Water-based conductive coating as well as preparation method and application thereof

Abstract

The invention provides a water-based conductive coating as well as a preparation method and application thereof. The water-based conductive coating comprises the following raw material components in parts by weight: 10-20 parts of a modified carbon material and a binder and 60-75 parts of water, the mass ratio of the binder to the modified carbon material is (0.5-1.5): 1; the modified carbon material is obtained by grafting modification of a carbon material. The slurry stability and solvent resistance of the water-based conductive coating are remarkably improved, no negative effect is generated, meanwhile, the peel strength is enhanced, and the surface contact resistance is reduced.

Description

Technical Field

[0001] The present invention relates to the field of cathode materials for lithium batteries, and particularly to an aqueous conductive coating, a preparation method thereof, and uses thereof. Background Art

[0002] With the rapid development of the new energy industry, people have put forward higher requirements for the safety performance and electrical performance of batteries. As the current collector for loading active materials in the positive and negative electrodes of lithium batteries, its main function is to collect the electrons generated by the active materials and output current externally, thereby realizing the process of converting chemical energy into electrical energy. Existing current collectors are usually composed of various conductive metal foils, such as copper foils, aluminum foils, etc. In the traditional production process of battery positive electrode sheets, the positive and negative electrode slurries are directly coated on the surface of the current collector using a coater and dried by hot air to obtain an electrode active material layer. However, the smooth metal current collector cannot fully contact with the active material particles, resulting in limited adhesion of the current collector foil to the active material, a large battery contact impedance, and some active materials may also fall off during cycling, greatly affecting the performance of the battery.

[0003] Currently, the commonly used method in the market is to coat a conductive carbon material on the surface of the current collector foil to improve the peel strength between the electrode active material layer and the current collector, and at the same time reduce the contact resistance between the two. Its effect can only meet general usage requirements and cannot meet higher usage requirements. For example, when used in lithium iron phosphate system batteries, it is required that the peel strength between lithium iron phosphate and the current collector be as large as possible and the surface contact resistance be as small as possible, otherwise it is easy to cause an increase in internal resistance and a reduction in cycle life during use. Summary of the Invention

[0004] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide an aqueous conductive coating, a preparation method thereof, and uses thereof to solve the problems in the prior art.

[0005] To achieve the above and other related purposes, the present invention is obtained through the following technical solutions.

[0006] The present invention provides an aqueous conductive coating, and the aqueous conductive coating includes the following raw material components in parts by weight:

[0007] Modified carbon material and binder 10 - 20 parts by weight

[0008] Water 60 - 75 parts by weight;

[0009] The mass ratio of the binder to the modified carbon material is (0.5 - 1.5):1;

[0010] The modified carbon material is obtained by graft modification of a carbon material.

[0011] Preferably, the carbon material is selected from one or more of conductive carbon black, acetylene black, conductive graphite, carbon nanotubes, and graphene.

[0012] Preferably, the binder is selected from one or several of polyacrylic acid, acrylic resin, polyurethane resin, polyethylene, and ethylene resin.

[0013] Preferably, the raw material components of the water-based conductive coating further include auxiliary agents.

[0014] More preferably, the auxiliary agent includes one or more of defoamers, thickeners, and pH regulators.

[0015] More preferably, in the water-based conductive coating, the content of the auxiliary agent is 0.5 - 3.3 wt%.

[0016] Further preferably, the defoamer is selected from one or more of polyether defoamers, polyether-modified silicone defoamers, and fatty acid ester defoamers.

[0017] Further preferably, the thickener is selected from one or more of natural polysaccharides, polyacrylate thickeners, and polyurethane thickeners.

[0018] Further preferably, the pH regulator is selected from one or more of sodium hydroxide, calcium hydroxide, and ammonia water.

[0019] Further preferably, in the water-based conductive coating, the dosage of the defoamer is 0.1 - 0.3 parts by weight.

[0020] Further preferably, in the water-based conductive coating, the dosage of the thickener is 0.5 - 2.0 parts by weight.

[0021] Further preferably, in the water-based conductive coating, the dosage of the pH regulator is 0.5 - 1.0 parts by weight.

[0022] Preferably, the pH of the water-based conductive coating is 4.5 - 5.5.

[0023] Preferably, the particle size D of the water-based conductive coating 50 <2 μm, D 100 <15 μm.

[0024] Preferably, the graft modification means that the carbon material is first contacted with an initiator, and then contacted with a graft modifier and reacted.

