A method for preparing a safety slurry and the structure of the safety slurry and battery safety coating.

Abstract

This invention relates to the field of battery technology, specifically to a method for preparing a safe slurry, comprising: S1, initial pre-dispersion of mixed ceramic materials and solvent; S2, second pre-dispersion after adding a dispersant; S3, third pre-dispersion after adding a conductive agent and then stirring and dispersing again; S4, fourth pre-dispersion and stirring and dispersing after adding a binder; S5, stirring and dispersing after adding a dispersant; and S6, slow stirring and defoaming followed by reverse stirring, finally discharging the material slowly to obtain the safe slurry. The preparation method of this application, through multiple pre-dispersions and stirring, can more effectively break up particle aggregates, reduce the interaction forces between particles, and thus obtain a more uniform particle distribution. The phased addition of the dispersant ensures a suitable viscosity of the mixture, and the mixture exhibits good dispersion during stirring. Furthermore, this invention also discloses a safe slurry and a safety coating structure for batteries.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a method for preparing a safety slurry and the structure of the safety slurry and battery safety coating. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, high discharge platform, long cycle life, and no memory effect, and are widely used in mobile phones, cameras, laptops, and other fields, as well as in the power battery fields of electric bicycles and electric vehicles. As one of the main components of lithium batteries, the safety performance of the electrodes is a key factor to consider during battery design. Coating the electrodes with a battery safety coating is a common method in the battery industry to improve battery safety performance.

[0003] The existing method for mixing battery safety slurries involves simultaneously mixing the components in a certain proportion. Since the rotation speed setting is related to physical properties such as the density difference between the solid and liquid phases, the liquid phase density, the solid phase concentration, the liquid phase viscosity, and the particle size, the existing method is prone to agglomeration when dispersing small-particle-size ceramic materials, resulting in poor final dispersion.

[0004] The uniformity and stability of the slurry dispersion have a significant impact on the coating effect. The smaller the particle size of the ceramic material, the more prone it is to agglomeration, and existing dispersion methods are ineffective at dispersing small ceramic particles. Therefore, existing battery safety coatings use ceramic materials with larger particle sizes to achieve uniform slurry dispersion. However, larger particle sizes not only cause a loss of battery energy density but also affect the adhesion, conductivity, and mechanical strength of the safety coating, thereby impacting battery safety performance.

[0005] Therefore, there is an urgent need to invent a method for preparing a safe slurry to solve the aforementioned technical problems. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for preparing a safe slurry, which addresses the shortcomings of existing technologies and enables uniform diffusion of ceramic materials, exhibiting good dispersion effects in each step.

[0007] To solve the above-mentioned technical problems, this application adopts the following technical solution: providing a method for preparing a safe slurry, comprising the following steps:

[0008] S1. Add 80-95 parts by weight of ceramic material and 120-200 parts by weight of solvent to a mixing tank and pre-stir to achieve the first pre-dispersion and obtain mixture I.

[0009] S2. Add 0.01 to 5 parts of dispersant to the mixture I in step S1, and pre-stir to achieve a second pre-dispersion, thus obtaining mixture II;

[0010] S3. Add 1 to 5 parts of conductive agent to the mixture II in step S2, pre-stir to achieve the third pre-dispersion, and obtain mixture III. Stir and disperse mixture III.

[0011] S4. Add 2 to 10 parts of binder to the mixture III in step S3, and pre-stir to achieve the fourth pre-dispersion, to obtain mixture IV. Stir and disperse mixture IV.

[0012] S5. Add 0.01 to 5 parts of dispersant to the mixture IV in step S4 and stir to disperse, so as to obtain mixture V;

[0013] S6. Slowly disperse and reverse the mixture V from step S5 to defoam, and finally slowly discharge the material to obtain a safe slurry.

[0014] The stirring temperature is 25℃±3℃.

