Lithium ion battery negative electrode CMC / SBR system dry slurry mixing method, negative electrode slurry and lithium battery

Abstract

The invention provides a lithium ion battery negative electrode CMC / SBR system dry slurry mixing method, which comprises the following steps: S1, taking artificial graphite, a conductive agent and sodium carboxymethyl cellulose, mixing, and uniformly stirring the powder; adding deionized water, and uniformly stirring to obtain a mixed material I; s2, adding sodium carboxymethyl cellulose into the mixed material I again, and uniformly stirring; deionized water is continuously added, vacuum stirring is conducted, and a mixed material II is obtained; s3, styrene-butadiene latex is added into the mixed material II, vacuum stirring is continued, and the lithium ion battery negative electrode slurry is obtained. The negative electrode slurry prepared by the dry slurry mixing process provided by the invention has good uniformity, dispersity and stability; a pole piece prepared from the negative electrode paste is high in adhesion, and a prepared battery cell is lower in impedance; and meanwhile, the gluing dispersion time and CMC sol equipment are saved, the production efficiency is high, the cost is low, and the method is suitable for vigorous popularization and application.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery negative electrode slurry preparation, and specifically relates to a CMC / SBR system dry slurry mixing method for lithium ion battery negative electrodes, negative electrode slurry and a lithium battery. Background Art

[0002] Lithium-ion batteries, the core energy source for modern portable electronic devices and electric vehicles, have a direct impact on their efficiency and endurance. During the slurry mixing stage, slurry quality, such as stability, uniformity, and consistency, plays a decisive role in the internal resistance, capacity, cycle life, rate capability, consistency, safety, and yield of the final assembled lithium-ion battery product, accounting for over 80% of its overall performance.

[0003] Currently, the glues used in lithium battery negative electrode slurries are mainly divided into two categories: linear polymer PAA is the main one, and modified styrene butadiene latex SBR is used in conjunction with CMC. The PAA-based slurry mixing process has a basic mixing process of PAA dilution-conductive agent-artificial graphite-viscosity adjustment and dilution. The CMC / SBR-based slurry mixing process has a basic mixing process of CMC sol-conductive agent-artificial graphite-SBR dispersion-viscosity adjustment and dilution. This is the mainstream mixing process currently used by major domestic battery manufacturers. In comparison, the CMC / SBR collaborative use system is favored by major battery manufacturers due to its excellent dynamic performance and the good flexibility of the coated electrode, which facilitates process assembly.

[0004] The existing publicly available CMC / SBR collaborative use system generally has the following process steps: pre-solidify CMC powder, dispersant, and deionized water; add negative electrode conductive agent and stir; add graphite and stir; add SBR and stir; adjust viscosity and discharge. This process requires the addition of ethanol dispersant for wet mixing to ensure the uniformity of slurry dispersion. However, for SBR emulsions, emulsifiers have a certain solubility in ethanol systems, which destroys the stability of the emulsifier and SBR colloid combination, making the SBR emulsion at risk of demulsification, resulting in a significant deterioration in the electrode bonding strength after slurry coating. Summary of the Invention

[0005] In view of this, the present invention provides a CMC / SBR system dry slurrying method for lithium ion battery negative electrode, negative electrode slurry and lithium battery, so that the prepared negative electrode slurry has good stability, excellent dispersion effect, good processing performance, and at the same time shortens the slurrying time and improves production efficiency (see the process flow chart Figure 1 ).

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A dry slurrying method for a CMC / SBR system of a lithium ion battery negative electrode comprises the following steps: S1. Take artificial graphite, conductive agent, and sodium carboxymethyl cellulose, mix them, and stir the powder evenly; then add deionized water and stir evenly to obtain mixed material I; S2. Add sodium carboxymethyl cellulose to the mixed material I again and stir evenly; continue to add deionized water and stir under vacuum to obtain mixed material II; S3. Add styrene-butadiene latex to the mixed material II and continue vacuum stirring to obtain the negative electrode slurry for the lithium-ion battery.

