WO2024017543A1

WO2024017543A1 - Method for producing an electrode of a battery cell

Info

Publication number: WO2024017543A1
Application number: PCT/EP2023/065869
Authority: WO
Inventors: Gerold HÜBNER; Miriam Kunze; Jessica Maria Hüsker
Original assignee: Volkswagen Aktiengesellschaft
Priority date: 2022-07-19
Filing date: 2023-06-13
Publication date: 2024-01-25
Also published as: DE102022207329B3

Abstract

The invention relates to a method for producing an electrode (1) of a battery cell, the method having at least the following steps: a) providing a carrier material (2) of the electrode (1); b) coating the carrier material (2) with * an additive that has a plurality of pores and is elastically deformable and * an active material mixture, and forming a coating (3); c) calendering the coated carrier material (2), wherein at least the coating (3) is compressed during calendering and thus a porosity of the coating (3) is reduced; d) enlarging, in a self-induced manner, at least one thickness (4, 5) of the coating (3) due to an elastic spring-back of the additive and thus setting the porosity of the coating (3).

Description

Method for producing an electrode of a battery cell

The invention relates to a method for producing an electrode of a battery cell. In particular, an active material that is arranged on a carrier material should still have sufficient pores even after calendering, so that continuous wetting with electrolyte is possible. The carrier material includes in particular a band-shaped carrier material.

Batteries, especially lithium-ion batteries, are increasingly being used to power motor vehicles. Batteries are typically composed of cells, with each cell having a stack of anode, cathode and separator sheets. At least some of the anode and cathode sheets are designed as current collectors to divert the current provided by the cell to a consumer arranged outside the cell.

When producing a lithium-ion battery cell, a so-called carrier material, in particular a band-shaped carrier material, e.g. B. a carrier film, coated on both sides with a slurry (hereinafter also referred to as active material mixture) using an application tool. The slurry consists of several components, including an active material, conductive carbon black, binders, solvents and possibly other additives. After the coating has been carried out on one side, the coated carrier material is subjected to a drying process in order to evaporate the solvent contained and to firmly bond the remaining components to the carrier film. The carrier film forms a current conductor for the battery cell.

The coating created in this way is porous. The porosity is reduced by calendering, as the coating is compacted here. Densification is required to increase specific capacity (based on volume) and electrical conductivity. The active material mixture is compressed by at least 20% (approx. 40%) during calendering. The calendering process is similar to the rolling process.

The anode consists in particular of graphite as the active material; the anode also contains z. B. SBR as a binder material, CMS as a thinner and conductive carbon. In particular, an attempt is made to To achieve a density of the active material of 1.6 g/cm ³ [grams/cubic centimeter] in order to increase the volumetric energy density of the battery cell. High density also increases the conductivity of the battery cell.

To ensure the rapid charging capability of electrodes of lithium-ion battery cells, minimization of the lithium-ion transport resistance is a prerequisite. This can be achieved by minimizing the electrode thickness, but this comes at the expense of capacity and high energy density. Therefore, high thicknesses of the active material mixture are usually aimed for in order to enable the longest possible battery range. However, these large thicknesses increase the contact resistance of the electrodes.

A high lithium ion transport rate requires the most intensive penetration of the electrode with electrolyte and short transport routes throughout the entire thickness of the electrode coating in order to quickly make lithium ions available even in the inner areas of the electrode. Active material that is not sufficiently wetted with electrolyte is not available for the cell reaction and therefore does not contribute to the cell performance/capacity, i.e. reduces the gravimetric and volumetric energy density. To minimize the internal contact resistance, ensure the adhesion of the active material to the current collector and set a specific energy density, electrodes are calendered before cell construction. During calendering, the coating of the electrode carrier material is compressed by at least 20% and the density of the coating is correspondingly increased. This means that the calendering step significantly reduces the porosity of the electrode.

Are known e.g. B. Post-treatment of the finished electrodes, for example using the finest needles on a roll, to form channels in the electrode structure. Laser treatment of electrodes is also known. Furthermore, the imprinting of a preferred direction of the active materials by an external magnetic field and the associated targeted minimization of tortuosity is known.

