Binders, carbon-coated pastes, carbon-coated current collectors, methods of making the same, and electrodes and batteries

Abstract

The application relates to a binder, a carbon coating slurry, a carbon coating current collector and a preparation method thereof, and an electrode and a battery, the preparation method of the binder comprising the following steps: mixing an alkaline divalent metal ion compound and a polymer binder in a solvent to obtain a mixed solution; and performing a cross-linking reaction on the mixed solution to prepare the binder; wherein the polymer binder contains a carboxyl group in a structural unit; and the cross-linking reaction is performed under weak acid conditions, and the pH of the weak acid conditions satisfies 5<=pH<7. The alkaline divalent metal ion compound is used for cross-linking the polymer binder with a carboxyl group in a polymer monomer, the divalent metal ion is used for end-capping the carboxyl group and simultaneously used as an intermediate linking matrix to form a reticular polymer binder, and the binder has the characteristics of low cost and high bonding performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a binder, carbon-coated slurry, carbon-coated current collector, preparation method thereof, electrode and battery. BACKGROUND

[0002] Lithium batteries have the advantages of long recycling life, environmental protection and energy saving, and the development of lithium batteries is becoming more and more demanding, requiring higher energy density and higher safety performance.

[0003] At present, with the development of technology and demand, the requirements for lithium ion battery current collectors are becoming higher and higher. On the basis of traditional current collectors, composite aluminum / copper current collector carbon-coated functional coated current collector products are developed. However, the traditional carbon-coated current collector has the problems of low adhesion of carbon-coated layer and high cost. SUMMARY

[0004] Therefore, it is necessary to provide a binder, carbon-coated slurry, carbon-coated current collector, preparation method thereof, electrode and battery. The alkaline divalent metal ion compound is used to crosslink the polymer binder with carboxyl in the structural unit, so as to form a network crosslinked structure, thereby improving the adhesion of the carbon-coated layer of the carbon-coated current collector.

[0005] In a first aspect, the present application provides a preparation method of a binder, which comprises:

[0006] mixing an alkaline divalent metal ion compound and a polymer binder in a solvent to obtain a mixed solution; and performing crosslinking reaction on the mixed solution to obtain the binder; wherein

[0007] the structural unit of the polymer binder contains carboxyl;

[0008] the crosslinking reaction is performed under weak acid conditions, and the pH of the weak acid conditions satisfies 5≤pH<7, for example, pH is 5.0, 5.2, 5.4, 5.6, 5.8, 6.0, 6.2, 6.4, 6.6, 6.8 or 6.9.

[0009] In some embodiments, the alkaline divalent metal ion compound comprises at least one of calcium acetate, calcium hydroxide, calcium bicarbonate and calcium oxalate.

[0010] In some embodiments, the polymer binder comprises polyacrylic acid.

[0011] In some embodiments, the number average molecular weight of the polymer binder is 6000-10000, for example, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500 or 10000.

[0012] In some embodiments, the number of carboxyl groups in the polymer binder is N1, the number of divalent metal ions in the basic divalent metal ion compound is N2, the cross-linking parameter of the cross-linking reaction is defined as n = 2N2 / N1, the cross-linking parameter n in the cross-linking reaction is 0.5-0.9, for example, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89 or 0.90, preferably 0.75-0.85.

[0013] In some embodiments, the mass ratio of the basic divalent metal ion compound to the polymer binder is (1-3):(15-17), for example, 1:15, 1:16, 1:17, 2:15, 2:16, 2:17, 3:15, 3:16 or 3:17.

[0014] In some embodiments, the temperature of the cross-linking reaction is 25-35℃, for example, 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, 31℃, 32℃, 33℃, 34℃ or 35℃.

[0015] In some embodiments, the pH in the cross-linking reaction satisfies 6≤pH<7, for example, 6.0, 6.2, 6.4, 6.6, 6.8 or 6.9.

[0016] In some embodiments, the cross-linking reaction is carried out under the condition of stirring and dispersion.

[0017] Optionally, the tangential velocity of the stirring and dispersion is 12-15 m / s, for example, 12.0 m / s, 12.5 m / s, 13.0 m / s, 13.5 m / s, 14.0 m / s, 14.5 m / s or 15.0 m / s.

[0018] Optionally, the time of the stirring and dispersion is 90-120 min, for example, 90 min, 95 min, 100 min, 105 min, 110 min, 115 min or 120 min.

[0019] In a second aspect, the present application provides a binder prepared by the preparation method of the binder of the first aspect.

