Hot melt adhesive film as well as preparation method and application thereof

Abstract

The invention belongs to the field of batteries, and particularly relates to a hot melt adhesive film and a preparation method and application thereof. The hot melt adhesive film comprises the following raw material components in parts by mass: 30-60 parts of matrix resin; 15 to 40 parts of a tackifier; 0-10 parts of a viscosity modifier; 0-2 parts of an antioxidant; 0-2 parts of a cross-linking agent; 0-2 parts of a coupling agent; 0-15 parts of a flame retardant; and 0-15 parts of a pore forming agent. According to the hot melt adhesive film prepared through the technical scheme, the synthesized matrix resin contains the composite multi-element flame retardant, the flame retardant effect can be achieved in the thermal runaway process of cell needling, the safety performance of a battery is improved, the number of holes in the adhesive film can be increased by adding the pore forming agent, and the thermal runaway performance of the battery is improved. By adding the viscosity modifier, the hot melt adhesive film is easy to form by hot pressing.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and in particular relates to a hot melt adhesive film and a preparation method and application thereof. Background Art

[0002] With the development of lithium-ion batteries, people are increasingly pursuing high-capacity, high-energy-density batteries. Prismatic lithium-ion batteries offer high packaging reliability, high system energy efficiency, relative lightness, high energy density, and a relatively simple structure. Expansion is relatively easy, and the large cell capacity results in a relatively simple system configuration, easy monitoring, and high stability. Currently, winding cells is highly mechanized, fast, and has guaranteed uniformity, making it conducive to large-scale production and one of the primary assembly methods for power batteries. In order to manufacture high-capacity, high-energy-density, and low-cost batteries, we need to increase the coating amount and compaction density of the pole pieces, use thinner, non-adhesive-coated diaphragms, and wind more and more layers, which can cause many problems during the winding core manufacturing process.

[0003] The following problems exist in the manufacturing and use of large-capacity thick-wound battery cells:

[0004] During the hot pressing production process, thick core rolls are prone to light transmission or breakage due to the large bends at the inner corners under high pressure, seriously affecting the consistency and safety of lithium batteries. This is usually solved by applying tape, but this method is prone to lithium deposition at the tape application area and uneven core rolls.

[0005] Large-capacity square-shell batteries are prone to thermal runaway, explosion and fire during the needle penetration test. During the battery vibration process, the pole coils become loose, which can easily cause the positive and negative poles to overlap and lead to internal short circuits. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a hot melt adhesive film and a preparation method and application thereof.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A hot melt adhesive film, characterized by comprising the following raw material components in parts by weight:

[0009]

[0010]

[0011] Preferably, the following raw material components are included:

[0012]

[0013] More preferably, the following raw material components are included in parts by mass: 50 parts of base resin, 22 parts of tackifier, 5 parts of viscosity regulator, 1 part of antioxidant, 1 part of cross-linking agent, 1 part of coupling agent, 10 parts of flame retardant and 10 parts of pore-forming agent.

[0014] The matrix resin includes one or a mixture of at least two of ethylene-vinyl acetate copolymer EVA resin, polyamide PA, polyolefin, polylactide, polyethylene oxide, and polyvinyl alcohol; preferably, it is ethylene-vinyl acetate copolymer EVA resin, and the content of vinyl acetate monomer VA in the EVA resin is 10-25%; more preferably, it is 12%-15%.

[0015] The tackifier includes one or a mixture of at least two of rosin resin and its derivatives, terpene resin and its derivatives, petroleum resin and its derivatives;

[0016] Preferably, the tackifier is one of rosin glycerol ester, hydrogenated rosin resin, α-terpene resin, lemon terpene resin, C5 petroleum resin, C5 hydrogenated petroleum resin, C9, or a mixture of at least two thereof;

[0017] The viscosity modifier is wax, including one of Fischer-Tropsch wax, polyethylene wax, microcrystalline wax, and paraffin wax, or a mixture of at least two thereof; preferably polyethylene wax;

[0018] Preferably, the antioxidant comprises one or a mixture of at least two of dicinnamoylthiodipropionate DLTDP, distearoylthiodipropionate DSTDP, 2,6-di-tert-butyl-p-cresol, and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate;

[0019] The coupling agent includes one or a mixture of silane coupling agent, titanate coupling agent, aluminate coupling agent, bimetallic coupling agent, phosphate coupling agent, borate coupling agent, chromium complex and coupling agent of higher fatty acid, alcohol and ester;

[0020] Preferably, the crosslinking agent comprises one or a mixture of at least two of dicumyl peroxide, benzoyl peroxide, dicumyl hydroperoxide, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-isopropylimidazole, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, triethylenetetramine, dimethylaminopropylamine, and diethylaminopropylamine.

[0021] The flame retardant includes one or a mixture of a halogen-free inorganic flame retardant or an organic flame retardant;

[0022] Preferably, the flame retardant is a mixture of a halogen-free inorganic flame retardant and an organic flame retardant; the mass ratio of the halogen-free inorganic flame retardant to the organic flame retardant is 1:1;

[0023] Preferably, the halogen-free inorganic flame retardant comprises one or a mixture of at least two of aluminum hydroxide, aluminum oxide, magnesium hydroxide, and magnesium oxide;

[0024] Preferably, the organic flame retardant comprises one or a mixture of at least two of melamine phosphate, borohydride siloxane, ammonium polyphosphate and pentaerythritol;

[0025] Preferably, the pore-forming agent comprises one or a mixture of at least two of sodium bicarbonate, ammonium bicarbonate, calcium carbonate, chitosan, polyethylene glycol, polyvinyl alcohol, and polyvinyl acid.

