High-safety porous composite diaphragm and preparation method thereof

Abstract

The invention discloses a high-safety porous composite diaphragm and a preparation method thereof, and relates to the technical field of batteries. Comprising the following steps: step 1, preparing a base membrane with a ceramic coating on one side for later use; 2, coating the other surface of the base membrane with a polysulfonamide coating to obtain a wet coating diaphragm; 3, the wet coating diaphragm is placed in a coagulating bath to be soaked; and washing and drying to form a polysulfonamide coating, thereby obtaining the high-safety porous composite diaphragm. The high-safety porous composite diaphragm has the beneficial effects that the advantages of a polymer coating and a ceramic coating are combined, and the high-safety porous composite diaphragm has low thermal shrinkage rate and high diaphragm rupture temperature. Moreover, compared with an inorganic particle coating film, the coating film has higher thermal stability and surface density; meanwhile, compared with other heat-resistant polymers, the polysulfonamide is excellent in performance, simple in formula, convenient to operate and low in cost.

Description

Technical Field

[0001] The invention relates to the technical field of batteries, in particular to a high-safety porous composite diaphragm and a preparation method thereof. Background Art

[0002] With the continuous development of the new energy industry, lithium-ion batteries, as the key technology of the industry, are increasingly becoming an important demand for the development of the industry with high energy density, high heat resistance and high safety. As the only insulating material in the battery, the diaphragm mainly functions to "block electrons and pass ions". The performance of the diaphragm has an important impact on the safety and electrochemical performance of the battery. The industry is developing day by day and has higher requirements for the performance of the diaphragm. Improving the performance of the diaphragm has a far-reaching impact on the overall performance of the battery.

[0003] Traditional polyolefin separators have advantages such as low cost and excellent chemical stability, but their thermal stability and electrolyte affinity are poor, and they are prone to shrinkage and film rupture under high temperature conditions. They are difficult to be directly applied to lithium-ion batteries. They are often improved by heat-resistant coating layers. Conventional coating materials include alumina, boehmite, aramid, etc. Due to the high density of inorganic particles such as alumina, the surface density of the coating film is greatly increased. At the same time, if the inorganic particle coating is to show excellent thermal shrinkage performance at higher temperatures, such as 150°C, it has higher requirements for factors such as particle size, resulting in higher costs. At the same time, due to its stiffness, it is difficult for the inorganic particle coating film to maintain morphological integrity at high temperatures, especially under conditions of >160°C, that is, it is difficult for the inorganic particle coating to improve the film rupture temperature. Aramid is an organic coating material that has been studied more. It has advantages such as excellent heat resistance and excellent electrolyte affinity, but it has disadvantages such as high price, complex formula, and high risk of equipment loss.

[0004] Therefore, in order to solve the above problems, the present invention prepares a high-safety porous composite diaphragm. Summary of the invention

[0005] The object of the present invention is to provide a highly safe porous composite diaphragm and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for preparing a high-safety porous composite diaphragm comprises the following steps:

[0008] Step 1: Prepare a base film with a ceramic coating on one side for later use;

[0009] Step 2: coating the other side of the base film with a sulfone coating to obtain a wet coating diaphragm;

[0010] Step 3: soak the wet coating membrane in a coagulation bath; wash with water, and dry to form an aromatic sulfone coating to obtain a highly safe porous composite membrane.

[0011] More optimally: the thickness of the ceramic coating is 1-4 μm; its material includes one of boehmite and alumina; the base film is a polyethylene film, its porosity is 40-50%, and its thickness is 7-9 μm.

[0012] More optimally, the aromatic sulfone coating comprises the following raw materials: by weight, 5.5-8 parts of aromatic sulfone, 0.2-3 parts of auxiliary agent, 0.5-5 parts of inorganic filler, and 100 parts of solvent.

[0013] More optimally, the weight average molecular weight of the aromatic sulfone fiber is between 500,000 g / mol and 800,000 g / mol.

[0014] More preferably: the auxiliary agent includes one or more of polyvinyl pyrrolidone, silane coupling agent, and fatty acid;

[0015] The inorganic filler has an average particle size of 200-750 nm; it includes one or more of aluminum oxide, titanium oxide, magnesium oxide, silicon oxide, and boehmite;

[0016] The solvent includes one or more of N-methyl-2-pyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0017] More optimally, the thickness of the aromatic sulfone coating is 0.5-5 μm, and the porosity is 30%-70%.

[0018] More optimally: the coagulation bath is a 35-55% N-methylpyrrolidone-water solution; the coagulation bath temperature is 20-40°C; the drying process: the moisture is dried in an oven at 50°C, 55°C, and 60°C respectively.

