WO2006013044A1

WO2006013044A1 - Galvanic element

Info

Publication number: WO2006013044A1
Application number: PCT/EP2005/008133
Authority: WO
Inventors: Thomas Wöhrle; Fatima Birke-Salam; Claudia Rathmann; Peter Birke; Heinrich Stelzig; Arno Perner; Dejan Ilic
Original assignee: Varta Microbattery Gmbh
Priority date: 2004-07-28
Filing date: 2005-07-27
Publication date: 2006-02-09
Also published as: DE102004038072A1

Abstract

The invention relates to a galvanic element comprising at least one lithium-intercalating electrode and a largely flexible, electrically conductive housing, in which a lithium-intercalating electrode is provided in the form of a cathode, and this cathode is bonded in a fixed manner to the housing with the aid of at least one electrically conductive bonding agent. This bonding agent is preferably an electrically conductive polymer, i.e. a chemical adhesion promoter. The fixed bond between the cathode and the housing simultaneously serving as a collector results in forming an element of the aforementioned type, particularly provided in the form of a primary lithium flat cell for use in so-called smart cards.

Description

description

Galvanic element

The invention relates to a galvanic element having at least one lithium-intercalating electrode and a largely flexible, elekt¬ risch conductive housing. In particular, this gal¬ vanischen element is a so-called lithium primary cell.

Galvanic elements of the type mentioned in the introduction are already known, and their construction is addressed, for example, in DE-A1-101 25 619. These may be thin (about 400 microns), flexible lithium cells, in particular as primary cells, d. H. non-rechargeable. Such thin, flexible cells have particular advantages when used in a smart card versus a thin button cell, which may not be inherently flexible. The flexible cell can join bends of a card, while a thin button cell can break out of the card during such bends.

In the known cells, the cathode is loosely inserted into the metallic Folien¬ housing. The metallic housing takes over the same time Function of the collector (current conductor). The disadvantage here is that the cathode can move. In addition, the presence of free electrolyte present can form an electrically insulating boundary layer between the cathode and the metallic housing. This can result in an undesirable isolation effect which causes an elevated internal cell resistance.

Frequently, metallic lithium is used as the anode in such galvanic cells; this is contacted over the entire surface against a metallic copper foil. These, usually roughened, copper foil is housing and current conductor at the same time.

The cathode contains manganese dioxide which is a lithium intercalating active material and a polymer binder which is typically a polyvinylidene difluoride-hexafluoropropylene copolymer (for example Kynar ™ Flex 2801 from Atofina). The electrolyte used is an about 1 M solution of lithium perchlorate (UCIO4) in common organic carbonates (eg propylene carbonate). Within the cathode is an approximately 35 microns thick aluminum expanded metal foil laminated, which contacts the cathode to a metallic copper foil. This copper foil is current collector and housing at the same time. The two films (copper housing film and cathode) are, as described above, loose, d. H. without firm connection to each other.

Accordingly, the object of the invention is to avoid the disadvantages of known lithium cells with a flexible housing or at least largely exclude them. In particular, especially with the so-called lithium flat cells, the life of such galvanic elements should be improved in order to make them even more suitable for use in the so-called smart cards. This object is achieved by the galvanic element having the features of claim 1. Preferred embodiments of this galvani¬ schen element are described in the dependent claims 2 to 12 ben. The wording of all claims is hereby incorporated by reference into the content of this specification.

The galvanic element of the type mentioned above is characterized by the fact that a lithium-intercalating electrode is formed as a cathode and this cathode is firmly connected to the housing by means of at least one electrically conductive connection means. Due to the permanent, permanent connection of the cathode with the same time serving as a collector / current collector housing a whole Rei¬ hey of advantages can be achieved, which will be explained later in more detail. The previous loose application of the cathode to the housing, even when using roughened films as a housing, do not lead to the erfindungs¬ contemporary fixed connection of the cathode to the housing.

