Composite cover structure for a button cell with steel housing and button cell

Abstract

A composite cover structure for a button cell with a steel casing, characterized in that it comprises: a pole terminal (1) with a connection terminal (11), wherein the connection terminal (11) is provided on the underside of the pole terminal (1); a first hot-melt adhesive layer (2), a modified layer (3), and a second hot-melt adhesive layer (4), which are stacked on top of one another and placed on the connection terminal (11); a cover body (5) which is mounted below the second hot-melt adhesive layer (4) and placed on the connection terminal (11), wherein the cover body (5) has a rounded edge structure on its circumference; and wherein, upon reaching a certain temperature inside the cell, both the first hot-melt adhesive layer (2) and the second hot-melt adhesive layer (4) soften and the pole terminal (1) opens to relieve the cell.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the technical field of the production process of the cells and, in particular, relates to a composite cover structure for a button cell with a steel casing and a button cell. STATE OF THE ART

[0002] With the development of portable electronic devices, smart wearable devices, medical instruments, etc., batteries have been increasingly miniaturized, resulting in a battery with small size, high specific energy, good sealing, low self-discharge, and high reliability. Due to its shape, it resembles a button, and is therefore called a button cell or button battery. There are many types of button cells, among which lithium-ion button cells have the highest energy density and the highest operating voltage, and by solving the problems of industrial production, they could gain wider application.

[0003] Steel-cased button cells are divided into three components: cover, cell core, and casing. The cover is divided into a fused composite cover and a riveted cover. The cell core is divided into a laminated core and a wound core, and the casing is made of stainless steel. It has the following disadvantages: 1. The fused composite cover requires surface treatment of the metal parts before fusion welding. The metal parts are stacked during the treatment process, resulting in incomplete surface treatment during fusion welding.However, the metal components with incomplete surface treatment are fusion-welded into a composite cover, which may lead to high internal resistance and the formation of composite channels when the cell is stored at high temperatures and high humidity, which in turn may cause cell leakage; 2. When combining the composite cover and the casing, laser welding forms a sealed chamber, so an explosion-proof valve must be provided. Since the existing explosion-proof valves are realized by laser notching, the cost is high, the precision is high, the depth of the notch cannot be fully checked, and the opening pressure of the notch is too high; 3. The mating for closing the composite cover and the casing is performed by gap fitting.At present, flat covers are used in most cases, which due to the tolerance will cause the outer edge of the cover to get stuck in the edge of the case when closing, which will reduce the yield of the closing process and the welding effect of sealing and welding the top cover is poor. CONTENT OF THE PRESENT UTILITY MODEL

[0004] One of the objects of the present invention is to overcome the disadvantages of the prior art and to provide a composite cover structure for a button cell with a steel casing, in which the internal gases of the cell can be vented by optimizing the composite cover structure, thus avoiding the risk of combustion and explosion due to excessive internal pressure in the cell.

[0005] In order to achieve the above object, the present invention uses the following technical solution.

[0006] A composite cover structure for a steel-cased button cell is provided, comprising: a pole terminal having a connection terminal, the connection terminal being provided on the underside of the pole terminal; a first hot-melt adhesive layer, a modified layer, and a second hot-melt adhesive layer stacked on top of each other and placed on the connection terminal; a cover body mounted below the second hot-melt adhesive layer and placed on the connection terminal, the cover body having a rounded edge structure on its periphery; and wherein, upon reaching a certain temperature inside the cell, both the first hot-melt adhesive layer and the second hot-melt adhesive layer soften and the pole terminal opens to relieve the cell.

[0007] Preferably, the thickness T of the cover body and the radius R of the rounded corner satisfy the following relationship: T <R≤3T.

[0008] Preferably, the first hot-melt adhesive layer, the modified layer, the second hot-melt adhesive layer and the cover body are each provided with a through-hole that mates with the connection terminal.

[0009] Preferably, an orthogonally projected area of the through-hole of the cover body represents S1 and an overlapping area of the orthogonal projections of the pole terminal and the cover body represents S2, wherein S1 and S2 satisfy the following relationship: S1 / S2 = m% and m = 8-20, and more preferably m=12-15.

[0010] Preferably, the pole terminal and the cover body are firmly connected to each other by heating and pressing.

[0011] Preferably, the surface of the second hot-melt adhesive layer which is in contact with the cover body is nickel-plated.

