A dry mixing process for lithium ion batteries

Abstract

The application discloses a kind of lithium ion battery dry mixing process, it is related to lithium ion battery technical field, including the following steps, part of positive electrode material and conductive agent are added into stirring device, stirring mixes, binder and remaining positive electrode material are added into stirring device, stirring mixes, carbon nanotube and anhydrous ethanol are added into container, ultrasonic stirring, again, alumina sol is added into container, continue stirring, the mixture in container is added into solvent, stirring mixes, obtain mixed solvent, solvent is added into stirring device, stirring mixes, again, mixed solvent continues to be added into stirring container device, stirring mixes, slurry prepared by the application has high solid content, good dispersion effect, small viscosity and high viscosity stability.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a dry mixing process for lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries have advantages such as high energy density, wide operating temperature range, long cycle life and environmental friendliness. Commonly used lithium-ion battery cathode materials include nickel-cobalt-manganese ternary materials and lithium iron phosphate.

[0003] Currently, the preparation process of lithium-ion battery cathode materials requires mixing. Mixing methods include wet process, dry process, and solvent impregnation process. Among them, the dry mixing process is simple and has a short processing time, but it has problems such as poor uniformity. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention provides a dry mixing process for lithium-ion batteries.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] 1. A dry mixing process for lithium-ion batteries, comprising the following steps:

[0007] S1. Add a portion of the positive electrode material and conductive agent to the stirring device and stir to mix;

[0008] S2. Add the binder and remaining positive electrode material to the stirring device and stir to mix;

[0009] S3. Add carbon nanotubes and anhydrous ethanol to a container, stir ultrasonically, then add alumina sol to the container and continue stirring.

[0010] S4. Add the mixture in the container to part of the solvent, stir and mix to obtain a mixed solvent;

[0011] S5. First, add the remaining solvent to the stirring device and stir to mix. Then, continue to add the mixed solvent to the stirring container and stir to mix.

[0012] Carbon nanotubes are added as a conductive adhesive in the mixing process. Due to their small particle size and large specific surface area, carbon nanotubes are prone to agglomeration. Dispersing the carbon nanotubes in anhydrous ethanol before mixing them with alumina sol facilitates more uniform mixing within the alumina sol and prevents agglomeration. Uniformly coating the alumina sol onto the positive electrode material reduces the contact area with the electrolyte, thereby improving the cycle life of the lithium-ion battery.

[0013] As a preferred embodiment, in steps S1 and S2, the mass ratio of the two additions of positive electrode material is (1-2):1.

[0014] As a preferred embodiment, in step S5, the mass ratio of the solvent in the solvent and the mixed solvent is (1-2):1.

[0015] As a preferred embodiment, the preparation method of alumina sol includes the following steps:

[0016] Powdered alumina monohydrate was added to deionized water and stirred. Then nitric acid was added and stirring continued. The mixture was then added to a high-pressure hydrothermal reactor and stirred continuously at 140-150℃ for 2-3 hours. After cooling, alumina sol was obtained.

[0017] As a preferred embodiment, the molar ratio of hydrogen ions in the nitric acid to aluminum ions in the monohydrated alumina is (0.02-0.05):1; the mass fraction of the alumina sol is 12-15%; and the particle size of the alumina sol is less than 1 μm. The alumina sol prepared by the hydrothermal method has a small particle size, which is more conducive to uniform dispersion on the surface of the cathode material.

[0018] As a preferred embodiment, in step S1, the stirring conditions are: revolution, speed 25-30 rpm, and stirring time 0.5-1 h.

[0019] As a preferred embodiment, in step S2, both revolution and rotation stirring are performed simultaneously. The revolution stirring conditions are: 50-55 rpm and 0.5-1 h; the rotation stirring conditions are: 500-700 rpm and 0.5-1 h.

[0020] As a preferred embodiment, in step S3, the particle size of the carbon nanotubes is 5-20 nm, and the mass ratio of the carbon nanotubes to the cathode material is (0.05-0.1):1.