[0026] The present invention also includes a method for preparing the hot melt adhesive film, comprising the following steps: heating and melting the base resin, tackifier, and viscosity regulator in a preset ratio, wherein the heating and melting temperature is between 80 and 230°C; after the resin is completely molten, the remaining components are added and heated and mixed to obtain a mixed adhesive; and the mixed adhesive is formed to obtain a porous hot melt adhesive film.

[0027] Preferably, the mixed rubber material is compression molded using a flat-plate vulcanizing machine;

[0028] Preferably, the temperature of the mixed rubber material molded using a flat vulcanizing machine is between 65° C. and 130° C., and the pressure of pressing the hot melt adhesive film is between 0.2 and 2.5 MPa.

[0029] The present invention also includes an application of the hot melt adhesive film, wherein the hot melt adhesive film is applied to the bonding of a rolled electrode assembly.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The hot melt adhesive film prepared by the technical solution of the present application has high mechanical strength and corrosion resistance, and can be used inside the battery; it plays a role in protecting the electrode during the hot pressing process;

[0032] Specifically, it contains a composite multi-element flame retardant, which can play a flame retardant role during thermal runaway caused by acupuncture of the battery cell, thereby improving the safety performance of the battery. The addition of a pore-forming agent can increase the number of pores in the adhesive film. The addition of a viscosity regulator makes the hot-melt adhesive film easy to be hot-pressed into a film. The addition of an antioxidant, a coupling agent and a cross-linking agent can prevent the hot-melt adhesive film from being easily oxidized and discolored in the air. The main resin and the filler are better combined during the mixing process, making it easier for the flame retardant and the pore-forming agent to play their role. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a plan view of the porous hot-melt adhesive film composite structure of Example 6;

[0034] Figure 2 This is a schematic diagram of the bottom of the porous hot-melt adhesive film composite structure after being inserted into the roll core in Example 6;

[0035] Figure 3 This is a schematic diagram of the top of the porous hot-melt adhesive film composite structure after being inserted into the roll core in Example 6;

[0036] Figure 4 This is a schematic diagram of the bottom of the battery electrode assembly formed after the heat conducting plate is removed in Example 7;

[0037] Figure 5 This is a schematic diagram of the top of the battery electrode assembly formed after the heat conducting plate is removed in Example 7;

[0038] Figure 6 This is a rendering of the battery electrode group formed after the heat conducting plate is removed in Example 7. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and the best embodiments.

[0040] Example 1

[0041] A process for preparing a hot melt adhesive film comprises the following steps:

[0042] 1) Add 50 parts of ethylene acetate (EVA) resin (12% VA content, same below) as the base resin, 22 parts of C5 petroleum resin as the tackifier, and 5 parts of polyethylene wax as the viscosity modifier in a mixer and heat to 140±5°C until they are completely softened and melted;

[0043] 2) Add 1 part of antioxidant 2,6-di-tert-butyl-p-cresol (antioxidant 264), 1 part of silane coupling agent KH550-MH, 1 part of crosslinking agent dicumyl peroxide, 5 parts of halogen-free inorganic flame retardant magnesium hydroxide, 5 parts of organic flame retardant melamine phosphate, and 10 parts of pore-forming agent sodium bicarbonate, adjust the temperature to 125±5°C, and mix and disperse evenly;

[0044] 3) The evenly mixed adhesive material is spread flat on a smooth heat-resistant steel plate, and then molded using a flat vulcanizer at a molding temperature of 85°C, a pressure of 1 MPa, and a time of 60 min. After drying, it is set aside. The thickness of the film is controlled to obtain a first hot melt adhesive film of 1 mm and a second hot melt adhesive film of 3 mm thickness.

[0045] Example 2

[0046] A process for preparing a hot melt adhesive film comprises the following steps:

[0047] 1) Add 50 parts of polyethylene oxide (PEO), 22 parts of hydrogenated rosin resin, and 5 parts of polyethylene wax in a mixer and heat to 140±5°C until they are softened and melted.

[0048] 2) Add 1 part of 2,6-di-tert-butyl-p-cresol (antioxidant 264), 1 part of phosphate coupling agent, 1 part of cross-linking agent dicumyl peroxide, 10 parts of magnesium hydroxide, and 10 parts of sodium bicarbonate, adjust the temperature to 125±5°C, and mix and disperse evenly;

[0049] 3) The evenly mixed adhesive material is spread flat on a smooth heat-resistant steel plate, and then molded using a flat vulcanizer at a molding temperature of 90°C, a pressure of 0.5-1 MPa, and a time of 5 minutes. After drying, the film thickness is controlled to be between 0.5-1.5 mm to obtain the first hot melt adhesive film and between 2-4 mm to obtain the second hot melt adhesive film.

