Dry film manufacturing method, rolling device, dry film, and substrate coated with dry film

Abstract

To provide a method for applying a dry film to a substrate in an efficient and mechanically stable manner.SOLUTION: The present invention relates to a method for manufacturing a dry film 3, in which a dry powder mixture is processed into a dry film 3 by a rolling device including a first roll 2a and a second roll 2b. The first roll 2a has a higher circumferential rotational speed than the second roll 2b. The dry film 3 is attached to the first roll 2a, and the ratio between the peripheral speed of rotation of the first roll 2a and the peripheral speed of rotation of the second roll 2b is maintained between 10:5 and 10:1.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a substrate, a rolling apparatus, a dry film, and a substrate coated with a dry film. [Background technology]

[0002] The production of battery electrodes requires the application of layers with thicknesses of 50 μm to 100 μm at high web speeds to metal current collectors. This is usually realized by wet-chemical roll-to-roll processes from suspensions of the active material in aqueous or organic solvents. This requires high energy inputs both for the dispersion of the active material and for drying the layer. Increasing efforts are being made to realize coatings in a solvent-free and therefore dry manner. For this, a dry powder mixture of active material, conductive additives and suitable binders needs to be converted into a mechanically loaded layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 7,352,558 [Patent Document 2] German Patent No. 102010044552 [Patent Document 3] German Patent No. 102014208145 Summary of the Invention [Problem to be solved by the invention]

[0004] The method by which pressing into a free-standing film is realized is known from the prior art, as disclosed in US Pat. No. 5,399,633. For this purpose, a three-stage process is carried out in which a dry powder mixture is fibrillated by an air jet mill, the powder is conveyed to a calender nip where it is pressed into a free-standing film. The standing film is applied to a current collector, as is usually done. Although this method allows for continuous processing, the multi-stage nature, especially the intermediate step of the awkward free-standing film, is problematic.

[0005] Another method, disclosed in US Pat. No. 5,399,366, applies a dry powder mixture to a target substrate by electrostatic powdering and downstream heat treatment for mechanical stabilization with a thermoplastic binder. The drawback of this is that the application of the powder must be followed by mechanical stabilization by sealing or calendaring, thus requiring additional process steps. Furthermore, this method requires the use of a planar target substrate.

[0006] From US Pat. No. 5,399,637 a battery cell with coated electrodes and its manufacture is known. The battery is equipped with recyclable electrodes based on dry particles.

[0007] The object of the present invention is therefore to propose a method which avoids said drawbacks and thus allows a dry film to be applied to a substrate in an efficient and mechanically stable manner. [Means for solving the problem]

[0008] According to the invention, this object is achieved by a manufacturing method according to claim 1, a rolling device according to claim 16, a dry film according to claim 20, a substrate coated with a dry film according to claim 20 and an electrochemical element according to claim 22. Advantageous embodiments and refinements are set forth in the dependent claims.

[0009] In a method for producing a dry film, a dry powder mixture is processed into a dry film by a rolling apparatus having a first roll and a second roll, where the first roll has a higher peripheral rotational speed than the second roll, and the resulting dry film is attached to the first roll.

[0010] The rolling device, operating at different rotational peripheral speeds of the two rolls, provides mechanical stabilization and film formation on the first roll, which rotates faster than the second roll, thus avoiding the formation of a free-standing film and allowing further processing of the dry film supported or mounted on the first roll.

[0011] Typically, the dry film after the two-roll process is applied to a substrate, preferably laminated to the substrate, but alternatively or additionally, this can be done already in the production of the dry film. As long as the substrate has sufficient roughness, for example designed as a metal wire mesh or carbon fiber mat, the dry film can also be pressed onto the substrate with an effective interlock. However, it can also be provided to peel off the dry film from the first roll, for example by a doctor blade. Due to the different roll speeds (which affect the spacing of the structures formed in the dry film) and pressing forces (which affect the structure height of these structures), the dry film produced usually has a fibril structure with a roughness Ra of 10 μm or less.

[0012] It may be provided that the ratio of the rotational peripheral speed of the first roll to the rotational peripheral speed of the second roll is between 10:9 and 10:1. Preferably, a ratio of 10:7 to 10:3, particularly preferably 2:1, is maintained. As a result, shear forces are applied to the powder in the gap between the two rolls, which causes fibrillation along the running direction. The dry film can thus be formed with a corrugated structure, in which the periodicity of the structure is recognizable due to the different roll speeds.

[0013] The circumference of the first roll typically corresponds to that of the second roll, resulting in a simple construction with two rolls of the same diameter, however, it is also possible to design the first and second rolls with different diameters and therefore different roll circumferences, for example to achieve a defined rotation speed depending on the respective circumference.

