Composite coating diaphragm with low internal stress and low water content and preparation method thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly discloses a composite coating diaphragm with low internal stress and low water content, which comprises a battery diaphragm and coatings coated on two sides of the battery diaphragm, the composite coating is formed on the two sides of the battery diaphragm after the two sides of the battery diaphragm are coated with coating slurry and then are subjected to drying treatment and annealing cooling treatment; the coating slurry comprises the following raw materials in parts by weight: 60-120 parts of ceramic particles, 60-120 parts of reinforced particles, 1-2 parts of a dispersing agent, 25-35 parts of an adhesive and 240 parts of deionized water. The invention provides a composite coating diaphragm with low internal stress and low water content and a preparation method thereof, so as to improve the quality and performance of a coated ceramic diaphragm, thereby improving the overall performance and reliability of a lithium ion battery.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a composite coating diaphragm with low internal stress and low water content and a preparation method thereof. Background Art

[0002] Lithium-ion battery technology continues to develop in modern society, and its application scope is becoming increasingly wide. As a key component to isolate the positive and negative electrodes of the battery, the coated diaphragm can block the current flow of the positive and negative electrodes when the battery heats up to prevent the battery from exploding. Among them, ceramic coated diaphragms are widely used due to their good thermal stability and high strength. However, in the actual coating process, ceramic diaphragms are prone to internal stress. The emergence of this internal stress will affect the mechanical strength of the diaphragm, such as tensile strength and tear strength. These strength indicators directly affect whether the diaphragm will rupture or puncture during use, thereby affecting the safety of the battery. In addition, since the diaphragm has a certain water content, water vapor will be generated when the battery is used to generate heat, causing the battery to bulge, affecting the battery life. Finally, the hardness of a single ceramic coated diaphragm is too high, which is easy to cause mechanical wear in the actual production process, and the production cost is too high. Summary of the invention

[0003] The purpose of the present invention is to overcome the above problems existing in the prior art and provide a composite coating diaphragm with low internal stress and low water content and a preparation method thereof, so as to improve the quality and performance of the coated ceramic diaphragm, thereby improving the overall performance and reliability of lithium-ion batteries.

[0004] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0005] An embodiment of the first aspect of the present invention provides a composite coating separator with low internal stress and low water content, comprising a battery separator and a coating applied on both sides of the battery separator;

[0006] The composite coating is a coating formed on both sides of the battery separator after coating slurry on both sides of the battery separator, and then drying, annealing and cooling treatment;

[0007] The coating slurry comprises the following raw materials in parts by weight: 60-120 parts of ceramic particles, 60-120 parts of reinforcing particles, 1-2 parts of dispersant, 25-35 parts of adhesive, and 240 parts of deionized water.

[0008] Further, the D50 of the ceramic particles is not greater than 1.5 μm;

[0009] The D50 of the reinforcing particles is not greater than 1.3 μm;

[0010] The D50 of the ceramic particles is greater than the D50 of the reinforcing particles.

[0011] Furthermore, the mass ratio of the ceramic particles to the reinforcement particles is 1:(0.5-2), preferably, the mass ratio of the ceramic particles to the reinforcement particles is 1:1.

[0012] Further, the reinforcing particles are boehmite particles;

[0013] The dispersant is a carboxylic acid dispersant;

[0014] The binder is any one or more of sodium carboxymethyl cellulose and acrylate emulsion mixed in any proportion.

[0015] Furthermore, the model of the acrylic emulsion is LIB-S105.

[0016] The embodiment of the second aspect of the present invention provides a method for preparing a composite coating diaphragm with low internal stress and low water content, the preparation method comprising the following steps:

[0017] S1: Raw material mixing

[0018] In a high-speed stirring tank, ceramic particles, reinforcing particles and deionized water are added, and after mixing and stirring, a mixed slurry is formed;

[0019] S2: Add dispersant

[0020] Adding a dispersant into the mixed slurry, mixing and stirring to form a dispersed slurry;

[0021] S3: Adding binder

[0022] Adding a binder into the dispersed slurry, mixing and stirring to form a coating slurry;

[0023] S4: coating and drying

[0024] The coating slurry is applied to the surface of the battery separator by using a roller coater, and the coated battery separator is dried;

[0025] S5: Annealing and curing

[0026] The battery separator after drying is annealed and cooled to room temperature to prepare a composite coating separator.

