Superfine composite carbon particles subjected to pre-dispersion treatment, carbon slurry and current collector

Abstract

The invention discloses pre-dispersed superfine composite carbon particles, carbon slurry and a current collector, and belongs to the technical field of battery materials. The superfine composite carbon particles are obtained by sequentially carrying out quenching treatment and freeze drying on carbon dispersion liquid, the quenching treatment mode comprises liquid nitrogen treatment or dry ice treatment. The superfine composite carbon particles subjected to pre-dispersion treatment can be dispersed until D50 is less than or equal to 300nm by directly adding a liquid-phase solvent without sanding, and then can be coated on the surface of a current collector to obtain an ultrathin carbon coating after being simply and uniformly stirred with an adhesive, and the coating is uniform in color, free of spot defects, strong in covering power, smooth in surface and free of granular sensation; moreover, the ultrathin carbon coating can greatly reduce the gram weight of the primer, is beneficial to thinning the pole piece, and is beneficial to improving the energy density of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to pre-dispersed ultrafine composite carbon particles, carbon slurry and current collector. Background Art

[0002] The application of carbon-coated aluminum foil in lithium iron phosphate batteries has significantly improved battery performance compared to plain aluminum foil. As end users pursue cost reduction and efficiency improvements, the coating thickness of carbon-coated aluminum foil is continuously decreasing. Conventional conductive carbon particles are relatively easy to disperse, but their large particle size prevents thin coatings. Furthermore, carbon nanotubes are entangled by strong van der Waals forces, making them difficult to disperse, and their small size cannot fully exploit their advantages. Consequently, the thickness of carbon-coated aluminum foil has remained in the micrometer range, unable to be reduced to the nanometer level. This also limits the energy and power density of the battery.

[0003] Traditional carbon nanotubes or graphene dispersions are produced as low-concentration liquids with high viscosity and bulk, making them difficult to store and transport. Dispersions are vulnerable to high and low temperature shocks, resulting in high freight costs for long-distance transport. They are also prone to agglomeration and coarsening at high temperatures, or freezing and solidification at low temperatures. They are also susceptible to the introduction of impurities due to environmental influences. For example, high humidity in summer often introduces excess water impurities into carbon nanotube NMP dispersions during production, significantly limiting their use in lithium batteries.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The object of the present invention is to provide a pre-dispersed ultrafine composite carbon particle, carbon slurry and current collector to solve or improve the above technical problems.

[0006] The present invention can be achieved like this: In a first aspect, the present invention provides a pre-dispersed ultrafine composite carbon particle, wherein the ultrafine composite carbon particle is obtained by sequentially subjecting a carbon dispersion to rapid cooling and freeze drying; The carbon dispersion is obtained by sand-milling a mixture of a conductive agent, a dispersant and water; The solid content of the carbon dispersion is ≤3wt%; the mass ratio of the conductive agent to the dispersant is 95:5 to 99.5:0.5; Rapid cooling methods include liquid nitrogen treatment or dry ice treatment.

[0007] In an optional embodiment, the conductive agent includes at least three of single-walled carbon tubes, multi-walled carbon tubes, VGCF, graphene and conductive carbon black; The dispersant is a maleic anhydride multipolymer with a weight average molecular weight of 5000-20000, and the glass transition temperature of the dispersant is 140-160°C.

[0008] In an optional embodiment, the sanding time is 3 hours to 18 hours.

[0009] In an optional embodiment, the freeze-drying time is not less than 48 hours.

[0010] In a second aspect, the present invention provides a carbon slurry, which is obtained by mixing a binder, the pre-dispersed ultrafine composite carbon particles according to any one of the aforementioned embodiments, and a solvent.

[0011] In an optional embodiment, the solid content of the carbon slurry is 2 wt % to 4 wt %; and the mass ratio of the pre-dispersed ultrafine composite carbon particles to the binder is 40:60 to 70:30.

