DE102020114016A1 - Plasma treatment of a carrier film for an electrode of a lithium-ion battery - Google Patents

Abstract

According to a method for processing a carrier film (2) for an electrode of a lithium-ion battery, at least part of the carrier film (2) is introduced into a process chamber (4) and a plasma is generated in the process chamber (4) to carry out a plasma treatment will. A layer of material on a surface of the part of the carrier film (2) is exposed to the plasma in order to at least partially remove the layer of material from the surface.

Description

The present invention relates to a method for processing a carrier film for an electrode of a lithium-ion battery, a device for processing such a carrier film and a method for producing a lithium-ion battery.

Lithium-ion battery cells contain an anode and a cathode, which are separated by a separator. The electrodes have electrically conductive carrier films on which active materials are applied. A metal foil, such as an aluminum foil, is used as the carrier foil, for example for the cathode. The aluminum foil is produced in a foil rolling mill and prepared for further processing in the production facility for the lithium-ion cell.

It can take days or weeks between the production of the film and its processing in the manufacturing facility. The aluminum foil is exposed to air during storage and transport as well as during the processing steps at elevated temperatures, which means that a native oxide layer of aluminum oxide with a thickness in the nanometer range is formed on the surfaces of the aluminum foil. This native oxide layer is problematic, on the one hand, because, as a good electrical insulator, it impairs the electrical contacting of the active materials and, on the other hand, also because it impairs the mechanical adhesion of the active material to the carrier film. The same also applies to other carrier foils, for example copper foils, on which, for example, copper sulfide or copper oxide can form.

Both the deteriorated electrical contact and the deteriorated mechanical adhesion lead to an increased contact resistance, which makes the electrical charge exchange between the active material and the carrier film more difficult. This increases the ohmic resistance or the impedance of the cell, which in turn leads to a thermal load being induced in the cell when an electrical load is applied. Overall, the performance of the cell is reduced.

To prevent this, the carrier films can be pretreated, for example, with a primer or pretreatment agent, which is also referred to as a primer, which is applied to the film after the production process in the rolling mill in order to prevent oxide formation. However, this method is associated with very high costs.

Alternatively, an alkali, for example aqueous potassium hydroxide solution, can be used in a wet chemical process in order to remove the oxide layer from the carrier film. The problem here, however, is that the subsequently applied, optionally predried active materials would at least partially lose their lithium storage capacity due to adhering water and alkali metal ions, so that after the wet-chemical step, very laborious cleaning and drying of the surfaces is necessary. This leads to increased time and energy consumption and thus also to increased costs and complex process management.

Mechanical removal of the oxide layer is also conceivable. Due to the small thickness of the oxide layer and the mechanical properties of the carrier film itself, however, it is difficult to establish the mechanical contact with the carrier film in a reproducible and uniform manner without damaging the carrier film.

Against this background, it is an object of the present invention to provide an improved concept for processing a carrier film for an electrode of a lithium-ion accumulator, which enables a higher performance of the resulting lithium-ion accumulators while keeping the costs and the manufacturing process complexity low .

According to the invention, this object is achieved by the respective subject matter of the independent claims. Advantageous further developments and preferred embodiments are the subject matter of the dependent claims.

The improved concept is based on the idea of at least partially removing a material layer on the surface of the carrier film by means of a plasma treatment.

According to the improved concept, a method for processing, in particular for contactless processing, of a carrier film for an electrode of a lithium-ion battery is specified. In this case, at least part of the carrier film is introduced into a process chamber, in particular by means of a conveying device, and a plasma is generated in the process chamber in order to carry out a plasma treatment. A layer of material on a surface of the portion of the carrier film is exposed to the plasma to at least partially remove the layer of material from the surface.

Here and in the following, a plasma treatment can in principle be understood to mean a process for plasma cleaning or a process for dry etching using a plasma. While with plasma cleaning chemically not or only weakly bound residues or Other substances are removed from the surface of the treated object, material is removed during dry etching.

The dry etching can be designed, for example, as a plasma etching process. This is a chemical dry etching process in which a chemical reaction of the material layer on the surface of the carrier film with the plasma takes place, so that the material layer is chemically converted.

A part of the resulting reaction products, in particular a gaseous part, can be removed from the process chamber in order to at least partially remove the material layer from the surface. A further part of the reaction products, in particular a solid part, can optionally remain on the surface and, for example, form a chemical bond with the carrier film.

