Packaging film of aluminum plastic film for hot box test

Abstract

The invention discloses a packaging film of an aluminum-plastic film for hot box testing, the packaging film sequentially comprises a bonding layer, a core layer and a heat sealing layer, the bonding layer is prepared by mixing maleic anhydride modified polypropylene, co-polypropylene and a vinyl or allyl elastomer, the melting point of the maleic anhydride modified polypropylene is 140-160 DEG C, the melt index is 3-8 g / min, and the vicat softening point is 110-150 DEG C; the core layer is prepared by mixing co-polypropylene and a vinyl or propenyl elastomer; the heat sealing layer is prepared by mixing co-polypropylene, an ethylene or propylene-based elastomer, low-melting-point acid modified polyolefin and a slipping agent, and the melting point of the low-melting-point acid modified polyolefin is 70-95 DEG C. The low-melting-point acid modified polyolefin with the melting point of 70-95 DEG C is added into the heat sealing layer, so that the packaging tension of the packaging film at the temperature of 130 DEG C is reduced, and the packaging film meets the hot box test requirement of the lithium ion battery monomer at the temperature of 130 DEG C.

Description

Technical Field

[0001] This invention relates to the field of battery packaging materials technology, and more specifically to an aluminum-plastic film packaging film that meets the requirements of hot box testing. Background Technology

[0002] Lithium-ion battery technology is becoming increasingly mature, and soft-pack aluminum-plastic film batteries, with their advantages of lightweight and safety, are widely used in 3C electronic products, power batteries, and energy storage. To improve the safety of lithium-ion batteries, the national standard GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles" stipulates in section 8.1.5.3 that for lithium-ion battery cells, the temperature chamber should be heated from the ambient temperature to 130℃±2℃ at a rate of 5℃ / min, and maintained at this temperature for 30 minutes before stopping heating, requiring that the cell not catch fire or explode.

[0003] Chinese invention patent application CN114074461A discloses a novel safety aluminum-plastic film, comprising an outer protective layer, a middle aluminum foil layer, and an inner heat-sealing layer stacked sequentially. The inner heat-sealing layer includes an adhesive MPP layer, a PP layer, and a heat-sealing PP layer stacked sequentially. The side closer to the lithium battery is a single-layer heat-sealing PP layer, while the side farther from the lithium battery is the adhesive MPP layer. The heat-sealing PP layer is a low-melting-point PP layer. The modified heat-sealing PP material has a melting point of 100–110°C. When heated to 100–140°C, its heat-sealing strength is 2–100 N, significantly lower than the conventional heat-sealing strength of 80–120 N. This allows the soft packaging of the lithium battery to be easily opened by the internal gas at high temperatures, preventing excessively high internal temperatures and thus preventing fires. This patent does not address the electrolyte resistance of the PP film. Furthermore, the melting point of the heat-sealing PP material in this patented solution is 100–110°C. A melting point that is too low will reduce the electrolyte resistance of the PP film, affecting the lifespan of the lithium battery. While the heat-sealing strength of the PP layer in this patent at 100–140°C (2–100 N) is lower than the heat-sealing strength of conventional encapsulation materials (80–120 N) in some ranges, it still overlaps with the heat-sealing strength of conventional encapsulation materials in others. Therefore, this patent does not address whether the heat-sealed PP can pass the hot box test. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing an aluminum-plastic encapsulation film that meets the requirements of hot box testing, enabling the battery to remain at 130°C for 30 minutes without catching fire or exploding.