[0012] In an alternative embodiment, the adhesive includes at least one of PAA and PVDF.

[0013] In an optional embodiment, the viscosity of the carbon slurry is ≤600 mPa·s; the D 50 ≤300nm.

[0014] In a third aspect, the present invention provides a current collector comprising a current collector body and a carbon coating disposed on at least one surface of the current collector body, wherein the carbon coating is obtained by coating and drying the carbon slurry according to any one of the aforementioned embodiments.

[0015] In an optional embodiment, the thickness of the carbon coating is 60 nm to 300 nm.

[0016] The beneficial effects of the present invention include: The pre-dispersed ultrafine composite carbon particles provided by the present invention are obtained by sequentially subjecting a carbon dispersion to rapid cooling and freeze drying, wherein the carbon dispersion is obtained by sand grinding a mixture of a conductive agent, a dispersant and water.

[0017] The above-mentioned ultrafine composite carbon particles after pre-dispersion treatment are easy to store and transport, are not easily affected by the environment and introduce impurities, and do not need sand grinding and can be dispersed directly into D by adding liquid solvent. 50 ≤300nm, and then simply stirred evenly with the adhesive, it can be coated on the surface of the current collector to obtain an ultra-thin carbon coating. The coating has uniform color, no spots or defects, strong covering power, and a smooth surface without graininess. Moreover, the ultra-thin carbon coating can greatly reduce the weight of the primer, which is beneficial to the thinning of the electrode and the improvement of the energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 This is a cross-sectional SEM image of the current collector prepared in Example 5 of the present invention. DETAILED DESCRIPTION

[0020] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0021] The pre-dispersed ultrafine composite carbon particles, carbon slurry and current collector provided by the present invention are described in detail below.

[0022] The invention provides ultrafine composite carbon particles that have been pre-dispersed. The ultrafine composite carbon particles are obtained by sequentially subjecting a carbon dispersion to rapid cooling and freeze drying.

[0023] The carbon dispersion is obtained by sand-milling a mixture of a conductive agent, a dispersant and water.

[0024] In some optional embodiments, the conductive agent may include at least three of single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), VGCF, graphene, and conductive carbon black (e.g., Super P). This combination of three materials facilitates the creation of a three-dimensional conductive structure within and on the surface of the coating, reducing the internal resistance of the electrode and enhancing machinability.

[0025] In some optional embodiments, the dispersant is a maleic anhydride multipolymer having a weight average molecular weight of 5,000 to 20,000 and a glass transition temperature of 140° C. to 160° C.

[0026] In some optional embodiments, sand grinding can be performed in a sand mill. The grinding beads used for sand grinding can be zirconium beads, and the diameter of the zirconium beads can be 0.3 μm to 1 μm. The sand grinding time can be 3 hours to 18 hours, such as 3 hours, 5 hours, 8 hours, 10 hours, 12 hours, 15 hours, or 18 hours, or other values ​​within the range of 3 hours to 18 hours.

[0027] If the sanding time is too short, the entangled carbon tubes are not completely separated and the slurry is likely to have a granular feel; if the sanding time is too long, the loss of carbon tubes and zirconium beads is very large and the electrical properties of the coating layer will also deteriorate.

[0028] In some optional embodiments, the solid content of the carbon dispersion is ≤3 wt %, such as 3 wt %, 2.5 wt %, 2 wt %, 1.5 wt %, 1 wt %, 0.5 wt %, or 0.1 wt %, or other values ​​within the range of ≤3 wt %. The mass ratio of the conductive agent to the dispersant can be from 95:5 to 99.5:0.5, such as 95:5, 96:4, 97:3, 98:2, 99:1, or 99.5:0.5, or other values ​​within the range of 95:5 to 99.5:0.5.

[0029] In some optional embodiments, the carbon dispersion is a stable and uniform black liquid.

[0030] In some optional embodiments, the rapid cooling method may include liquid nitrogen treatment or dry ice treatment. In some optional embodiments, the freeze-drying time is not less than 48 hours.