The plasma can be, for example, a reductively effective plasma, so that the material layer is reduced by the plasma treatment.

The dry etching can be designed, for example, as a physical dry etching process, for example as a cathode sputtering process or sputtering process, in particular as a DC sputtering process.

For this purpose, for example, an inert gas plasma, for example an argon plasma, in particular an argon low-pressure plasma, can be used. Ions contained in the inert gas plasma are then accelerated in the direction of the carrier film by an applied voltage and, when they strike the material layer, knock particles out of it, so that the material layer is at least partially removed.

The dry etching can also be designed as a physico-chemical dry etching, which is also referred to as plasma-assisted etching, for example as reactive ion etching, as reactive ion depth etching or as reactive ion beam etching.

The fact that the material layer is at least partially removed from the surface can therefore be understood in particular to mean that at least one component of the material layer, for example oxygen, is removed, as for example during plasma etching. As an alternative or in addition, the at least partial removal of the material layer can be understood to mean that the material layer or the named component is removed from the surface at least in a spatial sub-area of the latter.

To generate the plasma, the process chamber can, for example, first be evacuated. A starting gas can then be introduced into the process chamber or into an antechamber, in particular by means of a corresponding gas supply infrastructure. The process chamber filled with starting gas can then be ignited by means of an ignition device in order to generate the plasma, or the antechamber filled with starting gas can be ignited in order to generate the plasma and then introduce it into the process chamber. Alternatively, a feed line filled with the starting gas can also be ignited by means of the ignition device in order to generate the plasma and then introduce it into the process chamber.

The ignition device can contain, for example, a microwave source and irradiate the starting gas with microwave radiation for ignition.

The carrier film can in particular be present as a film web, also referred to as a film strip, or as part of a film web.

The method according to the improved concept enables effective cleaning of the surface from the material layer. Corresponding preparation of the carrier film according to the improved concept results in improved electrical contact between the carrier film and active materials of the electrode and improved mechanical adhesion of the active materials to the carrier film.

According to the improved concept, this is possible in particular without a primer, such as primer, and without wet-chemical process steps with correspondingly complex drying.

The improved concept therefore offers an inexpensive and less complex possibility of reducing the contact resistance in lithium-ion batteries and thereby improving their overall performance.

According to the improved concept, mechanical processing of the carrier film to remove the material layer is also dispensed with. This can prevent damage to the carrier film. The reductive plasma treatment enables a particularly uniform, defined and gentle removal or chemical conversion of the material layer, even with very thin material layers and carrier foils and correspondingly mechanically sensitive carrier foils. The process can be carried out continuously, for example during the production of the carrier film in a rolling mill. This also reduces the additional time required for the Removal of the material layer small or negligible.

According to at least one embodiment, the plasma treatment is designed as a dry etching process, in particular as a plasma etching process.

According to at least one embodiment, the carrier film is moved translationally relative to the irradiation device, in particular along the translation direction, which can correspond, for example, to a longitudinal direction of the film strip.

For example, the film is passed through the process chamber as part of the film web, in particular during the plasma treatment. The process chamber has in particular an inlet and an outlet for the carrier film as well as corresponding sealing devices in order to keep the process pressure in the process chamber low, for example in a range below 100 Pa, in particular between 20 and 60 Pa. This enables continuous treatment of the carrier film.

In alternative embodiments, the carrier film can be provided as a film roll, introduced into the process chamber and at least partially unrolled within the process chamber. The process chamber, which can also be referred to as an autoclave or vacuum chamber, can be evacuated after the carrier film has been introduced. The unrolled part of the carrier film can then be exposed to the plasma as described. The film can then be rolled up again, in particular within the process chamber.

This enables a batch process to be implemented in which the technical effort required to generate and maintain the vacuum in the process chamber is low.

According to at least one embodiment, the carrier film is designed as a metal film, and the material layer is present as a metal oxide layer on the surface, in particular before the at least partial removal or chemical conversion of the material layer.

According to at least one embodiment, the carrier film is designed as an aluminum foil, and the material layer is present as an aluminum oxide layer on the surface, in particular before the at least partial removal or chemical conversion of the material layer.

The aluminum oxide layer can in particular be a so-called native aluminum oxide layer. The native aluminum oxide layer can, for example, be present essentially continuously on the surface of the carrier film and, for example, if it is formed at room temperature, have a thickness of less than 20 nm, for example 10 nm or less.

According to at least one embodiment, the plasma contains a reductively active plasma, for example a hydrogen plasma.

