Ceramic slurry and preparation method, positive electrode sheet and lithium ion battery

Abstract

This invention relates to the field of battery technology, and in particular to a ceramic slurry and its preparation method, a positive electrode sheet, and a lithium-ion battery. The ceramic slurry comprises ceramic particles, a binder, and a solvent; the solvent is a mixture of NMP and acetone, and the binder is a composite of polyacrylic acid and polyvinylidene fluoride. Increasing the concentration of polar functional groups in the polyacrylic acid system can improve the overall cohesiveness of the ceramic slurry, and this method can effectively resist shrinkage stress in the material zone and solvent migration.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a ceramic slurry and its preparation method, a positive electrode sheet, and a lithium-ion battery. Background Technology

[0002] Currently, lithium-ion batteries are widely used in electric vehicles, energy storage, and consumer electronics. Lithium-ion battery positive electrode sheets typically have a ceramic insulating layer coated at the edges to prevent short circuits. This layer covers the metal foil at the electrode edge, preventing metal burrs from piercing the separator or causing direct contact between the positive and negative electrode foils, thus improving battery safety and reducing short circuits caused by contact between the positive and negative electrodes during manufacturing and thermal runaway during use. In actual coating processes, there is often no significant barrier between the positive electrode slurry and the ceramic slurry at the contact area, sometimes leading to cross-penetration and the formation of an interpenetrating layer. In severe cases, a 0-1mm overlap can occur between the positive electrode material and the ceramic layer, resulting in mutual dissolution. This anomaly reduces insulation performance, complicates subsequent cutting processes such as positioning and edge clamping, produces excess burrs at the edges, increases the risk of accidental short circuits between the positive and negative electrodes, and affects battery performance, including cycle life.

[0003] However, most of the cathode coating ceramic slurries currently used use polyvinylidene fluoride (PVDF), the same as the cathode slurry, as a binder. From a formulation perspective, changing the type of PVDF, adjusting the ratio, and the ceramic homogenization process cannot effectively improve the miscibility. In addition, NMP is currently used as the only solvent. In the actual coating process, the difference in evaporation rate and solid content between the material zone and the ceramic zone causes solvent migration, which brings ceramic particles into the material zone and forms miscibility. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and defects of the prior art and to provide a ceramic slurry and its preparation method, a positive electrode sheet, and a lithium-ion battery.

[0005] To achieve the above objectives, this application adopts the following solution: A ceramic slurry includes ceramic particles, a binder, and a solvent; the solvent is a mixture of NMP and acetone, and the binder is a composite of polyacrylic acid and polyvinylidene fluoride.

[0006] The mass ratio of the binder to the ceramic particles is (10-20): (80-90); preferably 12:88.

[0007] The mass ratio of NMP to acetone is (80-95):(5-20); preferably 90:10.

[0008] The mass ratio of the polyacrylic acid and polyvinylidene fluoride is (1-2): (1-2), preferably (3-6): (6-7), and more preferably 6:6; preferably, the molecular weight of the polyacrylic acid is 400,000–1,000,000 Da, more preferably 600,000–800,000 Da; and the molecular weight of the polyvinylidene fluoride is 800,000–1,300,000 Da.

[0009] The ceramic particles include at least one of the following powders: aluminum oxide, boehmite, silicon dioxide, titanium dioxide, magnesium dioxide, barium sulfate, zirconium oxide, calcium oxide, and magnesium hydroxide; preferably boehmite.

[0010] The solid content of the ceramic slurry is 40%±3%, and the viscosity is 5000mPa·s-8000mPa·s.

[0011] The present invention also includes a method for preparing the ceramic slurry, comprising the following steps: S1: mixing and dispersing the binder polyvinylidene fluoride with a portion of NMP to prepare a PVDF adhesive, preferably with a solid content of 9±5%; S2: Add polyacrylic acid liquid, with a solid content of 13±5%; S3: Add ceramic particles and continue dispersion, gradually increasing the rotation speed to ensure that the binder molecules fully coat the ceramic particles, forming a stable dispersion system. At the same time, it promotes molecular chain entanglement and enhances cohesion, with a solid content of 43±5%. S4: Add all acetone to enhance the cooling of the stirred tank; solid content 42±5%; S5: The viscosity is precisely adjusted to 5000-8000 mPa·s with the remaining NMP, and the solid content is 40%±3%, further optimizing the intermolecular forces and ensuring the stability of the adhesive solution; S6: Pulping is complete. Vacuum is applied to remove air bubbles.

