Polyamide composite film for packaging solid-state battery and preparation method of polyamide composite film

Abstract

The invention discloses a polyamide composite film for packaging a solid-state battery and a preparation method of the polyamide composite film, the film comprises four film layer structures which are a polyester layer, a barrier bonding layer, an EVOH barrier layer and a polyamide surface layer in sequence from top to bottom; wherein the components of the polyester layer comprise copolymerized polyester, silicone resin and carbon nanospheres, and the components of the barrier bonding layer comprise polyolefin hot melt adhesive resin and graphene; the EVOH barrier layer comprises the following components: EVOH and graphene; the polyamide surface layer comprises the components of polyamide and graphene. According to the polyamide composite film for solid-state battery packaging, the oxygen permeation amount and the water vapor permeation amount are obviously reduced, meanwhile, the good pit punching depth and heat conduction performance are achieved, the film has the excellent barrier performance, pit punching performance and size stability, the heat conduction performance and corrosion resistance are improved, and the service life of the film is prolonged. The aluminum-plastic film is especially suitable for an aluminum-plastic film protection layer for solid-state battery packaging.

Description

Technical Field

[0001] This application belongs to the field of film packaging technology, specifically relating to a polyamide composite film for solid-state battery encapsulation and its preparation method. Background Technology

[0002] Aluminum-plastic film, as the core packaging material for pouch lithium batteries, has a classic three-layer structure: BOPA / AL / CPP. To achieve good electrolyte resistance, a PET resin layer is added to this three-layer structure, creating a BOPET / BOPA / AL / CPP structure. The polyamide (BOPA) layer, acting as a protective layer for the aluminum foil, primarily provides excellent mechanical strength and flexibility to ensure the foil does not break during the punching process, meeting the packaging requirements of lithium batteries.

[0003] Solid-state battery encapsulation film, also known as solid-state battery outer packaging material or solid-state battery soft-pack material, is a key material that wraps around the outside of solid-state battery cells, providing protection, insulation, and barrier functions. Functionally similar to the aluminum-plastic film commonly used in liquid lithium batteries, its performance requirements are more stringent. Specifically, it includes: (1) Extremely high barrier properties: Especially for materials that are extremely sensitive to moisture, such as sulfide solid electrolytes, even trace amounts of water vapor can cause them to decompose and fail, seriously affecting battery performance and lifespan. Therefore, the encapsulation film must have extremely high water and oxygen barrier properties, typically requiring a water vapor permeability of ≤ 10⁻ 6 g / m 2 / day. Simultaneously, it is necessary to effectively block oxygen to prevent external oxygen from entering and causing oxidation of the electrode materials.

[0004] (2) Excellent mechanical properties: The battery will undergo slight volume expansion and contraction during charging and discharging (the volume change of solid-state batteries is usually more significant than that of liquid batteries). The encapsulation film needs to have good flexibility, ductility and puncture resistance to remain intact and unbroken under long-term deformation conditions.

[0005] (3) Chemical stability and corrosion resistance: It must be able to resist the chemical erosion of the battery internal materials (such as electrolytes and electrode active materials), especially under harsh conditions such as high temperature, without reacting, degrading or degrading.

[0006] (4) Thermal management performance: It needs to have a certain thermal conductivity to assist in battery heat dissipation, and at the same time, it should be able to effectively block the spread of heat in the event of thermal runaway.

[0007] Existing BOPA films suffer from poor thermal conductivity and insufficient barrier properties (PA has limited barrier capabilities against water vapor and oxygen, with relatively high water and oxygen permeability), making them a "weak link" in the entire aluminum-plastic film barrier system. Therefore, there is an urgent need to develop a polyamide film with high water and oxygen barrier properties, excellent heat dissipation, good corrosion resistance, and sufficient mechanical strength and toughness to meet the performance requirements of solid-state batteries for aluminum-plastic film flexible packaging materials. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies—namely, the lack of high barrier properties, thermal conductivity, and corrosion resistance in single biaxially oriented nylon 6 materials, which makes it difficult to meet the requirements of soft packaging for solid-state batteries—this application provides a polyamide composite film for solid-state battery encapsulation, the technical solution of which is as follows: The polyamide composite film for solid-state battery encapsulation provided in this application includes a four-layer film structure, which from top to bottom consists of a polyester layer, a barrier adhesive layer, an EVOH barrier layer, and a polyamide surface layer. By weight, the polyester layer comprises: 96-99 parts copolyester, 0.1-1 parts silicone resin, and 0.5-3 parts carbon nanospheres; the barrier adhesive layer comprises: 97-99.5 parts polyolefin hot melt adhesive resin and 0.5-3 parts graphene; the EVOH barrier layer comprises: 97-99.5 parts EVOH resin and 0.5-3 parts graphene; and the polyamide surface layer comprises: 97-99.5 parts polyamide resin and 0.5-3 parts graphene.

