Negative electrode electrode paste, negative electrode binder and preparation method of negative electrode binder

Abstract

The embodiments of the present application provide a negative electrode paste, a negative electrode binder and a preparation method of the negative electrode binder, which relate to the technical field of batteries. Through the embodiments of the present application, before preparing the negative electrode paste, the materials of the negative electrode binder can be tested to realize that after determining the preferred materials of the negative electrode binder, the target negative electrode binder is made. In this process, since the embodiments of the present application determine the preferred combination of the negative electrode binder before preparing the negative electrode paste, therefore, through the embodiments of the present application, the reasonable matching type selection and dosage of CMC and SBR can be determined quickly and accurately, achieving the benefits of effectively shortening the evaluation cycle, avoiding processing risks in advance, and reducing the development cost.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a negative electrode paste, a negative electrode binder, and a preparation method of the negative electrode binder. Background Art

[0002] Currently, lithium-ion batteries have been rapidly developed in the fields of portable electronic devices, electric vehicles, and energy storage due to their high energy density, long cycle life, and pollution-free characteristics. Producing electrode paste is an important process in the production of lithium-ion batteries, and the produced electrode paste needs to have good fluidity and leveling property.

[0003] In the negative electrode paste, the negative electrode binder needs to tightly bond the active material, the conductive agent, and the current collector to keep the electrode sheet having good electronic conductivity and structural integrity, improve the infiltration of the electrolyte, and promote the electrode-electrolyte interface transfer of lithium ions. Therefore, how to ensure the performance of the negative electrode binder is an important problem that needs to be solved urgently in the battery design and development. Summary of the Invention

[0004] In view of this, the embodiments of the present application provide a negative electrode paste, a negative electrode binder, and a preparation method of the negative electrode binder, so as to quickly and accurately determine a reasonable selection and dosage of the matching of CMC and SBR, achieving the benefits of effectively shortening the evaluation cycle, avoiding processing risks in advance, and reducing the development cost.

[0005] In a first aspect, a preparation method of a negative electrode binder is provided, and the method includes:

[0006] Performing viscosity tests on each alternative carboxymethyl cellulose sodium (CMC) glue solution to determine at least one target CMC glue solution;

[0007] Performing matching tests on each alternative styrene-butadiene rubber (SBR) solvent and each of the target CMC glue solutions to determine a target SBR material and a target CMC material whose matching degree meets a predetermined condition; and

[0008] Using the target SBR material and the target CMC material as the negative electrode binder materials to prepare a target negative electrode binder.

[0009] In some embodiments, the method further includes:

[0010] Preparing a negative electrode paste based on the target negative electrode binder; and

[0011] Performing performance tests on the negative electrode paste.

[0012] In some embodiments, the performing viscosity tests on each alternative CMC glue solution includes:

[0013] Using a rheometer, viscosity tests are performed on each of the alternative CMC solutions at a predetermined shear rate.

[0014] In some embodiments, the alternative CMC solutions are prepared based on the following steps:

[0015] According to a first parameter, at least one alternative CMC material is determined, the first parameter including at least the degree of substitution and viscosity of the alternative CMC material; and

[0016] Weigh a predetermined mass of the alternative CMC material and mix it with water and stir to prepare an alternative CMC solution with a first concentration.

[0017] In some embodiments, a compatibility test is performed on each alternative styrene-butadiene rubber (SBR) solvent and each of the target CMC solutions, including:

[0018] Prepare products corresponding to the target CMC solutions; and

[0019] Based on each alternative SBR solvent and the products corresponding to each target CMC solution, a compatibility test is performed.

[0020] In some embodiments, the products corresponding to the target CMC solutions include CMC films;

[0021] The CMC films are prepared based on the following steps:

[0022] For each of the target CMC solutions, coat the target CMC solution onto a foil and allow it to dry naturally to form a CMC film.

[0023] In some embodiments, the products corresponding to the target CMC solutions include semi-finished films;

[0024] The semi-finished films are prepared based on the following steps:

[0025] Mix the negative electrode active material powder with a conductive agent to obtain a mixed solution;

[0026] For each of the target CMC solutions, add the target CMC solution with a second concentration to the mixed solution a predetermined number of times to obtain a semi-finished slurry, the predetermined number of times corresponding to a predetermined solid content; and

[0027] Coat the semi-finished slurry onto a foil and allow it to dry naturally to form a semi-finished film.