[0025] Preferably, the reaction medium for the graft modification is water.

[0026] Preferably, before the graft reaction, the carbon material is ultrasonically treated.

[0027] More preferably, the ultrasonic power is 200 - 400 W.

[0028] More preferably, the ultrasonic treatment time is 0.5 - 2 h.

[0029] More preferably, the initiator is selected from one or more of potassium persulfate, sodium persulfate, and ammonium persulfate.

[0030] More preferably, the mass ratio of the initiator to the carbon material is (0.4 - 1.0) : (80 - 100).

[0031] More preferably, the graft modifier is selected from one or more of styrene sulfonate, polystyrene sulfonate, polyacrylate, polyacrylic acid, and polyvinyl alcohol.

[0032] More preferably, the mass ratio of the graft modifier to the carbon material is (10 - 20) : (80 - 100).

[0033] The present invention also discloses a preparation method of the above - mentioned water - based conductive coating. After uniformly mixing the raw materials, sand grinding is carried out to obtain the water - based conductive coating.

[0034] The present invention also discloses the use of the above - mentioned water - based conductive coating as a coating for the positive current collector of a battery.

[0035] The present invention discloses a water - based conductive coating, its preparation method and use. The modified carbon material in the present invention is obtained by polymer graft modification of carbon materials using high - energy ultrasonic irradiation. With the multiple effects of ultrasonic dispersion, pulverization, activation, and initiation, the modifier monomers are rapidly polymerized and grafted onto the surface of the carbon material under mild conditions to obtain polymer - grafted carbon materials. Active groups such as carboxyl groups, sulfonic acid groups, and hydroxyl groups are introduced into the carbon materials, significantly improving the slurry stability and solvent resistance of the water - based conductive coating, and no negative effects are produced. When coated on the current collector foil, it can also enhance the peel strength between the current collector and the electrode active material layer, increase the adhesion of the electrode active material layer to the current collector, and reduce the surface contact resistance between the two. Detailed Embodiments

[0036] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0037] Before further describing the specific embodiments of the present invention, it should be understood that the protection scope of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the embodiments of the present invention are for describing specific embodiments, rather than limiting the protection scope of the present invention. The test methods without specific conditions noted in the following examples are generally carried out under conventional conditions or according to the conditions recommended by each manufacturer.

[0038] When the embodiments give a numerical range, it should be understood that unless otherwise specified in the present invention, both endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art of this technology. In addition to the specific methods, equipment, and materials used in the embodiments, according to the knowledge of those skilled in the art of this technology and the description of the present invention, any methods, equipment, and materials similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention can also be used to implement the present invention.

[0039] The present invention provides an aqueous conductive coating, and the aqueous conductive coating comprises the following raw material components in parts by weight:

[0040] Modified carbon material and binder 10 - 20 parts by weight

[0041] Water 60 - 75 parts by weight;

[0042] The mass ratio of the binder to the modified carbon material is (0.5 - 1.5):1; the modified carbon material is obtained by graft modification of the carbon material.

[0043] For example, the mass ratio of the binder to the modified carbon material can be 0.5:1, 1:1, 1.5:1. When the amount of the binder is too small, the solvent resistance of the conductive coating coated on the current collector foil decreases, and the peel strength between the electrode active material layer and the current collector decreases. If it is too much, the conductivity of the current collector will decrease significantly, and the surface contact resistance between the electrode active material layer and the current collector will increase significantly. The mass ratio of the modified carbon material to the binder is preferably (0.5 - 1):1.

[0044] For example, the total amount of the modified carbon material and the binder is 10 parts by weight, 20 parts by weight. If the total content of the modified carbon material and the binder is too low, the solvent resistance of the conductive coating coated on the current collector foil decreases, and the peel strength and surface contact resistance between the electrode active material layer and the current collector deteriorate; if it is too large, the coating of the current collector will be too thick, increasing the surface contact resistance between the electrode active material layer and the current collector.

[0045] In a specific embodiment, the carbon material is selected from one or more of conductive carbon black, acetylene black, conductive graphite, carbon nanotubes, and graphene.

[0046] In a more specific embodiment, the carbon material is conductive carbon black and conductive graphite.