[0050] Example 3

[0051] A process for preparing a hot melt adhesive film comprises the following steps:

[0052] 1) Add 55 parts of polycaprolactone, 20 parts of α-terpene resin, and 5 parts of microcrystalline wax in a mixer and heat to 120±5°C until they are softened and melted;

[0053] 2) Then, add 1 part of 2,6-di-tert-butyl-p-cresol (antioxidant 264), 1 part of phosphate coupling agent, 1 part of cross-linking agent dicumyl peroxide, 5 parts of magnesium hydroxide, 7 parts of melamine phosphate, and 5 parts of polyethylene glycol and adjust the temperature to 100±5°C and mix and disperse evenly;

[0054] 3) The evenly mixed adhesive material is spread flat on a smooth heat-resistant steel plate, and then molded using a flat vulcanizer at a molding temperature of 80°C, a pressure of 0.5-1 MPa, and a time of 30-60 minutes. After drying, the film thickness is controlled to be between 0.5-1.5 mm to obtain the first hot melt adhesive film and between 2-4 mm to obtain the second hot melt adhesive film.

[0055] Example 4

[0056] A process for preparing a hot melt adhesive film comprises the following steps:

[0057] 1) According to the mass ratio, 30 parts of ethylene-vinyl acetate copolymer resin with a vinyl acetate (VA) content of 12%, 20 parts of polyethylene-vinyl acetate copolymer resin with a vinyl acetate (VA) content of 15%, 22 parts of C5 petroleum resin, and 5 parts of polyethylene wax were heated in a mixer to 150±5°C until they were completely softened and melted;

[0058] 2) Add 1 part of 2,6-di-tert-butyl-p-cresol (antioxidant 264), 1 part of silane coupling agent KH550-MH, 1 part of crosslinking agent diisopropylbenzene hydroperoxide, 10 parts of magnesium hydroxide, 5 parts of borohydride siloxane, and 5 parts of ammonium bicarbonate, adjust the temperature to 130±5°C, and mix and disperse evenly;

[0059] 3) The evenly mixed adhesive material is spread flat on a smooth heat-resistant steel plate, and then molded using a flat vulcanizer at a molding temperature of 90°C, a pressure of 0.5-1 MPa, and a time of 5 minutes. After drying, the film thickness is controlled to be between 0.5-1.5 mm to obtain the first hot melt adhesive film and between 2-4 mm to obtain the second hot melt adhesive film.

[0060] Example 5

[0061] A process for preparing a hot melt adhesive film comprises the following steps:

[0062] 1) Add 25 parts of polyethylene oxide, 25 parts of polyvinyl alcohol, 22 parts of C5 petroleum resin, and 5 parts of polyethylene wax in a mixer and heat to 150±5°C until they are softened and melted;

[0063] 2) Add 1 part of 2,6-di-tert-butyl-p-cresol (antioxidant 264), 1 part of silane coupling agent KH550-MH, 1 part of cross-linking agent benzoyl peroxide, 5 parts of magnesium oxide, 5 parts of melamine phosphate, and 10 parts of ammonium bicarbonate, adjust the temperature to 130±5°C, and mix and disperse evenly;

[0064] 3) The evenly mixed adhesive material is spread flat on a smooth heat-resistant steel plate, and then molded using a flat vulcanizer at a molding temperature of 90°C, a pressure of 0.5-1 MPa, and a time of 5 minutes. After drying, the film thickness is controlled to be between 0.5-1.5 mm to obtain the first hot melt adhesive film and between 2-4 mm to obtain the second hot melt adhesive film.

[0065] Comparative Example 1

[0066] A process for preparing a hot melt adhesive film comprises the following steps:

[0067] 1) Add 30 parts of EVA resin with a vinyl acetate (VA) content of 12%, 24 parts of C5 petroleum resin, and 10 parts of polyethylene wax in a mixer and heat to 140±5°C until they are completely softened and melted;

[0068] 2) Add 2 parts of dicinnamoylthiodipropionate DLTDP, 2 parts of silane coupling agent KH550-MH, 2 parts of crosslinking agent dicumyl peroxide, 15 parts of aluminum oxide, and 15 parts of melamine phosphate, and mix and disperse evenly at a temperature of 125±5°C;

[0069] 3) The evenly mixed adhesive material is spread flat on a smooth heat-resistant steel plate, and then molded using a flat vulcanizer at a molding temperature of 85°C, a pressure of 0.8 MPa, and a time of 30 to 90 minutes. After drying, the film thickness is controlled to be between 0.5 and 1.5 mm to obtain the first hot melt adhesive film and between 2 and 4 mm to obtain the second hot melt adhesive film.

[0070] Comparative Example 2

[0071] A process for preparing a hot melt adhesive film comprises the following steps:

[0072] 1) According to the mass ratio, 60 parts of EVA resin with a vinyl acetate (VA) content of 12% and 40 parts of C5 petroleum resin were heated to 140±5°C in a mixer to soften and melt them completely. No other additives were added, and the two were mixed and dispersed evenly;

[0073] 2) The evenly mixed adhesive material is spread flat on a smooth heat-resistant steel plate, and then molded using a flat vulcanizer at a molding temperature of 85°C, a pressure of 0.5 MPa, and a time of 30 to 60 minutes. After drying, the film thickness is controlled to be between 0.5 and 1.5 mm to obtain the first hot melt adhesive film and between 2 and 4 mm to obtain the second hot melt adhesive film.

[0074] Comparative Example 3

[0075] A process for preparing a hot melt adhesive film comprises the following steps:

[0076] 1) Add 37 parts of EVA resin with a vinyl acetate (VA) content of 12% and 40 parts of C5 petroleum resin in a mixer and heat to 140±5°C until they are completely softened and melted;

[0077] 2) Add 1 part of distearoyl thiodipropionate DSTDP, 1 part of titanate coupling agent, 1 part of dicumyl peroxide, 5 parts of magnesium hydroxide, 5 parts of aluminum hydroxide, and 10 parts of calcium carbonate, adjust the temperature to 125±5°C, and mix and disperse evenly;

[0078] 3) The evenly mixed adhesive material is spread flat on a smooth heat-resistant steel plate, and then molded using a flat vulcanizer at a molding temperature of 85°C, a pressure of 0.5 MPa, and a time of 30 minutes. After drying, the film thickness is controlled to be between 0.5-1.5 mm to obtain the first hot melt adhesive film and between 2-4 mm to obtain the second hot melt adhesive film.