[0015] The beneficial effects are as follows: The method for preparing the safe slurry of this application can ensure that fine ceramic particles are uniformly dispersed in the slurry, avoiding particle agglomeration, thereby improving the overall performance and stability of the slurry. Through multiple pre-dispersion steps and stirring dispersion, particle aggregates can be broken more effectively, reducing the interaction force between particles, thereby obtaining a more uniform particle distribution, which can effectively improve the dispersion effect of ceramic particles. The phased addition of dispersant can ensure that the viscosity of the mixture is appropriate, and the mixture has a good dispersion effect during stirring, ensuring that the slurry has excellent performance. The reasonable dispersion and mixing process contributes to the mechanical strength, wear resistance and conductivity of the final slurry, thereby improving the practical application effect of the slurry. The final defoaming step can remove the bubbles generated during the mixing process, ensuring the uniformity and smoothness of the slurry and reducing defects in subsequent coating processes.

[0016] Specifically, in steps S1 to S5, the stirring linear velocity is 9 to 15 m / s; in step S6, the slow stirring dispersion has a revolution speed of 10 to 30 rpm and a rotation speed of 0 rpm for 10 to 120 min; the slow stirring discharge has a revolution speed of 10 to 30 rpm and a rotation speed of 50 to 500 rpm for 10 to 120 min; in steps S1 to S4, the pre-stirring revolution speed is 10 to 20 rpm and the stirring rotation speed is 2000 to 4000 rpm, wherein the pre-stirring time in steps S1, S3, and S4 is 5 to 15 min. In step S2, the pre-stirring time is 20–40 min; in step S3, the stirring rotation speed is 20–40 pm, the stirring rotation speed is 4000–5000 rpm, and the stirring time is 40–80 min; in step S4, the stirring rotation speed is 20–40 pm, the stirring rotation speed is 4000–5000 rpm, and the stirring time is 180–250 min; in step S5, the stirring rotation speed is 20–40 rpm, the stirring rotation speed is 2000–4000 rpm, and the stirring time is 10–20 min.

[0017] Specifically, the dispersant in step S2 is a solute, specifically polyvinylpyrrolidone; the dispersant in step S5 is a solvent, specifically isopropanol; and the solvent in step S1 is N-methylpyrrolidone.

[0018] Specifically, the solid content of the mixture obtained in steps S1 to S5 is between 20% and 40%.

[0019] Specifically, the ceramic material is at least one of boehmite and alumina, the binder is at least one of PVDF, SBR, PAA and CMC, the conductive agent is at least one of conductive carbon black, carbon nanotubes and graphene, and the dispersant is at least one of polyvinylpyrrolidone and isopropanol.

[0020] The second objective of this invention is to provide a safe slurry prepared by the above-described method, comprising the following components in parts by weight: 80-95 parts ceramic material, 2-10 parts binder, 1-5 parts conductive agent, and 0.01-5 parts dispersant, wherein the ceramic material has a particle size D10 of 0.1-0.15 μm or greater than 0.3 μm, D50 of 0.1-2.5 μm, D90 of 0.5-5 μm, D99 of 1-10 μm, and a specific surface area of ​​1-40 m². 2 / g.

[0021] The beneficial effects of this invention are as follows: By controlling the particle size of the ceramic material, the ceramic material can be well dispersed during the stirring and dispersion process. The ceramic particles are more evenly distributed in the safety coating, reducing possible voids and defects in the safety coating. This enhances the adhesion between the battery safety coating structure and the active material and current collector. Furthermore, the increased specific surface area increases the contact area between the ceramic material and the binder, improving the adhesion between the safety coating and the substrate. Because the smaller particle size results in a more continuous and dense conductive network, the conductivity in the safety coating structure is more uniform, without any breaks. The smaller particles can fill the tiny pores and defects in the coating, increasing its density and compactness, thereby improving mechanical strength. This prevents the safety coating from cracking due to stress concentration during use, forming a uniform and dense safety coating that provides more comprehensive protection. Under stress, it can more effectively disperse impact forces, reducing the possibility of cracking and the risk of puncture or short circuit. This results in a battery safety coating structure with better adhesion, conductivity, and mechanical strength.