It is preferred in the invention if the electrically conductive connecting means is an electrically conductive (chemical) substance. Such a bonding agent can also be referred to as a (chemical) adhesion promoter, which ensures that the cathode adheres firmly and permanently to the housing. Such an adhesion promoter may preferably be an electrically conductive polymer, in particular an electrically conductive (organic) polymer. Such polymers will be explained in more detail below. The electrically conductive substance (bonding agent) serving as connection means is present in preferred embodiments of the invention in the form of a layer between the cathode and the housing. In this case, the cathode is in particular completely connected to the housing via this layer, for example adhesively bonded thereto. To form this layer, the electrically conductive substance is applied either to the cathode or preferably to the corresponding housing section. - -

brought, for example by lamination or spraying and then, optionally after a drying step, the respective other part, preferably the cathode, placed on the layer and so made the solid compound.

The thickness of the layer is expediently chosen to be as small as possible in the described embodiments, in order to avoid unnecessary material expenditure and not unnecessarily increase the overall height of the galvanic element. Accordingly, layer thicknesses <50 μm, in particular <20 μm, are preferred. In particular, the layer thickness of the electrically conductive substance is <5 μm.

As already mentioned, the electrically conductive substance is preferably an electrically conductive polymer. In a first group of such polymers, the electrical conductivity can be produced by adding electrically conductive additives / additives to a polymer that is not electrically conductive per se. Such additives / additives may, for example, be carbon blacks or graphites which are mixed in (incorporated into) the polymer, for example in acrylates. An example of such an electrically conductive polymer is the product Electrodag EB-012 from the Acheson Co. Companies Company, USA. Polyvinylidene difluoride (PVDF), which has been modified with acid groups, can also be rendered electrically conductive by admixing conductive carbon black as an electrically conductive additive.

A second group of electrically conductive polymers are polymers which themselves are electrically conductive. Accordingly, it is then not necessary to add electrically conductive additives such as graphite or carbon black as a conductive component. Such electrically conductive polymers are offered, for example, by the company DELO Industrie Klebstoffe GmbH & Co. KG, Germany. In a further development, the housing of the galvanic elements according to the invention is preferably a so-called foil housing. In the case of such film housings, the housing parts which are later joined together are preferably made of film material. This film material then provides the corresponding flexibility of the electrically conductive housing as a whole. In order to achieve the highest possible flexibility, the film thickness is selected as low as possible, in particular <100 μm. The film thickness / film thickness of the film housing is preferably <50 μm.

The necessary electrical conductivity of the housing, so that this can simultaneously take over the function of the collector / Stromableiters, can be achieved in principle in different ways. For example, electrically conductive plastics, in particular as a film material, can be used. However, embodiments in which the housing is made of at least one metal, preferably at least one metal foil, are preferred. Metals and metal foils are available inexpensively in large quantities and have a high electrical conductivity. In such embodiments, it is again preferred if the metal is copper or a copper alloy, in particular a copper-magnesium alloy. In accordance with the above statements, these metals / metal alloys are preferably used as films for producing a Folien¬ housing.

In further preferred embodiments of the inventive galvanic element, the inside of the housing, ie the side facing the cathode when the housing is connected to the cathode, is roughened. As a result, the formation of a fixed connection between the cathode and the housing is supported, for example by improved adhesion of the electrically conductive substance to the roughened inside of the housing. The galvanic elements according to the invention can be used in particular in so-called flat cells, as used, for example, in the so-called smart cards. In this case, the galvanic element responsible for the energy supply must under no circumstances be higher than the smartcard itself. Accordingly, in preferred embodiments of the invention, the existing housing is flat, ie at most a few millimeters high. This height of the housing is preferably <1 mm, in particular <500 microns.

In the case of the galvanic elements according to the invention, the electrical capacitance of the galvanic element is preferably <100 mAh, in particular <50 mAh.

