CH719222A2 - BUTTON BATTERY COMPRISING A SEAL BLOCK AND METHOD FOR PRODUCING SUCH A BATTERY. - Google Patents

Abstract

According to the invention, a button battery (1) is provided which comprises a sealing block, comprising one of the terminals (9) of the battery, an electrically insulating portion (17) and a circumferential wall portion (15) . The insulating portion (17) forms a hermetic connection with the terminal (9) and with the wall portion (15), which can be obtained by processes applied in glass-metal type technology. The sealing block is in the form of a receptacle and one or more components of the cell such as the anode (8), the separator sheet (7) and the cathode (3) can be inserted into the said receptacle form before the stack assembly. The wall portion (15) forms part of the second terminal and is attached to the remainder of said second terminal by an electrically conductive and hermetically sealed connection such as a circumferential solder joint (16). A battery according to the invention can be produced by inserting one or more components of the battery into the sealing block and attaching the wall portion (15) of the sealing block to the remainder (2) of the second terminal , for example by welding. The invention also relates to a method for producing a button battery according to the invention.

Description

Field of the invention

The present invention relates to button-shaped batteries, in particular to the sealing of these batteries.

State of the art

[0002] Button-shaped batteries, also briefly called "button batteries" or "button cells", are widely used to power small electrical appliances and devices. Various types of button cells are used, distinguished by various dimensions and by the materials used for the electrodes and the electrolyte. A type commonly used for low voltage devices such as wristwatches and the like is often referred to as a "CR" type battery, where the C refers to the chemistry of the electrodes and the R to the round shape of the battery. CR batteries include a lithium-based anode and a cathode comprising manganese dioxide as the active material. The electrolyte can be a solid or liquid organic material. Other types are coded as LR, SR or PR batteries, respectively known as alkaline batteries, silver oxide batteries and zinc-air batteries. The last three battery types include a water-based electrolyte.

[0003] All button cells comprise round metal terminals, one of which is usually called the cup, the other the cover, between which the electrodes and the electrolyte are contained.

[0004] A common problem encountered in button cells comprising a liquid electrolyte is electrolyte leakage. Electrolyte leakage occurs when the battery is not properly sealed so that its electrolyte can escape from the inside to the atmosphere.

[0005] For silver oxide batteries, zinc-air batteries and alkaline batteries, the electrolyte is typically a strong alkaline solution, containing NaOH and KOH, among other chemicals. For lithium cells, the electrolyte is typically one or more organic solvents having lithium salts dissolved therein. Both of these electrolytes will harm the environment and humans. The strong alkaline solution is highly corrosive and even a small amount causes corrosion of metals. If it reaches the eyes, mouth, skin, and even if inhaled, it can cause severe damage to human organs.

[0006] Commonly, button batteries are closed by crimping the cup onto a plastic gasket, which separates the cup and the cover. However, especially for small button cells, the crimp strength is often insufficient, increasing the risk of electrolyte leakage.

Summary of the invention

The invention aims to provide a solution to the problems described above. This object is achieved by a button battery and by a method of producing said battery in accordance with the appended claims.

[0008] According to the invention, a button battery is provided which comprises a sealing block, comprising one of the terminals of the battery, an electrically insulating portion and a circumferential wall portion. The insulating portion forms a hermetically sealed connection with the terminal and with the wall portion, namely a gas-tight and liquid-tight connection, which can be obtained by methods applied in a technology of the glass-metal type. The insulating portion can thus for example be a glass portion. The sealing block is in the form of a receptacle and one or more components of the cell such as the anode, the separator sheet and the cathode can be inserted into the said receptacle form before the assembly of the cell. The circumferential wall portion of the sealing block forms part of the second terminal and is attached to the remainder of said second terminal by an electrically conductive and hermetically sealed connection such as a circumferential solder joint. The terminals can be formed from stainless steel or any other suitable metal.