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

[0006] An aluminum-plastic encapsulation film for hot box testing comprises, in sequence, an adhesive layer, a core layer, and a heat-sealing layer. The adhesive layer is made of a mixture of maleic anhydride-modified polypropylene, copolymerized polypropylene, and vinyl or propylene-based elastomers. The maleic anhydride-modified polypropylene has a melting point of 140–160°C, a melt index of 3–8 g / min, and a Vicat softening point of 110–150°C. The core layer is made of a mixture of copolymerized polypropylene and vinyl or propylene-based elastomers. The heat-sealing layer is made of a mixture of copolymerized polypropylene, ethylene or propylene-based elastomers, low-melting-point acid-modified polyolefin, and a slip agent. The low-melting-point acid-modified polyolefin has a melting point of 70–95°C. This invention reduces the encapsulation pull of the encapsulation film at 130°C by adding a low-melting-point acid-modified polyolefin with a melting point of 70–95°C to the heat-sealing layer, thereby enabling the encapsulation film to meet the hot box testing requirements of lithium-ion battery cells at 130°C.

[0007] As a preferred technical solution, the adhesive layer contains 30-70 wt% maleic anhydride-modified polypropylene, 20-40 wt% copolymerized polypropylene, and 10-30 wt% vinyl or propylene-based elastomer; the core layer contains 70-90 wt% copolymerized polypropylene and 10-30 wt% vinyl or propylene-based elastomer; and the heat-sealing layer contains 49-85 wt% copolymerized polypropylene, 9.9-30 wt% vinyl or propylene-based elastomer, 5-20 wt% low-melting-point modified polyolefin, and 0.1-1 wt% slip agent.

[0008] As a preferred technical solution, the total thickness of the encapsulation film is 20-50 μm, and the thickness ratio of the adhesive layer, core layer and heat-sealing layer is 1:3-5:1.

[0009] As a preferred technical solution, the copolymer polypropylene in the core layer and the heat-sealing layer is either a binary random copolymer polypropylene or a ternary copolymer polypropylene.

[0010] As a preferred technical solution, the low-melting-point acid-modified polyolefin in the heat-sealing layer is maleic anhydride-modified polypropylene.

[0011] As a preferred technical solution, the melting point of the encapsulation film is 110-155°C.

[0012] As a preferred technical solution, the encapsulation film has an encapsulation tensile force of less than 4N / 10mm at 130℃.

[0013] As a preferred technical solution, the slip agent in the heat-sealing layer is erucamide.

[0014] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, by adding low-melting-point acid-modified polyolefin with a melting point of 70-95°C to the heat-sealing layer, the encapsulation pull of the encapsulation film at 130°C is reduced, thereby enabling the encapsulation film to meet the hot box test requirements of lithium-ion battery cells at 130°C.

[0015] To more clearly illustrate the structural features, technical means, and specific objectives and functions achieved by the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention;

[0017] Figure 2 This is a graph showing the electrolyte peel strength test curve according to an embodiment of the present invention.

[0018] Explanation of reference numerals in the attached diagram:

[0019] 10. Adhesive layer 20. Core layer 30. Heat seal layer. Detailed Implementation

[0020] In the description of this invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the indicated position or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0022] like Figure 1As shown, the present invention provides an aluminum-plastic film for use in hot box testing, comprising an adhesive layer 10, a core layer 20, and a heat-sealing layer 30. The adhesive layer 10 is made of a mixture of maleic anhydride-modified polypropylene, copolymer polypropylene, and vinyl or propylene-based elastomer. The maleic anhydride-modified polypropylene has a melting point of 140–160°C, a melt index of 3–8 g / min, and a Vicat softening point of 110–150°C. The core layer 20 is made of a mixture of copolymer polypropylene and vinyl or propylene-based elastomer, and mainly serves as a heat-sealing skeleton support. The heat-sealing layer 30 is made of a mixture of copolymer polypropylene, ethylene or propylene-based elastomer, low-melting-point acid-modified polyolefin, and a slip agent. The low-melting-point acid-modified polyolefin has a melting point of 70–95°C. This invention reduces the encapsulation pull of the encapsulation film at 130°C by adding a low-melting-point acid-modified polyolefin with a melting point of 70-95°C to the heat-sealing layer. This allows the encapsulation film to meet the hot box test requirements of lithium-ion battery cells at 130°C. By selecting maleic anhydride polypropylene with a high Vicat softening point and low melt index, the adhesion of the encapsulation film to the metal at high temperatures can be guaranteed. This also allows the encapsulation film to achieve a stable connection with the aluminum foil layer in the middle of the aluminum-plastic film through the adhesive layer even at high temperatures.

