Photocurable dry-process carbon-based coating slurry, carbon-coated current collector, and preparation method therefor and use thereof

Abstract

Provided are a photocurable dry-process carbon-based coating slurry, a carbon-coated current collector, and a preparation method therefor and a use thereof. The provided slurry comprises a first mixture and polytetrafluoroethylene; the first mixture comprises a conductive agent, a conductive additive, and a photocurable binder; the mass ratio of the first mixture to the polytetrafluoroethylene is 100:(0.1-1); and the conductive additive is vapor-grown carbon nanofibers. The solid content of the photocurable dry-process carbon-based coating slurry is greater than or equal to 95%. Thus, the prepared carbon-coated current collector material is more uniform and has low resistance.

Description

Photocurable dry carbon coating slurry and carbon coating current collector and preparation method and use thereof Technical Field

[0001] The present application relates to the technical field of current collectors, and in particular to a photocurable dry carbon coating slurry and a carbon coating current collector as well as a preparation method and use thereof. Background Art

[0002] The development of batteries has become an area of ​​concern for more and more people. With the continuous development of the battery industry, carbon-coated current collectors have emerged, which coat the copper and aluminum foils used for positive and negative electrodes with highly conductive carbon materials. The existing coating technology is conventionally wet coating, and the carbon-coated current collector is generally coated by gravure coating. The carbon-coated slurry is a mixed slurry prepared by wet method, which is usually a certain proportion of conductive powder, resin, dispersant, and solvent. It is mixed into a suspension liquid slurry with a uniform phase by stirring, dispersing, sanding or grinding. The slurry is then coated on the surface of the supporting substrate at a certain surface density by gravure coating, transfer coating, slit extrusion coating, etc., and then cured by baking and other methods to prepare a coated product.

[0003] However, the carbon-coated current collector prepared by this wet coating process usually has some disadvantages: 1. The wet coating process requires a heat source for drying, and the process consumes huge energy; 2. The slurry for wet coating is mixed and prepared using a solvent, resulting in large amounts of wastewater and exhaust gas emissions; 3. During the wet coating drying process, the evaporation of the solvent during drying will cause the binder to float, resulting in uneven distribution of the coating structure; 4. Due to insufficient drying, the wet coating process may result in insufficient volatilization of the solvent and residues, which will affect the electrical performance of the battery prepared using the carbon-coated current collector.

[0004] The carbon-coated current collectors need further improvement.

[0005] Summary of the Invention

[0006] This application aims to address, at least to some extent, one of the technical problems in the related art. This application prepares a dry slurry using a conductive agent, a conductive additive, a light-curing adhesive, and polytetrafluoroethylene as raw materials. This slurry can be applied using high-voltage electrostatic spraying and cured using a UV light source, eliminating the need for drying and preventing uneven coatings. Furthermore, dry spraying reduces the need for solvent homogenization, reduces wastewater and exhaust emissions, and protects the environment.

[0007] Specifically, this application provides the following technical solutions:

[0008] In a first aspect, the present application provides a photocurable dry carbon coating slurry comprising: a first mixture and polytetrafluoroethylene (PTFE); the first mixture comprising a conductive agent, a conductive additive, and a photocurable binder, the mass ratio of the first mixture to the PTFE being 100:(0.1-1), and the conductive additive being vapor-grown carbon nanofibers; the photocurable dry carbon coating slurry having a solids content of ≥95%. The photocurable dry carbon coating slurry provided herein has a high solids content, resulting in a highly uniform coating product, and the carbon-coated current collector prepared therefrom exhibits good electrical properties and low resistance.

[0009] According to an embodiment of the present application, the above-mentioned photocurable dry carbon coating slurry may further include the following technical features:

[0010] According to an embodiment of the present application, the conductive agent is selected from at least one of graphite, graphene, carbon black, and carbon tubes.

[0011] According to an embodiment of the present application, the light-curing adhesive is selected from at least one of polyurethane acrylate, α-cyanoacrylate, pentaerythritol triacrylate (PETA), and hydroxyethyl methacrylate (HEMA).