[0019] More optimally: The preparation process of aromatic sulfone coating is:

[0020] S1: mixing the aromatic sulfone fiber with the solvent and fully dissolving them to form a homogeneous solution to obtain a feed solution A;

[0021] S2: Add the auxiliary agent and inorganic filler into the solvent, stir and disperse them evenly to obtain liquid B;

[0022] S3: Mix the feed liquid A and the feed liquid B, and stir them thoroughly to obtain the aromatic sulfone fiber coating.

[0023] More optimally: the coating method is a gravure coating method.

[0024] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0025] The present invention provides a high-safety porous composite membrane combining a heat-resistant polymer coating and a ceramic coating and a preparation method thereof; wherein the heat-resistant polymer coating is made of sulfone as the main material; during the preparation process, a polyolefin membrane with a ceramic coating (i.e., an inorganic particle coating) on ​​one side is used as a base membrane, and a sulfone coating is coated on the other side to obtain an asymmetric composite membrane. The details are as follows:

[0026] (1) Inorganic particles have excellent hardness and stiffness. Unlike polymers that undergo secondary transitions at glass transition temperatures, boehmite-coated base films exhibit better high-temperature resistance, but due to poor flexibility, their film rupture temperature is usually low, generally less than 160°C. In contrast, the glass transition temperature of aromatic sulfone exceeds 300°C, and it has excellent creep resistance at high temperatures; therefore, combining a polymer coating (based on aromatic sulfone) with an inorganic particle coating can significantly improve the deformation resistance and impact resistance of the composite diaphragm at high temperatures. At the same time, this combination can also make up for the low stability of conventional inorganic particle-coated films at higher temperatures, reduce the thermal shrinkage of the diaphragm at 150°C and above, and increase the film rupture temperature, thereby effectively improving the safety of the battery;

[0027] (2) The membrane structure prepared by this scheme is an asymmetric membrane, which has the advantages of both sulfone coated membrane and ceramic coated membrane, and can significantly improve the electrochemical performance while ensuring battery safety. On the one hand, the polymer coating uses sulfone as the main material, and utilizes its strong polar groups and porous structure after film formation to effectively improve the electrolyte wettability of the diaphragm; on the other hand, the heat-resistant polymer coating reduces the overall surface density of the diaphragm while ensuring the heat resistance of the diaphragm, making the prepared diaphragm thinner. The reduction in the surface density of the diaphragm and the improvement in the electrolyte wettability help to enhance the electrochemical performance of the battery, thereby improving the battery cycle efficiency;

[0028] (3) Compared with coating only with an inorganic particle layer, this solution has higher thermal stability and surface density. At the same time, compared with other heat-resistant polymers such as polyimide, aramid and other polymer coating materials, aramid has the advantages of good performance, simple formula, convenient operation and low cost, which meets production needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the structure of the high-safety porous composite diaphragm obtained in Example 1;

[0030] Figure 2 This is the surface morphology of the aromatic sulfone coating;

[0031] Figure 3 It is the structural formula of aromatic sulfone. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0033] In the following embodiments, parts are parts by mass; it should be noted that there is no special restriction on the purchase manufacturers of all raw materials involved in the present invention.

[0034] Embodiment 1: A method for preparing a high-safety porous composite diaphragm, comprising the following steps:

[0035] Step 1: preparing a base film coated with ceramic on one side (the base film is a polyethylene film with a porosity of 40%-50% and a thickness of 9 μm; the ceramic coating is boehmite coated with a thickness of 2 μm);

[0036] Step 2: coating an aromatic sulfone coating on the other side of the polyolefin-based film coated with boehmite on one side to obtain a wet coating separator;

[0037] Step 3: The wet coating membrane is immersed in a coagulation bath (NMP mass fraction is 50%) at 35°C, and then washed and dried, and the moisture is dried in an oven at 50°C, 55°C, and 60°C, respectively, to form an aromatic sulfone coating, and obtain a highly safe porous composite membrane; wherein the thickness of the aromatic sulfone coating is 2 μm;

[0038] Among them, the preparation process of aromatic sulfone coating is:

[0039] S1: 5.5 parts of aromatic sulfone fiber and 80 parts of solvent (N-methyl-2-pyrrolidone) are mixed and dissolved fully to form a homogeneous solution to obtain feed solution A;

[0040] S2: Add 0.2 parts of auxiliary agent (silane coupling agent A151) and 0.5 parts of inorganic filler (boehmite, particle size of 500 nm) to 20 parts of solvent (N-methyl-2-pyrrolidone), stir and disperse them evenly to obtain liquid B;

[0041] S3: Mix the feed liquid A and the feed liquid B, and stir them thoroughly to obtain the aromatic sulfone fiber coating.