[0023] Specifically, in the adhesive layer 10, the proportion of maleic anhydride-modified polypropylene is 30-70 wt%, the proportion of copolymerized polypropylene is 20-40 wt%, and the proportion of vinyl or propylene-based elastomer is 10-30 wt%; in the core layer 20, the proportion of copolymerized polypropylene is 70-90 wt%, and the proportion of vinyl or propylene-based elastomer is 10-30 wt%; in the heat-sealing layer 30, the proportion of copolymerized polypropylene is 49-85 wt%, the proportion of vinyl or propylene-based elastomer is 9.9-30 wt%, the proportion of low-melting-point modified polyolefin is 5-20 wt%, and the proportion of slip agent is 0.1-1 wt%.

[0024] In this invention, the total thickness of the encapsulation film is 20–50 μm, the thickness ratio of the adhesive layer 10, core layer 30, and heat-sealing layer 30 is 1:3–5:1, the melting point of the encapsulation film is 110–155°C, and the encapsulation tensile strength of the encapsulation film at 130°C is less than 4 N / 10 mm. The copolymer polypropylene in the core layer 20 and heat-sealing layer 30 is either binary random copolymer polypropylene or ternary copolymer polypropylene, the low-melting-point acid-modified polyolefin in the heat-sealing layer 30 is maleic anhydride-modified polypropylene, and the slip agent in the heat-sealing layer 30 is erucamide.

[0025] Example 1

[0026] An aluminum-plastic encapsulation film for use in hot box testing comprises, in sequence, an adhesive layer, a core layer, and a heat-sealing layer. The total thickness of the encapsulation film is 40 μm, and the thickness ratio of the adhesive layer, core layer, and heat-sealing layer is 1:3:1. In the adhesive layer, the proportions of maleic anhydride-modified polypropylene (35 wt%), copolymerized polypropylene (35 wt%), and vinyl or propylene-based elastomer (30 wt%) are present. In the core layer, the proportions of copolymerized polypropylene (70 wt%) and vinyl or propylene-based elastomer (30 wt%) are present. In the heat-sealing layer, the proportions of copolymerized polypropylene (54 wt%), vinyl or propylene-based elastomer (30 wt%), low-melting-point modified polyolefin (15 wt%), and slip agent (1 wt%) are present.

[0027] Example 2

[0028] An aluminum-plastic encapsulation film for use in hot box testing comprises, in sequence, an adhesive layer, a core layer, and a heat-sealing layer. The total thickness of the encapsulation film is 40 μm, and the thickness ratio of the adhesive layer, core layer, and heat-sealing layer is 1:4:1. In the adhesive layer, the proportions of maleic anhydride-modified polypropylene are 40 wt%, copolymerized polypropylene is 35 wt%, and vinyl or propylene-based elastomer is 25 wt%. In the core layer, the proportions of copolymerized polypropylene are 80 wt% and vinyl or propylene-based elastomer is 20 wt%. In the heat-sealing layer, the proportions of copolymerized polypropylene are 69 wt%, vinyl or propylene-based elastomer is 20 wt%, low-melting-point modified polyolefin is 10 wt%, and slip agent is 1 wt%.

[0029] Comparative Example 1

[0030] An aluminum-plastic encapsulation film for use in hot box testing comprises, in sequence, an adhesive layer, a core layer, and a heat-sealing layer. The total thickness of the encapsulation film is 40 μm, and the thickness ratio of the adhesive layer, core layer, and heat-sealing layer is 1:8:1. In the adhesive layer, the proportions of maleic anhydride-modified polypropylene (35 wt%), copolymerized polypropylene (35 wt%), and vinyl or propylene-based elastomer (30 wt%) are present. In the core layer, the proportions of copolymerized polypropylene (70 wt%) and vinyl or propylene-based elastomer (30 wt%) are present. In the heat-sealing layer, the proportions of copolymerized polypropylene (54 wt%), vinyl or propylene-based elastomer (30 wt%), low-melting-point modified polyolefin (15 wt%), and slip agent (1 wt%) are present.