[0047] In a further specific embodiment, the dosage ratio of conductive carbon black to conductive graphite is (3 - 6):1. For example, it can be 3:1, 4:1, 5:1, 6:1. The combined use of conductive carbon black and conductive graphite will result in a better modification effect, better solvent resistance of the coating formed on the surface of the current collector foil by the water-based conductive coating, and also improve the peel strength between the current collector and the electrode active material layer and reduce the surface contact resistance between the two.

[0048] In a specific embodiment, the binder is selected from one or several of polyacrylic acid, acrylic resin, polyurethane resin, polyethylene, and vinyl resin. The binder is in a solution state and viscous state, and its viscosity at 25°C is 50 - 500 mPa·s.

[0049] In a specific embodiment, the raw material components of the water-based conductive coating include auxiliary agents.

[0050] In a more specific embodiment, the auxiliary agent includes one or more of defoamers, thickeners, and pH regulators.

[0051] Auxiliary agents are commonly used additives for preparing current collector coatings. The function of the defoamer is to eliminate the foam in the coating; the function of the thickener is to increase the viscosity of the coating and maintain the relative stability of the system; the function of the pH regulator is to adjust the acidity and alkalinity in the coating so that the pH of the coating is maintained at 4.5 - 5.5.

[0052] In a more specific embodiment, in the water-based conductive coating, the dosage of the auxiliary agent is 0.5 - 3.3 parts by weight.

[0053] In a further specific embodiment, the defoamer is selected from one or more of polyether defoamers, polyether-modified silicone defoamers, alcohol defoamers, and fatty acid ester defoamers.

[0054] The polyether defoamers include GPE-type defoamers, GP-type defoamers, and GPES-type defoamers.

[0055] The polyether-modified silicone defoamers include one or more of polyether silicone oil, polyether-modified silicone, polyether polysiloxane copolymer, and polyether silane.

[0056] The alcohol defoamers are selected from one or more of alkynediol defoamers, polyethylene glycol, diethylhexanol, isooctanol, and isoamyl alcohol.

[0057] The fatty acid ester defoamer includes one or both of stearate and propylene glycol fatty acid ester.

[0058] In a further specific embodiment, the thickener is selected from one or more of polysaccharide thickeners, polyacrylate thickeners, and polyurethane thickeners. The polysaccharide thickeners are selected from one or more of starches, celluloses, pectins, and alginic acids.

[0059] The polyacrylate thickener is polyacrylate.

[0060] The polyurethane thickener is polyurethane.

[0061] The starch thickeners are selected from one or both of tapioca starch and corn starch.

[0062] The cellulose thickeners include sodium carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl methyl cellulose.

[0063] The alginic acid thickeners are selected from one or more of alginic acid, sodium alginate, and propylene glycol alginate.

[0064] In a further specific embodiment, the pH regulator is selected from one or more of sodium hydroxide, calcium hydroxide, and ammonia water.

[0065] In a further specific embodiment, in the aqueous conductive coating, the dosage of the defoamer is 0.1-0.3 wt%. Specifically, it can be 0.1 wt%, 0.2 wt%, or 0.3 wt%.

[0066] In a further specific embodiment, in the aqueous conductive coating, the dosage of the thickener is 0.5-2.0 parts by weight. Specifically, it can be 0.5 part by weight, 1.0 part by weight, 1.5 parts by weight, or 2.0 parts by weight.

[0067] In a further specific embodiment, in the aqueous conductive coating, the dosage of the pH regulator is 0.5-1.0 parts by weight. It can be 0.5 part by weight, 0.7 part by weight, 0.9 part by weight, or 1.0 part by weight.

[0068] In a specific embodiment, the pH of the aqueous conductive coating is 4.5-5.5.

[0069] In a specific embodiment, the particle size D of the aqueous conductive coating 50 <2 μm, D 100 <15 μm.

[0070] In a specific embodiment, the graft modification means that the carbon material is first contacted with an initiator, and then contacted with a graft modifier and reacted.

[0071] In a specific embodiment, the reaction medium for the graft modification is water.

[0072] In a specific embodiment, before the graft reaction, the carbon material is ultrasonically treated.

[0073] In a more specific embodiment, the ultrasonic power is 200 - 400 W. The ultrasonic power can be 200 W, 300 W, or 400 W. If the ultrasonic power is too low, it will affect the grafting rate of the modified carbon material, thus affecting the performance of the waterborne conductive coating. If the ultrasonic power is too high, too many groups will be grafted on the surface of the carbon material, resulting in a decrease in the conductivity of the modified carbon material and an increase in the surface contact resistance between the electrode active material layer and the carbon-coated aluminum foil. The ultrasonic power is preferably 300 W.

