Current collector composite slurry, preparation method of current collector composite slurry, composite positive current collector and application of composite positive current collector

Abstract

The invention relates to the technical field of batteries, in particular to current collector composite slurry and a preparation method thereof, and a composite positive current collector and application thereof. The preparation method of the current collector composite slurry comprises the following steps: performing first mixing on a solvent, a dispersing agent and a surfactant to obtain a first system; the first system, a first carbon material and a positive charge modifier are subjected to second mixing, the first carbon material is selected from graphite and / or graphene, and a second system is obtained; third mixing is conducted on the second system and a second carbon material, the second carbon material is selected from conductive carbon black, then high-pressure homogeneous stripping treatment is conducted, and a composite stripping solution is obtained; and performing fourth mixing on the composite stripping liquid and a binder to obtain the current collector composite slurry. According to the method disclosed by the invention, electrostatic self-assembly between the carbon materials can be realized, the interface connection force between the carbon materials can be improved, the phenomena of sheet layer stacking of the first carbon material and agglomeration of the second carbon material can be prevented, the stability of the slurry is good, and the electrochemical performance of the composite current collector is favorably improved.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a current collector composite slurry and a preparation method thereof, a composite positive electrode current collector and applications thereof. Background Art

[0002] Metal current collectors in lithium batteries have the function of attaching active materials and collecting electrons for conductivity. The particle size of the active materials in lithium battery electrodes is relatively large, which reduces the contact area between the particles and the current collector, reduces the conduction path of electrons, thereby increasing resistance and reducing the adhesion between the active materials and the current collector. Carbon-coated current collectors are made by coating the surface of metal foil with dispersed conductive carbon materials. This coating can provide excellent static conductivity, increase the contact area between the electrode active materials and the current collector, thereby collecting the microcurrent of the active materials, reducing the contact resistance between the positive electrode material and the current collector, and improving the adhesion between the two, thereby improving the overall performance of the battery.

[0003] However, the carbon coating layer mainly composed of conductive graphite and conductive carbon black still has point-to-point contact with the active material, resulting in poor conductivity of the electrode and insufficient peeling strength of the active material due to insufficient contact area. The carbon coating layer mainly composed of graphene can achieve ball-to-surface contact between the active material and the carbon coating layer by utilizing the characteristics of the ultra-thin flexible sheet structure, increasing the contact area and improving the conductivity and peeling strength of the electrode. However, there is insufficient interface bonding force in the middle of the coating, resulting in insufficient stability of the spatial network structure, poor adhesion of the carbon coating layer, and easy falling off.

[0004] Therefore, how to improve the interfacial connection force between carbon materials in the graphene current collector slurry, thereby maintaining the stability of the spatial network structure of the coating, ensuring the excellent conductive performance of the current collector while improving the adhesion between the carbon coating layer and the metal foil is a technical problem that needs to be solved urgently in this field.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] One object of the present invention is to provide a method for preparing a current collector composite slurry to solve the above-mentioned technical problems, which can improve the interfacial connection force between the first carbon material and the second carbon material in the graphene current collector slurry, thereby maintaining the stability of the spatial network structure of the coating, ensuring the excellent conductive performance of the current collector, and at the same time improving the adhesion between the carbon coating layer and the current collector base layer.

[0007] Another object of the present invention is to provide a current collector composite slurry having excellent stability.

[0008] Another object of the present invention is to provide a composite positive electrode current collector.

[0009] Another object of the present invention is to provide a positive electrode sheet.

[0010] Another object of the present invention is to provide a battery.

[0011] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0012] A method for preparing a current collector composite slurry comprises the following steps:

[0013] The solvent, dispersant and surfactant are first mixed to obtain a first system; the first system, a first carbon material and a positive charge modifier are second mixed, and the first carbon material is selected from graphite and / or graphene to obtain a second system; the second system and a second carbon material are third mixed, and the second carbon material is selected from conductive carbon black, and then subjected to high-pressure homogenization stripping treatment to obtain a composite stripping liquid; the composite stripping liquid and a binder are fourth mixed to obtain a current collector composite slurry.

[0014] In some embodiments, the mass ratio of the solvent, the dispersant, and the surfactant is (850-950):(1-5):(0.5-1.5).

[0015] In some embodiments, the dispersant includes at least one of sodium carboxymethyl cellulose, sodium dodecyl sulfate, polyvinyl pyrrolidone and xanthan gum.

[0016] In some embodiments, the surfactant includes at least one of ethanol, isopropanol, dipropylene glycol, ethoxylated acetylenic alcohols, lauryl alcohol, and polyether polyols.

