A high-performance BOPP membrane for composite current collectors and its preparation method

Abstract

This invention belongs to the field of composite current collector base film technology, specifically relating to a high-performance BOPP film for composite current collectors and its preparation method. First, PP masterbatch is mixed with functional additives and composite fillers, melt-extruded, and biaxially stretched into a film to obtain a PP base film. Then, the PP base film is subjected to corona treatment, and a coating solution is uniformly coated onto the PP base film using an online coating method. Finally, it is cured into a film and then pulled and wound to obtain the final product. The composite filler is obtained by feeding MAH-g-PP and nanoparticles into an extruder, simultaneously adding stearic acid lubricant and polyvinyl alcohol, and extruding and granulating. The beneficial effects of this invention are: the addition of MAH-g-PP treated nanoparticles to PP significantly improves the mechanical strength of the base film; the formation of a cured coating on the surface of the base film significantly improves the interfacial bonding force with metal ions; and the synergistic effect of these two factors improves the heat resistance of the base film.

Description

Technical Field

[0001] This invention relates to the field of composite current collector base membrane technology, specifically to a high-performance BOPP membrane for composite current collectors and its preparation method. Background Technology

[0002] Composite current collectors are a new type of battery material, consisting of a polymer material intermediate layer and a metal conductive layer, and have advantages such as being lightweight, corrosion-resistant, and low-cost. The polymer material layer is typically a film made of PET, PP, or PI as the intermediate support layer. Biaxially oriented polypropylene (BOPP) film is widely used due to its excellent dielectric properties, high insulation strength, low cost, and high chemical stability.

[0003] However, direct application of BOPP membranes still faces some challenges, such as low mechanical strength, poor dimensional stability at high temperatures, and weak adhesion between the membrane surface inertness and the metal layer, all of which affect the conductivity and long-term stability of the current collector. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention first adds composite fillers to PP masterbatch to improve its mechanical properties, and then coats it with a coating liquid after stretching into a film to enhance its adhesion to the metal layer. Through this dual modification, the dimensional stability of the base film is effectively improved.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a high-performance BOPP membrane for composite current collectors includes the following steps:

[0007] 1) PP masterbatch is mixed with functional additives and composite fillers, melt-extruded, and biaxially stretched into a film to obtain PP base film;

[0008] 2) The PP base film is subjected to corona treatment, and the coating solution is evenly coated on the PP base film using an online coating method;

[0009] 3) Heat and set the coated film to solidify it into a film, then pull and wind it up to obtain the final product;

[0010] The functional additives include antioxidants, lubricants, and nucleating agents;

[0011] The composite filler is obtained by feeding MAH-g-PP and nanoparticles into an extruder, while adding stearic acid lubricant and polyvinyl alcohol, and then extruding and granulating.

[0012] The coating solution comprises 25-40 wt% brush-like polymer emulsion, 5-15 wt% silica sol, 5-20 wt% aqueous polyurethane dispersion, 0.1-0.5 wt% wetting and leveling agent, 0.1-0.3 wt% defoamer, 0.2-1 wt% thickener, and the balance being deionized water;

[0013] The preparation process of the brush-like polymer is as follows:

[0014] S1. Deionized water, emulsifier, 2-isopropenyl-2-oxazoline, and glycidyl methacrylate monomer are added to a stirred tank in a certain proportion to form a monomer emulsion.

[0015] S2. Add deionized water and emulsifier to the reactor and heat to 80±5℃. Add initiator and two-thirds of the monomer emulsion and react for 30 min.

[0016] S3. Slowly add the remaining monomer emulsion dropwise into the reactor, heat to 90°C, and react for 2 hours;

[0017] S4. Reduce the temperature to 50℃, slowly add ethylenediamine, and maintain the temperature for 4 hours. After the reaction is complete, adjust the pH to 8±0.5 to obtain the final product.

[0018] Furthermore, by weight, the raw materials include 100 parts PP, 4-8 parts functional additives, and 12-25 parts composite fillers.

[0019] Furthermore, the preparation process of the composite filler is as follows: nano-alumina powder is dispersed in an ethanol solution, ultrasonically treated to form a suspension, KH-560 is slowly added dropwise to the suspension, the temperature is raised to 60-80℃, refluxed for 4-6 hours, carboxylated graphene is added to the suspension, stirred and refluxed overnight, and after the reaction is completed, centrifuged, washed and dried to obtain nanoparticles.