[0031] It should be noted that the present invention can ensure efficiency and improve production continuity and stability by first subjecting the carbon dispersion to rapid cooling treatment and then freeze-drying, compared with direct freeze-drying.

[0032] Continuing from the above, the pre-dispersed ultrafine composite carbon particles provided by the present invention are easy to store and transport, are not easily affected by the environment and introduce impurities, and do not require sanding. They can be directly dispersed to a D50 ≤ 300nm by adding a liquid solvent. After simple stirring with an adhesive, they can be coated on the surface of the current collector to obtain an ultra-thin carbon coating. The coating has uniform color, no spots or defects, strong hiding power, and a smooth surface without graininess. Moreover, the ultra-thin carbon coating can greatly reduce the weight of the base coating, which is beneficial for thinning the electrode and improving the energy density of the battery. In other words, the pre-dispersed ultra-fine composite carbon particles are similar to instant coffee particles and can meet the requirements of ultra-thin coating by simple stirring and dispersion.

[0033] Accordingly, the present invention also provides a carbon slurry, which is obtained by mixing a binder, the pre-dispersed ultrafine composite carbon particles, and a solvent. The mixing process does not require sanding, and high-speed stirring can be performed directly.

[0034] In some optional embodiments, the adhesive may include at least one of PAA and PVDF, and the solvent may include at least one of water, NMP, and other organic solvents.

[0035] In some optional embodiments, the solid content of the carbon slurry is 2 wt% to 4 wt%, such as 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt% or 4 wt%, etc., or other values ​​within the range of 2 wt% to 4 wt%.

[0036] If the solid content of the carbon slurry is lower than 2wt%, the slurry stability becomes poor and is prone to deterioration during storage; if the solid content of the carbon slurry is higher than 4wt%, it is not conducive to thin coating and reducing the amount of carbon material used.

[0037] The mass ratio of the pre-dispersed ultrafine composite carbon particles to the binder can be 40:60 to 70:30, such as 40:60, 45:55, 50:50, 55:45, 60:40, 65:35 or 70:30, or other values ​​within the range of 40:60 to 70:30.

[0038] If the mass ratio of the pre-dispersed ultrafine composite carbon particles to the adhesive is less than 40:60 (such as 30:70), the electrical properties of the coating will deteriorate; if the mass ratio of the pre-dispersed ultrafine composite carbon particles to the adhesive is greater than 70:30 (such as 80:20), it is not conducive to the adhesion of the coating, resulting in a decrease in the electrode peeling force.

[0039] In some optional embodiments, the carbon slurry is a stable and uniform black liquid.

[0040] In some optional embodiments, the viscosity of the carbon slurry is ≤600 mPa·s; and the D50 of the particles in the carbon slurry is ≤300 nm.

[0041] If the viscosity of the carbon slurry is greater than 600mPa·s, it is not conducive to thin coating; if the D50 of the particles in the carbon slurry is greater than 300nm, the coating surface will have a granular feel and the slurry stability will deteriorate.

[0042] In addition, the present invention also provides a current collector, which includes a current collector body and a carbon coating disposed on at least one side of the current collector body. The carbon coating is obtained by coating and drying the above-mentioned carbon slurry.

[0043] The coating method may be, for example, gravure coating.

[0044] In some optional embodiments, the thickness of the carbon coating may be 60 nm to 300 nm, such as 60 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm or 300 nm, or other values ​​within the range of 60 nm to 300 nm.

[0045] The carbon coating is smooth, uniform, and free of graininess, with a metallic luster. Furthermore, it is an ultrathin coating, capable of maintaining excellent electrical and mechanical properties despite its thinness. Current collectors with this ultrathin coating are ultrathin carbon-coated current collectors, which maintain excellent electrical conductivity and are resistant to wipes and electrolyte immersion, making them suitable for energy storage and power lithium battery applications.