A cell according to the invention can be produced by inserting one or more components of the cell into the sealing block in the form of a receptacle and fixing the wall portion of said block to the rest of the second terminal, by example by welding.

[0010] The invention allows the use of glass-metal type technology in a process for producing button cells of different shapes and sizes, comprising small cells for which the current seal represents a risk of electrolyte leak. This risk is reduced or essentially eliminated by the superior quality of the joints of the metal-glass type that a cell according to the invention comprises.

Brief description of figures

- Figures 1a and 1b show front and planar sectional views of a button cell as currently known in the art. – Figures 2a and 2b show views in frontal and planar section of a button battery according to one embodiment of the invention. – Figures 3a to 3d illustrate a number of steps in a process for producing a cell according to the embodiment shown in Figures 2a and 2b. – Figures 4a to 4d illustrate steps of a method of producing a battery according to another embodiment of the invention.

Detailed Description of Embodiments of the Invention

[0012] A prior art button battery will first be described in order to define its various components, before describing the characteristic elements of a battery according to the invention. Figures 1a and 1b show a button cell 1 as currently known in the art. The battery comprises a metal cup 2, usually made of stainless steel, which forms the positive terminal of the battery. The cathode 3 is placed inside the cup 2. The cathode illustrated in Figure la is formed as a pellet obtainable by compression of a cathode powder into a metal support 4, which has the shape of a ring having a bottom band 5 and a side wall 6. Alternatively, the cathode powder can be compressed into a metal mesh. The support 4 or the mesh are intended to increase the mechanical stability of the compacted cathode powder.

As shown in Figure 1a, the compacted cathode material 3 is at the same level as the lower surface of the ring-shaped strip 5, and these elements are both in physical contact with the bottom of the cup 2. above pad 3 is a separator sheet 7, which separates the cathode pad 3 from the anode 8 of the cell located above the separator sheet 7. The anode 8 is covered by a metal cover 9 which forms the negative terminal of battery 1, usually also made of stainless steel. The negative terminal 9 comprises a flat round contact surface 11 and a vertical wall portion 12 oriented away from the contact surface 11. Similarly, the positive terminal 2 comprises a flat round contact surface 13 and a portion of wall 14 facing away from said contact surface 13. Contact surfaces 11 and 13 are configured to electrically connect to respective contacts of a battery-powered device.

The separator 7 can be a sheet of solid electrolyte superimposed on the cathode 3, in which case the cathode 3 also comprises the solid electrolyte mixed together with the active material. As a variant, cell 1 may comprise a liquid electrolyte. In this case, the cathode 3 is immersed in this liquid electrolyte and the separator 7 can be a porous polymer film which is itself electrically insulating, but which can absorb the liquid electrolyte in order to conduct the ions from the anode 8 towards the cathode 3.

An electrically insulating seal 10 is inserted between the outer edges of the cup 2 and the cover 9, separating the positive and negative terminals and isolating the interior of the battery 1 from the external atmosphere. As indicated in the introduction, the side wall 14 of the cup 2 is crimped onto the seal 10, but this way of sealing the battery leads to a risk of electrolyte leakage when a liquid electrolyte is used, especially for smaller batteries.

The present invention solves this problem by providing a way to apply a glass-to-metal type seal in a button cell. Since the invention is not limited to the use of glass as sealing material, this type of sealing will hereinafter be referred to as “insulator-to-metal” sealing. It is understood, however, that this term refers to the known technology in which an electrically insulating material, for example glass, is chemically bonded to a metal, so as to form a hermetic seal between the solid state insulation and the metal, and in which the expansion coefficients of the metal and the insulation coincide so that the joint is maintained within a given temperature range. This technology is known from applications in the fields of construction, automotive, optics and many others.

