DE102019105119A1 - Metal-polymer current arrester for a battery cell of a motor vehicle - Google Patents

Abstract

The present invention relates to current arresters (1) for a battery cell, the current arrester (1) having a support area (2) and a line area (3), the support area (2) having a polymer film and the line area (3) an electrically conductive material and wherein the support area (2) is mechanically coupled to the line area (3); and wherein the support area (2) is designed to interrupt a circuit leading via the line area (3) by at least partial melting of the support area (2) in the event of a short circuit in the battery cell.

Description

The present invention relates to a metal-polymer current arrester for a battery cell of a motor vehicle according to claim 1. Furthermore, the invention relates to a battery cell with the aforementioned current arrester according to claim 10. Furthermore, the present invention relates to a motor vehicle equipped with this battery cell according to claim 11.

Electrodes for battery cells typically include anodes and cathodes with massive current collectors, which are constructed either from copper or from aluminum and have an active material coating. For example, an anode with a solid copper current collector and an active material coating on both sides is provided, and a cathode with a solid aluminum current collector and an active material coating on both sides

Both current conductors are made of solid copper, typically 5 to 30 µm or solid aluminum, typically 5 to 30 µm. The electrode tracks are rolled up into a cell roll, separated by separators. Alternatively, individual electrode sheets can also be punched out and stacked on top of one another separately by a separator. This manufacturing method produces battery cells with electrode stacks in contrast to battery cells with electrode coils.

In the side area without active material coating, the individual electrode windings of the cell coil are welded together for the anode and the cathode, typically by ultrasonic welding, spot welding or laser welding.

In the event of a fault in the lithium-ion cell, for example due to overheating, internal short-circuit or overcharging, the cell materials can react exothermically with one another and, in the worst case, lead to a cell fire.

With this thermal runaway of the battery cell ("thermal runaway"), the aluminum current arresters in particular also influence the amount of energy released during the thermal runaway. The aluminum reacts as a reducing agent with the metal oxides from the cathode, releasing a lot of heat and is oxidized in the process, or the metal oxides contained in the cathode are reduced.

The high surface area of the entire aluminum current arrester in direct contact with the cathode active material metal oxides additionally intensifies the reaction (reduction-oxidation reaction).

It is therefore an object of the present invention to provide a current conductor for a battery cell which has a low aluminum content.

This object is achieved by a current arrester, a battery cell and a motor vehicle according to Claims 1, 10 and 11. Advantageous embodiments and developments can be found in the subclaims, the following description and the figures.

The current conductor for a battery cell according to a first aspect of the present invention comprises a support area and a line area, wherein the support area comprises a polymer film and the line area comprises an electrically conductive material and wherein the support area is mechanically coupled to the line area; and wherein the support area is designed to interrupt a circuit leading via the line area in the event of a short circuit in the battery cell by at least partially melting the support area.

Compared to current arresters in solid construction, the present invention offers the advantage of reduced material use of reactive substances and the adaptation of the line cross-sections of current paths in a battery cell in order to provide a safety mechanism for increased currents.

In other words, the current arrester has an overcurrent protection device which, by melting away a supporting area mechanically coupled to the line area, interrupts the circuit in order to reduce the increased current intensity.

The current flow through the battery cell can be interrupted on the one hand as a result of melting away or thermally induced mechanical destruction of the polymer substrate on which the metal layer is applied, or on the other hand as a result of the metal layer applied to the polymer substrate being melted / oxidized. This can happen due to the reduced conductor cross-section compared to a solid current collector foil, similar to a fuse. This melting away or the destruction of the material can take place in those areas in which the fault occurs, and not just in an area provided for it.

In the area outside the electrode coating, the current arrester can furthermore have solid copper or solid aluminum. This area can connect to the carrying area. That's why everyone else can Assembly steps of the battery cell are retained in the first order, such as ultrasonic welding or other manufacturing steps.

The present invention advantageously enables the potentially critical local short circuit - in which the current density is significantly, by a factor of 10 or higher, above the normal operating current densities - to lead to a temperature rise that melts the support layer of the current conductor aluminum coating or causes mechanical deformation of the Base layer allows.

