CN115275090B

CN115275090B - A method for homogenizing negative electrode slurry

Info

Publication number: CN115275090B
Application number: CN202211035531.5A
Authority: CN
Inventors: 朱智渊
Original assignee: Eve Power Co Ltd
Current assignee: Eve Power Co Ltd
Priority date: 2022-08-26
Filing date: 2022-08-26
Publication date: 2024-12-13
Anticipated expiration: 2042-08-26
Also published as: CN115275090A

Abstract

The present invention provides a method for homogenizing negative electrode slurry, the method comprising the following steps: (1) mixing a negative electrode material, a conductive agent and a dispersant, and then stirring in one step to obtain a mixture; (2) mixing the mixture with a solvent, and then stirring in two steps to obtain a mixed slurry; (3) mixing the mixed slurry with the solvent, and then stirring in three steps to obtain a half-step slurry; (4) mixing the half-step slurry with a binder, and then stirring in four steps to obtain the negative electrode slurry; wherein the mass ratio of the negative electrode material, the conductive agent and the dispersant is (90-97):(0.5-0.75)a:a, a=0.17x+0.3y-0.47z, x is the D50 of the negative electrode material, y is the tap density of the negative electrode material, and z is the specific surface area of the negative electrode material. The homogenizing method of the present invention can improve production efficiency, reduce manufacturing cost, and improve the uniformity of the negative electrode slurry to obtain a high-stability electrode sheet.

Description

Method for homogenizing negative electrode slurry

Technical Field

The invention belongs to the technical field of lithium ion batteries, and relates to a method for homogenizing negative electrode slurry.

Background

The lithium ion battery has the advantages of high energy density, high working voltage, environmental friendliness and strong manufacturability and processability, and is widely applied to the fields of mobile phones, notebook computers, electric automobiles and energy storage at present. Along with the acceleration of the life pace of people and the intelligent popularization of communication equipment such as mobile phones, the demand for high-energy-density batteries is increasing. Sodium carboxymethylcellulose (CMC) is generally required to be added in the preparation process of the negative electrode slurry, so that the negative electrode slurry can thicken and stabilize the slurry to prevent the negative electrode active material from settling.

The negative electrode material has the characteristics of porosity, high specific surface area, low tap density and the like, is difficult to disperse in the homogenizing process, can cause slurry sedimentation and agglomeration, has poor uniformity of a negative electrode sheet coated by the negative electrode material, and finally greatly affects the battery performance.

At present, main stream enterprises adopt methods of adding dispersing agents or increasing CMC content and the like to adjust slurry homogenization.

CN113045777a discloses a negative electrode dispersing agent and a lithium ion battery containing the dispersing agent, which adopts the addition of the negative electrode dispersing agent to improve the stability and uniformity of the negative electrode slurry, but the dispersing agent cannot be discharged in the baking process, and has a great influence on the long-term service life of the battery.

CN109802097a discloses a high-capacity cylindrical 18650 lithium ion battery cathode homogenate stirring process, which prepares sodium carboxymethyl cellulose and deionized water into a glue solution, and adds the glue solution into the slurry four times, wherein the slurry stirring time is longer, and the production efficiency is reduced.

Disclosure of Invention

The invention aims to provide a method for homogenizing negative electrode slurry, which can improve the production efficiency, reduce the manufacturing cost and improve the uniformity of the negative electrode slurry to prepare a pole piece with high stability.

In order to achieve the aim of the invention, the invention adopts the following technical scheme:

In a first aspect, the present invention provides a method for homogenizing a negative electrode slurry, the method comprising the steps of:

(1) Mixing a negative electrode material, a conductive agent and a dispersing agent, and then stirring in one step to obtain a mixture;

(2) Mixing the mixture obtained in the step (1) with a first solvent, and then stirring in two steps to obtain mixed slurry;

(3) Mixing the mixed slurry obtained in the step (2) with a second solvent, and then stirring in three steps to obtain half-step slurry;

(4) Mixing the half-step slurry obtained in the step (3) with a binder, and stirring in four steps to obtain the negative electrode slurry;

The mass ratio of the anode material to the conductive agent to the dispersing agent in the step (1) is (90-97) (0.5-0.75) a: a, a=0.17x+0.3y-0.47 z, wherein x is the median particle diameter D50 of the anode material, y is the tap density of the anode material, and z is the specific surface area of the anode material.