[0046] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0047] Example 1 This embodiment provides a carbon coating on the surface of a current collector, and the preparation method thereof includes: S1: Preparation of ultrafine composite carbon particles from carbon dispersion.

[0048] Single-walled carbon nanotubes, multi-walled carbon nanotubes, Super P and maleic anhydride multipolymer (weight-average molecular weight of 8600, glass transition temperature of 140°C) were mixed in a mass ratio of 1:1:1:0.1, deionized water was added as a solvent, and the mixture was stirred evenly to obtain a mixture with a solid content of 3wt%; the mixture was ground with 1μm zirconium beads in a sand mill for 18 hours to obtain a carbon dispersion.

[0049] S2: Preparing ultrafine composite carbon particles that have been pre-dispersed.

[0050] The carbon dispersion was rapidly cooled with liquid nitrogen and then freeze-dried for 50 hours to obtain pre-dispersed ultrafine composite carbon particles.

[0051] S3: preparing carbon slurry.

[0052] The pre-dispersed ultrafine composite carbon particles were mixed with the binder PAA in a mass ratio of 1:1 (50:50), deionized water was added as a solvent, and the mixture was stirred to prepare a slurry to obtain a carbon slurry with a solid content of 3 wt%.

[0053] S4: preparing a carbon coating.

[0054] The carbon slurry was coated on the front and back surfaces of the positive electrode current collector with a thickness of 14 μm and baked at 120° C. for 3 min to obtain an ultra-thin carbon coating.

[0055] Example 2 The difference between this embodiment and embodiment 1 is that in S1, the mass ratio of single-walled carbon nanotubes, multi-walled carbon nanotubes, Super P and maleic anhydride multi-polymer is 0.5:0.5:2:0.1.

[0056] Example 3 This example differs from Example 1 in that, in S1, a mixture of multi-walled carbon nanotubes, VGCF, graphene, and maleic anhydride multipolymer was mixed in a mass ratio of 0.5:2:0.5:0.1, and deionized water was added as a solvent. The solid content of the mixture was also 3 wt%.

[0057] Example 4 This embodiment differs from embodiment 1 in that, in S1, a mixture of single-walled carbon nanotubes, VGCF, Super P, and maleic anhydride multipolymer was mixed in a mass ratio of 2:0.5:0.5:0.1, and deionized water was added as a solvent. The solid content of the mixture was also 3 wt%.

[0058] Example 5 This example differs from Example 1 in that, in S1, a mixture of single-walled carbon nanotubes, multi-walled carbon nanotubes, VGCF, and a maleic anhydride multipolymer was mixed in a mass ratio of 1:1:1:0.05, and deionized water was added as a solvent. The solid content of the mixture was also 3 wt%.

[0059] Example 6 The difference between this embodiment and embodiment 1 is that in S3, 3 wt % of isopropyl alcohol is further added to the carbon slurry.

[0060] Example 7 The difference between this embodiment and embodiment 1 is that in S3, 1 wt % of isopropyl alcohol is further added to the carbon slurry.

[0061] Example 8 The difference between this embodiment and embodiment 1 is that in S4, the baking temperature is 160°C.

[0062] Example 9 The difference between this embodiment and embodiment 1 is that in S1, the sand grinding process first uses 1 μm zirconium beads to grind for 10 hours, and then changes to 0.3 μm zirconium beads to grind for another 1 hour.

[0063] Example 10 The difference between this embodiment and embodiment 1 is that in S1, 0.6 μm zirconium beads are used for grinding for 15 hours.

[0064] Example 11 The difference between this embodiment and embodiment 1 is that in S1, the solid content of the carbon dispersion is 1 wt %.

[0065] Example 12 The difference between this embodiment and embodiment 1 is that in S1, the solid content of the carbon dispersion is 2 wt %.