[0022] Specifically, the mass ratio of the adhesive to the conductive agent is (1-5):1.

[0023] The third objective of this invention is to provide a battery safety coating structure, which is formed by coating the aforementioned safety slurry on both sides of the current collector in the thickness direction, including the aforementioned safety coating material coated on both sides of the current collector in the thickness direction. The surface of the coating structure is further coated with an active material layer, and the area of ​​the coating structure is greater than or equal to the area of ​​the active material layer.

[0024] The beneficial effects are as follows: By applying a battery safety coating structure to the surface of the current collector, the current collector and the active material of the battery are isolated. When the battery is punctured and short-circuited, the current on the active material needs to pass through the battery safety coating structure to reach the current collector. This ensures that the battery is connected to the safety coating structure during the short circuit, increasing the resistance of the battery during the short circuit and preventing the battery from overheating and catching fire after being punctured. Furthermore, the safety coating can prevent Al-Anode short circuits, greatly reducing the risk of battery smoke and fire.

[0025] Specifically, the adhesion force between the safety coating structure and the current collector is greater than or equal to 400 N / m, the thickness of the safety coating structure is 1–5 μm, and the areal density is 7 mg / 1540.25 mm. 2 ~10mg / 1540.25mm 2 .

[0026] Specifically, the diaphragm resistance of the safety coating structure is 0.2 to 3 Ω. Attached Figure Description

[0027] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 This is a flowchart illustrating Embodiment 1 of this application;

[0029] Figure 2 This is a top view of Embodiment 3 of the present invention;

[0030] Figure 3 This is a cross-sectional view of Embodiment 3 of the present invention;

[0031] Figure 4 This is one of the microscopic morphology images of the electrode cross-section in Example 3 of this invention;

[0032] Figure 5 This is the second microscopic morphology diagram of the electrode cross-section in Example 3 of the present invention.

[0033] Wherein: 1-Safety coating structure; 2-Active material layer; 3-Current collector. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terminology used in the specification of this application is for the purpose of describing specific embodiments only and is not intended to limit this application.

[0035] The following is in conjunction with the appendix Figures 1-5 The present invention will be described in further detail, but this is not intended to limit the invention.

[0036] The applicant discovered that in the prior art, the battery safety coating may crack or peel under mechanical stress or impact, and may fail to maintain good insulation or stability under high temperature conditions, leading to a decrease in the safety performance of the battery when subjected to short circuits or thermal runaway. This is because the battery safety coating has poor adhesion, making it prone to detachment under impact, causing the battery safety coating to fail. Furthermore, the battery safety coating expands at high temperatures, causing cracks and preventing it from maintaining its insulation performance. These phenomena are due to the large particle size of the ceramic materials used in the prior art, which easily leads to stress concentration in the safety coating, reducing the adhesion between the safety coating and the current collector 3, making it easier to peel off under impact, increasing the risk of crack formation. Additionally, the uneven thermal expansion of larger particles at high temperatures may cause cracks in the coating, affecting insulation and stability. Conversely, using ceramic materials with smaller particle sizes is prone to agglomeration, resulting in uneven dispersion of the ceramic material in the battery coating structure 1. Existing methods for mixing battery safety coatings involve simultaneously mixing components in a certain proportion, without considering the relationship between rotation speed and physical properties such as the density difference between the solid and liquid phases, liquid density, solid concentration, liquid viscosity, and particle size. Existing methods often result in agglomeration and poor dispersion when dispersing small-particle-size ceramic materials. Therefore, this applicant proposes an improved method for preparing safety slurry. This method adjusts the viscosity of the mixture by adding dispersant in stages, and controls the shear effect of the fluid on the ceramic material by controlling the stirring time and rotation speed, thus maintaining good dispersion during the stirring process. Furthermore, by controlling the order of addition of different components and performing multiple pre-dispersion and dispersion stirring steps, the viscosity of the mixture in each step is adjusted to achieve sufficient dispersion of each component.