[0020] MAH-g-PP and nanoparticles are fed into an extruder, along with stearic acid lubricant and polyvinyl alcohol, and then extruded and granulated to obtain the final product.

[0021] Furthermore, the mass ratio of nano-alumina powder, KH-560, and carboxylated graphene in the nanoparticles is 20~60:2~6:100.

[0022] Furthermore, in the composite filler, the mass ratio of MAH-g-PP, nanoparticles, stearic acid lubricant and polyvinyl alcohol is 10:15~20:0.1~0.2:0.2~1.

[0023] Furthermore, the functional additives include an antioxidant, a lubricant, and a nucleating agent in a mass ratio of 2:3:5; the antioxidant is antioxidant 1010; the lubricant is pentaerythritol stearate; and the nucleating agent is an aryl diamide nucleating agent.

[0024] Furthermore, in the preparation of the brush polymer, the molar ratio of 2-isopropenyl-2-oxazoline, glycidyl methacrylate, initiator, and ethylenediamine is 1.5~3:1:0.01:1.2; the amount of emulsifier is 2~5% of the monomer mass.

[0025] Furthermore, the emulsifier is a mixture of OP-10 and SDS; the initiator is potassium persulfate.

[0026] The present invention further provides a high-performance BOPP membrane for composite current collectors prepared by the preparation method described above.

[0027] Nanoparticles, using KH-560 as a coupling agent, anchor nano-alumina within the interlayer structure of carboxylated graphene, forming an alumina-graphene nanoparticle filler. Adding this filler to PP effectively improves the material's mechanical properties. However, nanoparticle fillers are not suitable for direct mixing and granulation with PP masterbatch, as uneven dispersion easily leads to performance degradation. In this application, maleic anhydride-grafted polypropylene (MAH-g-PP) is first used to pretreat the nanoparticles. Since MAH-g-PP contains polypropylene segments, it has good compatibility with PP masterbatch. Furthermore, by adding a small amount of lubricant and polyvinyl alcohol for coating, the dispersibility of the nanoparticles in the matrix is ​​greatly improved, avoiding stress concentration caused by agglomeration and, to a certain extent, increasing the tensile strength and impact strength of the base film.

[0028] A coating solution containing silica sol, brushed polymer, and polyurethane dispersion is cured on the surface of a base film to form a coating. The brushed polymer, which contains multiple active sites, can act as an interface enhancer. Through chemical reactions between the hydroxyl, oxazoline, and amino groups in the polymer and the epoxy, acid anhydride, and carboxyl groups in the base film, covalent bonds, hydrogen bonds, and intermolecular forces are formed, making the coating firmly bonded to the base film. At the same time, it can also chelate with the metal layer to form coordination bonds, which has a strong adsorption capacity for metal ions and thus a strong adhesion to the metal layer.

[0029] The synergistic effect of composite fillers and coatings significantly improves the dimensional stability of the base film under high-temperature conditions, ensuring the safety of the battery.

[0030] Compared with the prior art, the beneficial effects of the present invention are: the mechanical strength of the base film is significantly improved by adding nanoparticles treated with MAH-g-PP to PP; the interfacial bonding force with metal ions is significantly improved by forming a cured coating on the surface of the base film; and the synergistic effect of the two improves the heat resistance of the base film. Detailed Implementation

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Example: A high-performance BOPP membrane for composite current collectors

[0034] The BOPP film of this application contains 100 parts PP, 4 to 8 parts functional additives, and 12 to 25 parts composite filler. After the raw materials are stretched into a film, a coating liquid needs to be coated on its surface.

[0035] The functional additives include an antioxidant, a lubricant, and a nucleating agent in a mass ratio of 2:3:5; the antioxidant is antioxidant 1010; the lubricant is pentaerythritol stearate; and the nucleating agent is an aryl diamide nucleating agent.

[0036] The preparation process of the composite filler is as follows:

[0037] 30 g of nano-alumina powder was dispersed in 400 ml of ethanol solution and sonicated to form a suspension. 1.5 g of KH-560 was slowly added dropwise to the suspension and the temperature was raised to 60-80 °C. The mixture was refluxed for 4-6 h. 50 g of carboxylated graphene was added to the suspension and stirred and refluxed overnight. After the reaction was completed, the mixture was centrifuged, washed and dried to obtain nanoparticle filler.