[0066] Example 13 The difference between this embodiment and embodiment 1 is that in S3, the pre-dispersed ultrafine composite carbon particles and PAA are mixed in a mass ratio of 3:2 (60:40).

[0067] Example 14 The difference between this embodiment and embodiment 1 is that in S3, the solvent of the carbon slurry is NMP and the adhesive is PVDF.

[0068] Example 15 The difference between this embodiment and embodiment 1 is that in S3, the solvent of the carbon slurry is deionized water and n-butanol in a mass ratio of 90%:10%.

[0069] Example 16 The difference between this embodiment and embodiment 1 is that in S3, the pre-dispersed ultrafine composite carbon particles and PAA are mixed in a mass ratio of 2:3 (40:60).

[0070] Comparative Example 1 In this comparative example, a commercially available conductive carbon black slurry with a solid content of 12.5 wt % was used. The conductive carbon black and the adhesive PAA were used in a ratio of approximately 1:1. The slurry was directly applied to both sides of a plain aluminum foil with a thickness of 14 μm and dried to form a carbon coating with a thickness of 1 μm on one side.

[0071] Comparative Example 2 In this comparative example, a commercially available conductive carbon black slurry with a solid content of 12.5 wt % was used. The conductive carbon black and the adhesive PAA were used in a ratio of approximately 1:1. The slurry was directly coated on both sides of a plain aluminum foil with a thickness of 14 μm and dried to form a carbon coating with a thickness of 2 μm on one side.

[0072] Comparative Example 3 This comparative example is a commercially available carbon-coated aluminum foil with a thickness of 12 μm. The thickness of the conductive carbon black coating on both sides of the aluminum foil is 0.5 μm.

[0073] Comparative Example 4 This comparative example is a commercially available carbon-coated aluminum foil with a thickness of 14 μm. The thickness of the conductive carbon black coating on both sides of the aluminum foil is 2 μm.

[0074] Test Example 1 ①. The thicknesses (measured on a single side) of the carbon coatings prepared in Examples 1 to 16 and Comparative Examples 1 to 4 were compared. The thicknesses of the carbon coatings were measured by slicing the current collector and then measuring with a scanning electron microscope.

[0075] The cross-sectional SEM image of the current collector of Example 5 is as follows: Figure 1 As shown by Figure 1 It can be seen that while the carbon coating prepared in Example 5 is ultrathin, it has a significant surface roughness, which helps maintain the electrode peel strength and battery cycling performance. Furthermore, the carbon tubes are evenly distributed within the microstructure and interpenetrate each other, ensuring that the current collector can fully collect the microcurrent from the active material, which helps reduce stress and cracking, and maintain the battery's rate performance.

[0076] ②, the solid content of the carbon slurry in Examples 1 to 16 and Comparative Examples 1 to 2 and the D50 For comparison, D 50 The solid content was measured by laser particle size analyzer and the solid content was measured by heating weight loss method.

[0077] The comparison results are shown in Table 1.

[0078] Table 1 Comparison results

[0079] It can be seen from Table 1 that by mixing three or more conductive carbon materials, the ultra-thin carbon coating prepared by the preparation method provided by the present invention has conductive carbon materials of different shapes interconnected and entangled with each other in the microstructure, which can inhibit polarization expansion and enhance the mechanical strength of the electrode, which is beneficial to the thick coating of lithium iron phosphate and cost reduction and yield improvement.

[0080] In addition, the single-layer thickness of the carbon coating in the embodiment of the present invention is less than 300 nm, which greatly reduces the weight of the primer compared to the commercially available current collector with a single-layer carbon coating of 0.5 μm to 2 μm (such as Comparative Examples 1 to 4), which is conducive to thinning the electrode and significantly improving the energy density of the battery.