[0017] In some embodiments, the first mixing specifically includes: dispersing the solvent and the dispersant, and then mixing with the surfactant; the rotation speed of the dispersing treatment is 2500 to 3500 rpm, and the time of the dispersing treatment is 20 to 60 minutes.

[0018] In some embodiments, the graphite is selected from at least one of natural flake graphite, expanded graphite and recycled graphite; and the graphene is selected from at least one of physical graphene and redox graphene.

[0019] In some embodiments, the average particle size of the first carbon material is 10 to 500 μm.

[0020] In some embodiments, the positive charge modifier includes at least one of alkylammonium chloride, benzalkonium chloride, and benzalkonium chloride.

[0021] In some embodiments, the mass ratio of the first carbon material to the positive charge modifier is (20-40):(0.2-1).

[0022] In some implementations, the second mixing speed is 1000-2000 rpm, and the second mixing time is 5-20 min.

[0023] In some embodiments, the mass ratio of the first carbon material to the second carbon material is (20-40):(20-40).

[0024] In some implementations, the rotation speed of the third mixing is 1000-2000 rpm, and the time of the third mixing is 5-20 min.

[0025] In some embodiments, the high pressure homogenization stripping treatment is performed at a pressure of 600 to 800 bar and for a time of 1 to 5 hours.

[0026] In some embodiments, the binder includes at least one of modified polyacrylic acid, modified polyacrylonitrile, modified polyvinyl alcohol and styrene-butadiene latex.

[0027] In some embodiments, the mass ratio of the first carbon material to the binder is (20-40):(40-60).

[0028] In some implementations, the rotation speed of the fourth mixing process is 800 to 3000 rpm, and the time of the fourth mixing process is 20 to 60 minutes.

[0029] A current collector composite slurry is prepared by the current collector composite slurry preparation method.

[0030] A composite positive electrode current collector comprises a current collector base layer and a carbon coating layer arranged on at least one side surface of the current collector base layer, wherein the carbon coating layer is prepared from a current collector composite slurry; the current collector composite slurry is prepared by the current collector composite slurry preparation method.

[0031] In some embodiments, the resistivity of the carbon coating layer is 40 to 110 mΩ·cm.

[0032] In some embodiments, the peeling force of the carbon coating layer is 650-730 N / m.

[0033] In some embodiments, the carbon coating layer has a dyne value of 58-66.

[0034] In some embodiments, the surface density of the carbon coating layer is 0.6 to 1.2 mg / cm 2 ;

[0035] In some embodiments, the method for preparing the composite positive electrode current collector specifically includes: coating the current collector composite slurry on at least one surface of a current collector substrate, and drying at 75 to 140° C. for 30 to 90 seconds.

[0036] A positive electrode sheet comprises the composite positive electrode current collector and a positive electrode material layer located on at least one side surface of the composite positive electrode current collector.

[0037] In some embodiments, the resistivity of the positive electrode sheet is 170 to 290 Ω·cm.

[0038] In some embodiments, the peel strength of the positive electrode sheet is 47 to 60 N / m.

[0039] A battery comprises the positive electrode sheet.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The preparation method of the current collector composite slurry of the present invention, the dispersant in the first system can enhance the spatial stability of the current collector slurry, the surfactant can adjust the surface tension of the first system to be close to the surface energy of graphite, realize the effective combination of the solvent and the surface of the first carbon material, and is conducive to improving the subsequent stripping efficiency; the positive charge modifier can modify the surface of the first carbon material appropriately with positive charge; the second carbon material can be used as an intercalation agent, inserted between the first carbon material sheets after stripping, and carbon black will introduce functional groups (such as oxygen, hydroxyl, carboxylic acid group) during the preparation process. These functional groups have electron affinity and dissociation energy, so that the carbon black surface is negatively charged. The negatively charged second carbon material and the positively charged first carbon material are in situ composited to prevent the first carbon material sheets from stacking and agglomerating, thereby improving the stripping efficiency of the first carbon material. Through the coordination of each step, the electrostatic self-assembly of the first carbon material and the second carbon material can be achieved, and the interface connection force between the first carbon material and the second carbon material can be improved. At the same time, in this case, the carbon black is attached to the surface of the first carbon material, which can prevent the first carbon material sheets from stacking, carbon black agglomeration, etc., and the slurry stability is good.

[0042] (2) The current collector composite slurry of the present invention has excellent stability, which is beneficial to improving the electrochemical performance of the current collector.

[0043] (3) The carbon coating layer of the composite positive electrode current collector of the present invention has good spatial structural stability, low resistivity, suitable peel strength and dyne value, and the composite positive electrode current collector has excellent electrochemical performance.

[0044] (4) The battery of the present invention has excellent cycle performance, rate performance and safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 This is a scanning electron microscope image of the carbon coating layer of the composite positive electrode current collector of Example 1 of the present invention.

