Preparation process of negative electrode slurry, negative electrode sheet and battery

Abstract

The application provides a preparation process of negative electrode slurry, a negative electrode sheet and a battery, under the preparation process, long-term dispersion stability of the negative electrode slurry can be realized under low solid content of 30-40% and low viscosity of 300-1050 mPa·S. The negative electrode slurry can be used to realize coating with an area density of not higher than 17 g / m 2 2, and obvious scratches will not be generated in the coating process, so that the negative electrode sheet has good appearance morphology, and can be applied to the preparation and production of actual lithium ion batteries.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion batteries, and particularly relates to a preparation process of negative electrode slurry, a negative electrode sheet and a battery. BACKGROUND

[0002] With the application of lithium ion batteries in the automobile industry, people require shorter charging time and stronger acceleration charging performance, and therefore the high-rate charging and discharging performance of power batteries is required to be higher and higher. For example, in some special vehicle models, the rate requirement is far higher than the existing level, and a rate of >100C or a higher rate performance is required. In order to achieve such a high rate of charging and discharging, the electrode thickness needs to be very thin and the area density needs to be very small.

[0003] At present, the most widely used negative electrode slurry in the market is graphite negative electrode slurry, and the conventional graphite negative electrode slurry has a solid content of 48-55% and a viscosity of 3500-8000 mPa·s. If the solid content and the viscosity of the graphite enrichment slurry are lower, the dispersion stability of the slurry will be poor, and the storage time will be short. Even if the coating is carried out at a low solid content and a low viscosity, re-agglomeration is easy to occur, and scratches are also caused in the coating process, so that the negative electrode sheet cannot be normally used, and therefore the low-area-density coating of the negative electrode cannot be realized.

[0004] In the existing industrialization factory, the minimum single-area density of the negative electrode slurry coating can be about 25 g / m 2 . When the area density is further reduced, a large number of scratches will occur on the electrode sheet, and the extrusion coating die lip will be scratched, so that the manufacturability is very low.

[0005] Therefore, a preparation process of negative electrode slurry with low solid content and low viscosity is provided, so that the negative electrode slurry can be long-term dispersion stable at a low solid content and a low viscosity, and a negative electrode sheet with a lower area density can be prepared, which is of great significance to solve the problem of fast charging at a high rate of the existing lithium ion battery. SUMMARY

[0006] In order to solve the problems and deficiencies in the prior art, the present application provides a preparation process of negative electrode slurry, a negative electrode sheet and a battery. In the preparation process, the negative electrode slurry can be long-term dispersion stable at a low solid content of 30-40% and a low viscosity of 300-1050 mPa·s. The negative electrode slurry can be used for coating with an area density of not higher than 17 g / m 2 , and no obvious scratches will occur in the coating process, so that the negative electrode sheet has a good appearance and can be applied to the preparation and production of actual lithium ion batteries.

[0007] According to a first aspect of the present application, a preparation process of negative electrode slurry is provided, which comprises the following steps:

[0008] Step 1. Mix the thickening agent with solvent B-1 to obtain a main liquid; low-speed stirring and high-speed stirring are carried out simultaneously during mixing, the low-speed stirring rate is 5-30 rpm, the high-speed stirring linear velocity is 10-20 m / s, and the mixing time is 120-400 min; Step 2. Mix the powder conductive agent B and the negative electrode active material, then add the first part of the main liquid B to continue mixing to obtain a first mixed liquid B; low-speed stirring is carried out during mixing, the low-speed stirring rate is 10-30 rpm, and the mixing time is 120-165 min; Step 3. Mix the second part of the main liquid B into the first mixed liquid B to obtain a second mixed liquid B; low-speed stirring and high-speed stirring are carried out simultaneously during mixing, the low-speed stirring rate is 15-30 rpm, the high-speed stirring linear velocity is 10-20 m / s, and the mixing time is 30-60 min; Step 4. Mix the binder B into the second mixed liquid B to obtain a third mixed liquid B; low-speed stirring and high-speed stirring are carried out simultaneously during mixing, the low-speed stirring rate is 15-30 rpm, the high-speed stirring linear velocity is 10-20 m / s, and the mixing time is 30-90 min; Step 5. Adjust the viscosity of the third mixed liquid B to 300-1050 mPa.s, and the solid content to 30-40%, to obtain a negative electrode slurry.

[0009] In the prior art, in order to improve the energy storage capacity of the battery, the surface density of the pole piece is often increased. Increasing the solid content of the slurry is one of the main ways to increase the density of the positive pole piece. Generally, there is a certain relationship between the solid content and the viscosity, the higher the solid content, the higher the viscosity. Therefore, the current main research direction is more inclined to increase the solid content and viscosity of the slurry. On the other hand, the viscosity and solid content of the slurry are important factors affecting its stability. Under high solid content and high viscosity, the stability of the slurry is often higher. If the solid content and viscosity of the slurry are to be further reduced, it is not feasible to directly add a solvent, because after adding the additional solvent, the solid content and viscosity of the slurry are reduced, which leads to poor stability of the slurry, which is not conducive to the further application of the slurry, such as the production of positive pole pieces. During the coating process, heavy agglomeration and coating scratches are prone to occur.

[0010] At the same time, as a multi-component non-equilibrium system, the biggest problem of the slurry is that the internal particles are agglomerated due to electrostatic attraction, van der Waals force or hydrogen bonding, or are settled under the action of gravity, thereby affecting the dispersion uniformity and stability of the slurry. Therefore, to make a stable slurry, the influence of multiple factors such as material properties, formula, stirring process, and environment should be considered comprehensively.

[0011] In the preparation process of the negative electrode slurry provided by the application, the thickening agent is first wetted and dispersed by a solvent to obtain a main liquid, and then the main liquid is added twice to a solid mixture formed by the negative electrode active material and the powder conductive agent B. The first part of the main liquid B is added by only low-speed stirring and mixing, which can preliminarily perform macroscopic dispersion, i.e., the large powder clusters in the solution are broken up, so that the thickening agent, the negative electrode active material and the powder conductive agent B can be uniformly distributed in the solution in the form of fine powder clusters. At the same time, because the first part of the main liquid B is added for mixing, it belongs to liquid-solid mixing, and if high-speed stirring is applied at this time, the thickening agent, the negative electrode active material and the powder conductive agent B in the solution are more likely to form clusters and are not easy to disperse, even if continuous stirring for a long time, a molecularly uniform (microscopic dispersion) mixture cannot be obtained, which is not conducive to the long-term dispersion stability of the slurry. Moreover, directly applying high-speed stirring in solid-liquid mixing can also easily cause great damage to the equipment.

