Ceramic slurry, its preparation method and application

Abstract

The application discloses a kind of ceramic slurry and its preparation method and application.The ceramic slurry provided by the application includes base material and solvent;The base material includes the following components: ceramic base material, thickening agent and additive;The ceramic base material is boehmite;The thickening agent is one or more of polyvinylidene fluoride, carboxymethyl cellulose, methyl cellulose and polyacrylate;The additive is one or more of polyacrylic acid, polyvinyl acetal and polyvinyl acetate.The application selects PAA as an additive, which is used with the base material boehmite and PVDF (polyvinylidene fluoride), to significantly improve the cohesiveness of the slurry while ensuring the advantages of the original slurry.The finished slurry is not prone to sedimentation, has high adhesion, good insulation performance, shortens the slurry mixing time and improves the efficiency;And the improved ceramic slurry coated insulation coating has strong adhesion to aluminum foil, and will not fall off after electrolyte immersion, improving the safety performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery manufacturing technology, specifically relating to an insulating coating ceramic slurry for the edge of a lithium battery positive electrode sheet, its preparation method, and its application. Background Technology

[0002] To improve the safety of lithium batteries, an insulating coating is typically applied to the edges of the positive electrode during the coating process. This prevents the negative electrode from directly covering the positive current collector during winding or stacking. After the positive and negative electrodes are coated with the insulating coating, the edge of the negative electrode corresponds to the positive electrode insulating layer. If there are burrs or dust on the edge of the negative electrode, the insulating coating on the positive electrode edge can prevent the negative electrode edge from piercing the separator and directly contacting the positive electrode foil, thus preventing short circuits within the battery.

[0003] The current mainstream method for preparing insulating coatings is to first use PVDF (polyvinylidene fluoride) and solvent NMP (1-methyl-2-pyrrolidone) to form a slurry. After the slurry is formed, ceramic base material (boehmite) is added and mixed and dispersed to form a ceramic slurry. However, this ceramic slurry has a long mixing time and a dispersion time of 4 hours. It also has the disadvantage of being easy to fall off after being soaked in electrolyte. Summary of the Invention

[0004] The purpose of this invention is to provide a ceramic slurry for edge insulation coating of lithium battery positive electrode sheet, which has a short slurry mixing process and is not easy to fall off after being soaked in electrolyte, thus meeting the requirements of actual production.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a ceramic slurry, comprising a base material and a solvent; the base material comprises the following components: a ceramic base material, a thickener, and an additive; the ceramic base material is boehmite; the thickener is one or more selected from polyvinylidene fluoride, carboxymethyl cellulose, methyl cellulose, and polyacrylate; the additive is one or more selected from polyacrylic acid, polyvinyl acetal, and polycarbonate.

[0006] This invention significantly improves the adhesiveness of slurry by selecting suitable thickeners and additives and applying them in combination with boehmite, while ensuring the original advantages of the slurry.

[0007] In one specific embodiment of the present invention, the thickener is polyvinylidene fluoride (PVDF).

[0008] In one specific embodiment of the present invention, the additive is polyacrylic acid (PAA).

[0009] In this invention, the mass fraction of the additive in the base material is 12-20%, preferably 12-15%.

[0010] In this invention, the mass fraction of the thickener in the base material is 0.5%-10%, preferably 2-4%.

[0011] In this invention, the ceramic slurry has the following characteristics: viscosity range of 2000-6000 mPa.s, specifically 3230 mPa.s; solid content range of 25-50%, specifically 27.8%; and fineness range of 5-50 μm, specifically 23 μm.

[0012] Secondly, the present invention provides a method for preparing the above-mentioned ceramic slurry, comprising the following steps: S1. Mix the ceramic base material, thickener and additives to obtain a mixed powder; S2. Add solvent to the mixed powder obtained in step S1 and disperse to obtain a dispersion. S3. Defoam the dispersion obtained in step S2 to obtain the ceramic slurry.

[0013] The present invention adopts the method of first mixing powder and then dispersing it with solvent, which is beneficial to improving the dispersibility of the slurry and thus obtaining a ceramic slurry with better performance.

[0014] In this invention, in step S1, the mixing is carried out using a double planetary dispersion vessel. The mixing conditions are: a revolution speed of 5~30 rpm / min and a time of 5~15 min; preferably, the revolution speed is 15 rpm and the time is 15 min.

[0015] In this invention, in step S2, the solvent is NMP (N-methyl-2-pyrrolidone); the mass fraction of NMP in the dispersion is 80%~88%.