[0009] In some embodiments, the polyamide composite film for solid-state battery encapsulation comprises a polyester layer, a barrier adhesive layer, an EVOH barrier layer, and a polyamide surface layer. By mass fraction, the polyester layer comprises 96-99% copolyester, 0.1-1% silicone resin, and 0.5-3% carbon nanospheres; the barrier adhesive layer comprises 97-99.5% polyolefin hot melt adhesive resin and 0.5-3% graphene; the EVOH barrier layer comprises 97-99.5% EVOH resin and 0.5-3% graphene; and the polyamide surface layer comprises 97-99.5% polyamide resin and 0.5-3% graphene.

[0010] In some embodiments, the copolyester is one or more combinations of ethylene glycol-1,4-cyclohexanediol terephthalate, ethylene glycol-1,4-butylene terephthalate, ethylene glycol adipate, ethylene glycol-2,6-naphthalenedicarboxylate, and ethylene glycol-furandicarboxylate.

[0011] In some embodiments, the silicone resin is an ester-modified silicone resin; its chemical formula is: (CH3)3SiO[Si(CH3)(CH2COOR)O] n Si(CH3)2COOR, where n is 1 to 300, R is a hydrocarbon group, and the molecular weight is 1000 to 100000 g / mol.

[0012] In some embodiments, the carbon nanospheres have a particle size of 50–500 nm.

[0013] In some embodiments, the polyolefin hot melt adhesive resin is one or more combinations of maleic anhydride-grafted metallocene polyethylene wax hot melt adhesive and maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive.

[0014] In some embodiments, the thickness of the graphene sheets is 1–50 nm.

[0015] In some embodiments, the polyamide resin is polymerized from at least one monomer selected from polyamide-6, polyamide-66, polyamide-56, polyamide-11, polyamide-12, polyamide-1010, and polyamide-1212; the polyamide resin has a melting point ≤230°C.

[0016] In some embodiments, the total thickness of the polyamide composite film for solid-state battery encapsulation is 18–40 μm, the thickness of the polyester layer is 1–5 μm, the thickness of the barrier adhesive layer is 1–5 μm, and the thickness of the EVOH barrier layer is 1–5 μm.

[0017] This application also provides a method for preparing polyamide composite films for solid-state battery encapsulation as described above, comprising the following preparation steps: S1. The components in the copolyester layer are blended in proportion, melt-blended, extruded and granulated by a twin-screw extruder, and the resulting masterbatch is dried for later use. S2. The components in the barrier adhesive layer are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder, and the resulting masterbatch is dried for later use. S3. The components of the EVOH barrier layer are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder, and the resulting masterbatch is dried for later use. S4. Mix the components of the polyamide surface layer in proportion, melt-blend, extrude, and granulate them using a twin-screw extruder, and dry the resulting masterbatch for later use. S5. The masterbatch obtained in S1 is fed into the first extruder to make a polyester layer; the masterbatch obtained in S2 is fed into the second extruder to make a barrier adhesive layer; the masterbatch obtained in S3 is fed into the third extruder to make an EVOH barrier layer; the masterbatch obtained in S4 is fed into the fourth extruder to make a polyamide surface layer. The extruder temperature and T-die temperature of the first and fourth extruders are controlled at 175–240℃, the extruder temperature and T-die temperature of the second extruder are controlled at 135–180℃, and the extruder temperature and T-die temperature of the third extruder are controlled at 165–190℃. S6. Using the LISIM synchronous stretching method, each layer in S5 is extruded and rapidly cooled into a casting. After being humidified and cleaned in a hot steam bath at 60-80℃, and the surface moisture is removed by hot air, the casting is then subjected to biaxial stretching at a stretching temperature of 160-190℃ and a setting temperature of 180-210℃. The stretching ratio is 2.5×2.5-3.3×3.3, thus obtaining the polyamide composite film for solid-state battery encapsulation.

