DRY COATING AND SELF-STANDING LAYERS WITH ALIGNED PARTICLES

Abstract

A method of dry coating of surfaces of a carrier and/or of production of self-standing layers, especially for use in lithium ion batteries having improved properties, is proposed, wherein the coating is effected at least by means of a particle-comprising powder in the dry state, especially having a solvent content of less than 1% by weight, and alignment of the particles is conducted in order to reduce the ionic resistance of the powder layer. The alignment of the particles additionally comprises fluidization of the powder.

Claims

1. A method of dry coating of surfaces of a carrier and/or of production of self-standing layers for use in lithium ion batteries, wherein the coating is effected at least by means of a particle-comprising powder in the dry state, with a solvent content of less than 1% by weight, wherein an alignment of the particles is conducted in order to reduce the ionic resistance of the powder layer, wherein the alignment of the particles comprises fluidization of the powder and/or fluidization is conducted before and/or during the alignment of the particles, which improves the alignability by reducing the mechanical interactions between the particles.

2. The method according to claim 1, wherein the fluidization includes a method step: in which the powder and/or the carrier is subjected to a vibration and/or to a mechanical oscillation, and/or in which the vibration is caused by an ultrasound source, and/or in which an electrical voltage is applied to the powder and/or the carrier, and it is simultaneously subjected to a magnetic field, and/or in which a gas stream is introduced into the powder.

3. The method according to claim 1, wherein the coating of the surface and/or the application of the powder to the carrier is followed by compression of the powder, wherein the compression of the powder is effected by mechanical compression and/or under the action of heat.

4. The method according to claim 1, wherein a binder is added to the powder in order to improve the application to the surface and/or the integrity of the coating.

5. The method according to claim 1, wherein the carrier used is a conveyor belt and/or a film and/or a film transported on a conveyor belt.

6. The method according to claim 1, wherein the ratio of the number of particles that can be seen in a carrier cross section and have an angle between the respective longest particle axis that can be seen in cross section and transport direction of between 60° and 90° to the total number of particles that can be seen is at least 10%.

7. The method according to claim 1, wherein the ratio of the reflectivity of the (004) plane at about 54.7° to the (110) plane at about 77.5°, ascertained by means of x-ray diffraction with copper anode radiation having a wavelength of about 1.54 ångströms in the carrier produced is at least 5.

8. The method according to claim 1, wherein the MacMullin number of the carrier produced is at least 5% less than a comparable electrode having the same composition and same weight by surface area and same thickness that has been produced without the method.

9. A dry coating apparatus for dry coating of surfaces of an electrode as carrier in the production of lithium ion batteries, and for performance of the method according to claim 1, comprising: a transport device comprising a conveyor belt and/or a conveying device as carrier and/or for transport of a film as carrier, a coating device for application of the powder in the dry state, with a solvent content of less than 1% by weight, to the carrier, wherein there is an alignment device for alignment of the particles, in order in particular to reduce the ionic resistance of the powder layer.

10. The dry coating apparatus according to claim 9, wherein the alignment apparatus and/or the transport device is set up for fluidization of the powder in order to reduce the interaction between the particles in the alignment of the particles, and for this purpose comprises: a vibration device and/or an ultrasound source, in order to subject the powder and/or the carrier to vibration and/or mechanical oscillation, and/or a magnet device, in order to subject the powder and/or the carrier to a magnetic field, and an AC current source, in order to apply an AC voltage to the powder, and/or an apparatus for introduction of a gas into the powder.

11. The dry coating apparatus according to claim 10, wherein the transport device and/or at least one storage apparatus of the transport device comprises at least one roller, wherein the at least one roller is/are each designed as an electrode for application of the voltage to the powder layer, and/or at least one roller comprises an outer wall and a magnet device that are respectively mounted as a ring around the axis of rotation of the roller, with the outer wall in particular designed to rotate about the axis of rotation counter to the magnet device, and/or the magnet device is designed as a Halbach cylinder.

12. The dry coating apparatus according to claim 9, wherein a compression apparatus for compression of the layer of powder on the carrier is provided, which comprises: a driven roller by means of which the carrier is guided and/or can be guided, and/or a press belt tensioned such that it pushes the carrier against the roller over a transport zone section, and/or at least two rollers arranged so as to rotate in the opposite sense from the respectively adjacent rollers, in order thus to guide the carrier and/or the powder layer through their interspaces, and/or an apparatus for the generation of heat.

13. A dry coating apparatus for dry coating of surfaces of an electrode as carrier in the production of lithium ion batteries, and for performance of the method according to claim 1.

