Ceramic separator, method for manufacturing a ceramic separator, and lithium battery

Abstract

The present application relates to the technical field of battery separator, in particular to a ceramic separator, a preparation method of the ceramic separator and a lithium battery. The preparation method of the ceramic separator comprises coating a slurry containing ceramic particles and a water-soluble adhesive, a solvent A and a solvent B on a base film, wherein the surface tension of the solvent A and the solvent B is different. The ceramic separator formed by the preparation method comprises a base film and a ceramic coating arranged on the surface of the base film, and the ceramic coating comprises ceramic particles with contact points of adjacent ceramic particles bonded. The preparation method of the ceramic separator provided by the present application makes the exposed surface area of the ceramic particles in the ceramic separator large, without a continuous adhesive film covering, thereby avoiding the adhesive from blocking the micropores on the surface of the ceramic particles. Meanwhile, the ion transmission path is short, and the efficiency of the lithium battery is improved.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, and more specifically, to ceramic separators, methods for preparing ceramic separators, and lithium batteries. Background Technology

[0002] Currently, lithium-ion battery separator coatings primarily utilize a slurry system consisting of ceramic particles, polymer binders, solvents, and additives. This slurry is then applied to the surface of a base film (PE / PP) using gravure or microgravure coating. During the subsequent drying process, the solvent evaporates uniformly, and the polymer binder, as the solvent decreases, precipitates indiscriminately on and between the ceramic particles, forming a film and ultimately creating the coating structure. The resulting coating structure typically consists of a base film, a binder underlayer (usually a continuous binder phase), ceramic particles, and a binder top layer. Due to the simultaneous evaporation of the solvent during drying and the non-directional precipitation of the binder, the binder indiscriminately coats the surface of the ceramic particles and is located between the particles. Therefore, the surface of the ceramic particles is completely encapsulated by a continuous binder film, resulting in a coating with no exposed ceramic particle surfaces or very few exposed surfaces. However, lithium-ion transport requires contact with the ceramic surface or passage through the interparticle spaces. The binder coating on the particles blocks the micropores of the ceramic surface, increasing ion transport impedance. Meanwhile, the precipitation of the binder during the drying process is random, meaning the distribution of the precipitated binder is uncontrollable, resulting in high tortuosity and long ion transport paths.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a ceramic separator, a method for preparing the ceramic separator, and a lithium battery. The method for preparing the ceramic separator provided in this invention results in a large exposed surface area of ​​the ceramic particles, without continuous binder film coating, thus avoiding binder clogging of the micropores on the surface of the ceramic particles. Simultaneously, the ion transport path is short, improving the efficiency of the lithium battery.

[0005] This invention is implemented as follows: In a first aspect, the present invention provides a method for preparing a ceramic diaphragm, comprising: coating a slurry containing ceramic particles and a water-soluble binder, solvent A and solvent B onto a base film, wherein the surface tensions of solvent A and solvent B are different; The slurry meets the following requirement: Ω=(V B +V binder ) / (m 陶瓷 ×DBP), where 0.4≤Ω≤0.8; V B V represents the volume of solvent B, in ml. binder The volume of solids in a water-soluble adhesive is expressed in ml; m 陶瓷The value represents the mass of the ceramic particles, in grams; DBP represents the oil absorption value of the ceramic particles, in ml / g.

[0006] In an optional embodiment, the surface tension of solvent A is lower than that of solvent B; the evaporation rate of solvent A is faster than that of solvent B. In an optional embodiment, solvent A is an alcohol solvent or a ketone solvent, preferably a C1-C5 monohydric alcohol or a C3-C5 ketone solvent; more preferably, it is any one of isopropanol, ethanol, and acetone. Preferably, solvent B is water; Preferably, the slurry further includes additives, wherein the additives include wetting agents, preferably silanes, and more preferably polyether-modified siloxanes; Preferably, the amount of the additive is 1-3% of the mass of the ceramic particles.

[0007] In an optional embodiment, the DV of the ceramic particles 50 =0.6-1.0μm; oil absorption value DBP=70-80ml / 100g.