[0007] Furthermore, the effective material mass ratio of the artificial graphite, the conductive agent, the twice added sodium carboxymethyl cellulose, and the styrene-butadiene latex is (93-98): (0.5-2): (0.5-2): (1-3); Wherein, the mass ratio of sodium carboxymethyl cellulose in step S1 and step S2 is (30-50): (50-70).

[0008] In some specific embodiments, preferably, the solid content of the mixed material I is 60%-75%; the solid content of the mixed material II is 40%-60%.

[0009] Furthermore, the water content of the sodium carboxymethyl cellulose is 0% to 12% (i.e., the effective mass is 88% to 100%); and the solid content of the styrene-butadiene latex is 40% to 50%.

[0010] Furthermore, the powder stirring conditions in step S1 are as follows: revolution speed 10-30 rpm, rotation speed 500-1000 rpm, temperature 20-30°C, stirring time 15-30 min; After adding deionized water in step S1, the stirring conditions are as follows: revolution speed 10-30 rpm, temperature 20-30° C., and stirring time 60-90 min.

[0011] Furthermore, the stirring conditions after adding sodium carboxymethyl cellulose again in step S2 are as follows: revolution speed 10-30 rpm, rotation speed 200-500 rpm, temperature 20-30° C., and stirring time 5-10 min; After adding deionized water in step S2, the vacuum stirring conditions are as follows: revolution rate 10-30 rpm, rotation rate 2000-4000 rpm, temperature 20-30°C, pressure -95-100 kPa, and stirring time 60-90 min.

[0012] Furthermore, the stirring conditions in step S3 are as follows: revolution rate 10-30 rpm, rotation rate 1000-2000 rpm, temperature 20-30° C., pressure -95-100 kPa, and stirring time 15-30 min.

[0013] In some specific embodiments, preferably, step S3 further includes adding water of corresponding mass according to the viscosity requirement of the negative electrode slurry of the lithium-ion battery.

[0014] A lithium battery contains the negative electrode slurry prepared by the above method.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The dry slurrying process of the lithium battery negative electrode CMC / SBR synergistic system provided by the present invention, compared with the traditional process, optimizes the slurrying process angle, ensures the uniformity of the negative electrode slurry (the difference in solid content between the upper and lower layers is within 0.22%, and the difference in viscosity between the upper and lower layers is within 131 CP), dispersibility (no gel, no sedimentation, and good filtration performance through a 150-mesh sieve), and stability (the fluctuation of the solid content of the upper and lower layers is within 0.4% after standing for 48 hours). At the same time, it also removes the dispersant raw material that has a destructive effect on the SBR emulsion, effectively improving the process processing performance and battery electrochemical performance of the battery (the peel strength of the prepared electrode reaches 11.1 N*m -1 , cohesive strength reaches 151.52 N*m -1 ; The DCIR of the prepared battery cell at room temperature is 61.32 mohm and the DCIR at low temperature is 706.69 mohm).

[0016] At the same time, this process also saves the time for sizing and dispersion (the entire preparation process takes 155 to 250 minutes, while the conventional process usually takes 120 to 240 minutes for CMC sol alone, and the complete slurry mixing time often takes more than 360 minutes), replacing CMC sol equipment, greatly improving production efficiency and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the slurry mixing process of the CMC / SBR system dry slurry mixing process for the lithium ion battery negative electrode provided by the present invention.

[0018] Figure 2 The diagram shows the slurry kneading state of the dry slurry process of the CMC / SBR system for lithium-ion battery negative electrode.

[0019] Figure 3 The following are comparison diagrams of SBR emulsion in ethanol solvent and deionized water solvent respectively. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below in conjunction with specific examples so that those skilled in the art can more clearly understand the present invention. Unless otherwise specified, the technical means used in the following examples are conventional means well known to those skilled in the art, and all reagents and consumables are commercially available products.

[0021] Example 1 This embodiment provides a dry slurrying method for a CMC / SBR system negative electrode for a lithium ion battery, which is as follows: S1. Place 3200 g of artificial graphite (Gr), 33.3 g of conductive agent (SP), and 10.8 g of sodium carboxymethyl cellulose (CMC, 92.5% active ingredient) in a stirring apparatus. Adjust the following parameters: revolution speed 20 rpm, rotation speed 800 rpm, temperature 23°C, and stirring time 20 minutes. After the powders are stirred, add 1526.7 g of deionized water and continue stirring at the following conditions: revolution speed 20 rpm, temperature 23°C, and stirring time 80 minutes. Finally, a mixture with a solids content of approximately 68% is obtained, Material I.