[0016] In this invention, step S2 involves two stages of dispersion: First stage: Disperse the mixture under the conditions of a revolution speed of 5~30 rpm / min and a rotation speed of 500~1300 rpm / min; Second stage: The mixture obtained in the first stage is further dispersed under the conditions of vacuum degree of -95Kpa, revolution speed of 5~30rpm / min and rotation speed of 500~1300rpm / min.

[0017] In a specific embodiment of the present invention, the dispersion is performed as follows: first, the mixture is dispersed for 10 minutes at a revolution speed of 5-30 rpm / min and a rotation speed of 500-1300 rpm / min; then, the tank is opened and scraped; and then, it is dispersed for 90 minutes at a vacuum of -95 kPa, a revolution speed of 5-30 rpm / min, and a rotation speed of 500-1300 rpm / min. After the dispersion is completed, the viscosity, solid content, and fineness of the dispersion are tested, and defoaming is performed after the standard is met. Preferably, the vacuum is -95 kPa, the revolution speed is 15 rpm / min, and the rotation speed is 1200 rpm / min.

[0018] In this invention, the defoaming conditions are: a vacuum degree of -95 kPa, a revolution speed of 5-20 rpm / min, a rotation speed of 100-500 rpm / min, and a time of 15-30 min. Preferably, the vacuum degree is -95 kPa, the revolution speed is 10 rpm, the rotation speed is 100 rpm, and the time is 20 min.

[0019] Thirdly, the present invention provides a positive electrode composite electrode, comprising an electrode substrate and a coating covering its edges; the coating is formed from the above-mentioned ceramic slurry.

[0020] Fourthly, the present invention provides a lithium-ion battery, including a positive electrode; the positive electrode sheet is the above-mentioned positive electrode composite sheet.

[0021] Compared with the prior art, the beneficial effects achieved by the present invention are: This invention selects suitable thickeners and additives to be used in conjunction with boehmite as the base material. This significantly improves the slurry's adhesion while maintaining its original advantages, making the finished slurry less prone to settling, greatly shortening the slurry mixing time and increasing mixing efficiency. Simultaneously, the insulating coating formed by the slurry on the electrode surface adheres more strongly to the aluminum foil and will not peel off after electrolyte immersion, improving battery safety performance. Furthermore, the slurry mixing method provided by this invention is simple, safe, and controllable, making it suitable for industrial production. Attached Figure Description

[0022] Figure 1 This is a flow chart of the preparation process of the ceramic slurry described in this invention. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0024] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0025] Unless otherwise specified, all reagents, materials, instruments, etc. used in the following examples are commercially available.

[0026] Example 1: Preparation of ceramic slurry The specific steps are as follows: S1. Feeding. In the double planetary dispersion vessel, first add 80 kg of boehmite, then add 11.3 kg of PAA (polyacrylic acid), and finally add 2.8 kg of PVDF (polyvinylidene fluoride); S2, Dry mixing: The orbital speed of the dual planetary dispersion kettle is set to 30 rpm for 10 min to premix the powder. S3, Scraping the tank: After dry mixing, add 242 kg of solvent NMP, revolve at 15 rpm, rotate at 1200 rpm, disperse for 10 min, open the lid and scrape the wall and the stirring rod; S4. Secondary dispersion: First, evacuate to -95KPa, then revolve at 15rpm and rotate at 1200rpm, and continue dispersion for 90min; S5. After dispersion, the slurry was sampled and tested. The viscosity was 3230 mPa·s, the solid content was 27.8%, and the fineness was 23 μm. The slurry properties met the coating requirements.

[0027] S6. Defoaming and Discharge: Set the stirring rod to revolve at 10 rpm and rotate at 100 rpm, apply vacuum at -95 kPa, and discharge the material after defoaming for 20 minutes.

[0028] The experimental results show that the total mixing time is 130 minutes, which is much shorter than the existing mixing time of 4 hours.

[0029] Test case The ceramic slurry prepared in the example was coated on the edge of the positive electrode to obtain a ceramic positive electrode sheet.

[0030] 1. Electrolyte immersion test Test procedure: Take 5-7 ceramic positive electrode plates, put them into the electrolyte, and soak them in a high-temperature environment of 45℃ for 15 days.

[0031] The results showed that the ceramic on the electrode had no abnormal openings or peeling, and the ceramic did not fall off even after repeated rubbing by hand, indicating good adhesion and meeting battery safety requirements.