[0012] Then, when the second part of the main liquid B is added for mixing, low-speed stirring and high-speed stirring are simultaneously performed, which belongs to liquid-liquid mixing. Before the two solutions are mixed, the materials and the solvent in the solutions reach a relatively stable state, and at this time, the simultaneous application of low-speed stirring and high-speed stirring is conducive to the macroscopic dispersion and the microscopic dispersion of the slurry, and finally makes the slurry reach a stable dispersion state at the molecular level. That is, the thickening agent, the conductive agent and the binder B can be uniformly and stably coated on the surface of the negative electrode active material particles, and the van der Waals force, the electrostatic repulsion force, the steric hindrance repulsion force and other interactions between the thickening agent, the conductive agent, the binder B, the negative electrode active material and the solvent in the slurry reach a high stable state, so that the slurry has high dispersion stability. Therefore, the slurry in the application can maintain long-term stability even at a low solid content and a low viscosity, and can prevent heavy agglomeration and scratches from occurring in the coating process, which is conducive to the preparation of a negative electrode sheet with a low surface density, so as to achieve the purpose of preparing a lithium battery with a high rate of fast charging.

[0013] It should be further pointed out that the paddle shape in low-speed stirring is generally a twisted blade shape, and the paddle shape in high-speed stirring is generally a disc shape with teeth, and of course the paddle shapes of low-speed stirring and high-speed stirring can be adjusted according to specific conditions. Moreover, the two-step addition of the binder at the end also affects the stability of the final negative electrode slurry, and the two-time addition of the binder is conducive to the uniform and stable dispersion of the binder in the slurry system provided by the application, and further promotes the stability of the slurry.

[0014] Preferably, in step 1, when the main liquid is formed, the mass ratio of the thickening agent to the solvent B-1 is 0.005-0.03:1. Under this mass ratio, the solvent can fully wet and disperse the thickening agent, and there is enough solvent in the formed main liquid, which promotes the good dispersion of the subsequent powder conductive agent B, the negative electrode active material and the binder B.

[0015] Preferably, in step 1, the thickening agent comprises a carboxymethyl cellulose thickening agent; in step 2, the powder conductive agent B comprises a carbon black conductive agent; the negative electrode active material comprises a graphite active material; in step 4, the binder B comprises an LA aqueous binder B, and the effective component of the LA aqueous binder B comprises a polyacrylic compound and an acrylonitrile multi-polymer.

[0016] Preferably, the carboxymethyl cellulose thickening agent comprises at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, and lithium carboxymethyl cellulose.

[0017] Preferably, the carbon black conductive agent comprises at least one of acetylene black, SP, and Ketjen black.

[0018] Preferably, the graphite active material comprises at least one of natural graphite and artificial graphite.

[0019] Preferably, the LA aqueous binder B comprises at least one of LA132, LA133, and LA136.

[0020] Preferably, the solid content of the LA aqueous binder B is 4-15%. The use of the LA aqueous binder B with a lower solid content has smaller viscosity and stirring resistance, which is conducive to the uniform dispersion of the LA aqueous binder B in the slurry and the formation of a stable suspension dispersion system with other materials in the slurry.

[0021] Preferably, the solvent B-1 comprises water.

[0022] Preferably, in step 2, the D50 of the negative electrode active material is 1-20 μm. The negative electrode slurry has a certain relationship with the D50 of the negative electrode active material, because the effective component of the negative electrode active material accounts for the largest proportion in the negative electrode slurry, and the dispersion stability of the negative electrode active material particles has a very key influence on the stability of the negative electrode slurry. Controlling the D50 of the negative electrode active material within the above range is conducive to the appropriate steric hindrance between the negative electrode active material particles, so that the particles have stable interaction forces, and the negative electrode active particles also have stable interaction forces with other materials in the slurry, forming a relatively stable suspension dispersion system.

[0023] Preferably, in steps 1-2 and 4, the mass ratio of the negative electrode active material: main liquid B: binder B: powder conductive agent B is 1:(0.2-0.8):(0.1-0.6):(0.005-0.05). Guaranteeing the mass ratio of the above materials within the above range can not only ensure that the materials have stable interaction forces in the formed mixed system to form a long-term stable dispersion suspension system, but also ensure that the negative electrode sheet prepared by using the negative electrode slurry system has good conductivity and structural stability, etc., so as to ensure that the battery prepared by the negative electrode sheet has good cycle performance.

[0024] Preferably, in step 2, the first part of the main liquid B accounts for 40-50% of the mass of the main liquid; the second part of the main liquid B accounts for 50-60% of the mass of the main liquid. The first part of the main liquid B accounts for a small proportion because the main liquid initially only contains thickening agents and solvents, and the solid content of the main liquid is low, so a small proportion of the main liquid can fully wet and disperse the powder conductive agent B and the negative electrode active material, and at the same time, a well-dispersed suspension system can be initially formed under low-speed stirring. The second part of the main liquid B accounts for a large proportion, and at this time, the solid content and viscosity of the first mixed liquid B are higher, which is conducive to reducing the dispersion resistance and improving the dispersion efficiency and effect.

[0025] Preferably, step 2 is divided into three steps, and the specific operation is as follows: step 2.1. low-speed stirring is first performed, the low-speed stirring rate is 15-20 rpm, and the mixing time is 30-45 min; step 2.2. after step 2.1 is completed, the slurry on the stirrer is scraped down and low-speed stirring is continued, the low-speed stirring rate is 20-30 rpm, and the mixing time is 45-60 min; step 2.3. after step 2.2 is completed, the slurry on the stirrer is scraped down and low-speed stirring is continued, the low-speed stirring rate is 20-30 rpm, and the mixing time is 45-60 min. When the first part of the main liquid B is mixed with the powder conductive agent B and the negative electrode active material, a large amount of powder conductive agent B and positive electrode active material solid particles are added at one time, and low-speed stirring and dispersion are performed in three steps, which is conducive to the full wetting and dispersion of the powder conductive agent B and the negative electrode active material in the solution, so that the negative electrode active material, the thickening agent and the powder conductive agent B can be well macroscopically dispersed, and a foundation is laid for subsequent further slurry to achieve micro-dispersion, i.e. molecular-level dispersion.

