Preparation method of in-situ polymerization ceramic slurry and coated diaphragm

Abstract

The invention provides a preparation method of in-situ polymerization ceramic slurry and a coated diaphragm, the surfaces of ceramic particles are coated with allylamine resin with a cross-linked structure through an in-situ polymerization method, and then the coated ceramic is prepared into slurry to be coated on the surface of a polyolefin diaphragm. The preparation method comprises the following steps: A, mixing ceramic powder with a prepared allyl amine monomer, and adding an initiator to carry out in-situ solution polymerization; and B, mixing the ceramic aqueous solution subjected to in-situ polymerization with aids such as a thickening agent and a binder to prepare slurry, and coating the surface of the polyolefin diaphragm with the slurry. According to the invention, the allylamine resin with a cross-linked structure is coated on the surface of the aluminum oxide ceramic particles in situ to prepare the aluminum oxide coating slurry, so that on one hand, the problem that the aluminum oxide slurry is easy to agglomerate is solved, and on the other hand, the coating diaphragm prepared from the slurry has good affinity to an electrolyte and can improve the liquid absorption rate of the electrolyte.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a preparation method of an in-situ polymerized ceramic slurry and a coating diaphragm. Background Art

[0002] As one of the core components of lithium-ion batteries, the performance of the diaphragm directly affects the internal resistance, safety and capacity performance of the battery. Although traditional polyolefin diaphragms have basic performance advantages, they are limited by the material itself and have poor affinity for the electrolyte. They are prone to shrinkage and deformation in high-temperature environments, which may cause battery short circuits and even trigger serious safety hazards such as thermal runaway. In order to solve these problems, the industry generally adopts a surface coating method to significantly improve the performance of the diaphragm by coating the diaphragm with high-performance materials such as ceramic alumina, PAA, PVDF or aramid. By coating different materials on the surface, not only is the interfacial adhesion between the diaphragm and the electrode enhanced, and the affinity of the electrolyte improved, but its high temperature resistance and mechanical strength are also improved simultaneously. This is also a major trend in the future development of diaphragms.

[0003] A ceramic-coated separator is a lithium-ion separator formed by coating a polyolefin-based membrane with an inorganic ceramic material, such as ceramic alumina. This separator improves the separator's high-temperature stability, mitigates thermal shrinkage of the base membrane, and reduces the risk of thermal runaway. It also enhances the separator's mechanical strength, reduces the possibility of puncture short circuits, and improves the separator's wettability with the electrolyte. However, when preparing the ceramic slurry, the ceramic particles are highly active and prone to agglomeration and sedimentation. This not only creates production challenges, but also affects the quality of the coated separator due to the large agglomerated particles. Summary of the Invention

[0004] In response to the above-mentioned deficiencies in the prior art, the present invention provides a method for preparing an in-situ polymerized ceramic slurry and a coated diaphragm, which inhibits particle agglomeration, reduces the sedimentation rate of the slurry, and improves the liquid absorption rate of the coated diaphragm.

[0005] The technical solution provided by the present invention is: an in-situ polymerized ceramic slurry is prepared from the following raw materials in parts by weight: 80-100 parts of coated ceramic aqueous solution, 3-5 parts of CMC thickener, 1-3 parts of acrylic resin glue, and 0.1-0.5 parts of sodium hexametaphosphate; The coated ceramic aqueous solution is obtained by coating a layer of allylamine polymer with a cross-linked structure on the surface of ceramic particles through an in-situ polymerization method.

[0006] Furthermore, in the in-situ polymerization reaction, the weight proportions of the components are: 25 to 35 parts of ceramic particles, 10 to 15 parts of allylamine monomers, and 0.5 to 2 parts of initiator.

[0007] Furthermore, the initiator is one of VA-044 and V50.

[0008] Furthermore, the ceramic particles are alumina ceramics with a particle size of 50 to 2000 nm.