[0032] 2. Ceramic insulation performance test Test procedure: Use an insulation tester, set the voltage to 200V, and test the insulation resistance between ceramic zones, between ceramic zones and aluminum foil zones, and between ceramic zones and material zones.

[0033] The results show that the insulation resistance between ceramic zones, between ceramic zones and aluminum foil zones, and between ceramic zones and material zones all exceed 10 MΩ, meeting the battery insulation requirements.

[0034] 3. Slurry settling test, Test procedure: Take one small bottle of the slurry obtained in step S5 of the example, seal it, and let it stand at room temperature for 24 hours.

[0035] The results showed that after 24 hours of standing at room temperature, the solid content of the upper slurry changed by 0.28%; after 48 hours of standing, the solid content changed by 0.43%, which met the requirements for slurry standby time in actual production.

[0036] Comparative experiment: According to the ceramic slurry preparation method in the above embodiments, the PAA binder is replaced with PVDF, and the ratio of PVDF to boehmite is 12.5:87.5, 15:85, and 20:80. The powders in the three ratios are processed into ceramic slurries through steps S1-S6 respectively. The obtained ceramic slurries are coated on the edge of the positive electrode to obtain a ceramic positive electrode sheet.

[0037] Test procedure: Take 5-7 ceramic positive electrode plates, put them into the electrolyte, and soak them in a high temperature environment of 45℃ for 7 days.

[0038] Test results show that the ceramic openings and peeling on the comparison electrode are abnormal, and the ceramic falls off and detaches when rubbed by hand, which does not meet production requirements.

[0039] In summary, the above results demonstrate that the slurry prepared according to the present invention can meet the actual production requirements, and the slurry mixing method is reasonable and effective.

[0040] In this invention, the thickener polyvinylidene fluoride can be replaced with carboxymethyl cellulose, methyl cellulose or polyacrylate, and the additive polyacrylic acid can be replaced with polyvinyl acetal or polycarbonate. It can also improve the adhesion of the slurry while ensuring the original advantages of the slurry, but the overall effect is not as good as in Example 1.

[0041] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A ceramic slurry, comprising a base material and a solvent; The base material comprises the following components: ceramic base material, thickener, and additives; The ceramic base material is boehmite; The thickener is one or more of polyvinylidene fluoride, carboxymethyl cellulose, methyl cellulose, and polyacrylate; The additive is one or more of polyacrylic acid, polyvinyl acetal, and polycarbonate.

2. The ceramic slurry according to claim 1, characterized in that, In the base material, the mass fraction of the additive is 12-20%; the mass fraction of the thickener is 0.5-10%.

3. The ceramic slurry according to claim 1 or 2, characterized in that, The ceramic slurry has the following characteristics: viscosity range of 2000-6000 mPa·s, solid content range of 25-50%, and fineness range of 5-50 μm.

4. The method for preparing the ceramic slurry according to any one of claims 1-3, comprising the following steps: S1. Mix the ceramic base material, thickener and additives to obtain a mixed powder; S2. Add solvent to the mixed powder obtained in step S1 and disperse to obtain a dispersion. S3. Defoam the dispersion obtained in step S2 to obtain the ceramic slurry.

5. The preparation method according to claim 4, characterized in that, In step S1, the mixing conditions are: revolution speed of 5~30 rpm / min and time of 5~15 min.

6. The preparation method according to claim 4 or 5, characterized in that, In step S2, the solvent is NMP; the mass fraction of NMP in the dispersion is 80%~88%.

7. The preparation method according to any one of claims 4-6, characterized in that, In step S2, the dispersion is divided into two stages: First stage: Disperse the mixture under the conditions of a revolution speed of 5~30 rpm / min and a rotation speed of 500~1300 rpm / min; Second stage: The mixture obtained in the first stage is further dispersed under the conditions of vacuum degree of -95Kpa, revolution speed of 5~30rpm / min and rotation speed of 500~1300rpm / min.

8. The preparation method according to any one of claims 4-7, characterized in that, The defoaming conditions are: vacuum degree of -95 kPa, revolution speed of 5-20 rpm / min, rotation speed of 100-500 rpm / min, and time of 15-30 min.

9. A positive electrode composite electrode, comprising an electrode substrate and a coating covering its edges; The coating is formed from the ceramic slurry according to any one of claims 1-3.

10. A lithium-ion battery, comprising a positive electrode; wherein the positive electrode is the positive electrode composite electrode as described in claim 9.

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