[0027] Furthermore, during the mixing and stirring processes in step S1, step S2 and step S3, the mixing and stirring rates are all 25-45 rpm / min, and the mixing and stirring time is all 30-60 min.

[0028] Furthermore, in step S4, during the coating process, the coating rate is 80-130 m / min, and the coating environment temperature is 24-26°C.

[0029] Furthermore, in step S4, during the drying process, the drying temperature is 65-75° C. and the drying time is 18-24 min.

[0030] Furthermore, in step S5, the cooling rate of the annealing cooling treatment is 1.0-3.0°C / min.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The low internal stress and low water content composite coating diaphragm provided by the present invention is a battery diaphragm coated with a composite coating on both sides. The composite coating is a coating formed on both sides of the battery diaphragm after coating a coating slurry on both sides of the battery diaphragm and then undergoing a drying treatment and an annealing and cooling treatment. The main components of the coating slurry include ceramic particles, reinforcing particles, a dispersant, a binder and deionized water.

[0033] 2. In the present invention, ceramic particles and reinforcing particles are used as functional coatings to reduce the internal stress and water content of the battery separator. Specifically, the composite coating combines the characteristics of ceramic and reinforcing particles. The reinforcing particles are boehmite particles. The D50 of the ceramic particles is greater than the D50 of the reinforcing particles. The larger-sized ceramic particles form additional gaps in the coating layer, which can promote the rapid evaporation of water and provide the battery separator with a larger free space for movement, thereby effectively reducing the internal stress generated by the battery separator during use. The reinforcing particles are boehmite particles, which have the characteristics of reduced hardness and can reduce mechanical wear during the coating process. Therefore, the use of ceramic particles and reinforcing particles as functional coatings combines the advantages of ceramic particles and reinforcing particles, which not only improves the mechanical strength of the battery separator, but also ensures the stability and safety of the prepared battery in long-term cyclic use when the battery separator is applied to the battery.

[0034] 3. In the present invention, after the coating slurry is coated on the surface of the battery separator using a roller coater, it is then dried to allow the coating slurry to be initially solidified on the surface of the battery separator. After the drying, it is annealed and cooled. The cooling rate of the annealing and cooling treatment is set so that the coating slurry initially solidified on the surface of the battery separator is gradually cooled until a composite coating is formed on the surface of the battery separator, thereby further enhancing the stability and performance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0036] Figure 1 It is a flow chart of an embodiment of the second aspect of the present invention. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] An embodiment of the first aspect of the present invention provides a composite coating separator with low internal stress and low water content, comprising a battery separator and a composite coating coated on both sides of the battery separator;

[0039] The composite coating is a coating formed on both sides of the battery separator after the coating slurry is applied on both sides of the battery separator, and then subjected to drying treatment, annealing and cooling treatment;

[0040] The coating slurry includes the following raw materials in parts by weight: 60-120 parts of ceramic particles, 60-120 parts of reinforcing particles, 1-2 parts of dispersant, 25-35 parts of adhesive, and 240 parts of deionized water;

[0041] Preferably, the coating slurry comprises the following raw materials in parts by weight: 95 parts of ceramic particles, 95 parts of reinforcing particles, 1.5 parts of dispersant, 30.65 parts of binder, and 240 parts of deionized water;

[0042] In the raw materials of the coating slurry, the D50 of the ceramic particles is not greater than 1.5 μm; the D50 of the reinforcing particles is not greater than 1.3 μm; and the D50 of the ceramic particles is greater than the D50 of the reinforcing particles;

[0043] The mass ratio of the ceramic particles to the reinforcing particles is 1:(0.5-2), preferably, the mass ratio of the ceramic particles to the reinforcing particles is 1:1;

[0044] Wherein, the reinforcing particles are boehmite particles;

[0045] The dispersant is a carboxylic acid dispersant;

[0046] The binder is any one or more of sodium carboxymethyl cellulose and acrylate emulsion mixed in any proportion. Preferably, the binder is acrylate emulsion, and the selected acrylate emulsion is an ultra-high peel strength diaphragm binder, model LIB-S105; the use of ultra-high peel strength diaphragm binder acrylate emulsion can further improve the stability of the prepared coating slurry, thereby improving the adhesion between the composite coating and the battery diaphragm, and further allowing the prepared composite coating diaphragm to have lower internal stress and water content.