The known methods require in particular the integration of additional system components in the production system, which is associated with costs and effort. In addition, there is a risk that areas of an electrode will be damaged during follow-up treatment, especially during laser treatment. During laser treatment, a large amount of active material is still removed, but this removed material is no longer used. This increases the costs of the electrode. From US 7 767 346 B2 an active material for an electrode is known which has a high porosity and therefore only has a reduced volume fluctuation between charging and discharging.

JP 2001 196 065 A1 is directed to an active material that has active material and polymeric additives that are connected to one another via binder material. The additives should have a pore control function so that volume fluctuations between loading and unloading are reduced.

JP 2001 185 152 A is directed to an electrode additive that has an elastic structure. This is also intended to achieve reduced volume fluctuations between loading and unloading.

The object of the present invention is to at least partially solve the problems mentioned with reference to the prior art. In particular, a method is to be proposed by which the porosity of an active material can be advantageously adjusted and maintained beyond calendering.

A method with the features according to claim 1 contributes to solving these tasks. Advantageous further training is the subject of the dependent patent claims. The features listed individually in the patent claims can be combined with one another in a technologically sensible manner and can be supplemented by explanatory facts from the description and/or details from the figures, with further embodiment variants of the invention being shown.

A method for producing an electrode of a battery cell is proposed. The method has at least the following steps: a) providing a (e.g. band-shaped) carrier material for an electrode; b) Coating the carrier material with

• an additive that has a large number of pores and is elastically deformable and

• an active material mixture; and

forming a coating; c) calendering the coated carrier material; wherein at least the coating is compacted during calendering and thus the porosity of the coating is reduced; d) self-induced increase in at least one thickness of the coating due to an elastic springback of the additive and thus adjustment of the porosity of the coating.

The above (non-exhaustive) division of the process steps into a) to d) is primarily intended to serve only as a distinction and not to impose any order and/or dependency. The frequency of the process steps can also vary. It is also possible for process steps to at least partially overlap each other in time. Steps a) to d) are preferably carried out in the specified order.

The electrode to be produced is intended in particular for use in a lithium-ion battery cell. The electrode in particular comprises a carrier material, e.g. B. a copper or aluminum foil. The carrier material used consists in particular of 4 to 12 pm thick copper for the anode and 8 to 15 pm thick aluminum for the cathode. In step b), the carrier material is coated with the coating at least on one largest side surface, possibly also on the largest side surfaces opposite one another.

In particular, the active material mixture for a cathode comprises at least (one of) conductive carbon black (e.g. carbon black), NMC (lithium-nickel-cobalt-manganese as a lithium-storing active material), PVDF (polyvinylidene fluoride); for an anode at least (one of) graphite (as lithium-storing active material), CNT (carbon nano tubes), SBR (styrene-butadiene rubber as binder material), CMC (carboxymethyl cellulose polymer). The components of the material that are not binder material are, in particular, classified as active material.

According to step a), in particular a carrier material for an electrode is provided. The carrier material is provided in particular as a band-shaped carrier material and possibly as an endless material. The band-shaped endless material is conveyed in particular along a conveying direction, at least during steps b) and c), preferably (also) during step d).

According to step b), the carrier material is coated with an additive that has a large number of pores and is elastically deformable. The carrier material is further coated with the active material mixture. The additive and the active material mixture together form the coating. In particular, the coating is additionally smoothed in step b) or the thickness of the coating is adjusted.

In particular, the coating is additionally heated or dried in step b) so that solvents can evaporate from the coating.

According to step c), the coated carrier material or the coating is calendered. At least the coating (the carrier material is usually solid and is therefore not further compacted) is compacted during calendering, thereby reducing the porosity of the coating.

During calendering, the coated carrier material is guided through a roller arrangement, which may be temperature-controlled and can therefore heat the coated carrier material. The coating is compacted via the rollers. There is usually an increase in density (a reduction in porosity) of the coating of at least 20%.