[0008] In an optional embodiment, the water-soluble adhesive is an aqueous emulsion adhesive; preferably, it is an acrylic adhesive. Preferably, the dry weight of the water-soluble adhesive is 3-6% of the weight of the ceramic particles; Preferably, the average particle size of the water-soluble adhesive is ≤ 150 nm; Preferably, the solid content of the water-soluble adhesive is 12-18%.

[0009] In an optional embodiment, the slurry has a solid content of 30-40%.

[0010] Secondly, embodiments of the present invention provide a ceramic diaphragm, which is prepared by the above-described method for preparing a ceramic diaphragm. The diaphragm includes a base film and a ceramic coating disposed on the surface of the base film. Adjacent ceramic particles in the ceramic coating are bonded at contact points. The exposed surface area of ​​the ceramic particles in the ceramic coating is more than 90%.

[0011] In an optional embodiment, the ceramic particles are connected to the base film by point bonding; Preferably, the ceramic particles are connected to the base film by bonding the contact points of the ceramic particles and the base film.

[0012] In an optional embodiment, the ceramic particles of the ceramic coating have adhesive only at the contact points between adjacent ceramic particles and at the contact points between the ceramic particles and the base film; the surface of the remaining ceramic particles does not contain adhesive.

[0013] Thirdly, the present invention provides a lithium battery comprising the ceramic separator described in the foregoing embodiments.

[0014] The present invention has the following beneficial effects: The present invention provides a ceramic separator and its preparation method. The preparation method makes the ceramic coating of the ceramic separator bonded at the contact points, that is, the contact points of the adjacent ceramic particles are provided with adhesive, while other areas of the ceramic particles do not contain adhesive, that is, the adhesive does not wrap the ceramic particles, thereby increasing the exposed area of ​​the ceramic particles in the ceramic coating, reducing ion transport impedance, and improving battery performance. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a scanning electron microscope image of the coating slurry provided in Embodiment 1 of the present invention; Figure 2 This is a scanning electron microscope image of the coating slurry provided in Comparative Example 3 of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0018] In a first aspect, the present invention provides a ceramic diaphragm comprising a base membrane, which is a commercially available base membrane, such as a PE base membrane, and a ceramic coating disposed on the surface of the base membrane. The ceramic coating is formed by bonding ceramic particles to the surface of the base membrane using an adhesive.

[0019] In this embodiment of the invention, an adhesive is provided at the contact point between the ceramic particles and the base film, that is, the contact point between the ceramic particles and the base film is bonded together, and the two form a spot weld. Furthermore, the adhesive is distributed in a discrete point shape rather than a continuous bond, thereby shortening the ion transport path and improving battery performance.

[0020] Furthermore, the ceramic coating includes ceramic particles bonded at the contact points of adjacent ceramic particles; that is, adhesive is placed at the contact points between adjacent ceramic particles in the ceramic coating, meaning that adjacent ceramic particles are also spot welded; while the surface of other areas of the ceramic particles is exposed, and the surface of the ceramic particles is not covered with adhesive, that is, the ceramic particles are not covered with a continuous adhesive film, which avoids the adhesive clogging the micropores on the surface of the ceramic particles, reduces the ion transport impedance, and improves the battery performance.

[0021] Furthermore, the exposed surface area of ​​the ceramic particles in the ceramic coating is more than 90%. Specifically, in the embodiments of the present invention, the ceramic particles in the ceramic coating have adhesive only at the contact points between adjacent ceramic particles and at the contact points between the ceramic particles and the base film. The surface of the remaining ceramic particles does not contain adhesive, which can ensure the exposed surface area of ​​the ceramic particles, reduce ion impedance, shorten the ion transport path, and improve battery performance.

[0022] Secondly, the present invention provides a method for preparing the ceramic diaphragm described in the foregoing embodiments, comprising the following operations: S1, forming a slurry; A slurry is formed by mixing ceramic particles, a water-soluble binder, solvent A, solvent B, and additives (including but not limited to wetting agents and dispersants). Specifically, a dispersant (including but not limited to CMC), solvent B, and ceramic particles are mixed and ball-milled to form a ceramic dispersion.