[0009] The present invention uses an in-situ polymerization method to coat the surface of ceramic particles with an allylamine polymer. This polymer is copolymerized by MAA or DAA and TAA, wherein TAA acts as a cross-linking agent and a reactive monomer at the same time, and copolymerizes with the chain-like MAA or DAA to form a polymer with a three-dimensional network structure, which is coated on the surface of the ceramic. On the one hand, each structural unit of the allylamine polymer contains an amino group, which can easily form hydrogen bonds with water, further improving the compatibility with the system; on the other hand, coating the polymer on the surface of the ceramic particles inhibits the agglomeration of the particles and reduces the sedimentation rate of the slurry. This cross-linked structure of the allylamine resin has a large specific surface area, which improves the liquid absorption rate of the coated diaphragm. In-situ polymerization refers to the free radical polymerization of allylamine monomers on the surface of the ceramic, which is coated on the surface of the ceramic to obtain an in-situ polymerized ceramic solution.

[0010] Another technical solution provided by the present invention is a method for preparing an in-situ polymerized ceramic slurry, comprising the following steps: (1) Mixing the allylamine monomer with concentrated hydrochloric acid, stirring at high speed at -10 to 0°C, and controlling the pH to be acidic, to obtain an aqueous solution of the allylamine hydrochloride monomer; monitoring the pH of the solution during the mixing process, and controlling the amount of hydrochloric acid added according to the amount of the allylamine monomer and the given pH value; (2) Slowly add the ceramic particles to the aqueous solution of allylamine hydrochloride monomer, stir evenly, introduce nitrogen to replace it to ensure an oxygen-free environment, then slowly add the initiator and continue stirring, raise the temperature to 55-65°C to start polymerization, and the reaction time is 3-5 hours. After the reaction is completed, let it stand at room temperature, add NaOH to adjust the pH to obtain an in-situ polymerization-coated ceramic aqueous solution; (3) The coated ceramic aqueous solution obtained in step (2) is mixed evenly with a CMC thickener, an acrylic resin glue, and a dispersant according to a proportion to obtain an in-situ polymerization ceramic slurry.

[0011] Furthermore, the allylamine monomer is obtained by mixing allylamine (MAA) or diallylamine (DAA) and triallylamine (TAA), respectively. In the allylamine monomer, the molar ratio of the two monomers is DAA:TAA=10:0.1~1, and MAA:TAA=10:1~2.

[0012] Furthermore, the concentration of concentrated hydrochloric acid in step (1) is 36-38%, and after the allylamine monomer is mixed with the concentrated hydrochloric acid, the pH is controlled to be 2-3.

[0013] Furthermore, NaOH is added in step (2) to adjust the pH to 5-8.

[0014] A coated diaphragm is prepared by coating the in-situ polymerized ceramic slurry on one or both sides of a PP or PE diaphragm by roller coating or spraying. The coating layer thickness is controlled to be 1-5 μm.

[0015] Compared with the prior art, the present invention has the following beneficial effects: Using an in-situ polymerization method, an allylamine polymer is coated on the surface of ceramic particles. The polymer barrier inhibits ceramic particle agglomeration, significantly improving the dispersion of the particles and extending the settling time of the ceramic slurry. Furthermore, the excellent dispersion of the ceramic further enhances coating efficiency and processability, ensuring a more uniform coating and helping to improve the performance of the separator.

[0016] The ceramic coating proposed in this invention is a copolymer of MAA or DAA and TAA, forming a cross-linked three-dimensional network structure with a large number of internal pores, which greatly increases the specific surface area of ​​the polymer. The separator prepared with this ceramic slurry has excellent liquid absorption and retention. DETAILED DESCRIPTION

[0017] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the examples. The examples are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention. Example 1

[0018] Mix 5.15 mol of allylamine monomers (DAA:TAA = 10:1) with 5.25 mol of concentrated hydrochloric acid, stirring continuously at -10°C and maintaining a pH of 2.3 to obtain a hydrochloride aqueous solution. Then, add 1.036 kg of ceramic particles, continue stirring, and flush the solution with nitrogen three times. Then, add 45 g of initiator VA-044, heat to 60°C, and stir for 4 hours. Then, add NaOH to adjust the pH to between 6 and 8 to obtain an aqueous solution of in-situ polymerized ceramics.