[0079] Comparative Example 4

[0080] A process for preparing a hot melt adhesive film comprises the following steps:

[0081] 1) Add 60 parts of EVA resin (with a vinyl acetate (VA) content of 12%), 27 parts of C5 petroleum resin, and 10 parts of polyethylene wax in a mixer and heat to 140±5°C until they are softened and melted;

[0082] 2) Add 1 part of 2,6-di-tert-butyl-p-cresol (antioxidant 264), 1 part of silane coupling agent KH550-MH, and 1 part of crosslinking agent dicumyl peroxide, adjust the temperature to 125±5°C, and mix and disperse evenly;

[0083] 3) The mixed adhesive is spread flat on a smooth heat-resistant steel plate and then molded using a flat vulcanizer at a molding temperature of 85°C, a pressure of 1 MPa, and a time of 30 minutes. After drying, the film thickness is controlled to be between 0.5-1.5 mm to obtain a first hot melt adhesive film and between 2-4 mm to obtain a second hot melt adhesive film;

[0084] Comparative Example 5

[0085] A process for preparing a hot melt adhesive film comprises the following steps:

[0086] 1) Add 50 parts of EVA resin with a vinyl acetate (VA) content of 12%, 25 parts of C5 petroleum resin, and 5 parts of polyethylene wax in a mixer and heat to 140±5°C until they are completely softened and melted;

[0087] 2) Add 5 parts of magnesium oxide, 5 parts of aluminum oxide, and 10 parts of calcium carbonate, adjust the temperature to 125±5°C, and mix and disperse evenly;

[0088] 3) The mixed adhesive is spread flat on a smooth heat-resistant steel plate and then molded using a flat vulcanizer at a molding temperature of 85°C, a pressure of 0.5 MPa, and a time of 30 minutes. After drying, the film thickness is controlled to be between 0.5-1.5 mm to obtain a first hot melt adhesive film and between 2-4 mm to obtain a second hot melt adhesive film;

[0089] The hot melt adhesive films synthesized in the examples and comparative examples were characterized, and the mechanical strength, corrosion resistance, melting temperature and melt viscosity of the different adhesive films were compared.

[0090] 1. Mechanical Strength: According to mechanical properties testing standards, first use a cutter to cut the sample into a dumbbell shape. The sample length is 25mm, width is 6mm, and thickness is 2mm. The tensile rate of the universal electronic tensile testing machine is set to 100mm / min. The tensile strength and elongation at break are calculated using the formula. The 180° or 90° peel test (ASTM D3330) is used to measure the force required to peel the film from the substrate. Hot melt bonding is performed at 190℃ for 30s.

[0091] 2. Corrosion resistance: Expose the thermal adhesive film to an acid medium and regularly observe changes in quality, surface morphology, or mechanical property degradation.

[0092] 3. Melting temperature and melt viscosity: Use a melting point meter to visually observe the temperature at which the hot melt film becomes transparent or flows, and roughly measure the softening point of the hot melt. Use a rotational rheometer to measure the shear viscosity of the film melt at a controlled temperature and analyze its rheological behavior. The test data are shown in Table 1 below:

[0093] Table 1 Performance parameters of different films

[0094]

[0095] As shown in Table 1, the appropriate proportions of the components in Example 1 allow the hot melt adhesive film to perform effectively on the core. The addition of inorganic and organic flame retardants can achieve a good flame retardant effect, and the addition of pore-forming agents can increase the number of pores in the film. Compared with Example 1, Example 2 uses polyethylene oxide (PEO) as the main resin, which has good water binding, slightly poor mechanical strength, slightly poor corrosion resistance, and a similar film softening point. Compared with Example 1, Example 3 uses polycaprolactone as the main resin, which has basically the same mechanical strength, good corrosion resistance, and a low film softening point. Compared with Example 1, Example 4 uses two ethylene-vinyl acetate copolymer resins with different vinyl acetate (VA) contents as the main resin, which has good mechanical strength, good corrosion resistance, and a similar film softening point. Compared with Example 1, Example 5 uses polyethylene oxide and polyvinyl alcohol as the main resin, which has slightly better mechanical strength, similar corrosion resistance, and a similar film softening point.

[0096] Comparative Example 1 contains the least amount of main resin, the most additives, and the bulk of fillers. The hot melt adhesive exhibits poor tensile and peel strengths, and the film requires a high temperature to soften. The viscosity after melting is low, making it difficult to achieve a bonding effect after heating. Comparative Example 2, which only incorporates the main resin and tackifying resin without any additives, results in excessively high viscosity and poor fluidity, making it difficult to hot-press into a thin film. Due to uneven crosslinking between the main resin and tackifying resin, the film exhibits slightly weaker mechanical strength and corrosion resistance, making it unsuitable for use within batteries. Comparative Example 3, which does not incorporate a viscosity modifier and has an equal ratio of main resin to tackifying resin, exhibits higher viscosity and poor fluidity, making it difficult to hot-press into a film. The low amount of main resin added results in slightly poorer mechanical properties. Due to the highest tackifying resin content, the film's softening point is determined by the tackifying resin. Comparative Example 4, which contains the most main resin and no flame retardant or pore-forming fillers, softens easily during hot pressing, but lacks flame retardancy or porosity, and its mechanical strength is reduced. Because the main resin content is the highest, the softening point of the film is determined by the main EVA resin. In Comparative Example 5, where no antioxidant, coupling agent, or crosslinking agent was added, the hot-melt adhesive film was easily oxidized and discolored in air. The main resin and filler did not bond well during the mixing process, resulting in a slight decrease in the film's mechanical strength. The flame retardant and pore-forming agents, acting as additives, were not effective, and corrosion resistance was significantly reduced.