[0021] As a preferred embodiment, in step S3, the mass ratio of the alumina to the positive electrode material is (0.01-0.02):1.

[0022] As a preferred embodiment, in step S5, the remaining solvent is added to the stirring device, and stirring is performed simultaneously by revolution and rotation. The revolution speed is 60-70 rpm, and the rotation speed is 600-700 rpm. After stirring for 1.5-2 hours, the mixed solvent is added to the stirring container again, and stirring is performed simultaneously by revolution and rotation. The revolution speed is 50-60 rpm, and the rotation speed is 900-1000 rpm. After stirring for 1.5-2 hours, the revolution speed is kept constant, and the rotation speed is adjusted to 1100-1200 rpm. Stirring is then performed for 1.5-2 hours.

[0023] The beneficial effects of this invention are:

[0024] (1) Carbon nanotubes are added to the mixing process as conductive adhesive. Carbon nanotubes have small particle size and large specific surface area, and are easy to agglomerate. Dispersing carbon nanotubes in anhydrous ethanol and then mixing them with alumina sol makes it easier to mix them evenly in alumina sol and avoid agglomeration.

[0025] (2) Alumina sol has a small particle size. It can be uniformly coated on the cathode material in the mixing process. The process is simple and can reduce the contact area between the cathode material and the electrolyte, thereby improving the cycle capacity of lithium-ion batteries. Attached Figure Description

[0026] Figure 1 This is the EDS mapping diagram of aluminum in the slurry of Example 1 after sintering. Detailed Implementation

[0027] To make the technical problems solved by the invention, the technical solutions and the beneficial effects clearer, the invention will be further explained below with reference to the embodiments and comparative examples.

[0028] Example 1

[0029] A dry mixing process for lithium-ion batteries includes the following steps: 50% by mass of the positive electrode material NCM811 and the conductive agent SP are added to a stirring device and mixed at 25 rpm for 0.5 hours using a revolution-stirring method; then, the binder PVDF and the remaining 50% by mass of the positive electrode material NCM811 are added to the stirring device, and simultaneous revolution-stirring and rotation-stirring are performed, with a revolution speed of 50 rpm and a rotation speed of 500 rpm for 0.5 hours; carbon nanotubes and anhydrous ethanol are added to a container and ultrasonically stirred; then, alumina sol is added to the container and stirring continues, with the mass ratio of carbon nanotubes to positive electrode material being 0.05:1, and the mass ratio of alumina to positive electrode material being... The mass ratio was 0.01:1, and the volume ratio of anhydrous ethanol to alumina sol was 1:1. The mixture in the container was added to 50% NMP by mass and stirred to obtain a mixed solvent. The remaining 50% NMP was added to the stirring device, and the mixture was stirred by both revolution and rotation at a speed of 60 rpm and 600 rpm for 1.5 hours. Then, the mixed solvent was added to the stirring container, and the mixture was stirred by both revolution and rotation at a speed of 50 rpm and 900 rpm for 1.5 hours. The revolution speed was kept constant, and the rotation speed was adjusted to 1200 rpm for 2 hours.

[0030] Example 2

[0031] A dry mixing process for lithium-ion batteries includes the following steps: Adding 2 / 3 of the mass of the positive electrode material NCM811 and the conductive agent SP to a stirring device, mixing at 25 rpm for 1 hour; then adding the binder PVDF and the remaining 1 / 3 of the mass of the positive electrode material NCM811 to the stirring device, simultaneously mixing by revolution and rotation, with a revolution speed of 50 rpm and a rotation speed of 500 rpm for 1 hour; adding carbon nanotubes and anhydrous ethanol to a container, ultrasonically stirring; then adding alumina sol to the container, continuing stirring, with the mass ratio of carbon nanotubes to positive electrode material being 0.06:1, and the mass ratio of alumina to positive electrode material being... The mass ratio is 0.01:1, and the volume ratio of anhydrous ethanol to alumina sol is 1:1. The mixture in the container is added to 1 / 3 of the mass of solvent NMP and stirred to obtain a mixed solvent. The remaining 2 / 3 of the solvent NMP is first added to the stirring device, and both revolution and rotation are performed simultaneously. The revolution speed is 60 rpm and the rotation speed is 600 rpm. After stirring for 2 hours, the mixed solvent is added back to the stirring container, and both revolution and rotation are performed simultaneously. The revolution speed is 50 rpm and the rotation speed is 900 rpm. After stirring for 1.5 hours, the revolution speed is kept constant, and the rotation speed is adjusted to 1200 rpm, and stirring is performed for 2 hours.