[0081] Test Example 2 The current collectors obtained in the above Examples 1 to 16 and Comparative Examples 1 to 4 are prepared into lithium iron phosphate batteries. The preparation of the batteries is as follows: the positive electrode sheet coated with lithium iron phosphate is rolled and then cut into pieces and die-cut, and dried to a moisture content of less than 200 ppm; the graphite negative electrode material and the negative electrode adhesive are slurried and then rolled and die-cut, and dried to a moisture content of less than 200 ppm to obtain a negative electrode sheet; the above-mentioned positive and negative electrode sheets are wound with a separator, and then a soft-pack battery is obtained through a subsequent process.

[0082] The internal resistance of the batteries tested using an electrochemical test channel showed no significant differences between the groups, all around 4.6 milliohms. Other indicators, such as high-temperature storage performance and room-temperature cycling degradation, also showed similar performance. These results demonstrate that the method provided by the present invention effectively solves the problem of rapid and efficient dispersion of the conductive agent, reducing costs and reducing the use of conductive carbon.

[0083] In summary, the pre-dispersed ultrafine composite carbon particles provided by the present invention are obtained by sequentially subjecting a carbon dispersion to rapid cooling and freeze drying, wherein the carbon dispersion is obtained by sand milling a mixture of a conductive agent, a dispersant, and water. The pre-dispersed ultrafine composite carbon particles are easy to store and transport, are not easily affected by the environment and are not easily introduced with impurities, and do not require sand milling and can be dispersed directly into the D 50≤300nm, and then simply stirred evenly with the adhesive, it can be coated on the surface of the current collector to obtain an ultra-thin carbon coating. The coating has uniform color, no spots or defects, strong covering power, and a smooth surface without graininess. Moreover, the ultra-thin carbon coating can greatly reduce the weight of the primer, which is beneficial to the thinning of the electrode and the improvement of the energy density of the battery.

[0084] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A pre-dispersed ultrafine composite carbon particle, characterized in that: The pre-dispersed ultrafine composite carbon particles are obtained by sequentially subjecting a carbon dispersion to rapid cooling and freeze drying. Wherein, the carbon dispersion is obtained by sand-milling a mixture of a conductive agent, a dispersant and water; The solid content of the carbon dispersion is ≤3wt%; the mass ratio of the conductive agent to the dispersant is 95:5 to 99.5:0.5; Rapid cooling methods include liquid nitrogen treatment or dry ice treatment.

2. The pre-dispersed ultrafine composite carbon particles according to claim 1, characterized in that: The conductive agent includes at least three of single-walled carbon tubes, multi-walled carbon tubes, VGCF, graphene and conductive carbon black; The dispersant is a maleic anhydride multipolymer with a weight average molecular weight of 5,000 to 20,000, and the glass transition temperature of the dispersant is 140° C. to 160° C.

3. The pre-dispersed ultrafine composite carbon particles according to claim 1, characterized in that: The sand grinding time of the carbon dispersion is 3h~18h.

4. The pre-dispersed ultrafine composite carbon particles according to any one of claims 1 to 3, characterized in that: The freeze-drying time should not be less than 48 hours.

5. A carbon slurry, characterized in that: The carbon slurry is obtained by mixing a binder, the pre-dispersed ultrafine composite carbon particles according to any one of claims 1 to 4, and a solvent.

6. The carbon slurry according to claim 5, characterized in that The solid content of the carbon slurry is 2wt% to 4wt%; the mass ratio of the pre-dispersed ultrafine composite carbon particles to the adhesive is 40:60 to 70:

30.

7. The carbon slurry according to claim 5, characterized in that The adhesive includes at least one of PAA and PVDF.

8. The carbon slurry according to any one of claims 5 to 7, characterized in that The viscosity of the carbon slurry is ≤600mPa·s; the D 50 ≤300nm.

9. A current collector, characterized in that: The current collector includes a current collector body and a carbon coating disposed on at least one side of the current collector body, wherein the carbon coating is obtained by coating and drying the carbon slurry according to any one of claims 5 to 8.

10. The current collector according to claim 9, characterized in that The thickness of the carbon coating is 60nm~300nm.

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