[0018] Compared with existing technologies, the polyamide composite film for solid-state battery encapsulation provided in this application has the following advantages: 1. The polyester layer is made of copolyester with excellent chemical resistance and corrosion resistance, and is designed as the outermost layer to protect the polyamide composite film, thereby improving the corrosion resistance of the composite film; at the same time, the copolyester has a low melting point processing temperature, ensuring that the polyamide composite film can be molded and processed. 2. Adding ester-modified silicone resin to the polyester layer improves its compatibility with the polyester and, in synergy with carbon nanospheres, provides excellent hydrophobic and slip properties. In addition, the carbon nanospheres also provide thermal conductivity.

[0019] 3. The barrier adhesive layer is designed with polyolefin hot melt adhesive resin (maleic anhydride-grafted metallocene polyethylene wax hot melt adhesive and / or maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive), which makes reasonable use of the hydrophobic properties of polyolefin. At the same time, after grafting maleic anhydride, it has good compatibility with polyester and EVOH, ensuring the interlayer bonding strength. 4. An EVOH barrier layer is designed to provide excellent oxygen barrier properties, and a polyamide surface layer provides excellent mechanical properties; the addition of nano-graphene provides dimensional stability, thermal conductivity, and barrier properties.

[0020] The polyamide composite film for solid-state battery encapsulation provided in this application has significantly reduced oxygen and water vapor permeability, while possessing good dent depth and thermal conductivity. This film has excellent barrier properties, dent performance and dimensional stability, and its thermal conductivity and corrosion resistance are improved, making it particularly suitable as an aluminum-plastic film protective layer for solid-state battery encapsulation. Attached Figure Description

[0021] Figure 1 This is a layer structure diagram of the polyamide composite film for solid-state battery encapsulation provided in this application.

[0022] Among them, 10 is the polyester layer, 20 is the barrier adhesive layer, 30 is the EVOH barrier layer, and 40 is the polyamide surface layer. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The technical features designed in the different implementations of this application described below can be combined with each other as long as they do not conflict with each other. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0024] In the description of this application, it should be noted that all terms used in this application (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains, and should not be construed as limiting this application; it should be further understood that the terms used in this application should be understood to have the same meaning as those in the context of this specification and the relevant field, and should not be understood in an idealized or overly formal sense, except as expressly defined in this application.

[0025] To verify the effectiveness of the proposed solution, the present application provides the following embodiments and comparative examples: Example 1 A polyamide composite film for solid-state battery encapsulation, such as Figure 1 As shown, it includes a four-layer film structure, which from top to bottom are a polyester layer 10, a barrier adhesive layer 20, an EVOH barrier layer 30, and a polyamide surface layer 40. The polyester layer 10 comprises, by mass percentage: 97.5% ethylene glycol terephthalate-1,4-cyclohexanediol ester, 0.5% silicone resin, and 2% carbon nanospheres; the barrier adhesive layer 20 comprises, by mass percentage: 98% maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive and 2% graphene; the EVOH barrier layer 30 comprises, by mass percentage: 98% EVOH resin and 2% graphene; and the polyamide surface layer 40 comprises, by mass percentage: 98% polyamide 6 and 2% graphene.

[0026] The raw materials are selected as follows: The silicone resin used is an ester-modified silicone resin. Its chemical formula is: (CH3)3SiO[Si(CH3)(CH2COOR)O] nThe formula is Si(CH3)2COOR, where n is 150, R is a hydrocarbon group, and the molecular weight is 20029 g / mol. The carbon nanospheres used have a particle size of 100 nm. The graphene sheets used have a thickness of 30 nm. The polyamide resin used is selected from polyamide 6; the melting point of the polyamide resin is 220℃. The EVOH resin used has an ethylene content of 32%.