14. An electrode for the production of lithium ion batteries, obtainable by a method according to claim 1, wherein the ratio of the number of particles that can be seen in an electrode cross section and have an angle between the respective longest particle axis that can be seen in cross section and transport direction of between 60° and 90° to the total number of particles that can be seen is at least 10%.

15. An electrode for the production of lithium ion batteries, obtainable by a method according to claim 1, wherein the MacMullin number of the electrode produced is at least 5% less than a comparable electrode having the same composition and same weight by surface area and same thickness that has been produced without the method.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Working examples of the present invention are presented in the drawings and are elucidated in detail below with reference to further details and advantages. The figures specifically show:

[0053] FIG. 1 is a dry coating apparatus according to the present invention with magnet device within the storage roller;

[0054] FIG. 2 is a dry coating apparatus according to the present invention with magnet device within the conveying device;

[0055] FIG. 3 is a dry coating apparatus according to the present invention with a combination of vibration device and magnet device;

[0056] FIG. 4 is a dry coating apparatus according to the present invention with introduction of a gas into the powder layer;

[0057] FIG. 5 is a dry coating apparatus according to the present invention with ultrasound exposure;

[0058] FIG. 6 is a dry coating apparatus according to the present invention with a series of storage rollers;

[0059] FIG. 7 is a dry coating apparatus according to the present invention with compression of the powder layer; and

[0060] FIG. 8 is a schematic detail of a guide within a dry coating apparatus according to the present invention in the region of the alignment and fluidization via a Lorentz force.

DETAILED DESCRIPTION OF THE INVENTION

[0061] FIG. 1 shows a dry coating apparatus 1 with a conveying device 2a which is designed here as a slide and via which the powder P, which constitutes an accumulation of particles, is conveyed in transport direction T in the direction of two counter-rotating rollers 2b, 2c. The outer wall 2f of the roller 2b rotates with rotational speed ω and in the opposite sense to the roller 2c with rotational speed ψ. The powder P accumulates in the region in which the two rollers 2b, 2c, or the outer surface thereof, are close to one another. At the point exactly between the rollers 2b, 2c, and at which the rollers have the lowest separation, the instantaneous belt speed vectors each point in exactly the same direction T (downward in FIG. 1). The powder P is compressed there to give a self-standing layer, the electrode E to be manufactured. Within the roller 2b, concentrically relative to the outer ring 2f, is mounted a magnet device 3 as alignment apparatus, which rotates with speed of rotation χ in the same direction as roller 2c, i.e. in the opposite sense to the outer ring 2f. The magnet device 3 generates a magnetic alternating field in that the magnet ring 3 takes the form of an outward-facing Halbach cylinder, i.e. generates a strong magnetic field at the surface of the outer ring 2f and a temporally and locally varying field with the rotation of the magnet ring 3.

[0062] FIG. 2 shows a dry coating apparatus 1 of similar construction to that in FIG. 1, except that the alignment apparatus 3 is not integrated into one of the rollers 2b, 2c, which always rotate in opposite senses, but into the conveying device 2a. The magnet device 3 may also take the form of a Halbach array in order to generate a locally varying field. In this embodiment, the alignment force is low where the rollers 2b, 2c approach one another. It is, therefore, to be expected that the degree of alignment in this embodiment will be somewhat lower if anything.

[0063] In FIG. 3, in turn, a combination of alignment apparatuses is used. Firstly, provided is a conveying device 2a (chute), via which the powder P moves in the direction of the counter-rotating rollers 2b, 2c. The powder P is compressed at the rollers 2b, 2c to give the self-standing electrode E without carrier.

[0064] In the conveying device 2a, the magnet device 3 in the form of a Halbach array generates a locally varying field with which particles in the powder P can be aligned while they are moving through the conveying device 2a.

[0065] For assistance of alignment, the powder P is fluidized in that a vibration device 3a is already coupled to the conveying device 2a, in order to set the conveying device 2a in a mechanical oscillation. The interactions between the particles become smaller, and these can additionally be oriented more easily via the magnet device 3 (as Halbach array).

[0066] For additional assistance of the alignment and fluidization, a further vibration device 3b is coupled mechanically to the roller 2b. This agitation effect which is caused by the roller 2b assists both the flow of the powder B and alignment.

[0067] The fluidization may, as described above, also be achieved by means of a gas which is introduced into the powder P. Such a design is shown in FIG. 4. The basic construction with conveying chute 2a and two counter-rotating rollers 2b, 2c is in principle the same as described in the designs above. An alignment apparatus in the form of a magnet 3 is integrated into the conveying device 2a. Both in the region of the conveying device 2a and in the region of the rollers 2b, 2c, the surfaces that come into contact with the powder are formed from a porous material. From the side remote from the powder P, a gas is introduced onto this porous surface, and is let through by the surface specifically because of its porous structure and ultimately penetrates into the powder layer P. This powder layer P is fluidized and improves the flow characteristics thereof, which assists the alignment of the particles.