[0026] Preferably, in step 5, the viscosity and solid content of the third mixed liquid B are adjusted by adding a second solvent; the second solvent includes water.

[0027] Preferably, after the viscosity and solid content of the third mixed liquid B are adjusted in step 5, it also needs to be treated to remove iron.

[0028] According to the second aspect of the present application, a negative electrode sheet is provided, and the negative electrode slurry used in the preparation of the negative electrode sheet is prepared by the above-mentioned preparation process of the negative electrode slurry; the areal density of the negative electrode sheet is 5-17 g / m 2 The negative electrode slurry prepared by the present application can still be stable without settling after long-term storage, and obvious re-agglomeration does not occur during low areal density coating, nor does it cause obvious scratches during the coating process, and has a good appearance, so that the low areal density coating of the negative electrode can be effectively realized, the charge-discharge rate of the battery is improved, and the charging time of the battery is reduced.

[0029] According to a third aspect of the present application, a battery is provided, comprising the negative electrode sheet as described above. The battery prepared by using the negative electrode sheet with lower areal density can achieve higher rate of charge and discharge, and greatly reduce the charging time of the battery.

[0030] Preferably, the battery further comprises a positive electrode sheet, and the areal density of the positive electrode sheet is 10-50 g / m 2 .

[0031] Preferably, the areal density of the positive electrode sheet is 10-35 g / m 2 .

[0032] Preferably, in the preparation of the positive electrode sheet, the preparation process of the positive electrode slurry comprises the following steps:

[0033] S1. mixing the binder with the first part of the first solvent to obtain a first mixed solution; the mixing is performed while low-speed stirring and high-speed stirring are simultaneously performed, the low-speed stirring rate is 15-30 rpm, the high-speed stirring linear velocity is 10-20 m / s, and the mixing time is 120-400 min; S2. adding the liquid conductive agent into the first mixed solution to obtain a second mixed solution; the mixing is performed while low-speed stirring and high-speed stirring are simultaneously performed, the low-speed stirring rate is 15-30 rpm, the high-speed stirring linear velocity is 10-20 m / s, and the mixing time is 60-120 min; S3. mixing the powder conductive agent with the second part of the first solvent to obtain a powder conductive agent mixed solution; adding the powder conductive agent mixed solution into the second mixed solution to obtain a main solution; the mixing is performed while low-speed stirring and high-speed stirring are simultaneously performed, the low-speed stirring rate is 15-30 rpm, the high-speed stirring linear velocity is 10-20 m / s, and the mixing time is 120-180 min; S4. mixing the positive electrode active material with the first part of the main solution to obtain a third mixed solution; the mixing is performed while low-speed stirring is performed, the low-speed stirring rate is 15-30 rpm, and the mixing time is 120-165 min; S5. adding the second part of the main solution into the third mixed solution to obtain a fourth mixed solution; the mixing is performed while low-speed stirring and high-speed stirring are simultaneously performed, the low-speed stirring rate is 15-30 rpm, the high-speed stirring linear velocity is 10-20 m / s, and the mixing time is 60-180 min; S6. adding the third part of the main solution into the fourth mixed solution to obtain a fifth mixed solution; the mixing is performed while low-speed stirring and high-speed stirring are simultaneously performed, the low-speed stirring rate is 15-30 rpm, the high-speed stirring linear velocity is 10-20 m / s, and the mixing time is 60-180 min; S7. adjusting the viscosity of the fifth mixed solution to 300-1500 mPa.s, and the solid content to 40-55%, to obtain the positive electrode slurry.

[0034] Preferably, in S1-S3, when the main liquid is formed, the mass ratio of the binder: the liquid conductive agent: the powder conductive agent: the first solvent is 1.0-4.0: 10.0-30.0: 1.0-7.0: 15.0-85.0; wherein the total mass of the first solvent is the sum of the mass of the first portion of the first solvent and the second portion of the first solvent. Preferably, in S1 and S3, the first solvent comprises N-methyl pyrrolidone.

[0035] Preferably, in S1, the binder comprises polyvinylidene fluoride; in S2, the effective ingredient in the liquid conductive agent comprises carbon nanotubes; in S3, the powder conductive agent comprises carbon black conductive agent; and in S4, the positive electrode active material comprises ternary positive electrode active material.

[0036] Preferably, the diameter of the carbon nanotubes is 5-40 nm, and the length is 20-300 μm.

[0037] Preferably, the carbon black conductive agent comprises at least one of acetylene black, SP, and Ketjen black.

[0038] Preferably, the ternary positive electrode active material comprises at least one of nickel-cobalt-manganese positive electrode active material and nickel-cobalt-aluminum positive electrode active material.

[0039] Preferably, the D50 of the positive electrode active material is 1-15 μm.

[0040] Preferably, in S2, the solid content of the liquid conductive agent is 4.0-10.0%.

[0041] Preferably, in S3, the solid content of the main liquid is 8-16%.

[0042] Preferably, S4 is divided into three steps, and the specific operation is as follows: S4.1. First, low-speed stirring is performed at a low-speed stirring rate of 15-20 rpm for 30-45 min; S4.2. After step S4.1 is completed, the slurry on the stirrer is scraped off and low-speed stirring is continued at a low-speed stirring rate of 20-30 rpm for 45-60 min; S4.3. After step S4.2 is completed, the slurry on the stirrer is scraped off and low-speed stirring is continued at a low-speed stirring rate of 20-30 rpm for 45-60 min.

[0043] Preferably, in S4, the mass ratio of the positive electrode active material to the main liquid is 1:0.2-1.

[0044] Preferably, in S4, the mass proportion of the first portion of the main liquid in the main liquid is 40-60%; in S5, the mass proportion of the second portion of the main liquid in the main liquid is 20-30%; and in S6, the mass proportion of the third portion of the main liquid in the main liquid is 20-30%.

[0045] Preferably, in S7, the viscosity and solid content of the fifth mixed solution are adjusted by adding a second solvent; the second solvent comprises N-methyl pyrrolidone.