[0028] In some embodiments, when performing the compatibility test on each alternative SBR solvent and each of the target CMC solutions to determine the target SBR material and target CMC material whose compatibility meets a predetermined condition, it includes:

[0029] Drop each of the alternative SBR solvents onto the surface of the article corresponding to each of the target CMC solutions;

[0030] Determine the contact angle between the surface of the article corresponding to the target CMC solution and the alternative SBR solvents on the surface of the semi-finished film; and

[0031] Determine that the materials corresponding to the contact angles less than the predetermined angle threshold are the target SBR material and the target CMC material.

[0032] In some embodiments, the performance testing of the finished slurry includes:

[0033] Conduct a three-stage jump shear test on the finished slurry, wherein the test conditions for the first stage in the three-stage jump shear test are the first shear rate and the first shear time, the test conditions for the second stage in the three-stage jump shear test are the second shear rate and the second shear time, and the test conditions for the third stage in the three-stage jump shear test are the third shear rate and the third shear time.

[0034] In a second aspect, a negative electrode binder is provided, which is prepared based on the preparation method of the negative electrode binder described in the first aspect.

[0035] In a third aspect, a negative electrode slurry is provided, which is prepared based on the negative electrode binder described in the second aspect.

[0036] Through the embodiments of the present application, before preparing the negative electrode slurry, the materials of the negative electrode binder can be tested first to determine the target negative electrode binder after determining the preferred materials of the negative electrode binder. During this process, since the preferred combination of the negative electrode binder is determined in advance before preparing the negative electrode slurry in the embodiments of the present application, therefore, through the embodiments of the present application, a reasonable CMC and SBR matching selection and dosage can be determined quickly and accurately, achieving the benefits of effectively shortening the evaluation cycle, avoiding processing risks in advance, and reducing development costs. Description of the Drawings

[0037] Through the following description of the embodiments of the present application with reference to the drawings, the above and other objects, features and advantages of the embodiments of the present application will become clearer. In the drawings:

[0038] Figure 1 It is a flowchart of the preparation method of the negative electrode binder in the embodiments of the present application;

[0039] Figure 2 It is a shear viscosity curve graph for viscosity testing of the alternative CMC solutions in the embodiments of the present application;

[0040] Figure 3Schematic diagram of the matching degree test results of the embodiments of the present application;

[0041] Figure 4 Schematic diagram of the three-stage jump shear test results in the embodiments of the present application. Detailed implementation manners

[0042] The following describes the present application based on embodiments, but the present application is not limited to these embodiments. In the following detailed description of the present application, some specific details are described in detail. Those skilled in the art can fully understand the present application without the description of these details. In order to avoid obscuring the essence of the present application, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0043] In addition, those of ordinary skill in the art should understand that the drawings provided herein are for illustrative purposes only, and the drawings are not necessarily drawn to scale.

[0044] Unless the context clearly requires otherwise, words such as "including" and "comprising" in the specification should be construed in an inclusive sense rather than an exclusive or exhaustive sense; that is, the meaning of "including but not limited to".

[0045] In the description of the present application, it should be understood that terms such as "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance. In addition, in the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0046] Currently, the production and manufacturing of lithium-ion batteries is a process tightly linked by individual process steps. Generally speaking, the production process of lithium-ion batteries includes electrode sheet manufacturing process, battery assembly process, and processes of injecting electrolyte, pre-charging, formation, and aging. Among them, each process can be further divided into several key steps, and each step will have a great impact on the final performance of lithium-ion batteries.

[0047] In the electrode sheet manufacturing process, it can be further divided into five processes: slurry preparation, slurry coating, electrode sheet rolling, electrode sheet slitting, and electrode sheet drying. In the battery assembly process, according to different battery specifications and models, it is generally divided into processes such as winding, casing insertion, and welding. Finally, the production and manufacturing of lithium-ion batteries are completed through processes of injecting electrolyte, pre-charging, formation, and aging.

[0048] The electrode sheet manufacturing process is the core process of the entire lithium battery manufacturing, which is related to the electrochemical performance of lithium-ion batteries. Among them, the performance of the electrode slurry plays a crucial role in the electrochemical performance of lithium-ion batteries. In lithium-ion batteries, the electrode slurry needs to have good fluidity and leveling property to ensure the requirements of subsequent slurry coating processes (electrode sheet coating thickness, coating uniformity, and coating flatness).

[0049] The electrode paste includes a positive electrode paste and a negative electrode paste. Among them, the positive electrode paste is composed of components such as a positive electrode binder, a conductive agent, and a positive electrode material, and the negative electrode paste is composed of components such as a negative electrode binder and graphite carbon powder.