[0027] The specific preparation process is as follows: S1. The components in the copolyester layer 10 are blended in proportion, melt-blended, extruded and granulated by a twin-screw extruder, and the resulting masterbatch is dried for later use. S2. The components in the barrier adhesive layer 20 are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder, and the resulting masterbatch is dried for later use. S3. The components of EVOH barrier layer 30 are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder, and the resulting masterbatch is dried for later use. S4. The components of polyamide surface layer 40 are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder, and the resulting masterbatch is dried for later use. S5. The masterbatch obtained in S1 is fed into the first extruder to produce the polyester layer 10; the masterbatch obtained in S2 is fed into the second extruder to produce the barrier adhesive layer 20; the masterbatch obtained in S3 is fed into the third extruder to produce the EVOH barrier layer 30; the masterbatch obtained in S4 is fed into the fourth extruder to produce the polyamide surface layer 40. The extruder temperature and T-die temperature of the first and fourth extruders are controlled at 175–240℃, the extruder temperature and T-die temperature of the second extruder are controlled at 135–180℃, and the extruder temperature and T-die temperature of the third extruder are controlled at 165–190℃. S6. Using the LISIM synchronous stretching method, each layer in S5 is extruded and rapidly cooled into a casting. After being humidified and cleaned in a hot steam bath at 60-80℃, and the surface moisture is removed by hot air, the casting is then subjected to biaxial stretching at a stretching temperature of 160-190℃ and a setting temperature of 180-210℃. The stretching ratio is 2.5×2.5-3.3×3.3, thus obtaining the polyamide composite film for solid-state battery encapsulation.

[0028] Example 2 A polyamide composite film for solid-state battery encapsulation, such as Figure 1As shown, it comprises a four-layer film structure, from top to bottom: a polyester layer 10, a barrier adhesive layer 20, an EVOH barrier layer 30, and a polyamide surface layer 40. The polyester layer 10 comprises, by mass percentage: 99.4% ethylene glycol terephthalate-1,4-cyclohexanediol ester, 0.1% silicone resin, and 0.5% carbon nanospheres. The barrier adhesive layer 20 comprises, by mass percentage: 99.5% maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive and 0.5% graphene. The EVOH barrier layer 30 comprises, by mass percentage: 99.5% EVOH resin and 0.5% graphene. The polyamide surface layer 40 comprises, by mass percentage: 99.5% polyamide 6 and 0.5% graphene.

[0029] The selection of other raw materials and the preparation process are the same as in Example 1.

[0030] Example 3 A polyamide composite film for solid-state battery encapsulation, such as Figure 1 As shown, it comprises a four-layer film structure, from top to bottom: a polyester layer 10, a barrier adhesive layer 20, an EVOH barrier layer 30, and a polyamide surface layer 40. The polyester layer 10 comprises, by mass percentage: 96% ethylene glycol terephthalate-1,4-cyclohexanediol ester, 1% silicone resin, and 3% carbon nanospheres. The barrier adhesive layer 20 comprises, by mass percentage: 97% maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive and 3% graphene. The EVOH barrier layer 30 comprises, by mass percentage: 97% EVOH resin and 3% graphene. The polyamide surface layer 40 comprises, by mass percentage: 97% polyamide 6 and 3% graphene.

[0031] The selection of other raw materials and the preparation process are the same as in Example 1.

[0032] Example 4 A polyamide composite film for solid-state battery encapsulation, such as Figure 1 As shown, it comprises a four-layer film structure, from top to bottom: a polyester layer 10, a barrier adhesive layer 20, an EVOH barrier layer 30, and a polyamide surface layer 40. The polyester layer 10 comprises, by mass percentage: 97.5% ethylene glycol terephthalate-2,6-naphthalenedicarboxylate, 0.5% silicone resin, and 2% carbon nanospheres. The barrier adhesive layer 20 comprises, by mass percentage: 98% maleic anhydride-grafted polyethylene wax hot melt adhesive and 2% graphene. The EVOH barrier layer 30 comprises, by mass percentage: 98% EVOH resin and 2% graphene. The polyamide surface layer 40 comprises, by mass percentage: 98% polyamide 6 / 66 copolymer and 2% graphene.

[0033] The selection of other raw materials and the preparation process are the same as in Example 1.

[0034] Comparative Example 1 (Basic Comparison: Commercially Available Products) Commercially available biaxially oriented nylon film with a thickness of 30 μm.

[0035] Comparative Example 2 (Compared with Example 1: No additives) A polyamide composite film for solid-state battery encapsulation includes a four-layer film structure, which from top to bottom consists of a polyester layer 10, a barrier adhesive layer 20, an EVOH barrier layer 30, and a polyamide surface layer 40. The polyester layer 10 comprises, by mass percentage: 100% ethylene glycol terephthalate-1,4-cyclohexanediethanol ester; the barrier adhesive layer 20 comprises, by mass percentage: 100% maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive; the EVOH barrier layer 30 comprises, by mass percentage: 100% EVOH resin; and the polyamide surface layer 40 comprises, by mass percentage: 100% polyamide 6.

