Method and apparatus for applying magnetic fields to an article

Abstract

Processes for applying magnetic fields to articles such as a layer or layer-coated articles, and more particularly to coatings having graphite particles, preferably for manufacture of negative electrodes having aligned graphite particles, for example for fast-charging lithium-ion batteries. The application of magnetic fields may be continuous. For this, magnetic tools with permanent magnets may be used for applying magnetic fields, wherein an article is moved relative to a magnetic tool. Application of magnetic field is made before the initiation of a drying phase and/or during a drying phase.

Claims

1. A method for producing an electrode for a lithium-ion battery, the method comprising the steps of: coating a homogeneous layer of a slurry mixture including flake graphite particles, deionized water as volatile liquid, a binder mix that includes carboxymethylcellulose and styrene-butadiene rubber (SBR) latex binder, and a thermoresponsive constituent that has mass fraction in the range of 0.1% to 0.4% by weight over a metallic surface of a current collector foil to produce coated current collector foil: transporting the coated current collector foil as transported, coated current collector foil on a production path; subjecting the transported, coated current collector foil to a continuously applied time-varying magnetic field to produce, in the layer of slurry mixture, controlled alignment of the Hake graphite particles on their vertical axes; and continuing to subject the transported, coated current collector foil to a magnetic field to maintain alignment of the flake graphite particles while simultaneously heating the transported, coated current collector foil to induce solidification and drying of the layer of slurry mixture to (a) preserve the alignment of the flake graphite particles and (b) prevent SBR latex binder migration.

2. The method for producing an electrode for a lithium-ion battery as claimed in claim 1, wherein: said step of subjecting the transported, coated current collector foil to a continuously applied time-varying magnetic field to produce, in the layer of slurry mixture, controlled alignment of the flake graphite particles on their vertical axes utilizes magnetic field flux density in the range of 0.1 to 0.5 T.

3. The method for producing an electrode for a lithium-ion battery as claimed in claim 1, wherein: said step of coating a homogeneous layer of a slurry mixture including flake graphite particles, deionized water as volatile liquid, a binder mix that includes carboxymethylcellulose and SBR latex binder, and a thermoresponsive constituent that has mass fraction in the range of 0.1% to 0.4% by weight over a metallic surface of a current collector foil to produce coated current collector foil utilizes a thermoresponsive constituent including at least one of either substituted or unsubstituted anhydroglucose rings.

4. The method for producing an electrode for a lithium-ion battery as claimed in claim 1, wherein: said step of coating a homogeneous layer of a slurry mixture including flake graphite particles, deionized water as volatile liquid, a binder mix that includes carboxymethylcellulose and SBR latex binder, and a thermoresponsive constituent that has mass fraction in the range of 0.1% to 0.4% by weight over a metallic surface of a current collector foil to produce coated current collector foil employs at least one thermoresponsive constituent selected from the group of thermoresponsive constituents consisting of methylcellulose, hydroxypropylcellulose, and Poly(N-Isopropylacrylamide).

5. The method for producing an electrode for a lithium-ion battery as claimed in claim 1, wherein: said step of coating a homogeneous layer of a slurry mixture including flake graphite particles, deionized water as volatile liquid, a binder mix that includes carboxymethylcellulose and SBR latex binder, and a thermoresponsive constituent that has mass fraction in the range of 0.1% to 0.4% by weight over a metallic surface of a current collector foil to produce coated current collector foil provides the homogeneous layer as a layer exhibiting a Lower Critical Solution Temperature (LCST) in the range of 30° C. to 60° C.

6. The method for producing an electrode for a lithium-ion battery as claimed in claim 1, wherein: said step of continuing to subject the transported, coated current collector foil to a magnetic field to maintain alignment of the flake graphite particles while simultaneously heating the transported, coated current collector foil to induce solidification and drying of the layer of slurry mixture to (a) preserve the alignment of the flake graphite particles and (b) prevent SBR latex binder migration removes less than 50% of the volatile liquid water.

7. The method for producing an electrode for a lithium-ion battery as claimed in claim 6, wherein: said step of continuing to subject the transported, coated current collector foil to a magnetic field to maintain alignment of the flake graphite particles while simultaneously heating the transported, coated current collector foil to induce solidification and drying of the layer of slurry mixture to (a) preserve the alignment of the flake graphite particles and (b) prevent SBR latex binder migration removes less than 10% of the volatile liquid water.

8. The method for producing an electrode for a lithium-ion battery as claimed in claim 1, wherein: said step of subjecting the transported, coated current collector foil to a continuously applied time-varying magnetic field to produce, in the layer of slurry mixture, controlled alignment of the flake graphite particles on their vertical axes includes subjecting the transported, coated current collector foil to a rotating magnetic field.

