阅读说明：本技术 用于涂层的生产的方法 (Method for the production of coatings ) 是由 M·科雷 于 2019-02-11 设计创作，主要内容包括：本发明涉及一种用于涂层的生产的方法,其特别适用于电极的制造,并且更特别地适用于锂离子电池中使用的电极的制造。一种用于由包含固体颗粒和热响应性组分的热响应性糊状物生产涂层的方法,所述涂层或层被涂覆到载体上、固化并干燥,其特征在于,在固化期间,从所述涂层除去少于80％的挥发性溶剂组分。(The present invention relates to a method for the production of a coating, which is particularly suitable for the manufacture of electrodes, and more particularly for the manufacture of electrodes used in lithium ion batteries. A method for producing a coating from a thermally responsive paste comprising solid particles and a thermally responsive component, said coating or layer being applied to a carrier, cured and dried, characterized in that during curing less than 80% of the volatile solvent component is removed from the coating.)

1. A method of producing a coating from a thermally responsive paste comprising solid particles and a thermally responsive component, said coating or layer being applied to a carrier, cured and dried, characterised in that during curing less than 80% of the volatile solvent component is removed from the coating.

2. Method according to claim 1, characterized in that the paste comprises magnetically sensitive components, in particular magnetically sensitive particles, preferably magnetically sensitive carbon particles, and particularly preferably magnetically sensitive graphite particles.

3. Method according to claim 1 or 2, characterized in that the paste used for layer formation is applied on the component, cured and dried.

4. A method for producing a coating from a thermally responsive paste (TR), characterized in that an additive comprising a thermally responsive component is added to the paste after adding an SBR binder to the paste.

5. A device for curing a coating comprising a thermo-responsive component in a continuous process, wherein the device has a coating nozzle (010), characterized in that the device comprises a batter curing device (060) arranged downstream of the coating nozzle (010) and before a dryer (020) and having at least one heating element (040) and a magnetic field device (50).

6. The device according to claim 5, characterized in that the heating element (40) has a heated blower, a heated roller, an infrared radiation heater, a heated LED, an induction heating device, a microwave device or a combination thereof.

7. An additive for addition to a paste, characterized in that:

it comprises a heat-responsive component (A), or

It comprises a thermally responsive component (A) and an antifoaming agent (B).

8. The additive according to claim 7, wherein the thermo-responsive component (A) comprises substituted and/or unsubstituted anhydroglucose rings.

9. Additive according to claims 7 and 8, characterized in that the antifoam (B) is silicone-based.

10. Additive according to one of claims 7 to 9, characterized in that the ratio between thermally responsive component (a) and antifoam (B) is 1: 0.001 to 0.01: 1.

11. additive according to one of claims 7 to 10, characterized in that it is contained in a paste for manufacturing electrodes.

12. A thermally responsive paste comprising solid particles, preferably graphite particles, and a thermally responsive component, wherein the thermally responsive component comprises substituted and/or unsubstituted anhydroglucose rings.

13. A thermally responsive paste according to claim 12, characterised in that it comprises an antifoaming agent (B).

14. A thermally responsive paste according to claim 12 or 13, characterised in that it is used for the manufacture of electrodes.

15. An electrode, characterized in that it is made of a thermoresponsive paste (TR).

16. The electrode of claim 15, comprising vertically aligned graphite particles.

Technical Field

The present invention relates to a coating production method which is particularly suitable for the manufacture of electrodes, and further particularly suitable for the manufacture of electrodes used in lithium ion batteries.

Background

Pastes, in particular pastes composed of carbon-based materials, in particular graphite, or especially pastes containing metal oxide particles, are used for the production of battery electrodes.

To make the negative electrode, carboxymethyl cellulose (CMC) was mixed with an aqueous suspension of graphite particles, and then a styrene-butadiene rubber latex binder (SBR-binder) was added. CMC has two functions. As surface modifier, on the one hand, it ensures that the graphite particles can be well dispersed in water, and on the other hand, it acts as a rheology modifier. In this second role, the CMC chains ensure that the resulting suspension forms a stable viscous paste with little precipitation, while having a sufficiently low viscosity at high shear rates to ensure bubble-free application to the carrier foil through the slit nozzle.