[0012] The stirring process in step S1 is 10±10 rpm, 10-20 min, scraping, 25±20 rpm, 2000±200 rpm, 20-40 min, scraping, 25±20 rpm, 2000±200 rpm, 20-40 min. The stirring process in step S2 is 25±20 rpm, 2000±200 rpm, 20-40 min; The stirring process in step S3 is 15±10 rpm for 5-20 min, followed by scraping at 25±20 rpm for 3000±300 rpm for 100-150 min. The stirring process in step S4 is 25±20 rpm, 500±100 rpm, 20-40 min.

[0013] The present invention also includes a positive electrode sheet, comprising a positive current collector and a positive active material layer and a ceramic insulating layer located on the positive current collector; the ceramic insulating layer is obtained by coating the ceramic slurry onto the positive current collector.

[0014] The present invention also includes a battery comprising the aforementioned positive electrode.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Improved Mixing Issues: The composite of polyacrylic acid and polyvinylidene fluoride (PVDF) simultaneously leverages the high adhesion, chemical stability, and electrolyte corrosion resistance of PVDF, while also utilizing the high cohesive strength of polyacrylic acid. This significantly enhances cohesiveness. A mixture of NMP and acetone is used as the solvent. The difference in evaporation rates (NMP boiling point 204℃, acetone boiling point 56℃) allows the ceramic slurry to lose liquid more quickly during coating and drying, rapidly increasing solids content and viscosity to further reduce ceramic particle migration and miscibility. Simultaneously, the increased solids content of the ceramic slurry, compared to the conventional 30% solids content, leads to a significant reduction in intermolecular distance and an increase in molecular contact points per unit volume. This also dramatically increases the probability of physical entanglement between long-chain molecules, allowing the two polymers to intertwine and form more complex three-dimensional structures. The increased concentration of polar functional groups in polyacrylic acid further enhances the overall cohesiveness of the ceramic slurry. This method effectively resists shrinkage stress and solvent migration in the material zone, reducing miscibility from ≥0.5mm to ≤0.2mm, meeting the requirements of the coating process. 2. Significantly improved production efficiency: Compared to the conventional method of slowing down the speed to improve mutual solubility, coating can be carried out at a speed increase of 30-50%, reducing the number of downtime adjustments and trial coatings, and shortening the production cycle; 3. Battery performance optimization: Improving the mutual solubility problem allows for the design of a more reasonable N / P ratio, reducing the waste of the negative electrode, making lithium ion insertion and extraction more uniform, extending battery cycle life, and reducing the risk of material loss and short circuits, thus improving safety performance and product consistency. 4. Strong process compatibility: Compared with existing pilot conventional processes, it does not require large-scale equipment modification and is easy to promote industrialization. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the method for preparing the ceramic slurry of the present invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0018] Example 1: According to Figure 1The process for preparing ceramic adhesive involves a boehmite:polyvinylidene fluoride:polyacrylic acid ratio of 88:6:6 (solvent: NMP, acetone = 95:5). The polyvinylidene fluoride has a molecular weight of 800,000–1,000,000 Da, and the polyacrylic acid has a molecular weight of 600,000–800,000 Da. S1: Take 15KG of NMP and 1.5KG of polyvinylidene fluoride and add them to the double planetary tank in sequence. The stirring steps are as follows: 10±1rpm, 15min (scraping), 25±1rpm, 2000±10rpm, 30min (scraping), 25±1rpm, 2000±10rpm, 30min, with a solid content of about 9.0%. S2: Add polyacrylic acid adhesive solution, and set the stirring steps to 25±1 rpm, 2000±10 rpm, 30 min to prepare the composite adhesive solution with a solid content of approximately 13.1%; S3: Add ceramic particles and continue to disperse. The stirring steps are set as follows: 15±1 rpm, 10 min (scraping), 25±1 rpm, 3000±10 rpm, 120 min, to ensure thorough stirring and dispersion, with a solid content of approximately 42.8%. S4: Add all acetone to enhance the cooling of the mixing tank. The stirring steps are set as follows: 25±1 rpm, 500±10 rpm, 30 min. Acetone is volatile, so enhancing the cooling of the mixing tank will result in a solid content of approximately 42.5%. S5: Add 3KG of NMP, and set the stirring steps as follows: 25±1rpm, 2000±10rpm, 30min. This step is for adjusting the viscosity and solid content. This step can be repeated multiple times. The solid content is about 40%. S6: Pulping complete, vacuuming, stirring speed 25rpm, vacuum degree ≤-85kpa, 90min; S7: The ceramic adhesive solution was tested and found to have a viscosity of 5500 mPa·s and a solid content of 40.1% and 39.8%, respectively. The test results were qualified. It was then transferred to the ceramic tank for the coating process, slowly stirred and circulated before coating. S8: With the electrode process parameters unchanged, the coating speed (10-15 m / min, based on 15 m / min in this application) is increased by 50% compared to the conventional ceramic slurry coating speed where mixing occurs. In this invention, there is no significant mixing (0.1 mm). 0.2mm); continuing to increase to 70%, slight mixing occurred (0.3mm). (0.5mm, meeting process standards). Considering the large fluctuations in mixing, and to ensure yield, production is carried out at a 50% increase in coating speed.