[0012] Preferably, the composite cover structure further comprises an insulating paper, wherein the insulating paper is glued to a side of the cover body facing the cell.

[0013] Preferably, the pole terminal, the first hot-melt adhesive layer, the modified layer, the second hot-melt adhesive layer and the cover body are joined to form a one-piece structure by heating and pressing.

[0014] Preferably, the first hot melt adhesive layer, the modified layer and the second hot melt adhesive layer consist of PP adhesive.

[0015] Preferably, the radius R of the rounded corner is greater than 0.1 mm.

[0016] It is preferably provided that the pole terminal is designed as a T-shaped structure and the cover body is designed as a U-shaped structure in cross section.

[0017] Another object of the present invention is to provide a button cell comprising a housing and a composite cover structure for a button cell with a steel housing as described above, wherein the cover body is embedded in the housing and the cover body is provided with a welding portion on its upper side.

[0018] Preferably, the groove depth H of the cover body and the radius R of the rounded corner satisfy the following relationship: 0.2H <R≤0.6H, und dass die Höhe A des Schweißabschnitts die folgende Beziehung erfüllt: A=H-R.

[0019] Preferably, the height A' of a welded, molten part of the weld section satisfies the following relationship: A'≤A.

[0020] The invention has the following advantageous aspects: In the present invention, the terminal, the first hot-melt adhesive layer, the modified layer, the second hot-melt adhesive layer, and the cover body are bonded by heating and pressing to form a composite cover structure, wherein the terminal is formed as a T-shaped structure and the cover body is formed as a U-shaped structure in cross section, which contributes to preventing the stacking of materials during surface treatment and improving the effect of the surface treatment. In the case of overcharging, high temperature, and short circuit of the cell, e.g., when the internal heat of the cell is greater than 120°C (e.g.,At temperatures above 130°C (e.g., 130°C), the first hot melt adhesive layer and the second hot melt adhesive layer begin to soften, and the connected terminal automatically opens, driven by the internal pressure of the cell to relieve the pressure, so that the gas inside the cell is released and the risk of combustion and explosion caused by excessive internal pressure of the cell is prevented, thus contributing to improving the safety of the cell. At the same time, with the U-shaped structure, the positioning structure can be arranged inside the casing and the welding structure can be arranged above the casing without occupying the radial space of the cell core. The ratio between the melting area and the cover area is limited to ensure the composite sealing, the composite strength of the composite cover structure, and the ability to function as a safe explosion-proof structure at the corresponding pressure values.By restricting the relationship of the welding section, the weld sealing between the composite cover structure and the housing and the stability of the welded structure are ensured. SHORT DESCRIPTION OF THE DRAWING

[0021] Features, advantages and technical effects of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings. Fig. 1 shows a schematic view of the structure of the present invention; Fig. Fig. 2 shows a schematic front view of the structure of a cover body of the present invention; Fig. 3 shows a schematic front view of the structure of the welded cover body of the present invention; Fig. Figure 4 shows a schematic view of the sorting of the present invention; and Fig.Figure 5 shows a schematic exploded view of the disassembly of a button cell of the present invention. List of reference symbols: 1 pole terminal; 11 Connection terminal 2 first hot melt adhesive layer; 3 modified layer; 4 second hot melt adhesive layer; 5 cover bodies; 6 insulating paper; 7 housings; 8 through hole; H Groove depth of the cover body; T thickness of the cover body; R radius of a rounded corner of the cover body; A height of the welding section of the cover body; A' height of the welded, molten part of the welding section of the cover body; S1 orthogonally projected area of the through hole of the cover body; S2 Overlap area of the orthogonal projections of the pole terminal and the cover body. DETAILED DESCRIPTION

[0022] For example, the description and claims use specific terms that refer to specific components. A person skilled in the art should be aware that hardware manufacturers may use different terms to refer to the same component. The description and claims do not use differences in the terms as a means of distinguishing the components, but rather use differences in the components' functions as the distinguishing criterion. For example, the term "comprise" used in the description and claims is an open term and should be interpreted as "comprising, but not limited to." "Essentially" means that a person skilled in the art is capable of solving the technical problem within an acceptable margin of error and, in principle, achieving the desired technical effect.

[0023] Furthermore, the terms “first” and “second” etc. are for descriptive purposes only and cannot be understood to indicate or imply relative importance.