[0037] Example 1

[0038] like Figure 1 As shown, the method for preparing the safe slurry in this embodiment includes the following steps:

[0039] S1. Add 80-95 parts by weight of ceramic material and 120-200 parts by weight of solvent to a mixing tank and pre-stir to achieve the first pre-dispersion and obtain mixture I.

[0040] S2. Add 0.01 to 5 parts of dispersant to the mixture I in step S1, and pre-stir to achieve a second pre-dispersion, thus obtaining mixture II;

[0041] S3. Add 1 to 5 parts of conductive agent to the mixture II in step S2, pre-stir to achieve the third pre-dispersion, and obtain mixture III. Stir and disperse mixture III.

[0042] S4. Add 2 to 10 parts of binder to the mixture III in step S3, and pre-stir to achieve the fourth pre-dispersion, to obtain mixture IV. Stir and disperse mixture IV.

[0043] S5. Add 0.01 to 5 parts of dispersant to the mixture IV in step S4 and stir to disperse, so as to obtain mixture V;

[0044] S6. Slowly disperse and reverse the mixture V from step S5 to defoam, and finally slowly discharge the material to obtain a safe slurry.

[0045] Pre-dispersion of solid materials with liquid media helps to break up particle aggregation, thereby reducing the energy and time required for subsequent dispersion processes.

[0046] The stirring temperature is 25℃±3℃.

[0047] By setting a reasonable stirring temperature, the mixture can have good molecular diffusion ability without the different components being denatured due to excessive temperature, thus affecting the mixing ability.

[0048] Preferably, in steps S1 to S6, the solid content of the prepared mixture is between 20% and 40%, ensuring that the solid content is not too high and the solvent can wet the surface of the ceramic material, and that the solid content is not too low, which can ensure better dispersion of the ceramic material.

[0049] Preferably, the stirring linear velocity in steps S1 to S5 is 9 to 15 m / s. This application controls the stirring linear velocity within a certain range to prevent excessive pressure on the mixture due to excessive stirring linear velocity, which may also increase frictional heat generation and affect the thermal stability of the material. It also achieves good stirring efficiency. When different radius dispersion discs are selected for stirring, the rotational speed can be calculated based on the linear velocity and the radius of the dispersion disc.

[0050] Preferably, this application uses a planetary mixer-dispersor, which consists of a twisted agitator and a serrated lotus-shaped dispersing disc. The twisted agitator allows the slurry to flow extensively within the disperser, forming a stable flow field and modifying the material surface. The serrated lotus-shaped dispersing disc rotates at high speed, creating a high-speed flow field and dispersing and shearing. The radius of the dispersing disc can be selected according to Table 1; choosing a dispersing disc of appropriate diameter ensures good mixing results.

[0051] Table 1

[0052]

[0053] In step S6, the slow stirring dispersion has an orbital speed of 10-30 rpm and a rotational speed of 0 rpm for 10-120 min; the slow stirring discharge has an orbital speed of 10-30 rpm and a rotational speed of 50-500 rpm for 10-120 min.

[0054] Preferably, in steps S1 to S4, the pre-stirring revolution speed is 10-20 rpm and the stirring rotation speed is 2000-4000 rpm. Specifically, the pre-stirring time in steps S1, S3, and S4 is 5-15 min; the pre-stirring time in step S2 is 20-40 min; the stirring and dispersing revolution speed in step S3 is 20-40 rpm, the stirring rotation speed is 4000-5000 rpm, and the stirring time is 40-80 min; the stirring and dispersing revolution speed in step S4 is 20-40 rpm, the stirring rotation speed is 4000-5000 rpm, and the stirring time is 180-250 min; and the stirring and dispersing revolution speed in step S5 is 20-40 rpm, the stirring rotation speed is 2000-4000 rpm, and the stirring time is 10-20 min.

