METHOD FOR PRODUCING A DRY FILM, ROLLING DEVICE, DRY FILM, AND SUBSTRATE COATED WITH THE DRY FILM

Abstract

The invention relates to a method for producing a dry film (3), wherein a dry powder mixture is processed into the dry film (3) by a rolling device comprising a first roller (2a) and a second roller (2b). The first roller (2a) has a higher circumferential rotational speed than the second roller (2b), and the dry film (3) is placed on the first roller (2a).

Claims

1. A method for producing a dry film (3), in which a dry powder mixture is processed into the dry film (3) by a rolling device having a first roll (2a) and a second roll (2b), wherein the first roll (2a) has a higher rotational peripheral speed than the second roll (2b) and the dry film (3) is mounted on the first roll (2a).

2. The method as claimed in claim 1, characterized in that a ratio of the rotational peripheral speed of the first roll (2a) to the rotational peripheral speed of the second roll (2b) of 10:9 to 10:1, preferably 10:7 to 10:3, particularly preferably 2:1, is maintained.

3. The method as claimed in claim 1, characterized in that the rolling device is a calender rolling device.

4. The method as claimed in claim 1, characterized in that, for the production of a dry film, a non-flowable powder mixture is used.

5. The method as claimed in claim 1, 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. The method as claimed claim 1, characterized in that the dry film (3) is applied to a substrate (4), wherein the substrate (4), for the application, is preferably moved at a speed corresponding to a speed which corresponds to the rotational peripheral speed of the first roll (2a).

7. The method as claimed in claim 5, characterized in that the substrate (4) is moved over the first roll (2a) while the dry film (3) is formed on the substrate (4).

8. The method as claimed in claim 1, characterized in that the dry film (3) is formed by the first roll (2a) and the second roll (2b) with a linear force, acting in the nip between the rolls, of 100 N/cm to 10 kN/cm, preferably 400 N/cm.

9. The method as claimed in claim 5, characterized in that the substrate (4) consisting of a metallic material is used.

10. The method as claimed in claim 5, characterized in that, prior to the lamination of the dry film (3) on a respective surface, the substrate (4) is provided with a, preferably thermoplastic, primer and/or a, preferably thermoplastic, binder.

11. The method as claimed in claim 5, characterized in that the substrate (4) consisting of an expanded metal, a metal wire mesh, a nonwoven fabric, a copper foil or an aluminum foil with an applied carbon primer is used.

12. The method as claimed in claim 1, characterized in that the dry film (3) is formed with a thickness less than 500 μm, preferably less than 300 μm, particularly preferably less than 150 μm.

13. The method as claimed in claim 1, characterized in that a dry powder mixture, which contains polytetrafluoroethylene, a conductive additive, porous carbon, a transition-metal oxide and/or sulfur is used.

14. The method as claimed in claim 1, characterized in that a dry film (3), which has anisotropically formed fibrils, is formed.

15. The method as claimed in claim 1, characterized in that, with an adhesion-enhancing primer layer on respective substrate surface regions for the formation of a structuring of the dry film (3), preferably in the form of strips or in the shape of a rectangle and, particularly preferably, in the direction of coating, is achieved.

16. A rolling device for implementing the method as claimed in claim 1, characterized in that a dry powder mixture is introduced into the nip between a first calender roll (2a) and a second calender roll (2b), and the first and the second calender roll (2a and 2b) are configured or driven such that the first calender roll (2a) has a higher rotational peripheral speed than the second calender roll (2b), and the first and the second calender roll (2a and 2b) respectively have an opposite direction of rotation.

17. The rolling device as claimed in claim 16, characterized in that, in addition to the dry powder mixture, a substrate (4) is fed through the nip.

18. The rolling device as claimed in claim 16, characterized in that two calender roll pairs comprising first and second calender rolls (2a and 2b) are arranged side by side in mirror symmetry such that, between two first calender rolls (2a) is configured a nip, through which dry film (3) is provided on two sides of a substrate (4) which is likewise fed through this nip, and the two first calender rolls (2a) have an opposite direction of rotation.

19. The rolling device as claimed in claim 16, characterized in that a further first calender roll (2a), which rotates about a rotational axis, is present, onto which a dry film formed between the first calender roll (2a) and the second calender roll (2b) can be wound following exit from the nip, and the two first calender rolls (2a) have the same rotational peripheral speed.

20. A dry film produced with a method as claimed in claim 14, characterized in that the fibrils have a length of 0.1 μm to 1000 μm.

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

22. An electrochemical store element or electrochemical converter, which has a dry film as claimed in claim 20.

Description

[0032] Illustrative embodiments of the invention are represented in the drawings and are explained below with reference to FIGS. 1 to 3, wherein:

[0033] FIG. 1 shows a lateral schematic view of a rolling device;

[0034] FIG. 2 shows a view, corresponding to FIG. 1, of a double rolling device, and

[0035] FIG. 3 shows a view, corresponding to FIG. 1, of the rolling device with substrate feed.

[0036] In FIG. 1 is represented in a schematic lateral view a rolling device, in which, from a powder conveyor 1, a dry powder mixture stored in the powder conveyor 1 makes its way onto two, in terms of their dimensions, identical chrome-plated calender rolls 2a and 2b and is transformed by these, by means of acting pressing and shearing forces, into a stable state. The first calender roll 2a is herein operated at a higher rotation speed than the second calender roll 2b, so that a forming dry film 3 remains on the first calender roll 2a after the combined pressing and shearing operation.