[0022] S2. Add 25.2 g of sodium carboxymethyl cellulose to mixed material I. Adjust the equipment parameters as follows: revolution speed 20 rpm, rotation speed 350 rpm, temperature 23°C, and stirring time 8 minutes. After stirring is complete, add 2283.7 g of deionized water and continue stirring under the following stirring conditions: revolution speed 20 rpm, rotation speed 3000 rpm, temperature 23°C, pressure -100 kPa, and stirring time 80 minutes. Finally, stirring is completed to obtain mixed material II with a solids content of approximately 46.2%.

[0023] S3. Add 166.7 g of styrene-butadiene latex (SBR, 40% solids content; the effective mass ratio of Gr:SP:CMC:SBR is 96:1:1:2) to mixed material II. Adjust the parameters: revolution speed 20 rpm, rotation speed 1500 rpm, temperature 23°C, pressure -100 kPa, and stirring time 20 min. The slurry viscosity is measured to be between 2000 and 5000 cP, which meets the processing window. After shipment and screening, the lithium-ion battery negative electrode slurry is obtained. The obtained lithium-ion battery negative electrode slurry can be further used to manufacture lithium-ion batteries.

[0024] Example 2 This embodiment provides a dry slurrying method for a CMC / SBR system negative electrode for a lithium ion battery, which is as follows: S1. Place 3200 g of artificial graphite (Gr), 33.4 g of conductive agent (SP), and 13 g of sodium carboxymethyl cellulose (CMC, 92.5% active ingredient) in a stirring apparatus. Adjust the following parameters: revolution speed 10 rpm, rotation speed 1000 rpm, temperature 20°C, and stirring time 30 minutes. After the powders are stirred, add 1527.7 g of deionized water and continue stirring under the following conditions: revolution speed 10 rpm, temperature 20°C, and stirring time 60 minutes. Finally, a mixture with a solids content of approximately 68% is obtained, Material I.

[0025] S2. Add 30.3 g of sodium carboxymethyl cellulose to mixed material I. Adjust the equipment parameters as follows: revolution speed 10 rpm, rotation speed 500 rpm, temperature 20°C, and stirring time 10 minutes. After stirring, add 2355.1 g of deionized water and continue stirring under the following stirring conditions: revolution speed 10 rpm, rotation speed 4000 rpm, temperature 20°C, pressure -95 kPa, and stirring time 60 minutes. Finally, stirring is completed to obtain mixed material II with a solids content of approximately 45.8%.

[0026] S3. Add 133.6 g of styrene-butadiene latex (SBR, 50% solids content; the effective mass ratio of Gr:SP:two-component CMC:SBR is 95.8:1:1.2:2) to mixed material II. Adjust the parameters: revolution speed 10 rpm, rotation speed 2000 rpm, temperature 20°C, pressure -95 kPa, and stirring time 15 minutes. The slurry viscosity was measured to be between 2000 and 5000 cP, which meets the processing window. After shipment and screening, the lithium-ion battery negative electrode slurry was obtained. The obtained lithium-ion battery negative electrode slurry can be further used to manufacture lithium-ion batteries.

[0027] Example 3 This embodiment provides a dry slurrying method for a CMC / SBR system negative electrode for a lithium ion battery, which is as follows: S1. Place 3200 g of artificial graphite (Gr), 33.4 g of conductive agent (SP), and 15.2 g of sodium carboxymethyl cellulose (CMC, effective mass 92.5%) in a stirring device. Adjust the device parameters as follows: revolution speed 30 rpm, rotation speed 500 rpm, temperature 30°C, and stirring time 15 min. After the powder is stirred, add 1528.7 g of deionized water and continue stirring. The stirring conditions are as follows: revolution speed 30 rpm, temperature 30°C, and stirring time 90 min. Finally, after stirring, a mixture with a solid content of approximately 68% is obtained (see the kneading state). Figure 1 ).