[0046] Preferably, in S7, after the viscosity and solid content of the fifth mixed solution are adjusted, the fifth mixed solution needs to be subjected to iron removal treatment. DETAILED DESCRIPTION

[0047] In order to enable those skilled in the art to better understand the technical scheme of the present application, the technical scheme in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments.

[0048] Embodiment 1

[0049] 1. Preparation of negative electrode slurry

[0050] In this embodiment, the negative electrode slurry is prepared according to the following steps:

[0051] Step 1. Mix thickener carboxymethyl cellulose 0.6 parts with water 37.9 parts to obtain a main solution; while mixing, low-speed stirring and high-speed stirring are simultaneously performed, the low-speed stirring rate is 17 rpm, the high-speed stirring linear speed is 15 m / s, and the mixing time is 260 min;

[0052] Step 2. Mix powder conductive agent B carbon black SP 1.2 parts and negative electrode active material artificial graphite 54.9 parts, then add first part of main solution B 16.9 parts (55% of the mass of the main solution) to continue mixing to obtain first mixed solution B, wherein the D50 of the negative electrode active material is 5 μm; while mixing, the following three steps are sequentially performed:

[0053] Step 2.1. First, low-speed stirring is performed, the low-speed stirring rate is 17 rpm, and the mixing time is 38 min;

[0054] Step 2.2. After step 2.1 is completed, the slurry on the stirrer is scraped down and low-speed stirring is continued, the low-speed stirring rate is 25 rpm, and the mixing time is 65 min;

[0055] Step 2.3. After step 2.2 is completed, the slurry on the stirrer is scraped down and low-speed stirring is continued, the low-speed stirring rate is 25 rpm, and the mixing time is 65 min;

[0056] Step 3. Add second part of main solution B 13.8 parts (45% of the mass of the main solution) to the first mixed solution B to mix to obtain second mixed solution B; while mixing, low-speed stirring and high-speed stirring are simultaneously performed, the low-speed stirring rate is 23 rpm, the high-speed stirring linear speed is 15 m / s, and the mixing time is 45 min;

[0057] Step 4. 18.3 parts of binder BLA132 (solid content 6%) was added into the second mixture B to obtain the third mixture B; the mixing was carried out with low speed stirring and high speed stirring at the same time, the low speed stirring rate was 22 rpm, the high speed stirring linear velocity was 15 m / s, and the mixing time was 60 min;

[0058] Step 5. The viscosity of the third mixture B was adjusted to 522 mPa.s, and the solid content was 32.0%, and after filtering to remove iron, the negative electrode slurry was obtained.

[0059] 2. Preparation of battery

[0060] (1) Preparation of negative electrode sheet

[0061] The negative electrode slurry prepared above was coated on the negative electrode current collector (copper foil), and by adjusting the coating parameters, the areal density of the final negative electrode sheet was 15.2 g / m 2 At this areal density, the negative electrode sheet had a good appearance without scratches.

[0062] (2) Preparation of positive electrode sheet

[0063] The positive electrode sheet with an areal density of 28.5 g / m 2 was selected in this embodiment (obtained by adjusting the coating parameters), and at this areal density, the positive electrode sheet had a good appearance without scratches.

[0064] The preparation process of the positive electrode slurry used in the positive electrode sheet of this embodiment included the following steps:

[0065] S1. 2.2 parts of binder PVDF was mixed with 18.0 parts of N-methyl pyrrolidone to obtain the first mixture; the mixing was carried out with low speed stirring and high speed stirring at the same time, the low speed stirring rate was 20 rpm, the high speed stirring linear velocity was 15 m / s, and the mixing time was 260 min;

[0066] S2. 13.3 parts of liquid conductive agent carbon nanotube dispersion (solid content 6%) was added into the first mixture to obtain the second mixture; the mixing was carried out with low speed stirring and high speed stirring at the same time, the low speed stirring rate was 28 rpm, the high speed stirring linear velocity was 15 m / s, and the mixing time was 90 min;

[0067] S3. 3.8 parts of powder conductive agent carbon black SP was mixed with 4.0 parts of N-methyl pyrrolidone to obtain the powder conductive agent mixture; the powder conductive agent mixture was added into the second mixture to obtain the main liquid; the mixing was carried out with low speed stirring and high speed stirring at the same time, the low speed stirring rate was 28 rpm, the high speed stirring linear velocity was 15 m / s, and the mixing time was 90 min; the solid content of the main liquid obtained in this step was 16%;

[0068] S4. The positive active material NCM811 120.4 parts is mixed with the first part of the main liquid 16.5 parts (40% of the mass of the main liquid), wherein the D50 of the positive active material is 7 μm, and the following three steps are sequentially performed:

[0069] S4.1. First, low-speed stirring is performed at a low-speed stirring rate of 17 rpm for 48 min;

[0070] S4.2. After step S4.1 is completed, the slurry on the stirrer is scraped off and low-speed stirring is continued at a low-speed stirring rate of 25 rpm for 50 min;

[0071] S4.3. After step S4.2 is completed, the slurry on the stirrer is scraped off and low-speed stirring is continued at a low-speed stirring rate of 25 rpm for 50 min;

[0072] S5. The second part of the main liquid 12.4 parts (30% of the mass of the main liquid) is added to the third mixed liquid for mixing to obtain a fourth mixed liquid; low-speed stirring and high-speed stirring are simultaneously performed during mixing, the low-speed stirring rate is 28 rpm, the high-speed stirring linear speed is 15 m / s, and the mixing time is 120 min;

[0073] S6. The third part of the main liquid 12.4 parts (30% of the mass of the main liquid) is added to the fourth mixed liquid for mixing to obtain a fifth mixed liquid; low-speed stirring and high-speed stirring are simultaneously performed during mixing, the low-speed stirring rate is 28 rpm, the high-speed stirring linear speed is 15 m / s, and the mixing time is 120 min;

[0074] S7. The viscosity of the fifth mixed liquid is adjusted to 480 mPa.s, and the solid content is 54.3%, and after filtering to remove iron, a positive electrode slurry is obtained.