9. The method for producing an electrode for a lithium-ion battery as claimed in claim 1, wherein: said step of subjecting the transported, coated current collector foil to a continuously applied time-varying magnetic field to produce, in the layer of slurry mixture, controlled alignment of the flake graphite particles on their vertical axes includes moving the current collector foil in a direction parallel to a tangent to a surface of a magnetic tool.

10. The method for producing an electrode for a lithium-ion battery as claimed in claim 1, wherein: said step of continuing to subject the transported, coated current collector foil to a magnetic field to maintain alignment of the flake graphite particles while simultaneously heating the transported, coated current collector foil to induce solidification and drying of the layer of slurry mixture to (a) preserve the alignment of the flake graphite particles and (b) prevent SBR latex binder migration includes heating with IR-heaters.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples will be further described below in two embodiments with reference to drawings. The drawings show:

(2) FIG. 1: general depiction for the method using a magnetic tool;

(3) FIG. 2: method using a planar-surface magnetic tool according to the present disclosure;

(4) FIG. 3: method using a magnetic tool having curved surface;

(5) FIG. 4: method using a magnetic tool formed as a rotatable roller;

(6) FIG. 5: method using a magnetic tool formed as a rotatable roller with wrapping of the article;

(7) FIG. 6: magnetic tool with magnetic surface and magnetic orientation directions;

(8) FIG. 7: examples of structure of a magnetic tool with planar surface;

(9) FIG. 8: examples of structure of a magnetic tool with cylindrical surface;

(10) FIG. 9: embodiments of magnet arrangement according to the present disclosure;

(11) FIG. 10: a scanning electron microscope micrograph at cross-section of a graphite coating manufactured without the use of a changing magnetic field;

(12) FIG. 11: a histogram of the orientation of layer planes in the cross-section of graphite coating manufactured without the application of a changing magnetic field;

(13) FIG. 12: a scanning electron microscope micrograph at cross-section of a graphite coating manufactured based on a changing magnetic field;

(14) FIG. 13: a histogram of the orientation of layer planes in the cross-section of graphite coating manufactured with the application of a changing magnetic field.

DETAILED DESCRIPTION

Example 1 (Coating with Halbach Array and without Thermoresponsive Constituent)

(15) 97 g of flake-shaped graphite are kneaded with 25 g of carboxymethylcellulose (CMC) solution (2% by weight) and 41 g of deionized water for 1 hour, and subsequently diluted by stirring with another 25 g of CMC Solution (2% by weight) and 30 g deionized water. Afterwards 5 g of a SBR latex (40% by weight) is introduced to this mixture and stirred for 2 minutes.

(16) The so-obtained graphite paste is then applied with a doctor blade as a fluid film onto a current collector foil 025 (copper foil 15 μm), that was previously clamped between two rubber rollers that are not depicted. Subsequently, both of these rubber rollers are brought to rotation by means of an electric motor, so that the current collector foil 025 moves with the coating thereon, in the present example at a speed of 3 m/min, in the direction of movement 045 (see for example FIG. 1).

(17) Thereupon, a magnetic tool having a magnetic surface 013 and in the form of a rigid, planar magnetic tool 010 comprising a package having a plurality of permanent magnets 075 (FIG. 7) in a Halbach array arrangement is directed to the article 020, in this example below the moving article 020.

(18) A distance 071 is provided between the magnetic tool 010 and the article 020. The magnetic field of the tool 010 has a side with strong magnet field 072 and a side with weak magnet field 073. FIG. 7 furthermore shows a permanent magnet 074 with continuously changing magnetization. The strong magnetic field 072 is always preferably facing the article 020.

(19) The magnetic field of the tool 010 acts on the moving, coated current collector foil 025, which in this example represents the moving article 020. The relative movement between the moving article 020 (the coated current collector foil 025) and the magnetic tool 010 generates a time-varying magnetic field in the article 020, which leads to the vertical alignment of the graphite particles.

(20) Afterwards, hot air 030 is blown with hot air guns onto the current collector foil 025, which is moving together with the liquid graphite coating, and in this manner, the graphite coating is brought to dryness. By this, the volatile constituent (water) is removed, and the vertically aligned graphite particles are immobilized.

Example 2 (Coating with Halbach Array and Thermoresponsive Gelification)

(21) 97 g flake-shaped graphite is kneaded with 7.5 g of carboxymethylcellulose (CMC) solution (2% by weight), 23.3 g of a methylcellulose (MC) solution (1.5% by weight, thermoresponsive constituent) and 34.7 g deionized water for 1 h, and subsequently diluted by stirring with another 7.5 g of carboxymethylcellulose (CMC) solution (2% by weight), 23.3 g of a methylcellulose (MC) solution (1.5% by weight) and 10 g of deionized water.