In the reductive plasma treatment, excited hydrogen molecules and / or hydrogen radicals react in particular with oxygen in the material layer, in particular the metal oxide, for example with the formation of water vapor as a reaction product. This removes the oxygen in the material layer from the surface. The metal that is also formed as a result of the reduction remains, for example, on the surface.

The plasma treatment advantageously only reduces the uppermost material layer, ie in particular the aluminum oxide layer, and thereby converts it into metallic aluminum with the formation of water vapor, while the metallic aluminum of the carrier film remains largely unaffected. As a result, the aluminum oxide layer can be selectively and gently removed with the process or converted into conductive aluminum.

According to at least one embodiment, the carrier foil is designed as a copper foil, and the material layer is present as a copper oxide layer and / or copper sulfide layer on the surface, in particular before the at least partial removal or chemical conversion of the material layer.

According to at least one embodiment, the carrier film is provided as a film web, and the surface is passed through the process chamber for the plasma treatment by means of a conveying device in accordance with a longitudinal direction of the film web.

For example, for this purpose the film web can be unrolled from a film roll by means of the conveying device. The longitudinal direction of the film web can then be understood as the unwinding direction.

According to at least one embodiment, a further surface of the carrier film, in particular a further surface of the carrier film opposite the surface, is also exposed to the plasma during the plasma treatment in order to at least partially remove a further material layer on the further surface. If the surface of the carrier film is considered to be the front side, the further surface is in particular a rear side of the carrier film. The same procedure can be used for the rear as with regard to the front side, in particular in the case of an aluminum carrier film, the native aluminum oxide layer can also be correspondingly removed or chemically reacted on the rear side.

Alternatively, a separate plasma treatment can be provided for the further surface, possibly in the same or a different process chamber.

According to at least one embodiment, at least the part of the carrier film is introduced into a further process chamber before the plasma treatment is carried out. In the further process chamber, an oxidatively active further plasma is generated in order to carry out a further plasma treatment. The surface is exposed to the further plasma in order to clean the surface.

According to at least one embodiment, the further plasma is generated in the process chamber before the plasma treatment is carried out, and in particular before the plasma is generated, in order to carry out the further plasma treatment. The surface is exposed to the further plasma in order to clean the surface.

In other words, the further plasma treatment preceding the plasma treatment can be carried out in the same process chamber as the plasma treatment or in a different process chamber.

In particular, the further plasma treatment is designed as a plasma cleaning process.

As a result of the further plasma treatment, in particular organic contaminants can be removed from the carrier film. As a result, the subsequent plasma treatment can remove the material layer more reliably and more thoroughly. The impurities can result, for example, from a lubricant or release agent, for example kerosene, as can be used in film rolling.

According to at least one embodiment, after the further plasma treatment has been carried out and before the plasma treatment has been carried out, reaction products that have arisen from the further plasma treatment are removed from the process chamber, for example pumped out, in particular by means of a pumping device.

According to at least one embodiment, the further plasma contains an oxygen plasma.

According to at least one embodiment, the further plasma is irradiated with UV radiation during the further plasma treatment.

As a result, it can be achieved that shorter-chain reaction products arise which can be removed more easily.

The active material can contain, for example, lithium-nickel-cobalt-aluminum oxide, NCA, or lithium-nickel-manganese-cobalt oxide, NMC.

According to the improved concept, a method for producing a lithium-ion accumulator is also specified. For this purpose, a carrier film is provided for an electrode of the lithium-ion accumulator, and the carrier film is processed according to a method for processing the carrier film according to the improved concept.

According to the improved concept, a device for processing a carrier film for an electrode of a lithium-ion accumulator is also specified. The device has a process chamber and a conveying device which is set up to introduce at least part of the carrier film into the process chamber. The device has an ignition device which is set up to generate a plasma in the process chamber in order to carry out a plasma treatment. The process chamber is designed in such a way that a material layer on a surface of the part of the carrier film is exposed to the plasma in order to at least partially remove the material layer from the surface.

The process chamber can in particular be part of a vacuum reactor.

According to at least one embodiment, the device has a gas supply infrastructure which is arranged and set up for supplying an output gas for generating the plasma into the process chamber.

According to at least one embodiment, the device has a first further gas supply infrastructure, which is arranged and set up for supplying a further starting gas for generating an oxidatively active further plasma into the process chamber.

In particular, the ignition device is set up to generate the further plasma in the process chamber in order to carry out a further plasma treatment. The process chamber is designed in such a way that the surface is exposed to the further plasma in order to clean the surface.