[0055] Specifically, the dispersant in step S2 is a solute, specifically polyvinylpyrrolidone; the dispersant in step S5 is a solvent, specifically isopropanol; and the solvent in step S1 is N-methylpyrrolidone.

[0056] Preferably, the combined use of polyvinylpyrrolidone (PVP) and isopropanol achieves better dispersion. PPVP is a polymer with polar groups (such as amino and carbonyl groups) that can interact with polar or charged groups on the surface of ceramic particles. This interaction helps the dispersant adhere to the particle surface, forming a protective layer and reducing the attraction between particles. The addition of PPVP reduces friction between ceramic particles, making them easier to flow and disperse in liquids. Furthermore, it reduces particle adhesion to equipment surfaces, improves processing performance, and can adjust the viscosity of the mixture, optimizing the flowability and uniformity of the slurry. Isopropanol has strong dissolving power and low surface tension, improving particle wettability and making particles easier to disperse in solvents. This helps break up particle agglomerates and promotes uniform distribution. The combined use of PPVP and isopropanol results in superior dispersion; PPVP provides stability and a protective layer, while isopropanol enhances wettability and adjusts viscosity.

[0057] In the subsequent step of preparing the safety coating structure 1, the solvents are N-methylpyrrolidone and isopropanol. The safety slurry needs to be applied to the current collector and dried in an oven to form the safety coating structure 1. Isopropanol and N-methylpyrrolidone will evaporate into the air. Isopropanol only plays a role in helping the ceramic material to disperse during the stirring and dispersion process, and will not remain in the final safety coating structure 1, thus preventing it from affecting the performance of the safety coating structure 1.

[0058] Preferably, the ceramic material is at least one of boehmite and alumina, the binder is at least one of PVDF, SBR, PAA, and CMC, the conductive agent is at least one of conductive carbon black, carbon nanotubes, and graphene, and the dispersant is at least one of polyvinylpyrrolidone and isopropanol. Materials within the above range maintain good compatibility through the preparation method of this application, reducing potential mixing problems.

[0059] Example 2

[0060] A safe slurry comprises the following components in parts by weight: 80-95 parts ceramic material, 2-10 parts binder, 1-5 parts conductive agent, and 0.01-5 parts dispersant. The ceramic material has a particle size of D10 of 0.1-0.15 μm or greater than 0.3 μm, D50 of 0.1-2.5 μm, D90 of 0.5-5 μm, and D99 of 1-10 μm, and a specific surface area of ​​1-40 m². 2 / g.

[0061] Preferably, the mass ratio of binder to conductive agent is (1-5):1. Within this range, the battery safety coating structure 1 of this application can form a conductive network structure. However, because the binder has low conductivity and poor bonding effect, when the content of conductive agent is too high, the conductivity increases while the bonding performance decreases, failing to provide suitable bonding strength. Furthermore, if the resistance is too low, it cannot provide sufficient insulation, and the needle penetration test cannot be passed 100%. When the binder content is too high, the bonding performance increases while the conductivity decreases, failing to form a conductive network. Excessive internal resistance of the battery leads to a rapid decline in the battery's capacity retention rate, significantly reducing the battery's lifespan.

[0062] Example 3

[0063] like Figures 2-5 As shown, a battery safety coating structure 1 is formed by the aforementioned safety slurry coated on both sides of the current collector 3 in the thickness direction. The safety coating structure 1 is further coated with an active material layer 2, and the area of ​​the safety coating structure 1 is greater than or equal to the area of ​​the active material layer 2.

[0064] Specifically, it includes 85% to 95% ceramic materials, 2% to 10% binder, 1% to 5% conductive agent, and 0.01% to 5% dispersant by mass.