[0050] Among them, the dosage of the binder is generally only about 1%, but the binder is an important material that determines the performance of the electrode paste. That is to say, the binder in the electrode paste is an indispensable raw material for preparing high-performance lithium-ion batteries.

[0051] At present, the most commonly used negative electrode binder is a binder composed of sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), and the commonly used negative electrode material is carbon powder. Among them, the surface of the carbon powder particles is hydrophobic. Since the CMC molecule has both a hydrophobic part and a hydrophilic part, CMC can be used as a slurry dispersant to prevent the slurry from settling and improve the uniformity of the electrode components. The surface of the SBR particles is carboxyl-modified. Due to its hydrophilic characteristics, SBR has a poor adsorption to carbon powder. Therefore, SBR needs to cooperate with CMC to play the role of a binder, tightly bond the active material, the conductive agent, and the current collector, keep the electrode sheet in good electronic conductivity and structural integrity, improve the infiltration of the electrolyte, and promote the electrode-electrolyte interface transmission of lithium ions.

[0052] In practical applications, if the characteristics or contents of CMC and SBR do not match, processing problems such as slurry settlement and coating delamination may occur. At the same time, particle aggregation will lead to a poor dispersion effect, thereby significantly degrading the performance (such as specific capacity, cycle performance, etc.) of the finally prepared lithium-ion battery. Therefore, determining the reasonable matching type selection and dosage of CMC and SBR is an important link in the battery design and development.

[0053] In the related art, in order to ensure the performance of lithium-ion batteries, the related art generally evaluates the electrode paste and the battery finished product one by one. However, due to the long cycle and different standards of the one-by-one evaluation method, this method is difficult to meet the rapid and accurate evaluation requirements when the battery products are rapidly updated.

[0054] Therefore, how to quickly and accurately determine the reasonable matching type selection and dosage of CMC and SBR is an urgent problem to be solved at present.

[0055] To solve the above problems, the embodiments of the present application provide a negative electrode binder and a negative electrode paste. Among them, the negative electrode binder can be prepared based on the preparation method of the negative electrode binder in the embodiments of the present application, and the negative electrode paste can be prepared based on the negative electrode binder prepared in the embodiments of the present application.

[0056] Such as Figure 1As shown, the preparation method of the negative electrode binder may include the following steps:

[0057] In step 11, viscosity tests are performed on each alternative CMC solution to determine at least one target CMC solution.

[0058] In the embodiments of the present application, before performing the viscosity test, the embodiments of the present application may first select alternative CMC materials according to the parameters of CMC to prepare each alternative CMC solution.

[0059] Among them, the alternative CMC materials can be classified into high degree of substitution and low molecular weight, high degree of substitution and high molecular weight, low degree of substitution and high molecular weight, and low degree of substitution and low molecular weight according to the parameters. Then, the embodiments of the present application can prepare alternative CMC solutions with a viscosity range of 1000 - 40000 mPa·s (millipascal seconds), and among them, the preferred viscosity range of the alternative CMC solutions can be 10000 - 25000 mPa·s.

[0060] In a preferred embodiment, the preparation process of the alternative CMC solution in step 11 can be carried out as follows: according to the first parameter, determine at least one alternative CMC material, and then weigh a predetermined mass of the alternative CMC material and mix it with water and stir to prepare an alternative CMC solution with a first concentration.

[0061] Among them, the first parameter includes at least the degree of substitution and viscosity of the alternative CMC material. The degree of substitution (DS) of CMC refers to the average number of hydrogens on the hydroxyl groups of each glucose residue ring of the cellulose macromolecule being replaced by carboxymethyl groups. Viscosity is a physical and chemical property of a substance, defined as a pair of parallel plates with an area of A and a distance of dr between them. When a certain liquid is filled between the plates, if a thrust F is applied to the upper plate, the force required to cause a change in velocity is defined as viscosity.

[0062] For example, there are three specifications of alternative CMC materials, including CMC-A, CMC-B, and CMC-C. Among them, the degree of substitution of CMC-A is 0.6 - 0.7, and the viscosity of a 1% mass fraction CMC-A solution is 3000 - 4000 mPa·s. The degree of substitution of CMC-B is 0.87 - 1.05, and the viscosity of a 1% mass fraction CMC-B solution is 2000 - 3000 mPa·s. The degree of substitution of CMC-C is 0.65 - 0.75, and the viscosity of a 1% mass fraction CMC-C solution is 3000 - 4000 mPa·s.