[0074] In a more specific embodiment, the ultrasonic treatment time is 0.5 - 2 h. For example, it can be 0.5 - 1 h or 1 h - 2 h.

[0075] In a more specific embodiment, the initiator is selected from one or more of potassium persulfate, sodium persulfate, and ammonium persulfate.

[0076] In a more specific embodiment, the mass ratio of the initiator to the carbon material is (0.4 - 1.0):(80 - 100). For example, it can be (0.4 - 0.6):(80 - 100), (0.6 - 0.8):(80 - 100), or (0.8 - 1.0):(80 - 100). When the amount of the initiator relative to the carbon material is too small, the modification effect will be poor. Specifically, when forming a current collector coating in the waterborne coating, the solvent resistance performance will become poor, the peel strength between the current collector and the electrode active material layer will decrease to a certain extent, and the surface contact resistance between the two will increase. When too much, the grafting rate of the modified carbon material will be too high. Too many groups grafted on the carbon material will cause the conductivity of the modified carbon material itself to decrease, resulting in a decrease in the conductivity of the current collector and an increase in the surface contact resistance between the current collector and the electrode active material layer.

[0077] In a specific embodiment, the graft modifier is selected from one or more of styrene sulfonate, polystyrene sulfonate, polyacrylate, polyacrylic acid, and polyvinyl alcohol.

[0078] In a specific embodiment, the mass ratio of the graft modifier to the carbon material is (10 - 20):(80 - 100). For example, it can be (10 - 12):(80 - 100), (12 - 14):(80 - 100), (14 - 15):(80 - 100), (15 - 17):(80 - 100), (17 - 20):(80 - 100). When the amount of the graft modifier is too small relative to the carbon material, the modification effect will be poor. Specifically, when forming a current collector coating in the waterborne coating, the solvent resistance performance will deteriorate, the peel strength between the current collector and the electrode active material layer will decrease to a certain extent, and the surface contact resistance between the two will increase; when it is too much, the grafting rate of the modified carbon material will be too high, and too many grafted groups on the carbon material will cause the conductivity of the modified carbon material itself to decrease, resulting in a decrease in the conductivity of the current collector and an increase in the surface contact resistance between the current collector and the electrode active material layer. The mass ratio of the graft modifier to the carbon material is preferably (10 - 15):(80 - 100).

[0079] The present invention also discloses a preparation method of the above-mentioned waterborne conductive coating. After mixing the raw materials evenly, perform sanding to obtain the waterborne conductive coating.

[0080] In a specific embodiment, the addition order of the raw material components is water, binder, and modified carbon material in sequence.

[0081] In a more specific embodiment, the addition order of the raw material components is water, pH regulator, thickener, binder, defoamer, and modified carbon material in sequence.

[0082] The present invention also discloses the use of the above-mentioned waterborne conductive coating as a coating for the positive electrode current collector of a battery.

[0083] In a more specific embodiment, the thickness of the cured coating of the coating for the positive electrode current collector of the battery is 1 - 2 μm.

[0084] The following specific embodiments illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0085] Example 1

[0086] This example provides a waterborne conductive coating, and the preparation method is as follows.

[0087] (1) Preparation of modified carbon material

[0088] Add conductive carbon black into an eggplant-shaped flask, and then successively add the initiator potassium persulfate, the modifier sodium polystyrene sulfonate and water. The mass ratio of the initiator, the modifier and the carbon material is 0.4:15:87.6, and the amount of water used is 50% of the total amount of the initiator, the modifier and the carbon material. Purge with nitrogen to remove oxygen for 10 min, and then use an ultrasonic crusher to ultrasonicate for 1 h at a power of 300 W. Filter and dry the reaction solution to obtain the modified carbon material.

[0089] (2) Preparation of waterborne conductive coating

[0090] Add 65 parts by weight of deionized water, the binder polyacrylic acid, 0.5 part by weight of the thickener sodium carboxymethyl cellulose, the modified carbon material and 0.3 part by weight of the diol defoamer into a rotating high-speed disperser and mix for 45 min. The mass ratio of the binder to the modified carbon material is 1:1. In the waterborne conductive coating, the total amount of the binder and the modified carbon material used is 20 parts by weight. Then, use a sand mill to grind for 60 min to obtain the waterborne conductive coating. The rotation speed of the high-speed disperser is 3000 rpm, the diameter of the zirconium beads of the sand mill is 0.7 mm, and the grinding speed is 1500 rpm.