[0047] Figure 2 This is a stability monitoring diagram of the current collector composite slurry of Example 1 of the present invention. DETAILED DESCRIPTION

[0048] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0049] According to one aspect of the present invention, the present invention relates to a method for preparing a current collector composite slurry, comprising the following steps:

[0050] The solvent, dispersant and surfactant are first mixed to obtain a first system; the first system, a first carbon material and a positive charge modifier are second mixed, and the first carbon material is selected from graphite and / or graphene to obtain a second system; the second system and a second carbon material are third mixed, and the second carbon material is selected from conductive carbon black, and then high-pressure homogenization stripping treatment is performed to obtain a composite stripping liquid; the composite stripping liquid and a binder are fourth mixed to obtain a current collector composite slurry.

[0051] In the preparation method of the current collector composite slurry of the present invention, the dispersant in the first system can enhance the spatial stability of the current collector slurry, the surfactant can adjust the surface tension of the first system to be close to the graphite surface energy, realize the effective combination of the solvent and the surface of the first carbon material, and help to improve the subsequent stripping efficiency; the positive charge modifier can modify the surface of the first carbon material with appropriate positive charge; the second carbon material can be used as an intercalation agent, inserted between the first carbon material sheets after stripping, and carbon black will introduce functional groups (such as oxygen, hydroxyl, carboxylic acid groups) during the preparation process. These functional groups often have electron affinity and dissociation energy, so that the carbon black surface is negatively charged, and the negatively charged second carbon material is in situ composited with the positively charged first carbon material, preventing the first carbon material sheets from stacking and agglomerating, and improving the stripping efficiency of the first carbon material. Through the coordination of each step, the electrostatic self-assembly of the first carbon material and the carbon black can be achieved, and the interface connection force between the first carbon material and the carbon black can be improved. At the same time, in this case, the carbon black is attached to the surface of the first carbon material, which can prevent the first carbon material sheets from stacking, carbon black agglomeration, etc., and the slurry has good stability, which is beneficial to improve the electrochemical performance of the current collector.

[0052] In some embodiments, the mass ratio of the solvent, dispersant, and surfactant is (850-950):(1-5):(0.5-1.5), such as 850:1:0.5, 890:3:1, 920:4:0.8, or 950:5:1.5, etc. The solvent, dispersant, and surfactant of the present invention adopt a suitable mass ratio, which is more conducive to ensuring the performance of the first system, facilitating subsequent operations, and improving the performance of the final slurry. In some embodiments, the dispersant includes at least one of sodium carboxymethyl cellulose, sodium dodecyl sulfate, polyvinyl pyrrolidone, and xanthan gum, such as a combination of sodium carboxymethyl cellulose and sodium dodecyl sulfate, a combination of polyvinyl pyrrolidone and xanthan gum, etc. In some embodiments, the surfactant includes at least one of ethanol, isopropanol, dipropylene glycol, ethoxylated acetylenic alcohol, lauryl alcohol, and polyether polyols, such as ethanol and isopropanol, dipropylene glycol, and ethoxylated acetylenic alcohol, etc.

[0053] In some embodiments, the first mixing specifically includes: dispersing the solvent and the dispersant, and then mixing with the surfactant; the speed of the dispersing treatment is 2500-3500rpm, such as 2500rpm, 280rpm, 3000rpm, 3200rpm, 3500rpm, etc., or any range between the two; the time of the dispersing treatment is 20-60min, such as 20min, 25min, 30min, 40min, 60min, etc., or any range between the two. By adopting appropriate dispersing treatment conditions, the material can be evenly dispersed.

[0054] In some embodiments, graphite is selected from at least one of natural flake graphite, expanded graphite and recycled graphite; graphene is selected from at least one of physical graphene and redox graphene; in some embodiments, the average particle size of the first carbon material is 10 to 500 μm, for example, 50 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 500 μm, etc., or any range value between the two.

[0055] In some embodiments, the positive charge modifier includes at least one of alkylammonium chloride, benzalkonium chloride and benzalkonium chloride, such as a combination of alkylammonium chloride and benzalkonium chloride, a combination of benzalkonium chloride and benzalkonium chloride, etc. In some embodiments, the mass ratio of the first carbon material to the positive charge modifier is (20-40):(0.2-1), such as 20:0.2, 25:0.3, 30:0.5, 35:0.8 or 40:1, etc. The present invention uses a positive charge modifier in an appropriate amount ratio, which can better modify the surface of the first carbon material with positive charge, laying a good foundation for the subsequent acquisition of a highly stable composite slurry.