[0020] In a third aspect, the present application provides a carbon coating slurry, which comprises, in terms of mass fraction:

[0021] Conductive agent 6-8 parts;

[0022] Binder 15-17 parts;

[0023] Solvent: 76-78 parts;

[0024] The adhesive is the adhesive as described in the second aspect.

[0025] In some embodiments, the conductive agent includes at least one of conductive carbon black, graphite, acetylene black, carbon nanotubes, doped carbon nanotubes, and graphene.

[0026] In some embodiments, the carbon coating slurry further includes functional additives, wherein the amount of the functional additives added is 1 to 3 parts by weight, that is, the carbon coating slurry comprises:

[0027]

[0028] In some embodiments, the carbon coating slurry further includes a wetting agent, wherein the amount of the wetting agent added is 4 to 6 parts by weight, that is, the carbon coating slurry comprises:

[0029]

[0030] In some embodiments, the carbon coating slurry includes:

[0031]

[0032] Fourthly, this application provides a method for preparing a carbon coating slurry as described in the third aspect, the method comprising:

[0033] A basic divalent metal ion compound and a polymer binder are mixed in a solvent to obtain a mixture; the mixture is then subjected to a crosslinking reaction to prepare an binder solution containing the binder as described in the second aspect.

[0034] The binder solution is mixed with the conductive agent to prepare the carbon coating slurry.

[0035] In some embodiments, the method includes adding a functional additive after the adhesive solution is mixed with the conductive agent.

[0036] In some embodiments, the method includes adding a wetting agent after mixing the adhesive solution with the conductive agent.

[0037] In some embodiments, the method includes: mixing the adhesive solution with the conductive agent, and then sequentially adding a functional additive and a wetting agent.

[0038] Fifthly, this application provides a carbon-coated current collector, the carbon-coated current collector comprising a current collector substrate and a carbon coating layer disposed on at least one side surface of the current collector substrate, the carbon coating layer being formed from the carbon coating slurry described in the third aspect.

[0039] In some embodiments, the current collector substrate includes copper foil, aluminum foil, composite copper foil, or composite aluminum foil.

[0040] In a sixth aspect, this application provides an electrode comprising a carbon-coated current collector as described in the fifth aspect, wherein at least one side surface of the carbon-coated current collector is provided with an active layer.

[0041] In some embodiments, the electrode is a positive electrode, which includes a carbon-coated current collector and a positive electrode active layer disposed on at least one side of the carbon-coated current collector. For example, the positive electrode active material in the positive electrode active layer includes lithium iron phosphate or nickel cobalt manganese material.

[0042] In some embodiments, the electrode is a negative electrode, which includes a carbon-coated current collector and a negative electrode active layer disposed on at least one side of the carbon-coated current collector. For example, the negative electrode active material in the negative electrode active layer includes graphite.

[0043] In a seventh aspect, this application provides a battery comprising electrodes as described in the sixth aspect.

[0044] In some embodiments, the battery includes a positive electrode, a negative electrode, and a separator. Both the positive electrode structure and the negative electrode structure adopt the electrode structure described in the sixth aspect. The positive electrode structure includes a carbon-coated current collector and a positive electrode active layer disposed on at least one side surface of the carbon-coated current collector. The negative electrode structure includes a carbon-coated current collector and a negative electrode active layer disposed on at least one side surface of the carbon-coated current collector.

[0045] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0046] This application has the following beneficial effects:

[0047] In this application, alkaline divalent metal ion compounds are used to crosslink polymer binders with carboxyl groups as structural units. While the divalent metal ions end the carboxyl groups, they can also serve as intermediate linking matrices to form a network polymer binder. Compared with sodium or lithium hydroxides for carboxyl end-capping, this method has the advantages of low cost and high bonding performance. Attached Figure Description

[0048] Figure 1 This is a diagram of the cross-linking structure of the binder containing calcium ions in this application. Detailed Implementation

[0049] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0051] In traditional technologies, carbon-coated current collectors are mainly carbon-coating slurries composed of conductive agents, binders, dispersants, and other additives. These slurries are then uniformly coated onto the current collector surface using gravure or micro-gravure coating methods. Taking polyacrylic acid binders as an example, they achieve a certain level of adhesion through chemical bonding with the aluminum foil surface. However, water is generated during the bonding process, leading to decreased water resistance and low peel strength. Furthermore, traditional technologies use sodium hydroxide or lithium hydroxide to end-cap the carboxyl groups to improve water resistance. However, lithium hydroxide is expensive, and sodium hydroxide is a nationally controlled hazardous chemical. Moreover, both sodium and lithium are monovalent ions, requiring large quantities during the end-capping process. Therefore, a low-cost binder with high adhesion performance is needed.