[0036] The preparation conditions are the same as in Example 1.

[0037] Comparative Example 3 (Comparison with Example 10: Polyester layer 10 without additives, key components missing) A polyamide composite film for solid-state battery encapsulation comprises a four-layer structure, consisting of a polyester layer 10, a barrier adhesive layer 20, an EVOH barrier layer 30, and a polyamide surface layer 40, from top to bottom. The polyester layer 10 comprises, by mass percentage: 100% ethylene glycol terephthalate-1,4-cyclohexanediol ester; the barrier adhesive layer 20 comprises, by mass percentage: 98% maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive and 2% graphene; the EVOH barrier layer 30 comprises, by mass percentage: 98% EVOH resin and 2% graphene; and the polyamide surface layer 40 comprises, by mass percentage: 98% polyamide 6 and 2% graphene.

[0038] The preparation conditions are the same as in Example 1.

[0039] Comparative Example 4 (Comparison of Alternative Components - Using Conventional Thermally Conductive / Barrier Fillers) The only difference from Example 1 is that the graphene in each layer is replaced with an equal amount (same weight parts) of conventional filler. In this comparative example: Polyester layer 10: Carbon nanospheres are replaced with ordinary fumed silica; Barrier adhesive layer 20, EVOH layer, and polyamide surface layer 40: carbon black is used instead of graphene; other preparation conditions are the same as in Example 1.

[0040] Comparative Example 5 (Simplified Layer Structure Comparison - Reduction of Functional Layers) The only difference from Example 1 is that this comparative example uses a three-layer structure: polyester layer 10 / EVOH barrier layer 30 / polyamide surface layer 40, with the middle barrier adhesive layer 20 removed. The components of each layer are the same as in Example 1.

[0041] Comparative Example 6 (Comparison of Key Additive Content Exceeding Standards) The only difference from Example 1 is that the total content of the filler is increased beyond the scope of this application, and the content of each layer of filler (carbon nanospheres, graphene) is 5% (correspondingly, the content of the base resin is reduced), specifically: The polyester layer 10 comprises, by mass percentage, 94.5% ethylene glycol terephthalate-1,4-cyclohexanediol ester, 0.5% silicone resin, and 5% carbon nanospheres; The components of the barrier adhesive layer 20, by mass percentage, include 95% maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive and 5% graphene; The components of the EVOH barrier layer 30, by mass percentage, include 95% EVOH resin and 5% graphene; The components of polyamide surface layer 40, by mass percentage, include: 95% polyamide 6 and 5% graphene. Other preparation conditions are the same as in Example 1.

[0042] Comparative Example 7: Polyamide surface layer without graphene (40) The only difference from Example 1 is that only one layer (polyamide surface layer 40) does not contain graphene (i.e., polyamide surface layer 40 is 100% polyamide resin), while the other three layers are exactly the same as in Example 1.

[0043] The films prepared in the examples and comparative examples were subjected to performance tests: 1. The testing standards or methods are as follows: Thickness: Tested according to GB / T20220-2006; Water vapor transmission rate: The water vapor transmission rate of the thin film was tested according to GB / T 1037-1988; Oxygen permeability: The oxygen permeability of the membrane was tested according to GB / T 1038-2000; the test conditions were 23℃, 80%RH, and humidification was applied to the upper layer on one side only.

[0044] Coefficient of friction: Tested according to GB / T10006-1988 "Determination of Coefficient of Friction of Plastic Films and Sheets"; Surface tension: The surface tension of the thin film was tested according to GB / T 14216-2008; Punch depth test: The polyamide films of the examples and comparative examples were used to prepare PA / AL / CPP composite films. The PA / AL / CPP composite films were clamped using punch molds used in lithium-ion battery aluminum-plastic packaging film factories. The films were tested using punch heads of different depths until the films were punctured. Corrosion resistance test: Using commercially available lithium battery electrolyte, the same amount of electrolyte was dropped onto the surface of the biaxially oriented polyamide film prepared in the above examples and the film in the comparative example. After being placed at 25°C and 50% RH for 2 hours, the electrolyte was gently wiped off with paper, and the corrosion on the surface was observed. Electrolyte corrosion resistance is indicated by "○", and non-electrolyte corrosion resistance is indicated by "△".