[0028] S2. Add 35.4 g of sodium carboxymethyl cellulose to mixed material I again and adjust the equipment parameters as follows: revolution speed 30 rpm, rotation speed 200 rpm, temperature 30°C, and stirring time 5 minutes. After stirring, add 2362.2 g of deionized water and continue stirring under the following stirring conditions: revolution speed 30 rpm, rotation speed 2000 rpm, temperature 30°C, pressure -98 kPa, and stirring time 90 minutes. Finally, stirring is completed to obtain mixed material II with a solid content of approximately 45.8%. The resulting lithium-ion battery negative electrode slurry can be further used to make lithium-ion batteries.

[0029] S3. Add 150.3 g of styrene-butadiene latex (SBR, 40% solids content; the effective mass ratio of Gr:SP:two-component CMC:SBR is 95.8:1:1.4:1.8) to mixed material II. Adjust the parameters: revolution speed 30 rpm, rotation speed 1000 rpm, temperature 30°C, pressure -98 kPa, and stirring time 15 minutes. The slurry viscosity was measured to be between 2000 and 5000 cP, which meets the processing window. After shipment and screening, the lithium-ion battery negative electrode slurry was obtained. The obtained lithium-ion battery negative electrode slurry can be further used to manufacture lithium-ion batteries.

[0030] Example 4 This embodiment provides a dry slurrying method for a CMC / SBR system negative electrode for a lithium ion battery, which is as follows: S1. Place 3200 g of artificial graphite (Gr), 33.4 g of conductive agent (SP), and 17.3 g of sodium carboxymethyl cellulose (CMC, 92.5% active ingredient) in a stirring apparatus. Adjust the following parameters: revolution speed 20 rpm, rotation speed 800 rpm, temperature 23°C, and stirring time 20 minutes. After the powders are stirred, add 1529.7 g of deionized water and continue stirring at the following conditions: revolution speed 20 rpm, temperature 23°C, and stirring time 80 minutes. Finally, a mixture with a solids content of approximately 68% is obtained, Material I.

[0031] S2. Add 40.4 g of sodium carboxymethyl cellulose to mixed material I again and adjust the equipment parameters as follows: revolution speed 20 rpm, rotation speed 350 rpm, temperature 23°C, and stirring time 8 minutes. After stirring is complete, add 2308 g of deionized water and continue stirring under the following stirring conditions: revolution speed 20 rpm, rotation speed 3000 rpm, temperature 23°C, pressure -100 kPa, and stirring time 80 minutes. Finally, stirring is completed to obtain mixed material II with a solids content of approximately 46.2%.

[0032] S3. Add 125.1 g of styrene-butadiene latex (SBR, 40% solids content; the effective mass ratio of Gr:SP:two-component CMC:SBR is 96:1:1.6:1.5) to mixed material II. Adjust the parameters: revolution speed 20 rpm, rotation speed 1500 rpm, temperature 23°C, pressure -100 kPa, and stirring time 20 min. The slurry viscosity was measured to be between 2000 and 5000 cP, which meets the processing window. After shipment and screening, the lithium-ion battery negative electrode slurry was obtained.

[0033] Comparative Example 1 This comparative example provides a method for preparing a negative electrode slurry for a lithium-ion battery, which is as follows: S1. Take 33.3 g of CMC and 2744.4 g of deionized water and stir them (stirring conditions are as follows: revolution rate 20 rpm, rotation rate 3000 rpm, temperature 23 °C, stirring time 240 min) until uniform, and obtain CMC glue.

[0034] S2. Add 33.3 g of SP to the CMC adhesive solution and stir (stirring conditions are as follows: revolution rate 20 rpm, rotation rate 3000 rpm, temperature 23 °C, stirring time 120 min) to obtain a conductive adhesive solution.

[0035] S3. Add 3200 g of Gr and 1068.6 g of deionized water to the conductive glue solution and stir (stirring conditions are as follows: revolution rate 20 rpm, rotation rate 3000 rpm, temperature 23°C, stirring time 240 min) to obtain the negative electrode active material solution.