[0052] The first aspect of this application provides a method for preparing an adhesive, the method comprising:

[0053] A basic divalent metal ion compound and a polymer binder are mixed in a solvent to obtain a mixture; the mixture is then subjected to a crosslinking reaction to prepare the binder; wherein...

[0054] The structural units of the polymer binder contain carboxyl groups;

[0055] The crosslinking reaction is carried out under weak acid conditions, wherein the pH of the weak acid conditions satisfies 5 ≤ ​​pH < 7.

[0056] In this application, alkaline divalent metal ion compounds are used to crosslink polymer binders with carboxyl groups as structural units. The pH of the mixture is controlled to maintain a weakly acidic system during the crosslinking process. While the divalent metal ions end the carboxyl groups, they can also serve as intermediate linking matrices. The divalent metal ions act as intermediate bridges to crosslink the polymer binders into chains in a "hand-in-hand" manner, forming a network polymer binder. Compared with sodium or lithium hydroxides for carboxyl end-capping, this method has the advantages of low cost and high bonding performance.

[0057] In this application, the pH of the crosslinking reaction is controlled to satisfy 5≤pH<7, so that the crosslinking process maintains a weak acid system, avoids violent crosslinking reaction, improves the crosslinking environment between polymer binder and alkaline divalent metal ion compound, and makes the final binder weakly acidic. When applied to carbon-coated current collectors, it can chemically react with oxides on the surface of the current collector substrate and improve adhesion.

[0058] In some embodiments, the solvent is selected from water, and optionally, after the solvent is added, the mass fraction of the polymer binder and the basic divalent metal ion compound in the mixture is 16.0% to 18.5%.

[0059] In some embodiments, the basic divalent metal ion compound may be an inorganic compound or an organic compound, wherein the organic compound includes, for example, at least one of calcium acetate and calcium oxalate, and the inorganic compound includes, for example, at least one of calcium hydroxide and calcium bicarbonate.

[0060] In some preferred embodiments, the basic divalent metal ion compound is calcium acetate, which is readily soluble in water and easier to process. During the crosslinking process in this application, the crosslinking method can be carboxyl group crosslinking between different polymer binder molecules, or carboxyl group crosslinking between two structural units on the same polymer binder. Figure 1 The diagram shows that calcium ions act as an intermediate bridge to crosslink the carboxyl groups in two polyacrylic acid molecules.

[0061] In some embodiments, the polymeric binder comprises polyacrylic acid.

[0062] In some embodiments, the number average molecular weight of the polymer binder is 6,000 to 10,000, and optionally, the number average molecular weight of the polyacrylic acid is 6,000 to 10,000.

[0063] In some embodiments, the relative amounts of the polymer binder and the basic divalent metal ion compound are represented by a crosslinking parameter. The number of carboxyl groups in the polymer binder is N1, and the number of divalent metal ions in the basic divalent metal ion compound is N2. The crosslinking parameter for the crosslinking reaction is defined as n = 2N2 / N1, and the crosslinking parameter in the crosslinking reaction is 0.5–0.9, preferably 0.75–0.85. Taking a 1 mol homopolymer polymer binder as an example, the number of carboxyl groups is calculated using the degree of polymerization of the polymer binder and the number of carboxyl groups present in a single structural unit. Specifically, N1 is the product of the degree of polymerization and the number of carboxyl groups in the structural unit. If the polymer binder is formed by polymerization of different monomers, the product of the degree of polymerization of the corresponding structural unit and the number of carboxyl groups in that structural unit is calculated separately, and then the sum of the number of carboxyl groups in each structural unit is calculated as N1.

[0064] In this application, by controlling the crosslinking parameters of the crosslinking reaction, it is ensured that the polymer adhesive still has some carboxyl groups after crosslinking. While ensuring that the adhesive has a crosslinked network structure, the overall adhesive is weakly acidic, effectively ensuring the bonding performance.

[0065] In some embodiments, the temperature of the crosslinking reaction is 25–35°C. In this application, by controlling the temperature of the crosslinking reaction to 25–35°C, the polymer chain polymerization structure in the polymer binder is preserved while ensuring that divalent metal ions crosslink with the carboxyl groups in the polymer binder to form a network structure, thereby improving the bonding performance.

[0066] In some embodiments, the pH in the crosslinking reaction satisfies 6 ≤ pH < 7.

[0067] In some embodiments, the crosslinking reaction is carried out under stirred dispersion conditions.