[0056] In some embodiments, the second mixing speed is 1000-2000rpm, such as 1000rpm, 1200rpm, 1500rpm, 1600rpm, 1800rpm, 2000rpm, etc., or any range between the two. The second mixing time is 5-20min, such as 5min, 7min, 10min, 15min, 20min, etc., or any range between the two. The second mixing of the present invention adopts appropriate conditions to ensure that the materials are fully mixed, the positive charge modifier plays a better role, and the second system is obtained.

[0057] In some embodiments, the mass ratio of the first carbon material to the second carbon material is (20-40):(20-40), such as 20:20, 20:25, 30:35, 40:20, 40:30, etc. The first carbon material and the second carbon material adopt an appropriate mass ratio, which is more conducive to synergistic effect and improves the electrochemical performance of the composite current collector.

[0058] In some embodiments, the third mixing speed is 1000-2000 rpm, such as 1000 rpm, 1200 rpm, 1500 rpm, 1800 rpm, 2000 rpm, etc., or any range between the two. The third mixing time is 5-20 min, such as 5 min, 10 min, 15 min, 20 min, etc. Appropriate third mixing conditions are more conducive to uniform dispersion of the second carbon material.

[0059] In some embodiments, the pressure of the high-pressure homogenization stripping treatment is 600-800 bar, such as 600 bar, 650 bar, 700 bar, 750 bar, 800 bar, etc., or any range between the two. The time is 1-5 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, etc., or any range between the two. The present invention adopts suitable high-pressure homogenization stripping treatment conditions, which is more conducive to the composite of the positively charged first carbon material and the negatively charged second carbon material, and improves the interfacial bonding force between the two.

[0060] In some embodiments, the binder includes at least one of modified polyacrylic acid, modified polyacrylonitrile, modified polyvinyl alcohol and styrene-butadiene latex, such as a combination of modified polyacrylic acid and modified polyacrylonitrile, a combination of modified polyacrylonitrile and modified polyvinyl alcohol, and the like.

[0061] In some embodiments, the mass ratio of the first carbon material to the binder is (20-40): (40-60), such as 20:40, 25:45, 30:50, 35:55 ​​or 40:60, etc. The present invention adopts a binder of a suitable mass ratio to ensure that the composite slurry has suitable bonding properties, so as to facilitate the subsequent composite with the current collector substrate, ensure that the formed carbon coating layer has suitable bonding properties with the current collector substrate, and ensure the mechanical properties and electrochemical properties of the coating.

[0062] In some embodiments, the rotation speed of the fourth mixing process is 800-3000 rpm, such as 800 rpm, 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, etc., or any range of two values; the time of the fourth mixing process is 20-60 min, such as 20 min, 30 min, 40 min, 50 min, 60 min, etc. The present invention adopts appropriate fourth mixing process conditions to ensure high stability of the current collector composite slurry.

[0063] According to another aspect of the present invention, the present invention also relates to a current collector composite slurry, which is prepared by the above-mentioned current collector composite slurry preparation method. The current collector composite slurry has excellent stability.

[0064] According to another aspect of the present invention, the present invention also relates to a composite positive electrode current collector, comprising a current collector base layer and a carbon coating layer arranged on at least one side surface of the current collector base layer; the carbon coating layer is prepared from the current collector composite slurry; the current collector composite slurry is prepared by the above-mentioned current collector composite slurry preparation method.

[0065] The carbon coating layer of the composite positive electrode current collector of the present invention has good spatial structural stability, low resistivity, suitable peel strength and dyne value, and the composite positive electrode current collector has excellent electrochemical performance.

[0066] In some embodiments, the resistivity of the carbon coating layer is 40 to 110 mΩ·cm, for example, 40 mΩ·cm, 50 mΩ·cm, 60 mΩ·cm, 70 mΩ·cm, 100 mΩ·cm, 110 mΩ·cm, etc.

[0067] In some embodiments, the peeling force of the carbon coating layer is 650 to 730 N / m, for example, 650 N / m, 660 N / m, 680 N / m, 700 N / m, 710 N / m, 730 N / m, etc.

[0068] In some embodiments, the dyne value of the carbon coating layer is 58-66, such as 60, 62, 64, 66, etc.

[0069] In some embodiments, the surface density of the carbon coating layer is 0.6 to 1.2 mg / cm 2 , for example 0.6 mg / cm 2 , 0.9mg / cm 2 , 1mg / cm 2 , 1.1mg / cm 2 , 1.2mg / cm 2 wait.

[0070] In some embodiments, the preparation method of the composite positive electrode current collector specifically includes: coating the current collector composite slurry to at least one side surface of the current collector base layer, and drying at 75 to 140° C. (e.g., 75° C., 90° C., 120° C. or 140° C.) for 30 to 90 seconds (e.g., 30 seconds, 40 seconds, 50 seconds, 60 seconds, 70 seconds, 80 seconds, 90 seconds, etc.).