[0075] (3) Battery assembly

[0076] The above positive electrode sheet, separator, and negative electrode sheet are sequentially assembled, the obtained battery cell is put into a shell, electrolyte is injected, formation and constant volume are performed, and a battery is obtained. The formula of the electrolyte is as follows: 1 mol / L LiPF6, ethylene carbonate EC + diethyl carbonate DEC + dimethyl carbonate DMC (volume ratio 1:1:1).

[0077] Example 2

[0078] 1. Preparation of negative electrode slurry

[0079] The preparation of the negative electrode slurry in this example is different from that in Example 1 in that in Step 1, when preparing the main liquid, thickener carboxymethyl cellulose 0.4 parts and water 22.7 parts are used, in Step 2, powder conductive agent B carbon black SP 1.2 parts and negative electrode active material artificial graphite 55.2 parts are used, in Step 4, binder B LA132 (solid content 6%) 18.3 parts are used, i.e. the mass ratio of negative electrode active material (artificial graphite) : main liquid B : binder B (LA132) : powder conductive agent B (carbon black SP) is 1 : 0.42 : 0.33 : 0.02; and in the final Step 5, after adjusting the viscosity and solid content of the third mixed liquid B, the viscosity of the negative electrode slurry is 413 mPa.s and the solid content is 31.8%. The rest is the same as in Example 1.

[0080] 2. Preparation of the battery

[0081] (1) Preparation of the negative electrode sheet

[0082] The negative electrode slurry prepared above is coated on the negative electrode current collector (copper foil), and by adjusting the coating parameters, the surface density of the final negative electrode sheet is 15.6 g / m 2 At this surface density, the negative electrode sheet has a good appearance and no scratches.

[0083] (2) Preparation of the positive electrode sheet

[0084] The positive electrode sheet with a surface density of 28.6 g / m 2 is selected in this example (obtained by adjusting the coating parameters), and at this surface density, the positive electrode sheet has a good appearance and no scratches.

[0085] In the positive electrode sheet of this example, the preparation process of the positive electrode slurry is the same as in Example 1.

[0086] (3) Assembly of the battery

[0087] The assembly of the battery in this example is the same as in Example 1.

[0088] Example 3

[0089] 1. Preparation of the negative electrode slurry

[0090] The preparation of the negative electrode slurry in this example is different from that in Example 1 in that in Step 1, when preparing the main liquid, thickener carboxymethyl cellulose 0.2 parts and water 11.4 parts are used, in Step 2, powder conductive agent B carbon black SP 1.2 parts and negative electrode active material artificial graphite 55.3 parts are used, in Step S4, binder BLA132 (solid content 6%) 18.3 parts are used, i.e. the mass ratio of negative electrode active material (artificial graphite) : main liquid B : binder B (LA132) : powder conductive agent B (carbon black SP) is 1 : 0.28 : 0.33 : 0.02; and in the final Step 5, after adjusting the viscosity and solid content of the third mixed liquid B, the viscosity of the negative electrode slurry is 335 mPa.s and the solid content is 31.9%. The rest is the same as in Example 1.

[0091] 2. Preparation of the battery

[0092] (1) Preparation of the negative electrode sheet

[0093] The negative electrode slurry prepared above is coated on the negative electrode current collector (copper foil), and by adjusting the coating parameters, the surface density of the final negative electrode sheet is 14.8 g / m 2 At this surface density, the negative electrode sheet has a good appearance and no scratches.

[0094] (2) Preparation of the positive electrode sheet

[0095] The positive electrode sheet with a surface density of 28.5 g / m 2 is selected in this example (obtained by adjusting the coating parameters), and at this surface density, the positive electrode sheet has a good appearance and no scratches.

[0096] In the positive electrode sheet of this example, the preparation process of the positive electrode slurry used is consistent with that in Example 1.

[0097] (3) Assembly of the battery

[0098] The assembly of the battery in this example is consistent with that in Example 1.

[0099] Example 4

[0100] 1. Preparation of the negative electrode slurry

[0101] The preparation of the negative electrode slurry in this example is different from that in Example 1 in that in Step 1, when preparing the main liquid, thickener carboxymethyl cellulose 0.5 parts and water 30.3 parts are used, in Step 2, powder conductive agent B carbon black SP 1.2 parts and negative electrode active material artificial graphite 55.7 parts are used, in Step 4, binder BLA132 (solid content 6%) 6.7 parts are used, i.e. the mass ratio of negative electrode active material (artificial graphite) : main liquid B : binder B (LA132) : powder conductive agent B (carbon black SP) is 1 : 0.56 : 0.12 : 0.02; and in the final Step 5, after adjusting the viscosity and solid content of the third mixed liquid B, the viscosity of the negative electrode slurry is 157 mPa.s and the solid content is 31.6%. The rest is the same as in Example 1.

[0102] 2. Preparation of the battery

[0103] (1) Preparation of the negative electrode sheet

[0104] The negative electrode slurry prepared above is coated on the negative electrode current collector (copper foil), and by adjusting the coating parameters, the surface density of the final negative electrode sheet is 15.2 g / m 2 At this surface density, the negative electrode sheet has a good appearance and no scratches.

[0105] (2) Preparation of the positive electrode sheet

[0106] The positive electrode sheet with a surface density of 28.5 g / m 2 is selected in this example (obtained by adjusting the coating parameters), and at this surface density, the positive electrode sheet has a good appearance and no scratches.

[0107] In the positive electrode sheet of this example, the preparation process of the positive electrode slurry is consistent with that in Example 1.

[0108] (3) Assembly of the battery

[0109] The assembly of the battery in this example is consistent with that in Example 1.

[0110] Example 5

[0111] 1. Preparation of the negative electrode slurry

[0112] The preparation of the negative electrode slurry in this example is different from that in Example 1 in that in Step 1, when preparing the main liquid, thickening agent carboxymethyl cellulose 0.5 parts and water 30.3 parts are used, in Step 2, powder conductive agent B carbon black SP 1.2 parts and negative electrode active material artificial graphite 54.0 parts are used, in Step 4, binder BLA132 (solid content 6%) 35.36 parts are used, i.e. the mass ratio of negative electrode active material (artificial graphite) : main liquid B : binder B (LA132) : powder conductive agent B (carbon black SP) is 1 : 0.57 : 0.65 : 0.02; and in the final Step 5, after adjusting the viscosity and solid content of the third mixed liquid B, the viscosity of the negative electrode slurry is 950 mPa.s and the solid content is 29.5%. The rest is the same as in Example 1.