The advantages of the galvanic elements according to the invention, which result from the solid bond between the cathode and the housing which acts as a collector, can be summarized as follows.

On the one hand, the improved mechanical contacting of the cathode on the electrically conductive housing improves the electrical connection. This results in an improved product quality, since less waste is produced on elements in which the electrical contact between the cathode and the housing is insufficient. In addition, the service life of the galvanic cell is increased since the connection of the cathode to the housing is more reliable and durable.

On the other hand, the permanent fixed connection between the cathode and the housing in the galvanic elements according to the invention is responsible for the fact that smartcards provided with the elements according to the invention have better alternating bending properties in the so-called ISO bending tests. The way primary lithium flat cells are and are incorporated into such smart cards is the Known specialist and, for example, from the unpublished DE 103 04 824 of the Applicant can be seen.

A further advantage is that the process reliability in the production process of a galvanic element according to the invention is increased. In the previous production conditions, in which the cathode is placed only loosely in or on the housing, the method can easily move into the region in which the corresponding housing parts are later joined (sealed) to one another. As a result, so far could cause problems in this sealing, beispiels¬, by the occurrence of leaks.

Finally, it should be mentioned as an important advantage that in the inventive galvanic elements, the aluminum, in particular the aluminum expanded metal, which was previously contained in the cathode, can be omitted. The electrically conductive connection means makes it possible to directly adhere the cathode to the electrically conductive housing. The elimination of the aluminum expanded metal naturally leads to a cost reduction due to the reduced material expenditure. In addition, however, an energy density gain is also achieved since, given the same structural height of the element or the cell, an increase in capacity can be achieved by introducing more cathode material (in the form of a higher cathode film). If, in the absence of the stretched metal, the cathode is still left in its weight per unit area, then a thinner cell with the same rated capacity is obtained.

The described and other advantages of the invention will become apparent from the following example taken in conjunction with the drawings and the dependent claims. The individual features can be realized individually or in combination with each other. In the drawing shows

1 shows a schematic representation of a housing part coated with an electrically conductive substance.

example

In the following, the preparation of a lithium primary cell according to the invention will be explained. The procedure is that the metal foil which forms the one housing half part, in the present case made of copper, is treated with an electrically conductive substance, the chemical adhesion promoter, and the thus pretreated housing half part enters the usual production process of such a primary lithium flat cell is articulated.

Accordingly, the production process for such an inventive galvanic element in the form of a primary lithium flat cell can be summarized schematically as follows:

1. Preparation of the cathode coating composition (cathode active composition)

2. Preparation of the so-called cathode film

3. Lamination of the cathode film onto the housing half part (so-called cup) made of copper foil pretreated according to the invention

4. Applying a lithium foil as an active anode material on the other housing half part (so-called cover) made of copper foil - -

5. Assembly of the primary flat cell, d. H. Producing the usual component sequence cathode, separator, anode

6. End sealing of the cell by connecting the two Gehäus¬ half-parts (cup with lid).

The concrete provision of the cell takes place in that at first on the rough layer of a copper housing film (thickness 35 μm, Schlenk, Germany) by means of the so-called air-brush technology a water-containing suspension of the product EB-012 ( Acheson, USA), an acrylate mixed with conductivity additives.

The more precise procedure when spraying this adhesion promoter can be explained in more detail with reference to FIG. 1. There is schematically the Gehäusehalbteil 1, d. H. the corresponding rough side of the copper housing film shown schematically. In order for an outer peripheral region 2 of the housing half-part 1 to be available for subsequent sealing of the cell, this region 2 is covered by a mask (not shown in FIG. 1). In this way, it is achieved that the layer of the electrically conductive substance (adhesion promoter) is formed only in the inner region 3 of the housing half-part 1. The coating with the adhesion promoter thus results in a region 2 of the housing half 1 of roughened copper foil without coating and a region 3 of the housing half-part 1 of roughened copper foil with coating. In area 3, the cathode (not shown) is then deposited and laminated later in the process.