[0023] The amount of dispersant used is 1-3% of the mass of the ceramic particles, for example, any value between 1%, 1.5%, 2%, 2.5%, 3%, or 1-3%. The DV of the ceramic particles... 50 =0.6-1.0μm; Oil absorption value (DBP) = 70-80ml / 100g. The DBP testing method is the same as that for carbon black, except that carbon black is replaced with ceramic particles. Using these ceramic particles is beneficial for forming a ceramic coating, thereby improving battery performance.

[0024] The water-soluble adhesive is an aqueous emulsion type adhesive; preferably an acrylic adhesive; this adhesive is the core of the connection, capable of bonding ceramic particles together and adhering them to the surface of the base film.

[0025] The dry weight of the water-soluble adhesive is 3-6% of the weight of the ceramic particles; for example, any value between 3%, 4%, 5%, 6%, or 3-6%. The water-soluble adhesive used in this invention has a drying rate far lower than the conventional 10%, further reducing the amount of water-soluble adhesive used and facilitating spot welding. The average particle size of the water-soluble adhesive is ≤ 150 nm; the solid content of the water-soluble adhesive is 12-18%.

[0026] Furthermore, a water-soluble binder was added to the ceramic dispersion and stirred until homogeneous under low-speed stirring (400-600 rpm).

[0027] Furthermore, solvent A is slowly added dropwise to reduce surface tension, causing the viscosity of the slurry to drop instantly, resulting in better flowability. The dropwise addition rate of solvent A is controlled at 3-5 ml / min to prevent localized demulsification. Simultaneously, a small amount of wetting agent is added to obtain the slurry.

[0028] The wetting agent is a silane, more preferably a polyether-modified siloxane (purchased from Aladdin or McLean); the amount of wetting agent is 1-3% of the mass of the ceramic particles, for example, any value between 1%, 1.5%, 2%, 2.5%, 3% or 1-3%.

[0029] Furthermore, solvent A and solvent B have different surface tensions and different volatility, which allows the water-soluble adhesive to undergo "phase separation" in the later stages of drying and use capillary force to "drive" the adhesive to the contact points between ceramic particles, forming a "spot weld" structure, thereby exposing most of the surface of the ceramic particles.

[0030] Specifically, the surface tension of solvent A is lower than that of solvent B; the evaporation rate of solvent A is faster than that of solvent B. Therefore, the difference in evaporation rate and solubility of the binary solvent system can be used to force the binder to undergo "phase separation" in the later stage of drying, forming spot welding, thus avoiding the binder from encapsulating ceramic particles and forming a continuous binder.

[0031] Specifically, solvent A is a low-surface-tension, volatile solvent with a surface tension of 20-28 mN / m. Examples include, but are not limited to, alcohols or ketones, preferably C1-C5 monohydric alcohols or C3-C5 ketones; more preferably, any one of isopropanol, ethanol, and acetone. The use of low-surface-tension solvent A in the initial stage reduces the surface tension of the slurry, ensuring good wetting of the micropores of the substrate film and ceramic particles.

[0032] Solvent B is a high-surface-tension, non-volatile solvent with a surface tension of 35-73 mN / m. Examples include, but are not limited to, solvent B being water (derived from deionized water and the moisture inherent in water-soluble adhesives). As a carrier in the later stages of drying, the high surface tension of solvent B is crucial for generating the "capillary migration driving force."

[0033] The inventors speculate that the "spot welding" process using solvent A and solvent B in the embodiments of the present invention is roughly as follows: Stage 1: Solvent A evaporates rapidly, at which point the slurry concentrates and the ceramic particles move closer together.

[0034] Stage 2: Solvent A has basically evaporated, and the surface tension of the slurry increases sharply. The originally stretched liquid film begins to become unstable, resulting in a "phase separation tendency due to surface energy differences".

[0035] Stage 3 (Capillary Liquid Bridge Migration): As solvent B further evaporates, the liquid surface contracts. According to the capillary pressure principle in physics, the liquid tends to remain at the narrowest slit with the smallest radius of curvature between ceramic particles, that is, it automatically contracts to the contact point of the ceramic particles with the lowest energy. The binder then migrates, exposing most of the surface of the ceramic particles.