[0068] Another means of transmitting a mechanical vibration to the carrier or powder layer is shown in FIG. 5. The carrier 4 is guided over the base B by means of a gas bearing 2e on an air cushion. Beneath the gas bearing 2e is disposed a magnet device 3 for alignment of the particles. The powder P applied to the carrier 4 is fluidized by means of an ultrasound source 3e that transmits the sound waves that it has emitted through the air onto the powder P or the carrier 4.

[0069] In the manufacture of the electrode E, for better control, particularly of the thickness of the electrode E, it is possible to provide a system of rollers 2b, 2c, 2d in series, as described in FIG. 6. Here too, the powder is compressed between the rollers 2b, 2c, and 2d. The gap between the rollers 2c, 2d is smaller than the gap between the rollers 2b, 2c, in order to be able to compress the layer more significantly and hence to make it thinner. The alignment of the particles is accomplished by means of a magnet device 3, which may likewise take the form of a Halbach array.

[0070] In FIG. 7, a revolving conveyor belt 4 is utilized, which is guided over the rollers 2b, 2c, 2d. The coating device 5 applies the powder P or the particles to the carrier belt 4. The coated carrier 4 runs over a gas bearing 2e which, toward the carrier 4, has a layer of porous material through which a gas/air flows out and forms an air cushion between carrier 4 and gas bearing 2e. Below the porous layer 2e is mounted a magnet device 3 (e.g. Halbach array), in order to act on the coating/the powder P. A further magnet device 3 (for example, in the form of a Halbach cylinder) is integrated into the roller 2b. The cylindrical magnet device 3 is in a coaxial arrangement with respect to the outer ring 2f. The two of these rotate in opposite senses. During the action of the cylindrical magnet device 3, the powder coating P is compressed by means of a press belt 6 which is run in a revolving manner on rollers 6a. For this purpose, the press belt 6 is pulled under tension against the coating P or against the carrier 4. In the region of the roller 2c, the electrode E can be detached in the region of an inflection in the transport pathway T.

[0071] A further principle of fluidization is shown in schematic form in FIG. 8. A carrier 4 runs in transport direction T over two rollers 2b, 2c. The roller 2c is disposed on the on the opposite side in relation to the carrier 4 and the coating P and compresses the layer P. Between the rollers 2b, 2c is disposed a gas bearing 2e, i.e. the carrier 4 runs on an air cushion in this region. Beneath the gas bearing 2e is provided a magnet device 3, and the carrier 4 with the coating P (powder) applied thereto is exposed to the magnetic field therefrom. In addition, a voltage is applied to the coating P, which leads to a flow of current. A force acting on the particles in the coating P that leads to fluidization and assists the alignment of the particles is brought about by the resulting Lorentz force. The rollers 2b, 2c are electrically conductive in that, for example, the surface thereof that comes into contact with the carrier 4 is electrically conductive. The carrier 4 may likewise be electrically conductive; for example, in the present case, it may typically be a copper foil for production of electrodes of lithium ion batteries. The roller 2c is in contact with the coating P, such that current flows not only through the carrier 4/the copper foil.

[0072] Common factors in all working examples and developments of the present invention are that: [0073] in the dry coating, an alignment of the particles is additionally conducted, for example, in order to reduce the ionic resistance of the powder layer in the case of a graphite coating for electrodes of a lithium ion battery. In an advantageous manner, the alignment of the particles can be assisted by fluidization of the powder, in that the interaction between the particles is reduced in the alignment of the particles, and [0074] the alignment of the particles comprises fluidization of the powder (P) and/or fluidization is conducted before and/or during the alignment of the particles, which improves alignability, especially by reducing the mechanical interactions between the particles.

LIST OF REFERENCE NUMERALS

[0075] 1 dry coating apparatus [0076] 2a conveying device [0077] 2b, 2c, 2d roller [0078] 2e gas bearing [0079] 2f outer ring [0080] 3 magnet device [0081] 3a, 3b vibration device [0082] 3c, 3d porous material for introduction of gas [0083] 3e sound source [0084] 4 carrier [0085] 5 coating device [0086] 6 press belt [0087] 6a roller for press belt storage [0088] B floor [0089] E electrode [0090] P powder [0091] transport direction [0092] U (AC) voltage source [0093] ω speed of rotation [0094] ψ speed of rotation [0095] χ speed of rotation