In the process of homogenizing the negative electrode slurry, the amount of the added dispersing agent is related to the D50, tap density and specific surface area of the negative electrode material, and the processing difficulty can be reduced by controlling the relation between the dispersing agent and the negative electrode material, so that the slurry stability is improved, the uniformity and consistency of the electrode plate are improved, and the performance of the battery cell is improved.

The larger the particle size of the anode material is, the smaller the specific surface area is, so the less the demand of the dispersing agent coated on the surface of the anode material is, if the added dispersing agent is excessive, the viscosity of the slurry is increased, the coating processing is not facilitated, otherwise, the surface of the anode material coated by the dispersing agent is incomplete, the viscosity of the slurry is lower, the coating processing is also not facilitated, and meanwhile, the pole piece is easy to crack due to the discharge of a large amount of moisture during baking. The larger the tap density is, the larger the slurry bulk density is, the tighter the contact between particles is, the more uniform the coating of the dispersing agent is, the better the slurry stability is, otherwise, the lower the tap density is, the lower the bulk density of the cathode material is, the particles are in a fluffy state, the more difficult to uniformly coat the dispersing agent, so that the slurry stability is poor, and the coating and other processing performances are poor. The larger the specific surface area is, the more pores of the cathode material are, and the more difficult and uniform the dispersing agent is coated, so that the kneading time, the dispersing agent consumption and the shearing speed are increased to different degrees. The particle size, the tap density and the specific surface area of the cathode material are mutually related, the particle size of the cathode material is small, the specific surface area is large, the tap density is low, and therefore the cathode material is difficult to process, and the particle size of the cathode material is large, the specific surface area is small, the tap density is high, and therefore the processing difficulty is relatively low.

Preferably, the negative electrode material of step (1) comprises any one or a combination of at least two of graphite, soft carbon, or hard carbon.

Preferably, the conductive agent includes any one or a combination of at least two of conductive carbon black, graphene, or carbon nanotubes.

Preferably, the dispersant comprises sodium carboxymethyl cellulose.

Preferably, the median particle diameter D50 of the negative electrode material in the step (1) is 5-20 μm, for example, 5 μm, 10 μm, 12 μm, 15 μm or 20 μm.

Preferably, the tap density of the anode material is 0.7-1.2 g/cm ³, for example, 0.7g/cm ³、0.8g/cm³、0.9g/cm³、1g/cm³、1.1g/cm³ or 1.2g/cm ³.

Preferably, the specific surface area of the anode material is 0.8-2.8 m ²/g, for example, 0.8m ²/g、1m²/g、1.5m²/g、2m²/g or 2.8m ²/g.

Preferably, the stirring speed of the one-step stirring in the step (1) is 1000-1800 rpm, for example, 1000rpm, 1200rpm, 1400rpm, 1600rpm, 1800rpm, etc.

Preferably, the one-step stirring time is 20-30 min, for example, 20min, 22min, 25min, 28min or 30 min.

In the step (1) of the invention, the one-step stirring is solid phase mixing stirring, and as the conductive agent particles are small and easy to agglomerate, the conductive agent clusters are unevenly dispersed due to the too slow stirring speed, and the graphite particles collide with each other to destroy the particle morphology due to the too fast stirring speed.

Preferably, the first solvent of step (2) comprises water.

Preferably, the mass ratio of the mixture to the first solvent is 100 (30-40), for example, 100:30, 100:32, 100:35, 100:38 or 100:40.

Preferably, the speed of the two-step stirring in the step (2) is 500-1200 rpm, for example, 500rpm, 600rpm, 800rpm, 1000rpm or 1200 rpm.

Preferably, the linear speed of the two-step stirring is (0.67-1.23) b m/s, wherein b=7.35a+0.73y.