[0036] S4. Add 166.7 g of SBR (SBR, solid content 40%; at this time, the effective material mass ratio of Gr:SP:CMC:SBR = 96:1:1:2) to the negative electrode active material solution, stir (stirring conditions are as follows: revolution rate 20 rpm, rotation rate 1500 rpm, temperature 23 ° C, pressure -100 kPa, stirring time 20 min) evenly, add deionized water and continue stirring to adjust the slurry viscosity to 2000~5000 CP to obtain the negative electrode slurry.

[0037] Comparative Example 2 This comparative example provides a method for preparing a negative electrode slurry for a lithium-ion battery, which is as follows: S1. Take 33.3 g of CMC, 33.3 g of anhydrous ethanol, and 2711.1 g of deionized water and stir them uniformly (stirring conditions are as follows: revolution rate 20 rpm, rotation rate 3000 rpm, temperature 23 °C, stirring time 240 min) to obtain CMC glue.

[0038] S2. Add 33.3 g of SP to the CMC adhesive solution and stir (stirring conditions are as follows: revolution rate 20 rpm, rotation rate 3000 rpm, temperature 23 °C, stirring time 120 min) to obtain a conductive adhesive solution.

[0039] S3. Add 3200 g of Gr and 1068.6 g of deionized water to the conductive glue solution and stir (stirring conditions are as follows: revolution rate 20 rpm, rotation rate 3000 rpm, temperature 23 °C, stirring time 240 min) to obtain the negative electrode active material solution.

[0040] S4. Add 166.7 g of SBR (SBR, solid content 40%; at this time, the effective material mass ratio of Gr:SP:CMC:SBR = 96:1:1:2) to the negative electrode active material solution, stir (stirring conditions are as follows: revolution rate 20 rpm, rotation rate 1500 rpm, temperature 23 ° C, pressure -100 kPa, stirring time 20 min) evenly, add deionized water and continue stirring to adjust the slurry viscosity to 2000~5000CP to obtain the negative electrode slurry.

[0041] Furthermore, in order to understand the performance of each negative electrode slurry prepared above, uniformity, dispersibility and stability tests were also carried out. The specific results are shown in Tables 1-3 below.

[0042] Table 1 Uniformity results of each negative electrode slurry

[0043] As can be seen from Table 1, under different material formulation systems, by testing the sampled slurries of different embodiments (the upper slurry is scooped out from the surface of the stirring kettle, and the lower layer leaks out from the leakage port of the stirring kettle, and the slurry sample is 600 mL), the solid content of the upper and lower layers of slurry in each embodiment varies from 0.03% to 0.22%, and the viscosity difference between the upper and lower layers varies from 65 to 131 CP, which meets the process document standard of "the difference in solid content between the upper and lower layers is ≤1%, and the difference in viscosity between the upper and lower layers is ≤500 CP". It is believed that the negative electrode slurry prepared by the dry process has good uniformity.

[0044] Table 2 Dispersion results of various negative electrode slurries

[0045] It can be seen from Table 2 that under different material formulation systems, by testing the sample retention of the slurry discharged from different embodiments (the upper slurry is scooped out from the surface of the stirring kettle, and the lower layer leaks out from the leakage port of the stirring kettle, and the slurry sample is 600 mL), the sieving performance of the upper and lower layers of slurry in each embodiment meets the process document standard "the discharged slurry has fluidity, and the time for sieving 300 mL of slurry is ≤90 s, and the time for sieving 500 mL of slurry is ≤300 s", and it is believed that the negative electrode slurry prepared by the dry process has good dispersibility.

[0046] Table 3 Stability results of various negative electrode slurries

[0047] It can be seen from Table 3 that under different material formulation systems, by testing the sampled slurries of different embodiments (the upper sample slurry was placed in a sealed beaker and the surface and bottom slurries of the stationary slurry were extracted and tested with a rubber-tipped dropper at a fixed time period), the difference in solid content of the upper slurry in each embodiment after standing for 24 h and 48 h was generally around 0.1%, which met the process document standard of "within 48 h of standing, the slurry had no stratification, sedimentation, etc., and the difference in solid content between the surface and bottom layers was ≤3%". It is believed that the negative electrode slurry prepared by the dry process has good stability.