[0047] like Figure 1As shown, an embodiment of the second aspect of the present invention provides a method for preparing a composite coating diaphragm with low internal stress and low water content, the preparation method comprising the following steps:

[0048] S1: Raw material mixing

[0049] In a high-speed stirring tank, ceramic particles, reinforcing particles and deionized water are added, and after mixing and stirring, a mixed slurry is formed;

[0050] S2: Add dispersant

[0051] Adding a dispersant into the mixed slurry, mixing and stirring to form a dispersed slurry;

[0052] S3: Adding binder

[0053] Adding a binder into the dispersed slurry, mixing and stirring to form a coating slurry;

[0054] In the mixing and stirring process in step S1, step S2 and step S3, the mixing and stirring rate is 25-45 rpm / min, and the mixing and stirring time is 30-60 min;

[0055] Wherein, preferably, the mixing stirring rate is 35 rpm / min, and the mixing stirring time is 40 min;

[0056] S4: coating and drying

[0057] The coating slurry is coated on the surface of the battery separator by using a roller coater, the coating speed is 80-130 m / min, the coating environment temperature is 24-26° C., and the coated battery separator is dried at 65-75° C. for 18-24 min;

[0058] Preferably, the coating speed is 120 m / min, the coating environment temperature is 25°C; the drying temperature is 70°C, and the drying time is 20 min;

[0059] S5: Annealing and curing

[0060] The dried battery separator is subjected to annealing and cooling treatment at a cooling rate of 1.0-3.0°C / min. After cooling to room temperature, a composite coating is formed on both sides of the battery separator to prepare a composite coating separator;

[0061] Preferably, during the annealing and cooling process, the cooling rate is 2°C / min.

[0062] The following are specific examples. In the following examples, unless otherwise specified, all raw materials can be obtained from commercial sources.

[0063] In the following examples, the dispersants are all carboxylic acid dispersants, with a model of VK.DP310, produced by Foshan Ward Polymer Materials Co., Ltd.

[0064] Example 1

[0065] This embodiment provides a composite coating diaphragm with low internal stress and low water content, including a battery diaphragm and a composite coating coated on both sides of the battery diaphragm, wherein the composite coating is a coating formed on both sides of the battery diaphragm after coating the coating slurry on both sides of the battery diaphragm, and then drying, annealing and cooling treatment;

[0066] The coating slurry includes the following raw materials in parts by weight: 95 parts of ceramic particles, 95 parts of reinforcing particles, 1.5 parts of dispersant, 30.65 parts of adhesive, and 240 parts of deionized water;

[0067] The D50 of ceramic particles is 1.5μm; the D50 of reinforcing particles is 1.3μm;

[0068] The reinforcing particles are boehmite particles;

[0069] The adhesive is acrylic emulsion, model LIB-S105.

[0070] This embodiment also provides a method for preparing a composite coating diaphragm with low internal stress and low water content, the preparation method comprising the following steps:

[0071] S1: According to the formula of the coating slurry provided in this embodiment, ceramic particles, reinforcing particles, dispersant, adhesive, and deionized water are weighed, and ceramic particles, reinforcing particles, and deionized water are added into a high-speed stirring tank, and mixed and stirred to form a mixed slurry;

[0072] S2: adding a dispersant into the mixed slurry, mixing and stirring to form a dispersed slurry;

[0073] S3: Adding a binder into the dispersed slurry, mixing and stirring to form a coating slurry;

[0074] Wherein, during the mixing and stirring process in step S1, step S2 and step S3, the mixing and stirring rate is 35 rpm / min, and the mixing and stirring time is 40 min;

[0075] S4: using a roller coater to apply the coating slurry to the surface of the battery separator, the coating speed is 120 m / min, the coating environment temperature is 25° C., and the coated battery separator is dried at 70° C. for 20 min;

[0076] S5: The battery separator after drying is subjected to annealing and cooling treatment at a cooling rate of 2°C / min. After cooling to room temperature, a composite coating is formed on both sides of the battery separator to prepare a composite coating separator.

