High-adhesion polyethylene wax composite separator and its application in lithium battery

Abstract

The application relates to the technical field of lithium battery separators, and specifically discloses a high-adhesion polyethylene wax composite separator and application of the high-adhesion polyethylene wax composite separator in lithium batteries. The high-adhesion polyethylene wax composite separator comprises a polyethylene wax coating layer, a ceramic coating layer and a polyethylene porous base film, and the polyethylene wax coating layer comprises the following raw materials in parts by weight: 50-70 parts of polyethylene wax, 5-15 parts of ethylene-vinyl acetate copolymer, 10-25 parts of reinforcing fibers, 0.5-2 parts of a flame retardant, 0.5-2 parts of an antioxidant, 2-4 parts of an interfacial compatibilizer and 2-4 parts of a polymer containing carboxyl, hydroxyl or amine groups. Under the joint action of the polyethylene wax, the ethylene-vinyl acetate copolymer, the reinforcing fibers, the interfacial compatibilizer and the polymer containing carboxyl, hydroxyl or amine groups, the adhesion between the polyethylene wax coating layer and other coating layers or the base film can be significantly improved, the peeling possibility is reduced, and the durability of the separator is improved.

Description

Technical Field

[0001] This invention relates to the technical field of lithium battery separators, and in particular to a high-adhesion polyethylene wax composite separator and its application in lithium batteries. Background Technology

[0002] In the construction of lithium batteries, the separator, as a key component, plays a crucial role in isolating the positive and negative electrodes, preventing short circuits, and ensuring the normal transport of lithium ions. Among them, polyethylene wax composite separators, as a novel high-performance separator material, have attracted much attention. Polyethylene wax composite separators exhibit excellent heat resistance and chemical corrosion resistance, maintaining stable performance in high-temperature and harsh environments, thereby ensuring the safety and reliability of lithium batteries in various application scenarios.

[0003] In related technologies, a method for preparing a separator for lithium-ion batteries is disclosed, comprising the following steps: Polyethylene wax particles and water are mixed uniformly to obtain an aqueous dispersion of polyethylene wax. The aqueous dispersion of polyethylene wax, polyacrylic acid, and sodium carboxymethyl cellulose are stirred and mixed uniformly, and water is added to adjust the solid content to obtain a polyethylene wax emulsion. Ceramic microparticles, sodium carboxymethyl cellulose, polyacrylic acid, and styrene-acrylic emulsion are stirred and mixed uniformly, and water is added to adjust the solid content to obtain a ceramic slurry. The polyethylene wax emulsion is coated on both sides of a porous substrate, dried, and then surface functionalized. An organic polyethylene wax coating with a thickness of 1 μm is formed on the surface of the polyethylene porous substrate, resulting in a polyethylene porous substrate membrane with an organic polyethylene wax coating. The ceramic slurry is coated on the surface of the surface-functionalized organic polyethylene wax coating, dried, and a ceramic coating with a thickness of 2 μm is formed on the surface of the organic polyethylene wax coating, resulting in a separator for lithium-ion batteries.

[0004] For the aforementioned lithium-ion battery separators, if the interfacial compatibility between the polyethylene wax coating, ceramic coating, and porous polyethylene base film is poor, their interaction forces will be weakened, and the adhesion between the coated polyethylene wax coating and ceramic coating and the porous polyethylene base film may be insufficient. During battery charging and discharging, due to changes in temperature and pressure, the coating may peel off or crack, leading to an internal short circuit in the battery. Therefore, how to reduce the peeling of the polyethylene wax coating from other coatings or base films in the aforementioned lithium-ion battery separators, thereby improving the durability of the separator, is a problem that needs to be studied. Summary of the Invention

[0005] To improve the durability of the separator, this application provides a high-adhesion polyethylene wax composite separator and its application in lithium batteries.