[0065] In order to improve the adhesion of the safety coating for batteries, this application uses ceramic materials with a specific particle size, which not only maintains the uniformity of the ceramic material dispersion but also ensures the adhesion of the safety coating structure 1, improves the overall structural strength of the safety coating, and has good insulation performance at high temperatures, ensuring that the battery of this application will not experience thermal runaway when punctured.

[0066] Preferably, the thickness of the safety coating structure 1 is 1–5 μm, and the areal density is 7 mg / 1540.25 mm. 2 ~10mg / 1540.25mm 2 The needle penetration rate can be improved by increasing the thickness, insulation effect, and mechanical properties of the safety coating structure 1. However, if the safety coating structure 1 is too thick, the energy density of the battery will be reduced. When the thickness of the safety coating structure 1 in this application is within the above-mentioned range, the insulation and mechanical properties of the safety coating structure 1 can be guaranteed.

[0067] Preferably, the adhesion force between the safety coating structure 1 and the current collector 3 is greater than or equal to 400 N / m. When the adhesion force is within the above range, it can ensure that the safety coating structure 1 and the current collector 3 do not peel off in the electrolyte environment. During needle penetration, the safety coating structure 1 and the current collector 3 also do not peel off. Simultaneously, the safety coating structure 1 can prevent Al-Anode short circuits and avoid battery thermal runaway.

[0068] Preferably, the diaphragm resistance of the safety coating structure 1 is 0.2 to 3 Ω. When the resistance of the safety coating structure 1 is within the above range, it can provide the necessary conductivity without affecting the insulation performance of the coating due to excessively low resistance.

[0069] Example 4

[0070] The method for preparing the safe slurry in this embodiment includes the following steps:

[0071] The total mass of the mixer is 4.613 kg. It is a 5L planetary mixer with a dispersion disc radius of 24.92 mm and a serrated lotus-shaped disc. The circulating water is on throughout the process, and the mixing temperature is 25℃±3℃.

[0072] 1) Add 2.515 kg of N-methylpyrrolidone solution;

[0073] 2) Add particles with a D10 greater than 0.3 μm, a D50 of 1.2–2.5 μm, a D90 < 5.0 μm, a D99 < 10 μm, and a specific surface area of ​​2–6 m². 2 1.3 kg of boehmite powder (g / g);

[0074] 3) Pre-dispersion: revolution at 15 rpm, rotation at 3620 rpm, time 10 min;

[0075] 4) Add 0.0014 kg of dispersant polyvinylpyrrolidone powder;

[0076] 5) Pre-dispersion: revolution at 15 rpm, rotation at 3620 rpm, time 30 min;

[0077] 6) Add 0.0258 kg of conductive agent Super P powder;

[0078] 7) Pre-dispersion: revolution at 15 rpm, rotation at 3620 rpm, time 10 min;

[0079] 8) Dispersed revolution at 30 rpm, rotation at 4330 rpm, time 60 min;

[0080] 9) Add 0.8065 kg of PVDF adhesive with a 7% solid content;

[0081] 10) Pre-dispersion: revolution at 15 rpm, rotation at 3620 rpm, time 10 min;

[0082] 11) Dispersed revolution at 30 rpm, rotation at 4330 rpm, time 210 min;

[0083] 12) Add 0.0645 kg of isopropanol dispersant solution;

[0084] 13) Dispersed revolution at 30 rpm, rotation at 3620 rpm, time 15 min;

[0085] 14) Stir slowly, 20 rpm for revolution and 0 rpm for rotation, for 30 minutes;

[0086] 15) Adjust viscosity and solid content, revolutionize at 25 rpm, rotate at 3620 rpm, time 20 min;

[0087] 16) Reverse defoaming: 20 rpm for revolution and 1200 rpm for rotation, for 30 minutes;

[0088] 16) Slowly stir the material during discharge, with a revolution of 20 rpm and a rotation of 200 rpm for 30 minutes;

[0089] 17) Measure the viscosity, solid content, and particle size of the slurry.