[0048] Based on the above results, it can be seen that the negative electrode slurry prepared by the process of this application has the characteristics of more uniform and stable dispersion, avoiding the processing difficulties such as sedimentation, stratification, and agglomeration caused by uneven dispersion. At the same time, it saves the glue dispersion time and CMC sol equipment, greatly improving production efficiency and reducing production costs.

[0049] Furthermore, the specific electrochemical properties of the negative electrode slurries prepared in the present application and the comparative example were also made into electrode sheets and battery cells and performance tests were carried out. The results are shown in Table 4.

[0050] Table 4 Comparison of dry and wet electrode and cell performance

[0051] As shown in Table 4, under the same material formulation system, Example 1 (dry process) has an improvement of about 14% in the bonding strength at the electrode level and an advantage of about 3% in the impedance at the cell level compared to Comparative Example 1 (wet process). It is believed that the dry process can provide a more stable and uniformly dispersed slurry during the slurry mixing process, which improves the overall performance. Comparative Example 2, after adding 1% of anhydrous ethanol dispersant to Comparative Example 1, has deteriorated in performance. The reason is that the addition of anhydrous ethanol with dispersing properties to the slurry system easily destroys the stability of the emulsifier and SBR colloid, making the SBR emulsion ineffective (see Figure 3 ).

[0052] The raw materials not specifically described in the present invention are all existing materials that can be directly purchased from the market.

[0053] The above is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A dry slurrying method for a CMC / SBR system negative electrode for a lithium ion battery, characterized in that: The following steps are involved: S1. Take artificial graphite, conductive agent, and sodium carboxymethyl cellulose, mix them, and stir the powder evenly; then add deionized water and stir evenly to obtain mixed material I; S2. Add sodium carboxymethyl cellulose to the mixed material I again and stir evenly; continue to add deionized water and stir under vacuum to obtain mixed material II; S3. Add styrene-butadiene latex to the mixed material II and continue vacuum stirring to obtain the negative electrode slurry for the lithium-ion battery.

2. The method according to claim 1, characterized in that the effective material mass ratio of the artificial graphite, the conductive agent, the twice-added sodium carboxymethyl cellulose, and the styrene-butadiene latex is (93-98): (0.5-2): (0.5-2): (1-3); in, The mass ratio of sodium carboxymethyl cellulose in step S1 and step S2 is (30-50): (50-70).

3. The method according to claim 1, characterized in that the solid content of the mixed material I is 60%-75%; the solid content of the mixed material II is 40%-60%.

4. The method according to any one of claims 1 to 3, characterized in that the water content of the sodium carboxymethyl cellulose is 0% to 12%; and the solid content of the styrene-butadiene latex is 40% to 50%.

5. The method according to any one of claims 1 to 3, characterized in that the powder stirring conditions in step S1 are as follows: revolution speed 10-30 rpm, rotation speed 500-1000 rpm, temperature 20-30°C, stirring time 15-30 min; After adding deionized water in step S1, the stirring conditions are as follows: revolution speed 10-30 rpm, temperature 20-30° C., and stirring time 60-90 min.

6. The method according to any one of claims 1 to 3, characterized in that the stirring conditions after adding sodium carboxymethyl cellulose again in step S2 are as follows: revolution rate 10-30 rpm, rotation rate 200-500 rpm, temperature 20-30°C, and stirring time 5-10 min; After adding deionized water in step S2, the vacuum stirring conditions are as follows: revolution speed 10-30 rpm, rotation speed 2000-4000 rpm, temperature 20-30°C, pressure -95-100 kPa, and stirring time 60-90 min.

7. The method according to any one of claims 1 to 3, characterized in that the stirring conditions in step S3 are as follows: revolution rate 10-30 rpm, rotation rate 1000-2000 rpm, temperature 20-30°C, pressure -95-100 kPa, and stirring time 15-30 min.

8. The method according to claim 7, characterized in that step S3 further comprises adding deionized water of corresponding mass according to the viscosity requirement of the lithium-ion battery negative electrode slurry.

9. A negative electrode slurry prepared by the method according to any one of claims 1 to 8. 10 . A lithium battery, characterized in that the lithium battery contains the negative electrode slurry according to claim 9 .

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