[0006] In a first aspect, this application provides a high-adhesion polyethylene wax composite separator, which adopts the following technical solution:

[0007] A high-adhesion polyethylene wax composite membrane includes a polyethylene wax coating, a ceramic coating, and a polyethylene porous base membrane. The polyethylene wax coating comprises the following raw materials in parts by weight: 50-70 parts polyethylene wax, 5-15 parts ethylene-vinyl acetate copolymer, 10-25 parts reinforcing fiber, 0.5-2 parts flame retardant, 0.5-2 parts antioxidant, 2-4 parts interface compatibilizer, and 2-4 parts polymer containing carboxyl, hydroxyl, or amine groups.

[0008] By employing the above technical solutions, the molecular chains of polyethylene wax form a network structure in the coating, which helps to enhance the cohesion and adhesion of the coating. The vinyl acetate portion in the ethylene-vinyl acetate copolymer molecular chain provides polar groups, which help to form hydrogen bonds with polymers containing carboxyl, hydroxyl, or amine groups, thereby improving the interlayer bonding strength. Reinforcing fibers can form a three-dimensional network structure in the coating, increasing the coating's cohesion and peel resistance. Interfacial compatibilizers act as bridges between the coating and other materials, reducing the interfacial tension between them and improving compatibility and bonding strength. Carboxyl, hydroxyl, and amine groups are all polar groups that can interact with polar groups in adjacent materials to form strong chemical bonds. Therefore, the combined effect of polyethylene wax, ethylene-vinyl acetate copolymer, reinforcing fibers, interfacial compatibilizers, and polymers containing carboxyl, hydroxyl, or amine groups helps to significantly improve the adhesion between the polyethylene wax coating and other coatings or base films, reducing the possibility of peeling and thus improving the durability of the diaphragm.

[0009] In one specific implementation, the interface compatibilizer includes at least one of polyethylene glycol terephthalate, polycaprolactone, or polyamide elastomer.

[0010] By adopting the above technical solution, the three components mentioned above all have good compatibility with polyethylene wax, and have short chain lengths and high activity. They can form a bridge between polyethylene wax and inorganic ceramics or polyethylene porous membranes, enhance their interaction, and help form a good interfacial bond.

[0011] In one specific implementation, the polyethylene wax coating further includes nano-silica or nano-alumina.

[0012] By employing the above-mentioned technical solutions, nano-silica and nano-alumina can improve the heat distortion temperature and thermal stability of the polyethylene wax coating, preventing the diaphragm from deforming or degrading in high-temperature environments. The small particle size of nano-silica and nano-alumina allows them to fill the tiny pores of the polyethylene wax coating, enhancing the diaphragm's barrier properties against gases and moisture, protecting the internal materials from external environmental corrosion, and thus further improving the diaphragm's durability.

[0013] In one specific implementation, the polymer containing carboxyl, hydroxyl, or amine groups is any one of polyacrylic acid, polymethacrylic acid, polyvinyl alcohol, or polyethyleneimine.

[0014] By employing the above-mentioned technical solutions, these polymers can form hydrogen bonds or ionic bonds with other components in the polyethylene wax coating and the base film, thereby significantly improving the adhesion and interlayer bonding strength of the diaphragm. Furthermore, these polymers possess good flowability and film-forming properties, which can improve the processing performance of the polyethylene wax coating, making it easier to spread and form a uniform film during the preparation process.

[0015] In one specific implementation, the reinforcing fiber is a cellulose nanofiber.

[0016] By adopting the above technical solutions, cellulose nanofibers possess excellent mechanical properties and a high specific surface area, effectively enhancing the tensile strength, tear strength, and puncture resistance of the composite separator. This allows it to withstand greater mechanical stress in applications such as batteries, thereby improving safety. Cellulose nanofibers also exhibit good thermal stability, which can, to some extent, increase the heat distortion temperature of the composite separator, preventing deformation under high-temperature conditions and maintaining the integrity and performance of the separator.

[0017] In one specific implementation, the flame retardant is ammonium polyphosphate or melamine.

[0018] By adopting the above technical solutions, both ammonium polyphosphate and melamine can improve the flame retardant properties of polyethylene wax composite membranes. Furthermore, they can also enhance the thermal and chemical stability of the polyethylene wax composite membranes, allowing them to maintain better performance under high temperatures or harsh environments.

[0019] In one specific feasible implementation, the antioxidant is a phosphite.