[0031] Comparative Example 2

[0032] An aluminum-plastic encapsulation film for use in hot box testing comprises, in sequence, an adhesive layer, a core layer, and a heat-sealing layer. The total thickness of the encapsulation film is 40 μm, and the thickness ratio of the adhesive layer, core layer, and heat-sealing layer is 1:3:1. The adhesive layer contains 35 wt% maleic anhydride-modified polypropylene, 35 wt% copolymerized polypropylene, and 30 wt% vinyl or propylene-based elastomer. The core layer contains 70 wt% copolymerized polypropylene and 30 wt% vinyl or propylene-based elastomer. The heat-sealing layer contains 79.5 wt% copolymerized polypropylene, 20 wt% vinyl or propylene-based elastomer, and 0.5 wt% slip agent.

[0033] Comparative Example 3

[0034] Commercially available: Polypropylene film (40μm), Zhangjiagang Kangdexin Optoelectronic Materials Co., Ltd., brand name: KCMF.

[0035] Comparative Example 4

[0036] Commercially available: Polypropylene film (40μm), Hubei Huishi Plastics Co., Ltd., brand name: PPC098.

[0037] In Examples 1-2 and Comparative Examples 1-2:

[0038] Maleic anhydride modified polypropylene can be selected from one of Mitsui's QF551 or QF840 or Arkema's 18722.

[0039] For binary random copolymer polypropylene, choose one of W331 or WFW4; for ternary copolymer polypropylene, choose one of TPC's FL7632 or FL7642.

[0040] The vinyl or propylene-based elastomer is selected from one of ElxonMobil Vistamaxx polyolefin elastomer and Mitsui TAFMER polyolefin elastomer;

[0041] The low-melting-point acid-modified polyolefin is selected from one of the PMA-L, PMA-K, and PMA-T series resins from Toyobo Co., Ltd.

[0042] The slip agent used is SE11PP-E (11% high-purity erucamide) from Jiangsu Jingliang Polymer Materials Co., Ltd.

[0043] The performance of the encapsulation films obtained in Examples 1-2 and Comparative Examples 1-4 is evaluated below:

[0044] 1. Measurement of encapsulated thin film DSC

[0045] The measurement method involved using a differential scanning calorimeter to measure the encapsulated film. During measurement, the heating rate was 5℃ / min, and the heating range was 25–180℃. The measurement results are shown in Table 1 below.

[0046] Table 1 Encapsulated Thin Film DSC

[0047] formula Starting point / ℃ Peak value / ℃ Termination point ℃ Implementation 1 122.17 134.45 140.14 Implementation 2 128.29 140.39 151.17 Comparative Example 1 131.35 145 152.61 Comparative Example 2 143.45 152.19 157.55 Comparative Example 3 152.31 163.65 169.32 Comparative Example 4 156.44 162.40 169.30

[0048] As shown in Table 1, the melting points of both the examples and the comparative examples are between 130 and 170°C, with the melting point of the examples being lower than that of the comparative examples.

[0049] 2. Measurement of Melt Flow Index of Encapsulated Films

[0050] The test was conducted using a melt flow indexer (such as the MFR series). The temperature was set to 230℃ and the load to 2.16 kg. At the set temperature, the sample was placed in the instrument, and a certain pressure was applied to allow the melt to flow out. The weight of the melt passing through the capillary over 10 minutes was recorded to calculate the melt flow index. The results are shown in Table 2 below:

[0051] Table 2 Melt Flow Index of Encapsulated Film

[0052] Group Melt index g / 10min Example 1 6.41 Example 2 6.68 Comparative Example 1 5.23 Comparative Example 2 4.47 Comparative Example 3 3.87 Comparative Example 4 4.75

[0053] As shown in Table 2, the melt flow index of Examples 1-2 is greater than that of Comparative Examples 1-4.