[0068] Optionally, the tangential velocity of the stirring and dispersion is 12–15 m / s. This application controls the tangential velocity of the stirring and dispersion to ensure crosslinking parameters while avoiding damage to the molecular chain polymerization bond structure of the polymer binder, thus giving the polymer binder an excellent crosslinked network structure.

[0069] Optionally, the stirring and dispersion time is 90 to 120 minutes. By controlling the stirring and dispersion time during the crosslinking reaction, this application ensures the integrity of the crosslinking network structure and the polymer bonds in the polymer binder while ensuring the crosslinking parameters, and avoids continuous high-speed dispersion from damaging the molecular bonds of the polymer binder and the structure of the network binder.

[0070] According to one specific embodiment, the method for preparing the adhesive includes the following steps:

[0071] A mixture of an alkaline divalent metal ion compound and a polymer binder was prepared in a solvent to obtain a mixture with a number average molecular weight of 6000–10000. The mixture was stirred and dispersed under the conditions of 25–35°C and pH 5 ≤ 7 to carry out a crosslinking reaction. The tangential speed of stirring and dispersion was 12–15 m / s, and the time was 90–120 min, to prepare a binder with a crosslinking parameter of 0.5–0.9.

[0072] A second aspect of this application provides an adhesive prepared by the method described above. In this application, an alkaline divalent metal ion compound is used to perform network crosslinking on a polymer adhesive containing carboxyl groups. The divalent metal ions act as an intermediate bridge, crosslinking the polymer adhesive into chains in a "hand-in-hand" manner, thereby forming a network-crosslinked adhesive, while simultaneously capping at least some of the carboxyl groups.

[0073] A third aspect of this application provides a carbon coating paste, which, by weight parts, comprises:

[0074] 6-8 parts of conductive agent;

[0075] 15-17 parts adhesive;

[0076] Solvent: 76-78 parts;

[0077] The adhesive is the adhesive as described in the second aspect.

[0078] In some embodiments, the conductive agent includes at least one of conductive carbon black, graphite, acetylene black, carbon nanotubes, doped carbon nanotubes, and graphene.

[0079] In some embodiments, the carbon coating slurry further includes functional additives, wherein the amount of the functional additives added is 1 to 3 parts by weight, and the carbon coating slurry comprises:

[0080]

[0081] In this application, divalent metal ions are used to crosslink the polymer binder in a network manner. After crosslinking, it can coat other functional additives and disperse them with conductive agents to increase other functionalities. For example, the functional additives can be conductive additives, such as doped carbon nanotubes, to further improve the conductivity of the carbon coating layer, or the functional additives can be heat-resistant additives to improve the heat resistance of the carbon coating layer.

[0082] In some embodiments, the carbon coating slurry further includes a wetting agent, wherein the amount of the wetting agent added is 4 to 6 parts by weight, and the carbon coating slurry comprises:

[0083]

[0084] In some embodiments, the wetting agent further includes anionic surfactants, such as sulfonates or sulfates, like LAS, sodium fatty alcohol sulfate (e.g., AES), or ammonium dodecyl ether sulfate (AESA).

[0085] In some embodiments, the wetting agent further includes silicone surfactants.

[0086] In some embodiments, the carbon coating slurry further includes a wetting agent and functional additives, the carbon coating slurry comprising:

[0087]

[0088] In some embodiments, the total mass of the conductive agent, binder, and solvent in the carbon coating slurry is 100 parts.

[0089] A fourth aspect of this application provides a method for preparing a carbon coating slurry as described in the third aspect, the method comprising:

[0090] A basic divalent metal ion compound and a polymer binder are mixed in a solvent to obtain a mixture; the mixture is then subjected to a crosslinking reaction to prepare an binder solution containing the binder as described in the second aspect.

[0091] The binder solvent is mixed with the conductive agent to prepare the carbon coating slurry.

[0092] In some embodiments, functional additives are added after the adhesive solvent is mixed with the conductive agent.

[0093] In some embodiments, a wetting agent is added after the adhesive solvent is mixed with the conductive agent.

[0094] In some embodiments, after the binder solvent is mixed with the conductive agent, a functional additive and a wetting agent are added sequentially.

[0095] The fifth aspect of this application provides a carbon-coated current collector, the carbon-coated current collector comprising a current collector substrate and a carbon coating layer disposed on at least one side surface of the current collector substrate, the carbon coating layer being formed from the carbon coating slurry described in the third aspect.

[0096] This application uses an adhesive with a mesh structure, which enables the current collector to resist electrolytes and NMP solvents, and effectively improves the peel strength of the carbon coating layer.