[0019] Example 2: The ceramic adhesive formulation is basically the same as that in Example 1, except that the ratio of polyvinylidene fluoride to polyacrylic acid is changed to 4:6 (the overall ratio to ceramic particles remains at 12:88). That is, by increasing the proportion of polyacrylic acid, the overall cohesive force is improved, and the ability to resist shrinkage stress and solvent migration in the material zone is enhanced.

[0020] With the electrode process parameters unchanged, the coating speed in step S8, which typically results in mixing of ceramic slurry, is increased by 70% compared to previous steps, with no significant mixing (0.1mm). 0.2mm); continuing to increase to 90%, mixing occurred (>0.5mm, not meeting process standards). Therefore, the coating speed was reduced to the level of conventional ceramic slurry coating, and after coating stabilized, there was no obvious mixing (0.1mm). (0.2mm), and the speed was increased by 70% from the conventional ceramic slurry coating speed where mixing occurs, and there was still no mixing. Therefore, by adjusting the proportion of polyacrylic acid, the present invention can further improve the mixing effect to a certain extent. In actual use, the speed can be adjusted as needed by comprehensively considering factors such as material cost and production capacity.

[0021] Example 3: The ceramic adhesive formulation is basically the same as that in Example 2, except that the ratio of polyvinylidene fluoride to polyacrylic acid is changed to 3:7 (the overall ratio to ceramic particles remains at 12:88). The overall cohesive strength is further improved by increasing the proportion of polyacrylic acid, which enhances the ability to resist shrinkage stress in the material zone and solvent migration. The homogenization process parameters were adjusted, mainly in step S2: adding polyacrylic acid adhesive. Due to the increased proportion, in order to ensure dispersion, the stirring step was set to 25±1 rpm, 2500±10 rpm, 60 min to prepare the composite adhesive. The other steps remained unchanged. The coating speed is increased by 70% based on the conventional ceramic slurry coating speed where mixing occurs in step S8. In this invention, there is no significant mixing (0.1mm). (0.2mm), but a new problem arose, namely, cracking after the ceramic was dried. Due to the increased polyacrylic acid content, the ceramic became more brittle after drying, which easily caused poor appearance and was not conducive to subsequent cutting. Therefore, the coating speed was reduced to the conventional ceramic slurry mixing speed and the coating temperature was significantly reduced. As a result, the cracking problem was solved, but the ceramic was not dried. After multiple adjustments, it was found that the window was too narrow and the coating could not be stable. Therefore, the present invention increases the proportion of polyacrylic acid, which can improve the mixing effect to a certain extent. Further increasing it will bring other abnormalities such as electrode cracking.