[0090] Example 5

[0091] The difference from Example 4 is that the boehmite powder used in step 2 is different, with a particle size D10 > 0.3 μm, D50 of 0.5–1.4 μm, D90 ≤ 3.0 μm, D99 ≤ 5.0 μm, and a specific surface area of ​​4–6 m². 2 / g;

[0092] Everything else is the same as in Example 4, and will not be repeated here.

[0093] Example 6

[0094] The difference from Example 4 is that the boehmite powder used in step 2 is different, with a particle size D10 > 0.1 μm, D50 of 0.3–0.6 μm, D90 ≤ 2.0 μm, D99 ≤ 3.0 μm, and a specific surface area of ​​8–16 m². 2 / g;

[0095] Everything else is the same as in Example 4, and will not be repeated here.

[0096] Example 7

[0097] The difference from Example 4 is that the boehmite powder used in step 2 is different, with particle sizes D10≤0.15μm, D50≤0.3μm, D90≤1.5μm, D99≤2μm, and a specific surface area of ​​18~32m². 2 / g;

[0098] Everything else is the same as in Example 4, and will not be repeated here.

[0099] Comparative Example 1

[0100] The difference from Example 4 is that the boehmite powder used in step 2 is different, with particle sizes D10 of 0.4 μm, D50 of 3.0 μm, D90 of 6.0 μm, and D99 of 12.0 μm.

[0101] Everything else is the same as in Example 4, and will not be repeated here.

[0102] Comparative Example 2

[0103] The difference from Example 4 is that the boehmite powder used in step 2 is different, with particle sizes D10 of 0.8, D50 of 6.0 μm, D90 of 10.0 μm, and D99 of 20.0 μm.

[0104] Everything else is the same as in Example 4, and will not be repeated here.

[0105] Adhesion test of safety coating

[0106] Test procedure: Attach double-sided adhesive tape to the steel plate, cut electrode sheets coated with safety slurry using a cutting knife, cut out small square strips that are not much different in size from the steel plate, attach them to the double-sided adhesive tape on the steel plate, press twice with a pressure roller, and measure the peel force on a tensile tester at a test speed of 200 mm / min.

[0107] Needle prick test method

[0108] After the electrode coated with safety slurry is made into a battery, a needle penetration test is performed.

[0109] 1) At 23±2℃, let stand for 5 minutes; charge to 4.2V with a constant current of 1C; then charge to 4.5V with a constant current and constant voltage of 0.7C, cut off current of 0.02C, and record voltage, internal resistance and thickness;

[0110] 2) The steel needle has a diameter of 4mm and a cone length of 14mm;

[0111] 3) Position the center, left (7.5mm from the edge), and right (7.5mm from the edge) of the largest surface of the battery cell directly below the probe. Close and lock the explosion-proof cabinet. Use a steel needle to completely pierce the battery cell at a speed of 40mm / s in one go and require the needle to remain in place for 10 minutes. Make a judgment when the surface temperature of the battery cell drops to 55℃. Record the temperature rise using a multi-channel thermometer.

[0112] Judgment criteria: No fire or explosion; sparks at the pinholes inside the battery cell are acceptable.

[0113] The test results are shown in Table 2.

[0114] Table 2

[0115]

[0116]

[0117] As shown in Examples 4-7 and Comparative Examples 1-2, the smaller the particle size of the ceramic material, the greater the bonding force. Furthermore, the greater the bonding force of the safety coating structure 1, the higher the needle penetration rate. This is because when the bonding force is high, the safety coating structure 1 is less likely to detach due to external forces, exhibiting good stability. Additionally, the appropriate particle size of the ceramic material results in better density of the safety coating structure 1, preventing debris from the current collector 3 from puncturing it, thus providing better insulation.