[0014] The rotating device can be configured as a calendar rotating device. Further compression of the dry film can be achieved by heatable rolls. The heatable roll or at least one heatable roll can promote the formation of a fibril structure. For polytetrafluoroethylene (PTFE) binders, the temperature of the at least one heatable roll should be between 80°C and 120°C.

[0015] The second roll, which preferably has a lower peripheral rotational speed than the first roll, is provided with a modification, preferably a coating on its surface, which coating is repellent and / or adhesion reducing to the dry film that forms. The dry film can be more easily removed. The coating can comprise or consist of polytetrafluoroethylene (PTFE), silicone and / or diamond-like carbon. Alternatively or additionally, the first roll can have a corresponding modification, which has an adhesion enhancing effect on the dry film that forms. For example, the modification can also be realized by roughening, in that the first roll has a surface with a greater roughness than the second roll. In particular, the surface of the second roll can be polished smooth.

[0016] The dry film is typically applied, and preferably laminated, to a substrate and moved at a speed corresponding to the peripheral speed of rotation of the first roll for application or lamination, thereby allowing for fluid transfer from the first roll of dry film to the substrate at mutually matched speeds.

[0017] Preferably, the substrate moves on the first roll while the dry film is formed on the substrate. As a result, the direct formation of the dry layer that occurs simultaneously with the substrate movement is promoted. If the substrate is directly fed onto the first roll together with the primer foil, an adhesion enhancing layer can be applied to the substrate.

[0018] It may be provided that the dry film is formed by the first roll and the second roll with a linear force of 100 N / cm to 10 kN / cm, preferably 400 N / cm, acting between the first roll and the second roll in the nip to achieve sufficient mechanical compression of the dry film.

[0019] Typically, the substrate is formed of or includes a metallic material such that it can function as an electrode in an energy storage unit.

[0020] Before laminating the dry film on the respective surface provided for application or lamination, the substrate can be provided with a primer and / or binder. Thus, the connection is improved. Preferably, for this purpose, a thermoplastic primer and / or a thermoplastic binder are used. Alternatively or additionally, reactive primers or adhesives can also be used. The primer layer can contain a conductive rust and / or thermoplastic component, preferably polyvinylpyrrolidone (PVP). Preferably, the substrate is formed from expanded metal, a metal wire mesh, a nonwoven fabric, a substrate with a structured surface that allows mechanical interlocking, or a metal foil, preferably copper foil or aluminum foil. Particularly preferably, copper foil or aluminum foil is used, to which a carbon primer is applied.

[0021] The dry film is typically formed with a thickness of less than 500 μm, preferably less than 300 μm, particularly preferably less than 150 μm, in order to obtain a dry film that is as thin as possible and at the same time mechanically stable.

[0022] Typically, a dry powder mixture is used that contains or includes conductive additives such as polytetrafluoroethylene, e.g. carbon nanotubes. In the case of carbon / sulfur cathodes, the dry powder mixture can contain porous carbon (e.g. porous rust or carbon nanotubes), sulfur, polytetrafluoroethylene, and, if necessary, further conductive additives. In the case of lithium-ion electrodes, in addition to polytetrafluoroethylene and additional conductive additives, active materials can also be used, preferably lithium ferrophosphate (LFP), lithium manganese oxide (LMO), nickel manganese cobalt (NMC), nickel-rich lithium nickel manganese cobalt oxide (NMC622 or NMC811), lithium nickel cobalt aluminum oxide (NCA), lithium cobalt oxide (LCO), lithium manganese nickel oxide (LMNO), and / or lithium titanate (LTO). Particularly advantageous are the methods described for cathode materials for lithium-ion batteries, since these materials are hardly processed in aqueous solutions.

[0023] In a rolling apparatus for carrying out this method, the dry powder mixture is fed from a powder conveyor into a nip between a first calendar roll (first roll) and a second calendar roll (second roll), the first and second calendar rolls being configured such that the first calendar roll has a higher peripheral rotational speed than the second calendar roll, and the first and second calendar rolls have opposite directions of rotation.

[0024] In addition to the dry powder mixture, a substrate, particularly a foil or mesh, can be fed through the nip.

[0025] It may be necessary to carry out so-called intermittent coating, for example for battery applications. This allows coating in the form of strips transverse to the direction of the coating. For this, the coating is hung at regular and precisely synchronized intervals to form uncoated strips. This synchronization and the precision of the producible shapes, as well as the accuracy of the edges, are only possible to a limited extent. In this way, the process speed of the intermittent formation of the coating on the dry film and substrate can be reduced by half compared to continuous coating (~30 m / min instead of ~60 m / min).