[0097] Optionally, the current collector substrate includes copper foil, aluminum foil, composite aluminum foil, or composite copper foil.

[0098] Optionally, the thickness of the carbon coating layer is 1–10 μm.

[0099] Optionally, the carbon coating layer is formed by coating the current collector substrate surface with carbon coating slurry and then drying it. For example, the coating method includes gravure coating.

[0100] According to one specific embodiment, the method for preparing the carbon-coated current collector includes the following steps:

[0101] A conductive agent, the binder, and a functional additive are mixed in a solvent. By mass, the conductive agent is 6-8 parts, the binder is 15-17 parts, the solvent is 76-78 parts, and the functional additive is 1-3 parts. Further, 4-6 parts of a wetting agent are added, and the mixture is dispersed and homogenized to form a carbon-coated slurry. The carbon-coated slurry is then gravure-coated onto the surface of the current collector substrate and dried at 80-120°C to obtain the carbon-coated current collector.

[0102] The sixth aspect of this application provides an electrode comprising a carbon-coated current collector as described in the fifth aspect, wherein at least one side surface of the carbon-coated current collector is provided with an active layer.

[0103] In some embodiments, the electrode is a positive electrode, which includes a carbon-coated current collector and a positive electrode active layer disposed on at least one side of the carbon-coated current collector. For example, the positive electrode active material in the positive electrode active layer includes lithium iron phosphate or nickel cobalt manganese material.

[0104] In some embodiments, the electrode is a negative electrode, which includes a carbon-coated current collector and a negative electrode active layer disposed on at least one side of the carbon-coated current collector. For example, the negative electrode active material in the negative electrode active layer includes graphite.

[0105] A seventh aspect of this application provides a battery comprising electrodes as described in the sixth aspect.

[0106] In some embodiments, the battery includes a positive electrode, a negative electrode, and a separator. Both the positive electrode structure and the negative electrode structure adopt the electrode structure described in the sixth aspect. The positive electrode structure includes a carbon-coated current collector and a positive electrode active layer disposed on at least one side surface of the carbon-coated current collector. The negative electrode structure includes a carbon-coated current collector and a negative electrode active layer disposed on at least one side surface of the carbon-coated current collector.

[0107] The following are specific embodiments of this application.

[0108] Calcium acetate was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with the grade C100139.

[0109] Polyacrylic acid with a number average molecular weight of 8000 was purchased from Jiangsu Debi New Material Technology Co., Ltd., and its grade was DC-611.

[0110] The doped carbon nanotubes were purchased from Jiangsu Tiannai Technology Co., Ltd., with the grade LB270-44.

[0111] Example 1

[0112] (1) Adhesive

[0113] Calcium acetate and polyacrylic acid with a number average molecular weight of 8000 were mixed in water to obtain a mixture with a mass fraction of 17% and a pH of 6. The mixture was stirred and dispersed at 30°C for a crosslinking reaction at a tangential speed of 13.5 m / s for 105 min. An adhesive with a crosslinking parameter of 0.8 was prepared and the prepared adhesive was denoted as F1.

[0114] (2) Carbon-coated current collector

[0115] By mass, 7 parts of conductive carbon black, 16 parts of an aqueous solution containing binder F1, and 5 parts of isopropanol are mixed in water, resulting in 77 parts of water by mass. The mixture is dispersed and homogenized to form a carbon coating slurry. The carbon coating slurry is then gravure-coated onto both sides of an aluminum foil with a thickness of 10 μm. The foil is then dried at 100°C to form a carbon coating layer with a thickness of 5 μm, thus preparing a carbon-coated current collector.

[0116] Example 2

[0117] (1) Adhesive

[0118] Calcium oxalate and polyacrylic acid with a number average molecular weight of 10,000 were mixed in water to obtain a mixture with a mass fraction of 18.5% and a pH of 6.5. The mixture was stirred and dispersed at 25°C for a crosslinking reaction at a tangential speed of 12 m / s for 90 min. An adhesive with a crosslinking parameter of 0.85 was prepared and the prepared adhesive was denoted as F2.

[0119] (2) Carbon-coated current collector

[0120] By mass, an aqueous solution containing 16 parts of binder F2, 7 parts of graphite, 2 parts of conductive additive, and 5 parts of isopropanol are sequentially mixed in water. The conductive additive is doped carbon nanotubes. After mixing, the mass of water is 77 parts. The mixture is dispersed and homogenized to form a carbon coating slurry. The carbon coating slurry is then gravure-coated onto both sides of an aluminum foil with a thickness of 10 μm. The slurry is then dried at 100°C to form a carbon coating layer with a thickness of 5 μm, thus preparing a carbon-coated current collector.