Preferably, the two-step stirring time is 30-40 min, for example, 30min, 32min, 35min, 38min or 40 min.

The two-step stirring process in the step (2) is a kneading process, the solvent is added to fully wet the cathode material, the conductive agent and the dispersing agent, meanwhile, the dispersing agent is dissolved in the solvent, and macromolecular chain structures of the dispersing agent are uniformly coated in graphite particles and the conductive agent through kneading, so that the thickening effect is realized. When the stirring paddle rotates, the slurry with high solid content can be sheared, and meanwhile, the slurry is extruded, so that the cathode material and the conductive agent dispersing agent chain are mixed more uniformly. The stirring linear speed is related to the property of the cathode material, and as the solid content of the slurry is higher in the step, if the shearing line speed of the stirring paddle is too high, the temperature of the slurry is increased, the long-chain structure of the dispersing agent is broken and destroyed due to the too high temperature, the thickening effect is lost, meanwhile, the coating on the surface of the graphite is uneven, the viscosity of the slurry is unstable and easy to settle, and if the shearing line speed of the stirring paddle is too low, the kneading of the slurry is incomplete, and the coating of the dispersing agent is incomplete.

Preferably, the second solvent of step (3) comprises water.

Preferably, the mass ratio of the mixed slurry to the second solvent is 100 (17-28), for example, 100:17, 100:18, 100:20, 100:25 or 100:28.

Preferably, the speed of the three-step stirring in the step (3) is 2000-2700 rpm, such as 2000rpm, 2200rpm, 2400rpm, 2500rpm or 2700 rpm.

Preferably, the linear speed of the three-step stirring is (0.89-1.56) b m/s.

Preferably, the three-step stirring time is 20-30 min, for example, 20min, 22min, 25min, 28min or 30 min.

The three-step stirring is mainly used for regulating and controlling the solid content of the slurry, so that the dispersant is uniformly coated on the surface of the anode material under the condition of higher solid content, the viscosity temperature of the slurry is ensured, and the coating condition is met.

Preferably, the solid content of the half-step slurry is 55-62%, for example, 55%, 56%, 58%, 60% or 62%.

Preferably, the binder of step (4) comprises styrene butadiene rubber.

Preferably, the mass ratio of the half-step slurry to the binder is 100 (1-3.5), for example, 100:1, 100:1.5, 100:2, 100:3 or 100:3.5.

Preferably, the speed of the four-step stirring in the step (4) is 500-1200 rpm, for example, 500rpm, 600rpm, 800rpm, 1000rpm or 1200 rpm.

Preferably, the linear velocity of the four-step stirring is (aXz+3.2y) m/s.

Preferably, the four-step stirring time is 30-40 min, for example, 30min, 32min, 35min, 38min or 40 min.

The four-step stirring in the step (4) of the invention adds the binder, mainly plays a role in bonding, so that the coated slurry is firmly bonded on the current collector, if the stirring speed is too high, the binder can be demulsified and the bonding effect can be lost, if the stirring speed is too low, the binder is unevenly dispersed, the phenomena of floating, blue and the like can occur, and the binder can not play a role in bonding.

Compared with the prior art, the invention has the following beneficial effects:

(1) The stirring method disclosed by the invention requires 100-140min in total from feeding to stirring completion, so that the anode homogenization time is greatly saved, the production efficiency is improved, and the production cost is reduced.

(2) The invention relates to the addition amount of the added dispersing agent to the graphite D50, the tap density and the specific surface area, is applicable to all anode materials for stirring and homogenizing, and has stronger universality.

Drawings

FIG. 1 is a graph showing a 24-hour viscosity change of a negative electrode slurry obtained by the homogenization method described in example 1.

Detailed Description

The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.