[0091] This example also provides a current collector, and the preparation method is as follows:

[0092] Coat the waterborne conductive coating prepared above on the current collector aluminum foil by using a gravure coating device, and dry it with hot air at 85 °C for 25 s. After curing, the carbon-coated aluminum foil with a coating thickness of 1.8 μm can be obtained.

[0093] Example 2

[0094] This example provides a preparation method of a waterborne conductive coating, which is basically the same as that of Example 1, except that the power of the ultrasonic crusher used is 400 W.

[0095] This example also provides a current collector, and the preparation method is the same as that of Example 1.

[0096] Example 3

[0097] This example provides a preparation method of a waterborne conductive coating, which is basically the same as that of Example 1, except that the carbon material is conductive carbon black and conductive graphite, and the mass ratio is 4:1.

[0098] This example also provides a current collector, and the preparation method is the same as that of Example 1.

[0099] Example 4

[0100] This example provides a preparation method of a waterborne conductive coating, which is basically the same as that of Example 1, except that: in step (1), the mass ratio of the initiator, the modifier and the carbon material is 0.8:15:87.6.

[0101] This embodiment also provides a current collector, and the preparation method is the same as that of Embodiment 1.

[0102] Embodiment 5

[0103] This embodiment provides a preparation method of an aqueous conductive coating, which is basically the same as that of Embodiment 1, except that the mass ratio of the initiator, the modifier and the carbon material is 0.8:10:87.6.

[0104] This embodiment also provides a current collector, and the preparation method is the same as that of Embodiment 1.

[0105] Embodiment 6

[0106] This embodiment provides a preparation method of an aqueous conductive coating, which is basically the same as that of Embodiment 1, except that the mass ratio of the initiator, the modifier and the carbon material is 0.8:20:87.6.

[0107] This embodiment also provides a current collector, and the preparation method is the same as that of Embodiment 1.

[0108] Embodiment 7

[0109] This embodiment provides a preparation method of an aqueous conductive coating, which is basically the same as that of Embodiment 1, except that the mass ratio of the binder to the modified carbon material is 0.5:1.

[0110] This embodiment also provides a current collector, and the preparation method is the same as that of Embodiment 1.

[0111] Embodiment 8

[0112] This embodiment provides a preparation method of an aqueous conductive coating, which is basically the same as that of Embodiment 1, except that the mass ratio of the binder to the modified carbon material is 1.5:1.

[0113] This embodiment also provides a current collector, and the preparation method is the same as that of Embodiment 1.

[0114] Embodiment 9

[0115] This embodiment provides a preparation method of an aqueous conductive coating, which is basically the same as that of Embodiment 1, except that the total amount of the binder and the modified carbon material is 10 parts by weight.

[0116] This embodiment also provides a current collector, and the preparation method is basically the same as that of Embodiment 1, and the coating thickness is 1.2 μm.

[0117] Embodiment 10

[0118] This embodiment provides a preparation method of an aqueous conductive coating, which is basically the same as that of Embodiment 1, except that: the modifier is polyacrylic acid.

[0119] This embodiment also provides a current collector, and the preparation method is the same as that of Embodiment 1.

[0120] Comparative Example 1

[0121] This comparative example is a comparative example of Embodiment 1, and the difference is only that no initiator and graft modifier are added in step (1).

[0122] Comparative Example 2

[0123] This comparative example is a comparative example of Embodiment 1, and the difference is only that an aqueous conductive coating is directly prepared from a carbon material without ultrasonic treatment or graft modification treatment.

[0124] Comparative Example 3

[0125] This embodiment provides a preparation method of an aqueous conductive coating, which is basically the same as that of Embodiment 1, except that: the mass ratio of the initiator, modifier and carbon material in step (1) is 1.2:20:87.6.

[0126] Comparative Example 4

[0127] This embodiment provides a preparation method of an aqueous conductive coating, which is basically the same as that of Embodiment 1, except that: the mass ratio of the initiator, modifier and carbon material is 0.1:8:87.6.

[0128] Comparative Example 5

[0129] This embodiment provides a preparation method of an aqueous conductive coating, which is basically the same as that of Embodiment 1, except that: the total content of the binder and the conductive carbon material is 8 parts by weight.