[0022] Example 4: The ceramic adhesive formulation is basically the same as that in Example 1, except that a long-chain polyvinylidene fluoride is used instead of polyvinylidene fluoride with a molecular weight of 1 million to 1.3 million Da. A higher molecular weight can correspondingly increase the cohesive force. The molecular weight of polyacrylic acid is 600,000 to 800,000 Da, which remains unchanged. S1: Take 15KG of NMP and 1.35KG of long-chain polyvinylidene fluoride and add them to the double planetary tank in sequence. The stirring steps are as follows: 10±1rpm, 15min (scraping), 25±1rpm, 2000±10rpm, 60min (scraping), 25±1rpm, 2000±10rpm, 30min, with a solid content of about 7.5%. S2: Add polyacrylic acid adhesive solution, and set the stirring steps to 25±1 rpm, 2000±10 rpm, 30 min to prepare the composite adhesive solution with a solid content of approximately 12.0%; S3: Add ceramic particles and continue to disperse. The stirring steps are set as follows: 15±1 rpm, 10 min (scraping), 25±1 rpm, 3000±10 rpm, 120 min, to ensure thorough stirring and dispersion, with a solid content of approximately 40.5%. S4: Add all acetone to enhance the cooling of the mixing tank. The stirring steps are set as follows: 25±1 rpm, 500±10 rpm, 30 min. Acetone is volatile, so enhancing the cooling of the mixing tank will result in a solid content of approximately 39.5%. S5: Add 0.5 kg of NMP. The stirring steps are set as follows: 25 ± 1 rpm, 2000 ± 10 rpm, 30 min. This step is for adjusting the viscosity and solid content. This step can be repeated multiple times. The solid content is about 40%. S6: Pulping complete, vacuuming, stirring speed 25rpm, vacuum degree ≤-85kpa, 90min; S7: The ceramic adhesive solution was tested and found to have a viscosity of 4580 mPa·s and a solid content of 39.3% and 38.5%, respectively. The test results were qualified. It was then transferred to the ceramic tank for the coating process, slowly stirred and circulated before coating. S8: Under the condition that the electrode process parameters remain unchanged, in conventional ceramic slurry coating speed operations where mixing occurs, the present invention shows no significant mixing (0.1mm). 0.2mm); further increasing by 50% resulted in slight mixing of materials (0.2mm). (0.4mm, meeting process standards) Changing the molecular weight of polyvinylidene fluoride has no significant impact on the mixing process; therefore, production is carried out with a 50% increase in coating speed.

[0023] Example 5: Basically the same as Example 1, except that the proportion of acetone in the slurry solvent is increased from 5% to 10%, so as to fix the material more quickly and prevent mixing by taking advantage of the low-temperature rapid evaporation characteristics of acetone; With the electrode process parameters unchanged, increasing the coating speed by 50% compared to the conventional ceramic slurry coating speed where mixing occurs, this invention shows no significant mixing (≤0.1mm); further increasing to 70% results in some mixing (0.1mm). 0.3mm, fully meeting process standards), continuing to increase to 80%, severe mixing occurred (0.8mm). (1.4mm, does not meet process standards), appropriately reducing the speed to 70% resulted in no obvious mixing (0.1mm). (0.3mm), therefore, compared with increasing the proportion of polyacrylic acid, increasing the proportion of acetone solvent can further improve the mixing effect. The continuously optimized ratio is adjusted to boehmite: polyvinylidene fluoride: polyacrylic acid = 88:6:6 (solvent is NMP: acetone = 90:10).