[0036] Driving force 1 (surface tension): Solvent A with low surface tension is enriched at the gas-liquid interface, generating Marangoni flow.

[0037] Driving force 2 (capillary pressure): The liquid is forced to contract, seeking the point of lowest energy—the narrow gap between ceramic particles or the narrow gap between ceramic particles and the base film (the point of minimum radius of curvature).

[0038] Result: The binder microphase was encapsulated in solvent B and was "drawn" to the contact point of the ceramic particles by the strong capillary "suction force".

[0039] Stage 4 (Cure and Set): Solvent B completely evaporates, the binder cures at the contact points, forming point-like liquid bridges, while the remaining surface of the particles is clean and free of adhesive.

[0040] Furthermore, in the embodiments of the present invention, the slurry meets the following requirement: Ω=(V B +V binder ) / (m 陶瓷 ×DBP), where 0.4≤Ω≤0.8; V B V represents the volume of solvent B, in ml. binder This indicates the volume of solids in a water-soluble adhesive; the unit is ml; m 陶瓷 The value of Ω represents the mass of the ceramic particles, expressed in grams (g); DBP represents the oil absorption value of the ceramic particles, expressed in ml / g. If Ω < 0.4, the slurry has broken into isolated small points. If the binder has not completed its precipitation before Ω drops to 0.4, it will lose its fluidity due to insufficient liquid and will directly "stick" to the ceramic particles in place, rather than into the gaps. If Ω > 0.8, the ceramic particles are still connected as a single sheet of liquid, and the binder is still in a "floating" state, without generating a centripetal force to converge towards the contact point. In this embodiment of the invention, Vb is calculated based on Ω.

[0041] It should be noted that the amount of solvent B mentioned above refers to the amount of water used in water-based emulsion adhesives, that is, the amount of solvent B added separately.

[0042] V binderThe volume representing the solid content of a water-soluble adhesive is calculated as: [mass of the emulsion formed by the water-soluble adhesive * solid content (%)] / density, where the density is 1 g / ml.

[0043] The DBP value mentioned above refers to the oil absorption value of ceramic particles, expressed in ml / g. This DBP value can be obtained through unit conversion.

[0044] Furthermore, the solid content of the slurry is 30-40%; for example, any value between 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or 30-40%.

[0045] S2, coating; The slurry formed in S1 is applied to the base film and dried to form a ceramic coating on the surface of the base film.

[0046] Thirdly, embodiments of the present invention provide a lithium battery comprising the above-mentioned ceramic separator.

[0047] The relevant performance testing methods of this invention are as follows: 1. The increment of the Grurlery value (s / 100cc) shall be tested in accordance with GB / T 36363-2018.

[0048] 2. Wetting speed test: (1) Cut the diaphragm to be tested into strips of 0.5 cm × 25 cm.

[0049] (2) Fix the diaphragm strip to be tested horizontally on the experimental support.

[0050] (3) Use a pipette to draw 20 μL of electrolyte and drop it onto the diaphragm to be tested, while starting the timer.

[0051] (4) Stop timing after 60 s, immediately mark the diffusion position of the electrolyte with a marker, and measure the diffusion distance.

[0052] (5) Calculate according to the following formula: Wetting rate = diffusion distance / diffusion time.

[0053] 3. Ionic conductivity test (1) Cut the diaphragm to be tested into a 31mm round piece, measure the thickness, and then bake it in a vacuum at 45℃ for more than 2 hours.

[0054] (2) Place the diaphragm to be tested into the mold provided with the instrument, place the positioning ring on it and fix it.

[0055] (3) Set the instrument parameters to perform EIS testing.

[0056] (4) Repeat the above steps to test the EIS data of the 1st, 2nd, 3rd and 4th membrane layers respectively.

[0057] (5) The membrane ionic conductivity was obtained by fitting and calculating the data using the instrument’s built-in software, and the average value was calculated for 5 parallel groups.

[0058] 4. Tortuousness test τ=[(ε×G0) / (ε0×G)] 1 / 2 Where ε is the porosity of the sample, G is the Gurley value of the sample, ε0 is the porosity of the base membrane, and G0 is the Gurley value of the base membrane; Porosity was tested in accordance with GB / T 36363-2018.