[0019] Take 85 parts of coated ceramic aqueous solution, 3.5 parts of CMC thickener, 1.6 parts of acrylic resin glue, and 0.26 parts of sodium hexametaphosphate to prepare ceramic slurry, and apply the ceramic slurry on a 12μm PP diaphragm by roller coating to obtain a ceramic coated diaphragm with a coating layer thickness of about 2um. Example 2

[0020] A total of 5.15 mol of allylamine monomers (DAA:TAA = 10:0.5) was mixed with 5.25 mol of concentrated hydrochloric acid and stirred continuously at -10°C, maintaining a pH of 2.3, to obtain a hydrochloride aqueous solution. 1.087 kg of ceramic particles were then added, stirring continuously, and the atmosphere was replaced with nitrogen three times. 45 g of initiator VA-044 was then added, and the temperature was raised to 60°C with stirring for 4 hours. NaOH was added to adjust the pH to approximately 6-8, resulting in an aqueous solution of in-situ polymerized ceramics.

[0021] Take 85 parts of coated ceramic aqueous solution, 3.5 parts of CMC thickener, 1.6 parts of acrylic resin glue, and 0.26 parts of sodium hexametaphosphate to prepare ceramic slurry, and apply the ceramic slurry on a 12μm PP diaphragm by roller coating to obtain a ceramic coated diaphragm with a coating layer thickness of about 2um. Example 3

[0022] Mix 5.15 mol of allylamine monomers (DAA:TAA = 10:1) with 5.25 mol of concentrated hydrochloric acid, stirring continuously at -10°C and maintaining a pH of 2.3 to obtain a hydrochloride aqueous solution. Add 0.864 kg of ceramic particles, continue stirring, and flush the solution with nitrogen three times. Then, add 45 g of initiator VA-044, heat to 60°C, and stir for 4 hours. Adjust the pH to 6-8 with the addition of NaOH to obtain an aqueous solution of in-situ polymerized ceramics.

[0023] Take 85 parts of coated ceramic aqueous solution, 3.5 parts of CMC thickener, 1.6 parts of acrylic resin glue, and 0.26 parts of sodium hexametaphosphate to prepare ceramic slurry, and apply the ceramic slurry on a 12μm PP diaphragm by roller coating to obtain a ceramic coated diaphragm with a coating layer thickness of about 2um. Example 4

[0024] Mix 6 mol of allylamine monomers (MAA:TAA = 10:2) with 6.12 mol of concentrated hydrochloric acid, stirring continuously at -10°C and maintaining a pH of 2.5 to obtain a hydrochloride aqueous solution. Add 0.844 kg of ceramic particles, continue stirring, and flush the solution with nitrogen three times. Then, add 48.8 g of initiator V50, heat to 60°C, and stir for approximately 4 hours. Adjust the pH to 6-8 with the addition of NaOH to obtain an aqueous solution of in-situ polymerized ceramics.

[0025] Take 85 parts of coated ceramic aqueous solution, 3.5 parts of CMC thickener, 1.6 parts of acrylic resin glue, and 0.26 parts of sodium hexametaphosphate to prepare ceramic slurry, and apply the ceramic slurry on a 12μm PP diaphragm by roller coating to obtain a ceramic coated diaphragm with a coating layer thickness of about 2um. Example 5

[0026] A total of 5.15 mol of allylamine monomers (DAA:TAA = 10:1) was mixed with 5.25 mol of concentrated hydrochloric acid and stirred continuously at -10°C, maintaining a pH of 2.3, to obtain a hydrochloride aqueous solution. 1.036 kg of ceramic particles were then added, stirring continuously, and the atmosphere was replaced with nitrogen three times. 45 g of initiator VA-044 was then added, and the temperature was raised to 60°C with stirring for 4 hours. NaOH was added to adjust the pH to approximately 6-8, resulting in an aqueous solution of in-situ polymerized ceramics.

[0027] Take 80 parts of coated ceramic aqueous solution, 3 parts of CMC thickener, 1.2 parts of acrylic resin glue, and 0.18 parts of sodium hexametaphosphate to prepare ceramic slurry, and apply the ceramic slurry on a 12μm PP diaphragm by roller coating to obtain a ceramic coated diaphragm with a coating layer thickness of about 2um.

[0028] Comparative Example 1 35 parts of ceramic particles, 65 parts of deionized water, 3 parts of CMC thickener, 1.2 parts of acrylic resin glue, and 0.3 parts of sodium hexametaphosphate are prepared into a normal ceramic slurry. The ceramic slurry is coated on a 12μm PP diaphragm by roller coating to obtain a ceramic coated diaphragm with a coating layer thickness of about 2um.