[0130] This embodiment also provides a current collector, and the preparation method is basically the same as that of Embodiment 1, and the coating thickness is 0.85 μm.

[0131] Comparative Example 6

[0132] This embodiment provides a preparation method of an aqueous conductive coating, which is basically the same as that of Embodiment 1, except that: the total content of the binder and the conductive carbon material is 30 parts by weight.

[0133] This embodiment also provides a current collector, and the preparation method is the same as that of Embodiment 1, and the coating thickness is 2.4 microns.

[0134] The slurry stability of the water-based conductive coatings prepared in Examples 1 to 12 and Comparative Examples 1 to 5 was tested, and the solvent resistance of the carbon-coated aluminum foils prepared in Examples 1 to 12 and Comparative Examples 1 to 5 was tested. The test results are shown in Table 1. The test methods are as follows:

[0135] (1) Solvent resistance

[0136] The carbon-coated aluminum foil was cut into a suitable size and fixed on a platform scale with a mass of 20 g. A cotton swab was dipped in the test solvent and wiped back and forth at the same position on the carbon-coated aluminum foil. The wiping force was controlled according to the mass of 20 ± 5 g shown on the platform scale, and the wiping distance was about 5 cm. One round trip was recorded as 1 time, and the number of wiping times when the aluminum foil substrate leaked was recorded. The test solvents were lithium battery electrolyte LB-304 and N-methylpyrrolidone respectively.

[0137] (2) Slurry stability

[0138] The water-based conductive coating was placed at room temperature for 60 days to observe whether there was precipitation, and the water-based conductive coating was placed at 50 °C for 30 days to observe whether there was precipitation.

[0139] Preparation of the positive electrode sheet of the battery: On the carbon-coated aluminum foils prepared in Examples 1 to 12 and Comparative Examples 1 to 5, the positive electrode slurry was hand-coated using a 10-μm doctor blade, and the coating thickness was 150 μm. It was dried in a vacuum oven at 125 °C for 300 s to obtain the positive electrode sheet. Preparation of the positive electrode slurry: 97 parts by weight of lithium iron phosphate, 1 part by weight of carbon black, 60 parts by weight of a 5 wt% PVDF solution (solvent: NMP), and 12 parts by weight of NMP were mixed evenly.

[0140] The peel strength and surface contact resistance of the above-prepared positive electrode sheets of the battery were tested. The test results are shown in Table 1. The test methods are as follows:

[0141] Peel strength: The positive electrode sheet was cut into a size of 300 mm * 15 mm and fixed on a test steel plate using 3M double-sided tape, and a 180° peel strength test was carried out using a universal testing machine. The test speed was 300 mm / min, and the test stroke was 50 mm.

[0142] Surface contact resistance: The surface contact resistance of the positive electrode sheet was tested using an ST 2258C four-probe tester.

[0143] Table 1

[0144]

[0145] As can be seen from Table 1, compared with Example 1, in Example 2, the ultrasonic power increased from 300 W to 400 W, more groups were grafted onto the surface of the carbon material, resulting in a slight decrease in the conductivity of the modified carbon material and a slight increase in the surface contact resistance between the electrode active material layer and the carbon-coated aluminum foil. Due to the increase in the grafting rate, the solvent resistance of the coating formed by the water-based coating and the peel strength between the carbon-coated aluminum foil and the electrode active material layer increased.

[0146] As can be seen from Examples 1 and 4, as the amount of initiator gradually increased, the grafting rate on the surface of the carbon material gradually increased, which had some adverse effects on the conductivity of the carbon material, and the surface contact resistance between the electrode active material layer and the carbon-coated aluminum foil gradually increased. However, the solvent resistance of the coating formed by the water-based coating and the peel strength between the carbon-coated aluminum foil and the electrode active material layer gradually increased.

[0147] As can be seen from Example 6 and Comparative Example 3, when the mass ratio of the initiator to the modifier and the carbon material increased from 0.8:20:87.6 to 1.2:20:87.6, the changes in the solvent resistance of the coating formed by the water-based coating and the peel strength between the carbon-coated aluminum foil and the electrode active material layer were not significant, but the surface contact resistance between the electrode active material layer and the carbon-coated aluminum foil increased significantly.

