A cpp film for solid-state batteries and a method for manufacturing the same

Abstract

The present application relates to the technical field of battery packaging materials, and particularly relates to a CPP film for solid-state batteries and a preparation method thereof, the CPP film for solid-state batteries comprises a three-layer structure of a corona layer, an intermediate layer and a heat-sealing layer; the corona layer is made of low-melting-point binary random copolymerized polypropylene and polybutene elastomer blend; the intermediate layer is made of low-melting-point block polypropylene and styrene elastomer blend; and the heat-sealing layer is made of high-melting-point binary random copolymerized polypropylene, polybutene elastomer and slip opening agent blend; due to the fact that the corona layer, the intermediate layer and the heat-sealing layer are all made of targeted elastomers and appropriate additive proportions, the impact resistance of the CPP film is greatly improved, the impact resistance is greater than or equal to 12 mm, and due to the fact that UHMW-PE ultrafine powder is used as a slip agent to compensate the impact resistance, the powder is not easy to precipitate and fall off, and the application demand can be better satisfied; the preparation method is simple in process flow, easy to prepare, and can meet the demand of mass production and manufacturing.

Description

Technical Field

[0001] This invention relates to the field of battery packaging materials technology, and in particular to a CPP film for solid-state batteries and its preparation method. Background Technology

[0002] Compared to traditional lithium-ion battery technology, solid-state batteries offer higher energy density, faster charging, and safer operation. In particular, solid-state batteries are less prone to short circuits due to lithium dendrites piercing the separator under high current, do not experience side reactions at high temperatures, and do not burn due to gas production. Therefore, safety is considered one of the fundamental driving forces behind the development of solid-state batteries. Solid-state lithium batteries eliminate the need for flexible films such as PE / PP separators, resulting in a rigid and brittle structure lacking elasticity. If a rigid metal casing is used, the hard casing and solid electrode assembly are easily squeezed and collided during the casing process, during charging and discharging, or during vibrations and impacts in the operating environment, leading to electrode assembly breakage. Therefore, almost all solid-state battery manufacturers use aluminum-plastic film pouch packaging. Solid-state batteries require a higher drawing depth for aluminum-plastic film, especially CPP (cut per inch) aluminum-plastic film; data shows that the drawing depth requirement for CPP aluminum-plastic film in solid-state batteries is ≥12mm.

[0003] Currently, commercially available dry-process aluminum-plastic composite films (CPP films) use a combination of homopolymer polypropylene, binary copolymer polypropylene, and ternary copolymer polypropylene, produced through a three-layer co-extrusion casting process. High-melting-point homopolymer polypropylene or binary block copolymer polypropylene forms the middle layer, while binary random copolymer polypropylene and ternary random copolymer polypropylene serve as heat-sealing and composite layers on both sides. Each layer, especially the middle layer, is supplemented with a small amount of ethylene-propylene elastomer to mitigate stress whitening. Dry-process CPPs designed and produced in this way can only achieve a drawing depth of approximately 7-8 mm, which is insufficient to meet the drawing depth requirements of solid-state batteries.

[0004] Currently, there is very little research on aluminum-plastic films and their CPP layers for solid-state batteries. Most studies focus on improving certain performance aspects through structural adjustments or improvements to the aluminum-plastic film, without addressing the enhancement of the drawing performance, especially the CPP layer. For example, literature CN109263220A adds four non-polar anchoring layers (plasma physical anchoring layers) to conventional aluminum-plastic films to improve their puncture resistance and meet the needs of solid-state batteries. Literature CN209224629U adds a fluoroplastic film layer, a polyvinylidene chloride film layer, and an aluminized ethylene-vinyl alcohol copolymer stretching film to a three-layer aluminum-plastic film structure to improve weather resistance, aging resistance, and chemical resistance for use in solid-state batteries. Literature CN216213735U provides an aluminum-plastic film for solid-state batteries with high-temperature resistance by adding a current collection mechanism, a high-temperature resistant mechanism, and a heat dissipation mechanism to the aluminum-plastic film.