[0121] Example 3

[0122] (1) Adhesive

[0123] Calcium bicarbonate and polyacrylic acid with a number average molecular weight of 6000 were mixed in water to obtain a 16% mass fraction mixture with a pH of 5.5. The mixture was stirred and dispersed at 25°C for a crosslinking reaction at a tangential speed of 15 m / s for 120 min. An adhesive with a crosslinking parameter of 0.75 was prepared and the prepared adhesive was designated as F3.

[0124] (2) Carbon-coated current collector

[0125] By mass, an aqueous solution containing 16 parts of binder F3, 7 parts of graphene, and 5 parts of isopropanol are sequentially mixed in water, resulting in a water mass of 77 parts. The mixture is dispersed and homogenized to form a carbon coating slurry. The carbon coating slurry is then gravure-coated onto both sides of an aluminum foil with a thickness of 10 μm. The slurry is dried at 100°C to form a carbon coating layer with a thickness of 5 μm, thus preparing a carbon-coated current collector.

[0126] Example 4

[0127] (1) Adhesive

[0128] Calcium acetate and polyacrylic acid with a number average molecular weight of 10,000 were mixed in water to obtain a mixture with a mass fraction of 17% and a pH of 5.8. The mixture was stirred and dispersed at 27°C for a crosslinking reaction at a tangential speed of 14 m / s for 110 min. An adhesive with a crosslinking parameter of 0.9 was prepared and the prepared adhesive was designated as F4.

[0129] (2) Carbon-coated current collector

[0130] Prepared according to the carbon-coated current collector preparation method of Example 1.

[0131] Example 5

[0132] (1) Adhesive

[0133] Calcium acetate and polyacrylic acid with a number average molecular weight of 7000 were mixed in water to obtain a mixture with a mass fraction of 18% and a pH of 5.9. The mixture was stirred and dispersed at 26°C for a crosslinking reaction at a tangential speed of 13 m / s for 105 min. An adhesive with a crosslinking parameter of 0.7 was prepared and the prepared adhesive was designated as F5.

[0134] (2) Carbon-coated current collector

[0135] Prepared according to the carbon-coated current collector preparation method of Example 1.

[0136] Example 6

[0137] (1) Adhesive

[0138] Calcium acetate and polyacrylic acid with a number average molecular weight of 8000 were mixed in water to obtain a mixture with a mass fraction of 16.5% and a pH of 5.0. The mixture was stirred and dispersed at 32°C for a crosslinking reaction at a tangential speed of 12 m / s for 90 min. An adhesive with a crosslinking parameter of 0.6 was prepared and the prepared adhesive was designated as F6.

[0139] (2) Carbon-coated current collector

[0140] Prepared according to the carbon-coated current collector preparation method of Example 1.

[0141] Example 7

[0142] (1) Adhesive

[0143] Calcium acetate and polyacrylic acid with a number average molecular weight of 6000 were mixed in water to obtain a mixture with a mass fraction of 17.5% and a pH of 6.2. The mixture was stirred and dispersed at 33°C for a crosslinking reaction at a tangential speed of 14 m / s for 95 min. An adhesive with a crosslinking parameter of 0.5 was prepared and the prepared adhesive was designated as F7.

[0144] (2) Carbon-coated current collector

[0145] Prepared according to the carbon-coated current collector preparation method of Example 1.

[0146] Example 8

[0147] The adhesive was prepared according to the preparation method of Example 1, except that the crosslinking parameter of the prepared adhesive was adjusted to 0.4, and the prepared adhesive was denoted as F8.

[0148] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder F8.

[0149] Example 9

[0150] The adhesive was prepared according to the preparation method of Example 1, except that the crosslinking parameter of the prepared adhesive was adjusted to 1, and the prepared adhesive was denoted as F9.

[0151] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder F9.

[0152] Example 10

[0153] The adhesive was prepared according to the preparation method of Example 1, except that the temperature of the crosslinking reaction was adjusted to 20°C, and the prepared adhesive was denoted as F10.

[0154] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder F10.

[0155] Example 11

[0156] The adhesive was prepared according to the preparation method of Example 1, except that the temperature of the crosslinking reaction was adjusted to 45°C, and the prepared adhesive was denoted as F11.

[0157] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder F11.

[0158] Example 12

[0159] The adhesive was prepared according to the preparation method of Example 1, except that the tangential speed of stirring and dispersing was adjusted to 10 m / s, and the prepared adhesive was denoted as F12.

[0160] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder F12.