Example 1

The present embodiment provides a method for homogenizing a negative electrode slurry, the method comprising the steps of:

(1) Adding artificial graphite, a conductive agent and sodium carboxymethylcellulose (CMC) into a double planetary mixer according to the mass ratio of 96.5:1.5:2.0, wherein the mixing speed is 1500rpm, and the mixing time is 25min, so as to obtain a mixture, wherein the median particle size D50=15 μm, the tap density is 0.95g/cm ³, the specific surface area is 1.8m ²/g, and a=2;

(2) Adding deionized water with the mass fraction of the mixture of 32%, controlling the stirring paddle speed to be 1000rpm, controlling the dispersion linear speed to be 14.6m/s, stirring for 35min, and controlling the temperature to be less than or equal to 28 ℃ to obtain mixed slurry, wherein b=15.4;

(3) Adding deionized water with the mass fraction of 22% of the mixed slurry, controlling the stirring paddle speed to 2300rpm, controlling the dispersion linear speed to 21.1m/s, controlling the solid content of the slurry to 57%, and stirring for 30min to obtain half-step slurry;

(4) Adding Styrene Butadiene Rubber (SBR) with the mass fraction of 1.5% of the half-step slurry, controlling the stirring paddle speed to 800rpm/min, controlling the dispersion linear speed to 6.6m/s, and stirring for 30min to obtain the negative electrode slurry.

The 24-hour viscosity change chart of the negative electrode slurry is shown in fig. 1.

Example 2

(1) Adding artificial graphite, a conductive agent and sodium carboxymethylcellulose (CMC) into a double planetary mixer according to the mass ratio of 96.2:1.42:2.38, wherein the mixing speed is 1500rpm, and the mixing time is 25min, so as to obtain a mixture, wherein the median particle size D50=15 μm, the tap density is 1g/cm ³, the specific surface area is 1m ²/g, and the a=2.38 of the artificial graphite;

(2) Adding deionized water with the mass fraction of the mixture of 32%, controlling the stirring paddle speed to 1000rpm, controlling the dispersion linear speed to 18.2m/s, stirring for 35min, and controlling the temperature to be less than or equal to 28 ℃ to obtain mixed slurry, wherein b=18.2;

(3) Adding deionized water with the mass fraction of 22% into the mixed slurry, controlling the stirring paddle speed to 2400rpm, controlling the dispersion linear speed to 21.84m/s, controlling the solid content of the slurry to 57%, and stirring for 30min to obtain half-step slurry;

(4) Adding Styrene Butadiene Rubber (SBR) with the mass fraction of 1.6% into the half-step slurry, controlling the stirring paddle speed to be 800rpm/min, controlling the dispersion linear speed to be 5.6m/s, and stirring for 30min to obtain the negative electrode slurry.

Example 3

This example differs from example 1 only in that the dispersion line speed of the two-step stirring in step (2) was 20m/s, and other conditions and parameters were exactly the same as in example 1.

Example 4

This example differs from example 1 only in that the dispersion line speed of the two-step stirring in step (2) was 12m/s, and other conditions and parameters were exactly the same as in example 1.

Example 5

This example differs from example 1 only in that the SBR mass is 4% of the half step slurry mass, the other conditions and parameters being exactly the same as example 1.

Example 6

This example differs from example 1 only in that the SBR mass is 0.6% of the half step slurry mass, with other conditions and parameters exactly the same as example 1.

Comparative example 1

This comparative example differs from example 1 only in that sodium carboxymethylcellulose is not added, and other conditions and parameters are exactly the same as example 1.

Comparative example 2

This comparative example differs from example 1 only in that no styrene-butadiene rubber was added, and other conditions and parameters were exactly the same as example 1.

Comparative example 3

This comparative example differs from example 1 only in that the various materials were directly mixed with the solvent.

Comparative example 4

This comparative example differs from example 1 only in that the mass ratio of artificial graphite to sodium carboxymethylcellulose is 96:3, and other conditions and parameters are exactly the same as example 1.

Comparative example 5

This comparative example differs from example 1 only in that the mass ratio of artificial graphite to sodium carboxymethylcellulose is 97:1.5, and other conditions and parameters are exactly the same as example 1.