[0012] According to an embodiment of the present application, the mass ratio of the conductive agent, the conductive additive, and the light-curing adhesive is (75-85): (3-7): (10-20). According to a preferred embodiment of the present application, the mass ratio of the conductive agent, the conductive additive, and the light-curing adhesive is 80:5:15.

[0013] The second aspect of the present application provides a method for preparing the photocurable dry carbon coating slurry described in the first aspect, comprising: mixing and stirring the conductive agent, conductive additive and photocurable binder for 30 to 60 minutes, and then mixing with polytetrafluoroethylene to obtain the photocurable dry carbon coating slurry.

[0014] A third aspect of the present application provides a method for preparing a carbon-coated current collector, comprising:

[0015] (1) applying the photocurable dry carbon coating slurry described in the first aspect of the present application to an aluminum foil by high-voltage electrostatic spraying to obtain a sprayed current collector;

[0016] (2) The sprayed current collector is photocured by ultraviolet light to obtain a carbon-coated current collector.

[0017] According to the embodiments of the present application, the above-mentioned preparation method may further include the following technical features:

[0018] According to an embodiment of the present application, the high-voltage electrostatic spray coating is performed by delivering a carrier gas through a pipeline to a 25kV high-voltage electrostatic spray gun, with the discharge port being 1.0 to 2.0 inches from the current collector, and the spraying angle being 30 to 90 degrees relative to the aluminum foil. According to a preferred embodiment of the present application, the discharge port is 1.0 to 1.5 inches from the current collector, and the spraying angle is 30 to 45 degrees relative to the aluminum foil.

[0019] According to an embodiment of the present application, the photocuring is performed by using a 2-3kW ultraviolet lamp tube at a height of 10 cm from the surface of the current collector to photocure the spray coating for 10-15 seconds.

[0020] The fourth aspect of the present application provides a carbon-coated current collector, which is prepared according to the preparation method described in any embodiment of the third aspect.

[0021] The fifth aspect of the present application provides an electrode comprising the carbon-coated current collector described in the fourth aspect.

[0022] The sixth aspect of the present application provides a battery comprising the electrode described in the fifth aspect.

[0023] The beneficial effects achieved by this application are:

[0024] (1) The photocurable dry carbon coating paste provided in the present application uses a photocurable adhesive, such as a cyanoacrylate adhesive, which has a high curing efficiency.

[0025] (2) The photocurable dry carbon coating slurry provided in this application uses vapor-grown carbon nanofibers and polytetrafluoroethylene (PTFE) as raw materials, which are bonded with a binder to form a fiber network with greater adhesion.

[0026] (3) This application adopts a high-voltage electrostatic spray coating method, and the coating surface density is simple to control. It can be adjusted by adjusting the spraying time, distance and angle, without changing the surface density by replacing the gravure roller of different specifications through wet coating;

[0027] (4) After the application adopts UV curing adhesive coating, the distribution of the conductive agent and adhesive phases of the coating is more uniform;

[0028] (5) The carbon-coated current collector is prepared by the method of the present application, and its preparation process is simple, reduces equipment, reduces energy consumption, reduces carbon dioxide emissions, and is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG1 is a schematic diagram of preparing a carbon-coated current collector provided in an embodiment of the present application.

[0030] FIG2 shows a photocurable structure formed by dry coating and a wet coating and drying structure provided in an embodiment of the present application.

[0031] FIG3 is a wet coating and drying structure provided in a comparative example of the present application.

[0032] Explanation of the accompanying figures: 1. Aluminum foil; 2. Dry coating layer; 3. UV curing area; 4. High-voltage electrostatic sprayer; 5. UV light source. DETAILED DESCRIPTION

[0033] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, but should not be understood as limiting the present application.

[0034] The present application provides a photocurable dry carbon coating slurry, comprising: a first mixture and polytetrafluoroethylene (PTFE); the first mixture comprises a conductive agent, a conductive additive and a photocurable adhesive, the mass ratio of the first mixture to the PTFE is 100:(0.1~1), and the conductive additive is vapor-grown carbon nanofiber; the solid content of the photocurable dry carbon coating slurry is ≥95%.

[0035] According to a specific embodiment, the solid content of the photocurable dry carbon coating slurry is ≥96%, ≥97%, ≥98%, or ≥99%.