According to at least one embodiment of the device, it has a further process chamber, the conveying device being set up to introduce at least the part of the carrier film into the further process chamber before the plasma treatment is carried out. The device has a further ignition device which is set up to generate an oxidatively active further plasma in the further process chamber in order to carry out a further plasma treatment, the further process chamber being designed in such a way that the surface is exposed to the further plasma around the surface to clean.

According to at least one embodiment, the device has a second further gas supply infrastructure which is arranged and set up for supplying a further starting gas for generating the further plasma into the further process chamber.

Further embodiments of the device according to the improved concept follow directly from the various embodiments of the method according to the improved concept and vice versa. In particular, the device according to the improved concept can carry out a method according to the improved concept or carries out such a method.

The figure shows a schematic representation of an exemplary embodiment of a device 1 for processing a carrier film 2 shown for an electrode of a lithium-ion battery according to the improved concept.

The device 1 has a conveying device with one or more propulsion means 6a , 6b , 6c, 6d, 6e and a control unit 5 to control the propulsion equipment 6a until 6e on. The propulsion means 6a until 6e can for example have rollers or rollers or roller pairs or roller pairs, by means of which the carrier film 2 in translation direction x can be moved. The device 1 can also be used, for example, to roll the carrier film 2 be used.

The device 1 has a vacuum reactor with a process chamber 4th in which the carrier film 2 can be introduced by means of the conveyor device, so that a surface 3 the carrier film 2 , for example a front side, in the process chamber 4th can be treated. Depending on the design, one of the surface 3 opposite further surface 3 ' , so in particular a back side, the carrier film 2 simultaneously with the surface 3 be treated. Alternatively, the further surface 3 ' separate from the surface 3 be treated.

By means of a gas supply device 7th A starting gas, for example hydrogen or a hydrogen-containing gas, can be fed into the process chamber 4th be introduced. At the process chamber 4th is also an ignition device 9 arranged, for example by microwave discharge, the starting gas in the process chamber 4th can ignite a reductively effective plasma, in particular a hydrogen plasma, in the process chamber 4th to create. This procedure is also known as direct plasma ignition. Alternatively, the plasma can also be ignited in an antechamber or the supply line, which is referred to as remote plasma ignition.

In the process chamber 4th is the surface 3 then exposed to the reductive plasma, leaving a layer of material on the surface 3 is removed by plasma etching. For example, the reaction products by means of a pump device 8th from the process chamber 4th removed.

In the case of an aluminum foil as the carrier foil 2 can thereby, for example, use a native aluminum oxide layer as a material layer from the surface 3 removed.

Optionally, the device 1 another vacuum reactor with another process chamber 4 ' in which the carrier film 2 can be introduced by means of the conveyor device, so that the surface 3 the carrier film 2 in the further process chamber 4 ' can be treated. The further vacuum reactor is connected upstream of the vacuum reactor, so that the surface 3 in the further process chamber 4 ' i.e. before treatment in the process chamber 4th can be treated.

By means of another gas supply device 7 ' a further starting gas, for example oxygen or an oxygen-containing gas, can be fed into the further process chamber 4 ' be introduced. At the other process chamber 4 ' is another ignition device 9 ' arranged, for example by microwave discharge, the starting gas in the further process chamber 4 ' can ignite to an oxidatively active plasma, in particular an oxygen plasma, in the further process chamber 4 ' to create. Alternatively, the plasma can be ignited using Remote Plasma Ignition.

In the further process chamber 4 ' is the surface 3 then exposed to the oxidatively active plasma, so that organic impurities on the surface 3 can be removed by plasma cleaning. For example, the reaction products can be removed by means of a further pump device 8th' from the further process chamber 4 ' removed.

With reference to the figure, a continuous process has been described in which the carrier film 2 starts especially at atmospheric pressure, then the process chamber 4th happens, within which there is a pressure of 20-60 Pa, for example, and then continues to run again under atmospheric pressure. Inside the process chamber 4th can the carrier film 2 be guided in a meandering shape, for example, in order to increase the achievable throughput.

Alternatively, the device 1 but also be designed to carry out a batch process in which the carrier film 2 as a film roll by means of a corresponding conveying device of the device 1 into the process chamber 4th is introduced and the process chamber 4th then evacuated. The carrier film 2 is then in the process chamber 4th unrolled, treated with the reductive plasma and inside the process chamber 4th rolled up again. The treatment with the oxidatively active plasma can also be carried out accordingly.