[0097] Example 6

[0098] The hot melt adhesive film prepared in Example 1 was used to prepare a composite structure for a battery electrode group.

[0099] The lithium iron phosphate positive electrode sheet (coating amount 40mg / cm 2 , compacted density is 2.5g / cm 3 ) and graphite negative electrode sheet (coating amount is 21mg / cm 2 , compacted density is 1.55g / cm 3 ) and a 7-micron-thick PE separator were wound to prepare multiple cores with a thickness of 34.2 mm ± 0.5;

[0100] For the convenience of explanation, the length, width and thickness of the hot melt adhesive film, the heat conducting plate and the liquid absorbing film are defined in this application; Figure 1 : The porous hot melt adhesive film composite structure is shown in the figure, wherein the X direction is the length direction, the Y direction is the width direction, and the Z direction is the thickness direction.

[0101] The thickness of the battery electrode group is Pz, the width is Py, and the length of the separator is Jx. 20mm<Pz<50mm, 80mm<Py<400mm, and 80mm<Jx<400mm; it depends on the battery electrode group. Taking the LP50194112 thick battery core as an example; the thickness of the LP50194112 assembled electrode group is Pz = 22.70mm, the width of the assembled electrode group is Py = 188.80, and the length of the separator is Jx = 106mm;

[0102] Figure 1 A battery electrode assembly structure is shown, including a heat conducting plate 5 and a hot melt adhesive film; the hot melt adhesive film includes a first hot melt adhesive film 1 provided on the upper and lower surfaces of the heat conducting plate 5 and a second hot melt adhesive film 2 covering the left and right ends of the heat conducting plate;

[0103] The width of the heat conducting plate is Dy, and the length of the heat conducting plate is Dx; Dy ≤ Py-Pz, preferably Dy = Py-Pz-4mm; Dx ≥ Jx, preferably Dx ≥ Jx + Pz; more preferably Dx = Jx + Pz; the heat conducting plate includes one of a stainless steel heat conducting sheet, a silicone heat conducting sheet, and a graphene heat conducting sheet, or a combination of at least two thereof; the thickness of the heat conducting plate is 2-3mm; the surface of the heat conducting plate is wrapped with a layer of high-temperature resistant tape; the tape thickness is less than 1mm;

[0104] In this application, a stainless steel heat conducting plate is used as a preferred example for description. The thickness of the heat conducting plate is 2-3 mm; specifically, it can be 2 mm or 3 mm. In this application, 2 mm is used as a preferred example for description. The surface of the heat conducting plate is wrapped with a layer of high temperature resistant tape; the thickness of the tape is less than 1 mm.

[0105] In this application, the width of the heat conducting plate Dy = Py-Pz-4 = 188.80-22.70-4 = 162.1 mm; the length of the heat conducting plate Dx = Jx+Pz = 106+22.70 = 128.7 mm is used as a preferred example for illustrative description, and the heat conducting plate extends out of the winding core to facilitate heat conduction.

[0106] A liquid absorbing film 3 is provided between the heat conducting plate and the first hot melt adhesive film 1;

[0107] Preferably, the width of the liquid-absorbing film is Xy, and the length of the liquid-absorbing film is Xx; Xy≤(Dy-(0.5-5) mm); more preferably, Xy=Dy-2 mm; preferably, Xx=Jx.

[0108] The liquid-absorbing membrane is a sponge-like liquid-absorbing membrane; the sponge-like liquid-absorbing membrane includes one of melamine sponge material, polyurethane porous sponge material, or EPDM rubber membrane material, or a mixture of at least two of them; the thickness of the liquid-absorbing membrane is 1.5-2.5 mm, specifically 1.5 mm, 2 mm, or 2.5 mm.

[0109] In this embodiment, Xy=Dy-2mm=162.1mm-2mm=160.1mm; Xx=Jx=106mm is used as a preferred embodiment for description. The thickness of the liquid-absorbing film is 2mm, and the film is a sponge-like liquid-absorbing film made of melamine sponge material.

[0110] The thickness of the second hot melt adhesive film is 2-4 mm; specifically, it can be 2 mm, 3 mm, or 4 mm. In this embodiment, 3 mm is used as a preferred example. The length of the second hot melt adhesive film is the same as the length of the separator, and the width is 1 / 2 of the thickness of the battery electrode assembly. The length of the second hot melt adhesive film is the same as the length of the separator, which is 106 mm. The width is 1 / 2 of the thickness of the battery electrode assembly = Pz * 1 / 2 = 22.70 mm * 1 / 2 = 11.35 mm.

[0111] Preferably, the thickness of the first hot melt adhesive film is 0.5-1.5 mm; specifically, it can be 0.5 mm, 1 mm, or 1.5 mm. This embodiment takes 1 mm as a preferred example for description.