[0026] It is possible to achieve such structuring by using an adhesion-promoting primer layer on the respective substrate surface with the method according to the invention. For this, the substrate surface on which the dry film is to be formed must be pre-coated with an adhesion-promoting primer layer in the desired shape. Here it is a layer of about 1 μm thickness (in the dry state), so it is easier to configure the primer layer instead of the actual electrode layer (various printing or spraying processes). Optional shapes (such as rectangular, or circular or other shapes) are also possible. In such a method (for example in FIG. 2), the dry film layer continues to be completely formed on the first calendar roll, which rotates faster. However, lamination with the dry film takes place only where the substrate surface is provided with a primer layer. The excess dry film (not transferred to the substrate surface) can be removed from the first calendar roll, reprocessed and reused. In this way, optional geometries can be realized with high precision without slowing down the process speed.

[0027] Also, two calendar roll pairs including a first and a second calendar roll can be arranged symmetrically side-by-side to form a nip between the two first calendar rolls, and similarly a dry film is applied to both sides of the substrate fed through this nip, with the two first calendar rolls rotating in opposite directions.

[0028] In a further embodiment, there may be an additional first calendar roll rotating about its axis of rotation, on which the dry film formed between the first and second calendar rolls may be wound after exiting the nip. The peripheral speeds of rotation of the two first calendar rolls must be the same. In this embodiment, the substrate, preferably a foil, may be fed with the dry film through the nip between the first and second calendar rolls and wound onto the additional first calendar roll.

[0029] The dry film has anisotropically formed fibrils. By shearing in the nip, these fibrils are preferably formed anisotropically in the running direction of the first roll and the second roll. The length of the fibrils is in the range of 0.1 μm to 1000 μm. Alternatively or additionally, the dry film with fibrils may have a roughness Ra of less than 10 μm. The dry film is usually disposed on a substrate.

[0030] Preferably, the electrochemical reservoir or electrochemical transducer comprises a dry film having the described properties, or a substrate comprising a dry film and having the described properties.

[0031] Dry-films and substrates provided with dry-films are preferably manufactured according to the described methods, and thus the described methods are adapted to manufacture dry-films and substrates provided with dry-films.

[0032] For production, non-flowable powder mixtures can also be used, the non-flowability of which can be determined under test conditions according to the German standard EN ISO 6186:1998 (as of August 1998). [Brief description of the drawings]

[0033] Exemplary embodiments of the invention are illustrated in the drawings and will now be described with reference to FIGS.

[0034] [Figure 1]FIG. 2 shows a schematic side view of a rotation device. [Diagram 2] FIG. 2 shows a view of a double rotating device corresponding to FIG. 1 . [Diagram 3] 2 shows a diagram of a rolling mill with substrate feeding corresponding to FIG. 1 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] In Fig. 1, a schematic side view of a rolling device is shown, in which a dry powder mixture stored on a powder conveyor 1 passes from the powder conveyor 1 towards two dimensionally identical chrome-plated calenders 2a and 2b, whereby the mixture is transformed into a stable state by the application of pressing and shearing forces, whereby the first calender roll 2a is operated at a higher rotational speed than the second calender roll 2b, so that the formed dry film 3 remains on the first calender roll 2a after the combined pressing and shearing operations.

[0036] In the illustrated exemplary embodiment, the used dry powder is present in a premixed state and consists of 90% by weight of Ketjen Black / Sulfur (1:2 m / m), 3% by weight of Polytetrafluoroethylene (PTFE) and 7% by weight of Multi-walled Carbon Nanotubes (MWCNT). For lithium-ion electrodes, 95% by weight of lithium manganate, 3% by weight of conductive additive (in this case multi-walled carbon nanotubes, MWCNT) and 2% by weight of PTFE are typically used. In the calender nip located between the first roll 2a and the second roll 2b, fibrillation of the dry powder mixture takes place, thereby producing a closed dry film 3.