[0042] Example 2: Compared with Example 1, the thickness of the aromatic sulfone coating is 5 μm; wherein, part of the formula of the aromatic sulfone coating in this example is adjusted as follows: the number of boehmite (inorganic filler) is 1 part, the number of polyvinyl pyrrolidone (PVP) K30 (auxiliary agent) is 1 part, and the other ingredients and conditions remain unchanged.

[0043] Example 3: Compared with Example 1, part of the formula of the aromatic sulfone coating in this example is adjusted to: 6 parts of aromatic sulfone, 0.5 parts of silane coupling agent A151 (auxiliary agent), 0.5 parts of alumina with a particle size of 200nm (inorganic filler), and the other ingredients and conditions remain unchanged.

[0044] Example 4: Compared with Example 3, the polyolefin-based membrane uses a polyethylene film with a thickness of 7 μm; part of the formula in the aromatic sulfone coating in this example is adjusted to: 7.5 parts of aromatic sulfone, 1 part of boehmite (inorganic filler) with a particle size of 500 nm, and the rest is the same.

[0045] Example 5: Compared with Example 4, the number of aromatic sulfone in the aromatic sulfone coating is 8 parts, and the rest is the same.

[0046] Example 6: Compared with Example 5, the polyolefin-based film uses a polyethylene film with a thickness of 9 μm; the number of boehmite (inorganic filler) in the aromatic sulfone coating is 3 parts, and the rest is the same.

[0047] Example 7: Compared with Example 6, the ceramic coating is made of boehmite with a thickness of 1 μm, and the rest is the same.

[0048] Example 8: Compared with Example 6, part of the formula in the aromatic sulfone coating is adjusted as follows: the number of boehmite (inorganic filler) is 5 parts, the number of polyvinyl pyrrolidone (PVP) K30 (auxiliary agent) is 2 parts, and the rest is the same.

[0049] Example 9: Compared with Example 6, the ceramic coating is made of aluminum oxide with a thickness of 2 μm, and the rest is the same.

[0050] Comparative Example 1: Compared with Example 6, part of the formula in the aromatic sulfone coating is adjusted as follows: the number of parts of boehmite (inorganic filler) is 8 parts, and the rest is the same.

[0051] Comparative Example 2: Compared with Example 6, the polyolefin-based membrane uses a polyethylene film with a thickness of 9 μm and a porosity of 30-40%, and the rest is the same.

[0052] Comparative Example 3: A polyethylene film (the porosity of the polyethylene film is 40%-50% and the thickness is 9 μm) is coated on one side with boehmite, and the thickness of the obtained boehmite coating is 2 μm.

[0053] Comparative Example 4: A polyethylene film (the porosity of the polyethylene film is 40%-50% and the thickness is 9 μm) is coated on both sides with boehmite, and the thickness of each side of the obtained boehmite coating is 2 μm.

[0054] Comparative Example 5: Compared with Example 6, the thickness of the aromatic sulfone coating is 5 μm, and the rest is the same.

[0055] Comparative Example 6: Compared with Example 6, the thickness of the boehmite coating is 5 μm, and the rest are the same.

[0056] The specific ingredients are shown in the following table:

[0057]

[0058]

[0059] Table 1 Testing experiment:

[0060] (1) Thermal shrinkage test

[0061] The diaphragms obtained in the examples and comparative examples were cut into 20×10 cm 2 Place the square between two A4 papers in a constant temperature drying oven, set the constant temperature to 150°C, and treat at the constant temperature for 1 hour. Compare and calculate the dimensional change ratio of the diaphragm before and after heat treatment.

[0062] (2) Membrane rupture temperature test

[0063] The diaphragms obtained in the examples and comparative examples were cut into 20×10 cm 2 Place the square between two A4 papers in a constant temperature drying oven, set the starting constant temperature to 130°C, and each constant temperature treatment lasts for 10 minutes with a temperature interval of 5°C until the diaphragm ruptures. This time is recorded as the diaphragm rupture temperature.

[0064] (3) Surface density test

[0065] The separators obtained in the examples and comparative examples were cut into 20×10 cm 2 The rectangle is weighed and its mass is defined as m0. The surface density is calculated according to the surface density formula = m0 / (0.02×d), where d is the coating thickness;

[0066] (4) Electrolyte contact angle test

[0067] The diaphragms obtained in the examples and comparative examples were cut into strips with a width of 1 cm and a length of 20 cm, and the two ends were straightened and fixed on the sample stage. The drop volume was set to 2 μL, and the cut angle when the droplet contacted the strip was the electrolyte contact angle;

[0068] (5) Liquid absorption test

[0069] The separators obtained in the examples and comparative examples were cut into pieces of 5×5 cm. 2 The square is weighed and defined as m0. It is immersed in electrolyte for 30 minutes. After removal, the electrolyte on its surface is wiped off and the mass at this time is weighed and defined as m1. The liquid absorption rate is calculated as (m1 / m0-m1).