[0036] According to a specific embodiment, the conductive agent includes but is not limited to graphite, graphene, carbon black or carbon tube.

[0037] According to a specific embodiment, the light-curing adhesive is selected from at least one of polyurethane acrylate, α-cyanoacrylate, pentaerythritol triacrylate (PETA), and hydroxyethyl methacrylate (HEMA).

[0038] According to a specific embodiment, the mass ratio of the conductive agent, the conductive additive and the photocurable adhesive is (75-85): (3-7): (10-20). According to a preferred embodiment, the mass ratio of the conductive agent, the conductive additive and the photocurable adhesive is 80:5:15. The conductive agent, the conductive additive and the photocurable adhesive in the provided photocurable dry carbon coating slurry need to be mixed in a certain proportion. If the content ratio changes, it will affect the spraying effect of the slurry, the uniformity of the subsequent coating structure prepared, and the conductivity. Taking the photocurable adhesive as an example, if the content of the mixed photocurable adhesive is too low, it will affect the bonding effect, resulting in a poor curing effect; if the content of the mixed photocurable adhesive is too high, part of the photocurable adhesive in the lower layer will not be absorbed, which will also affect the bonding effect, resulting in a poor curing effect.

[0039] The present application also provides a method for preparing the above-mentioned photocurable dry carbon coating slurry, comprising: mixing and stirring the conductive agent, conductive additive and photocurable binder for 30 to 60 minutes, and then mixing with polytetrafluoroethylene to obtain the photocurable dry carbon coating slurry.

[0040] The present application also provides a method for preparing a carbon-coated current collector, as shown in FIG1 , comprising:

[0041] (1) The above-mentioned photocurable dry carbon coating slurry is applied to an aluminum foil (as shown by reference numeral 1 in FIG. 1 ) by high-voltage electrostatic spraying (e.g., by using the high-voltage electrostatic sprayer 4 in FIG. 1 ) to obtain a sprayed current collector;

[0042] (2) The sprayed current collector is cured by ultraviolet light (e.g., using the ultraviolet light source 5 in FIG. 1 ) to obtain a carbon-coated current collector. The resulting carbon-coated current collector forms a dry coating layer as shown in FIG. 1 2 . A corresponding ultraviolet light-cured area is also shown in FIG. 1 for illustration, as indicated by reference numeral 3 in FIG. 1 .

[0043] According to a specific embodiment, the high-voltage electrostatic spray coating is to carry out the photocuring dry carbon coating slurry with a gas carrier and transport it to a 25kV high-voltage electrostatic spray gun through a pipeline. The distance between the discharge port and the aluminum foil is 1.0-2.0 inches, and the spraying angle is 30-90° to the aluminum foil. According to a specific embodiment, the spraying time is 0.2-0.6 seconds, for example, 0.5-0.6 seconds. The surface density of the sprayed layer is controlled by the spraying time, angle and distance; the spray coating amount is controlled by the carrier gas pressure. These parameter adjustments will affect the coating coverage, density, conductive penetration resistance and coating peel strength of the prepared current collector. According to a preferred embodiment, when the distance between the discharge port and the aluminum foil is 1.0-1.5 inches and the spraying angle is 30-45° to the aluminum foil, the various indicators of the prepared current collector are better.

[0044] According to a specific embodiment, the photocuring step involves curing the spray coating for 10-15 seconds using a 2-3kW UV lamp at a height of 10-15 cm from the current collector surface. This photocuring allows the photocurable cyanoacrylate adhesive in the dry slurry to cure and bond, thereby bonding the conductive coating to the current collector to form a carbon-coated current collector.

[0045] The present application also provides a carbon-coated current collector, which is prepared according to the above-mentioned preparation method.

[0046] As shown in Figure 2, the carbon-coated current collector prepared by the method provided in this application has a structure as shown in Figure 2. The binder fiber mesh adhesion evenly distributes the conductive material on the current collector surface, making the coating structure more uniform. Compared with the wet coating and drying structure, as shown in Figure 3, the coating has an uneven coating structure due to the relatively light binder floating up with the solvent during the solvent baking and evaporation process.