In other words, the present invention provides a current collector layer or a layered current collector, which is designed to interrupt the circuit by melting off a support layer of the layered current collector if the current intensity exceeds a certain value for a sufficient time, analogous to a fuse.

This fuse function is made possible by the melting point of the polymer film of approximately 100 ° C. or higher. Particularly for high currents, it can be provided that the thin metal coating on the polymer film burns through before the polymer film heats up significantly and pulls away / melts away.

In other words, the layer thickness of the metal coating on the polymer film is adapted to expected operating parameters, such as nominal current or short-circuit current or also the melting point of the base layer.

The present invention advantageously enables the low-resistance short-circuit current path via the aluminum current conductor to be destroyed by the fuse effect of the support layer of the current conductor layer and for the current to flow over a further distance through the relatively high-resistance cathode active material. This leads to a significantly higher short-circuit resistance and thus to a drop in the short-circuit power.

In other words, the battery cell hardly heats up - the melting point of a plastic - and only locally limited even in the event of a short circuit or at least further heating is avoided and the battery cell remains safe despite a short circuit. The flow of current is interrupted because a very high short-circuit resistance is given after the fuse effect of the base course with low heating power due to the interruption of the current path.

The present invention advantageously enables the effect of the strongly exothermic and unwanted thermite reaction of aluminum in the event of an accident or thermal burnout to be fundamentally inhibited by a reduced mass use of aluminum.

The present invention advantageously enables the proportion of aluminum built into the cathode current collector to be significantly reduced.

While a massive conventional Al current collector typically has thicknesses of 10 to 25 µm, the cathode unit presented here typically only has 0.1 mm to 5 µm of aluminum in the coated area (depending on the desired current-carrying capacity). This reduces the proportion of aluminum by a factor of 5 to 100.

Accordingly, with the present invention, much less aluminum is available for the thermite reaction. In the event of a thermal runaway of the cell, much less energy is released, which significantly increases the safety of the overall system.

The present invention advantageously enables the very thinly coated cathode current arrester to be made of aluminum with thicknesses of, for example, 0.1 μm to 5 μm and thus significantly thinner than conventional Al current arresters or Al conductor foils - both in the range from 10 to 25 μm - Is trained and is therefore significantly lighter.

This enables a better gravimetric energy density of the battery cell. The total thickness of the layer system also results from the polymer substrate film, which has a thickness in the range from 5 to 15 μm.

The present invention thus enables an advantage in comparison with the conventional current collector foils even in terms of the absolute thickness. However, the polymer film is even lighter than pure aluminum and enables a higher gravimetric energy density even with the same total thickness of the base layer.

The present invention advantageously enables the aluminum current arrester with thicknesses of, for example, 10-25 μm to enable the realization of potentially thinner conductor foils. Aluminum foils with a thickness of less than 12 µm are very difficult to manufacture and process. Therefore, there is a lower limit for the strength of conventional aluminum current collector foils. The metal-polymer current arresters of the present invention can, depending on the choice of the carrier film, also be made significantly thinner with potentially equally good further processing properties, for example by a Rolling out an initially thick aluminum foil applied to the polymer substrate.

The installation of a thinner current collector foil thus also increases the volumetric energy density of the cell. Depending on the material used and the process costs for the metal-polymer current arresters, the costs of the current arrester foils can potentially even be reduced.

For example, some of the expensive copper or aluminum is exchanged for cheap plastic film. The thinner the conventional conductor metal foils, the more difficult it is to calender the active material coated on them. The fact that the polymer layer is mechanically stable and pressure-resistant results in a similarly good or potentially even better processability.

In an advantageous embodiment of the present invention it is provided that the electrically conductive material of the line area is copper or a copper alloy.

In an advantageous embodiment of the present invention it is provided that the electrically conductive material of the conduction area is aluminum or an aluminum alloy.

In an advantageous embodiment of the present invention, it is provided that the current conductor also has a solid area which connects to the support area and / or the line area and which has the electrically conductive material in solid construction.

In an advantageous embodiment of the present invention it is provided that the line area and the solid area do not overlap one another.