According to step d), a self-induced increase in at least one thickness of the coating occurs due to an elastic springback of the additive. The springback causes in particular an increase in the porosity reduced by calendering.

In particular, this results in an adjustment of the porosity of the coating. In particular, this porosity of the coating produced in step d) is influenced by the properties of the additive. In particular, the active material mixture or the environmental conditions (temperature, humidity, etc.) also have a (smaller) influence on the porosity produced in step d).

A value for the porosity produced in step d) arises in particular as a function of time. Immediately after calendering, for example: B. only has a low porosity. The elastic springback causes a time-dependent gradual increase in porosity. After a certain period of time, a final porosity value is reached. This final porosity value can (also) be adjusted by tensioning the electrode, e.g. B. by arranging the electrode in a stack with other electrodes and / or by arranging the stack in a housing of a battery cell.

In particular, no later than fifteen minutes, preferably no later than two minutes, particularly preferably no later than 30 seconds, after the end of the calendaring In the area of the coating, the additive's recovery is at least 85% complete. i.e. that at this point the increase in porosity is almost complete.

The springback can e.g. B. can be determined in experiments. The formation of the porosity in step d) tends to reach a final porosity value over time. The porosity (or its course over time) can e.g. B. can be easily determined based on the change in the thickness of the coating. In particular, a change in the thickness of the coating is at least 85% complete by fifteen minutes at the latest, preferably by two minutes at the latest, particularly preferably by 30 seconds at the latest, after the calendaring of an area of the coating has ended.

In particular, a first thickness of the coating immediately after step c) is at least 10%, preferably at least 15%, particularly preferably at least 20% smaller than a second thickness after step d). The second thickness is in particular the intended thickness of the coating that occurs after a certain period of time (fifteen minutes, two minutes, 30 seconds). Alternatively, the second thickness is the final porosity value described above.

In particular, the additive is at least partially, in particular predominantly, preferably completely, open-pored. After step d), the active material mixture is at least partially arranged within at least some pores, preferably within all pores.

Alternatively or additionally, the additive is at least partially, in particular predominantly, preferably completely, closed-pore. In this case, the active material mixture cannot penetrate into the pores, but can only accumulate on the surface of the respective pore wall.

In particular, the additive and the active material mixture are mixed together before step b) and applied as a mixture to the carrier material in step b).

Alternatively or additionally, in step b), the additive and then the active material mixture are applied separately to the carrier material.

In particular, the additive comprises at least graphite or graphene. In particular, the active material mixture does not include any additional electrically conductive additional material. In particular, the electrical conductivity of the coating (if the additive comprises, for example, graphite or graphene) is ensured via the additive.

In particular, the additive includes a metal, a metal alloy, polyurethane or a binder material.

In particular, the additive includes a polymer material otherwise used as a binder material (e.g. CMC, SBR, PAA) or targeted modifications of these materials. In particular, the active material mixture does not contain any additional binder material.

In particular, the additive is provided in step b) as a large number of particles, as foam or as elastic threads.

In particular, it is proposed to introduce a (partially) elastic additive or several different (partially) elastic additives with high porosity and/or high spring force into an electrode.

The additive in particular has (partially) elastic structures that are open-pored or closed-pored.

In particular, the additive can be applied to the carrier material in step b) before the active material mixture. A thickness of 20 pm [micrometers] to 150 pm of the additive on the carrier material can be set. The additive can then be coated with the active material mixture (also referred to as electrode slip). Alternatively, the additive and active material mixture are mixed together and then applied together to the carrier material.

Due to the high porosity (open or closed porosity) of the additive, it is filled or impregnated with the active material mixture. In particular, the coating is dried in step b).

The coating is calendered in step c). The restoring force of the additive according to step d) causes the coating not to remain completely compressed, but to “spring back” again. Depending on the spring constant of the additive, the compression is greater or smaller. The following applies: the larger the spring constant, the lower the resulting compression after calendering.

With a closed-pore additive, the active material mixture does not penetrate the pores of the additive.

The desired bond between active material, binder material and carrier material created during calendering is retained, particularly during or after step d), so that the intended minimization of the ohmic resistance is not impaired.