After coating with the electrically conductive substance, ie the adhesion promoter, the housing half part (according to FIG. 1, housing half part 1) is dried at room temperature under normal ambient conditions over a period of 12 hours and then stored in a drying room. The result is a thin, uniform layer of adhesive mediator with a thickness between 1 and 3 microns. After drying, the layer of the adhesion promoter consists essentially of acrylate, conductive carbon black and conductive graphite.

Subsequently, under inert gas (argon), a prefabricated cathode (dimensions about 1.6 × 2.3 cm ² , impregnated with liquid lithium electrolyte) is placed in a copper foil housing whose roughened copper side is coated with the adhesion promoter in the manner described above is. Then, this cathode is laminated at a temperature between 120 ⁰ C and 130 ⁰ C with a so-called hand laminator (type IL-12HR Ibico, USA) on the same time serving as a collector housing half. In this way, the composite of the invention between the cathode and the housing. The cathode film deposited on the housing half-part can no longer be removed from the housing half-destructively without destruction.

The anode used is a lithium foil, which is pressed into the other housing half, here also from a copper foil, the so-called lid. This cover is roughened on its inside also in a übli¬ cher manner by copper crystallites (the so-called R _z value is typically about 2 microns).

Then the cell is completed in the usual way by the two Gehäusehalbteile (cup and lid) are interconnected. This is done by applying in each case an electrically insulating plastic sealing film in the regions of the cup and lid in which copper would strike copper, and then the two half-parts are connected to one another with the aid of an ultrasonic seal.

A galvanic element produced in this way, in particular in the form of the so-called primary lithium flat cell, is outstandingly suitable for incorporation in the so-called smart cards (active smartcards). she - -

are isokonform for this installation, since the so-called ISO bending test according to DIN-ISO 7816-1 and according to the test specification according to DIN-ISO / IEC 10/373 is met. In such active smart cards, the galvanic elements according to the invention have improved mechanical stability and thus a longer service life than the previously known elements.

Claims

claims

1. Galvanic element having at least one lithium-intercalating electrode and a largely flexible, electrically conductive housing, characterized in that a lithium-intercalating electrode is formed as a cathode and connected to the housing by means of at least one electrically conductive connection means firmly connected.

2. Galvanic element according to claim 1, characterized in that it is the connecting means is an electrically leitfähi¬ ge substance, preferably an electrically conductive polymer.

3. Galvanic element according to claim 2, characterized in that the connecting means is in the form of a layer between the cathode and the housing, wherein preferably the Ka¬ method is connected over this layer over its entire surface with the housing.

4. Galvanic element according to claim 3, characterized in that the thickness of the layer <50 microns, preferably <20 microns, in particular <5 microns, is.

5. Galvanic element according to one of claims 2 to 4, da¬ characterized in that the electrically conductive substance is a polymer having at least one electrically conductive additive. - IO * •

6. Galvanic element according to one of claims 2 to 4, da¬ characterized in that the substance is a polymer which is itself electrically conductive.

7. Galvanic element according to one of the preceding Ansprü¬, characterized in that it is in the housing is a film housing, wherein preferably the film thickness <100 microns, in particular <50 microns, is.

8. Galvanic element according to one of the preceding Ansprü¬ surface, characterized in that the housing is made of at least one metal.

9. Galvanic element according to claim 8, characterized in that it is the metal is copper or a copper alloy, in particular a copper-magnesium alloy is.

10. Galvanic element according to one of the preceding Ansprü¬ surface, characterized in that the cathode in the verbunde¬ NEN state facing inside of the housing is roughened.

11. Galvanic element according to one of the preceding claims, characterized in that the housing is a flat housing, wherein preferably the so-called height of the housing is <500 μm.

12. Galvanic element according to one of the preceding Ansprü¬ surface, characterized in that the electrical capacity of the galvanic element <100 mAh, preferably <50 mAh, be¬ contributes.