In an advantageous embodiment of the present invention it is provided that the line area has a thickness of 0.05 μm to 10 μm, preferably 0.1 μm to 5.0 μm, particularly preferably 0.2 μm to 2.5 μm.

In an advantageous embodiment of the present invention it is provided that the line area is thinned out by a rolling process.

In an advantageous embodiment of the present invention it is provided that the current arrester is designed as a cathode current arrester for a cathode of the battery cell.

In an advantageous embodiment of the present invention it is provided that the polymer film comprises polyethylene terephthalate, PET, polyethylene, PE, polypropylene, PP, or polyaramides, preferably poly (p-phenylene terephthalamide), PPTA, or poly (m-phenylene isophthalamide), PMPI.

According to a further, second aspect of the present invention, a battery cell is provided, comprising the current conductor according to the first aspect or an embodiment of the first aspect, a thickness ratio between the support area and the line area being provided so that a limit value for an aluminum content of the battery cell is not exceeded.

According to a further, third aspect of the present invention, a motor vehicle is provided, the motor vehicle comprising a battery cell according to the second aspect or an embodiment of the second aspect and comprising the current conductor according to the first aspect or an embodiment of the first aspect.

The features of the present invention described above can be combined with one another as far as possible, even if it is not explicitly described above.

Further features, advantages and possible applications of the present invention emerge from the following description of the exemplary embodiments and the figures.

All of the features described and / or shown in the figures, individually and in any combination, form the subject matter of the invention, regardless of their composition in the individual claims or their references. In the figures, the same reference symbols stand for the same or similar objects.

• 1 zeigt eine schematische Darstellung eines herkömmlichen Stromableiters zur Erläuterung der Erfindung;
• 2 zeigt eine schematische Darstellung eines Elektrodenstapels mit dazwischenliegendem Separator bzw. eines Wickels einer herkömmlichen Batteriezelle zur Erläuterung der Erfindung.
• 3 zeigt eine schematische Darstellung eines Stromableiters für eine Batteriezelle gemäß einem Ausführungsbeispiel der vorliegenden Erfindung;
• 4 zeigt eine schematische Darstellung eines Stromableiters gemäß einem Ausführungsbeispiel der vorliegenden Erfindung;
• 5 zeigt eine schematische Darstellung eines Stromableiters gemäß einem Ausführungsbeispiel der vorliegenden Erfindung.

The following is a brief description of figures of the present invention.

• 1 shows a schematic representation of a conventional current arrester to explain the invention;
• 2 shows a schematic representation of an electrode stack with an intervening separator or a coil of a conventional battery cell to explain the invention.
• 3 shows a schematic representation of a current conductor for a battery cell according to an embodiment of the present invention;
• 4th shows a schematic representation of a current conductor according to an embodiment of the present invention;
• 5 shows a schematic representation of a current conductor according to an embodiment of the present invention.

Referring to FIG 1 to 5 a detailed description of embodiments of the present invention.

The 1 shows a schematic representation of a conventional current arrester to explain the invention.

An anode and a cathode with current collectors are shown as examples 9 , which have solid copper, about 5 to 30 µm or solid aluminum, about 5 to 30 µm.

Along the current path, the current arresters have an essentially constant, generously dimensioned line cross-section, so that the line path at and is maintained even with currents that are significantly higher than the nominal current. The electrodes are made of the respective active material 4th surround. The term “essentially constant” means, for example, a deviation of less than 10% from a target value.

The 2 shows a schematic representation of a conventional battery cell to explain the invention.

The coated electrode tracks, for example for both the anode and the cathode, are separated by separators 6th rolled up to form a cell roll or stacked to form an electrode stack or electrode stack. In the lateral area without an active material coating, the individual electrode turns of the cell roll or the conductor tabs of the individual electrodes of the electrode stack are welded together, typically by ultrasonic welding, spot welding or laser welding.

In the in 2 The embodiment shown, two individual electrodes are connected to one another.

An electrode stack with an intervening separator or a coil is shown schematically in FIG 2 shown. In the 2 electrolyte and cell mechanics with housing and terminals are not shown.