Performance test:

The slurries prepared in examples 1-6 and comparative examples 1-5 were coated on copper foil, baked, cold-pressed, and striped to prepare a negative electrode sheet, and the stripping force and resistance were tested, and lithium iron phosphate, a conductive agent, a solvent, and polyvinylidene fluoride were stirred uniformly to prepare a positive electrode slurry, which was uniformly coated on carbon-coated aluminum foil, and baked, cold-pressed, and striped to prepare a positive electrode sheet. The positive pole piece, the negative pole piece and the coating diaphragm are assembled into a lithium iron phosphate battery, and DCR and cycle performance of the prepared lithium iron phosphate battery are tested, and test results are shown in Table 1:

TABLE 1

As can be seen from Table 1, the slurry prepared by the method of the invention can produce pole pieces with resistance below 2.36mΩ, pole piece stripping force above 0.32N, DCR below 15.5mΩ, and capacity retention rate above 95.8% after 1000 weeks at 25deg.C.

As can be seen from comparison of examples 1 and examples 3 to 4, in the homogenization process of the invention, the linear speed of stirring can affect the homogenization effect, and when the stirring paddle rotates, the slurry with high solid content can be sheared and extruded, so that the cathode material and the conductive agent dispersant chain are mixed more uniformly. The stirring linear speed is related to the property of the cathode material, and as the solid content of the slurry is higher in the step, if the shearing line speed of the stirring paddle is too high, the temperature of the slurry is increased, the long-chain structure of the dispersing agent is broken and destroyed due to the too high temperature, the thickening effect is lost, meanwhile, the coating on the surface of the graphite is uneven, the viscosity of the slurry is unstable and easy to settle, and if the shearing line speed of the stirring paddle is too low, the kneading of the slurry is incomplete, and the coating of the dispersing agent is incomplete.

As can be seen from the comparison of examples 1 and examples 5 to 6, the addition amount of the binder affects the homogenization effect, and if the addition amount of the binder is too low, the slurry viscosity is too low to be well adhered to the surface of the current collector, and if the addition amount of the binder is too large, the binder is difficult to disperse, and the dispersion is uneven, so that the adhesion effect cannot be achieved.

By comparing the embodiment 1 with the comparative examples 1-3, the invention reasonably controls the feeding sequence and the types of each stage in the homogenizing process, improves the stability of the slurry, improves the solid content of the slurry, and saves the coating baking cost.

As can be obtained by comparing the embodiment 1 with the comparative examples 4-5, in the process of homogenizing the anode slurry, the amount of the added dispersing agent is related to the D50, tap density and specific surface area of the anode material, the relation between the dispersing agent and the anode material is controlled, so that the processing difficulty can be reduced, the stability of the slurry is improved, the uniformity and consistency of the pole piece are improved, the battery cell performance is improved, the larger the particle size of the anode material is, the smaller the specific surface area is, the less the dispersing agent is required to be coated on the surface of the anode material, the viscosity of the slurry is increased if the added dispersing agent is excessive, the coating processing is not facilitated, otherwise, the surface of the anode material is not completely coated by the dispersing agent, the viscosity of the slurry is lower, the coating processing is also not facilitated, and the pole piece is easy to crack due to the discharge of a large amount of water during baking. The larger the tap density is, the larger the slurry bulk density is, the tighter the contact between particles is, the more uniform the coating of the dispersing agent is, the better the slurry stability is, otherwise, the lower the tap density is, the lower the bulk density of the cathode material is, the particles are in a fluffy state, the more difficult to uniformly coat the dispersing agent, so that the slurry stability is poor, and the coating and other processing performances are poor. The larger the specific surface area is, the more pores of the cathode material are, and the more difficult and uniform the dispersing agent is coated, so that the kneading time, the dispersing agent consumption and the shearing speed are increased to different degrees. The particle size, the tap density and the specific surface area of the cathode material are mutually related, the particle size of the cathode material is small, the specific surface area is large, the tap density is low, and therefore the cathode material is difficult to process, and the particle size of the cathode material is large, the specific surface area is small, the tap density is high, and therefore the processing difficulty is relatively low.

The applicant declares that the above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that are easily conceivable within the technical scope of the present invention disclosed by the present invention fall within the scope of the present invention and the disclosure.