[0020] By adopting the above technical solution, phosphite can not only effectively remove or reduce the active oxygen generated by polyethylene wax during processing, storage and use, thereby slowing down the oxidative degradation rate of the material, but also improve the hydrolysis resistance and thermal stability of the polyethylene wax coating and extend the service life of the diaphragm.

[0021] In one specific implementation, the ceramic coating comprises the following raw materials in parts by weight: 5-12 parts zirconium oxide powder, 1-2 parts sodium carboxymethyl cellulose, 3-5 parts polyacrylic acid liquid, and 7-10 parts styrene-acrylic emulsion.

[0022] By employing the above technical solutions, zirconium oxide exhibits high hardness and wear resistance, thereby improving the mechanical strength and durability of the diaphragm. Styrene-acrylic emulsion helps improve the water resistance and film-forming properties of the ceramic coating, ensuring that the coating maintains good performance even in humid environments. Polyacrylic acid liquid allows the ceramic coating to better adapt to the deformation of the diaphragm during use. Sodium carboxymethyl cellulose has good adhesion and dispersibility, ensuring that the components in the ceramic slurry are uniformly mixed and tightly bonded to the diaphragm surface. This contributes to the formation of a uniform and dense ceramic coating, improving the barrier properties of the diaphragm. Therefore, the above-mentioned ceramic coating can better resist physical damage during use, extending its service life. Furthermore, it also possesses excellent thermal stability and thermal conductivity, effectively reducing the coefficient of thermal expansion of the diaphragm at high temperatures and improving heat transfer efficiency.

[0023] Secondly, this application provides a method for preparing a high-adhesion polyethylene wax composite separator, which adopts the following technical solution:

[0024] A method for preparing a high-adhesion polyethylene wax composite separator includes the following steps:

[0025] Polyethylene wax and ethylene-vinyl acetate copolymer are added to xylene and heated until dissolved. Reinforcing fibers, flame retardants, antioxidants, interface compatibilizers, and polymers containing carboxyl, hydroxyl, or amine groups are added and mixed evenly to obtain a polyethylene wax coating liquid.

[0026] A polyethylene wax coating liquid is applied to both sides of a porous polyethylene base membrane and then dried to form a polyethylene wax coating.

[0027] A ceramic slurry is coated onto the surface of a polyethylene wax coating and dried. The ceramic slurry forms a ceramic coating, and the polyethylene wax coating and the ceramic coating together with a porous polyethylene base membrane form a separator for lithium-ion batteries.

[0028] By adopting the above technical solution, and by introducing ethylene-vinyl acetate copolymer, reinforcing fibers, interface compatibilizers, and polymers containing carboxyl, hydroxyl, or amine groups, the peeling phenomenon of polyethylene wax coating from other coatings or base films in high-adhesion polyethylene wax composite diaphragms can be effectively reduced, thereby improving the durability of the diaphragm.

[0029] Thirdly, this application provides an application of a high-adhesion polyethylene wax composite separator in lithium batteries, wherein the separator of the lithium battery is a high-adhesion polyethylene wax composite separator.

[0030] In summary, this application has the following beneficial effects:

[0031] 1. This application, through the combined action of polyethylene wax, ethylene-vinyl acetate copolymer, reinforcing fibers, interface compatibilizers, and polymers containing carboxyl, hydroxyl, or amine groups, helps to significantly improve the adhesion between the polyethylene wax coating and other coatings or base films, reducing the possibility of peeling and thus improving the durability of the diaphragm.

[0032] 2. Nano-silica or nano-alumina are preferred in this application, which can improve the thermal stability of the diaphragm.

[0033] 3. The method of this application can effectively reduce the peeling phenomenon between the polyethylene wax coating and other coatings or base films in high-adhesion polyethylene wax composite diaphragms, thereby improving the durability of the diaphragm. Detailed Implementation

[0034] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0035] Example

[0036] Example 1

[0037] This embodiment provides a high-adhesion polyethylene wax composite membrane, comprising a polyethylene wax coating, a ceramic coating, and a porous polyethylene base membrane.