The SBR binder ensures that the applied coating adheres to the carrier foil and that the coating has sufficient elasticity.

Depending on the shape of the graphite particles used herein, various solids contents can be obtained in the paste. Spherical particles generally can produce higher solids content. Generally, a high solids percentage is of concern because it can dry faster and is more energy efficient.

To increase the charge and discharge rates of lithium ion batteries, the graphite particles of the negative electrode may be aligned during the manufacture of the negative electrode. In this process, an adhesive layer is first applied to the foil carrier (copper foil) and then the graphite particles in the paste are vertically aligned to the foil carrier. Subsequent drying results in a negative electrode with vertically aligned graphite particles.

In conventional manufacturing of negative electrodes applied to lithium batteries, undesirable migration of the SBR binder occurs during drying of the wet coating. Especially if the applied paste is dried rapidly, i.e. at high temperature and strong air flow, the SBR binder particles will migrate to the surface of the coating (Langmuir, 2013, 29(26), page 8233-8244). This process may occur due to convection of the solvent (in this case water). Thus, in the finished dried electrode, this results in a lack of SBR binder at the interface between the copper foil and the graphite coating. This may result in poor adhesion of the coating on the foil carrier. This can adversely impair the electrochemical performance of the lithium ion battery thus manufactured. Therefore, to avoid binder migration in wet coatings, mild drying conditions of low temperature and low air flow are mostly used in industry. However, this leads to an undesirable slowing down of the electrode manufacturing process.

Some pastes for coating contain non-spherical particles. Pastes containing anisotropic particle shapes can generally only reach a low solids content. Pastes with flake-like particles (such as, for example, non-round flake-shaped graphite) represent examples of such cases. With these pastes, a low solids content can lead to significant convection currents which carry away particles inside the coating during drying. This process can result in coating weight per unit area of the coating being non-uniform. Furthermore, in the case of low coating weights per unit area, the drying process can also lead to cracking of the coating. In this case, the production of rapidly charging and discharging lithium ion batteries with vertically (i.e., orthogonal to the current collector foil) aligned graphite particles in sheet form presents particular challenges. Pastes used for this purpose generally contain a low solids content due to the platy sheet form of the particles. The vertical alignment of the graphite particles also facilitates crack formation. Furthermore, the vertical alignment of the particles may lead to stronger convection during drying, thereby increasing the adhesive migration, which may lead to poor adhesion of the coating to the foil carrier. Strong convection currents can also lead to loss of vertical alignment of the graphite particles during drying. Also, the strong airflow from the dryer can adversely affect the vertical alignment of the pellets.

Another problem in the manufacture of negative electrodes for use in lithium batteries is the irregularity in coating weight per unit area near the edges of the coating, particularly the discontinuous coating.

Irregularities in the coating weight per unit area can lead to undesired deposition of lithium on the electrode (compared to the desired intercalation into the electrode particles), especially if the coating weight per unit area is not sufficiently high. As a result of this deposition, a reduction in the lifetime and dendritic growth of the deposited lithium can result, which can lead to short circuits of the battery with dangerous consequences.

To address this problem, the coating edges resulting from the manufacture of the electrodes are typically cut off, wrapped with kapton tape (tape), or subsequently modified by ablation. This is cumbersome and represents an additional extra expense in the manufacture of the electrodes.

Disclosure of Invention

It is therefore a main object of the present invention to develop a simple method for producing coatings or layers, which can be used in particular for producing electrodes, and more particularly for producing electrodes for lithium ion batteries.

This object is achieved by the features of claim 1.

According to the invention, in order to produce a coating from a thermally responsive paste comprising solid particles and a thermally responsive component, the coating or layer is coated on a carrier, cured and dried. Here, at least 0.001% and less than 80% of the volatile components are removed from the coating during curing. The volatile component in which the solid particles are suspended is a solvent, such as water.

Advantageous embodiments of the invention are disclosed in the dependent claims.