[0045] Heat shrinkage rate: GB / T12027-2004 Test method for dimensional change rate of plastic films and sheets upon heating; Thermal conductivity test: The test shall be conducted in accordance with the requirements of GB / T 10297-2015 "Determination of thermal conductivity of non-metallic solid materials by hot wire method".

[0046] 2. The test evaluation results are shown in Table 1-2: Table 1

[0047] Table 2

[0048] Notes: 1. The polyester layer 10 has a thickness of 2μm, the barrier adhesive layer 20 has a thickness of 2μm, and the EVOH barrier layer 30 has a thickness of 2μm; the total thickness of the polyamide composite film for solid-state battery encapsulation is 30μm.

[0049] As can be seen from Examples 1-4 and Comparative Examples 1-3 in Table 1: First, a comparison of key performance indicators. 1. Barrier properties (oxygen and water vapor permeability) Examples 1-4: Oxygen permeability (0.21-0.45 cc / m³) 2 •day) and water vapor permeability (3.8-9.6 g / m 2 The extremely low levels of both 24h and 24h indicate that the film has excellent gas and water vapor barrier properties, which can meet the high barrier requirements of solid-state batteries.

[0050] Comparative Example 1 (commercially available product): Oxygen and water vapor permeability were significantly higher (35.6 cc / m³). 2 ·day and 208.4 g / m 2 •24h), indicating that the film of this application has significantly better barrier performance than traditional BOPA film.

[0051] Comparative Example 2 (without any additives) and Comparative Example 3 (polyester layer 10 without additives): Although their barrier properties were better than Comparative Example 1, they were worse than the Example 1 (oxygen permeability 1.05-1.17 cc / m). 2 • Day, water vapor permeability 27.8-28.4 g / m 2 (24h) This demonstrates that adding graphene and carbon nanospheres can effectively enhance barrier properties.

[0052] Comparative Example 4 (using conventional packing): Barrier performance was significantly reduced (oxygen permeability 4.35 cc / m³). 2 • Day, water vapor permeability 18.7 g / m 2 (24h), indicating that graphene and carbon nanospheres have better dispersion and barrier effects at the nanoscale than conventional fillers (such as carbon black and fumed silica).

[0053] Comparative Example 5 (reduced functional layer): Extremely high water vapor permeability (185.4 g / m²). 2 (24h), indicating that the barrier adhesive layer 20 is crucial for moisture barrier, and the absence of this layer will lead to a serious decline in performance.

[0054] Comparative Example 6 (Excessive Additives): Deteriorated Barrier Performance (Oxygen Permeability 13.5 cc / m³) 2 • Day, water vapor permeability 57.4 g / m 2 •24h), indicating that the additive content needs to be controlled within the optimized range, and excessive amounts will damage the film structure.

[0055] Comparative Example 7 (polyamide surface layer 40 without graphene): The barrier properties are similar to those of the examples, indicating that graphene plays a major role in barrier layers (such as EVOH layers), but the graphene in polyamide surface layer 40 is more important for thermal conductivity.

[0056] 2. Mechanical properties (depth of crater) Examples 1-4: The dent depth is relatively high (6.7-8.1 mm), indicating that the film has good deep-drawing performance and flexibility, which can meet the denting requirements in the battery packaging process.

[0057] Comparative Examples 1-5: The crater depth is relatively low (3.9-5.4 mm), indicating that the multi-layer structure and additives of this application synergistically improve the mechanical strength.

[0058] Comparative Example 6 (Excessive Additives): The dent depth was the lowest (3.9 mm), possibly due to excessive additives causing film embrittlement.

[0059] Comparative Example 7: The crater depth (6.8 mm) is similar to that of the Example, indicating that the graphene on the polyamide surface layer 40 has little impact on the crater performance and mainly depends on the layer structure design.

[0060] 3. Thermal conductivity Examples 1-4: The thermal conductivity is high (1.01-1.73 W / (m·K)). Thanks to the addition of graphene and carbon nanospheres, the heat dissipation capacity of the film is improved, which is beneficial to battery thermal management.

[0061] Comparative Examples 1-4 and 7: The low thermal conductivity (0.21-0.83 W / (m·K)) demonstrates that graphene and carbon nanospheres are key to improving thermal conductivity.

[0062] Comparative Example 6 (Excessive Additives): The thermal conductivity was the highest (2.04 W / (m·K)), but other properties (such as barrier and cratering) decreased, indicating that the additive content needs to be balanced.