The 3 shows a schematic representation of a current conductor for a battery cell according to an embodiment of the present invention.

The Indian 3 current arrester shown 1 for a battery cell comprises a support area 2 and a management area 3 , the carrying area 2 comprises a polymer film and the conduction area 3 comprises an electrically conductive material.

• - Lamination des elektrisch leitfähigen Materials auf den Tragbereich; und/oder
• - Bedampfen des Tragbereiches mit dem elektrisch leitfähigen Material zur Ausbildung des Leitungsbereiches erfolgen.

According to an embodiment of the present invention, the production of the line area can be done by:

• - Lamination of the electrically conductive material on the support area; and or
• - The support area is vaporized with the electrically conductive material to form the line area.

• - Gasphasenabscheidung (englisch chemical vapour deposition, CVD);
• - Sputtern, auch Kathodenzerstäubung genannt; oder
• - Elektrochemische Abscheidung, wobei beispielsweise zuerst eine dünne Kontaktschicht aufgebracht wurde.

Furthermore, the production of the line area can be done by:

• - gas phase deposition (English chemical vapor deposition, CVD);
• - sputtering, also called cathode atomization; or
• Electrochemical deposition, for example a thin contact layer being applied first.

The carrying area 2 is designed in the event of a short circuit in the battery cell by at least partial melting of the support area 2 one over the management area 3 to interrupt the leading circuit, since the carrying area with the line area 3 is mechanically connected and a melting of the support area 2 to a deformation and tearing off of the line area 3 leads.

According to one embodiment of the present invention, it is provided that the aluminum layer on the polymer film melts away or evaporates or oxidizes through due to its small cross section.

The carrying area 2 is formed according to one embodiment of the present invention as a flexible polymer film made of polyethylene terephthalate, PET, polyethylene, PE, polypropylene, PP or a polymer.

According to an embodiment of the present invention, the carrying area 2 be designed as an insulating carrier film.

According to an embodiment of the present invention, the line area 3 be designed as a current carrying area or a current conducting layer.

According to one exemplary embodiment of the present invention, the conductive layer can be applied not only by coating, but also by rolling / laminating a film on.

In the area outside the electrode coating, the current arrester is formed, for example in one embodiment, from solid copper or solid aluminum. Therefore, all further cell assembly steps can be retained in the first order, such as ultrasonic welding.

In addition to the fuse effect, it is also possible that, in the event of penetration or deformation of the electrode layers - and the resulting short circuit - the polymer film built into the current collector films acts as an insulation layer.

For example, in the event of a nail penetration of the battery cell and in particular the electrode coil or electrode stack, the polymer film can be smeared inwards and at least partially isolate the metallic defect from the electrodes and bring the battery cell into a short-circuited, but at least safe state.

The 4th shows a schematic representation of a battery cell according to an embodiment of the present invention.

According to one embodiment of the present invention, a solid area is created by hot pressing, lamination, gluing 5 to the carrying area 2 attached, which has an electrically conductive material in solid construction. In other words, the massive area 5 can be designed as a current collector foil containing aluminum.

The line area is formed by vapor deposition with aluminum, sputtering with aluminum, lamination of aluminum foil or suitable processes.

If a thin - 0.01 to 10 μm - aluminum layer has been applied beforehand by sputtering or evaporation, a subsequent galvanic deposition of a thicker aluminum layer is also possible according to a further embodiment of the present invention.

The 5 shows a schematic representation of a current conductor according to an embodiment of the present invention.

The Indian 5 The manufacturing process shown starts with an aluminum foil as the line area 3 .

A polymer film is then applied 2 and a second aluminum foil 3 and hot rolling or hot calendering. As a result of the rolling, the aluminum layers of the two pipe areas are thinned 3 above or below the carrying area 2 , also designed as a polymer film.

In this exemplary embodiment, three foils are rolled together and / or laminated, for example two aluminum foils and a polymer carrier foil in the middle, between the two aluminum foils. In this case it is not about a coating, but about rolling / laminating three foils together - two aluminum foils and a polymer carrier foil in the middle.