[0077] Example 2

[0078] This embodiment provides a composite coating diaphragm with low internal stress and low water content, including a battery diaphragm and a composite coating coated on both sides of the battery diaphragm, wherein the composite coating is a coating formed on both sides of the battery diaphragm after coating the coating slurry on both sides of the battery diaphragm, and then drying, annealing and cooling treatment;

[0079] The coating slurry includes the following raw materials in parts by weight: 60 parts of ceramic particles, 120 parts of reinforcing particles, 1 part of dispersant, 35 parts of adhesive, and 240 parts of deionized water;

[0080] The D50 of ceramic particles is 1.5μm; the D50 of reinforcing particles is 1.3μm;

[0081] The reinforcing particles are boehmite particles;

[0082] The adhesive is acrylic emulsion, model LIB-S105.

[0083] This embodiment also provides a method for preparing a composite coating diaphragm with low internal stress and low water content, the preparation method comprising the following steps:

[0084] S1: According to the formula of the coating slurry provided in this embodiment, ceramic particles, reinforcing particles, dispersant, adhesive, and deionized water are weighed, and ceramic particles, reinforcing particles, and deionized water are added into a high-speed stirring tank, and mixed and stirred to form a mixed slurry;

[0085] S2: adding a dispersant into the mixed slurry, mixing and stirring to form a dispersed slurry;

[0086] S3: Adding a binder into the dispersed slurry, mixing and stirring to form a coating slurry;

[0087] In the mixing and stirring process in step S1, step S2 and step S3, the mixing and stirring rate is 25 rpm / min, and the mixing and stirring time is 60 min;

[0088] S4: using a roller coater to coat the coating slurry on the surface of the battery separator, the coating speed is 80 m / min, the coating environment temperature is 26° C., and the coated battery separator is dried at 75° C. for 18 min;

[0089] S5: The battery separator after drying is subjected to annealing and cooling treatment at a cooling rate of 3.0°C / min. After cooling to room temperature, a composite coating is formed on both sides of the battery separator to prepare a composite coating separator.

[0090] Example 3

[0091] This embodiment provides a composite coating diaphragm with low internal stress and low water content, including a battery diaphragm and a composite coating coated on both sides of the battery diaphragm, wherein the composite coating is a coating formed on both sides of the battery diaphragm after coating the coating slurry on both sides of the battery diaphragm, and then drying, annealing and cooling treatment;

[0092] The coating slurry includes the following raw materials in parts by weight: 120 parts of ceramic particles, 60 parts of reinforcing particles, 2 parts of dispersant, 25 parts of adhesive, and 240 parts of deionized water;

[0093] The D50 of ceramic particles is 1.5μm; the D50 of reinforcing particles is 1.3μm;

[0094] The reinforcing particles are boehmite particles;

[0095] The adhesive is acrylic emulsion, model LIB-S105.

[0096] This embodiment also provides a method for preparing a composite coating diaphragm with low internal stress and low water content, the preparation method comprising the following steps:

[0097] S1: According to the formula of the coating slurry provided in this embodiment, ceramic particles, reinforcing particles, dispersant, adhesive, and deionized water are weighed, and ceramic particles, reinforcing particles, and deionized water are added into a high-speed stirring tank, and mixed and stirred to form a mixed slurry;

[0098] S2: adding a dispersant into the mixed slurry, mixing and stirring to form a dispersed slurry;

[0099] S3: Adding a binder into the dispersed slurry, mixing and stirring to form a coating slurry;

[0100] In the mixing and stirring process in step S1, step S2 and step S3, the mixing and stirring rate is 45 rpm / min, and the mixing and stirring time is 30 min;

[0101] S4: using a roller coater to apply the coating slurry to the surface of the battery separator, the coating speed is 130 m / min, the coating environment temperature is 24° C., and the coated battery separator is dried at 65° C. for 24 min;

[0102] S5: The battery separator after drying is subjected to annealing and cooling treatment at a cooling rate of 1.0°C / min. After cooling to room temperature, a composite coating is formed on both sides of the battery separator to prepare a composite coating separator.

[0103] Example 4

[0104] This embodiment provides a composite coating diaphragm with low internal stress and low water content. The difference from Embodiment 1 is that in this embodiment, the binder is replaced by sodium carboxymethyl cellulose.

[0105] This embodiment also provides a method for preparing a composite coating diaphragm with low internal stress and low water content. The preparation method is carried out with reference to the preparation method provided in Example 1.

[0106] Comparative Example 1

[0107] This comparative example provides a composite coating diaphragm with low internal stress and low water content. The difference from Example 1 is that in this comparative example, the D50 of the ceramic particles is 2.0 μm.