[0118] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept by means of the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for preparing a safe slurry, characterized in that, Includes the following steps: S1. Add 80-95 parts by weight of ceramic material and 120-200 parts by weight of solvent to a mixing tank and pre-stir to achieve the first pre-dispersion and obtain mixture I. S2. Add 0.01 to 5 parts of dispersant to the mixture I in step S1, and pre-stir to achieve a second pre-dispersion, thus obtaining mixture II; S3. Add 1 to 5 parts of conductive agent to the mixture II in step S2, pre-stir to achieve the third pre-dispersion, and obtain mixture III. Stir and disperse mixture III. S4. Add 2 to 10 parts of binder to the mixture III in step S3, and pre-stir to achieve the fourth pre-dispersion, to obtain mixture IV. Stir and disperse mixture IV. S5. Add 0.01 to 5 parts of dispersant to the mixture IV in step S4 and stir to disperse, so as to obtain mixture V. S6. Slowly disperse and reverse the mixture V from step S5 to defoam, and finally slowly discharge the material to obtain a safe slurry. The stirring temperature is 25℃±3℃, and the stirring linear velocity in steps S1~S5 is 9~15m / s. In step S6, the slow stirring dispersion has a revolution speed of 10~30rpm and a rotation speed of 0rpm for 10~120min; the slow stirring discharge has a revolution speed of 10~30rpm and a rotation speed of 50~500rpm for 10~120min. In steps S1~S4, the pre-stirring revolution speed is 10~20rpm and the stirring rotation speed is 2000~4000rpm. The pre-stirring time in steps S1, S3, and S4 is 5~15min, the pre-stirring time in step S2 is 20~40min, and the stirring dispersion revolution speed in step S3 is 20~40rpm and the stirring rotation speed is 4000~500rpm. The stirring speed in step S4 is 20-40 rpm, the stirring rotation speed is 4000-5000 rpm, and the stirring time is 180-250 min. In step S5, the stirring speed in step S2 is 20-40 rpm, the stirring rotation speed is 2000-4000 rpm, and the stirring time is 10-20 min. The dispersant in step S2 is a solute, specifically polyvinylpyrrolidone. The dispersant in step S5 is a solvent, specifically isopropanol. The solvent in step S1 is N-methylpyrrolidone. The ceramic material has a particle size D10 of 0.1-0.15 μm or greater than 0.3 μm, D50 of 0.1-2.5 μm, D90 of 0.5-5 μm, and D99 of 1-10 μm, and a specific surface area of ​​1-40 m². 2 / g.

2. The method for preparing the safe slurry as described in claim 1, characterized in that: The solid content of the mixture obtained in steps S1 to S5 is between 20% and 40%.

3. The method for preparing the safe slurry as described in claim 1, characterized in that: The ceramic material is at least one of boehmite and alumina, the binder is at least one of PVDF, SBR, PAA and CMC, and the conductive agent is at least one of conductive carbon black, carbon nanotubes and graphene.

4. A safe slurry prepared by the method for preparing safe slurry according to any one of claims 1 to 3, characterized in that: The components include the following parts by weight: 80-95 parts ceramic material, 2-10 parts binder, 1-5 parts conductive agent, and 0.01-5 parts dispersant.

5. The safe slurry as described in claim 4, characterized in that: The mass ratio of the adhesive to the conductive agent is (1~5):

1.

6. A safety coating structure for batteries, characterized in that: The safety coating structure (1) is formed by coating the safety slurry of any one of claims 4 or 5 on both sides of the current collector (3) in the thickness direction, and the surface of the safety coating structure (1) is further coated with an active material layer (2), the area of ​​the safety coating structure (1) being greater than or equal to the area of ​​the active material layer (2).

7. The battery safety coating structure as described in claim 6, characterized in that: The adhesion force between the safety coating structure (1) and the current collector (3) is greater than or equal to 400 N / m, the thickness of the safety coating structure (1) is 1~5 μm, and the areal density is 7 mg / 1540.25 mm. 2 ~10mg / 1540.25mm 2 .

8. The battery safety coating structure as described in claim 6, characterized in that: The film resistance of the safety coating structure (1) is 0.2~3Ω.

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