[0071] According to another aspect of the present invention, the present invention also relates to a positive electrode sheet, comprising a composite positive electrode current collector and a positive electrode material layer located on at least one side surface of the composite positive electrode current collector.

[0072] The positive electrode sheet of the present invention has excellent conductivity, high peeling strength and good structural stability.

[0073] In some embodiments, the resistivity of the positive electrode sheet is 170 to 290 Ω·cm, for example, 170 Ω·cm, 180 Ω·cm, 200 Ω·cm, 240 Ω·cm, 250 Ω·cm, 290 Ω·cm, etc.

[0074] In some embodiments, the peel strength of the positive electrode sheet is 47 to 60 N / m, for example, 47 N / m, 50 N / m, 52 N / m, 55 N / m, 58 N / m, 60 N / m, etc.

[0075] According to another aspect of the present invention, the present invention also relates to a battery, comprising the above-mentioned positive electrode sheet.

[0076] The battery of the present invention has excellent cycle performance, rate performance and safety performance.

[0077] The following is further explained in conjunction with specific embodiments and comparative examples.

[0078] Example 1

[0079] A method for preparing a current collector composite slurry comprises the following steps:

[0080] (a) 890 g of solvent and 3 g of dispersant are dispersed, the solvent is deionized water, the dispersant is sodium carboxymethyl cellulose, the speed of the dispersion is 3000 rpm, the time of the dispersion is 30 min, and then 1 g of surfactant is added, the surfactant is dipropylene glycol, to obtain a first system.

[0081] (b) Add 30 g of the first carbon material and 0.5 g of the positive charge modifier to the first system for a second mixing, wherein the first carbon material is selected from natural flake graphite, the average particle size of the first carbon material is 80 μm, and the positive charge modifier is benzalkonium chloride. The second mixing is stirring and dispersing at a rotation speed of 1500 rpm for 10 minutes to obtain a second system.

[0082] (c) The second system and 30g of the second carbon material are mixed for the third time, wherein the second carbon material is acetylene carbon black, and the third mixing is stirring dispersion, the speed is 1500rpm, and the time is 10min. Then the mixture is transferred to a high-pressure homogenizer for high-pressure homogenization and stripping treatment, the pressure of the high-pressure homogenization and stripping treatment is 700bar, and the time is 2h. A composite stripping liquid is obtained.

[0083] (d) The composite stripping liquid is mixed with 50 g of a binder for the fourth time, wherein the binder is a modified polyacrylic acid binder, and the fourth mixing is shear dispersion with a rotation speed of 1000 rpm and a time of 30 min to obtain a current collector composite slurry.

[0084] A method for preparing a composite current collector comprises the following steps:

[0085] The current collector composite slurry was evenly coated on aluminum foil and dried at 130 °C for 1 min to obtain a composite current collector with a surface density of 1 mg / cm 2 .

[0086] The scanning electron microscope image of the carbon coating layer of the composite positive electrode current collector of this embodiment is as follows Figure 1 shown.

[0087] The stability monitoring diagram of the current collector composite slurry of this embodiment is as follows: Figure 2 shown.

[0088] Example 2

[0089] A method for preparing a current collector composite slurry comprises the following steps:

[0090] (a) 900 g of solvent and 4 g of dispersant are dispersed, the solvent is deionized water, the dispersant is sodium dodecyl sulfate, the speed of the dispersion is 3200 rpm, the time of the dispersion is 25 min, and then 0.8 g of a surfactant is added, the surfactant is ethoxylated acetylenic alcohol, to obtain a first system.

[0091] (b) Add 35 g of the first carbon material and 0.7 g of the positive charge modifier to the first system for a second mixing, wherein the first carbon material is selected from natural flake graphite, the average particle size of the first carbon material is 100 μm, the positive charge modifier is benzalkonium chloride and alkylammonium chloride, and the second mixing is stirring and dispersing at a rotation speed of 1700 rpm for 8 minutes to obtain a second system.

[0092] (c) The second system and 35 g of the second carbon material are mixed for the third time, wherein the second carbon material is acetylene black, and the third mixing is stirring and dispersing, the speed is 1300 rpm, and the time is 25 min. Then the mixture is transferred to a high-pressure homogenizer for high-pressure homogenization and stripping treatment, the pressure of the high-pressure homogenization and stripping treatment is 750 bar, and the time is 1.5 h, to obtain a composite stripping liquid.

[0093] (d) The composite stripping liquid was mixed with 55 g of a binder for the fourth time. The binder was a modified polyacrylic acid binder. The fourth mixing was shear dispersion with a rotation speed of 1200 rpm and a time of 25 min to obtain a current collector composite slurry.