[0113] 2. Preparation of the battery

[0114] (1) Preparation of the negative electrode sheet

[0115] The negative electrode slurry prepared above is coated on the negative electrode current collector (copper foil), and by adjusting the coating parameters, the surface density of the final negative electrode sheet is 15.0 g / m 2 At this surface density, the negative electrode sheet has a good appearance and no scratches.

[0116] (2) Preparation of the positive electrode sheet

[0117] The positive electrode sheet with a surface density of 28.5 g / m 2 is selected in this example (obtained by adjusting the coating parameters), and at this surface density, the positive electrode sheet has a good appearance and no scratches.

[0118] In the positive electrode sheet of this example, the preparation process of the positive electrode slurry used is consistent with that in Example 1.

[0119] (3) Assembly of the battery

[0120] The assembly of the battery in this example is consistent with that in Example 1.

[0121] Example 6

[0122] 1. Preparation of the negative electrode slurry

[0123] The preparation of the negative electrode slurry in this example is different from that in Example 1 in that in Step 1, when preparing the main liquid, thickening agent carboxymethyl cellulose 0.8 parts and water 44.7 parts are used, in Step 2, powder conductive agent B carbon black SP 1.3 parts and negative electrode active material artificial graphite 53.8 parts are used, in Step 4, binder BLA132 (solid content 6%) 31.5 parts are used, i.e. the mass ratio of negative electrode active material (artificial graphite) : main liquid B : binder B (LA132) : powder conductive agent B (carbon black SP) is 1 : 0.85 : 0.59 : 0.02; and in the final Step 5, after adjusting the viscosity and solid content of the third mixed liquid B, the viscosity of the negative electrode slurry is 873 mPa.s and the solid content is 28.8%. The rest is the same as in Example 1.

[0124] 2. Preparation of the battery

[0125] (1) Preparation of the negative electrode sheet

[0126] The negative electrode slurry prepared above is coated on the negative electrode current collector (copper foil), and by adjusting the coating parameters, the surface density of the final negative electrode sheet is 15.0 g / m 2 At this surface density, the negative electrode sheet has a good appearance and no scratches.

[0127] (2) Preparation of the positive electrode sheet

[0128] In this example, the positive electrode sheet with a surface density of 28.5 g / m 2 is selected (obtained by adjusting the coating parameters), and at this surface density, the positive electrode sheet has a good appearance and no scratches.

[0129] In the positive electrode sheet of this example, the preparation process of the positive electrode slurry is consistent with that in Example 1.

[0130] (3) Assembly of the battery

[0131] In this example, the assembly of the battery is consistent with that in Example 1.

[0132] Example 7

[0133] The preparation of the negative electrode slurry in this example is different from that in Example 1 in that in Step 2, instead of mixing in three steps, one-step mixing is directly performed, specifically: the powder conductive agent B and the negative electrode active material are mixed, then the first part of the main liquid B is added thereto for further mixing, to obtain the first mixed liquid B, and the mixing is performed with low-speed stirring at a low-speed stirring rate of 25 rpm for 168 min; and in the final Step 5, after adjusting the viscosity and solid content of the third mixed liquid B, the viscosity of the negative electrode slurry is 872 mPa.s and the solid content is 27.5%. The rest is the same as in Example 1.

[0134] 2. Preparation of the battery

[0135] (1) Preparation of the negative electrode sheet

[0136] The negative electrode slurry prepared above was coated on a negative electrode current collector (copper foil), and by adjusting the coating parameters, a final negative electrode sheet having a surface density of 15.2 g / m2was obtained. 2 At this surface density, the negative electrode sheet had a good appearance and no scratches.

[0137] (2) Preparation of the positive electrode sheet

[0138] In this example, a positive electrode sheet having a surface density of 28.5 g / m2was selected (obtained by adjusting the coating parameters), and at this surface density, the positive electrode sheet had a good appearance and no scratches. 2

[0139] In the positive electrode sheet of this example, the preparation process of the positive electrode slurry was consistent with that of Example 1.

[0140] (3) Battery assembly

[0141] In this example, the battery assembly was consistent with that of Example 1.

[0142] Comparative Example 1

[0143] 1. Preparation of the negative electrode slurry

[0144] In this comparative example, the negative electrode slurry was prepared according to the following steps:

[0145] Step 1. Mix 0.6 parts of thickening agent carboxymethyl cellulose with 37.9 parts of water to obtain a main liquid; while mixing, low-speed stirring and high-speed stirring are simultaneously performed, the low-speed stirring rate is 17 rpm, the high-speed stirring linear speed is 15 m / s, and the mixing time is 260 min;

[0146] Step 2. Mix 1.2 parts of powder conductive agent B carbon black SP and 54.9 parts of negative electrode active material artificial graphite, then add 30.7 parts of the main liquid (all the main liquid) to it, and continue to mix to obtain a first mixed liquid B, wherein the D50 of the negative electrode active material is 5 μm; while mixing, first perform low-speed stirring at a rate of 25 rpm for 168 min; then simultaneously perform low-speed stirring and high-speed stirring at a rate of 23 rpm and a linear speed of 15 m / s for 45 min;

[0147] Step 3. Add 18.3 parts of binder B to the first mixed liquid B to obtain a second mixed liquid B; while mixing, simultaneously perform low-speed stirring and high-speed stirring at a rate of 25 rpm and a linear speed of 15 m / s for 120 min;

[0148] ​Step 4. The viscosity of the second mixed solution B was adjusted to 823 mPa.s, and the solid content was 30.5%. After removing iron by filtration, the negative electrode slurry was obtained.

[0149] 2. Preparation of the battery

[0150] (1) Preparation of the negative electrode sheet

[0151] The negative electrode slurry prepared above was coated on the negative electrode current collector (copper foil). By adjusting the coating parameters, the surface density of the final negative electrode sheet was 15.2 g / m 2 At this surface density, the negative electrode sheet had a good appearance without scratches.

[0152] (2) Preparation of the positive electrode sheet

[0153] The positive electrode sheet (obtained by adjusting the coating parameters) of this comparative example had a surface density of 28.5 g / m 2 At this surface density, the positive electrode sheet had a good appearance without scratches.