Claims

1. A method for homogenizing a negative electrode slurry, characterized in that the homogenization method comprises the following steps:

(1) mixing a negative electrode material, a conductive agent and a dispersant and stirring them in one step to obtain a mixed material;

(2) mixing the mixture obtained in step (1) with the first solvent and stirring in two steps to obtain a mixed slurry;

(3) mixing the mixed slurry obtained in step (2) with the second solvent and stirring in three steps to obtain a half-step slurry;

(4) mixing the half-step slurry obtained in step (3) with a binder, and stirring the mixture in four steps to obtain the negative electrode slurry;

Wherein, the mass ratio of the negative electrode material, the conductive agent and the dispersant in step (1) is (90-97):(0.5-0.75)a:a, a=0.17x+0.3y-0.47z, wherein x is the median particle size D50 of the negative electrode material, y is the tap density of the negative electrode material, and z is the specific surface area of the negative electrode material;

The linear velocity of the second-step stirring in step (2) is (0.67-1.23) b m/s, wherein b=7.35a+0.73y.

2. The homogenization method according to claim 1, characterized in that the negative electrode material in step (1) comprises any one of graphite, soft carbon, or hard carbon, or a combination of at least two of them.

3. The homogenization method according to claim 1, characterized in that the conductive agent in step (1) comprises any one of conductive carbon black, graphene or carbon nanotubes, or a combination of at least two of them.

4. The homogenization method according to claim 1, characterized in that the dispersant in step (1) comprises sodium carboxymethyl cellulose.

5. The homogenization method according to claim 1, characterized in that the median particle size D50 of the negative electrode material in step (1) is 5 to 20 μm.

6 . The homogenization method according to claim 1 , wherein the tap density of the negative electrode material in step (1) is 0.7 to 1.2 g/cm ³ .

7 . The homogenization method according to claim 1 , wherein the specific surface area of the negative electrode material in step (1) is 0.8 to 2.8 m ² /g.

8. The homogenization method according to claim 1, characterized in that the stirring speed of the one-step stirring in step (1) is 1000 to 1800 rpm.

9. The homogenization method according to claim 1, characterized in that the stirring time in step (1) is 20 to 30 minutes.

10. The homogenization method according to claim 1, characterized in that in step (2), the first solvent comprises water.

11. The homogenization method according to claim 1, characterized in that the mass ratio of the mixed material to the first solvent in step (2) is 100:(30-40).

12. The homogenization method according to claim 1, characterized in that the speed of the second-step stirring in step (2) is 500-1200 rpm.

13. The homogenization method according to claim 1, characterized in that the time of the two-step stirring in step (2) is 30 to 40 minutes.

14. The homogenization method according to claim 1, characterized in that the second solvent in step (3) comprises water.

15. The homogenization method according to claim 1, characterized in that the mass ratio of the mixed slurry to the second solvent in step (3) is 100:(17-28).

16. The homogenization method according to claim 1, characterized in that the speed of the three-step stirring in step (3) is 2000-2700 rpm.

17. The homogenization method according to claim 1, characterized in that the linear velocity of the three-step stirring in step (3) is (0.89-1.56) b m/s.

18. The homogenization method according to claim 1, characterized in that the time of the three-step stirring in step (3) is 20 to 30 minutes.

19. The homogenization method according to claim 1, characterized in that the solid content of the half-step slurry in step (3) is 55-62%.

20. The homogenization method according to claim 1, characterized in that the binder in step (4) comprises styrene-butadiene rubber.

21. The homogenization method according to claim 1, characterized in that the mass ratio of the half-step slurry to the binder in step (4) is 100:(1-3.5).

22. The homogenization method according to claim 1, characterized in that the speed of the four-step stirring in step (4) is 500-1200 rpm.

23. The homogenization method according to claim 1, characterized in that the linear velocity of the four-step stirring in step (4) is (a×z+3.2y) m/s.

24. The homogenization method according to claim 1, characterized in that the time of the four-step stirring in step (4) is 30 to 40 minutes.