In particular, for z. B. additive present as a polymer is deposited on the carrier material in a foam-like manner or in elastic threads, e.g. B. by electrospinning, or by blowing in gases during the drying phase of the additive (before deposition on the carrier material or by specifically selecting the drying conditions). In particular, this makes it possible to adjust the elastic deformability of the additive or the coating.

The additive can in particular be added as a large number of particles, with the individual particles unfolding again after calendering and thus expanding the coating or increasing its porosity or thickness.

In particular, the particles have a wide size distribution in order to be able to generate different pores in the electrode.

In particular, the additive is at least 30% formed from particles, at least 10% of which have a (non-compressed) size that differs by at least 30% from the largest or smallest particles.

In particular, the electrode provided as an anode has a major problem with closing or reducing the size of the pores at high calender compression or strong compaction. However, the proposed method steps can also be carried out for electrodes intended as cathodes. A battery cell is further proposed, at least comprising a battery cell housing and at least one electrode arranged therein, which is produced by the method described.

The battery cell in particular comprises a battery cell housing enclosing a volume and, arranged in the volume, at least a first electrode film of a first type of electrode, a second electrode film of a second type of electrode and a separator material arranged between them and a liquid electrolyte.

The battery cell is in particular a pouch cell (with a deformable battery cell housing consisting of a pouch film) or a prismatic cell (with a dimensionally stable battery cell housing). A pouch film is a known deformable housing part that is used as a battery cell housing for so-called pouch cells. It is a composite material, e.g. B. comprising a plastic and aluminum.

The battery cell is in particular a lithium-ion battery cell.

The individual foils of the plurality of electrodes designed as electrode foils are arranged one on top of the other and in particular form a stack. The electrode foils are each assigned to different types of electrodes, i.e. they are designed as an anode or a cathode. Anodes and cathodes are arranged alternately and separated from each other by the separator material.

A battery cell is a power storage device that, for example, B. is used in a motor vehicle to store electrical energy. In particular, z. B. a motor vehicle has an electric machine for driving the motor vehicle (a traction drive), the electric machine being able to be driven by the electrical energy stored in the battery cell.

A motor vehicle is further proposed, at least comprising a traction drive and a battery with at least one of the battery cells described, the traction drive being able to be supplied with energy by the at least one battery cell.

In particular, at least one system for data processing is provided which has means which are suitably equipped, configured or programmed to carry out the method or which carry out the method. The means include e.g. B. a processor and a memory in which commands to be executed by the processor are stored, as well as data lines or transmission devices that enable the transmission of commands, measured values, data or the like between the elements listed, e.g. B. a device for coating, a device for conveying the (coated) carrier material along a feed direction, a device for calendering or for compacting the coating, a device for checking or measuring individual properties of those produced with the method or with individual method steps Electrode, etc., enable.

A computer program is also proposed, comprising commands which, when the program is executed by a computer, cause it to carry out the described method or the steps of the described method.

A computer-readable storage medium is further proposed, comprising instructions which, when executed by a computer, cause it to carry out the described method or the steps of the described method.

The statements on the method can be transferred in particular to the battery cell, the motor vehicle, the data processing system and/or the computer-implemented method (i.e. the computer program and the computer-readable storage medium) and vice versa.

The use of indefinite articles (“a”, “an”, “an” and “an”), particularly in the patent claims and the description reflecting them, is to be understood as such and not as a numeral. Terms or components introduced accordingly are to be understood as meaning that they are present at least once and, in particular, can also be present multiple times.

As a precaution, it should be noted that the number words used here (“first”, “second”, ...) primarily serve (only) to distinguish between several similar objects, sizes or processes, i.e. in particular no dependency and/or order of these objects, sizes or prescribe processes to each other. If a dependency and/or sequence is required, this is explicitly stated here or it will be obvious to the person skilled in the art when studying the specifically described embodiment. To the extent that a component can occur multiple times (“at least one”), the description of one of these components can apply equally to all or part of the majority of these components, but this is not mandatory. The invention and the technical environment are explained in more detail below using the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments given. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other components and findings from the present description. In particular, it should be noted that the figures and in particular the proportions shown are only schematic. Show it:

1: a step c) of the method in a view along a feed direction of a coated carrier material; and

Fig. 2: steps c) and d) of the method in a side view.