[0063] Optionally, when preparing the alternative CMC solutions from the alternative CMC materials of the above three specifications, the alternative CMC solutions can be prepared at a mass concentration of, for example, 1.5% according to the actual situation. Of course, the alternative CMC solutions can also be prepared at other mass concentrations according to the actual situation. In this embodiment of the application, the case where the mass concentration is 1.5% is taken as an example for illustration.

[0064] Specifically, in this embodiment of the application, a certain amount of powders of CMC-A, CMC-B, and CMC-C can be weighed and dispersed in water, and then the equipment rotation speed can be set to 1500 revolutions per minute according to the process requirements, stirred for 2 - 5 hours, and left standing for more than 5 hours to prepare alternative CMC solutions (CMC-A solution, CMC-B solution, and CMC-C solution) with a mass concentration of 1.5%.

[0065] After the alternative CMC solutions are prepared, in a preferred embodiment, step 11 above can be performed as follows: Through a rheometer, the viscosity tests of each alternative CMC solution are carried out at a predetermined shear rate.

[0066] Among them, a rheometer is an instrument used to measure the rheological properties of polymer melts, polymer solutions, suspensions, emulsions, coatings, inks, and foods, etc. In this embodiment of the application, the viscosity of the alternative CMC solution at a predetermined shear rate can be measured by a rheometer, and the magnitude of this viscosity can characterize the rheology of the alternative CMC solution.

[0067] During the viscosity test, the predetermined shear rate can be a rate value or a rate range set according to the actual situation. For example, the shear rate can be 0.001 - 500S -1 , where the preferred range of the shear rate can be 0.01 - 100S -1 . In addition, during the viscosity test, the value range of the shear force can also be a value or a range set according to the actual situation. For example, the shear force can be a value selected from 0 - 200 Pa or 0 - 200 Pa.

[0068] Optionally, taking the alternative CMC solutions prepared from CMC-A, CMC-B, and CMC-C as the alternative CMC materials as an example, in this embodiment of the application, the viscosities of the three prepared alternative CMC solutions (CMC-A solution, CMC-B solution, and CMC-C solution) can be respectively tested by a rheometer within the shear rate range of 0.01 - 100S -1 .

[0069] As Figure 2 shown, Figure 2 This is the shear viscosity curve graph of the viscosity tests of the CMC-A solution, CMC-B solution, and CMC-C solution in this embodiment of the application. Among them, Figure 2The abscissa is used to represent the predetermined shear rate during viscosity testing, and the ordinate is used to represent the viscosity obtained by testing at the predetermined shear rate.

[0070] From Figure 2 the test results shown, within the range of 0.01 - 0.1 S -1 , the viscosities of CMC-A solution, CMC-B solution and CMC-C solution are stable. Among them, the relationship of viscosity magnitudes is CMC-A solution > CMC-C solution > CMC-B solution, which is basically consistent with the viscosity law in the first parameter.

[0071] As the shear speed increases, the shear viscosity curve of CMC-A solution fluctuates greatly and the viscosity value is high. The viscosity of CMC-B solution is small, and the viscosity of CMC-C solution is appropriate with a smooth curve. Thus, CMC-C solution can be directly used for subsequent tests, while CMC-A solution and CMC-B solution need to be adjusted before subsequent tests. For example, for CMC-A solution, in the embodiments of the present application, the mass concentration of CMC-A solution can be appropriately reduced (for example, reduced to 1.4%), so that the mass concentration of CMC-A solution is appropriate. For CMC-B solution, in the embodiments of the present application, the mass concentration of CMC-B solution can be appropriately increased (for example, increased to 1.7%), so that the concentration of CMC-B solution is appropriate.

[0072] After the viscosity test, in the embodiments of the present application, the alternative CMC solutions that meet the viscosity test conditions and / or the alternative CMC solutions that meet the viscosity test conditions after concentration adjustment can be used as the target CMC solutions.

[0073] In step 12, a matching degree test is performed on each alternative SBR solvent and each target CMC solution to determine the target SBR material and target CMC material whose matching degree meets the predetermined conditions.

[0074] Among them, the result of the matching degree test is an important basis for evaluating the matching degree between each alternative SBR solvent and each target CMC solution. The higher the matching degree, the better the performance of the negative electrode binder prepared by the two materials.

[0075] In a preferred embodiment, during the matching degree test, in the embodiments of the present application, the target CMC solution needs to be prepared into corresponding products first, and then the matching degree test is performed based on each alternative SBR solvent and the products corresponding to each target CMC solution.

[0076] Specifically, the process of the matching degree test can be executed as follows: prepare the products corresponding to the target CMC solution, and then perform the matching degree test based on each alternative styrene-butadiene rubber (SBR) solvent and the products corresponding to each target CMC solution.