[0005] Therefore, this application aims to provide a CPP thin film for solid-state batteries and a method for preparing the same, in order to better solve the above-mentioned technical problems. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a CPP film for solid-state batteries and its preparation method. The film is co-extruded and cast by blending polypropylene resin and functional elastomers. By selecting and controlling the proportions of polypropylene and functional elastomers in each layer, the film formed by co-extrusion and casting can meet the requirements of high drawing depth in solid-state battery packaging without stress whitening, and also has good heat-sealing performance and electrolyte resistance.

[0007] The technical solution adopted in this invention is:

[0008] A CPP film for solid-state batteries, wherein the CPP film has a three-layer structure consisting of a corona layer, an intermediate layer and a heat-sealing layer;

[0009] The corona layer is made of a blend of low-melting-point binary random copolymer polypropylene and polybutene elastomer.

[0010] The intermediate layer is made of a blend of low melt index block polypropylene and styrene-based elastomer;

[0011] The heat-sealing layer is made of a blend of high-melting-point binary random copolymer polypropylene, polybutene elastic material, and slip-resistant opening agent.

[0012] Furthermore, the total thickness of the CPP film is set to 35-80 μm, wherein the layer ratio of the corona layer, the intermediate layer and the heat-sealing layer is set to 1:3:1 to 1:6:1; the overall tensile strength of the CPP film with the intermediate layer as the main support layer is ≥30 MPa, the elongation at break is ≥900%, and the surface friction coefficient of the heat-sealing layer is ≤0.15.

[0013] Furthermore, the low-melting-point binary random copolymer polypropylene has a melting point range of 125℃ to 135℃, an ethylene content of 3% to 6%, and a melt index of 5 to 10 g / 10 min (230℃ / 2.16 kg); the density of the polybutene elastomer is less than 0.9 g / cm³. 3 Shore hardness 55-65A, melt index 1-12g / 10min (230℃ / 2.16Kg).

[0014] Furthermore, in the low-melting-point binary random copolymer polypropylene and polybutene elastomer blend, the weight percentage of the low-melting-point binary random copolymer polypropylene is 60% to 85%, preferably 70% to 80%. If the proportion of polybutene elastomer is too low, the corona layer of CPP will turn white during deep drawing; if the proportion of polybutene elastomer is too high, the mechanical strength of the corona layer will be insufficient, and it will be prone to cracking during deep drawing.

[0015] Specifically, polybutene elastomers can significantly improve the toughness of blended systems. Since ethylene has poor chemical resistance, if ethylene-propylene elastomers are used for toughening, the ethylene content is difficult to control, and the composite layer will delaminate after long-term use. Polybutene elastomers do not have this problem.

[0016] Furthermore, the low melt flow index block polypropylene has a melt flow index of 1-3 g / 10 min (230℃ / 2.16Kg) and a melting point of 160℃-170℃; the styrene elastomer is a hydrogenated styrene elastomer with a melt flow index of 1-30 g / 10 min and a tensile strength greater than 30 MPa. Compared with polyolefin elastomers, styrene elastomers can greatly improve the impact toughness of CPP.

[0017] The selected polybutene elastomer has a density of less than 0.9 g / cm³. 3 Shore hardness 55-65A, melt index 1-12g / 10min (230℃ / 2.16Kg).

[0018] Furthermore, in the aforementioned low melt flow index block polypropylene and styrene-based elastomer blend, the weight percentage of the low melt flow index block polypropylene is 15%–45%, preferably 25%–35%. If the styrene elastomer percentage is too low, the resulting CPP will lack toughness and is prone to cracking and stress whitening under deep drawing conditions; if the percentage is too high, the CPP will have a low permanent deformation rate during deep drawing, and after deep drawing, the high elastic recovery rate of the CPP will cause severe curling of the aluminum-plastic film towards the CPP layer, thus affecting subsequent battery manufacturing processes.

[0019] Furthermore, the high-melting-point binary random copolymer polypropylene has a melting point range of 145℃ to 155℃, an ethylene content of less than 3%, and a melt index of 5 to 10 g / 10 min (230℃ / 2.16Kg).