[0161] Example 13

[0162] The adhesive was prepared according to the preparation method of Example 1, except that the tangential speed of stirring and dispersing was adjusted to 17 m / s, and the prepared adhesive was designated as F13.

[0163] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder F13.

[0164] Example 14

[0165] The adhesive was prepared according to the preparation method of Example 1, except that the stirring and dispersion time was adjusted to 80 min, and the prepared adhesive was denoted as F14.

[0166] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder F14.

[0167] Example 15

[0168] The adhesive was prepared according to the preparation method of Example 1, except that the stirring and dispersion time was adjusted to 130 min, and the prepared adhesive was denoted as F15.

[0169] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder F15.

[0170] Comparative Example 1

[0171] Only polyacrylic acid with a number average molecular weight of 5000 is used as the binder, denoted as D-F1.

[0172] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder D-F1.

[0173] Comparative Example 2

[0174] Only polyacrylic acid with a number average molecular weight of 8000 is used as the binder, denoted as D-F2.

[0175] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder D-F2.

[0176] Comparative Example 3

[0177] The adhesive was prepared according to the preparation method of Example 1, except that calcium acetate was replaced with sodium hydroxide, and the number of molar sodium ions in sodium hydroxide was the same as the number of molar calcium ions. The resulting adhesive was denoted as D-F3.

[0178] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder D-F3.

[0179] Comparative Example 4

[0180] The adhesive was prepared according to the preparation method of Example 1, except that the pH of the crosslinking reaction was adjusted to 4 by adding hydrochloric acid to the mixture. The prepared adhesive was denoted as D-F4.

[0181] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder D-F4.

[0182] Comparative Example 5

[0183] The adhesive was prepared according to the preparation method of Example 1, except that the pH of the crosslinking reaction was adjusted to 7 by adding sodium hydroxide to the mixture. The prepared adhesive was designated as D-F5.

[0184] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder D-F5.

[0185] Comparative Example 6

[0186] The adhesive was prepared according to the preparation method of Example 1, except that calcium acetate was replaced with an equal number of moles of calcium hydroxide, and the pH was 4 during the preparation process. The resulting adhesive was denoted as D-F6.

[0187] The preparation method of the carbon-coated current collector according to Example 1 differs in that the binder is changed to binder D-F6.

[0188] Test case

[0189] The carbon-coated current collectors prepared in the above embodiments and comparative examples were subjected to peel strength tests, electrolyte wiping tests, and NMP wiping tests. The test methods included the following steps:

[0190] Peel strength test: The peel strength was tested according to GB / T 2792-2014.

[0191] Electrolyte wiping test: A lint-free cloth is soaked in electrolyte and the carbon coating layer is wiped repeatedly with a pressure of 10N. The number of wipings that cause damage to the carbon coating layer is measured. The electrolyte is 1M LiPF6, and the solvent in the electrolyte is ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) in a volume ratio of 1:1:1.

[0192] NMP wiping test: A lint-free cloth is soaked in NMP, and the carbon coating layer is wiped repeatedly with a pressure of 10N. The number of wiping cycles that cause damage to the carbon coating layer is measured.

[0193] The test results are shown in Table 1.

[0194] Table 1

[0195]

[0196]

[0197] As can be seen from the table above:

[0198] (1) Compared with Examples 8 and 9, Example 1 shows that by controlling the crosslinking parameters of the crosslinking reaction in this application, it is ensured that the polymer adhesive still has some carboxyl groups after crosslinking. While ensuring that the adhesive has a crosslinked network structure, the overall adhesive is weakly acidic, which effectively ensures the bonding performance.

[0199] (2) Compared with Examples 10 and 11, Example 1 shows that by controlling the temperature of the crosslinking reaction to 25-35°C, the polymer binder can ensure that the divalent metal ions and carboxyl groups in the polymer binder crosslink to form a network structure without destroying the molecular chain polymerization bond structure, thereby improving the bonding performance.

[0200] (3) Compared with Examples 12 and 13, Example 1 shows that the present application controls the tangential speed of stirring and dispersion, ensuring the crosslinking parameters while avoiding the polymer chain polymerization bond structure of the polymer binder.

[0201] (4) Compared with Examples 14 and 15, Example 1 shows that by controlling the stirring and dispersion time during the crosslinking reaction, this application avoids the destruction of the molecular bonds of the polymer binder and the structure of the network binder by continuous high-speed dispersion while ensuring the crosslinking parameters.