[0094] A method for preparing a composite current collector, except that the current collector composite slurry in this embodiment is used, other conditions are the same as those in Example 1.

[0095] Example 3

[0096] A method for preparing a current collector composite slurry, which differs from Example 1 in that:

[0097] The solvent is 950 g, the dispersant is 1 g, the surfactant is 0.5 g, the first carbon material is 20 g, the positive charge modifier is 0.2 g, the second carbon material is 20 g, and the binder is 40 g.

[0098] A method for preparing a composite current collector, except that the current collector composite slurry in this embodiment is used, other conditions are the same as those in Example 1.

[0099] Example 4

[0100] A method for preparing a current collector composite slurry, which differs from Example 1 in that:

[0101] The solvent is 850 g, the dispersant is 5 g, the surfactant is 1.5 g, the first carbon material is 40 g, the positive charge modifier is 1 g, the second carbon material is 40 g, and the binder is 60 g.

[0102] A method for preparing a composite current collector, except that the current collector composite slurry in this embodiment is used, other conditions are the same as those in Example 1.

[0103] Example 5

[0104] A method for preparing a current collector composite slurry comprises the following steps:

[0105] (a) 890 g of solvent and 3 g of dispersant are dispersed, the solvent is deionized water, the dispersant is sodium dodecyl sulfate, the speed of the dispersion is 3500 rpm, the time of the dispersion is 20 min, and then 1 g of a surfactant is added, the surfactant is ethoxylated acetylenic alcohol, to obtain a first system.

[0106] (b) Add 30 g of the first carbon material and 0.5 g of the positive charge modifier to the first system for a second mixing, wherein the first carbon material is selected from natural flake graphite, the average particle size of the first carbon material is 180 μm, the positive charge modifier is benzalkonium chloride, and the second mixing is stirring and dispersing at a rotation speed of 2000 rpm for 5 minutes to obtain a second system.

[0107] (c) The second system and 30 g of the second carbon material are mixed for the third time, wherein the second carbon material is acetylene carbon black, and the third mixing is stirring and dispersing, the speed is 1000 rpm, and the time is 20 min. Then the mixture is transferred to a high-pressure homogenizer for high-pressure homogenization and stripping treatment, the pressure of the high-pressure homogenization and stripping treatment is 800 bar, and the time is 1 hour, to obtain a composite stripping liquid.

[0108] (d) The composite stripping liquid is mixed with 50 g of a binder for the fourth time. The binder is a modified polyacrylic acid binder. The fourth mixing is shear dispersion with a rotation speed of 3000 rpm and a time of 40 min to obtain a current collector composite slurry.

[0109] A method for preparing a composite current collector, except that the current collector composite slurry in this embodiment is used, other conditions are the same as those in Example 1.

[0110] Example 6

[0111] A method for preparing a current collector composite slurry comprises the following steps:

[0112] (a) 890 g of solvent and 3 g of dispersant are dispersed, the solvent is deionized water, the dispersant is sodium dodecyl sulfate, the speed of the dispersion is 2500 rpm, the time of the dispersion is 40 min, and then 1 g of a surfactant is added, the surfactant is ethoxylated acetylenic alcohol, to obtain a first system.

[0113] (b) Add 30 g of the first carbon material and 0.5 g of the positive charge modifier to the first system for a second mixing, wherein the first carbon material is selected from natural flake graphite, the average particle size of the first carbon material is 40 μm, the positive charge modifier is benzalkonium chloride, and the second mixing is stirring and dispersing at a rotation speed of 2000 rpm for 5 minutes to obtain a second system.

[0114] (c) The second system and 30 g of the second carbon material are mixed for the third time, wherein the second carbon material is acetylene black, and the third mixing is stirring and dispersing, the speed is 1000 rpm, and the time is 20 min. Then the mixture is transferred to a high-pressure homogenizer for high-pressure homogenization and stripping treatment, the pressure of the high-pressure homogenization and stripping treatment is 600 bar, and the time is 5 h, to obtain a composite stripping liquid.

[0115] (d) The composite stripping liquid is mixed with 50 g of a binder for the fourth time, wherein the binder is a modified polyacrylic acid binder, and the fourth mixing is shear dispersion with a rotation speed of 800 rpm and a time of 40 min to obtain a current collector composite slurry.

[0116] A method for preparing a composite current collector, except that the current collector composite slurry in this embodiment is used, other conditions are the same as those in Example 1.

[0117] Example 7

[0118] A method for preparing a current collector composite slurry, which differs from Example 1 in that:

[0119] The first carbon material is redox graphene XGnP-Grade H from XG Sciences Inc.

[0120] A method for preparing a composite current collector, except that the current collector composite slurry in this embodiment is used, other conditions are the same as those in Example 1.