A further sub-task of the present invention is to develop a curing additive that can be added to the paste to impart curing properties thereto. Furthermore, especially for use in the production of lithium ion batteries, paste formulations and their production will be developed.

In addition, an electrode produced with the aid of this paste will be developed.

The method according to the invention makes it possible to convert a conventional paste into a thermally responsive paste, with which a better coating can be obtained. According to the invention, this can be achieved by adding a heat-responsive additive to a conventionally produced paste, i.e. a paste which does not contain curing ingredients.

The present invention enables a coating comprising solid particles to dry more quickly because it inhibits binder migration due to the curing/heat-responsive nature of the paste.

Furthermore, the present invention enables the coating weight per unit area to be made uniform, due to the curing (i.e. reinforcing) properties, even in the case of coatings made from pastes containing a low percentage of solids.

Furthermore, the present invention is capable of fixing the aligned particles due to the curing (i.e. reinforcing) properties, and in this way, preventing the orientation of the particles from being adversely affected during drying. In addition, the invention described herein improves the uniformity of coating weight per unit area near the edge of the coating due to the curing (i.e., reinforcing) characteristics.

Drawings

The invention is described below by means of several exemplary embodiments and with reference to the accompanying drawings. Shown in the drawings are:

FIG. 1: temperature-viscosity diagram, and

FIG. 2: construction of the apparatus for curing of the paste.

Detailed Description

Fig. 1 shows a graph showing a temperature-viscosity relationship in the case of the conventional paste KP, and also showing a temperature-viscosity relationship in the case of the thermally responsive paste TR. The viscosity of the respective pastes was measured using a Brookfield rheometer (spindle size 4 at 5 rpm). When the conventional paste KP becomes less viscous with an increase in temperature, the viscosity of the thermally responsive paste TR increases.

During the drying phase of a coating with a paste containing solid particles, convection currents occur within the coating. The particles from the SBR binder can be transported to the coating surface by such a flow transport, which occurs particularly strongly in the case of a fast drying process with high temperature and high gas flow. This process may occur due to convection of the solvent (in this case water). Thus, in the finished dried electrode, this results in a lack of SBR binder at the interface between the copper foil and the graphite coating. This can result in poor adhesion of the coating on the foil carrier 030 (fig. 2), which can adversely impair the electrochemical performance of the lithium ion battery so fabricated.

By the present invention, this problem can be solved by applying a curing/gelling component (component), such as a thermo-responsive component, which is included in the paste to be coated. Under the action of heat, the component(s), such as methylcellulose, cure the applied wet coating/layer without simultaneous removal of volatile components. Here, LCST (lowering of critical solution temperature) plays an important role. In the case of polymers containing substituted and unsubstituted anhydroglucose rings (such as, for example, methylcellulose or hydroxypropylcellulose), LCST is generally observed; or in the case where a polymer such as poly (N-isopropylacrylamides) is a component of the mixture, LCST is generally observed. At the same time, the transition of the polymer chains from the open-coil conformation to the compact conformation can be observed. Above the LCST, there is a miscible gap that can lead to curing of the coating/layer. In this process, the heat required to reach above the LCST may come from a heating element 040 (fig. 2), such as for example a heated blower, a heated (cylindrical) roller, an infrared radiant heater, a heated LED, a microwave device, an induction heating device or a combination thereof. In this example, respective heating elements 040 are arranged above and below the foil carrier 030.

Even a small weight percentage of the thermally responsive component, such as for example 0.25% by weight in the layer to be coated (corresponding to 0.5% by weight in the resulting dry coating in case the solids content is 50% by weight of the layer to be coated), is sufficient to cause curing of the paste when the temperature is raised above the LCST.

The increased viscosity in the coating results in a reduction of the flow transmission of the SBR binder particles during drying. In this way, a reduced concentration of SBR binder particles does not occur at the interface with the coated carrier foil. This allows good adhesion of the coating even when dried rapidly (high temperature, strong airflow). This means an acceleration of the electrode manufacturing process compared to conventional drying under milder conditions.