[0029] Diaphragm liquid absorption rate test: Take a 100mm*100mm specification diaphragm sample, weigh it, and record the weight m1. Place the diaphragm sample in the electrolyte and seal it for 1 hour, then take it out. Use dust-free paper to absorb the electrolyte on the diaphragm surface and weigh it, record the weight m2. Liquid absorption rate = (m2-m1) / 0.01. Test each sample 3 times and take the average value.

[0030] The slurries prepared in Examples 1-5 and Comparative Example 1 were subjected to a static stability test and a particle size distribution test. The electrolyte absorption of the coated separator was also tested, as shown in the following table.

[0031]

[0032] The table shows that after 24 hours of stabilization, the allylamine polymer-coated ceramic slurry exhibited no delamination and minimal change in D50, demonstrating improved dispersion and stability of the ceramic particles in the system using the polymer in situ coating. Copolymerization of DAA or MAA with TAA also exhibited similar effects, improving slurry stability. Furthermore, this porous polymer coating structure increased electrolyte absorption by the separator, providing excellent electrolyte retention.

[0033] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, several improvements and changes can be made without departing from the creative concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. An in-situ polymerized ceramic slurry, characterized in that: The invention is prepared from the following raw materials in parts by weight: 80-100 parts of coated ceramic aqueous solution, 3-5 parts of CMC thickener, 1-3 parts of acrylic resin glue, and 0.1-0.5 parts of sodium hexametaphosphate; The coated ceramic aqueous solution is obtained by coating a layer of allylamine polymer with a cross-linked structure on the surface of ceramic particles through an in-situ polymerization method.

2. The in-situ polymerized ceramic slurry according to claim 1, characterized in that: In the in-situ polymerization reaction, the weight proportions of the components added are: 25 to 35 parts of ceramic particles, 10 to 15 parts of allylamine monomers, and 0.5 to 2 parts of initiator.

3. The in-situ polymerized ceramic slurry according to claim 2, characterized in that: The initiator is one of VA-044 and V50.

4. The in-situ polymerized ceramic slurry according to claim 1, characterized in that: The ceramic particles are alumina ceramics with a particle size of 50 to 2000 nm.

5. The method for preparing an in-situ polymerized ceramic slurry according to any one of claims 1 to 4, characterized in that: The steps include: (1) Mixing allylamine monomers with concentrated hydrochloric acid, stirring at high speed at -10 to 0°C, and controlling the pH to be acidic to obtain an allylamine hydrochloride monomer aqueous solution; (2) Slowly add the ceramic particles to the aqueous solution of allylamine hydrochloride monomer, stir evenly, introduce nitrogen to replace it to ensure an oxygen-free environment, then slowly add the initiator and continue stirring, raise the temperature to 55-65°C to start polymerization, and the reaction time is 3-5 hours. After the reaction is completed, let it stand at room temperature, add NaOH to adjust the pH to obtain an in-situ polymerization-coated ceramic aqueous solution; (3) The coated ceramic aqueous solution obtained in step (2) is mixed evenly with a CMC thickener, an acrylic resin glue, and a dispersant according to a proportion to obtain an in-situ polymerization ceramic slurry.

6. The method for preparing an in-situ polymerized ceramic slurry according to claim 5, characterized in that: The allylamine monomers are obtained by mixing allylamine or diallylamine and triallylamine respectively. The molar ratio of the two monomers in the allylamine monomers is diallylamine:triallylamine=10:0.1-1, and allylamine:triallylamine=10:1-2.

7. The method for preparing an in-situ polymerized ceramic slurry according to claim 5, characterized in that: The concentration of concentrated hydrochloric acid in step (1) is 36-38%. After the allylamine monomer is mixed with the concentrated hydrochloric acid, the pH is controlled to be 2-3.

8. The method for preparing an in-situ polymerized ceramic slurry according to claim 5, characterized in that: In the step (2), NaOH is added to adjust the pH to 5-8.

9. A coated diaphragm, characterized in that: The coated diaphragm is prepared by coating the in-situ polymerized ceramic slurry according to any one of claims 1 to 4 on one or both sides of a PP or PE diaphragm by roller coating or spraying.

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