In one embodiment of the present invention, in the area outside the support area or the polymer film, the two aluminum foils are in contact with one another, electrically and / or mechanically.

Finally, there is an active material coating to form the electrode active materials 4th .

In the case of the 5 The embodiment shown is the protruding material of the line areas 3 to a massive area 5 rolled together. In this case it is not a matter of coating, but of rolling / laminating three foils together. Two aluminum foils and a polymer carrier foil in the middle.

The solid metal foil outside the area coated with active material results in the following advantages: Cell assembly processes, for example by ultrasonic welding of the current collector foils, can be retained.

In one embodiment of the present invention, both aluminum layers - the upper and the lower aluminum layer - and the metal-polymer current conductor are electrically connected to one another via the solid aluminum foil outside the coated area and are kept at the same electrical potential. This results in advantages in terms of cycling and the aging behavior of the cells.

When fast charging the battery cell or when the battery cell is heavily discharged, such as accelerating at full throttle in an electric car, up to several hundred amperes of (discharge) current can flow out of or into the battery cell. Under these extreme operating conditions of the battery cell, triggering of the fuse function of the metal-polymer current arrester of the battery cell must be prevented.

This danger exists in particular in the area of the electrode flags not coated with active material. The current density is highest there and the cooling due to the non-existent active material coating is worst. If no solid metal foil is installed in this area, a simple metalized polymer foil could inadvertently melt through under the high current load.

In addition, it should be noted that “comprehensive” does not exclude any other elements or steps and “one” or “one” does not exclude a large number. It should also be noted that features or steps that have been described with reference to one of the above exemplary embodiments can also be used in combination with other features or steps of other exemplary embodiments described above. Reference signs in the claims are not to be regarded as a restriction.

List of reference symbols

1

Current arrester

2

Carrying area

3

Management area

4th

Electrode active material

6th

Massive area

10

Battery cell

Claims (11)

Current arrester (1) for a battery cell, - wherein the current conductor (1) has a support area (2) and a line area (3), - wherein the support area (2) has a polymer film and the line area (3) comprises an electrically conductive material and wherein the support area (2) is mechanically coupled to the line area (3); and - The support area (2) being designed to interrupt a circuit leading via the line area (3) in the event of a short circuit in the battery cell by at least partial melting of the support area (2). Current arrester (1) Claim 1 wherein the electrically conductive material of the line region (3) is copper or a copper alloy; and / or wherein the electrically conductive material of the conduction area (3) is aluminum or an aluminum alloy. Current arrester (1) Claim 1 or 2 wherein the current arrester (1) furthermore has a solid area (5); which is made of solid construction and has an electrically conductive material. Current arrester after Claim 3 , wherein the solid area (5) adjoins the support area (2) and / or the line area (3); or wherein the line area (3) and the solid area (5) do not overlap one another. Current arrester after Claim 3 , wherein the line area (3) overlaps the solid area (5). Current collector (1) according to one of the preceding claims, wherein the line region (3) has a thickness of 0.05 µm to 10 µm, preferably 0.1 µm to 5.0 µm, particularly preferably 0.2 µm to 2.5 µm µm. Current conductor (1) according to one of the preceding claims, wherein the line region (3) is thinned by a rolling process. Current arrester (1) according to one of the preceding claims, wherein the current arrester (1) is designed as a cathode current arrester for a cathode of the battery cell. Current conductor (1) according to one of the preceding claims, wherein the polymer film comprises polyethylene terephthalate, PET, polyethylene, PE, polypropylene, PP or polyaramids, preferably poly (p-phenylene terephthalamide), PPTA, or poly (m-phenylene isophthalamide), PMPI, or electrically conductive polymers or poly (3,4-ethylenedioxythiophene) / polystyrene sulfonate (PEDOT: PSS), or polyanniline, or polyethylene with carbon black. Battery cell (10) comprising the current conductor (1) according to one of the preceding claims, wherein a thickness ratio between the support area (2) and the line area (3) is provided such that a limit value for an aluminum content of the battery cell is not exceeded. Motor vehicle comprising a battery cell (10) according to Claim 10 .

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