[0112] The first hot melt adhesive film includes a first upper hot melt adhesive film and a first lower hot melt adhesive film; the widths of the first upper hot melt adhesive film and the first lower hot melt adhesive film are Ry1 and Ry2, respectively, and the lengths are Rx1 and Rx2, respectively; the widths of the first upper hot melt adhesive film and the first lower hot melt adhesive film are equal to the width of the liquid absorbent film; Ry1=Ry2=Xy; the length of the first upper hot melt adhesive film is the sum of the length of the diaphragm and the thickness of the battery electrode group; Rx1=Jx+Pz; the length of the first lower hot melt adhesive film Rx2 is the sum of the length of the diaphragm and 1 / 2 of the thickness of the battery electrode group, Rx2=Jx+1 / 2Pz;

[0113] In this embodiment, the widths of the first upper hot melt adhesive film and the first lower hot melt adhesive film are equal to the width of the liquid absorbent film as a preferred example; Ry1 = Ry2 = Xy = 160.1 mm; the length of the first upper hot melt adhesive film is the sum of the length of the separator and the thickness of the battery electrode group; Rx1 = Jx + Pz = 106 + 22.70 = 128.7 mm;

[0114] The length Rx2 of the first lower hot melt adhesive film is the sum of the length of the diaphragm and 1 / 2 of the thickness of the battery electrode group; Rx2

[0115] =Jx+1 / 2Pz=106+11.35=117.35mm;

[0116] The method for preparing the porous hot melt adhesive film composite structure comprises the following steps:

[0117] 1) hot-pressing the liquid-absorbing film onto the first hot-melt adhesive film to synthesize a double-layer porous hot-melt adhesive composite film; the hot-pressing temperature is 60-120° C.; the hot-pressing pressure is 0.1-2.5 MPa; and the hot-pressing time is 10-60 seconds.

[0118] Specifically comprising the following steps: hot pressing a liquid-absorbing film onto the middle of a first upper hot melt adhesive film, with the upper and lower parts having the same size, hot pressing and laminating for 10 seconds on a flat vulcanizer at a temperature of 70°C and a pressure of 0.4 MPa, removing the sample and cooling it to room temperature to prepare an upper double-layer porous hot melt adhesive composite film;

[0119] A liquid-absorbing film was hot-pressed onto the middle of the first lower hot-melt adhesive film and overlapped with the bottom, and hot-pressed for 15 seconds on a flat-plate vulcanizer at a hot-pressing temperature of 70°C and a pressure of 0.4 MPa. The sample was removed and cooled to room temperature to prepare a lower double-layer porous hot-melt adhesive composite film;

[0120] 2) Two sheets of the upper double-layer porous hot melt adhesive composite film and the lower double-layer porous hot melt adhesive composite film obtained in step 1) are attached to the upper and lower surfaces of the heat conducting plate to obtain the porous hot melt adhesive film composite structure;

[0121] 3) Wrap the left and right ends of the double-layer porous hot melt adhesive composite film heat conducting plate with a second hot melt adhesive film.

[0122] Example 7

[0123] The porous hot-melt adhesive film composite structure obtained in Example 6 was used to prepare a battery electrode group.

[0124] The method for preparing the battery electrode group specifically comprises the following steps:

[0125] S1: Winding the positive and negative electrode sheets and the separator into a winding core 6 (as described in Example 6) according to the set winding tension, and pulling the winding core out from the winding needle with a gap left, without flattening it first;

[0126] S2: Insert the porous hot melt adhesive film composite structure into the core, with the length of the heat conducting plate at the bottom of the core extending beyond the core equal to the thickness Pz of the battery electrode assembly; place the heat conducting plate in the middle of the core in the width direction, with the length of the heat conducting plate extending beyond the core being Pz = 22.7 mm;

[0127] The first upper hot melt adhesive film on the upper surface of the heat conducting plate protrudes from the top and bottom of the reel core by a length of Pz*1 / 2=11.35 mm; the first lower hot melt adhesive film on the lower surface protrudes from the bottom of the reel core by a length of Pz*1 / 2=11.35 mm, with the top flush with the reel core.

[0128] S3: Lay the hot melt adhesive film leaking out of the core on the heat conducting plate on the top or bottom of the core, and then flatten the core. At this time, the bottom of the core is covered with hot melt adhesive film, and half of the top is covered with hot melt adhesive film; the top of the core 6 is as shown in FIG. Figure 3 (the side with the tab 7 is set as the top) as shown, the bottom of the winding core is as follows Figure 2 shown.

[0129] S4: Preheat the core obtained in S3 to soften the film. Then, heat press the preheated core using a hot press. Remove the heat conducting plate before the core cools down. The hot melt adhesive will fill the gaps within the core during the hot pressing process, effectively bonding the gaps.

[0130] Specifically: Place the core in an oven at 70 degrees Celsius for 30 minutes to soften the film slightly. The temperature can be between 65-75 degrees Celsius for 30-60 minutes.

[0131] Then use a hot press to heat press the preheated core (85℃, 4.5T, 120s). Take out the heat conducting plate 3 in time before the core cools down, glue the gap inside the core, and place it at room temperature to cool after the core is shaped. The top diagram is shown as follows. Figure 5 As shown, the bottom schematic diagram is as follows Figure 4 As shown, the actual shaping effect of the bottom after hot pressing is as follows Figure 6 During the hot pressing process, the hot melt adhesive is melted to fill the gaps inside the core. The hot melt adhesive films at the top and bottom can bond the top and bottom diaphragms together, which is beneficial for the shaping of the electrode group and prevents the core from loosening.