[0038] 10 g of MAH-g-PP and 18 g of nanoparticle filler were fed into an extruder, along with 0.1 g of stearic acid lubricant and 0.7 g of polyvinyl alcohol. The mixture was then extruded and granulated to obtain the final product.

[0039] The coating solution comprises 25-40 wt% brushed polymer emulsion, 5-15 wt% silica sol, 5-20 wt% aqueous polyurethane dispersion, 0.1-0.5 wt% wetting and leveling agent, 0.1-0.3 wt% defoamer, 0.2-1 wt% thickener, and the balance being deionized water.

[0040] And the remainder is deionized water. The preparation process of the brush-like polymer is as follows:

[0041] S1. Add 100g deionized water, 4g emulsifier (a mixture of OP-10 and SDS), 45g 2-isopropenyl-2-oxazoline, and 15g glycidyl methacrylate monomer to a stirred tank and stir at high speed to form a monomer emulsion.

[0042] S2. Add 50g of deionized water and 1g of emulsifier to the reactor, heat to 80±5℃ under nitrogen protection, add 0.3g of potassium persulfate initiator and two-thirds of the monomer emulsion, and react for 30min.

[0043] S3. Slowly add the remaining monomer emulsion dropwise into the reactor, heat to 90°C, and react for 2 hours;

[0044] S4. Reduce the temperature to 50℃, slowly add 7.5g of ethylenediamine, keep the temperature constant for 4 hours, and after the reaction is complete, adjust the pH to 8±0.5 to obtain the final product.

[0045] Example 1:

[0046] 1) Mix 100 parts of PP masterbatch with 4 parts of functional additives and 12 parts of composite filler, put them into a twin-screw extruder for melt extrusion, and then cut them into pellets by water cooling to obtain masterbatch;

[0047] 2) The masterbatch is fed into a biaxial stretching unit, melt-extruded at 220~250℃, and cast into sheets;

[0048] 3) The cast sheet enters the synchronous stretching device and is stretched bidirectionally at 150~170℃, with a longitudinal stretching ratio of 2~3.8 and a transverse stretching ratio of 2.5~4, to obtain a PP base film;

[0049] 2) The PP base film is subjected to corona treatment using an online coating method at a rate of 5 g / m². 2 The amount of coating liquid used should be evenly applied to the PP base film;

[0050] 3) Heat and set the coated film to solidify it into a film, then pull and wind it up to obtain the final product;

[0051] The coating liquid comprises 25 wt% brush-like polymer emulsion, 5 wt% silica sol, 20 wt% aqueous polyurethane dispersion, 0.2 wt% wetting and leveling agent, 0.1 wt% defoamer, 0.2 wt% thickener, and the balance being deionized water.

[0052] Example 2:

[0053] 1) Mix 100 parts of PP masterbatch with 6 parts of functional additives and 20 parts of composite filler, put them into a twin-screw extruder for melt extrusion, and then cut them into pellets by water cooling to obtain masterbatch;

[0054] 2) The masterbatch is fed into a biaxial stretching unit, melt-extruded at 220~250℃, and cast into sheets;

[0055] 3) The cast sheet enters the synchronous stretching device and is stretched bidirectionally at 150~170℃, with a longitudinal stretching ratio of 2~3.8 and a transverse stretching ratio of 2.5~4, to obtain a PP base film;

[0056] 2) The PP base film is subjected to corona treatment using an online coating method at a rate of 5 g / m². 2 The amount of coating liquid used should be evenly applied to the PP base film;

[0057] 3) Heat and set the coated film to solidify it into a film, then pull and wind it up to obtain the final product;

[0058] The coating liquid comprises 30 wt% brush-like polymer emulsion, 8 wt% silica sol, 12 wt% aqueous polyurethane dispersion, 0.2 wt% wetting and leveling agent, 0.1 wt% defoamer, 0.2 wt% thickener, and the balance being deionized water.