[0059] Peel strength testing shall be conducted in accordance with GB / T 2790-1995.

[0060] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0061] Example 1 This embodiment provides a method for preparing a ceramic diaphragm, including: Boehmite (purchased from Liyang Anode Shield New Material Technology Co., Ltd., BP07) was selected as the ceramic material; the oil absorption value of boehmite was measured and the average value was taken; the DBP of boehmite was 75ml / 100g.

[0062] 100g ceramic particles, 1g CMC dispersant (purchased from Shenzhen Yite Technology, S30-H6), approximately 5g binder (purchased from Indira, LA133) (33g emulsion, solid content 15%), 1g wetting agent (polyether modified siloxane, purchased from BYK Chemical, BYK-ET3036); Ω is 0.6; additionally added solvent B, water 40ml (total water volume 68ml, including 28ml water from the emulsion), and solvent A, isopropanol 131ml. The calculation of Ω is as follows: [40 + (33 * 0.15)] / (100 * 0.75) = 0.6.

[0063] Dissolve 1g of dispersant CMC in 40ml of deionized water, then add boehmite powder and disperse using a ball mill, controlling the DV. 50 =0.8±0.2um.

[0064] Under low-speed stirring (500 rpm), 33 g of polymer binder emulsion with a solid content of 15% and a water content of 75% was added to the above dispersion; its dry weight accounted for 5% of the mass of the ceramic particles.

[0065] Slowly add 131 ml of isopropanol (solvent A) to reduce surface tension; the slurry viscosity drops instantly, improving its fluidity. The dropping rate is controlled at 5 mL / min to prevent localized demulsification. Add a small amount of wetting agent, polyether-modified siloxane, at 1% of the ceramic particle mass, to obtain a coating slurry with a solid content of 35%.

[0066] A microgravure coating machine applies the slurry to the PE base film, with a coating thickness of 2μm. Then, it is dried in stages: 60℃ for 20 seconds (removing most of the good solvent); and 80℃ for 20 seconds (solvent B is first enriched and then evaporated, and the binder shrinks and is fixed towards the contact point).

[0067] Examples 2-4 Examples 2-4 provide a method for preparing a ceramic diaphragm. This method is identical to the method in Example 1, except for the amount of raw materials used. The contents of all other substances are the same as in Example 1. Details are as follows: Example 2: Ω=0.4; Coating slurry solid content 35%; Ceramic particle DBP=75ml / 100g; 100g ceramic particles; 1g dispersant; 5g binder (33g emulsion); 1g wetting agent; 25ml deionized water (total water volume is 53ml, including 28ml water in the emulsion); 146ml isopropanol.

[0068] Example 3: Ω=0.8; Coating slurry solid content 35%; Ceramic particle DBP=75ml / 100g; 100g ceramic particles; 1g dispersant; 5g binder (33g emulsion); 1g wetting agent; 55ml deionized water (total water volume is 83ml, including 28ml water in the emulsion); 116ml isopropanol.

[0069] Example 4 Ω=0.6; Coating slurry solid content 35%; Ceramic particle DBP=70ml / 100g; 100g ceramic particles; 1g dispersant; 5g binder (33g emulsion, 15% solids content); 1g wetting agent; V B 37ml of deionized water (total water volume is 65ml, including 28ml of water in the emulsion); 134ml of isopropanol.

[0070] Example 5 Ω=0.6; Coating slurry solid content 35%; Ceramic particle DBP=80ml / 100g; 100g ceramic particles; 1g dispersant; 5g binder; (33g emulsion, 15% solids content); 1g wetting agent; V B 43ml of deionized water (total water volume is 71ml, including 28ml of water in the emulsion); 128ml of isopropanol.

[0071] Example 6 Ω=0.6; Coating slurry solid content: 35%; Ceramic particle DBP=75ml / 100g; 100g ceramic particles; 1g dispersant; 3g binder (20g emulsion, 15% solids content); 1g wetting agent; V B 42ml of deionized water (total water volume is 59ml, including 17ml of water in the emulsion); 136ml of isopropanol.

