Button cell with electrode winding

Abstract

Rechargeable button cell comprising: - two metallic housing halves separated from each other by an electrically insulating seal, forming a housing with a flat bottom area and a flat top area parallel thereto; - an electrode-separator assembly within the housing, wherein the assembly is in the form of a preferably spiral winding, in the center of which an axial cavity is located and whose end faces point towards the flat bottom area and the flat top area; and - a winding core in the center of the winding, which at least partially fills the axial cavity, wherein - the electrode-separator assembly comprises at least one positive and at least one negative electrode intercalating lithium; - the button cell has contacts that electrically contact the electrodes with the housing halves; and - at least a partial section of the contacts in the bottom or top area.in the lid area of ​​the housing, it lies flat against the inside of the housing halves, and the conductors are pressed from the end faces of the winding against the flat bottom area and the flat lid area.

Description

The present invention relates to button cells with a housing consisting of two metallic housing halves, which contains a wound electrode-separator assembly. Button cells typically consist of a housing made up of two halves: a cell cup and a cell lid. These can be manufactured, for example, from nickel-plated deep-drawn sheet metal as stamped parts. Usually, the cell cup is positively polarized and the housing lid negatively polarized. The housing can contain a wide variety of electrochemical systems, such as zinc / MnO2, primary and secondary lithium systems, or secondary systems like nickel / cadmium or nickel / metal hydride. The liquid-tight seal of button cells is classically achieved by crimping the edge of the cell cup over the edge of the cell cap in conjunction with a plastic ring positioned between the cell cup and the cell cap, which simultaneously serves as a sealing element and for electrical insulation of the cell cup and the cell cap. Such button cells are described, for example, in DE 31 13 309. Alternatively, it is also possible to manufacture button cells in which the cell cup and cell lid are held together axially solely by a frictional connection and which do not have a crimped cup rim. Such button cells and a method for their manufacture are described in DE 102009017514 A1. Despite the various advantages that such button cells without crimping can offer, they are less resilient in the axial direction than comparable button cells with a crimped cup rim, particularly with regard to axial mechanical stresses originating within the button cell. For example, the electrodes of rechargeable lithium-ion systems are constantly subject to volume changes during charging and discharging processes. The resulting axial forces can, of course, lead to leaks more easily in button cells without crimping than in button cells with crimping. Electrolyte compositions for lithium-ion batteries are known from US patent 2009 / 0186263 A1. The described compositions are applicable to both button cells and cells with wound electrodes. EP 1968134 A1 describes winding cores for cylindrical round cells. US 7341802 B1 concerns a pole feedthrough for cells of button cell-like dimensions, suitable for use in hearing aids, for example. The present invention was based on the objective of providing a button cell in which the aforementioned problems do not occur or occur only to a significantly reduced extent. In particular, the button cell should be more resistant to axial mechanical loads than conventional button cells, especially when manufactured as a button cell without a crimped cup rim. This problem is solved by the button cell with the features of claim 1. Preferred embodiments of the button cell according to the invention are defined in dependent claims 2 to 10. A button cell according to the invention always comprises two metallic housing halves, separated from each other by an electrically insulating seal, forming a housing with a flat base and a parallel flat top. As mentioned above, the two housing halves are generally a so-called housing cup and a housing lid. Parts made of nickel-plated steel or sheet metal are particularly preferred as housing halves. Trimetals, for example, with the sequence nickel, steel (or stainless steel), and copper (where the nickel layer preferably forms the outer layer and the copper layer preferably the inner layer of the button cell housing), are also particularly suitable as metallic materials. A seal can be, for example, an injection-molded or a foil seal. The latter is described, for example, in DE 196 47 593. Within the housing, at least one positive and at least one negative electrode are arranged, each in the form of flat electrode layers. The electrodes are preferably connected to each other via a planar separator. Preferably, the electrodes are laminated or bonded to this separator. The electrodes and the separator typically have thicknesses only in the micrometer range. A porous plastic film generally serves as the separator. In the housing of a button cell according to the invention, this assembly is present in the form of a coil, in particular a spiral coil. Such coils can be produced quite simply using known methods (e.g., DE 36 38 793) by applying the electrodes, in particular in the form of strips, to a separator that is in the form of an endless strip, particularly by laminating them. The assembly of electrodes and separators is wound onto a so-called winding mandrel. After the coil is stripped from the winding mandrel, an axial cavity remains in the center of the coil, which means that the coil may, if necessary, relax into this cavity. However, this can, under certain circumstances, lead to problems with the electrical contact of the electrodes with the metallic housing halves, which will be described in more detail below. Within a button cell according to the invention, the electrode winding is arranged such that the end faces of the winding point towards the flat bottom and top areas. The electrode layers of the winding are thus oriented essentially orthogonally to the flat bottom and top areas of the housing. This allows radial forces, such as those occurring during the aforementioned charging and discharging processes of lithium-ion systems, to be absorbed much more effectively than in conventional lithium-ion button cells, where the electrode layers are stacked and arranged parallel to the flat bottom and top areas. Accordingly, the assembly of electrodes and separator in a button cell