[0063] 4. Surface properties (coefficient of friction and surface tension) Examples 1-4: The low coefficient of kinetic friction (0.11-0.21) and low surface tension (28-33 dyn) indicate that the film surface has good smoothness and is easy to process and handle.

[0064] 5. Dimensional stability (heat shrinkage rate) Examples 1-4: The low heat shrinkage rate (0.85-1.24%) indicates that the film has small dimensional changes and good stability under heating conditions.

[0065] Comparative Example 2 (without additives): The highest heat shrinkage rate (3.24%) was observed, proving that the additives can effectively inhibit heat shrinkage.

[0066] Comparative Example 6 (Excessive Additives): Lowest heat shrinkage rate (0.41%), but poor dent depth, possibly due to brittleness caused by excessive filler.

[0067] 6. Corrosion resistance All embodiments and comparative examples (except Comparative Example 1) are corrosion resistant (○), indicating that the layer structure and material selection of the thin film of this application can resist electrolyte erosion.

[0068] Comparative Example 1 (commercially available product): Not corrosion resistant (△), highlighting the improvement in corrosion resistance of the film in this application.

[0069] Second, overall conclusion The polyamide composite films of this application (Examples 1-4) exhibit significantly superior performance compared to the comparative examples in terms of barrier properties, thermal conductivity, mechanical properties, dimensional stability, and corrosion resistance through a four-layer structure (polyester layer 10, barrier adhesive layer 20, EVOH barrier layer 30, and polyamide surface layer 40) and the addition of nanomaterials (graphene and carbon nanospheres).

[0070] Key design elements include: Polyester layer 10: A specific ratio of silicone resin and carbon nanospheres added to a copolyester to provide hydrophobicity, slip properties, and thermal conductivity. Barrier adhesive layer 20: Maleic anhydride-grafted polyolefin hot melt adhesive ensures interlayer adhesion and moisture barrier. EVOH barrier layer 30: EVOH resin with added graphene enhances oxygen barrier properties and thermal conductivity. Polyamide surface layer 40: Polyamide resin with added graphene improves mechanical properties and thermal conductivity. Comparative examples show that the absence of any layer, the use of alternative fillers, or improper additive content all lead to performance degradation, validating the necessity and optimization scope of this application's design.

[0071] The polyamide composite film for solid-state battery encapsulation provided in this application has excellent barrier properties, dent resistance and dimensional stability, and improved thermal conductivity and corrosion resistance. It is particularly suitable for aluminum-plastic film packaging of solid-state batteries and can meet their stringent requirements for high barrier properties, high thermal conductivity, strong mechanical properties and good stability.

[0072] It should be noted that: In this article, polyamide-6, polyamide-66, polyamide-56, polyamide-11, polyamide-12, polyamide-1010, and polyamide-1212 are commonly referred to as PA-6, PA-66, PA-56, PA-11, PA-12, and PA-1010, respectively, in the industry.

[0073] LISIM is an abbreviation for Linear Synchronous Stretching. As the fourth generation of BOPA film technology, LISIM technology is currently the most advanced synchronous stretching technology in the industry. It combines the advantages of step-by-step stretching and mechanical synchronous stretching methods with magnetic levitation technology, and the resulting linear synchronous film combines the advantages of good mechanical strength, good ductility and good uniformity.

[0074] In this article, “~” is used to represent the range of values, and the range of values ​​represented by this expression includes two endpoint values.

[0075] In summary, the specific parameters or some commonly used reagents or raw materials in the above embodiments are specific or preferred embodiments under the concept of this application, and not limitations thereof; where no specific technology or conditions are specified in the embodiments, they shall be carried out in accordance with the technology or conditions described in the literature in this field or in accordance with the product instructions; where the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be obtained commercially.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A polyamide composite film for solid-state battery encapsulation, characterized in that, It includes a four-layer membrane structure, from top to bottom: a polyester layer, a barrier adhesive layer, an EVOH barrier layer, and a polyamide surface layer; By weight, the polyester layer comprises: 96-99 parts copolyester, 0.1-1 parts silicone resin, and 0.5-3 parts carbon nanospheres. The barrier adhesive layer comprises: 97-99.5 parts of polyolefin hot melt adhesive resin and 0.5-3 parts of graphene; The EVOH barrier layer comprises: 97-99.5 parts of EVOH resin and 0.5-3 parts of graphene; The components of the polyamide surface layer include: 97-99.5 parts of polyamide resin and 0.5-3 parts of graphene.