[0038] The polyethylene wax coating comprises the following raw materials: 60g polyethylene wax, 10g ethylene-vinyl acetate copolymer (Mitsui, grade 410), 18g cellulose nanofibers (model NFC-31L1), 1.2g ammonium polyphosphate, 1.2g phosphite, 3g polyethylene glycol terephthalate, and 3g polyacrylic acid (liquid, analytical grade).

[0039] The ceramic coating comprises the following raw materials: 8g of zirconium oxide powder (5000 mesh), 1.5g of sodium carboxymethyl cellulose, 4g of polyacrylic acid liquid (analytical grade), and 8.5g of styrene-acrylic emulsion.

[0040] This embodiment also provides a method for preparing a high-adhesion polyethylene wax composite separator, comprising the following steps:

[0041] According to the formulation of the polyethylene wax coating, polyethylene wax and ethylene-vinyl acetate copolymer are added to xylene, heated to 130°C, and stirred until completely dissolved. Then, cellulose nanofibers, ammonium polyphosphate, phosphite, polyethylene glycol terephthalate and polyacrylic acid are added, and the mixture is kept warm and stirred until it is evenly mixed to obtain the polyethylene wax coating liquid.

[0042] A polyethylene wax coating liquid is applied to both sides of a porous polyethylene base membrane and then dried to form a polyethylene wax coating with a thickness of 1 μm.

[0043] According to the formula of the ceramic coating, zirconium oxide powder, sodium carboxymethyl cellulose, polyacrylic acid liquid and styrene-acrylic emulsion are mixed evenly to obtain ceramic slurry.

[0044] A ceramic slurry is coated onto the surface of a polyethylene wax coating and dried. The ceramic slurry forms a ceramic coating with a thickness of 2 μm. The polyethylene wax coating, the ceramic coating, and the polyethylene porous base membrane together form a separator for lithium-ion batteries.

[0045] Example 2

[0046] The only difference between this embodiment and Embodiment 1 is that the polyethylene wax coating includes the following raw materials: 50g polyethylene wax, 15g ethylene-vinyl acetate copolymer (Mitsui, grade 410), 25g cellulose nanofibers (model NFC-31L1), 2g ammonium polyphosphate, 2g phosphite, 4g polyethylene glycol terephthalate, and 4g polyacrylic acid (liquid, analytical grade).

[0047] Example 3

[0048] The only difference between this embodiment and Embodiment 1 is that the polyethylene wax coating includes the following raw materials: 70g polyethylene wax, 5g ethylene-vinyl acetate copolymer (Mitsui, grade 410), 10g cellulose nanofibers (model NFC-31L1), 0.5g ammonium polyphosphate, 0.5g phosphite, 2g polyethylene glycol terephthalate, and 2g polyacrylic acid (liquid, analytical grade).

[0049] Example 4

[0050] The only difference between this embodiment and Example 1 is that, in the preparation of the polyethylene wax coating, an equal amount of polycaprolactone is used to replace polyethylene glycol terephthalate.

[0051] Example 5

[0052] The only difference between this embodiment and Example 1 is that, in the preparation of the polyethylene wax coating, an equal amount of polyamide elastomer (Arkema, grade 2533SN 01) is used to replace polyethylene glycol terephthalate.

[0053] Example 6

[0054] The only difference between this embodiment and Embodiment 1 is that, in the preparation of the polyethylene wax coating, an equal amount of polymethacrylic acid is used to replace polyacrylic acid.

[0055] Example 7

[0056] The only difference between this embodiment and Embodiment 1 is that, in the preparation of the polyethylene wax coating, an equal amount of polyvinyl alcohol is used to replace polyacrylic acid.

[0057] Example 8

[0058] The only difference between this embodiment and Embodiment 1 is that, in the preparation of the polyethylene wax coating, an equal amount of polyethyleneimine is used to replace polyacrylic acid.

[0059] Example 9

[0060] The only difference between this embodiment and Embodiment 1 is that, in the preparation of the polyethylene wax coating, an equal amount of melamine is used to replace ammonium polyphosphate.