In alternative embodiments, instead of the reactive plasma, an inert gas plasma, for example an argon plasma, can be used in order to remove the material layer by bombarding it with ions of the inert gas plasma in accordance with the principle of DC sputtering.

As described, the improved concept enables defined, uniform and very gentle removal or chemical conversion of the material layer from the carrier film, for example a native aluminum oxide layer from a very thin, about 15 µm or less thick, and sensitive aluminum carrier film in a continuous process. As a result, contact resistances can be reduced and ultimately the performance of the lithium-ion batteries can be improved.

List of reference symbols

1

contraption

2

Carrier film

3, 3 '

surfaces

4, 4 '

Process chambers

5

Control unit

6a, 6b, 6d

Propulsion means

6d, 6e 7, 7 '

Gas supply devices

8, 8 '

Pumping devices

9, 9 '

Ignition devices

x

Longitudinal direction

y

Transverse direction

Claims (12)

Method for processing a carrier film (2) for an electrode of a lithium-ion battery, wherein - at least part of the carrier film (2) is introduced into a process chamber (4), - A plasma is generated in the process chamber (4) in order to carry out a plasma treatment; and - A material layer on a surface (3, 3 ') of the part of the carrier film (2) is exposed to the plasma in order to at least partially remove the material layer from the surface (3, 3'). Procedure according to Claim 1 - The carrier film (2) is designed as an aluminum foil and the material layer is present as an aluminum oxide layer on the surface (3, 3 '); or - the carrier foil (2) is designed as a copper foil and the material layer is present as a copper oxide layer or as a copper sulfide layer on the surface (3, 3 '). Method according to one of the preceding claims, wherein the plasma contains a reductively active plasma, for example a hydrogen plasma, and / or the first plasma treatment is designed as a plasma etching process. Method according to one of the Claims 1 or 2 , wherein the plasma is an inert gas plasma, for example an argon plasma, and / or the first plasma treatment is configured as a physical dry etching process. The method according to any one of the preceding claims, wherein - At least the part of the carrier film (2) is introduced into a further process chamber (4 ') before the plasma treatment is carried out; - An oxidatively effective further plasma is generated in the further process chamber (4) for carrying out a further plasma treatment; and - The surface (3, 3 ') is exposed to the further plasma in order to clean the surface (3, 3'). Method according to one of the Claims 1 until 4th wherein - in the process chamber (4) before the plasma treatment is carried out to carry out a further plasma treatment, an oxidatively active further plasma is generated; and - the surface (3, 3 ') is exposed to the further plasma in order to clean the surface (3, 3'). Procedure according to Claim 6 , wherein after the further plasma treatment has been carried out and before the plasma treatment has been carried out, reaction products resulting from the further plasma treatment are removed from the process chamber (4). Method according to one of the Claims 5 until 7th , wherein the further plasma contains an oxygen plasma. Method for producing a lithium-ion accumulator, wherein - a carrier film (2) is provided for an electrode of the lithium-ion accumulator; and - the carrier film (2) according to a method according to one of the Claims 1 until 8th is processed. Device for processing a carrier film (2) for an electrode of a lithium-ion battery, comprising the device (1) - A process chamber (4) and a conveying device (6a, 6b, 6c, 6d, 6e), which is set up to introduce at least part of the carrier film (2) into the process chamber (4); - An ignition device (9) which is set up to generate a plasma in the process chamber (4) to carry out a plasma treatment, the process chamber (4) being designed in such a way that a material layer on a surface (3, 3 ') of the Part of the carrier film (2) is exposed to the plasma in order to at least partially remove the material layer from the surface (3, 3 '). Device according to Claim 10 , having - a further process chamber (4 '), the conveying device (6a, 6b, 6c, 6d, 6e) being set up to transfer at least the part of the carrier film (2) into the further process chamber (4') before the plasma treatment is carried out bring in; - Another ignition device (9 '), which is set up to generate a further plasma in the further process chamber (4') for carrying out a further plasma treatment, the further process chamber (4 ') being designed in such a way that the surface (3 , 3 ') is exposed to the further plasma in order to clean the surface (3, 3'). Device according to Claim 10 , comprising - a gas supply infrastructure (7), arranged and set up for supplying an output gas for generating the plasma into the process chamber (4); and - a further gas supply infrastructure, arranged and set up for supplying a further output gas for generating a further plasma into the process chamber (4).

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