[0054] 3. Packaging pull force test

[0055] The encapsulation films from Examples 1-2 and Comparative Examples 1-4 were fabricated into aluminum-plastic films according to the product structure: 25μPA+40μAL+40μPP. The aluminum-plastic films were then encapsulated under the following conditions: encapsulation temperature 180℃, encapsulation time 3 seconds, encapsulation pressure 0.35MPa, and seal thickness 190±5μm. Tensile testing was performed at both high and room temperatures. For the high-temperature tensile test, the temperature was set at 130℃, the holding time at 5 minutes, the sample width at 10±0.5mm, the sample length at 100mm, the clamping length at (50±5)mm, and the test speed at (175±20)mm / min. The maximum force (N / 10mm) was recorded. For the room-temperature tensile test, the sample width was 10±0.5mm, the sample length at 100mm, the clamping length at (50±5)mm, and the test speed at (175±20)mm / min. The maximum force (N / 10mm) was recorded. The test results are shown in the table below.

[0056] Table 3 Packaging Pull Force

[0057] Group Encapsulation pull force at high temperature (N / 10mm) Encapsulation pull force at room temperature (N / 10mm) Example 1 2.71 52.83 Example 1 1.63 51.09 Example 1 2.42 55.21 Example 2 3.84 54.30 Example 2 3.62 51.15 Example 2 3.21 56.40 Comparative Example 1 4.65 52.05 Comparative Example 1 5.11 55.95 Comparative Example 1 4.48 55.98 Comparative Example 2 6.5 55.706 Comparative Example 2 6.11 53.353 Comparative Example 2 6.36 56.231 Comparative Example 3 6.62 54.65 Comparative Example 3 6.29 53.69 Comparative Example 3 6.13 54.70 Comparative Example 4 10.26 54.65 Comparative Example 4 9.78 56.51 Comparative Example 4 10.22 55.76

[0058] As shown in Table 3, the encapsulation pull force at high temperature is less than 4N / 10mm in Examples 1-2 and greater than 4N / 10mm in Comparative Examples 1-4. The encapsulation pull force at room temperature in Examples and Comparative Examples meets the standard ≥33.3N / 10mm and the industry standard ≥50N / 15mm for "Aluminum-Plastic Composite Film for Lithium-ion Batteries".

[0059] 4. Electrolyte peel strength test of encapsulation film

[0060] The encapsulation films from Examples 1-2 and Comparative Examples 1-4 were respectively prepared into aluminum-plastic films according to the product structure: 25μPA + 40μAL + 40μPP. The prepared aluminum-plastic films were immersed in an electrolyte containing 1000ppm water at 85°C for 4h-72h-168h, and the PP-AL peel force was measured. During measurement, the peel speed was 175mm / min, and the peel angle was 180°. The test results are as shown in the attached instruction manual. Figure 2 As shown.

[0061] Therefore, it can be seen that the initial peel strength and electrolyte peel strength of the encapsulation films prepared in Examples 1-2 and Comparative Examples 1-4 all meet the usage requirements, with the industry standard for "Aluminum-Plastic Composite Film for Lithium-ion Batteries" being ≥6N / 15mm. This indicates that the encapsulation film prepared by this invention can meet the normal usage requirements of aluminum-plastic films.

[0062] 5. Battery thermal chamber test

[0063] The encapsulation films from Examples 1-2 and Comparative Examples 1-4 were fabricated into aluminum-plastic films according to the product structure: 25μPA+40μAL+40μPP. The aluminum-plastic films were then punched into shells (XX6090 Teflon core, 5mm+5mm). The punched aluminum-plastic films were then encapsulated under the following conditions: encapsulation temperature 180℃, encapsulation time 3s, encapsulation pressure 0.3MPa for side sealing; encapsulation temperature 190℃, encapsulation time 3s, encapsulation pressure 0.35MPa for top sealing; and encapsulation temperature 185℃, encapsulation time 4s, encapsulation pressure 0.35MPa for double sealing. The seal thickness was 185±10μm. Batteries with a capacity of 5300mAh were fabricated. The batteries were placed in an oven, and the ambient temperature was raised to 130℃±2℃ at a rate of 5℃ / min, and maintained at this temperature for 30 minutes before heating was stopped. The batteries were then observed for fire or explosion. The test results are shown in Table 4.