[0061] Example 10

[0062] The difference between this embodiment and Embodiment 1 lies only in that the polyethylene wax coating comprises the following raw materials: 60g of polyethylene wax, 10g of ethylene-vinyl acetate copolymer (Mitsui, grade 410), 18g of cellulose nanofibers (model NFC-31L1), 1.2g of ammonium polyphosphate, 1.2g of phosphite, 3g of polyethylene glycol terephthalate, 3g of polyacrylic acid (liquid, analytical grade), and 3g of nano-silica. In the preparation method of the high-adhesion polyethylene wax composite membrane: according to the ratio of the polyethylene wax coating, polyethylene wax and ethylene-vinyl acetate copolymer are added to xylene, heated to 130°C, and stirred until completely dissolved. Then, cellulose nanofibers, ammonium polyphosphate, phosphite, polyethylene glycol terephthalate, polyacrylic acid, and nano-silica are added, and the mixture is kept warm and stirred until homogeneous to obtain the polyethylene wax coating liquid.

[0063] Example 11

[0064] The difference between this embodiment and Embodiment 1 lies only in that the polyethylene wax coating comprises the following raw materials: 60g of polyethylene wax, 10g of ethylene-vinyl acetate copolymer (Mitsui, grade 410), 18g of cellulose nanofibers (model NFC-31L1), 1.2g of ammonium polyphosphate, 1.2g of phosphite, 3g of polyethylene glycol terephthalate, 3g of polyacrylic acid (liquid, analytical grade), and 3g of nano-alumina. In the preparation method of the high-adhesion polyethylene wax composite membrane: according to the ratio of the polyethylene wax coating, polyethylene wax and ethylene-vinyl acetate copolymer are added to xylene, heated to 130°C, and stirred until completely dissolved. Then, cellulose nanofibers, ammonium polyphosphate, phosphite, polyethylene glycol terephthalate, polyacrylic acid, and nano-alumina are added, and the mixture is kept warm and stirred until homogeneous to obtain the polyethylene wax coating liquid.

[0065] Example 12

[0066] The only difference between this embodiment and Embodiment 1 is that the ceramic coating includes the following raw materials: 5g of zirconium oxide powder (5000 mesh), 2g of sodium carboxymethyl cellulose, 5g of polyacrylic acid liquid (analytical grade), and 10g of styrene-acrylic emulsion.

[0067] Example 13

[0068] The only difference between this embodiment and Embodiment 1 is that the ceramic coating includes the following raw materials: 12g of zirconium oxide powder (5000 mesh), 1g of sodium carboxymethyl cellulose, 3g of polyacrylic acid liquid (analytical grade), and 7g of styrene-acrylic emulsion.

[0069] Comparative Example

[0070] Comparative Example 1

[0071] The only difference between this comparative example and Example 1 is that, in the preparation of the polyethylene wax coating, an equal amount of polyethylene wax is used to replace the ethylene-vinyl acetate copolymer.

[0072] Comparative Example 2

[0073] The only difference between this comparative example and Example 1 is that, in the preparation of the polyethylene wax coating, an equal amount of polyethylene wax is used to replace the cellulose nanofibers.

[0074] Comparative Example 3

[0075] The only difference between this comparative example and Example 1 is that, in the preparation of the polyethylene wax coating, an equal amount of polyethylene wax is used to replace polyacrylic acid.

[0076] Comparative Example 4

[0077] The only difference between this comparative example and Example 1 is that, in the preparation of the polyethylene wax coating, an equal amount of polyethylene wax is used to replace polyethylene glycol terephthalate.

[0078] Performance testing

[0079] The following performance tests were conducted on the high-adhesion polyethylene wax composite membranes prepared in Examples 1-13 and Comparative Examples 1-4:

[0080] Diaphragm peel strength test:

[0081] Take the diaphragms prepared in each embodiment and comparative example, cut them into diaphragm strips of 15mm*200mm, take a 15mm wide strip of 3M double-sided tape and stick it on a stainless steel plate, roll it back and forth twice with a roller, then turn the ceramic coating side of the diaphragm strip towards the tape and roll it back and forth three times (each back and forth roll for 10s), clamp the diaphragm strip vertically and centered in the upper and lower clamps of the testing instrument, the distance between the upper and lower clamps is 100mm, the lower edge of the steel plate is 2mm from the lower clamp, the testing speed is 50mm / min, and the peel strength is tested.

