In the case of a zinc / air cell, for example, an air cathode and a separator can be inserted into the second housing part, while a zinc anode in paste form is positioned in the first housing part, which is then inserted into the second housing part together with the zinc anode.

[0026] The inventive method for producing button cells with the above features a. to d. comprises the following steps: e. The inside and outside of the shell and the opening edge of the first housing part are coated with a liquid plastic precursor, f. The liquid plastic precursor is dried and / or hardened to form a solid plastic coating on the first housing part, wherein the opening edge of the first housing part points downwards at least temporarily vertically or with a deviation of a maximum of 5° from the vertical direction (the local direction of the acceleration of gravity of the Earth's gravitational field), and g. the housing is assembled from the first and the second housing part, wherein the plastic coating forms the sealing element.

[0027] To manufacture the button cell according to the invention, none of the conventional injection-molded or foil seals described above are used. Instead, the sealing element is formed on the shell of the first housing part from the plastic precursor.

[0028] The term "plastic precursor" refers to all single- and multi-component systems from which solid plastics can be obtained. The plastic precursor can be single monomers and / or pre-crosslinked monomer, oligomer, and polymer components. The plastic precursor can be crosslinked thermally and / or by radiation. Additives such as crosslinkers, photoinitiators, and radical initiators can be added to it. In particular, it can also contain solvents. Furthermore, the plastic precursor can also be a melt of a plastic.

[0029] Since, as mentioned at the beginning, a sealing element in head cells has not only a sealing but also an insulating function, the plastic precursor is preferably selected so that it has electrically insulating properties after drying and / or curing. In addition, it is generally preferred that the plastic precursor is chemically inert toward the aforementioned electrolytes after drying and / or curing, in particular toward aqueous alkaline electrolytes and / or organic electrolytes, especially those based on carbonate. Particularly preferred plastic precursors are precursors for plastics based on epoxy, polyester, polyamide, polyacrylate, polyethylene, polypropylene, polysulfone, or polyurethane.

[0030] The design of the drying and / or curing step depends on the material properties of the plastic precursor. If the plastic precursor is a melt of a plastic, only curing is required, which occurs automatically as the melt cools. However, if the plastic precursor consists of individual monomers and / or pre-crosslinked monomer, oligomer, and polymer components that require further crosslinking, possibly drying, for curing, the step can be more complex. In the case of crosslinking by radiation, for example, appropriate radiation sources must be used.

[0031] The assembly of the housing preferably comprises the above-described insertion of the first housing part into the second housing part and then the closure of the button cell, in particular by the aforementioned crimping.

[0032] In a particularly preferred embodiment, the process is characterized by one of the immediately following additional steps a. and b.: a. The first housing part is coated by immersing it in the liquid plastic precursor. b. The first housing part is coated by spraying or brushing the liquid plastic precursor onto the first housing part.

[0033] Coating according to step a. is particularly advantageous in some embodiments, since masking of areas of the housing part that are not to be coated can be omitted. In the simplest case, the first housing part can be immersed in the plastic precursor with the opening edge facing vertically downwards. In this case, the inside and outside surfaces, as well as the opening edge, of the first housing part are wetted with the plastic precursor.

[0034] It may be advantageous to completely coat the inside and outside of the shell of the first housing part with the liquid plastic precursor. However, in most preferred embodiments, only a partial coating of the inside and outside occurs.

[0035] In a further development of the invention, it may be preferable to coat the inside and outside of the shell and the opening edge of the first housing part with the liquid plastic precursor in two or more separate steps. For example, in a first step, the first housing part can be coated by immersing the first housing part in the liquid plastic precursor. In a second step, the coating can then be reinforced in at least one area by applying the liquid plastic precursor again. A drying and / or curing step can be included between the two steps. This allows the thickness of the plastic coating to be controlled locally if necessary.

[0036] In a further particularly preferred embodiment, the process is characterized by at least one of the immediately following additional steps a. to c.: a. An annular strip of constant width made of the liquid plastic precursor is applied to the inside of the shell of the first housing part, extending from the opening edge towards the bottom of the first housing part. b. An annular strip of constant width made of the liquid plastic precursor is applied to the outside of the shell of the first housing part, extending from the opening edge towards the bottom of the first housing part. c. The width of the annular strip applied to the outside of the shell of the first housing part exceeds the width of the annular strip applied to the inside of the shell of the first housing part.

[0037] Particularly preferably, steps a. and b., in particular steps a. to c., are implemented in combination with one another.

[0038] The annular strips of constant width are most easily achieved by immersing the first housing part, as described above, into the liquid plastic precursor with the opening edge pointing vertically downwards. In particular, this also allows for different strip widths on the inside and outside. Since vertical immersion traps an air bubble in the housing part that cannot be displaced, the plastic precursor cannot completely wet the inside of the shell, even with very deep immersion.

[0039] The height of the inner and outer coating can also be varied by appropriately angularly aligning the housing part during immersion.