2. The polyamide composite film for solid-state battery encapsulation according to claim 1, characterized in that: It consists of a polyester layer, a barrier adhesive layer, an EVOH barrier layer, and a polyamide surface layer; The polyester layer, by mass fraction, consists of 96-99% copolyester, 0.1-1% silicone resin, and 0.5-3% carbon nanospheres. The barrier adhesive layer is composed of 97-99.5% polyolefin hot melt adhesive resin and 0.5-3% graphene. The EVOH barrier layer is composed of 97-99.5% EVOH resin and 0.5-3% graphene; The polyamide surface layer is composed of 97-99.5% polyamide resin and 0.5-3% graphene.

3. The polyamide composite film for solid-state battery encapsulation according to claim 1, characterized in that, The copolyester is one or more of the following: ethylene glycol-1,4-cyclohexanediol terephthalate, ethylene glycol-1,4-butylene terephthalate, ethylene glycol-adipate terephthalate, ethylene glycol-2,6-naphthalenedicarboxylate, and ethylene glycol-furandicarboxylate. The silicone resin is an ester-modified silicone resin, and its chemical formula is: (CH3)3SiO[Si(CH3)(CH2COOR)O] n Si(CH3)2COOR, where n is 1 to 300, R is a hydrocarbon group, and the molecular weight is 1000 to 100000 g / mol.

4. The polyamide composite film for solid-state battery encapsulation according to claim 1, characterized in that, The carbon nanospheres have a particle size of 50–500 nm.

5. The polyamide composite film for solid-state battery encapsulation according to claim 1, characterized in that, The polyolefin hot melt adhesive resin is one or more of maleic anhydride-grafted metallocene polyethylene wax hot melt adhesive and maleic anhydride-grafted metallocene polypropylene wax hot melt adhesive.

6. The polyamide composite film for solid-state battery encapsulation according to claim 1, characterized in that, The thickness of the graphene sheets is 1–50 nm.

7. The polyamide composite film for solid-state battery encapsulation according to claim 1, characterized in that, The polyamide resin is polymerized from at least one monomer selected from polyamide-6, polyamide-66, polyamide-56, polyamide-11, polyamide-12, polyamide-1010, and polyamide-1212. The melting point of the polyamide resin is ≤230℃.

8. The polyamide composite film for solid-state battery encapsulation according to claim 1, characterized in that: The total thickness of the polyamide composite film for solid-state battery encapsulation is 18–40 μm, the thickness of the polyester layer is 1–5 μm, the thickness of the barrier adhesive layer is 1–5 μm, and the thickness of the EVOH barrier layer is 1–5 μm.

9. A method for preparing a polyamide composite film for solid-state battery encapsulation according to any one of claims 1-8, characterized in that, The preparation steps include the following: S1. The components in the copolyester layer are blended in proportion, melt-blended, extruded and granulated by a twin-screw extruder, and the resulting masterbatch is dried for later use. S2. The components in the barrier adhesive layer are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder, and the resulting masterbatch is dried for later use. S3. The components of the EVOH barrier layer are mixed in proportion, melt-blended, extruded and granulated by a twin-screw extruder, and the resulting masterbatch is dried for later use. S4. Mix the components of the polyamide surface layer in proportion, melt-blend, extrude, and granulate them using a twin-screw extruder, and dry the resulting masterbatch for later use. S5. The masterbatch obtained in S1 is fed into the first extruder to make a polyester layer; the masterbatch obtained in S2 is fed into the second extruder to make a barrier adhesive layer; the masterbatch obtained in S3 is fed into the third extruder to make an EVOH barrier layer; the masterbatch obtained in S4 is fed into the fourth extruder to make a polyamide surface layer. The extruder temperature and T-die temperature of the first and fourth extruders are controlled at 175–240℃, the extruder temperature and T-die temperature of the second extruder are controlled at 135–180℃, and the extruder temperature and T-die temperature of the third extruder are controlled at 165–190℃. S6. Using the LISIM synchronous stretching method, each layer in S5 is extruded and rapidly cooled into a casting. After being humidified and cleaned in a hot steam bath at 60-80℃, and the surface moisture is removed by hot air, the casting is then subjected to biaxial stretching at a stretching temperature of 160-190℃ and a setting temperature of 180-210℃. The stretching ratio is 2.5×2.5-3.3×3.3, thus obtaining the polyamide composite film for solid-state battery encapsulation.

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