[0154] The preparation process of the positive electrode slurry used in the positive electrode sheet of this comparative example was consistent with that of Example 1.

[0155] (3) Assembly of the battery

[0156] The assembly of the battery in this comparative example was consistent with that of Example 1.

[0157] Comparative Example 2

[0158] 1. Preparation of the negative electrode slurry

[0159] The preparation of the negative electrode slurry in this comparative example was carried out according to the following steps:

[0160] Step 1. The thickening agent carboxymethyl cellulose 0.6 parts was mixed with water 37.9 parts to obtain a main solution. The mixing was carried out with low-speed stirring and high-speed stirring at the same time. The low-speed stirring rate was 17 rpm, the high-speed stirring linear speed was 15 m / s, and the mixing time was 260 min.

[0161] Step 2. The powder conductive agent B carbon black SP 1.2 parts and the negative electrode active material artificial graphite 54.9 parts were mixed, and then the main solution 30.7 parts (all the main solution) and the binder B 18.3 parts (all the binder B) were added and continued to be mixed to obtain the first mixed solution B. The D50 of the negative electrode active material was 5 μm. The mixing was carried out with low-speed stirring first. The low-speed stirring rate was 25 rpm, and the time was 168 min. Then the low-speed stirring and the high-speed stirring were carried out at the same time. The low-speed stirring rate was 23 rpm, the high-speed stirring linear speed was 15 m / s, and the mixing time was 105 min.

[0162] Step 3. The viscosity of the first mixed solution B was adjusted to 750 mPa.s, and the solid content was 29.7%. After removing iron by filtration, the negative electrode slurry was obtained.

[0163] 2. Preparation of the battery

[0164] (1) Preparation of the negative electrode sheet

[0165] The negative electrode slurry prepared above was coated on the negative electrode current collector (copper foil), and the coating parameters were adjusted so that the surface density of the final negative electrode sheet was 15.4 g / m 2 At this surface density, the negative electrode sheet had a good appearance without scratches.

[0166] (2) Preparation of the positive electrode sheet

[0167] The positive electrode sheet of this comparative example had a surface density of 28.5 g / m 2 which was obtained by adjusting the coating parameters, and at this surface density, the positive electrode sheet had a good appearance without scratches.

[0168] The preparation process of the positive electrode slurry used in the positive electrode sheet of this comparative example was consistent with that of Example 1.

[0169] (3) Assembly of the battery

[0170] The assembly of the battery in this comparative example was consistent with that of Example 1.

[0171] Comparative Example 3

[0172] 1. Preparation of the negative electrode slurry

[0173] The commercially available conventional graphite negative electrode slurry was directly used in this comparative example, wherein the viscosity was 3000 mPa.s, and the solid content was 53.0%.

[0174] 2. Preparation of the battery

[0175] (1) Preparation of the negative electrode sheet

[0176] The negative electrode slurry prepared above was coated on the negative electrode current collector (copper foil), and the coating parameters were adjusted so that the surface density of the final negative electrode sheet was 25 g / m 2 At this surface density, the negative electrode sheet had a good appearance without scratches.

[0177] (2) Preparation of the positive electrode sheet

[0178] The commercially available positive electrode sheet having a surface density of 50 g / m 2 was used in this comparative example, and at this surface density, the positive electrode sheet had a good appearance without scratches.

[0179] (3) Assembly of the battery

[0180] The assembly of the battery in this comparative example was consistent with that of Example 1.

[0181] Test Example

[0182] 1. Experimental construction

[0183] (1) Negative electrode slurry performance test

[0184] The viscosity and solid content of the negative electrode slurry prepared in all the above examples and comparative examples were statistically analyzed, and the solid content fluctuation value of the negative electrode slurry after 24h storage was calculated, with the formula as follows: solid content fluctuation value = solid content of lower layer of negative electrode slurry after 24h storage - solid content of negative electrode slurry before storage. As for the solid content of lower layer of negative electrode slurry after 24h storage, it means that the negative electrode slurry is placed in a beaker, and the negative electrode slurry at the bottom of the beaker is taken for testing after 24h storage; as for the solid content of negative electrode slurry before storage, it means that the negative electrode slurry is just mixed uniformly, and the solid content of the negative electrode slurry at any position of the beaker is taken for testing.

[0185] (2) Negative electrode sheet performance test

[0186] The surface density of the negative electrode sheet prepared in all the above examples and comparative examples was statistically analyzed, and the appearance of the negative electrode sheet after coating was observed.

[0187] (3) Battery performance test

[0188] The cycle capacity retention rate of the battery prepared in all the above examples and comparative examples was tested at discharge rates of 1C, 10C, 30C, 50C, 70C and 100C, respectively, with the specific charge and discharge test operation as follows: the battery after capacity distribution was charged to 4.2V at 1C constant current and constant voltage under the environment of 25℃, the cutoff current was 0.02C, and it was left for 5min, and then discharged to 3.0V at 1C, 10C, 30C, 50C, 70C and 100C, respectively. The calculation formula of capacity retention rate was: the discharge capacity at each rate divided by the reference capacity based on the discharge capacity at 1C.

[0189] The DCR (direct current resistance) of the battery prepared in all the above examples and comparative examples was tested, with the specific test method as follows: after 6000 cycles, the battery was discharged at 1C for 10S under 50% SOC, and the △V / △I was calculated.

[0190] 2. Experimental results

[0191] The performance test results of the negative electrode slurry, negative electrode sheet and battery prepared in all the above examples and comparative examples are shown in Tables 1 and 2.

[0192] Table 1 Performance test results of negative electrode slurry and negative electrode sheet in examples and comparative examples

[0193]

[0194] Table 2 Performance test results of batteries in examples and comparative examples

[0195]

[0196]

[0197] As can be seen from Tables 1 and 2, the negative electrode slurry prepared by the pulping process of the present application has the characteristics of low viscosity and low solid content, the slurry is stable, has good coating performance, and at the same time meets the requirements of low area density coating and maintains good appearance of the electrode sheet. And the battery prepared by using the above-mentioned negative electrode sheet with low area density has good fast charging performance, still has high cycle capacity retention rate after charging and discharging at high rate, and has low resistance, thus greatly optimizing the fast charging performance of the battery. For specific performance data, please refer to Examples 1-7.