[0108] This comparative example also provides a method for preparing a composite coating diaphragm with low internal stress and low water content. The preparation method is carried out with reference to the preparation method provided in Example 1.

[0109] Comparative Example 2

[0110] This comparative example provides a composite coating diaphragm with low internal stress and low water content. The difference from Example 1 is that in this comparative example, the reinforcing particles are replaced with calcium carbonate powder, and the D50 of the reinforcing particles is 1.3 μm.

[0111] This comparative example also provides a method for preparing a composite coating diaphragm with low internal stress and low water content. The preparation method is carried out with reference to the preparation method provided in Example 1.

[0112] Comparative Example 3

[0113] This comparative example provides a composite coating diaphragm with low internal stress and low water content, which is different from Example 1 in that, in this comparative example, the dispersant is citric acid.

[0114] This comparative example also provides a method for preparing a composite coating diaphragm with low internal stress and low water content. The preparation method is carried out with reference to the preparation method provided in Example 1.

[0115] Comparative Example 4

[0116] This comparative example provides a composite coating diaphragm with low internal stress and low water content, and its raw material composition is made with reference to Example 1.

[0117] This comparative example also provides a method for preparing a composite coating diaphragm with low internal stress and low water content. In this preparation method, compared with Example 1, in step S4, during the coating process, the coating rate is replaced with 60 m / min, and the coating environment temperature is increased to 30°C, and the remaining operation processes are carried out with reference to Example 1.

[0118] Comparative Example 5

[0119] This comparative example provides a composite coating diaphragm with low internal stress and low water content, and its raw material composition is made with reference to Example 1.

[0120] This comparative example also provides a method for preparing a composite coating diaphragm with low internal stress and low water content. In this preparation method, compared with Example 1, in step S4, during the drying process, the drying temperature is replaced with 85°C, and the drying time is shortened to 10 minutes. The remaining operation processes are carried out with reference to Example 1.

[0121] Comparative Example 6

[0122] This comparative example provides a composite coating diaphragm with low internal stress and low water content, and its raw material composition is made with reference to Example 1.

[0123] This comparative example also provides a method for preparing a composite coating diaphragm with low internal stress and low water content. In the preparation method, compared with Example 1, in step S5, the cooling rate of the annealing cooling treatment is replaced with 5°C / min, and the remaining operation processes are carried out with reference to Example 1.

[0124] Experimental example

[0125] The internal stress and water content of the composite coating membranes prepared in Examples 1-4 and Comparative Examples 1-6 were tested, and compared with the internal stress and water content of ordinary ceramic coating membranes, and the internal stress change rate (%) and the water content change rate (%) were calculated. The calculation formula is as follows:

[0126]

[0127] The calculation results are shown in Table 1;

[0128] Table 1

[0129]

[0130]

[0131] It can be seen from the data in Table 1 that, compared with the common ceramic coating diaphragm, the composite coating diaphragm prepared in Example 1 has its internal stress reduced by 54% and its water content reduced by 32%.

[0132] By comparing the data in comparative example 1 with the data in example 1, it can be seen that increasing the ceramic particles will lead to a decrease in the porosity of the coating, thereby affecting the volatilization of water;

[0133] By comparing the data in Comparative Example 2 with the data in Example 1, it can be seen that when the boehmite particles are replaced with calcium carbonate particles, the internal stress increases, thereby reducing the wear resistance of the coating and affecting the long-term stability of the battery separator;

[0134] By comparing the data in Comparative Example 3 with the data in Example 1, it can be seen that changing the type of dispersant will affect the stability of the slurry and the uniformity of the coating, thereby affecting the internal stress and water content of the prepared composite coating diaphragm;

[0135] By comparing the data in Comparative Example 4 with the data in Example 1, it can be seen that reducing the coating rate and increasing the coating environment temperature will affect the uniformity of the coating and the surface characteristics after drying, thereby resulting in a lower internal stress change rate and a lower water content change rate relative to Example 1;

[0136] By comparing the data of Example 4 and Example 1, the binder used in Example 1 is acrylate emulsion, and the binder used in Example 4 is sodium carboxymethyl cellulose. The internal stress change rate and the water content change rate in Example 4 are lower than those in Example 1, indicating that the use of acrylate emulsion as a binder can reduce the internal stress and water content of the prepared composite coating diaphragm;

[0137] By comparing the data in Comparative Example 5 with the data in Example 1, it can be seen that increasing the drying temperature and shortening the drying time will affect the curing degree and pore structure of the coating, thereby causing the internal stress change rate and the water content change rate to be lower than that in Example 1;

[0138] By comparing the data in Comparative Example 6 with the data in Example 1, it can be seen that increasing the cooling rate of the annealing cooling treatment to 5°C / min will affect the degree of fusion between particles, thereby affecting the final performance of the coating.