[0121] Example 8

[0122] A method for preparing a current collector composite slurry, which differs from Example 1 in that:

[0123] The first carbon material is the physical graphene GR-EG10A produced by Hunan Gaorui Power Materials Co., Ltd.

[0124] A method for preparing a composite current collector, except that the current collector composite slurry in this embodiment is used, other conditions are the same as those in Example 1.

[0125] Comparative Example 1

[0126] A method for preparing a current collector composite slurry, which differs from Example 1 in that:

[0127] No positive charge modifier was added.

[0128] A method for preparing a composite current collector, except that the current collector composite slurry in this comparative example is used, other conditions are the same as those in Example 1.

[0129] Comparative Example 2

[0130] A method for preparing a current collector composite slurry, which differs from Example 1 in that:

[0131] No high pressure homogenization stripping treatment is performed.

[0132] A method for preparing a composite current collector, except that the current collector composite slurry in this comparative example is used, other conditions are the same as those in Example 1.

[0133] Comparative Example 3

[0134] A method for preparing a current collector composite slurry comprises the following steps:

[0135] 890g of solvent, 3g of dispersant, 1g of surfactant, 30g of the first carbon material, 0.5g of positive charge modifier, 30g of the second carbon material and 50g of binder are mixed at a rotation speed of 1500rpm for 10min; the solvent is deionized water, the dispersant is sodium carboxymethyl cellulose, the surfactant is dipropylene glycol, the first carbon material is natural flake graphite, the second carbon material is acetylene carbon black, and the binder is modified polyacrylic acid binder to obtain a current collector composite slurry.

[0136] A method for preparing a composite current collector, except that the current collector composite slurry in this comparative example is used, other conditions are the same as those in Example 1.

[0137] Comparative Example 4

[0138] A method for preparing a current collector composite slurry, which differs from Example 1 in that:

[0139] Without adding the first carbon material, the mass of the second carbon material is 60 g.

[0140] Comparative Example 5

[0141] A method for preparing a current collector composite slurry, which differs from Example 7 in that:

[0142] Without adding the second carbon material, the mass of the first carbon material is 60 g.

[0143] Comparative Example 6

[0144] A method for preparing a current collector composite slurry, which differs from Example 8 in that:

[0145] Without adding the second carbon material, the mass of the first carbon material is 60 g.

[0146] Experimental example

[0147] 1. Composite current collector coating performance test

[0148] The composite current collector was cut into five discs with a radius of 16 mm, tested by a two-probe method, and the average value was taken to obtain the coating resistivity.

[0149] The foil was cut into 2cm*20cm strips, bonded to the stainless steel plate with 3M tape, the electrode strips were bonded to the tape, the electrode was stretched 90°, repeated 5 times, and the average value was taken to obtain the coating peel strength.

[0150] Use a special dyne pen to draw a line on the coating surface. If the line remains stable and does not break, it means that the surface energy is greater than or equal to the marked value of the pen; if the line breaks, it means that the surface energy is lower than the marked value. According to the different dyne value levels of dyne pens, the surface energy of the material can be tested step by step.

[0151] The coating performance test results of the composite current collector are shown in Table 1.

[0152] Table 1 Coating performance test results of composite current collector

[0153]

[0154]

[0155] 2. Performance test of pole piece

[0156] The composite current collectors of each embodiment and comparative example are respectively prepared into batteries, comprising the following steps:

[0157] Prepare lithium iron phosphate positive electrode slurry, the formula is 96.5 parts of high carbon coated lithium iron phosphate powder, 2 parts of PVDFHSV900, 1.5 parts of conductive carbon black SuperP Li, 100 parts of N-methylpyrrolidone. Use a double planetary disperser to mix dry powder, knead high solid content, and dilute and homogenize. Then, the slurry is evenly coated on the composite current collector prepared above, baked at 110℃ for 3h, and then roller pressed (density 2.4g / cm 3 ).

[0158] Positive electrode resistivity test: Cut the electrode into five discs with a radius of 16 mm, test them using the two-probe method, and take the average value to obtain the electrode resistivity.

[0159] Positive electrode peeling strength test: Cut the foil into 2cm×20cm strips, adhere them to the stainless steel plate with 3M tape, adhere the electrode strips to the tape, stretch the electrode at 90°, repeat 5 times, take the average value, and get the electrode peeling strength.

[0160] The performance test results of the positive electrode are shown in Table 2.

[0161] Table 2 Performance test results of positive electrode

[0162]

[0163]

[0164] It can be seen from Table 1 and Table 2 that the carbon coating layer prepared from the current collector composite slurry obtained by the method of each embodiment of the present invention has high conductivity, suitable peel strength and dyne value, and the corresponding positive electrode sheet has excellent conductivity and suitable peel strength.