[0020] Furthermore, in the blend of high-melting-point binary random copolymer polypropylene, polybutene elastomer, and slip sealant, the weight percentage of the high-melting-point binary random copolymer polypropylene is 70%–85%, preferably 75%–80%, and the weight percentage of the slip sealant is no more than 10%. The high melting point of the high-melting-point binary random copolymer polypropylene ensures excellent heat-sealing strength of the heat-sealing layer under high-temperature heat-sealing conditions. However, if the proportion is too high, the heat-sealing layer will lack toughness and is prone to cracking and whitening under high-depth drawing conditions. On the other hand, if the proportion of polybutene elastomer is too high, the heat-sealing strength will be reduced due to the excessive butene content in the blend.

[0021] Furthermore, the styrene-based elastomer is any one of SEBS, SIBS, SEPS, and SEEPS; the slip-forming agent is ultra-high molecular weight polyethylene powder.

[0022] Specifically, the slip-resistant opening agent of the heat-sealing layer of this CPP film is a slip masterbatch, using ultra-high molecular weight polyethylene (UHMW-PE) ultrafine powder as the slip agent and high-melting-point binary random copolymer polypropylene as the carrier. This slip masterbatch possesses high-temperature slip resistance and compensates for drawing depth. During high-temperature lamination of aluminum-plastic film (80℃ / 30S) and storage (55℃ / 2 days), the slip agent does not migrate, eliminating the need for a secondary application of slip agent before the aluminum-plastic film leaves the factory.

[0023] Based on the same inventive concept, this application also provides a method for preparing the above-mentioned CPP thin film for solid-state batteries, comprising the following preparation steps:

[0024] S1. Raw materials for blending to prepare corona layer, intermediate layer and heat seal layer;

[0025] S2. The raw materials for the corona layer, intermediate layer and heat-sealing layer are fed into the three extruders corresponding to the three-layer co-extrusion casting machine. After setting the thickness ratio of the three layers, CPP film is produced by co-extrusion casting process.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. The solid-state battery CPP film provided by this invention has a three-layer structure consisting of a corona layer, an intermediate layer, and a heat-sealing layer. The corona layer is made of a blend of low-melting-point binary random copolymer polypropylene and polybutene elastomer. The intermediate layer is made of a blend of low-melting-index block polypropylene and styrene elastomer. The heat-sealing layer is made of a blend of high-melting-point binary random copolymer polypropylene, polybutene elastomer, and a slip-forming agent. By selecting the appropriate elastomers and proportions for each layer, and designing the slip material in the heat-sealing layer, the tensile properties and long-lasting slip properties of CPP are significantly improved. This effectively overcomes the problems of whitening, cracking, breakage, and powdering caused by friction during the deep-drawing process of aluminum-plastic film, as well as the instability and failure of slip properties during storage. It eliminates the need for secondary coating of slip agent and possesses excellent heat-sealing performance and electrolyte resistance.

[0028] 2. The preparation method provided by this invention has a simple process flow, is easy to prepare, and meets the needs of mass production. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the preparation process of the CPP film in an embodiment of the present invention. Detailed Implementation

[0030] To facilitate understanding of the present invention, it will be described more fully below through embodiments, and preferred embodiments of the present invention are given below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Any other implementation schemes obtained by modifying or equivalently substituting the technical solutions of the present invention without inventive step are all within the protection scope of the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0032] The numerical values ​​disclosed in the embodiments of this invention are approximate values, not definitive values. Where error or experimental conditions permit, all values ​​within the error range may be included, and the specific numerical values ​​disclosed in the embodiments of this invention are not limited to those specified.

[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0034] Example 1

[0035] This embodiment provides a method for preparing a CPP film, including the following steps:

[0036] S1. The corona layer raw material was prepared using 70% low-melting-point binary random copolymer polypropylene and 30% polybutene elastomer. The low-melting-point binary random copolymer polypropylene (TPC Singapore FL7642) has a melting point of 128℃ and a melt index of 7 g / min. The polybutene elastomer (Ryander Basel Koattro KT MR 05) has a density of 0.87 g / cm³. 3 Shore hardness 60A;

[0037] The intermediate layer material was prepared using 65% low melt index block copolymer polypropylene (Hanwha Total CF200) and 35% styrene elastomer (Kraton D1170).