[0077] Among them, the products corresponding to the target CMC glue solution include CMC glue film and / or semi-finished film.

[0078] In a preferred embodiment, the products corresponding to the target CMC glue solution may include CMC glue film. Furthermore, the preparation process of the CMC glue film can be carried out as follows: for each target CMC glue solution, coat the target CMC glue solution onto the foil, and make the CMC glue film through natural drying.

[0079] Among them, the foil can be a copper foil or a foil made of other applicable materials.

[0080] For example, for the CMC-A glue solution, after the viscosity test of the CMC-A glue solution in the embodiments of the present application, the mass concentration of the CMC-A glue solution can be adjusted to 1.4% first, and the CMC-A glue solution with a mass concentration of 1.4% is used as the target CMC glue solution.

[0081] Specifically, in the embodiments of the present application, a predetermined proportion of CMC-A powder can be dispersed in water, then stirred at a speed of 1500 revolutions per minute for 2-5 hours, and then left standing for more than 5 hours to obtain the CMC-A glue solution.

[0082] Then, in the embodiments of the present application, the CMC-A glue solution with a mass concentration of 1.4% can be coated onto a clean and smooth copper foil through a 200mm blade, and naturally dried in an environment of 20°C - 100°C for 30min - 120min to make the CMC-A glue film.

[0083] In a preferred embodiment, the products corresponding to the target CMC glue solution may include semi-finished film. Furthermore, the preparation process of the semi-finished film can be carried out as follows: mix the negative electrode active material powder with the conductive agent (SP) to obtain a mixed solution, then for each target CMC glue solution, add the target CMC glue solution with the second concentration to the mixed solution a predetermined number of times to obtain a semi-finished slurry, and then coat the semi-finished slurry onto the foil and make the semi-finished film through natural drying.

[0084] Among them, the negative electrode active material powder can be one or several of natural carbon powder, artificial carbon powder, mesophase carbon microspheres, silicon carbon, etc.

[0085] Since during the viscosity test, if the alternative CMC glue solution meets the conditions of the viscosity test, then in the embodiments of the present application, there is no need to adjust the mass concentration of the alternative CMC glue solution and use the alternative CMC glue solution as the target CMC glue solution. At this time, the second concentration is the above-mentioned first concentration. If the alternative CMC glue solution does not meet the conditions of the viscosity test, then in the embodiments of the present application, the mass concentration of the alternative CMC glue solution can be adjusted first and the adjusted alternative CMC glue solution is used as the target CMC glue solution. At this time, the second concentration is the adjusted mass concentration.

[0086] In addition, the predetermined number of times can correspond to a predetermined solid content. That is to say, in the embodiments of the present application, the target CMC sizing solution with a second concentration can be added to the mixture of toner and conductive agent in multiple times. Among them, the timing of each addition can be when the solid content of the mixture reaches a certain threshold. The solid content is the mass percentage of the remaining part after drying the emulsion or coating under specified conditions.

[0087] For example, for the CMC-A sizing solution, after viscosity testing the CMC-A sizing solution in the embodiments of the present application, the mass concentration of the CMC-A sizing solution can be first adjusted to 1.4%, and the CMC-A sizing solution with a mass concentration of 1.4% is used as the target CMC sizing solution (wherein, in the embodiments of the present application, a predetermined proportion of CMC-A powder can be dispersed in water, and then stirred at a speed of 1500 revolutions per minute for 2 - 5 hours, and then left standing for more than 5 hours to obtain the CMC-A sizing solution). Then, in the embodiments of the present application, the toner and the conductive agent can be mixed to obtain a mixture.

[0088] After obtaining the mixture, in the embodiments of the present application, the CMC-A sizing solution with a mass concentration of 1.4% can be added to the mixture in three times (predetermined number of times). Specifically, the first time can be when the solid content of the mixture reaches 85 - 80% (the preferred range can be 82% - 81%, and the embodiments of the present application take 81% as an example), the second time can be when the solid content of the mixture reaches 70 - 65% (the preferred range can be 68% - 66%, and the embodiments of the present application take 67% as an example), and the third time can be when the solid content of the mixture reaches 52 - 45% (the preferred range can be 50% - 47%, and the embodiments of the present application take 50% as an example).

[0089] In this way, through the above process, in the embodiments of the present application, a semi-finished slurry with a mass percentage of negative active material of 90 - 98% (the preferred range can be 94% - 98%, and the embodiments of the present application take 96.5% as an example), a mass percentage of conductive agent of 0 - 3% (the preferred range can be 1% - 2%, and the embodiments of the present application take 1.5% as an example), and a mass percentage of CMC-A of 1 - 5% (the preferred range can be 2% - 3%, and the embodiments of the present application take 2% as an example) can be prepared.