according to the invention preferably has one of the following layer sequences: negative electrode / separator / positive electrode / separator or positive electrode / separator / negative electrode / separator. The button cell according to the invention described herein has separate conductors that connect the electrodes to the housing halves. According to the invention, at least a section of the surge arrester(s) lies flat against the inside of the housing halves in the base or lid area of ​​the housing. The electrical contact between the surge arrester(s) and the inside of the housing is ideal when they are at least lightly pressed against the housing, which is also provided for in the invention. This can be achieved surprisingly efficiently by a suitable arrangement of a winding core in a button cell according to the invention. According to the present invention, a button cell according to the invention has a fixed core in the center of the winding, which at least partially fills the axial cavity in the center of the winding. Such a core fixes the electrode winding in the radial direction and prevents a possible implosion of the winding into the axial cavity. With such relaxation of the winding, the pressure exerted by the end faces of the winding in the axial direction, and thus in the direction of any conductors that may be arranged there, also decreases. If this is prevented, no problems arise with the electrical contact between the electrodes and the metallic housing halves. In addition, such a winding core also improves the stability of the button cell according to the invention against external mechanical influences. Damage to the electrode winding in the button cell by external mechanical pressure in the axial direction is generally no longer possible. According to the preferred embodiment of the electrode winding as a spiral electrode winding, the aforementioned axial cavity in the center of the winding is preferably substantially cylindrical (in particular circular cylindrical). On the outer side, it is bounded by the winding, and on the end face by corresponding surfaces of the bottom or top area of ​​the button cell housing. Accordingly, the winding core contained in a button cell according to the invention is preferably designed as a cylinder, in particular as a hollow cylinder. The height of such a cylinder preferably corresponds to the respective distance between the flat bottom area and the parallel flat top area. In particularly preferred embodiments, the winding core can exhibit radially self-expanding properties. For example, it is possible to insert the winding core in a radially compressed configuration into the axial cavity of the winding of a button cell according to the invention. Upon relaxation of the radially compressed winding core, it exerts a radial pressure on the surrounding electrode winding, thus ensuring contact pressure also in the axial direction. For example, an axially slotted hollow cylinder can be used as a radially self-expanding winding core. Alternatively, other radially self-expanding materials, such as those based on plastic, are also conceivable. The winding core is preferably made of a metal such as stainless steel or of plastic. The button cell according to the invention is, as described above, a rechargeable button cell. The electrode-separator assembly comprises at least one positive and at least one negative electrode that intercalates lithium. The height-to-diameter ratio of button cells is, by definition, less than 1. Particularly preferably, this ratio in a button cell according to the invention is between 0.1 and 0.9, especially between 0.15 and 0.7. The height is understood to be the distance between the flat base and the parallel flat top. The diameter refers to the maximum distance between two points on the casing of the button cell. The aforementioned and further advantages of the invention will become apparent from the following description of the drawing in conjunction with the dependent claims. The individual features of the invention can be implemented individually or in combination with one another. The described embodiments serve only to illustrate and facilitate a better understanding of the invention and are in no way to be understood as limiting. Character description Fig. 1 schematically shows the cross-section of a preferred embodiment of a button cell 100 according to the invention. This comprises a metallic cup part 101 and a metallic lid part 102. The two parts are sealed together by a gasket 110. Together they form a housing with a flat base area 103 and a parallel flat lid area 104. In its operating state, these flat areas 103 and 104 form the terminals of the button cell, from which current can be drawn by a device. The cell cover 102 is inserted into the cell cup 101 so that the outer surfaces of the cell cover and the cell cup overlap, with the inner radius of the cell cup 101 being essentially constant in the overlapping area in the direction of the cut edge. The edge of the cell cup 101 is therefore not crimped over the edge 111 of the cell cover 102; thus, in the preferred embodiment of a button cell 100 according to the invention described here, it is a crimp-free button cell. Inside the electrode is an assembly consisting of a strip-shaped electrode 108, a strip-shaped electrode 109, and the strip-shaped separators 107. The assembly of electrodes 108 and 109 and separators 107 is arranged in the form of a coil, the ends of which point towards the flat base region 103 and the parallel flat top region 104. The assembly is wound onto the core 112 in the center of the button cell 100. Both the core 112 and the electrodes and separators wound around it are oriented orthogonally to the flat base and top regions 104 and 103. If the electrodes gain or lose volume during a charging or discharging process, the resulting mechanical forces act predominantly radially and can be absorbed by the casing of the button cell 100. The positive and negative electrodes are contacted with the housing halves, cup and lid, via the surge arrester 105 and the surge arrester 106. The surge arrester 105 is made of aluminum, the surge arrester 106 of nickel (or alternatively, copper). Both surge arresters are thin foils that lie flat between the ends of the winding and the flat lid and bottom sections 103 and 104, respectively. A constant, slight contact pressure is maintained on the surge arresters by the winding core 112. The surge arresters are preferably separated from the ends of the winding by a separate insulating element (not shown in the drawing), for example, a thin foil.