[0059] Example 3:

[0060] 1) Mix 100 parts of PP masterbatch with 8 parts of functional additives and 25 parts of composite filler, put them into a twin-screw extruder for melt extrusion, and then cut them into pellets by water cooling to obtain masterbatch;

[0061] 2) The masterbatch is fed into a biaxial stretching unit, melt-extruded at 220~250℃, and cast into sheets;

[0062] 3) The cast sheet enters the synchronous stretching device and is stretched bidirectionally at 150~170℃, with a longitudinal stretching ratio of 2~3.8 and a transverse stretching ratio of 2.5~4, to obtain a PP base film;

[0063] 2) The PP base film is subjected to corona treatment using an online coating method at a rate of 5 g / m². 2 The amount of coating liquid used should be evenly applied to the PP base film;

[0064] 3) Heat and set the coated film to solidify it into a film, then pull and wind it up to obtain the final product;

[0065] The coating liquid comprises 40 wt% brush-like polymer emulsion, 15 wt% silica sol, 5 wt% aqueous polyurethane dispersion, 0.5 wt% wetting and leveling agent, 0.1 wt% defoamer, 0.8% thickener, and the balance being deionized water.

[0066] Comparative Example 1:

[0067] 1) Mix 100 parts of PP masterbatch with 8 parts of functional additives, 10 parts of MAH-g-PP, 5 parts of nano alumina, and 10 parts of graphene oxide, and put them into a twin-screw extruder for melt extrusion. After water cooling and pelletizing, the masterbatch is obtained.

[0068] 2) The masterbatch is fed into a biaxial stretching unit, melt-extruded at 220~250℃, and cast into sheets;

[0069] 3) The cast sheet enters the synchronous stretching device and is stretched bidirectionally at 150~170℃, with a longitudinal stretching ratio of 2~3.8 and a transverse stretching ratio of 2.5~4, to obtain a PP base film;

[0070] 2) The PP base film is subjected to corona treatment using an online coating method at a rate of 5 g / m². 2 The amount of coating liquid used should be evenly applied to the PP base film;

[0071] 3) Heat and set the coated film to solidify it into a film, then pull and wind it up to obtain the final product;

[0072] The coating liquid comprises 30 wt% brush-like polymer emulsion, 8 wt% silica sol, 12 wt% aqueous polyurethane dispersion, 0.2 wt% wetting and leveling agent, 0.1 wt% defoamer, 0.2 wt% thickener, and the balance being deionized water.

[0073] Comparative Example 2:

[0074] 1) Mix 100 parts of PP masterbatch with 8 parts of functional additives and 25 parts of composite filler, put them into a twin-screw extruder for melt extrusion, and then cut them into pellets by water cooling to obtain masterbatch;

[0075] 2) The masterbatch is fed into a biaxial stretching unit, melt-extruded at 220~250℃, and cast into sheets;

[0076] 3) The cast sheet enters the synchronous stretching device and is stretched bidirectionally at 150~170℃, with a longitudinal stretching ratio of 2~3.8 and a transverse stretching ratio of 2.5~4, to obtain a PP base film;

[0077] 2) The PP base film is subjected to corona treatment using an online coating method at a rate of 5 g / m². 2 The amount of coating liquid used should be evenly applied to the PP base film;

[0078] 3) Heat and set the coated film to solidify it into a film, then pull and wind it up to obtain the final product;

[0079] The coating liquid comprises 8 wt% silica sol, 42 wt% aqueous polyurethane dispersion, 0.2 wt% wetting and leveling agent, 0.1 wt% defoamer, 0.2 wt% thickener, and the balance being deionized water.

[0080] application:

[0081] A conductive layer is prepared on the surface of the base film by electroplating, thus obtaining the composite current collector.

[0082] Mechanical properties of the biaxial BOPP films prepared in Examples 1-3 and Comparative Examples 1-2 were tested in accordance with GB / T16958-2008 standard.

[0083] The adhesive force test method for composite current collectors is performed in accordance with patent CN116504992A;

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

[0085] Table 1

[0086]

[0087] Comparative Example 1 used untreated and uncomposite nanoparticles (directly added MAH-g-PP, nano-alumina, and graphene oxide). The results showed that its properties (tensile strength, thermal shrinkage, and puncture strength) were the worst among all samples. This indicates that untreated nanoparticles are prone to aggregation, leading to stress concentration and thus performance degradation. Comparative Example 2 used the composite filler of this invention, but the coating solution lacked the crucial "brush-like polymer emulsion." The results showed that its adhesion (1.9 N / cm) was significantly lower than other examples using complete coating solutions (2.9-3.5 N / cm), proving that the brush-like polymer with abundant active groups (hydroxyl, oxazoline, amino) in the coating solution is key to generating strong adhesion. The technical solution of this application significantly improves both the mechanical properties of the base film and its adhesion to the metal layer.