Fig. 1 shows a step c) of the method in a view along a feed direction 6 of a coated carrier material 2. Fig. 2 shows steps c) and d) of the method in a side view. 1 and 2 are described together below.

According to step a), a carrier material 2 of an electrode 1 is provided. The carrier material 2 is provided as a band-shaped carrier material 2 and thereby as an endless material. The band-shaped endless material is conveyed along a feed direction 6 (conveying direction) during steps c) and d) shown.

According to step b), the carrier material 2 is coated with an additive that has a large number of pores and is elastically deformable. Furthermore, the carrier material 2 is coated with the active material mixture. The additive and the active material mixture together form the coating 3.

According to step c), the coated carrier material 2 or the coating 3 is calendered. The coating 3 is compacted during calendering and thus the porosity of the coating 3 is reduced.

The endless material, comprising the carrier material 2 and the coating 3 applied on both sides, is conveyed between two conveyor rollers 7 along a feed direction 6 through calendering rollers 8. The conveyor rollers 7 and the calendering rollers 8 each rotate about their respective axis of rotation 9. During calendering, the coated carrier material 2 is guided through a roller arrangement with calendering rollers 8, which may be tempered and can therefore heat the coated carrier material 2. The coating 3 is compacted via the calendering rollers 8. There is usually an increase in density (a reduction in porosity) of the coating 3 of at least 20%.

According to step d) (i.e. along the feed direction 6 immediately after the calendering rollers 8), a self-induced increase in thickness 4, 5 of the coating 3 occurs due to an elastic springback of the additive. The springback causes an increase in the porosity reduced by calendering.

A thickness 4.5 of the coating 3, which is present in front of the calendering rollers 8 in the feed direction 6, is reduced to a first thickness 4 by the calendering rollers 8. The first thickness 4, which is present immediately after step c), i.e. immediately after the calendering rollers 8 in the feed direction 6, is less than a second thickness 5, which is present after step d). The second thickness 5 is the intended thickness of the coating 3, which occurs after a certain period of time (five minutes, two minutes, 30 seconds), which occurs here shortly before the electrode 1 is wound on the rear conveyor roller 7.

List of reference symbols Electrode Carrier material Coating First thickness Second thickness Feed direction Conveyor rollers Calendering roller Rotary axis

Claims

Claims Method for producing an electrode (1) of a battery cell; wherein the method has at least the following steps: a) providing a carrier material (2) for the electrode (1); b) coating the carrier material (2).

• an active material mixture; and

forming a coating (3); c) calendering the coated carrier material (2); wherein at least the coating (3) is compacted during calendering and thus a porosity of the coating (3) is reduced; d) Self-induced increase in at least one thickness (4, 5) of the coating (3) due to an elastic springback of the additive and thus adjustment of the porosity of the coating (3). Method according to claim 1, wherein a first thickness (4) of the coating (3) immediately after step c) is at least 5% smaller than a second thickness (5) after step d). Method according to one of the preceding claims, wherein the additive is at least partially open-pored and the active material mixture after step d) is at least partially arranged within at least some pores. Method according to one of the preceding patent claims, wherein the additive is at least partially closed-pore. Method according to one of the preceding claims, wherein the additive and the active material mixture are mixed together before step b) and applied as a mixture to the carrier material (2) in step b). Method according to one of the preceding patent claims 1 to 4, wherein in step b) first the additive and then the active material mixture are applied separately from one another. Method according to one of the preceding claims, wherein the additive comprises at least graphite or graphene. Method according to claim 7, wherein the active material mixture does not comprise any additional electrically conductive additional material. Method according to one of the preceding claims 1 to 7, wherein the additive comprises a metal, a metal alloy, polyurethane or a binder material. Method according to one of the preceding claims, wherein the additive in step b) is provided as a plurality of particles, as foam or as elastic threads.