[0148] As can be seen from Examples 1, 6 to 7, when the mass ratio of the binder to the modified carbon material increased from 0.5:1 to 1:1, as the amount of the binder gradually increased, the surface contact resistance between the electrode active material layer and the carbon-coated aluminum foil showed a slight increasing trend, the solvent resistance of the coating formed by the water-based coating and the peel strength between the carbon-coated aluminum foil and the electrode active material layer gradually increased. When the mass ratio of the binder to the modified carbon material increased to 1.5:1, the solvent resistance of the coating formed by the water-based coating, the peel strength between the carbon-coated aluminum foil and the electrode active material layer, and the surface contact resistance between the electrode active material layer and the carbon-coated aluminum foil all increased significantly.

[0149] As can be seen from Examples 1, 9 and Comparative Example 5, when the amounts of the binder and the modified carbon material were 10 - 20 parts by weight, as the amounts of the binder and the modified carbon material gradually increased, the solvent resistance of the coating formed by the water-based coating and the peel strength between the carbon-coated aluminum foil and the electrode active material layer increased significantly, the conductivity of the coating increased, and thus the surface contact resistance between the electrode active material layer and the carbon-coated aluminum foil decreased significantly.

[0150] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. An aqueous conductive coating, characterized in that, The raw material components include the following parts by weight: Modified carbon material and binder: 10 - 20 parts by weight Water: 60 - 75 parts by weight; The mass ratio of the binder to the modified carbon material is (0.5 - 1.5):1; The modified carbon material is obtained by grafting modification of the carbon material.

2. The aqueous conductive coating according to claim 1, wherein The carbon material is selected from one or more of conductive carbon black, acetylene black, conductive graphite, carbon nanotubes, and graphene; And / or, the binder is selected from one or several of polyacrylic acid, acrylic resin, polyurethane resin, polyethylene, and ethylene resin; And / or, the raw material components of the aqueous conductive coating further include auxiliary agents; And / or, the aqueous conductive coating further includes water; And / or, the pH of the aqueous conductive coating is 4.5 - 5.5; And / or, the particle size D of the aqueous conductive coating 50 < 2 μm, D 100 < 15 μm.

3. The water-based conductive coating according to claim 2, characterized in that, The auxiliary agent includes one or more of defoaming agents, thickeners, and pH regulators; And / or, in the aqueous conductive coating, the dosage of the auxiliary agent is 0.5 - 3.3 parts by weight.

4. The water-based conductive coating according to claim 3, wherein The defoaming agent is selected from one or more of polyether defoaming agents, polyether-modified silicone defoaming agents, alcohol defoaming agents, and fatty acid ester defoaming agents; And / or, the thickener is selected from one or more of polysaccharide thickeners, polyacrylate thickeners, and polyurethane thickeners; And / or, the pH regulator is selected from one or more of sodium hydroxide, calcium hydroxide, and ammonia water.

5. The aqueous conductive coating according to claim 3, characterized in that, In the aqueous conductive coating, the dosage of the defoaming agent is 0.1 - 0.3 parts by weight; And / or, in the aqueous conductive coating, the dosage of the thickener is 0.5 - 2.0 parts by weight; And / or, in the aqueous conductive coating, the content of the pH regulator is 0.5 - 1.0 parts by weight.

6. The water-based conductive coating according to claim 1, wherein The grafting modification means that the carbon material is first contacted with an initiator, and then contacted with a grafting modifier and reacted; And / or, the reaction medium for the grafting modification is water; And / or, before the grafting reaction, the carbon material is subjected to ultrasonic treatment.

7. The water-based conductive coating according to claim 6, characterized in that, The ultrasonic power is 200 - 400W; And / or, the ultrasonic treatment time is 0.5 - 2h.

8. The aqueous conductive coating according to claim 6, wherein The initiator is selected from one or more of potassium persulfate, sodium persulfate, and ammonium persulfate; And / or, the mass ratio of the initiator to the carbon material is (0.4 - 1.0):(80 - 100); And / or, the grafting modifier is selected from one or more of styrene sulfonate, polystyrene sulfonate, polyacrylate, polyacrylic acid, and polyvinyl alcohol; And / or, the mass ratio of the grafting modifier to the carbon material is (10 - 20):(80 - 100).

9. A preparation method of the aqueous conductive coating according to any one of claims 1 to 8, characterized in that, After mixing the raw material components evenly and then performing sand grinding, an aqueous conductive coating can be obtained.

10. Use of the aqueous conductive coating according to any one of claims 1 - 8 as a coating for the positive current collector of a battery.

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