[0032] Example 3

[0033] A dry mixing process for lithium-ion batteries includes the following steps: 50% by mass of the positive electrode material NCM811 and the conductive agent SP are added to a stirring device and mixed at 30 rpm for 1 hour using a revolution-stirring method; then, the binder PVDF and the remaining 50% by mass of the positive electrode material NCM811 are added to the stirring device, and simultaneous revolution-stirring and rotation-stirring are performed, with a revolution speed of 55 rpm and a rotation speed of 700 rpm for 0.5 hours; carbon nanotubes and anhydrous ethanol are added to a container and ultrasonically stirred; then, alumina sol is added to the container, and stirring continues. The mass ratio of carbon nanotubes to positive electrode material is 0.1:1, and the mass ratio of alumina to positive electrode material is... The mass ratio was 0.02:1, and the volume ratio of anhydrous ethanol to alumina sol was 1:1. The mixture in the container was added to 50% NMP by mass and stirred to obtain a mixed solvent. The remaining 50% NMP was added to the stirring device, and the mixture was stirred by both revolution and rotation at a speed of 70 rpm and 700 rpm for 2 hours. Then, the mixed solvent was added to the stirring container, and the mixture was stirred by both revolution and rotation at a speed of 60 rpm and 1000 rpm for 2 hours. After stirring for 2 hours, the revolution speed was kept constant, and the rotation speed was adjusted to 1100 rpm for 2 hours.

[0034] In Examples 1-3, the preparation method of alumina sol includes the following steps:

[0035] Powdered alumina monohydrate was added to deionized water and stirred. Then, nitric acid was added and stirring continued. The mixture was then added to a high-pressure hydrothermal reactor and stirred continuously at 140-150℃ for 2-3 hours. After cooling, an alumina sol with a mass fraction of 12% was obtained. The molar ratio of hydrogen ions in nitric acid to aluminum ions in alumina monohydrate was 0.02:1, and the particle size of the alumina sol was less than 1 μm.

[0036] Comparative Example 1

[0037] The difference between Comparative Example 1 and Example 1 is that the mixed solvent does not include alumina sol.

[0038] Comparative Example 2

[0039] Compared with Example 1, Comparative Example 2 differs in that: during the mixing process, the stirring device only uses revolution stirring, excluding rotation stirring.

[0040] Comparative Example 3

[0041] Compared with Example 1, Comparative Example 3 differs in that: the mixture in the container is added to all the solvent NMP, stirred and mixed to obtain a mixed solvent, the mixed solvent is added to a stirring device, and both revolution and rotation are performed simultaneously. The revolution speed is 60 rpm and the rotation speed is 600 rpm. After stirring for 1.5 hours, the revolution speed is adjusted to 50 rpm and the rotation speed to 900 rpm. After stirring for 1.5 hours, the revolution speed is kept constant, and the rotation speed is adjusted to 1200 rpm. Stirring is then performed for 2 hours.

[0042] The fineness, solid content, viscosity, and viscosity change of the slurries from Examples 1-3 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1.

[0043]

[0044]

[0045] As shown in Table 1, the viscosity and viscosity change performance of the slurry in Example 1 are better than those in Comparative Example 1. The fineness, viscosity and viscosity change performance of the slurry in Example 1 are also better than those in Comparative Example 2 and Comparative Example 3.