[0038] The corona layer was prepared using 75% high-melting-point binary random copolymer polypropylene, 15% polybutene elastomer, and 10% slip masterbatch. The low-melting-point binary random copolymer polypropylene (FL7642, TPC Singapore) had a melting point of 151℃ and a melt index of 7 g / min. The polybutene elastomer (Koattro KT MR 05, LyondellBasell) had a density of 0.87 g / cm³. 3With a Shore hardness of 60A, the slip masterbatch uses high-melting-point binary random polypropylene (rPP-2) as a carrier and ultra-high molecular weight polyethylene ultrafine powder as a slip agent (Mitsui Chemicals MIPELON). TM PM200 is produced by twin-screw granulation at a temperature of 210℃.

[0039] S2. According to the weight ratio, the above-mentioned corona layer, intermediate layer, and heat-sealing layer raw materials are respectively fed into the three extruders corresponding to the three-layer co-extrusion casting machine (screw diameters are respectively). With an aspect ratio of 32, the thickness ratio of the three layers is set to 1:6:1, and CPP film is produced by co-extrusion casting process.

[0040] Example 2

[0041] The difference between the CPP film preparation method provided in this embodiment and that in Example 1 is:

[0042] The corona layer raw material was prepared using 80% low-melting-point binary random copolymer polypropylene and 20% polybutene elastomer.

[0043] The rest is the same as in Example 1.

[0044] Example 3

[0045] The difference between the CPP film preparation method provided in this embodiment and that in Example 1 is:

[0046] The intermediate layer material is prepared using 75% low melt index block copolymer polypropylene and 25% styrene elastomer.

[0047] The rest is the same as in Example 1.

[0048] Example 4

[0049] The difference between the CPP film preparation method provided in this embodiment and that in Example 1 is:

[0050] The corona layer raw material was prepared using 80% high-melting-point binary random copolymer polypropylene, 10% polybutene elastomer, and 10% slip masterbatch.

[0051] The rest is the same as in Example 1.

[0052] Example 5

[0053] The difference between the CPP film preparation method provided in this embodiment and that in Example 3 is:

[0054] The corona layer was prepared using 80% low-melting-point binary random copolymer polypropylene and 20% polybutene elastomer.

[0055] The rest is the same as in Example 3.

[0056] Example 6

[0057] The difference between the CPP film preparation method provided in this embodiment and that in Example 3 is:

[0058] The corona layer was prepared using 80% high-melting-point binary random copolymer polypropylene, 10% polybutene elastomer, and 10% slip masterbatch.

[0059] The rest is the same as in Example 3.

[0060] Comparative Example 1

[0061] This comparative example provides a method for preparing a CPP film, comprising the following steps:

[0062] S1. A corona layer is prepared using 10% binary random copolymer polypropylene with a melting point of 135℃ and 90% ethylene propylene elastomer (commercially available).

[0063] The intermediate layer was prepared using 65% low melt index block copolymer polypropylene and 35% ethylene propylene elastomer.

[0064] The corona layer was prepared using 80% of binary random copolymer polypropylene (commercially available) with a melting point of 145℃, 15% of ethylene propylene elastomer, and 5% of erucamide slip masterbatch (commercially available).

[0065] S2. Set the thickness ratio of the three layers to 1:6:1, and produce CPP film through co-extrusion casting process.

[0066] Comparative Example 2

[0067] This comparative example provides a method for preparing a CPP film, comprising the following steps:

[0068] S1. A corona layer was prepared using a 70% low-melting-point binary random copolymer polypropylene and a 30% polybutene elastomer.

[0069] The intermediate layer was prepared using 90% low melt index block copolymer polypropylene and 10% styrene elastomer.

[0070] The corona layer was prepared using 90% high-melting-point binary random copolymer polypropylene, 5% polybutene elastomer, and 5% erucamide slip masterbatch (commercially available).

[0071] S2. Set the thickness ratio of the three layers to 1:6:1, and produce CPP film through co-extrusion casting process.

[0072] The CPP films prepared in Examples 1-6, Comparative Examples 1 and 2 were fabricated into dry-process aluminum-plastic films. The drawing performance of the aluminum-plastic films was tested using a drawing tester to evaluate the drawing resistance of the CPP films. Test items included stress whitening, cracking, and precipitation. Thirty samples were tested each time, and the test results are shown in the table below.

[0073]

[0074]

[0075] Note 1: The thickness of all CPP film samples tested above is 80µm.