[0024] In the present invention, the terms "assemble," "connect," "connect," and "attach," etc., unless otherwise specified, are to be understood broadly. e.g., the elements may be connected either fixedly, detachably, or integrally; connected either mechanically or electrically; connected either directly or indirectly via an intermediate means; or the elements may be internally connected. Those of ordinary skill in the art will understand the specific meaning of the above terms in the present invention depending on specific situations.

[0025] In the following, the present invention will be described in connection with the Fig. 1 to 5, but the present invention is not limited thereto. Embodiment

[0026] A steel-cased button cell is provided, comprising a cell core, a casing 7, and a composite cover structure. A composite cover structure is provided, comprising: a pole terminal 1 having a connection terminal 11, the connection terminal 11 being provided on the underside of the pole terminal 1; a first hot-melt adhesive layer 2, a modified layer 3, and a second hot-melt adhesive layer 4, which are stacked on top of one another and placed on the connection terminal 11; a cover body 5, which is mounted below the second hot-melt adhesive layer 4 and placed on the connection terminal 11, wherein, in a package, the cover body 5 is embedded in the casing 7 to form a chamber for accommodating the cell core.

[0027] The pole terminal 1 is designed as a T-shaped structure and the connection terminal 11 is directed towards the interior of the battery. The cover body 5 is made of a stainless steel cover and is U-shaped, i.e. the cover body 5 has a rounded edge structure on its circumference, with the rounded point facing towards the interior of the battery. The rounded corner structure can prevent the lower edge of the cover body 5 from scratching the winding core, thereby preventing damage to the winding core, but also prevents the outer edge of the cover body 5 from getting stuck in the housing edge when the cover is closed, which serves the positioning in the housing and significantly improves the yield of the closing process and the efficiency of the closing process.

[0028] Since the first hot-melt adhesive layer 2, the modified layer 3, and the second hot-melt adhesive layer 4 within the composite cover are in contact with the electrolyte and air and are prone to delamination and thus failure, leading to electrolyte leakage, it is necessary to nickel-plate the surface of the cover body 5 that is in contact with the second hot-melt adhesive layer 4 to ensure the stability of the adhesion between the second hot-melt adhesive layer 4 made of PP and the metal cover body 5. At the same time, the bonding surfaces of both the pole terminal 1 and the cover body 5 must be cleaned and passivated to prevent connection failure.

[0029] Since the existing explosion-proof valves are realized by laser notching, the cost is high, the precision is high, and the depth of the notch cannot be fully controlled. Therefore, in the present invention, the terminal block 1, the first hot-melt adhesive layer 2, the modified layer 3, the second hot-melt adhesive layer 4, and the cover body 5 are bonded into a composite cover structure by heating and pressing, wherein the terminal block 1 is formed as a T-shaped structure and the cover body 5 is formed as a U-shaped structure in cross section, which contributes to preventing the stacking of materials during surface treatment and improving the effect of the surface treatment. In the case of overcharging, high temperature, and short circuit of the cell, for example, when the internal heat of the cell is greater than 120°C (for example,at 130°C), the first hot-melt adhesive layer 2 and the second hot-melt adhesive layer 4 begin to soften, and the connected pole terminal 1 opens automatically, driven by the internal pressure of the cell to relieve the pressure, so that the gas inside the cell is discharged and the risk of combustion and explosion caused by the excessive internal pressure of the cell is prevented, which contributes to improving the safety of the cell.

[0030] In the composite cover structure for a steel-cased button cell of the present invention, the first hot-melt adhesive layer 2, the modified layer 3, the second hot-melt adhesive layer 4, and the cover body 5 are each provided with a through-hole that mates with the terminal 11. The terminal 11 can be passed through the first hot-melt adhesive layer 2, the modified layer 3, the second hot-melt adhesive layer 4, and the cover body 5, so that the terminal 11 can be connected to the positive electrode or negative electrode of the winding core.

[0031] In the present invention, the radius R of the rounded corner is greater than 0.1 mm, and when the cover is closed with the housing 7, the rounded corner plays a guiding role, thereby preventing the K value from being poor due to a too small rounded corner or the generation of excessive resistance when scratching a right-angled corner with the interior of the housing 7 or the penetration of metal dust caused by scratching into the interior of the cell, so as to avoid problems such as the inability to position the cover, deformation of the cover, poor welding, or failure of the cell core. In this embodiment, it is provided that the thickness T of the cover body 5 and the radius R of the rounded corner satisfy the following relationship: T <R≤3T.For example, if the thickness T of the cover body 5 is 0.1 mm, the relationship between the radius R of the rounded corner of the cover body 5 and the thickness T is: 0.1 mm < R ≤ 0.3 mm, for example, R can be 0.15 mm, 0.2 mm, or 0.3 mm. By restricting this relationship, it can ensure that the cover body 5 and the housing 7 are better matched and play a better role in constraining, thus improving the stability and reliability of the button cell housing structure.