[0082] Thermal stability test:

[0083] Place the diaphragm in a 200°C oven for 1 hour and check the dimensional changes. Calculate the heat shrinkage using the following formula: Heat shrinkage (200°C / 1h) = (Previous size - Post-baking size) / Original size x 100%.

[0084] The test results are shown in Table 1.

[0085] Table 1

[0086]

[0087] As can be seen from Example 1 and Comparative Examples 1-4, and Table 1, compared to Example 1, the diaphragm peel strength of Comparative Examples 1-4 is significantly lower, and the thermal shrinkage is significantly greater. This indicates that using the raw material ratio and preparation method of Example 1 helps to reduce the peeling of the polyethylene wax coating from other coatings or base films in the upper diaphragm and improves the thermal stability of the diaphragm, which helps to improve the durability of the diaphragm.

[0088] As can be seen from Examples 1-13 and Table 1, the peel strength of the diaphragms in Examples 1-13 is greater than 500 N / m, and the thermal shrinkage is less than 1%. This indicates that using the raw material ratios and process conditions within the range of Examples 1-13 can help obtain diaphragms with high adhesion and high thermal stability.

[0089] Moreover, compared to Example 1, the diaphragm peel strength and thermal shrinkage of Examples 10-11 are significantly increased. This indicates that the addition of nano-silica or nano-alumina helps to further reduce the peeling of the polyethylene wax coating in the upper diaphragm from other coatings or base films and improves the thermal stability of the diaphragm.

[0090] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-adhesion polyethylene wax composite diaphragm, characterized in that, The product comprises a polyethylene wax coating, a ceramic coating, and a porous polyethylene base membrane. The polyethylene wax coating is located on the surface of the porous polyethylene base membrane, and the ceramic coating is located on the surface of the polyethylene wax coating. The polyethylene wax coating comprises the following raw materials in parts by weight: 50-70 parts polyethylene wax, 5-15 parts ethylene-vinyl acetate copolymer, 10-25 parts reinforcing fiber, 0.5-2 parts flame retardant, 0.5-2 parts antioxidant, 2-4 parts interface compatibilizer, and 2-4 parts polymer containing carboxyl, hydroxyl, or amine groups. The interface compatibilizer includes... The ceramic coating comprises at least one of ethylene glycol terephthalate, polycaprolactone, or polyamide elastomer; the polymer containing carboxyl, hydroxyl, or amine groups is any one of polyacrylic acid, polymethacrylic acid, polyvinyl alcohol, or polyethyleneimine; the reinforcing fiber is cellulose nanofiber; the flame retardant is ammonium polyphosphate or melamine; the antioxidant is phosphite; and the ceramic coating comprises the following raw materials in parts by weight: 5-12 parts zirconium oxide powder, 1-2 parts sodium carboxymethyl cellulose, 3-5 parts liquid polyacrylic acid, and 7-10 parts styrene-acrylic emulsion.

2. The high-adhesion polyethylene wax composite diaphragm according to claim 1, characterized in that, The polyethylene wax coating also includes nano-silica or nano-alumina.

3. A method for preparing a high-adhesion polyethylene wax composite separator according to any one of claims 1-2, characterized in that, Includes the following steps: Polyethylene wax and ethylene-vinyl acetate copolymer are added to xylene and heated until dissolved. Reinforcing fibers, flame retardants, antioxidants, interface compatibilizers, and polymers containing carboxyl, hydroxyl, or amine groups are added and mixed evenly to obtain a polyethylene wax coating liquid. A polyethylene wax coating liquid is applied to both sides of a porous polyethylene base membrane and then dried to form a polyethylene wax coating. A ceramic slurry is coated onto the surface of a polyethylene wax coating and dried. The ceramic slurry forms a ceramic coating, and the polyethylene wax coating and the ceramic coating together with a porous polyethylene base membrane form a separator for lithium-ion batteries.

4. The application of the high-adhesion polyethylene wax composite separator according to any one of claims 1-2 in lithium batteries, characterized in that, The separator of the lithium battery is a high-adhesion polyethylene wax composite separator.

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