[0037] The rotation speeds of the first roll 2a and the second roll 2b are in the range of 10:9 to 10:4, in the illustrated exemplary embodiment, about 2:1, i.e. 10 mm / s:5 mm / s or 20 mm / s:10 mm / s. In further exemplary embodiments, depending on the parameter window and the powder conditions, even 80 mm / s:40 mm / s can be used as rotation speeds. Here, higher rotation speeds result in thinner dry films with a more pronounced corrugated structure or fewer fibrils, and thus a lower surface roughness Ra. In the illustrated exemplary embodiment, the fibrils have an average length of 10 μm and are formed anisotropically in the running direction of the rolls 2a and 2b. As a result of the rotation speed, a shear force is applied to the powder in the nip, the latter having a width of 50 μm in the illustrated exemplary embodiment, but which can also be between 10 μm and 300 μm wide, along the running direction, causing fibrillation. This results in mechanical stabilization and film formation on the faster rotating first roll 2a, avoiding the formation of a free-standing film (which can, however, be achieved by mechanical removal from the roll 2a, for example by a doctor blade, if necessary). Instead, a dry film 3 supported on the faster roll 2a is obtained, which is advantageous, especially for dry films with a thickness of less than 200 μm, due to their limited mechanical stability.

[0038] In the illustrated exemplary embodiment, the first roll 2a and the second roll 2b can each be heated to a temperature of 100° C. Furthermore, the first roll 2a can be provided with an adhesion enhancing surface to which the dry film 3 adheres, while the second roll 2b has an adhesion reducing surface for the dry film. In the illustrated exemplary embodiment, the acting linear force between the first roll 2a and the second roll 2b amounts to 400 N.

[0039] Subsequent lamination to a current collector with a thermoplastic primer or binder allows the dry film 3 to be removed from the first roll 2a, thus producing, for example, a solvent-free produced electrode.

[0040] In Fig. 2, in a view corresponding to Fig. 1, an exemplary embodiment is shown in which there is a symmetrical construction of two rotating devices shown in Fig. 1. As in the following figures, there are repeated features in this view, which are given the same reference symbols.

[0041] In the illustrated exemplary embodiment, the substrate 4 is fed between two rotating devices arranged in mirror symmetry with respect to one another. The two first rolls 2a, on which the dry film 3 runs respectively, are opposite each other, with both sides facing one of the rolls, so that the substrate 4 can be provided with a dry film 3 on both sides. For this, the substrate 4 is moved at a speed that corresponds exactly to the peripheral rotational speed of the two first rolls 2a. In the illustrated exemplary embodiment, apart from the mirror symmetry arrangement, the two rotating devices are constructed identically, therefore in particular have equal dimensions and operate at equal rotational or peripheral rotational speeds. In further exemplary embodiments, dry films 3 that differ from one another in terms of composition can also be applied to the substrate 4, but in the exemplary embodiment shown in FIG. 2 the dry films 3 are identical.

[0042] Furthermore, the described method allows for the fabrication of electrodes with alternative current collectors as substrate 4, e.g., perforated substrates with low basis weight, such as perforated metal foils or conductive woven fabrics. In the exemplary embodiment shown in Figure 2, substrate 4 is an aluminum foil with a carbon primer as a double-sided coating.

[0043] Continuous film production of battery electrodes for primary and secondary batteries, e.g. lithium-ion batteries, lithium-sulfur batteries, sodium-sulfur batteries, solid-state batteries, supercap electrodes, electrodes for fuel cells, electrodes for electrolytic cells, electrodes for further electrochemical elements. Filter membranes or adsorptive coatings by the use of porous particles, decorative layers, optical layers for absorption and / or layers of moisture-sensitive or solvent-sensitive materials are also made possible.

[0044] 3 shows, in a schematic side view corresponding to FIG. 1, a further exemplary embodiment of the invention, in which the substrate 4 is wound in the form of a foil on a substrate roll 5 and introduced in the form of a foil into the nip, whereby the formed dry film 3 is directly laminated in the nip to the substrate 4. In this exemplary embodiment, the dry film 3 is no longer in direct contact on the first roll 2a, and thus does not come into contact in direct contact, but only runs indirectly over the first roll 2a and is wound up on the next roll 2a.

[0045] The described method therefore allows the production of electrodes directly from premixed dry film powders, without an additional step for the purpose of fibrillation, so that a free-standing film does not have to be formed either. The method can be used for a prefibrillation, which allows an increase in the mechanical stability of the dry film. Furthermore, the free-standing film can be realized by separation from the carrier roll. The load and density can be set by the circumferential or rotational circumferential speed of the first roll 2a and the second roll 2b and the pressing force acting in the direction of the calendar nip or the nip between the rolls. The dry film formation is realized in a self-dosing manner, the resulting layer thickness originating from the used pressing force of the two rolls 2a and 2b. By the continuous input of a certain (adapted to the process parameters) powder amount, for example via the powder conveyor 1 or the supply substrate, the pre-dosing is realized. In this way, the layer thickness is influenced as well.