[0072] Example 7 Ω=0.6; Coating slurry solid content 35%; Ceramic particle DBP=75ml / 100g; 100g ceramic particles; 1g dispersant; 6g binder (40g emulsion, 15% solids content); 1g wetting agent; V B 39ml of deionized water (total water volume is 73ml, including 34ml of water in the emulsion) and 128ml of isopropanol.

[0073] Example 8 Ω=0.6; Coating slurry solid content 35%; Ceramic particle DBP=75ml / 100g; 100g ceramic particles; 1g dispersant; 5g binder (42g emulsion, 12% solids content); 1g wetting agent; V B 40ml of deionized water (total water volume is 77ml, including 37ml of water in the emulsion) and 122ml of isopropanol.

[0074] Example 9 Ω=0.6; Coating slurry solid content 35%; Ceramic particle DBP=75ml / 100g; 100g ceramic particles; 1g dispersant; 5g binder (28g emulsion, 18% solids content); 1g wetting agent; V B 40ml of deionized water (total water volume is 52ml, including 12ml of water in the emulsion) and 136ml of isopropanol.

[0075] Comparative Examples 1-3 Comparative Examples 1-3 provide a method for preparing a ceramic diaphragm. The operation of this method is the same as that of Example 1, except that the amount of raw materials used is different. The content of other substances is the same as that of Example 1, as detailed below: Comparative Example 1 Ω=0.2; Ceramic slurry solid content 35%; Ceramic particles DBP=75ml / 100g; 100g ceramic particles; 1g dispersant; 5g binder (33g emulsion); 1g wetting agent; 10ml of deionized water (total water volume is 38ml, including 28ml of water in the emulsion); 161ml of isopropanol.

[0076] Comparative Example 2 Ω=1.0; Ceramic slurry solid content 35%; Ceramic particles DBP=75ml / 100g; 100g ceramic particles; 1g dispersant; 5g binder (33g emulsion); 1g wetting agent; 70ml of deionized water (total water volume is 98ml, including 28ml of water from the emulsion); 101ml of isopropanol.

[0077] Comparative Example 3 The ceramic slurry uses only deionized water and does not use solvent A. The slurry contains 100g of ceramic particles, 1g of dispersant, 5g of binder (33g of emulsion), 1g of wetting agent, and 151ml of deionized water (total water volume is 179ml, including 28ml of water from the emulsion).

[0078] Performance testing The ceramic diaphragms of Examples 1-9 and Comparative Examples 1-3 were subjected to performance tests, and the test results are shown in Table 1 below.

[0079] Table 1 Test Results

[0080] As shown in Table 1, (1) Ω in the range of 0.4-0.8 is the core to achieving "point adhesion". Comparative Example 1 (Ω=0.2) has good air permeability but its peel strength drops sharply to 13 N / m, indicating that the solvent dries up too early, causing the adhesive to fail to generate capillary migration; while Comparative Example 2 (Ω=1.0) has high peel strength, but the increase in air permeability soars to 48 s / 100cc and the conductivity drops sharply, indicating that the liquid fills the gaps, causing the adhesive to form a film indiscriminately and block the pores. Only when Ω is in the range of 0.4-0.8 (Examples 1-3) can the surface tension gradient of the binary solvent and the capillary suction force work together perfectly to precisely drive the adhesive to shrink to the particle contact point, achieving a balance between high adhesion and high permeability.

[0081] (2) Data from Example 4 (DBP=70ml / 100g) and Example 5 (DBP=80ml / 100g) show that as long as Ω is within the range of 0.4-0.8, the amount of water in the formula can be dynamically adjusted. Regardless of the fluctuation of oil absorption value between batches of powder, the final air permeability (4~6 s / 100cc) and peel strength (39~42 N / m) remain at an extremely high level.

[0082] (3) Examples 6 and 7 tested the effects of different adhesive dosages (3% and 6%). Example 6, even with only a very low adhesive dosage of 3%, achieved an effective peel strength of 30 N / m (meeting the coating process requirements) due to the "precise spot welding" effect of the dotted structure, and its ionic conductivity reached the highest in the group at 1.3612 mS / cm. Example 7 (6% adhesive dosage) achieved an even higher peel strength of 50 N / m, surpassing the bonding effect of the traditional 10% adhesive dosage (Comparative Example 3). This demonstrates that "discrete dotted bonding" greatly improves the efficiency of adhesive use.