[0165] The carbon coating layer prepared by the current collector composite slurry obtained by the methods of each comparative example has poor conductivity, low peel strength and low dyne value, and the corresponding positive electrode sheet has poor conductivity and low peel strength.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a current collector composite slurry, characterized in that: The following steps are involved: The solvent, the dispersant and the surfactant are first mixed to obtain a first system; performing a second mixing of the first system, a first carbon material and a positive charge modifier, wherein the first carbon material is selected from graphite and / or graphene, to obtain a second system; The second system and a second carbon material are mixed for a third time, wherein the second carbon material is selected from conductive carbon black, and then subjected to a high-pressure homogenization stripping treatment to obtain a composite stripping liquid; The composite stripping liquid and the binder are mixed for the fourth time to obtain a current collector composite slurry.

2. The method for preparing the current collector composite slurry according to claim 1, characterized in that: Contains at least one of the following features (1) to (4): (1) The mass ratio of the solvent, the dispersant and the surfactant is (850-950):(1-5):(0.5-1.5); (2) the dispersant comprises at least one of sodium carboxymethyl cellulose, sodium dodecyl sulfate, polyvinyl pyrrolidone and xanthan gum; (3) The surfactant comprises at least one of ethanol, isopropanol, dipropylene glycol, ethoxylated acetylenic alcohol, lauryl alcohol and polyether polyol; (4) the first mixing specifically comprises: dispersing the solvent and the dispersant, and then mixing with the surfactant; The rotation speed of the dispersion treatment is 2500-3500 rpm, and the time of the dispersion treatment is 20-60 min.

3. The method for preparing the current collector composite slurry according to claim 1, characterized in that: Contains at least one of the following features (1) to (5): (1) The graphite is selected from at least one of natural flake graphite, expanded graphite and recycled graphite; the graphene is selected from at least one of physical graphene and redox graphene; (2) The average particle size of the first carbon material is 10 to 500 μm; (3) the positive charge modifier comprises at least one of alkylammonium chloride, benzalkonium chloride and benzalkonium chloride; (4) The mass ratio of the first carbon material to the positive charge modifier is (20-40):(0.2-1); (5) The rotation speed of the second mixing is 1000-2000 rpm, and the time of the second mixing is 5-20 min.

4. The method for preparing the current collector composite slurry according to claim 1, characterized in that: Contains at least one of the following features (1) to (6): (1) The mass ratio of the first carbon material to the second carbon material is (20-40):(20-40); (2) The rotation speed of the third mixing is 1000-2000 rpm, and the time of the third mixing is 5-20 min; (3) The pressure of the high-pressure homogenization stripping treatment is 600 to 800 bar, and the time is 1 to 5 hours; (4) The binder comprises at least one of modified polyacrylic acid, modified polyacrylonitrile, modified polyvinyl alcohol and styrene-butadiene latex; (5) The mass ratio of the first carbon material to the binder is (20-40):(40-60); (6) The rotation speed of the fourth mixing process is 800 to 3000 rpm, and the time of the fourth mixing process is 20 to 60 minutes.

5. A current collector composite slurry, characterized in that: The composite slurry is prepared by the method for preparing the current collector according to any one of claims 1 to 4.

6. A composite positive electrode current collector, characterized in that: It comprises a current collector base layer and a carbon coating layer arranged on at least one side of the current collector base layer, wherein the carbon coating layer is prepared from a current collector composite slurry; the current collector composite slurry is prepared by the preparation method of the current collector composite slurry according to any one of claims 1 to 5.

7. The composite positive electrode current collector according to claim 6, characterized in that: Contains at least one of the following features (1) to (5): (1) The resistivity of the carbon coating layer is 40 to 110 mΩ·cm; (2) The peeling force of the carbon coating layer is 650-730 N / m; (3) The dyne value of the carbon coating layer is 58 to 66; (4) The surface density of the carbon coating layer is 0.6 to 1.2 mg / cm 2 ; (5) The method for preparing the composite positive electrode current collector specifically comprises: coating the current collector composite slurry onto at least one surface of a current collector substrate, and drying at 75 to 140° C. for 30 to 90 seconds.

8. A positive electrode sheet, characterized in that: It comprises the composite positive electrode current collector according to claim 6 or 7 and a positive electrode material layer located on at least one side surface of the composite positive electrode current collector.

9. The positive electrode sheet according to claim 8, characterized in that: Contains at least one of the following features (1) to (2): (1) The resistivity of the positive electrode sheet is 170 to 290 Ω·cm; (2) The peel strength of the positive electrode sheet is 47 to 60 N / m.

10. A battery, characterized in that: Including the positive electrode sheet as described in claim 9.

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