[0032] In this embodiment, the pole terminal 1, the first hot-melt adhesive layer 2, the modified layer 3, the second hot-melt adhesive layer 4, and the cover body 5 are bonded into a one-piece structure by heating and pressing. The first hot-melt adhesive layer 2, the modified layer 3, and the second hot-melt adhesive layer 4 are made of PP adhesive, with the PP sol content ranging from 30% to 70%, whereby the cell has improved sealing and insulating properties. In this embodiment, an orthogonally projected area of the through-hole 8 of the cover body 5 represents S1, and an overlap area of the orthogonal projections of the pole terminal 1 and the cover body 5 represents S2, where S1 and S2 satisfy the following relationship: S1 / S2 = m% and m = 8-20. More preferably, m = 12-15, and S1 / S2 can be, for example, B. 0.08, 0.1, 0.12, 0.15 or 0.2.When S1 and S2 satisfy the above relationship, and the bonding distance between the terminal 1 and the cover body 5 is greater than 1.2 mm, the strength of the cover body 5 reaches 180 N, and the electrolyte-resistant environmental test at a high temperature of 85°C can reach 72 hours without breakdown channel, which can ensure the bond sealing and bond strength of the composite cover structure, and also ensures that the composite cover can play a safe explosion-proof function under the corresponding pressure value. The corresponding pressure value is the pressure value inside the cell during thermal runaway of the cell, which is approximately 0.6 to 1.4 MPa. Different designs of the material or size of the cell, etc., cause the internal pressure of the cell during thermal runaway of the button cell to fluctuate in the range of 0.6 to 1.4 MPa, generally around 1 MPa.

[0033] The cover body 5 is provided with a welding portion on its upper surface. It should be noted that, during cell manufacturing, the cover body 5 has a rounded edge structure around its periphery and is formed into a U-shaped structure in cross section, and the cover body 5 is embedded in the casing 7 to facilitate the positioning of the two when closing. Furthermore, the welding surface of the cover body 5 and the casing 7 is welded from above, which not only has a short welding time and low heat conduction, but also brings a simple mechanical design and low cost, improving welding efficiency and yield without compromising welding quality, and at the same time does not occupy the radial space of the cell core.In addition, the cover body 5 and the housing 7 fit together seamlessly, and the edge of the cover body 5 is guided by a rounded corner so as to adapt to the inner wall of the housing 7, wherein the cover body 5 is embedded in the housing 7 under the action of gravity and the upper end surface of the housing 7 acts as a boundary to prevent excess pressure from causing the cover body 5 to be embedded too deeply, and wherein the housing 7 is preferably a steel housing.

[0034] In this embodiment, it is provided that the groove depth H of the cover body 5 and the radius R of the rounded corner satisfy the following relationship: 0.2H <R≤0.6H, und dass die Höhe A des Schweißabschnitts die folgende Beziehung erfüllt: A=H-R. Wenn beispielsweise die Nutentiefe H des Abdeckkörpers 5 gleich 0,5 mm ist, ist das Verhältnis zwischen dem Radius R der abgerundeten Ecke des Abdeckkörpers 5 und der Nutentiefe H: 0,1 mm<R≤0,3 mm, und das Verhältnis zwischen der Höhe A des Schweißabschnitts des Abdeckkörpers 5 und der Nutentiefe H des Abdeckkörpers 5 und dem Radius R der abgerundeten Ecke ist: 0,2 mm<A≤0,4 mm. In dieser Ausführungsform ist vorgesehen, dass die Höhe A' eines geschweißten, geschmolzenen Teils des Schweißabschnitts die folgende Beziehung erfüllt: A'≤A.The relationship between the height of the welded portion, the groove depth, and the radius of the rounded corner of the cover body 5, and the height of a welded, molten part of the welded portion complies with the above-mentioned constraints, thereby ensuring the weld seal between the composite cover structure and the housing, as well as the stability of the welded structure. If the height A' of the welded, molten part of the welded portion is greater than A, there is an increased risk of welding debris falling into the cell interior, which may lead to cell interior contamination.