[0198] In Comparative Example 1, the main liquid is added in one step, i.e., the main liquid is directly mixed in its entirety; in Comparative Example 2, the main liquid and the binder are added at the same time and in their entirety; and in Comparative Example 3, a conventional negative electrode slurry on the market is used, which has high solid content and viscosity, and the electrode sheet has high area density. The above reasons all result in the decrease of the storage stability of the negative electrode slurry (large fluctuation of the solid content after 24 hours), and the slurry material is not dispersed or appears re-agglomeration after dispersion, thus causing light scratches on the negative electrode sheet and poor coating appearance, resulting in the significant decrease of the cycle capacity retention rate of the battery at high rate (such as 70C and 100C), and the increase of the DCR of the battery, and poor fast charging performance. It can also be seen that the slurry with high viscosity and solid content in Comparative Example 3 cannot be used to coat the electrode sheet with low area density, and the negative electrode sheet with low area density cannot be prepared.

[0199] Further observation of Examples 1-4 shows that when the ratio of the materials in the preparation of the negative electrode slurry is changed, although the viscosity, solid content and storage stability of the positive electrode slurry are not much different, the performance of the battery prepared therefrom will be affected to some extent in terms of the capacity retention rate at high rate. The battery prepared in Example 1 has better comprehensive performance.

[0200] Comparing Example 1 with Examples 5-6, the mass ratio of the negative electrode active material (artificial graphite), the main liquid B, the binder B (LA132) and the powder conductive agent B (carbon black SP) in the preparation of the negative electrode slurry in Examples 5 and 6 is not within the range of 1:(0.2-0.8):(0.105-0.6):(0.005-0.0405), which results in the decrease of the interaction force of the materials when mixed, and causes the 24-hour storage stability of the slurry to be somewhat poor, and the capacity retention rate of the battery at high rate to be somewhat decreased.

[0201] Comparing Example 1 and Example 7, the one-step low-speed stirring in Step 2 in Example 7 instead of the three-step low-speed stirring can cause slight aggregation of the slurry, poor 24h storage stability, and thus slight scratches during rolling into the negative electrode sheet, resulting in a decrease in the capacity retention rate of the battery at a high rate.

[0202] The above examples are only used to illustrate the technical solutions of the present application, but not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the above examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently, and these modifications or replacements are within the protection scope of the present application.

Claims

1. A process for preparing a negative electrode slurry, characterized by, The preparation method comprises the following steps: Step 1. Mixing the thickening agent and the solvent B-1 to obtain a main liquid B; the mixing is performed while low-speed stirring and high-speed stirring are simultaneously performed, the low-speed stirring rate is 5-30 rpm, the high-speed stirring linear velocity is 10-20 m / s, and the mixing time is 120-400 min; Step 2. Mixing the powder conductive agent B and the negative electrode active material, and then adding the first part of the main liquid B to continue mixing to obtain a first mixed liquid B; the mixing is performed while low-speed stirring is performed, the low-speed stirring rate is 10-30 rpm, and the mixing time is 120-165 min; Step 3. Adding the second part of the main liquid B into the first mixed liquid B to mix to obtain a second mixed liquid B; the mixing is performed while low-speed stirring and high-speed stirring are simultaneously performed, the low-speed stirring rate is 15-30 rpm, the high-speed stirring linear velocity is 10-20 m / s, and the mixing time is 30-60 min; Step 4. Adding the binder B into the second mixed liquid B to mix to obtain a third mixed liquid B; the mixing is performed while low-speed stirring and high-speed stirring are simultaneously performed, the low-speed stirring rate is 15-30 rpm, the high-speed stirring linear velocity is 10-20 m / s, and the mixing time is 30-90 min; Step 5. Adjusting the viscosity of the third mixed liquid B to 300-1050 mPa.s and the solid content to 30-40% to obtain the negative electrode slurry.

2. The process for preparing the negative electrode slurry according to claim 1, wherein: In the step 1, when the main liquid B is formed, the mass ratio of the thickening agent to the solvent B-1 is 0.005-0.03:

1.

3. The preparation method of the negative electrode slurry according to claim 1, characterized in that: In the step 1, the thickening agent comprises a carboxymethyl cellulose thickening agent; In the step 2, the powder conductive agent B comprises a carbon black conductive agent; and the negative electrode active material comprises a graphite active material; In the step 4, the binder B comprises an LA water-based binder B, and the effective component of the LA water-based binder B comprises a polyacrylic compound or an acrylonitrile multi-polymer.

4. The process for preparing the negative slurry according to claim 3, wherein the step of mixing the lithium metal powder and the solvent is performed at a temperature of 20 to 30°C. The solid content of the LA water-based binder B is 4-15%.

5. The process for preparing the negative slurry of claim 1, wherein the process is characterized by: In the step 2, the D50 of the negative electrode active material is 1-20 μm.

6. The preparation process of the negative electrode slurry as described in claim 1, characterized in that: In the third mixed liquid B, the mass ratio of the negative electrode active material to the main liquid B to the binder B to the powder conductive agent B is 1:(0.2-0.8):(0.05-0.6):(0.005-0.05).

7. The process for preparing the negative slurry according to claim 1, wherein the step of mixing the lithium metal powder, the carbon material, and the binder is performed at a temperature of 20 to 100°C. In the step 2, the mass proportion of the first part of the main liquid B in the main liquid B is 40-50%; The mass proportion of the second part of the main liquid in the main liquid B is 50-60%.

8. The process for preparing the negative electrode slurry according to claim 1, wherein The step 2 is divided into three steps, and the specific operations are as follows: Step 2.

1. First, low-speed stirring is performed, the low-speed stirring rate is 15-20 rpm, and the mixing time is 30-45 min; Step 2.

2. After the step 2.1 is completed, the slurry on the stirrer is scraped down to continue low-speed stirring, the low-speed stirring rate is 20-30 rpm, and the mixing time is 45-60 min; Step 2.

3. After the end of step 2.2, the slurry on the stirrer is scraped down and low speed stirring is continued at a rate of 20-30 rpm for a mixing time of 45-60 min.

9. A negative electrode sheet characterized by comprising: The negative electrode slurry is prepared by the process of any one of claims 1-8. The face density of the negative electrode sheet is 5 to 17 g / m 2 .

10. A battery, characterized by: The negative electrode sheet of claim 9.

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