[0040] The different thicknesses of the resulting coating on the inside and outside can be associated with significant advantages. As a rule, it is advantageous for the outer shell to be more or less completely coated with the plastic precursor. In these areas, direct contact between the first and second housing parts must be prevented to avoid an electrical short circuit. On the other hand, an inner coating of the plastic precursor can prevent an electrode from making electrical contact with the first housing part. For this reason, in some embodiments, it is desirable for only a thin strip of the inner shell surface, directly adjacent to the opening edge, to be coated with the plastic precursor.

[0041] In some other embodiments, the strip is also very wide on the inside to cover areas of the housing part that are subject to particularly high mechanical stress during the deep-drawing process. These mechanical stresses can lead to defects in the metal surface of the housing part, which in turn can cause gassing and thus a loss of cell performance.

[0042] A button cell according to the invention that can be produced according to the above method is characterized, in addition to the features a. to d. already mentioned above, in particular by the following additional features: e. The inside and outside of the casing and the opening edge of the first housing part are coated with a solid plastic coating which is integrally bonded to the sides and the edge and which forms the sealing element arranged between the housing parts, and f. The plastic coating is thicker in the area of ​​the opening edge than in areas of the casing spaced apart from the opening edge.

[0043] The material bond results from the fact that the plastic coating is not manufactured separately like traditional sealing elements and then mechanically applied to the first housing part. Instead, the plastic coating is formed in direct contact with the first housing part, namely on its shell. The plastic coating is preferably not removable from the first housing part without damaging it.

[0044] In a particularly preferred embodiment, the button cell is characterized by at least one of the following additional features a. to c.: a. The first housing part is single-walled and has a terminal cut edge as the opening edge. b. The thickness of the solid plastic coating increases in the axial direction toward the cut edge. c. The solid plastic coating has a drop-shaped cross-section in the area of ​​the opening edge.

[0045] Particularly preferably, features a. and b., in particular features a. to c., are implemented in combination with one another.

[0046] A single-walled design of the first housing part should be understood in particular to mean that the first housing part does not have a double-walled edge formed by folding, such as the one in Fig. 1and 2 of JP 2002-373711 A, which has an axially aligned terminal section folded over by an angle of 180°. Instead, it is preferred that the casing has a straight or at least predominantly straight profile in the axial direction up to the opening edge, in particular the opening edge formed as a cutting edge.

[0047] The process according to the invention allows the production of very thin and at the same time very secure sealing elements.

[0048] Generally, it is desirable for the inside of the shell of the first housing part to have the thinnest possible plastic coating to minimize the capacitance losses associated with the coating. On the other hand, the opening edge should ideally have a thicker coating to prevent damage to the plastic coating in the area of ​​the opening edge during housing assembly. This cannot be achieved with film seals, such as those described in DE 196 47 593 A1, which have a uniform thickness. Injection-molded sealing elements can be produced with different thicknesses in different areas. However, very thin thicknesses are difficult to achieve or complicate the assembly process.

[0049] On the other hand, sealing elements with thin walls that are simultaneously specifically reinforced in the area of ​​the opening edge can be easily manufactured according to the present invention. Consequently, the aforementioned single-walled housing parts with a cut edge can also be used according to the present invention.

[0050] Of particular importance is the above-described orientation of the first housing part during drying and / or curing. According to the invention, the opening edge of the first housing part points downwards, at least temporarily, vertically or with a maximum deviation of 5° from the vertical direction, so that the plane of the opening edge of the first housing part intersects the vertical direction at right angles or with a deviation of < 5° from the vertical direction. Vertical orientation is particularly preferred. This ensures that the plastic coating has the same thickness at every point on the opening edge. If the first housing part were aligned at an angle, a "drip nose" would form at the lowest point of the opening edge. As a result, the coating would be thicker at this point, which could result in leaks.

[0051] The extent to which the vertical alignment of the first housing part can be deviated from depends, among other things, on the properties of the plastic precursor. The higher its viscosity, the greater the deviation from the vertical alignment can be.

[0052] Further features, details, and advantages of the invention will become apparent from the claims and the summary, both of which are incorporated by reference into the description, the following description of a preferred embodiment of the invention, and the drawings. Here, schematically: Fig. 1 a cross-sectional view of an embodiment of a button cell according to the invention and the individual steps of its production.

[0053] To manufacture the button cell 100, the first housing part 101 and the second housing part 102 are provided (step A). ​​Both housing parts 101 and 102 can be made, for example, of nickel-plated sheet steel or trimetal. The first housing part 101 has the circular base 101a, the hollow cylindrical shell 101b, the transition region 101c, and the opening edge 101d defining a circular opening. The second housing part 102 has the circular base 102a, the hollow cylindrical shell 102b, the transition region 102c, and the opening edge 102d defining a circular opening. The housing parts 101 and 102 are both single-walled, and their opening edges 101d and 102d are both formed as terminal cut edges.

[0054] In step B, the housing part 101 is immersed in a vertical orientation into a bath containing the liquid plastic precursor 105. The casing 101b of the housing part 101 is wetted on the inside and outside with the liquid plastic precursor 105. The wetted areas are each formed as annular strips of constant width and extend from the opening edge 101d toward the bottom 101a of the first housing part 101, whereby the inside of the casing 101b is not completely wetted due to air 106 trapped during immersion. Accordingly, the width of the annular strip applied to the outside of the casing 101b of the first housing part 101 exceeds the width of the annular strip applied to the inside of the casing 101b of the first housing part 101.