[0088] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A method for preparing a high-performance BOPP membrane for composite current collectors, characterized in that, Includes the following steps: 1) PP masterbatch is mixed with functional additives and composite fillers, melt-extruded, and biaxially stretched into a film to obtain PP base film; 2) The PP base film is subjected to corona treatment, and the coating solution is evenly coated on the PP base film using an online coating method; 3) Heat and set the coated film to solidify it into a film, then pull and wind it up to obtain the final product; The functional additives include antioxidants, lubricants, and nucleating agents; The composite filler is obtained by feeding MAH-g-PP and nanoparticles into an extruder, while adding stearic acid lubricant and polyvinyl alcohol, and then extruding and granulating. The coating solution comprises 25-40 wt% brush-like polymer emulsion, 5-15 wt% silica sol, 5-20 wt% aqueous polyurethane dispersion, 0.1-0.5 wt% wetting and leveling agent, 0.1-0.3 wt% defoamer, 0.2-1 wt% thickener, and the balance being deionized water; The preparation process of the brush-like polymer is as follows: S1. Deionized water, emulsifier, 2-isopropenyl-2-oxazoline, and glycidyl methacrylate monomer are added to a stirred tank in a certain proportion to form a monomer emulsion. S2. Add deionized water and emulsifier to the reactor and heat to 80±5℃. Add initiator and two-thirds of the monomer emulsion and react for 30 min. S3. Slowly add the remaining monomer emulsion dropwise into the reactor, heat to 90°C, and react for 2 hours; S4. Lower the temperature to 50℃, slowly add ethylenediamine, and maintain the temperature for 4 hours. After the reaction is complete, adjust the pH to 8±0.5 to obtain the final product. The preparation process of the composite filler is as follows: nano-alumina powder is dispersed in an ethanol solution, ultrasonically treated to form a suspension, KH-560 is slowly added dropwise to the suspension, the temperature is raised to 60-80℃, refluxed for 4-6 hours, carboxylated graphene is added to the suspension, stirred and refluxed overnight, and after the reaction is completed, centrifuged, washed and dried to obtain nanoparticles. MAH-g-PP and nanoparticles are fed into an extruder, along with stearic acid lubricant and polyvinyl alcohol, and then extruded and granulated to obtain the final product.

2. The method for preparing a high-performance BOPP membrane for composite current collectors as described in claim 1, characterized in that, By weight, the raw materials include 100 parts PP, 4-8 parts functional additives, and 12-25 parts composite filler.

3. The method for preparing a high-performance BOPP membrane for composite current collectors as described in claim 1, characterized in that, The mass ratio of nano-alumina powder, KH-560, and carboxylated graphene in the nanoparticles is 20~60:2~6:

100.

4. The method for preparing a high-performance BOPP membrane for composite current collectors as described in claim 1, characterized in that, In the composite filler, the mass ratio of MAH-g-PP, nanoparticles, stearic acid lubricant and polyvinyl alcohol is 10:15~20:0.1~0.2:0.2~1.

5. The method for preparing a high-performance BOPP membrane for composite current collectors as described in claim 1, characterized in that, The functional additives include an antioxidant, a lubricant, and a nucleating agent in a mass ratio of 2:3:5; the antioxidant is antioxidant 1010; the lubricant is pentaerythritol stearate; and the nucleating agent is an aryl diamide nucleating agent.

6. The method for preparing a high-performance BOPP membrane for composite current collectors as described in claim 1, characterized in that, In the preparation of the brush polymer, the molar ratio of 2-isopropenyl-2-oxazoline, glycidyl methacrylate, initiator, and ethylenediamine is 1.5~3:1:0.01:1.2; the amount of emulsifier is 2~5% of the monomer mass.

7. The method for preparing a high-performance BOPP membrane for composite current collectors as described in claim 1, characterized in that, The emulsifier is a mixture of OP-10 and SDS; the initiator is potassium persulfate.

8. A high-performance BOPP membrane for composite current collectors prepared by any one of claims 1-7.

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