[0035] In the composite cover structure for a button cell with a steel case in the present invention, this composite cover structure further comprises an insulating paper 6, wherein the insulating paper 6 is adhered to a cell-facing side of the cover body 5 to prevent the positive electrode adapter from coming into contact with the negative electrode and causing a short circuit, which contributes to improving the safety of the cell.

[0036] The production of the button cell includes: 1, The positive pole terminal: The aluminum plate is punched into two cylindrical terminals of different sizes, the lower terminal being the connection terminal 11 with a T-shaped cross section; 2, The stainless steel cover: The stainless steel plate is formed into a U-shaped circle by punching, which is perforated in the middle so that the T-shaped pole terminal 1 can pass through the circle, the cross section being U-shaped; 3, The hot melt adhesive layer 2, the modified layer 3, the second hot melt adhesive layer 4: The three layers of PP material are punched out into a circular mass with a knife punch, and the T-shaped pole terminal 1 is passed through the central opening; 4, The positive pole terminal and the stainless steel cover are brought into the cleaning and passivation system and subjected to rinsing, pickling, passivation and other processes; 5, The stainless steel cover, PP adhesive and positive pole terminal are inserted into a composite tool in sequence, which are bonded together by heating and pressing to produce a composite cover. 6, The stainless steel housing: The stainless steel plate is formed into a barrel-shaped housing 7 by punching, the housing 7 is degreased and deburred by means of a cleaning device; 7, Winding core: The cut positive and negative electrode plates are provided with positive and negative electrode tabs using a plate manufacturing process. The subsequent winding process creates a cylindrical winding core, with the positive and negative electrode tabs extending from both ends of the winding core at a guide angle of 90° ± 15°. 8. Assembly: The negative electrode tab leading from the winding core is connected to the bottom of the casing 7 by laser welding, and the cell core is inserted into the casing 7 after welding. Then, the positive electrode tab leading from the winding core is connected to the pole terminal 1 of the composite cover by laser welding, and insulating paper 6 is applied between the cover body 5 and the winding core; 9, The welded cell is transferred to the liquid injection process, during the liquid injection, the seal is opened, and after the liquid injection, the cover is closed with the opening of the housing 7, and after the closing, the laser welding is carried out for sealing; 10, The sealed cell is cleaned and rested, then the cell is activated and charged through a forming process and capacity sorting.

[0037] In order to prove that for S1 / S2, the requirements for cell pressure opening during thermal runaway can be effectively met and also the sealing performance and mechanical properties of the cell can be maintained under normal use, the pressure test for cell opening due to failure is carried out, using 10 samples for 1 group and the test data are shown in Table 1 below. Table 1 S1 / S2 is 0.04, the test temperature is 130 °C, the opening pressure at cell failure (unit: MPa) is S1 / S2 is 0.05, the test temperature is 130 °C, the opening pressure at cell failure (unit: MPa) is S1 / S2 is 0.08, the test temperature is 130 °C, the opening pressure at cell failure (unit: MPa) is S1 / S2 is 0.12, the test temperature is 130 °C, the opening pressure at cell failure (unit: MPa) is S1 / S2 is 0.15, the test temperature is 130 °C, the opening pressure at cell failure (unit: MPa) is S1 / S2 is 0.2, the test temperature is 130 °C, the opening pressure at cell failure (unit: MPa) is 1.851 1.508 1.383 1.184 0.900 0.656 1.880 1.661 1.375 1.152 0.929 0.628 1.875 1.640 1.354 1.163 0.928 0.621 1.850 1.671 1.361 1.160 0.914 0.682 1.836 1.612 1.386 1.163 0.935 0.607 1.876 1.540 1.392 1.166 0.915 0.658 1.879 1.646 1.394 1.154 0.935 0.603 1.837 1.671 1.373 1.195 0.929 0.635 1.886 1.568 1.388 1.178 0.924 0.602 1.896 1.582 1.390 1.147 0.929 0.666

[0038] From the test data in Table 1 above, it can be seen that a ratio of S1 to S2 in the range of 8% to 20% can effectively meet the requirements (0.6 to 1.4Mpa) for the pressure opening in the event of cell failure, and also that the sealing performance and mechanical properties of the cell can be maintained under normal use when the orthogonal projected area of the through hole of the cover body is 5 S1mm at a test temperature of 130°C. 2and the overlap area of the orthogonal projections of the pole terminal 1 and the cover body 5 S2mm 2 If the ratio of S1 to S2 is in the range of 12% to 15%, the opening pressure value is closer to 1 MPa.