[0064] Table 4. Hot Box Test Results

[0065] Group Is there a fire? Did it explode? Example 1 no no Example 2 no no Comparative Example 1 yes no Comparative Example 2 yes no Comparative Example 3 yes no Comparative Example 4 yes yes

[0066] As shown in Table 4, Examples 1 and 2 both passed the hot box test. Considering the encapsulation pull at high temperature, Comparative Examples 1-4 failed the hot box test due to fire. Based on the encapsulation pull test results at high temperature, it can be inferred that to meet the hot box test requirements, the encapsulation pull at high temperature needs to be less than 4N / 10mm.

[0067] In summary, this invention reduces the encapsulation pull of the encapsulation film at 130°C by making the heat-sealing layer thickness account for more than 15% of the overall thickness of the encapsulation film, and by adding a low-melting-point acid-modified polyolefin with a melting point of 70-95°C to the heat-sealing layer. This allows the encapsulation film to meet the requirements for normal use of lithium-ion batteries, while also meeting the requirements for hot box testing of lithium-ion battery cells at 130°C.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the actual technology of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A sealing film for aluminum-plastic film used in hot box testing, comprising, in sequence, an adhesive layer, a core layer, and a heat-sealing layer, characterized in that, The adhesive layer is made of a mixture of maleic anhydride-modified polypropylene, copolymer polypropylene, and vinyl or propylene-based elastomer. The maleic anhydride-modified polypropylene has a melting point of 140–160°C, a melt index of 3–8 g / min, and a Vicat softening point of 110–150°C. The core layer is made of a mixture of copolymer polypropylene and vinyl or propylene-based elastomer. The heat-sealing layer is made of a mixture of copolymer polypropylene, ethylene or propylene-based elastomer, low-melting-point acid-modified polyolefin, and a slip agent. The low-melting-point acid-modified polyolefin has a melting point of 70–95°C.

2. The encapsulation film for aluminum-plastic film used in hot box testing according to claim 1, characterized in that, The adhesive layer contains 30-70 wt% maleic anhydride-modified polypropylene, 20-40 wt% copolymerized polypropylene, and 10-30 wt% vinyl or propylene-based elastomer; the core layer contains 70-90 wt% copolymerized polypropylene and 10-30 wt% vinyl or propylene-based elastomer; the heat-sealing layer contains 49-85 wt% copolymerized polypropylene, 9.9-30 wt% vinyl or propylene-based elastomer, 5-20 wt% low-melting-point modified polyolefin, and 0.1-1 wt% slip agent.

3. The encapsulation film for aluminum-plastic film used in hot box testing according to claim 1, characterized in that, The total thickness of the encapsulation film is 20-50 μm, and the thickness ratio of the adhesive layer, core layer and heat-sealing layer is 1:3-5:

1.

4. The encapsulation film for aluminum-plastic film used in hot box testing according to claim 1, characterized in that, The copolymer polypropylene in the core layer and heat-sealing layer is either a binary random copolymer polypropylene or a ternary copolymer polypropylene.

5. The encapsulation film for aluminum-plastic film used in hot box testing according to claim 1, characterized in that, The low-melting-point acid-modified polyolefin in the heat-sealing layer is maleic anhydride-modified polypropylene.

6. The encapsulation film for aluminum-plastic film used in hot box testing according to claim 1, characterized in that, The melting point of the encapsulation film is 110–155°C.

7. The encapsulation film for aluminum-plastic film used in hot box testing according to claim 1, characterized in that, The encapsulation film has an encapsulation tensile force of less than 4N / 10mm at 130°C.

8. The encapsulation film for aluminum-plastic film used in hot box testing according to claim 1, characterized in that, The slip agent in the heat-sealing layer is erucamide.

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