[0076] Note 2: During the testing process, it was found that no powder shedding was observed because the UHMW-PE ultrafine powder used in Examples 1-6 was used as a slip agent.

[0077] As can be seen from the above test results, the dry-process aluminum-plastic film made using the CPP film provided in this application has greatly improved the depth resistance of the CPP film, achieving a depth resistance of ≥12mm, because the corona layer, intermediate layer and heat-sealing layer are all made with targeted elastomers and appropriate addition ratios. In addition, because UHMW-PE ultrafine powder is used as a slip agent to compensate for the depth resistance, it is not easy to precipitate and shed powder, which can better meet the application requirements.

[0078] In summary, the CPP film provided in this application consists of a three-layer structure: a corona layer, an intermediate layer, and a heat-sealing layer. By selecting appropriate elastomers and their proportions for each layer, and designing the slip material for the heat-sealing layer, the tensile properties and long-lasting slip properties of CPP are significantly improved. This effectively overcomes the problems of whitening, cracking, breakage, and powdering caused by friction during the deep-drawing process of aluminum-plastic film, as well as the instability and failure of slip properties during storage. It eliminates the need for secondary coating of slip agent and possesses excellent heat-sealing performance and electrolyte resistance, showing promising application prospects.

[0079] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A CPP film for solid-state batteries, characterized by, The CPP film is a three-layer structure composed of a corona layer, an intermediate layer and a heat-sealing layer; The corona layer is made of a low-melting-point binary random copolymerized polypropylene and a polybutene-based elastomer blend; The intermediate layer is made of a low-melting-point block polypropylene and a styrene-based elastomer blend; The heat-sealing layer is made of a high-melting-point binary random copolymerized polypropylene, a polybutene-based elastomer and a slip opening agent blend; The low-melting-point binary random copolymerized polypropylene has a melting point ranging from 125 DEG C to 135 DEG C, an ethylene content of 3% to 6%, and a melt index of 5 to 10 g / 10 min under the test conditions of 230 DEG C and 2.16 Kg; the polybutene-based elastomer has a density less than 0.9 g / cm 3 3, a Shore hardness of 55 to 65 A, and a melt index of 1 to 12 g / 10 min under the test conditions of 230 DEG C and 2.16 Kg; in the low-melting-point binary random copolymerized polypropylene and polybutene-based elastomer blend, the low-melting-point binary random copolymerized polypropylene accounts for 60% to 85% by weight. The low-melting-point block polypropylene has a melt index of 1-3 g / 10 min and a melting point of 160-170 DEG C under the test conditions of 230 DEG C and 2.16 Kg; the styrene-based elastomer is a hydrogenated modified styrene elastomer, which has a melt index of 1-30 g / 10 min and a tensile strength greater than 30 MPa; The weight percentage of the styrene-based elastomer in the low-melting-point block polypropylene and styrene-based elastomer blend is 15-45%; The high-melting-point binary random copolymerized polypropylene has a melting point range of 145-155 DEG C and an ethylene content of less than 3%, and a melt index of 5-10 g / 10 min under the test conditions of 230 DEG C and 2.16 Kg; The weight percentage of the high-melting-point binary random copolymerized polypropylene in the high-melting-point binary random copolymerized polypropylene, polybutene-based elastomer and slip opening agent blend is 70-85%, and the weight percentage of the slip opening agent is not more than 10%; The slip opening agent is an ultrahigh molecular weight polyethylene powder.

2. The CPP film for solid-state batteries according to claim 1, characterized by The total thickness of the CPP film is 35-80 um, and the layer ratio of the corona layer, the intermediate layer and the heat-sealing layer is 1:3:1 to 1:6:

1.

3. The CPP film for solid-state batteries according to claim 1, characterized by The styrene-based elastomer is any one of SEBS, SIBS, SEPS and SEEPS.

4. The production method of CPP film for solid-state batteries according to any one of claims 1 to 3, characterized in that, The preparation steps include: S1. Blending the raw materials for the corona layer, the intermediate layer and the heat-sealing layer; S2. Putting the raw materials for the corona layer, the intermediate layer and the heat-sealing layer into the corresponding three extruders of a three-layer co-extrusion casting machine, setting the three-layer thickness ratio, and then preparing the CPP film by a co-extrusion casting process.

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