[0039] If S1 / S2<8%, the opening pressure of the cell in case of failure is too high, which may cause a safety hazard to the user during use; if S1 / S2>20%, the sealing performance and mechanical properties of the cell will be significantly reduced, affecting the quality of the cell.

[0040] Given the disclosure and teachings of the above description, those skilled in the art will also be able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or variations made by one skilled in the art based on the present invention are within the scope of the present invention. Although some specific terms are used in this description, they are for convenience only and do not constitute a limitation on the present invention.

Claims

[1] Composite cover structure for a button cell with steel casing, characterized by that it includes: a pole terminal (1) with a connection terminal (11), wherein the connection terminal (11) is provided on the underside of the pole terminal (1); a first hot-melt adhesive layer (2), a modified layer (3) and a second hot-melt adhesive layer (4) stacked on top of each other and placed on the terminal (11); a cover body (5) mounted below the second hot-melt adhesive layer (4) and placed on the connection terminal (11), the cover body (5) having a rounded edge structure on its circumference; and wherein when a certain temperature is reached inside the cell, both the first hot-melt adhesive layer (2) and the second hot-melt adhesive layer (4) soften and the pole terminal (1) opens to relieve the cell. [2] Composite cover structure for a button cell with steel casing according to claim 1, characterized by that the thickness T of the cover body (5) and the radius R of the rounded corner satisfy the following relationship: T <R≤3T. [3] Composite cover structure for a button cell with steel casing according to claim 1, characterized by that the first hot-melt adhesive layer (2), the modified layer (3), the second hot-melt adhesive layer (4) and the cover body (5) are each provided with a through-hole (8) which mates with the connection terminal (11). [4] Composite cover structure for a button cell with steel casing according to claim 3, characterized by that an orthogonally projected area of the through-hole (8) of the cover body (5) stands for S1 and an overlapping area of the orthogonal projections of the pole terminal (1) and the cover body (5) stands for S2, where S1 and S2 satisfy the following relationship: S1 / S2 = m% and m = 8-20. [5] Composite cover structure for a button cell with steel casing according to claim 1, characterized by that the pole terminal (1) and the cover body (5) are firmly connected to each other by heating and pressing. [6] Composite cover structure for a button cell with steel casing according to claim 1, characterized by that the surface of the second hot-melt adhesive layer (4) which is in contact with the cover body (5) is nickel-plated. [7] Composite cover structure for a button cell with steel casing according to claim 1, characterized by that it further comprises an insulating paper (6), wherein the insulating paper (6) is glued to a side of the cover body (5) facing the cell. [8] Composite cover structure for a button cell with steel casing according to claim 1, characterized by that the pole terminal (1), the first hot-melt adhesive layer (2), the modified layer (3), the second hot-melt adhesive layer (4) and the cover body (5) are connected to form a one-piece structure. [9] Composite cover structure for a button cell with steel casing according to claim 1, characterized by that the first hot melt adhesive layer (2), the modified layer (3) and the second hot melt adhesive layer (4) consist of PP adhesive. [10] Composite cover structure for a button cell with steel casing according to claim 1, characterized by that the radius R of the rounded corner is greater than 0.1 mm. [11] Composite cover structure for a button cell with steel casing according to claim 1, characterized by that the pole terminal (1) is designed as a T-shaped structure and the cover body (5) is designed as a U-shaped structure in cross section. [12] Button cell, characterized by that it comprises a housing (7) and a composite cover structure for a button cell with a steel housing according to one of claims 1 to 11, wherein the cover body (5) is embedded in the housing (7) and the cover body (5) is provided with a welding section on its upper side. [13] Button cell according to claim 12, characterized by that the groove depth H of the cover body (5) and the radius R of the rounded corner satisfy the following relationship: 0.2H <R≤0.6H, und dass die Höhe A des Schweißabschnitts die folgende Beziehung erfüllt: A=H-R. [14] Button cell according to claim 13, characterized by that the height A' of a welded, molten part of the weld section satisfies the following relationship: A'≤A.

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