(22) Afterwards 5 g of a SBR latex (40% by weight) is introduced to this mixture and stirred for 2 minutes.

(23) The so-obtained graphite paste is then coated with a doctor blade as a fluid film in a thickness of 200 μm on a current collector foil 025 (copper foil 15 μm) that was previously clamped between two rubber rollers that are not depicted. Subsequently, both of these two rubber rollers are brought to rotation by means of an electric motor, so that the current collector foil 025 moves with the coating thereon, in the present example at a speed of 3 m/min, in the direction of movement 045 (see for example FIG. 1).

(24) Thereafter, a magnetic tool having a magnetic surface 013 and in the form of a rigid, planar magnetic tool 010 comprising a package having a plurality of permanent magnets 075 (FIG. 7) in the arrangement of a Halbach array is directed to the object 020, in this example below the moving, coated current collector foil 025. A distance 071 is provided between the magnetic tool 010 and the article 020. The magnetic field of the tool 010 has a side with strong magnet field 072 and a side with weak magnet field 073. FIGS. 7 and 8 furthermore show a permanent magnet 074 with continuously changing magnetization. The strong magnetic field 072 is always preferably facing the object 020.

(25) The magnetic field of the tool 010 acts on the moving, coated current collector foil 025, which in this example also represents the moving article 020. The relative motion between the moving article 020 (the coated current collector foil 025) and the magnetic tool 010 creates a time-varying magnetic field in the article 020 which leads to the vertical alignment of the graphite particles.

(26) In following, heat is applied to the moving coated current collector foil 025 by means of IR radiant heaters. The action of heat causes gelification of the coating. Thereafter, the magnetic tool 010 below the current collector foil 025 is removed and hot air 030 is blown with hot air guns onto the coating, and in this manner, the graphite coating is brought to dryness (FIG. 1).

(27) Examples with a cylindrical magnetic tool 011 are shown in FIGS. 4, 5, and 8. This tool 011 in turn has a magnetic surface 013 and a rotating roller 012. The article 020 wraps around the tool 011 with a defined wrapping angle 022 of, for example 160°.

(28) The permanent magnets 075 may be formed as segments 078 and/or be arranged perpendicular to or at an angle 077 to the axis of rotation.

(29) FIG. 10 shows a scanning electron microscope micrograph of a cross section of a graphite coating with flake-form graphite obtained without exposure to a magnetic field. The flaky graphite particles lie parallel to the underlying current collector foil 025.

(30) FIG. 11 shows a histogram of the alignment distribution of the graphite particles in a graphite coating obtained without the action of a magnetic field.

(31) FIG. 13 shows a histogram of the alignment distribution of the graphite particles in a graphite coating obtained by the example-described method in a magnetic field. The flaky graphite particles in their majority lie vertically (at 90° angle) to the underlying copper foil, the current collector foil 025.

(32) A scanning electron microscope micrograph of a cross section of the obtained graphite coating of the example shows the vertical alignment of the flake-shaped graphite particles in FIG. 12. Depicted is a scanning electron micrograph of a cross section of an aligned graphite coating with flake-form graphite obtained in a magnetic field by a method described in the examples.

(33) The flaky graphite particles in their majority stand vertical (at 90° angle) to the underlying copper foil, the current collector foil 025.

(34) The analysis of the coating by means of an X-ray diffraction instrument (Rigaku Smart Lab®) shows in FIG. 11 a significantly increased amount of graphite particles whose (110)-plane, the plane which is parallel to the graphene sheets of the graphite particles, are aligned vertically, that is 90°, to the current collector foil 025, in comparison to a graphite coating which is not exposed to a rotating magnetic field (FIG. 13).

(35) The obtained graphite coating with the vertically aligned flake-shaped particles contained therein is subsequently calendered to a porosity of 30%.

(36) Further subsequent analysis of the compressed graphite coating by means of an X-ray diffraction instrument (Rigaku Smart Lab®) yields a furthermore, significantly increased intensity for graphite particles whose (110)-plane, that is the plane which is parallel to the graphene layers of the graphite particles, is aligned vertically to the current collector foil 025.

LIST OF REFERENCE LABELS

(37) 010 magnetic tool 011 cylindrical magnetic tool 012 (fixed) center, around which a rotatable cylinder moves 013 magnetic surface of the magnetic tool 020 moved article upon which the magnetic field acts 022 contact arc/wrap angle 025 current collecting foil 030 External effect, for example warm air, light radiation, X-radiation/X-rays 045 direction of movement of article 071 separation distance between magnetic tool and article 072 strong magnetic field 073 weak magnetic field 074 permanent magnet with continuously varying magnetization 075 permanent magnet 077 angle 078 permanent magnetic segment