[0090] Then, in the embodiments of the present application, the above semi-finished slurry can be coated on a clean and smooth copper foil with a 200 mm doctor blade, and naturally dried in an environment of 20°C - 100°C for 30 min - 120 min to form a semi-finished film.

[0091] After preparing the CMC film and / or semi-finished film, in the embodiments of the present application, the matching degree test can be carried out based on the CMC film and / or semi-finished film.

[0092] In a preferred embodiment, step 12 above can be performed as follows: Drop each alternative SBR solvent onto the surface of the product corresponding to each target CMC solution, determine the contact angle between the surface of the product corresponding to the target CMC solution and the alternative SBR solvent on the surface of the semi-finished film, and determine that the material corresponding to the contact angle less than the predetermined angle threshold is the target SBR material and the target CMC material.

[0093] Optionally, when it comes to the material corresponding to the alternative SBR solvent, the embodiments of the present application can estimate the matching degree according to the parameters of the alternative SBR material.

[0094] For example, there are three existing alternative SBR materials: SBR-A, SBR-B, and SBR-C. Among them, the particle size of SBR-A is 100 nm, the solid content is 50%, and the surface is not modified. The particle size of SBR-B is 120 nm, the solid content is 40%, and the surface is modified with functional groups. The particle size of SBR-C is 80 nm, 10% acrylate is blended, and the solid content is 45%. Through the parameters of the alternative SBR materials, the embodiments of the present application can estimate the matching degree to verify the final test results and improve the test effect.

[0095] Taking CMC-A as an example, through the above parameters, it can be estimated that among SBR-A, SBR-B, and SBR-C, the matching of SBR-B and SBR-C with CMC-A is better. That is to say, through the parameters of the alternative SBR materials, the embodiments of the present application can estimate that the matching of SBR-B and SBR-C with CMC-A will be better than that of SBR-A with CMC-A.

[0096] After estimating the matching degree, the embodiments of the present application can make the alternative SBR materials into solvents and perform a matching degree test based on each alternative SBR solvent and the product corresponding to each target CMC solution.

[0097] Taking the CMC-A solution as an example, the embodiments of the present application can use a microinjector to drop about 1-50 μL (taking 10 μL as an example) of SBR-A solvent, SBR-B solvent, and SBR-C solvent onto the surface of the CMC film and / or semi-finished film made of the CMC-A solution respectively. Among them, the height difference between the starting point of the drop of SBR-A solvent, SBR-B solvent, and SBR-C solvent and the test substrate (the surface of the CMC film and / or semi-finished film made of the CMC-A solution) is 1-6 cm (taking 1 cm as an example), the environmental temperature is 25 °C, and the humidity is less than 80%.

[0098] After dropping SBR-A solvent, SBR-B solvent, and SBR-C solvent onto the surface of the CMC film and / or semi-finished film made of CMC-A glue solution respectively, the embodiments of the present application can determine the contact angle between each drop of liquid and its corresponding substrate, and determine the result of the matching degree test based on this contact angle.

[0099] As Figure 3 shown, Figure 3 This is a schematic diagram of the matching degree test result of the embodiments of the present application. Among them, the tested substrate is the CMC film and semi-finished film made of CMC-A glue solution, and the reagents are SBR-A solvent, SBR-B solvent, and SBR-C solvent.

[0100] The result of the matching degree test shows that Figure 3 the contact angle between SBR-A solvent and CMC-A film and CMC-A semi-finished film is the largest, indicating that the matching between SBR-A and CMC-A is poor. If the two are used as the binder of the carbon powder negative electrode, phenomena such as SBR floating, uneven distribution, and slurry sedimentation may occur. The contact angles between SBR-C and CMC-A film and CMC-A semi-finished film are both the smallest, indicating that the matching between SBR-C and CMC-A is better, which is conducive to playing a synergistic role and forming a uniform and stable slurry.

[0101] Furthermore, due to the good matching between SBR-C and CMC-A, therefore, the embodiments of the present application can use SBR-C as the target SBR material and CMC-A as the target CMC material.

[0102] That is to say, in the embodiments of the present application, the two materials with the smallest contact angle during the matching degree test can be determined as the target SBR material and the target CMC material. In another case, the embodiments of the present application can also determine the materials corresponding to the contact angles less than the predetermined angle threshold as the target SBR material and the target CMC material.