[0070] (6) Tensile strength test

[0071] The diaphragms obtained in the examples and comparative examples were cut into strips with a width of 1.5 cm and fixed in a fixture with a fixed spacing of a universal tensile machine, and biaxially stretched at a rate of 25 cm / min. The strength when the strips broke was the tensile strength. The obtained data are shown in the following table:

[0072]

[0073]

[0074] Table 2

[0075] Conclusion: The thermal shrinkage rates of the diaphragms prepared in Examples 1 to 6 of this scheme are all below 5% under the condition of 150°C / h, and the membrane breaking temperatures are all above 200°C. The high-temperature thermal stability is significantly improved compared with the conventional inorganic particle coating membrane. The electrolyte contact angle and liquid absorption rate in the examples are also better than those in Comparative Example 3, and as the content of aromatic sulfone increases, the liquid absorption rate and tensile strength also continue to increase. Examples 5, 6, and 8 show that when the content of boehmite increases under the same aromatic sulfone content, the liquid absorption rate continues to increase, and the tensile strength decreases. This is related to the fact that after the inorganic particles are filled with polymers, the density of the continuous phase structure is disturbed to a certain extent.

[0076] In summary, Example 6 has the best comprehensive performance. At the same time, by comparing Example 6 with Comparative Examples 5 and 6, it is found that increasing the thickness of the inorganic particle layer will lead to an excessive increase in the membrane surface density and a decrease in the membrane rupture temperature, while increasing the thickness of the polymer coating can increase the membrane rupture temperature and electrolyte wettability of the membrane.

[0077] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for preparing a high-safety porous composite diaphragm, characterized in that: The following steps are involved: Step 1: Prepare a base film with a ceramic coating on one side for later use; Step 2: coating the other side of the base film with a sulfone coating to obtain a wet coating diaphragm; Step 3: placing the wet coating diaphragm in a coagulation bath for immersion treatment; The polysulfone coating is formed by washing with water and drying to obtain a highly safe porous composite diaphragm.

2. The method for preparing a high-safety porous composite diaphragm according to claim 1, characterized in that: The thickness of the ceramic coating is 1-4 μm; The material thereof comprises one of boehmite and alumina; the base film is a polyethylene film, the porosity of which is 40-50% and the thickness is 7-9 μm.

3. The method for preparing a high-safety porous composite diaphragm according to claim 1, characterized in that: The aromatic sulfone coating comprises the following raw materials: by weight, 5.5-8 parts of aromatic sulfone, 0.2-3 parts of auxiliary agent, 0.5-5 parts of inorganic filler and 100 parts of solvent.

4. The method for preparing a high-safety porous composite diaphragm according to claim 3, characterized in that: The weight average molecular weight of the aromatic sulfone fiber is 500000 g / mol-800000 g / mol.

5. The method for preparing a high-safety porous composite diaphragm according to claim 3, characterized in that: The auxiliary agent includes one or more of polyvinyl pyrrolidone, silane coupling agent, and fatty acid; The inorganic filler has an average particle size of 200-750 nm; it includes one or more of aluminum oxide, titanium oxide, magnesium oxide, silicon oxide, and boehmite; The solvent includes one or more of N-methyl-2-pyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

6. The method for preparing a high-safety porous composite diaphragm according to claim 3, characterized in that: The thickness of the aromatic sulfone coating is 0.5-5 μm, and the porosity is 30%-70%.

7. The method for preparing a high-safety porous composite diaphragm according to claim 1, characterized in that: The coagulation bath is a 35-55% N-methylpyrrolidone-water solution; the coagulation bath temperature is 20-40°C; the drying process is: drying the water in an oven at 50°C, 55°C, and 60°C respectively.

8. The method for preparing a high-safety porous composite diaphragm according to claim 3, characterized in that: The preparation process of aromatic sulfone coating is: S1: mixing the aromatic sulfone fiber with the solvent and fully dissolving them to form a homogeneous solution to obtain a feed solution A; S2: Add the auxiliary agent and inorganic filler into the solvent, stir and disperse them evenly to obtain liquid B; S3: Mix the feed liquid A and the feed liquid B, and stir them thoroughly to obtain the aromatic sulfone fiber coating.

9. The method for preparing a high-safety porous composite diaphragm according to claim 3, characterized in that: The coating method is a gravure coating method.

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