[0024] In summary, the composite of polyacrylic acid and polyvinylidene fluoride of this invention can simultaneously leverage the high adhesion, chemical stability, and electrolyte corrosion resistance of polyvinylidene fluoride, while also utilizing the high cohesive strength of polyacrylic acid. The cohesive strength is significantly enhanced. The solvent used is a mixture of NMP and acetone. Through the difference in evaporation rates (NMP boiling point 204℃, acetone boiling point 56℃), the ceramic slurry loses liquid more quickly during coating and drying, rapidly increasing the solid content and viscosity to further reduce ceramic particle migration and miscibility. Simultaneously, the increased solid content of the ceramic slurry, compared to the conventional 30% solid content, leads to a significant reduction in intermolecular distance due to the increased polymer molecular concentration. This method increases the number of molecular contact points per unit volume; simultaneously, the probability of "physical entanglement" between long-chain molecules increases dramatically, and the entanglement of two polymers can form more complex three-dimensional structures; the increased concentration of polar functional groups in polyacrylic acid can improve the cohesiveness of the overall ceramic slurry. This method can effectively resist shrinkage stress in the material zone and solvent migration, reducing the degree of miscibility from ≥0.5mm to ≤0.2mm, meeting the requirements of the coating process; at the same time, compared with the conventional method of reducing the speed to improve miscibility, coating can be carried out at a speed increase of 30-70%, increasing the production capacity by more than 30% compared with the traditional process, reducing the number of downtime adjustments and trial coatings, and shortening the production cycle; The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0025] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A ceramic slurry, characterized by, It includes ceramic particles, a binder, and a solvent; the solvent is a mixture of NMP and acetone, and the binder is a composite of polyacrylic acid and polyvinylidene fluoride.

2. The ceramic slurry of claim 1, wherein, The mass ratio of the binder to the ceramic particles is (10-20): (80-90); preferably 12:

88.

3. The ceramic slurry according to claim 1, characterized in that, The mass ratio of NMP to acetone is (80-95):(5-20); preferably 90:

10.

4. The ceramic slurry according to claim 1, characterized in that, The mass ratio of the polyacrylic acid and polyvinylidene fluoride is (3-6): (6-7), more preferably 6:6; preferably, the molecular weight of the polyacrylic acid is 400,000–1,000,000 Da, more preferably 600,000–800,000 Da; the molecular weight of the polyvinylidene fluoride is 800,000–1,300,000 Da.

5. The ceramic slurry according to claim 1, characterized in that, The ceramic particles include at least one of the following powders: aluminum oxide, boehmite, silicon dioxide, titanium dioxide, magnesium dioxide, barium sulfate, zirconium oxide, calcium oxide, and magnesium hydroxide; preferably boehmite.

6. The ceramic slurry according to claim 1, characterized in that, The solid content of the ceramic slurry is 40%±3%, and the viscosity is 5000mPa·s-8000mPa·s.

7. A method for preparing a ceramic slurry according to any one of claims 1-6, characterized in that, The process includes the following steps: S1: Mixing and dispersing the adhesive polyvinylidene fluoride with a portion of NMP to prepare a PVDF adhesive solution, preferably with a solid content of 9±5%; S2: Add polyacrylic acid liquid, with a solid content of 13±5%; S3: Add ceramic particles and continue dispersion, gradually increasing the rotation speed to ensure that the binder molecules fully coat the ceramic particles, forming a stable dispersion system. At the same time, it promotes molecular chain entanglement and enhances cohesion, with a solid content of 43±5%. S4: Add all acetone to enhance the cooling of the stirred tank, solid content 42±5%; S5: Adjust the viscosity to 5000-8000 mPa·s with residual NMP, with a solid content of 40%±3%, further optimizing intermolecular forces and ensuring the stability of the adhesive solution; S6: Pulping is complete. Vacuum is applied to remove air bubbles.

8. The method for preparing ceramic slurry according to claim 7, characterized in that, The stirring process in step S1 is 10±10 rpm, 10-20 min, scraping, 25±20 rpm, 2000±200 rpm, 20-40 min, scraping, 25±20 rpm, 2000±200 rpm, 20-40 min. The stirring process in step S2 is 25±20 rpm, 2000±200 rpm, 20-40 min; The stirring process in step S3 is 15±10 rpm for 5-20 min, followed by scraping at 25±20 rpm for 3000±300 rpm for 100-150 min. The stirring process in step S4 is 25±20 rpm, 500±100 rpm, 20-40 min.

9. A positive electrode plate, characterized in that, It includes a positive current collector and a positive active material layer and a ceramic insulating layer located on the positive current collector; the ceramic insulating layer is obtained by coating the ceramic slurry according to any one of claims 1-6 onto the positive current collector.

10. A battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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