[0046] The mechanical stability of the dry film 3 is set by the pressing force and rotation speed (shear rate) used. Given equal rotation speeds of the rolls 2a and 2b, in comparison with a free-standing film simply pressed in the nip, the dry film 3 produced with the proposed method shows a significantly increased mechanical stability.

[0047] Only the features of the various embodiments disclosed in the exemplary embodiments may be combined with each other and claimed separately.

Claims

1. The method for producing the dry film (3) includes the steps of: The dry powder mixture is processed into the dry film (3) by a rolling device having a first roll (2a) and a second roll (2b); Here, the first roll (2a) has a higher rotational peripheral speed than the second roll (2b), and the dry film (3) is attached to the first roll (2a), The ratio of the rotational peripheral speed of the first roll (2a) to the rotational peripheral speed of the second roll (2b) is maintained at 10:5 to 10:

1.

2. 2. The method according to claim 1, wherein the ratio of the peripheral speed of the first roll (2a) to the peripheral speed of the second roll (2b) is maintained at 10:5 to 10:

3.

3. 3. The method according to claim 1, wherein the rolling device is a calender rolling device.

4. 4. The method according to claim 1, wherein a non-flowable powder mixture is used for the production of the dry film.

5. 5. The method according to any one of claims 1 to 4, characterized in that the first roll (2a) is provided with an adhesion-enhancing modification and / or the second roll (2b) is provided with an adhesion-reducing modification.

6. Method according to any one of the preceding claims, characterized in that the dry film (3) is applied to a substrate (4).

7. 6. The method according to claim 5, characterized in that the substrate (4) moves over the first roll (2a) while the dry film (3) is being formed on the substrate (4).

8. The method according to any one of claims 1 to 7, characterized in that the dry film (3) is formed by the first roll (2a) and the second roll (2b) with a linear force of 100 N / cm to 10 kN / cm exerted in the nip between the rolls.

9. Method according to any one of claims 5 to 7, characterized in that a substrate (4) made of a metallic material is used.

10. A method according to any one of claims 5 to 8, characterized in that the substrate (4) is provided with a primer and / or a binder before the dry film (3) is laminated to the respective surface.

11. 10. The method according to claim 5, wherein a substrate (4) is used which consists of expanded metal, a metal wire mesh, a nonwoven fabric, copper foil or aluminium foil coated with a carbon primer.

12. The method according to any one of the preceding claims, characterized in that the dry film (3) is formed with a thickness of less than 500 μm.

13. The method according to any one of claims 1 to 12, characterized in that the dry powder mixture comprises a conductive additive, porous carbon, a transition metal oxide and / or sulfur.

14. Method according to any one of the preceding claims, characterized in that the dry film (3) is formed with anisotropically formed fibrils.

15. Method according to any one of the preceding claims, wherein the structuring of the dry film (3) is achieved by having an adhesion-promoting primer layer on the respective substrate surface area.

16. a dry powder mixture is introduced into a nip between a first calender roll (2a) and a second calender roll (2b), said first calender roll (2a) and said second calender roll (2b) being configured or driven such that said first calender roll (2a) has a higher peripheral speed of rotation than said second calender roll (2b) and said first calender roll (2a) and said second calender roll (2b) have opposite directions of rotation, 16. A rolling mill for carrying out the method according to claim 1, characterized in that the ratio of the peripheral speed of the first calender roll (2a) to the peripheral speed of the second calender roll (2b) is maintained between 10:5 and 10:

1.

17. 17. A rolling mill according to claim 16, characterized in that in addition to the dry powder mixture a substrate (4) is fed through the nip.

18. Two calendar roll pairs, including the first calendar roll (2a) and the second calendar roll (2b), are arranged side by side in a mirror symmetrical manner so that a nip is formed between the two first calendar rolls (2a) and the dry film (3) is provided between the nip, and the dry film (3) is likewise produced on two sides of a substrate (4) fed through the nip; 17. Rolling device according to claim 16, characterized in that the directions of rotation of the two first calender rolls (2a) are opposite.

19. 17. The rolling device according to claim 16, characterized in that there is a further first calender roll rotating about an axis of rotation, on which the dry film formed between the first calender roll and the second calender roll is present and which can be wound up after leaving the nip, the two first calender rolls (2a) having the same peripheral rotation speed.

20. A dry film produced by the method according to any one of claims 1 to 15, characterized in that the fibrils have a length of 0.1 µm to 1000 µm.

21. 21. The dry film of claim 20, characterized in that the dry film (3) is applied to a substrate (4).

22. 22. An electrochemical storage element or electrochemical converter comprising the dry film of claim 20 or 21.

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