[0132] S5: After the core is shaped, it is placed at room temperature to cool down to obtain the battery electrode group and proceed to the subsequent assembly process.

[0133] It should be noted that the comparative example of the present application is only for the convenience of comparison and is still one of the embodiments.

[0134] Comparative Example 6

[0135] The difference between Comparative Example 6 and Example 7 is that the core is prepared by the same process as Example 6, and the porous hot-melt adhesive film composite structure of the present application is not used; the core is directly placed in an oven and preheated at 70 degrees for 30 minutes; the preheated core is subjected to a hot pressing process (85°C, 4.5T, 120s) using a hot press, and after the core is shaped, it is placed at room temperature to cool; the cooled core is assembled into the shell, and the subsequent assembly process is carried out.

[0136] Comparative Example 7

[0137] The difference between Comparative Example 7 and Example 7 is that the core is not preheated, and the other processes are the same as Example 7, that is, the preheating part in step S3) of Example 4 is not included.

[0138] Comparative Example 8

[0139] Compared with Example 7, Comparative Example 8 does not include a liquid-absorbing film in the porous hot-melt adhesive film composite structure; the processes of other embodiments are the same as those of Example 7, specifically including: directly attaching the first upper hot-melt adhesive film and the first lower hot-melt adhesive film to the upper and lower surfaces of the high-temperature resistant tape heat-conducting plate coated with high-temperature resistant tape, and then wrapping the second hot-melt adhesive film on the left and right ends of the heat-conducting plate, together forming a hot-melt adhesive film composite device that does not contain a sponge porous liquid-absorbing film.

[0140] Comparative Example 9

[0141] Comparative Example 9 Compared with Example 7, the preparation process of the hot melt adhesive film in the porous hot melt adhesive film composite structure is different, and the porous hot melt adhesive film does not contain a flame retardant;

[0142] The preparation process of hot melt adhesive film includes the following steps:

[0143] 1) Add 60 parts of ethylene acetate (EVA) resin (12% VA content, same below) as the base resin, 22 parts of C5 petroleum resin as the tackifier, and 5 parts of polyethylene wax as the viscosity modifier in a mixer and heat to 140±5°C until they are completely softened and melted;

[0144] 2) Add 1 part of antioxidant 2,6-di-tert-butyl-p-cresol (antioxidant 264), 1 part of silane coupling agent KH550-MH, 1 part of crosslinking agent dicumyl peroxide, 5 parts of halogen-free inorganic flame retardant magnesium hydroxide, 5 parts of organic flame retardant melamine phosphate, and 10 parts of pore-forming agent sodium bicarbonate, adjust the temperature to 125±5°C, and mix and disperse evenly;

[0145] 3) The mixed adhesive material is spread flat on a smooth heat-resistant steel plate and then molded using a flat vulcanizer at a molding temperature of 85°C, a pressure of 1 MPa, and a time of 60 minutes. After drying, the film thickness is controlled to obtain a first hot melt adhesive film of 1 mm and a second hot melt adhesive film of 3 mm thickness;

[0146] Table 2 shows the state of the winding core and the electrode after hot pressing of Example 7 and Comparative Examples 6-9; Table 3 shows the saturation and cycle conditions of the LP50194112 batteries prepared in Example 7 and Comparative Examples 6-9; Table 4 shows the safety test results of the LP50194112 batteries prepared in Example 7 and Comparative Examples 6-9.

[0147] Table 2

[0148]

[0149] Table 3

[0150]

[0151] Table 4

[0152]

[0153]

[0154] Needle penetration test: According to GBT31485-2015, a 100% SOC soft-pack battery is placed on a flat surface. A 5mm high-temperature resistant steel needle is used to penetrate the battery at right angles to the surface at a speed of (25±5) mm / s. The penetration position is at the geometric center of the puncture surface. The battery is observed for 1 hour.

[0155] Vibration test: A 50% SOC battery was mounted on a vibration platform and vibrated at a frequency of 7Hz to 200Hz in both forward and reverse directions. Each cycle lasted 15 minutes. The sample was vibrated 12 times in each of three mutually perpendicular directions for a total of 3 hours, and the weight and voltage changes were monitored in real time.

[0156] From Table 2-4 and Figure 6 It can be seen that, compared with Example 7, Comparative Example 6 follows the conventional production process, does not use a porous hot melt adhesive composite structure, and the core undergoes normal preheating + hot pressing treatment, and then is assembled into the shell. After hot pressing, the core of Comparative Example 6 is relatively loose as a whole. When the core is disassembled, it can be seen that the internal electrode sheet, the positive electrode sheet, is bent and translucent, and the negative electrode sheet loses powder at the bend, which affects the capacity and safety performance of the battery. Compared with Example 7, the core of Comparative Example 7 is not preheated, and the core is directly hot pressed. Although it can achieve a certain hot pressing shaping effect, the hot pressing time is very short, and the hot melt adhesive film cannot be in a molten and softened state in a short time. The C angle position cannot be filled during the hot pressing process. The hot melt adhesive film cannot play a buffering role, and does not play a good role in inward folding and light transmission and material loss (as shown in Table 2). Compared with Example 7, Comparative Example 8 does not contain a sponge-like porous liquid-absorbing film in the porous hot melt adhesive film composite structure, which reduces the liquid saturation capacity of the battery cell (as shown in Table 3). Compared with Example 7, in Comparative Example 9, the hot melt adhesive film is not mixed with the flame retardant additive, the liquid saturation capacity of the battery cell is slightly reduced, and the needle puncture and vibration safety test processes are not improved (as shown in Tables 3 and 4).