[0083] (4) By adjusting the proportion of added water, Examples 8 (12% concentration emulsion) and 9 (18% concentration emulsion) also achieved excellent performance almost identical to the baseline group (Example 1). This indicates that the core mechanism of the present invention lies in the "volume matching of the added free high surface tension solvent B with the liquid bridge", and is not limited by the proportion of water in the emulsion from the upstream supplier, further expanding the flexibility of patent implementation.

[0084] Detection example Scanning electron microscopy was performed on the coating slurries of Example 1 and Comparative Example 3. The results are shown in [reference needed]. Figure 1 and Figure 2 .according to Figure 1 and Figure 2 As can be seen, the "spot welding" method used in this embodiment of the invention allows more ceramic particles to be retained, thereby improving battery performance.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a ceramic diaphragm, characterized in that, include: A slurry containing ceramic particles, a water-soluble binder, solvent A, and solvent B is coated onto a base film, wherein solvent A and solvent B have different surface tensions. The slurry meets the following requirement: Ω=(V B +V binder ) / (m 陶瓷 ×DBP), where 0.4≤Ω≤0.8; V B V represents the volume of solvent B, in ml. binder The volume of solids in a water-soluble adhesive is expressed in ml; m 陶瓷 The value represents the mass of the ceramic particles, in grams; DBP represents the oil absorption value of the ceramic particles, in ml / g.

2. The preparation method according to claim 1, characterized in that, The raw materials forming the slurry meet at least one of the following requirements: (1) The surface tension of solvent A is lower than that of solvent B; the evaporation rate of solvent A is faster than that of solvent B; (2) The water-soluble adhesive is a water-based emulsion adhesive; (3) The dry weight of the water-soluble adhesive is 3-6% of the weight of the ceramic particles; (4) The average particle size of the water-soluble adhesive is ≤ 150 nm; (5) The solid content of the water-soluble adhesive is 12-18%; (6) The DV of the ceramic particles 50 =0.6-1.0μm; Oil absorption value DBP = 70-80ml / 100g.

3. The preparation method according to claim 1, characterized in that, The slurry also includes additives, wherein the additives include wetting agents.

4. The preparation method according to claim 3, characterized in that, The raw materials forming the slurry meet at least one of the following requirements: (1) The wetting agent is a silane-based substance; (2) The amount of the additive is 1-3% of the mass of the ceramic particles; (3) The water-soluble adhesive is an acrylate adhesive.

5. The preparation method according to claim 3, characterized in that, The raw materials forming the slurry meet at least one of the following requirements: (1) The surface tension of solvent A is 20-28 mN / m, and the surface tension of solvent B is 35-73 mN / m; (2) Solvent A is an alcohol solvent or a ketone solvent; (3) Solvent B is water; (4) The wetting agent is a polyether-modified siloxane.

6. The preparation method according to claim 1, characterized in that, The solid content of the slurry is 30-40%.

7. A ceramic diaphragm, characterized in that, It is prepared by the method of ceramic membrane preparation according to any one of claims 1-6, comprising a base membrane and a ceramic coating disposed on the surface of the base membrane, wherein adjacent ceramic particles in the ceramic coating are bonded at contact points, and the exposed surface area of ​​the ceramic particles in the ceramic coating is more than 90%.

8. The ceramic diaphragm according to claim 7, characterized in that, The ceramic diaphragm meets the following requirements: The ceramic particles are connected to the base film by point bonding.

9. The ceramic diaphragm according to claim 7, characterized in that, The ceramic diaphragm meets at least one of the following requirements: (1) The ceramic particles are connected to the base film by bonding the contact points of the ceramic particles and the base film. (2) Except for the contact points between adjacent ceramic particles and the contact points between the ceramic particles and the base film, the surface of the remaining ceramic particles does not contain adhesive.

10. A lithium battery, characterized in that, It includes the ceramic diaphragm as described in claim 7.

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