[0047] According to a specific embodiment, the present application provides a photocurable dry carbon coating slurry, comprising: stirring a carbon black conductive agent Li-400, vapor-grown carbon nanofibers (VG-CNF), and a photocurable cyanoacrylate binder at a mass ratio of 80:5:15 for 30 minutes; then, mixing the above mixed powder with 0.1-1wt% PTFE to obtain a dry slurry with a solid content of ≥95%. The slurry thus prepared is independent and soft. The provided carbon-coated current collector can be used in the field of batteries. For this purpose, the present application also provides an electrode, including the above-mentioned carbon-coated current collector. A battery is also provided, including the above-mentioned electrode.

[0048] The technical solutions of this application are described in detail below with reference to the examples. The reagents used in the examples are commonly used in the art. The vapor-grown carbon nanofibers used were purchased from Showa Denko; Li-400 was purchased from Nippon Electric Chemical; and cyanoacrylate was purchased from Henkel Loctite.

[0049] Example 1

[0050] Example 1 A photocurable dry carbon coating slurry and a carbon coating current collector thereof were prepared by the following method, including:

[0051] (1) Carbon black conductive agent Li-400, vapor-grown carbon nanofibers (VG-CNF), and photocurable cyanoacrylate binder were stirred at a mass ratio of 80:5:15 for 30 minutes. To prepare a free-standing and flexible dry film, the mixed powder was mixed with 0.5 wt% PTFE to obtain a photocurable dry carbon coating slurry with a solid content of ≥95%.

[0052] (2) The prepared slurry is electrostatically sprayed dry-processed, and the carrier gas is transported to a 25kV high-voltage electrostatic spray gun through a pipeline. The distance between the discharge port and the current collector aluminum foil is 1.5 inches, the spraying angle is 45° to the aluminum foil, the spraying time is 0.5 seconds, and the size of the sprayed particles formed is 100-200 μm.

[0053] (3) The sprayed current collector is passed through a UV lamp with a UV light of 2-3kW at a height of 10 cm from the current collector surface. The sprayed layer is photocured by UV light for 10-15 seconds to cure the photocurable cyanoacrylate adhesive in the dry slurry, and the conductive coating is bonded to the current collector to prepare a carbon-coated current collector.

[0054] The above experiment was used as experimental group 1 to study the effects of different high-voltage electrostatic spraying process parameters on the results. The results are summarized as follows:

[0055] Compared with experimental group 1, experimental group 2 has a distance of 1.5 inches from the discharge port to the current collector, a spraying angle of 45° to the aluminum foil, a spraying time of 0.2 seconds, and a size of the sprayed particles formed of 50 to 150 μm.

[0056] Compared with experimental group 1, experimental group 3 has a distance of 1.5 inches from the discharge port to the current collector, a spraying angle of 45° to the aluminum foil, a spraying time of 0.5 seconds, and a size of the sprayed particles formed of 250 to 450 μm.

[0057] Compared with experimental group 1, experimental group 4 has a distance of 1.5 inches from the discharge port to the current collector, a spraying angle of 90° to the aluminum foil, a spraying time of 0.5 seconds, and a size of the sprayed particles formed of 80 to 180 μm.

[0058] Compared with experimental group 1, experimental group 5 has a distance of 1.5 inches from the discharge port to the current collector, a spraying angle of 30° to the aluminum foil, a spraying time of 0.6 seconds, and a size of the sprayed particles formed of 120 to 240 μm.

[0059] Compared with experimental group 1, experimental group 6 has a distance of 1.5 inches from the discharge port to the current collector, a spraying angle of 60° to the aluminum foil, a spraying time of 0.2 seconds, and a size of the sprayed particles formed of 60 to 170 μm.

[0060] The results are shown in Table 1.

[0061] Table 1 Parameters of current collectors prepared by different spraying processes

[0062] The results show that different spraying processes produce different current collector parameters, which affect coating coverage, coating surface density, current collector conductive penetration resistance, and coating peel strength. When the discharge port is 1.0-1.5 inches from the current collector, the spray angle is 30-45 degrees relative to the aluminum foil, and the spray time is 0.5-0.6 seconds, the resulting current collector parameters are all improved, including higher coating coverage, greater coating surface density, lower current collector conductive penetration resistance, and stronger coating peel strength, resulting in better results.