[0103] In step 13, the target negative electrode binder is prepared using the target SBR material and the target CMC material as the negative electrode binder materials.

[0104] Through the embodiments of the present application, before preparing the negative electrode slurry, the materials of the negative electrode binder can be tested first to realize that after determining the preferred materials of the negative electrode binder, the target negative electrode binder is made. During this process, since the embodiments of the present application determine the preferred combination of the negative electrode binder before preparing the negative electrode slurry, therefore, through the embodiments of the present application, the reasonable matching type selection and dosage of CMC and SBR can be determined quickly and accurately, achieving the benefits of effectively shortening the evaluation cycle, avoiding processing risks in advance, and reducing development costs.

[0105] In a preferred embodiment, the embodiment of the present application may also perform: preparing a negative electrode slurry based on a target negative electrode binder, and performing a performance test on the negative electrode slurry.

[0106] Among them, the coating process of the negative electrode slurry is a high shear rate process. After coating on the current collector, the negative electrode slurry will be leveled under the action of gravity and surface tension on the current collector. The leveling process is a low shear rate process, so the shear viscosity of the slurry is not too high in the high shear rate range, otherwise it will easily cause coating difficulties. In the low shear rate range, the viscosity of the negative electrode slurry is preferably able to gradually recover to the high viscosity before coating in an appropriate time. If the recovery time is too long, indicating that the viscosity of the negative electrode slurry is low, it will be easy to have tailing or the thickness of the lower edge is higher than the thickness of the upper coating. If the recovery time is too short, the leveling time of the negative electrode slurry is short, resulting in poor leveling effect and easy appearance of wavy ripples.

[0107] Specifically, the embodiment of the present application can prepare the negative electrode slurry by referring to the above-mentioned process of preparing the semi-finished film.

[0108] Taking the target SBR material as SBR-C and the target CMC material as CMC-A as an example, in the embodiment of the present application, the active material powder (such as carbon powder) and the conductive agent are first mixed to prepare a mixture, and then the CMC-A glue with a mass concentration of 1.4% is added to the mixture three times. The first time can be when the solid content of the mixed solution reaches 81%, the second time can be when the solid content of the mixed solution reaches 67%, and the third time can be when the solid content of the mixed solution reaches 50%.

[0109] Finally, in the embodiment of the present application, SBR-C can be added and mixed evenly to obtain a negative electrode slurry, in which the mass percentage of carbon powder is 96%, the mass percentage of the conductive agent is 1.0%, the mass percentage of CMC-A is 1.2%, and the mass percentage of SBR-C is 1.8%.

[0110] Therefore, the embodiment of the present application can perform a performance test on the negative electrode slurry by means of a shear test to ensure that the negative electrode slurry can gradually recover to the high viscosity before coating in an appropriate time.

[0111] In a preferred embodiment, the process of performing a performance test on the negative electrode slurry may be performed as follows: performing a three-stage jump shear test on the negative electrode slurry.

[0112] Among them, in the embodiments of the present application, a three-stage jump shear test can be performed on the negative electrode paste by a rheometer. The test conditions in the first stage of the three-stage jump shear test are the first shear rate and the first shear time. The test conditions in the second stage of the three-stage jump shear test are the second shear rate and the second shear time. The test conditions in the third stage of the three-stage jump shear test are the third shear rate and the third shear time.

[0113] Among them, the first shear rate, the first shear time, the second shear rate, the second shear time, the third shear rate and the third shear time can be reasonable values set according to the actual situation. For example, the first shear rate can be 0.01S -1 , the first shear time can be 60S, the second shear rate can be 100S -1 , the second shear time can be 120S, the third shear rate can be 0.01S -1 , and the third shear time can be 240S.

[0114] Taking the negative electrode paste prepared with the target SBR material as SBR-C and the target CMC material as CMC-A as the negative electrode binder material as an example, as Figure 4 shown, Figure 4 is a schematic diagram of the results of the three-stage jump shear test in the embodiments of the present application. Among them, the abscissa is used to characterize the shear time during the three-stage jump shear test, and the ordinate is used to characterize the viscosity of the negative electrode paste during the test at different stages.

[0115] As Figure 4 shown, in the first stage, the viscosity of the negative electrode paste at a high shear rate is 11000mPa.s - 13000mPa.s. After the low shear rate in the second stage, the viscosity recovery time of the negative electrode paste from the second stage to the third stage is 14s. Therefore, Figure 4 the fluidity and leveling property of the negative electrode paste shown have good viscosity and recovery time.