[0037] In the represented illustrative embodiment, the used dry powder exists in the premixed state and comprises 90 percent by weight Ketjenblack/sulfur (1:2 m/m), 3 percent by weight polytetrafluoroethylene (PTFE) and 7 percent by weight multi-walled carbon nanotubes (MWCNT). For a lithium ion electrode, 95 percent by weight lithium manganese oxide, 3 percent by weight a conductive additive (in this case multi-walled carbon nanotubes, MWCNT) and 2 percent by weight PTFE is typically used. In a calender nip located between the first roll 2a and the second roll 2b, a fibrillation of the dry powder mixture takes place, whereby the closed dry film 3 is produced.

[0038] The rotation speeds of the first roll 2a and of the second roll 2b lie within a range between 10:9 and 10:4, in the shown illustrative embodiment around 2:1, namely either 10 mm/s:5 mm/s or 20 mm/s:10 mm/s. In further Illustrative embodiments, depending on the parameter window and powder condition, 80 mm/s:40 mm/s can however also be used as the rotation speeds. Higher rotation speeds hereupon result in thinner dry films having a less pronounced corrugated structure or less pronounced fibrils, thus a lower surface roughness R.sub.a. In the shown illustrative embodiment, the fibrils have a length of, on average, 10 μm, and are formed anisotropically in the running direction of the rolls 2a and 2b. As a result of the rotation speeds, to the powder in the nip, which latter, in the represented illustrative embodiment, has a width of 50 μm ima but can also be between 10 μm and 300 μm in width, is applied a shearing force, which produces a fibrillation along the running direction. This results in a mechanical stabilization and film formation on the first roll 2a rotating at higher speed, and the formation of a free-standing film is avoided (where necessary, however, can be achieved by mechanical removal, for instance by means of a doctor blade, from the roll 2a). Instead, a dry film 3 supported on the faster roll 2a is obtained, which is of advantage, especially for dry films having a thickness less than 200 μm, due to the limited mechanical stability.

[0039] In the represented illustrative embodiment, the first roll 2a and the second roll 2b can respectively be heated to a temperature of 100° C. Moreover, 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 a, for the dry film, adhesion-reducing surface. In the represented illustrative embodiment, an acting linear force between the first roll 2a and the second roll 2b amounts to 400 N.

[0040] By subsequent lamination to a current collector provided with thermoplastic primer or binder, the dry film 3 can be removed from the first roll 2a, and thus, for instance, an electrode produced in a solvent-free manner can be generated.

[0041] In FIG. 2 is represented, in a view corresponding to FIG. 1, an illustrative embodiment in which a symmetrical construction made up of two of the rolling devices shown in FIG. 1 exists. Recurring features are in this figure, as also in the following figure, provided with identical reference symbols.

[0042] In the represented illustrative embodiment, the substrate 4 is fed through between two rolling devices, which are arranged in mirror symmetry to one another. The two first rolls 2a, on which respectively one of the dry films 3 is run, are mutually facing, so that the substrate 4 can on both sides be provided with the dry film 3, since both surfaces are respectively facing toward one of the rolls 2a. To this end, the substrate 4 is moved at a speed which precisely corresponds to the rotational peripheral speed of the two first rolls 2a. In the shown illustrative embodiment, the two rolling devices, apart from the mirror-symmetrical arrangement, are identically constructed, thus have, in particular, equal dimensions, and are operated at equal rotation speeds or rotational peripheral speeds. In further Illustrative embodiments, dry films 3 which differ from one another in terms of their composition can also be applied to the substrate 4, yet in the illustrative embodiment represented in FIG. 2 the dry films 3 are identical.

[0043] Moreover, the described method allows the production of an electrode with alternative current collectors as the substrate 4, for example perforated substrates with low basis weight, such as perforated metal foils or conductive fabrics. In the illustrative embodiment shown in FIG. 2, the substrate 4 is an aluminum foil having a carbon primer as the two-sided coating.

[0044] A continuous film production for battery electrodes for primary and secondary batteries, for example 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, but also filter membranes or adsorptive coatings through the use of porous particles, decorative layers, optical layers for absorption and/or layers of moisture-sensitive or solvent-sensitive materials is thus enabled.

[0045] FIG. 3 shows in a schematic lateral view corresponding to FIG. 1 a further illustrative embodiment of the invention, in which the substrate 4 is wound in the form of a foil onto a substrate roller 5 and is introduced in foil form into the nip, so that the forming dry film 3 is laminated directly in the nip to the substrate 4. In this illustrative embodiment, the dry film 3 is no longer mounted directly, thus in directly touching contact, on the first roll 2a, but is run only indirectly on the first roll 2a and wound onto a further roll 2a.

[0046] The described method therefore allows an electrode to be produced directly from a premixed dry film powder without additional steps for fibrillation purposes, so that also no free-standing film has to be formed. The method can be employed for a prefibrillation, in which an enhancement of the mechanical stability of the dry film is possible. Moreover, the free-standing film can be realized by detachment from the carrier roller. By the peripheral speed or the rotational peripheral speeds of the first roll 2a and the second roll 2b and of the pressing force acting in the direction of the calender nip or a nip between rolls, a load and density can be set. The dry film formation is realized in a self-dosing manner, the resulting layer thickness derives from the used pressing force of the two rolls 2a and 2b. Via a continuous input of a specific (process-parameter-adapted) powder quantity, for instance via the powder conveyor 1 or a feed substrate, a pre-dosing is realized. In this way, the layer thickness can likewise be influenced.

[0047] The mechanical stability of the dry film 3 is set by the pressing forces and rotation speeds (shearing rates) which are used. In comparison to free-standing films, which, given equal rotation speeds of the rolls 2a and 2b, have merely been pressed in the nip, the dry films 3 produced with the proposed method exhibit a considerably increased mechanical stability.

[0048] Only those features of the various embodiments which are disclosed in the Illustrative embodiments can be combined with one another and individually claimed.