Figures 2a and 2b illustrate an example of a button cell according to the invention. A number of the components described above can be recognized, and are indicated by the same reference numerals: the cup 2 with its contact surface 13 and its side wall 14, the cathode 3, the separator sheet 7, the anode 8, the negative terminal 9 with its contact surface 11 and the side wall 12. The cathode 3 in this case can be a compressed pellet which is not compressed into a ring-shaped support but which is compressed into a mesh ( not visible on the drawing but known as such). For silver oxide batteries, for example, the cathode pellet can be compressed directly into cup 2.

It is further observed that the cup 2 is welded to a metal ring 15 which is partially inserted into the cup 2 and welded to the cup 2 by a weld joint 16.

An electrically insulating portion 17 is present between the vertical wall 12 of the negative terminal 9 and the metal ring 15. The connection between the insulating portion 17 and the terminal 9 on one side and the metal ring 15 of the the other side is of the insulator-metal type as defined above, namely the ring 15, the insulating portion 17, for example a glass portion, and the negative terminal 9 form a block of firmly bonded materials in which the insulating portion 17 is firmly bonded to negative terminal 9 and metal ring 15 and wherein the expansion coefficients of insulating portion 17 and metal parts coincide within a given temperature range. This block of firmly bonded materials is referred to as a "sealing block" in the appended claims.

In the assembled cell shown in Figure 2, the positive terminal is now formed by the cup 2 and the metal ring 15. The metal ring 15 together with the solder joint 16 and the vertical wall of the cup 2 now define the vertical wall of the positive terminal. The insulator 17 forms an electrical insulation between the two terminals 9 and 2+15 while also sealing the interior of the cell with respect to the atmosphere. The hermetic seal obtained by the insulator-metal bonds is of much better quality than that which can be obtained by the seal shown in Figures 1a and 1b. By this hermetic seal and by the solder joint 16 which forms an equally hermetic but electrically conductive connection, the cell is thus isolated from the atmosphere in a reliable manner, ensuring that no electrolyte can escape.

A number of key process steps required to produce the battery of Figure 2 are illustrated in Figures 3a to 3d. The sealing block formed of the negative terminal 9, the insulator 17 and the metal ring 15 is shown in Figure 3a. This block can be produced using techniques known from insulator-to-metal bonding technology.

[0022] Depending on the materials that are used, it may be required to perform a pretreatment on the metal surfaces that are to be bonded to the insulation, such as a cleaning step, an oxidation step or the application a reactive layer on the metal surface which is to be bonded to the insulation.

As shown in Figure 3b, the anode 8 is then inserted into the sealing block. The anode 8 can be a solid piece of anode material, for example lithium in the case of a CR battery, or it can be a paste of particles of negative active material, as in a silver oxide battery. where a zinc paste is used for the anode. In the latter case, the anode material fills the internal volume of the sealing block (ie there is no space between the side wall 12 of the negative terminal and the anode 8).

As illustrated in Figure 3c, the cathode pellet 3 and the separation sheet 7 are placed inside the cup 2. When a liquid electrolyte is used, this liquid electrolyte is then added to the cup 2, so that the liquid is absorbed by the cathode 3 and by the separation sheet 7. As shown in Figure 3d, the sealing block comprising the anode 8 is then inserted inside the wall vertical 14 of the cup 2, until the anode 8 is in contact with the separating sheet 7. The height of the vertical wall 14 and of the metal ring 15 is configured so that this wall 14 and the metal ring 15 overlap at this point. Solder joint 16 is then applied by a suitable soldering process, thereby obtaining the fully sealed cell shown in Figures 2a and 2b.

The invention is not limited to a cell having the geometry illustrated in Figures 2 and 3. The main feature of the invention is that a sealing block is produced before the block of the cell as such. The two terminals of the assembled cell have a receptacle shape, comprising a flat round contact surface and a vertical side wall facing away from the contact surface. The sealing block includes one of the cell terminals, an insulating portion and a circumferential wall portion which will form part of the other terminal in the assembled cell. The end portions of the sealing block are electrically isolated from each other by the insulating material which is firmly bonded to said portions, forming a hermetic seal between the insulating material and the respective portions. The wall portion of the sealing block is attached to the remainder of said other electrode by an electrically conductive and closed connection, such as a circumferential solder joint.