Coatings made of pastes with a low solids percentage present another problem, since here too, strong transport flows occur during the drying phase. In this process, the strong transport flow results in an uneven coating weight per unit area (see table 1, electrode type 3). By using a curing/gelling component, such as for example a thermally responsive component contained in the paste to be coated, the transport flow is reduced.

Table 1:

table 1 shows the effect of the thermally responsive component a in the paste on the porosity and uniformity of the electrodes made therefrom. For this purpose, three samples were punched out of the electrode and characterized for coating weight per unit area and thickness. Electrodes made from the thermally responsive paste exhibit higher porosity/lower density. Electrodes produced with the low percent solids thermally responsive paste TR exhibit a more uniform coating weight per unit area than electrodes produced with the low percent solids conventional paste KP.

The increased porosity and uniform coating weight per unit area of the electrode manufactured with the thermally responsive paste TR indicate that the particles contained in the paste are fixed by the thermally responsive component a.

In the case of coatings with aligned particles, the use of a cured paste is also advantageous. Drying processes performed after aligning the particles in the field may lead to undesirable changes in the orientation of the aligned particles during the process. In particular, air drying in an oven by means of a blower has a significant influence on the orientation of the aligned particles, in particular because the vertical alignment of the graphite particles, which is produced by the action of the magnetic field (magnetic field means 050), can be influenced during drying in the dryer 020. Loss of alignment of the graphite particles can in turn reduce the electrochemical performance of the electrode during charging and discharging. The use of a curing component may avoid interference with the orientation of the aligned particles.

In the case of graphite particles, the alignment previously accomplished in a magnetic field can be maintained for a long period of time by curing the wet coating. This allows subsequent drying without the application of a magnetic field, since movement within the coating, for example by convection, is prevented and the composition does not change its orientation.

By using hardening additives, such as thermally responsive additives which may exemplarily comprise methylcellulose and additionally silicone-based antifoam agent B, the conventionally produced pastes can also be converted into thermally responsive pastes by simple mixing. In this way, an improvement in the electrode performance can be achieved without expensive adjustment. The addition of a heat responsive additive to the paste may result in thickening of the paste upon mixing. In this process, it seems that the order of addition of the additives plays an important role. If the heat-responsive additive is added after the addition of the SBR binder, the curing of the paste under stirring is minimized.

The use of the heat-responsive component a, such as, for example, methyl cellulose, may cause air inclusion (generation of bubbles and foam). Therefore, pastes containing such thermally responsive components also show a tendency to entrap entrapped air. In the case of coatings, such air inclusions can cause defects. This must be avoided. Air inclusions can be effectively avoided by adding an antifoam B, for example based on silicone. The concentration and type of antifoam B is important since the addition of antifoam B may also lead to defects in the coating. In this process, it is important to keep the amount of antifoam B added as low as possible.

Another aspect of the invention relates to the mixing of another solid particle additionally with an active material present as a main component in a thermally responsive paste. In the particular case where the particle sizes of the solid materials are different, a higher solids concentration can be achieved in this case. This is particularly useful when using flake graphite as the active material, because by adding another type of solid particles, less water is used in the paste, which accelerates drying, and in the case of aligned graphite, can better align the graphite particles in the dried electrode. Possible other solid particles in the process may be another type of graphite particles, alumina particles, silicon particles, silica particles or similar solid particles.

Another aspect of the invention relates to a device for curing a heat-responsive paste TR or layer. The paste curing device 060 is located between the coating nozzle 010 and the dryer 020. The purpose of the paste curing device 060 is to cure a moist and fluid coating comprising a curing component, such as a thermally responsive component, on the foil carrier 030 so that the coating reaches the dryer 020 in a cured/gelled state for subsequent drying. The paste curing device 060 comprises heating elements 040 such as, for example, heated blowers, heated rollers, IR radiant heaters, devices for emitting microwaves, induction heating devices, or combinations thereof. Furthermore, the paste curing device 060 may further comprise magnetic field means 050 in order to align particles in the paste to be cured. The magnetic field means 050 provides alignment of particles in the still wet and fluid coating. The heating element 040 then ensures the fixing of the aligned particles in the thermally responsive paste TR. By subsequent drying in a dryer 020, a dry coating with aligned particles can be obtained in this way.