Claims

Rechargeable button cell comprising: - two metallic housing halves separated from each other by an electrically insulating seal, forming a housing with a flat bottom area and a flat top area parallel thereto; - an electrode-separator assembly within the housing, wherein the assembly is in the form of a preferably spiral winding, in the center of which an axial cavity is located and whose end faces point towards the flat bottom area and the flat top area; and - a winding core in the center of the winding, which at least partially fills the axial cavity, wherein - the electrode-separator assembly comprises at least one positive and at least one negative electrode intercalating lithium; - the button cell has contacts that electrically contact the electrodes with the housing halves; and - at least a partial section of the contacts in the bottom or top area.in the lid area of ​​the housing, it lies flat against the inside of the housing halves, and the conductors are pressed from the end faces of the winding against the flat bottom area and the flat lid area. Button cell according to claim 1, characterized in that the winding core is designed as a hollow cylinder. Button cell according to claim 1 or claim 2, characterized in that the winding core is radially self-expanding. Button cell according to one of the preceding claims, characterized in that the winding core is an axially slotted hollow cylinder. Button cell according to one of the preceding claims, characterized in that the winding core is made of metal or plastic. Button cell according to one of the preceding claims, characterized in that it has a ratio of casing to diameter between 0.1 and 0.

9. Button cell according to one of the preceding claims, characterized in that one of the conductors is a thin metal foil made of aluminium, which lies flat between one of the end faces of the winding and the flat top or bottom area. Button cell according to one of the preceding claims, characterized in that one of the conductors is a thin metal foil made of nickel or copper, which lies flat between one of the end faces of the winding and the flat top or bottom area. Button cell according to one of the preceding claims, characterized in that the current collectors are separated from the end faces of the winding by a separate insulator element, for example by a thin film. Button cell according to one of the preceding claims, characterized in that the metallic housing parts each comprise a jacket area in addition to the flat bottom area and the flat lid area.

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