In the embodiment of Figures 2 and 3, the sealing block comprises the negative terminal 9, the insulating portion 17 and the metal ring 15. Said metal ring represents the aforementioned circumferential wall portion, which in this case part of the positive terminal. The positive terminal is formed by the cup 2 and said metal ring 15 welded to each other by the circumferential solder joint 16.

[0027] The process for producing a cell according to the invention generally comprises the following steps: Production of a sealing block as described above. This block comprises a receptacle-shaped terminal and a circumferential wall portion. Consequently the block itself is also in the form of a receptacle. – Placement of one or more of the components of the battery in the receptacle formed by the sealing block and/or in the receptacle formed by the remainder of the other terminal, if said remainder is in the form of a receptacle, said components comprising a cathode, an anode and a separator sheet. – If a liquid electrolyte is applied, adding said liquid electrolyte to the receptacle formed by the sealing block or to the receptacle formed by the remainder of the other terminal, if said remainder is in the form of a receptacle. The liquid electrolyte is added to a receptacle comprising an electrode material capable of absorbing the electrolyte. This can be the sealing block comprising an anode paste such as a zinc paste in the case of a silver oxide cell, or the cup 2 in the embodiment shown in Figure 3c , where the electrolyte is absorbed by the cathode pellet 3, or the sealing block comprising the anode, the cathode and the separator, as in the embodiment shown in Figure 4b. The liquid electrolyte can be added in multiple steps, for example before and after adding the separator sheet 7 to one of the receptacles. The liquid electrolyte is added to only one of the receptacles, since otherwise the liquid electrolyte would leak when assembling the receptacles. – Assembly of the sealing block to the rest of the other electrode. When a liquid electrolyte is used, this implies that a receptacle comprising the liquid electrolyte (this may be the sealing block or the rest of the other electrode) is positioned with the receptacle facing upwards, after which the the other part is placed above the receptacle.

In the embodiment of Figures 2 and 3, the anode 8 is inserted into the sealing block 9, 17, 15, while the cathode 3 and the separating sheet 7 are inserted into the cup 2 before bring these parts together to assemble the complete stack.

[0029] Figures 4a to 4d illustrate another embodiment of the method of the invention and of a cell according to the invention and produced by said method. The sealing block is shown in Figure 4a, and again comprises the negative battery terminal 9 with its contact surface 11 and its side wall 12, the insulating portion 17 and a circumferential wall portion 15. The vertical wall 12 of the negative terminal 9 is inclined with respect to the contact surface 11 of the terminal, and the wall portion 15 comprises an inclined portion 15a which is approximately parallel to the wall 12 of the negative terminal and to a straight portion 15b. This sealing block 9, 17, 15 forms a receptacle capable of containing the three main components of the battery, as illustrated in FIG. 4b: the anode 8, the separation sheet 7 and the cathode 3. An electrolyte liquid can be added at this point, or between the insertion of the separator 7 and the cathode 3 with a possible second addition of liquid electrolyte after the insertion of the cathode 3. Then, as illustrated in Figure 4c, a round metallic flat portion 2' having an outer diameter corresponding to the outer diameter of the wall portion 15 of the sealing block is fitted to said wall portion 15 and hermetically connected thereto by a welded sealing joint 16 circumferential , leading to the finished stack shown in Figure 4d. In this embodiment, therefore, the wall portion 15 of the sealing block forms the entire side wall of the positive terminal 2'+15 in the assembled cell. The shape of this battery, characterized by the sloping side walls, conforms to the standard shape used for certain types of battery such as CR batteries and silver oxide batteries.