[0202] (5) Compared with Comparative Examples 1-3, it can be seen that in this application, alkaline divalent metal ion compounds are used to crosslink polymer binders with carboxyl groups in the structural unit. While the divalent metal ions end the carboxyl groups, they can also serve as intermediate linking matrix. The divalent metal ions act as intermediate bridges to crosslink the polymer binders into chains in a "hand-in-hand" manner, forming a network polymer binder. Compared with sodium or lithium hydroxides for carboxyl end-capping, it has the advantages of low cost and high bonding performance.

[0203] (6) Compared with Comparative Examples 4-6, Example 1 shows that the pH of the crosslinking reaction is controlled at 5-7 in this application, so that the crosslinking process is maintained in a weak acid system, which improves the crosslinking environment between the polymer binder and the alkaline divalent metal ion compound. Moreover, the final binder has weak acidity, which can produce a chemical effect on the oxides on the surface of the current collector substrate when applied to the carbon-coated current collector, thereby improving the adhesion.

[0204] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0205] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing an adhesive, characterized in that, The method for preparing the adhesive includes: An alkaline divalent metal ion compound and a polymer binder are mixed in a solvent to obtain a mixture; the mixture is then subjected to a crosslinking reaction to prepare the binder. Wherein, the alkaline divalent metal ion compound is an alkaline calcium ion compound, which includes at least one of calcium acetate, calcium hydroxide, calcium bicarbonate, and calcium oxalate; the structural unit of the polymer binder contains a carboxyl group, the number of carboxyl groups in the polymer binder is N1, the number of divalent metal ions in the alkaline divalent metal ion compound is N2, the crosslinking parameter of the crosslinking reaction is defined as n = 2N2 / N1, and the crosslinking parameter n in the crosslinking reaction is 0.5~0.9; The crosslinking reaction is carried out under weak acid conditions, wherein the pH of the weak acid conditions satisfies 5 < pH < 7, and the temperature of the crosslinking reaction is 25~35℃; the crosslinking reaction is carried out under stirring and dispersion conditions, wherein the tangential speed of the stirring and dispersion is 12~15m / s, and the stirring and dispersion time is 90~120min.

2. The method for preparing the adhesive as described in claim 1, characterized in that, The method for preparing the adhesive satisfies at least one of the following conditions: (1) The polymer binder includes polyacrylic acid; (2) The number average molecular weight of the polymer binder is 6000~10000; (3) The crosslinking parameter n in the crosslinking reaction is 0.75~0.85; (4) The pH in the cross-linking reaction satisfies 6 ≤ pH < 7.

3. An adhesive, characterized in that, The adhesive is prepared by the method for preparing the adhesive according to claim 1 or 2.

4. A carbon coating paste, characterized in that, The carbon coating paste comprises, by weight parts: 6-8 parts of conductive agent; 15-17 parts adhesive; Solvent: 76-78 parts; The adhesive is the adhesive described in claim 3.

5. The carbon coating slurry according to claim 4, characterized in that, The carbon coating slurry satisfies at least one of the following conditions: (1) The conductive agent includes at least one of conductive carbon black, graphite, acetylene black, carbon nanotubes, doped carbon nanotubes and graphene. (2) The carbon coating slurry also includes functional additives, and the amount of the functional additives added is 1 to 3 parts by mass. (3) The carbon coating slurry also includes a wetting agent, and the amount of the wetting agent added is 4 to 6 parts by mass.

6. A method for preparing the carbon coating slurry according to claim 4 or 5, characterized in that, The method includes: An alkaline divalent metal ion compound and a polymer binder are mixed in a solvent to obtain a mixture; the mixture is then subjected to a crosslinking reaction to obtain a binder solution containing the binder. The binder solution is mixed with the conductive agent to prepare the carbon coating slurry.

7. The method according to claim 6, characterized in that, The method satisfies at least one of the following conditions: (1) Functional additives are added after the adhesive solution is mixed with the conductive agent; (2) A wetting agent is added after the adhesive solution is mixed with the conductive agent.

8. A carbon-coated current collector, characterized in that, The carbon-coated current collector includes a current collector substrate and a carbon coating layer disposed on at least one side surface of the current collector substrate, the carbon coating layer being formed from the carbon coating slurry as described in claim 4 or 5.

9. The carbon-coated current collector as described in claim 8, characterized in that, The current collector substrate includes copper foil, aluminum foil, composite copper foil, or composite aluminum foil.

10. An electrode, characterized in that, The electrode includes the carbon-coated current collector as described in claim 8 or 9, wherein at least one side surface of the carbon-coated current collector is provided with an active layer.

11. A battery, characterized in that, The battery includes the electrodes as described in claim 10.

Images