[0116] After verification, based on the negative electrode paste shown Figure 4 , the appearance of the electrode sheet of the lithium-ion battery is normal. Subsequently, through conventional electrode sheet processing and battery testing, it is also verified that the binder combination (the binder combination of SBR-C and CMC-A as the negative electrode binder) has good adhesion and electrical performance.

[0117] It should be noted that the values in the embodiments of the present application are examples in the explanation. The specific values in the actual application of the embodiments of the present application are not limited to the above values.

[0118] In another embodiment of the present application, the embodiment of the present application further provides a negative electrode binder, wherein the composite material of the negative electrode binder can be determined based on the above embodiments.

[0119] Furthermore, after the embodiment of the present application determines the preferred material combination of the negative electrode binder, the negative electrode paste can be prepared based on each preferred composite material of the negative electrode binder.

[0120] In another embodiment of the present application, the embodiment of the present application further provides a negative electrode paste. When the embodiment of the present application determines the preferred material combination of the negative electrode binder, the active material powder can be first mixed with the conductive agent, then the preferred target CMC material can be added in multiple times, and finally the preferred target SBR material can be added to obtain the negative electrode paste by mixing.

[0121] Through the embodiment of the present application, the materials of the negative electrode binder can be tested before preparing the negative electrode paste, so as to realize that after determining the preferred materials of the negative electrode binder, the target negative electrode binder can be made. During this process, since the embodiment of the present application determines the preferred combination of the negative electrode binder before preparing the negative electrode paste, the reasonable CMC and SBR matching selection and dosage can be quickly and accurately determined through the embodiment of the present application to prepare a negative electrode binder with higher performance.

[0122] Furthermore, based on the negative electrode binder with higher performance, the embodiment of the present application can prepare a negative electrode paste with higher performance, realizing the benefits of effectively shortening the evaluation cycle, avoiding processing risks in advance, and reducing the development cost.

[0123] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for preparing a negative electrode binder, characterized in that, The method includes: Determine at least one alternative sodium carboxymethyl cellulose (CMC) material according to a first parameter, where the first parameter includes at least the degree of substitution and viscosity of the alternative CMC material; Weigh a predetermined mass of the alternative CMC material and mix it with water and stir to prepare an alternative CMC glue solution with a first concentration; Conduct a viscosity test on each of the alternative CMC glue solutions to determine at least one target CMC glue solution; Prepare products corresponding to the target CMC glue solution; Drop each alternative styrene-butadiene rubber (SBR) solvent onto the surface of the products corresponding to each of the target CMC glue solutions; Determine the contact angle between the surface of the product corresponding to the target CMC glue solution and the alternative SBR solvent; Determine that the material corresponding to the contact angle less than a predetermined angle threshold is the target SBR material and the target CMC material; and Use the target SBR material and the target CMC material as the negative electrode binder material to prepare a target negative electrode binder; Wherein, the product corresponding to the target CMC glue solution includes a CMC film or a semi-finished film; The CMC film is prepared based on the following steps: For each of the target CMC glue solutions, coat the target CMC glue solution onto a foil and dry it naturally to form a CMC film; The semi-finished film is prepared based on the following steps: Mix the negative electrode active material powder and the conductive agent to obtain a mixed solution; For each of the target CMC glue solutions, add the target CMC glue solution with a second concentration to the mixed solution a predetermined number of times to obtain a semi-finished slurry, where the predetermined number of times corresponds to a predetermined solid content; and Coat the semi-finished slurry onto a foil and dry it naturally to form a semi-finished film.

2. The method according to claim 1, characterized in that, The method further includes: Prepare a negative electrode slurry based on the target negative electrode binder; and Conduct a performance test on the negative electrode slurry.

3. The method according to claim 1, characterized in that The conducting a viscosity test on each of the alternative CMC glue solutions includes: Using a rheometer, conduct a viscosity test on each of the alternative CMC glue solutions at a predetermined shear rate.

4. The method according to claim 2, wherein The conducting a performance test on the negative electrode slurry includes: Conduct a three-stage jump shear test on the negative electrode slurry, where the test conditions in the first stage of the three-stage jump shear test are a first shear rate and a first shear time, the test conditions in the second stage of the three-stage jump shear test are a second shear rate and a second shear time, and the test conditions in the third stage of the three-stage jump shear test are a third shear rate and a third shear time.

5. A negative electrode binder, characterized in that, The negative electrode binder is prepared based on the preparation method of the negative electrode binder according to claim 1.

6. A negative electrode paste, characterized in that, The negative electrode slurry is prepared based on the negative electrode binder according to claim 5.

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