Improving electrode performance (better adhesion, more uniform coating weight per unit area, better alignment in the case of oriented particles) with a thermally responsive paste TR can only be achieved in part by applying heat from a 020 dryer, i.e., without the paste curing device 060 described herein. However, in this way, the curing of the heat-responsive paste TP and the drying thereof may be difficult to separate from each other. In this way, mixing effects (partly binder migration, partly loss of orientation of the particles, etc.) may occur.

The above-described device to be used according to the present invention, as described in the exemplary embodiments, is not limited by any particular special conditions in terms of its size, form, design, choice of materials and technical concept, and thus selection criteria known in the field of application may be employed without limitation.

The description of fig. 2 yields further details, objects and advantages of the inventive subject matter. In fig. 2, a preferred embodiment of the invention is shown by way of example. The features gleaned from the description and the drawings may be used in accordance with the invention either individually or in any combination.

Example (c):

production of thermally responsive additive:

a mass of 1.2g of organomodified silicone copolymer defoamer was mixed with 75g of a filtered 2 wt.% methylcellulose solution in a planetary centrifugal mixer at 2000rpm for 10 minutes. Any bubbles that may be contained are then removed by a mixer defoaming procedure.

Production of thermally responsive paste TP:

a mass of 97 grams of flake-shaped graphite was kneaded with 42.5 grams of carboxymethyl cellulose (CMC) solution (2 wt.%) and 30.67 grams of deionized water in a planetary mixer at 1200rpm for 6 minutes. To obtain good intermixing, the mixture was stirred by hand occasionally (i.e., from time to time). Subsequently, 8.53g of deionized water was added to the mixture and mixed again at 1200rpm for 1.5 minutes. An SBR latex binder (40 wt.% solids) with a mass of 5g was mixed into the mixture. As a final step, 17.5g of a heat responsive additive (1.6 wt.% defoamer-methylcellulose mixture) was added to the mixture and mixed by hand.

Production of a thermally responsive paste TP with two different main solid compositions:

a mass of 73g of flake-shaped graphite was mixed with rounded graphite and then kneaded with 60g of carboxymethyl cellulose (CMC) solution (2 wt.%) and 57g of deionized water in a planetary centrifugal mixer at 1200rpm for 6 minutes. To obtain good intermixing, the mixture was stirred by hand occasionally (i.e., from time to time). Subsequently, 63g of deionized water was added to the mixture and mixed again at 1200rpm for 1.5 minutes. An SBR latex binder (40 wt.% solids) with a mass of 5g was mixed into the mixture. As a final step, 15g of a heat responsive additive (2 wt.% defoamer-methylcellulose mixture) was added to the mixture and mixed by hand.

The heat-responsive paste TR is generated from a conventional paste KP:

17.5g of a thermally responsive additive (1.6% defoamer-methylcellulose mixture) was added to a conventional paste containing 97g of flake graphite, 50g of carboxymethyl cellulose (CMC) solution (2 wt.%), and a mixture of 55g of deionized water and 5g of SBR latex binder (40 wt.%), and mixed by hand.

The electrodes are made with a thermally responsive paste TR:

the graphite paste thus obtained was applied as a fluid film to a collector foil (copper foil 15 μm) with a doctor blade. Infrared radiant heaters are operated to cure the deposited coating. Subsequent drying produces a porous electrode.

The vertically aligned electrodes are made from the thermally responsive paste TR:

the graphite paste thus obtained was applied as a fluid film to a collector foil (copper foil 15 μm) with a doctor blade. Infrared radiant heaters are operated to cure the deposited coating. Thus, vertically aligned particles are bound. Subsequent drying produces a porous electrode with vertically aligned graphite particles.

A negative electrode having vertically aligned graphite particles and made of the thermally responsive paste TR may be used in a lithium ion battery together with a cathode, a separator and an organic electrolyte.

List of reference marks

010 coating nozzle

020 dryer

030 foil Carrier

040 heating element

050 magnetic field device

060 paste curing unit

A thermally responsive component

B antifoam agent (antifoam agent)

KP conventional paste

TR thermo-responsive paste