[0157] In summary, the present application utilizes a modified hot melt adhesive film, a sponge-like liquid-absorbing film, and a heat-conducting plate to prepare a porous hot melt adhesive film composite structure. The porous hot melt adhesive composite film composed of the modified hot melt adhesive film and the sponge-like liquid-absorbing film inside the core can not only improve the problem of internal C-angle pole piece shedding and light transmission during the hot pressing process, but also serve as a liquid storage module to store electrolyte during the battery cycle. At the same time, the hot melt adhesive film itself has a low melting point and contains flame retardant additives. When the battery thermal runaway occurs, the matrix resin A can flow into the core pole piece in a molten state to hinder the reaction. Combined with the use of internal flame retardants, thermal runaway of the battery cell can be effectively prevented.

[0158] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A hot melt adhesive film, characterized in that: The invention comprises the following raw material components in parts by weight:

2. The hot melt adhesive film according to claim 1, characterized in that: The invention comprises the following raw material components in parts by weight:

3. The hot melt adhesive film according to claim 1 or 2, characterized in that: The invention comprises the following raw material components in parts by weight: 50 parts of base resin, 22 parts of tackifier, 5 parts of viscosity regulator, 1 part of antioxidant, 1 part of cross-linking agent, 1 part of coupling agent, 10 parts of flame retardant and 10 parts of pore-forming agent.

4. The hot melt adhesive film according to any one of claims 1 to 3, characterized in that: The matrix resin includes one or a mixture of at least two of ethylene-vinyl acetate copolymer EVA resin, polyamide PA, polyolefin, polylactide, polyethylene oxide, and polyvinyl alcohol; preferably, it is ethylene-vinyl acetate copolymer EVA resin, and the content of vinyl acetate monomer VA in the EVA resin is 10-25%; more preferably, it is 12%-15%.

5. The hot melt adhesive film according to any one of claims 1 to 4, characterized in that: The tackifier includes one or a mixture of at least two of rosin resin and its derivatives, terpene resin and its derivatives, petroleum resin and its derivatives; Preferably, the tackifier is one of rosin glycerol ester, hydrogenated rosin resin, α-terpene resin, lemon terpene resin, C5 petroleum resin, C5 hydrogenated petroleum resin, C9, or a mixture of at least two of them.

6. The hot melt adhesive film according to any one of claims 1 to 5, characterized in that: The viscosity modifier is wax, including one of Fischer-Tropsch wax, polyethylene wax, microcrystalline wax, and paraffin wax, or a mixture of at least two thereof; Preferably, the antioxidant comprises one or a mixture of at least two of dicinnamoylthiodipropionate DLTDP, distearoylthiodipropionate DSTDP, 2,6-di-tert-butyl-p-cresol, and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; Preferably, the coupling agent includes one or a mixture of silane coupling agent, titanate coupling agent, aluminate coupling agent, bimetallic coupling agent, phosphate coupling agent, borate coupling agent, chromium complex and coupling agent of higher fatty acid, alcohol, ester; Preferably, the crosslinking agent comprises one or a mixture of at least two of dicumyl peroxide, benzoyl peroxide, dicumyl hydroperoxide, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-isopropylimidazole, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, triethylenetetramine, dimethylaminopropylamine, and diethylaminopropylamine.

7. The hot melt adhesive film according to any one of claims 1 to 6, characterized in that: The flame retardant includes one or a mixture of a halogen-free inorganic flame retardant or an organic flame retardant; Preferably, the flame retardant is a mixture of a halogen-free inorganic flame retardant and an organic flame retardant; the mass ratio of the halogen-free inorganic flame retardant to the organic flame retardant is 1:1; Preferably, the halogen-free inorganic flame retardant comprises one or a mixture of at least two of aluminum hydroxide, aluminum oxide, magnesium hydroxide, and magnesium oxide; Preferably, the organic flame retardant comprises one or a mixture of at least two of melamine phosphate, borohydride siloxane, ammonium polyphosphate and pentaerythritol; Preferably, the pore-forming agent comprises one or a mixture of at least two of sodium bicarbonate, ammonium bicarbonate, calcium carbonate, chitosan, polyethylene glycol, polyvinyl alcohol, and polyvinyl acid.

8. A method for preparing a hot melt adhesive film according to any one of claims 1 to 7, characterized in that: The steps include: Heat and melt the base resin, tackifier and viscosity modifier according to a preset ratio, and mix them together at a temperature between 80 and 230°C. After the mixture is completely molten, the remaining components are added and heated and mixed to obtain a mixed rubber material; The mixed adhesive material is formed into a porous hot melt adhesive film.

9. The method for preparing a hot melt adhesive film according to claim 8, characterized in that: The mixed rubber material is molded using a flat vulcanizing machine; Preferably, the temperature of the mixed rubber material molded using a flat vulcanizing machine is between 65° C. and 130° C., and the pressure of pressing the hot melt adhesive film is between 0.2 and 2.5 MPa.

10. Use of the hot melt adhesive film according to any one of claims 1 to 7, characterized in that: The hot melt adhesive film is used for bonding rolled electrode groups.

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