[0139] The present invention provides a composite coating diaphragm with low internal stress and low water content, in which a composite coating is coated on both sides of a battery diaphragm. The composite coating is a coating formed on both sides of the battery diaphragm after coating a coating slurry on both sides of the battery diaphragm and then undergoing a drying treatment, an annealing and a cooling treatment. The main components of the coating slurry include ceramic particles, reinforcing particles, a dispersant, a binder and deionized water. The present invention also provides a method for preparing a composite coating diaphragm with low internal stress and low water content. By optimizing the reaction conditions in the preparation process of the composite coating diaphragm with low internal stress and low water content, the composite coating on the prepared composite coating diaphragm has good stability, thereby ensuring the stability and performance of the prepared composite coating diaphragm.

[0140] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0141] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A composite coating diaphragm with low internal stress and low water content, characterized in that: It includes a battery separator and a composite coating applied on both sides of the battery separator; The composite coating is a coating formed on both sides of the battery separator after coating slurry on both sides of the battery separator, and then drying, annealing and cooling treatment; The coating slurry comprises the following raw materials in parts by weight: 60-120 parts of ceramic particles, 60-120 parts of reinforcing particles, 1-2 parts of dispersant, 25-35 parts of adhesive, and 240 parts of deionized water.

2. A composite coating diaphragm with low internal stress and low water content according to claim 1, characterized in that: The D50 of the ceramic particles is not greater than 1.5 μm; The D50 of the reinforcing particles is not greater than 1.3 μm; The D50 of the ceramic particles is greater than the D50 of the reinforcing particles.

3. The composite coating diaphragm with low internal stress and low water content according to claim 1, characterized in that: The mass ratio of the ceramic particles to the reinforcing particles is 1:(0.5-2).

4. The composite coating diaphragm with low internal stress and low water content according to claim 1, characterized in that: The reinforcing particles are boehmite particles; The dispersant is a carboxylic acid dispersant; The binder is any one or more of sodium carboxymethyl cellulose and acrylate emulsion mixed in any proportion.

5. A composite coating diaphragm with low internal stress and low water content according to claim 4, characterized in that: The model of the acrylic emulsion is LIB-S105.

6. A method for preparing a composite coating diaphragm with low internal stress and low water content according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: S1: Raw material mixing In a high-speed stirring tank, ceramic particles, reinforcing particles and deionized water are added, and after mixing and stirring, a mixed slurry is formed; S2: Add dispersant Adding a dispersant into the mixed slurry, mixing and stirring to form a dispersed slurry; S3: Adding binder Adding a binder into the dispersed slurry, mixing and stirring to form a coating slurry; S4: coating and drying The coating slurry is applied to the surface of the battery separator by using a roller coater, and the coated battery separator is dried; S5: Annealing and curing The battery separator after drying is annealed and cooled to room temperature to prepare a composite coating separator.

7. The method for preparing a composite coating diaphragm with low internal stress and low water content according to claim 6, characterized in that: During the mixing and stirring process in step S1, step S2 and step S3, the mixing and stirring rate is 25-45 rpm / min, and the mixing and stirring time is 30-60 min.

8. The method for preparing a composite coating diaphragm with low internal stress and low water content according to claim 6, characterized in that: In step S4, during the coating process, the coating rate is 80-130 m / min, and the coating environment temperature is 24-26°C.

9. The method for preparing a composite coating diaphragm with low internal stress and low water content according to claim 6, characterized in that: In step S4, during the drying process, the drying temperature is 65-75° C. and the drying time is 18-24 min.

10. The method for preparing a composite coating diaphragm with low internal stress and low water content according to claim 6, characterized in that: In step S5, the cooling rate of the annealing cooling treatment is 1.0-3.0°C / min.

Images