[0055] After the housing part 101 is withdrawn from the bath containing the liquid plastic precursor 105, the liquid plastic precursor 105 is dried to form a solid plastic coating on the first housing part and is cured thermally and with radiation (step C). During the entire drying process, the opening edge 101d of the first housing part 101 points vertically downward.

[0056] The result of the drying and curing is shown in D. During the drying and curing process, a portion of the liquid plastic precursor 105 applied to the casing 101b was able to flow downwards to the cut edge 101d and collect there. The result: The plastic coating 103 was thicker in the area of ​​the opening edge 101d than in areas of the casing 101b spaced apart from the opening edge 101d. It has a drop-shaped cross-section in the area of ​​the cut edge 101d.

[0057] In the button cell shown under E, the plastic coating 103 forms the sealing element that electrically insulates the housing parts 101 and 102 from each other and seals the housing. The active components contained in the housing (electrodes, separator, electrolyte) are not shown for clarity.

Claims

1. Method for producing a button cell (100) which comprises a. a housing (101, 102, 103) having an interior space (104) in which • a positive electrode and • a negative electrode and • a separator are arranged, wherein b. the housing comprises • a cup-shaped, metallic first housing part (101) and • a cup-shaped, metallic second housing part (102) and • an electrically insulating sealing element (103) between the housing parts (101, 102), and c. the housing parts (101, 102) each comprise • a circular bottom (101a, 102a), • a hollow-cylindrical side wall (101b, 102b), • a circumferential transition region (101c, 102c) connecting the bottom and the side wall, and • an opening periphery (101d, 102d) defining a circular opening, wherein d. the bottoms (101a, 102a) and side walls (101b, 102b) each have an inner side facing into the interior space and an outer side facing in the opposite direction and the opening peripheries (101d, 102d) each lie in a plane oriented parallel to the respective bottom, wherein the method comprises the following steps: e. the inner side and the outer side of the side wall (101b) and the opening periphery (101d) of the first housing part (101) are coated with a liquid polymer precursor (105), f. the liquid polymer precursor (105) is dried and / or cured to form a solid polymer coating on the first housing part, wherein the opening periphery (101d) of the first housing part is perpendicular for at least part of the time or points downward with a deviation of not more than 5° from the vertical direction, and g. the housing is made up of the first housing part (101) and the second housing part (102), wherein the polymer coating forms the sealing element (103).

2. Method according to Claim 1 having the following additional feature: a. coating of the first housing part (101) is carried out by dipping the first housing part into the liquid polymer precursor (105).

3. Method according to Claim 1 having the following additional feature: a. coating of the first housing part is carried out by spraying or brushing the first housing part with the liquid polymer precursor.

4. Method according to one of Claims 1 to 3 having at least one of the following additional features: a. a ring-shaped strip composed of the liquid polymer precursor (105) and having a constant width is applied to the inner side of the side wall (101b) of the first housing part (101), said strip extending from the opening periphery (101d) in the direction of the bottom (101a) of the first housing part (101); b. a ring-shaped strip composed of the liquid polymer precursor (105) and having a constant width is applied to the outer side of the side wall (101b) of the first housing part (101), said strip extending from the opening periphery (101d) in the direction of the bottom (101a) of the first housing part (101); c. the width of the ring-shaped strip applied to the outer side of the side wall (101b) of the first housing part (101) exceeds the width of the ring-shaped strip applied to the inner side of the side wall of the first housing part.

5. Button cell (100) comprising a. a housing (101, 102) having an interior space (104) in which • a positive electrode and • a negative electrode and • a separator are arranged, wherein b. the housing comprises • a cup-shaped, metallic first housing part (101) and • a cup-shaped, metallic second housing part (102) and • an electrically insulating sealing element (103) between the housing parts, and c. the housing parts each comprise • a circular bottom (101a, 102a), • a hollow-cylindrical side wall (101b, 102b), • a circumferential transition region (101c, 102c) connecting the bottom and the side wall, and • an opening periphery (101d, 102d) defining a circular opening, wherein d. the bottoms (101a, 102a) and side walls (101b, 102b) each have an inner side facing into the interior space and an outer side facing in the opposite direction and the opening peripheries (101d, 102d) each lie in a plane oriented parallel to the respective bottom, characterized in that e. the inner side and the outer side of the side wall (101b) and the opening periphery (101d) of the first housing part (101) are coated with a solid polymer coating which is joined by material-to-material bonding to the sides and the opening periphery and forms the sealing element (103), and f. the polymer coating (103) is thicker in the region of the opening periphery (101d) than in regions of the side wall (101b) which are at a distance from the opening periphery (101d).

6. Button cell according to Claim 5 having at least one of the following additional features: a. the first housing part (101) is single-walled and has a terminal cut edge as opening periphery (101d); b. the thickness of the solid polymer coating (103) increases in the axial direction towards the cut edge (101d); c. the solid polymer coating (103) has a droplet-shaped cross section in the region of the opening periphery (101d).