[0030] Additional variations are within the scope of the present invention. For example, according to embodiments of the invention, the sealing block includes the positive terminal instead of the negative terminal. For example, the sealing block could comprise the cup 2, linked to an insulating portion and to at least part of the side wall of the negative terminal.

Similarly, the position of the electrodes 3 and 8 can be reversed compared to the embodiments shown in the drawings. For example in the case of the embodiment of FIGS. 2a and 2b, block 2+15 then becomes the negative terminal and cover 9 becomes the positive terminal. The above description is valid mutatis mutandis for this case.

In the embodiment of Figures 2a and 2b, the wall portions 14 and 15 could abut instead of overlapping along the circumference of the stack. Many other configurations are possible within the scope of the invention, and the embodiments shown serve as examples only.

While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustrations and description should be considered illustrative or exemplary and not restrictive. Other variations to the disclosed embodiments may be understood and made by those skilled in the art in the practice of the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "a" does not exclude a plurality. The mere fact that certain measures are cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference sign in the claims should not be construed as limiting the scope.

Claims (8)

A button cell (1', 1") comprising a receptacle-shaped positive metallic terminal and a receptacle-shaped negative metallic terminal, the terminals each comprising a round contact surface (13, 11), configured to electrically connect to a respective contact of a device powered by the battery, and a side wall (14, 15; 12) extending in the opposite direction to the contact surface, the battery further comprising a cathode (3) in electrical contact with the positive terminal, an anode (8) in electrical contact with the negative terminal, a separator (7) arranged between the anode and the cathode and an electrolyte configured to conduct the current between the anode and the cathode, characterized in that that : – the battery comprises a sealing block in the form of a receptacle comprising: o a first of said terminals, which can be either the positive terminal or the negative terminal, o a portion of circumferential wall (15), o an insulating portion (17) which electrically separates and insulates the first terminal from said wall portion (15), – said electrically insulating portion (17) is connected to the first terminal and to said wall portion (15, 15') by hermetically sealed connections, – said wall portion (15, 15') is part of the second terminal, and is fixed to the rest of said second terminal by an electrically conductive and hermetically sealed connection (16). 2. A button cell (1', 1") according to claim 1, wherein said first of the terminals is the negative terminal (9) and wherein said rest of the positive terminal is a cup-shaped element (2) having a vertical wall (14) so that the side wall of the positive terminal is formed by said vertical wall (14) and by said circumferential wall portion (15) being connected to each other by said connection (16) electrically driver. 3. A button cell (1', 1") according to claim 1 or 2, wherein said electrically conductive connection is a circumferential solder joint (16). 4. Button battery (1 ', 1 ") according to any one of the preceding claims, wherein said electrically insulating portion (17) is a glass portion. 5. A button cell (1', 1") according to any preceding claim, wherein said terminals are formed of stainless steel. 6. Button battery (1', 1") according to any one of the preceding claims, in which the electrolyte is a liquid electrolyte. 7. Button battery (1', 1") according to any one of the preceding claims, in which said battery is chosen from the group consisting of: a CR battery, an SR battery, an LR battery, a PR battery. 8. A method of producing a button battery (1', 1") according to any one of the preceding claims, comprising the steps of: – production of said receptacle-shaped sealing block by a bonding technique to bond the material of the insulating portion (17) to the material of the first terminal and the circumferential wall portion (15), - placement of one or more of the components of the battery in the receptacle formed by the sealing block and/or in the receptacle formed by the remainder of the second terminal, if said remainder is in the form of a receptacle, said components comprising a cathode (3), an anode (8) and a separation sheet (7), – if a liquid electrolyte is applied, adding said liquid electrolyte to the receptacle formed by the sealing block or to the receptacle formed by the remainder of the second terminal, if said remainder is in the form of a receptacle, – assembly of the sealing block to the rest of the second electrode, – fastening of the circumferential wall portion (15) of the sealing block to the remainder of the second electrode by said electrically conductive and hermetically sealed connection (16).