[0046] The slurry from Example 1 was dried in a drying oven for 10 hours, and then sintered at 700°C for 2 hours. Figure 1 This is the EDS mapping diagram of aluminum in the sintered powder of Example 1, from... Figure 1 It can be seen that aluminum oxide is coated on the surface of the cathode material and is distributed relatively evenly.

[0047] This invention uniformly coats alumina onto the cathode material. The alumina is added during the mixing process of the cathode material, which simplifies the modification process and avoids the problem of agglomeration of conductive adhesive. The slurry prepared by this invention has high solid content, good dispersion effect, low viscosity and high viscosity stability.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall fall within the protection scope of the present invention.

Claims

1. A dry mixing process for lithium-ion batteries, characterized in that, Includes the following steps: S1. Add a portion of the positive electrode material and conductive agent to the stirring device and stir to mix; S2. Add the binder and remaining positive electrode material to the stirring device and stir to mix; S3. Add carbon nanotubes and anhydrous ethanol to a container, stir ultrasonically, then add alumina sol to the container and continue stirring. S4. Add the mixture in the container to a portion of the solvent, stir and mix to obtain a mixed solvent; S5. First, add the remaining solvent to the stirring device and stir to mix. Then, continue to add the mixed solvent to the stirring container and stir to mix.

2. The dry mixing process for lithium-ion batteries according to claim 1, characterized in that, In steps S1 and S2, the mass ratio of the two additions of positive electrode material is (1-2):

1.

3. The dry mixing process for lithium-ion batteries according to claim 1, characterized in that, In step S5, the mass ratio of the remaining solvent to the solvent in the mixed solvent is (1-2):

1.

4. The dry mixing process for lithium-ion batteries according to claim 1, characterized in that, The preparation method of alumina sol includes the following steps: Powdered alumina monohydrate was added to deionized water and stirred. Then, nitric acid was added and stirring continued. The mixture was then added to a high-pressure hydrothermal reactor and stirred continuously at 140-150℃ for 2-3 hours. After cooling, alumina sol was obtained.

5. The dry mixing process for lithium-ion batteries according to claim 4, characterized in that, The molar ratio of hydrogen ions in the nitric acid to aluminum ions in the monohydrated alumina is (0.02-0.05):1; the mass fraction of the alumina sol is 12-15%; and the particle size of the alumina sol is less than 1 μm.

6. The dry mixing process for lithium-ion batteries according to claim 1, characterized in that, In step S1, the stirring conditions are: revolution, speed 25-30 rpm, stirring time 0.5-1 h.

7. The dry mixing process for lithium-ion batteries according to claim 1, characterized in that, In step S2, both revolution and rotation stirring are performed simultaneously. The revolution stirring conditions are: 50-55 rpm and 0.5-1 h; the rotation stirring conditions are: 500-700 rpm and 0.5-1 h.

8. The dry mixing process for lithium-ion batteries according to claim 1, characterized in that, In step S3, the carbon nanotubes have a particle size of 5-20 nm, and the mass ratio of the carbon nanotubes to the cathode material is (0.05-0.1):

1.

9. The dry mixing process for lithium-ion batteries according to claim 1, characterized in that, In step S3, the mass ratio of alumina to the cathode material is (0.01-0.02):

1.

10. The dry mixing process for lithium-ion batteries according to claim 1, characterized in that, In step S5, the remaining solvent is added to the stirring device, and stirring is performed simultaneously by revolution and rotation. The revolution speed is 60-70 rpm and the rotation speed is 600-700 rpm. After stirring for 1.5-2 hours, the mixed solvent is added to the stirring container again, and stirring is performed simultaneously by revolution and rotation. The revolution speed is 50-60 rpm and the rotation speed is 900-1000 rpm. After stirring for 1.5-2 hours, the revolution speed is kept constant, and the rotation speed is adjusted to 1100-1200 rpm. Stirring is performed for 1.5-2 hours.

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