[0063] Comparative Example 1

[0064] Comparative Example 1: A coated current collector was prepared by wet coating slurry, and the preparation method was as follows:

[0065] (1) The water-based binder and a certain amount of solvent were stirred using a double planetary disperser for 10 min at a stirring speed of 20 rpm;

[0066] (2) Then add 50% carbon black into the mixer and stir for 20 minutes at a stirring speed of 50 rpm and a dispersion speed of 4000 rpm;

[0067] (3) Then add the remaining 50% of carbon black into the mixer and stir for 90 minutes at a stirring speed of 50 rpm and a dispersion speed of 4000 rpm;

[0068] (4) PVP + remaining pure water were then added to the blender and stirred for 60 min at a stirring speed of 50 rpm and a dispersion speed of 4000 rpm;

[0069] (5) After stirring, the slurry is coated onto the surface of the current collector through a gravure coater, and then dried and rolled up to prepare a wet-coated current collector.

[0070] The aqueous binder used was polyacrylic acid resin, the dispersant was PVP, and the solvent was pure water. The results are shown in Table 3.

[0071] Table 2 Ratio of each ingredient

[0072] Table 3 Wet coating results

[0073] Comparing the results of Example 1 and Comparative Example 1, it can be seen that the wet coating method has a higher coating coverage rate because it performs a full coating operation. However, the coating layer density of Comparative Example 1 is relatively low, the current collector conductive penetration resistance is relatively high, and the coating peel strength is significantly lower than that of each group in Example 1. The overall performance of the current collector prepared by this method is inferior to that of the current collector prepared by the photocuring dry method of this application.

[0074] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0075] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A photocurable dry carbon coating slurry, comprising a first mixture and polytetrafluoroethylene; The first mixture includes a conductive agent, a conductive additive and a light-curing adhesive, the mass ratio of the first mixture to the polytetrafluoroethylene is 100:(0.1-1), and the conductive additive is vapor-grown carbon nanofiber; The solid content of the photocurable dry carbon coating slurry is ≥95%.

2. The photocurable dry carbon coating slurry according to claim 1, wherein: The photocurable adhesive is selected from at least one of polyurethane acrylate, α-cyanoacrylate, pentaerythritol triacrylate (PETA), and hydroxyethyl methacrylate (HEMA); Optionally, the conductive agent is selected from at least one of graphite, graphene, carbon black and carbon tube.

3. The photocurable dry carbon coating slurry according to claim 1 or 2, wherein: The mass ratio of the conductive agent, the conductive additive and the photocurable adhesive is (75-85): (3-7): (10-20).

4. The method for preparing a photocurable dry carbon coating slurry according to any one of claims 1 to 3, comprising: The conductive agent, conductive additive and light-curing binder are mixed and stirred for 30 to 60 minutes, and then mixed with polytetrafluoroethylene to obtain the light-curing dry carbon coating slurry.

5. A method for preparing a carbon-coated current collector, comprising: (1) applying the photocurable dry carbon coating slurry according to any one of claims 1 to 3 onto an aluminum foil by high-voltage electrostatic spraying to obtain a sprayed current collector; (2) The sprayed current collector is photocured by ultraviolet light to obtain a carbon-coated current collector.

6. The preparation method according to claim 5, wherein: The high-voltage electrostatic spray coating is to carry the photocurable dry carbon coating slurry in a gas carrier and transport it to a 25kV high-voltage electrostatic spray gun through a pipeline. The distance between the discharge port and the aluminum foil is 1.0 to 2.0 inches, and the spraying angle direction is 30 to 90 degrees to the aluminum foil.

7. The preparation method according to claim 5 or 6, wherein: The photocuring is to perform photocuring of the sprayed layer for 10-15 seconds by using a UV lamp with a UV light of 2-3 kW at a height of 10-15 cm from the surface of the sprayed current collector.

8. A carbon-coated current collector prepared by the preparation method according to any one of claims 5 to 7.

9. An electrode comprising the carbon-coated current collector according to claim 8.

10. A battery comprising the electrode according to claim 9.

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