Swelling tape and preparation method thereof

Abstract

The present invention provides a swelling tape, comprising an adhesive layer and a swelling layer, wherein the adhesive layer and the swelling layer are directly compounded, and the composite surface of the two is in an undulating, wrinkled shape. The swelling tape of the present invention provides uneven thickness variations in the adhesive layer, so that structural weak points exist on the adhesive layer. When immersed in an electrolyte, the structural weak points of the adhesive layer are easily dissolved in the electrolyte, providing more sufficient swelling space for the swelling layer. After swelling, the swelling layer can directly contact the bare battery cell from the original structural weak points of the adhesive layer, so that the gap between the bare battery cell and the shell can be more fully filled to achieve a better positioning effect, thereby improving the drop resistance of the lithium battery.

Description

Technical Field

[0001] The present invention belongs to the field of swelling tapes, and in particular relates to a swelling tape and a preparation method thereof. Background Art

[0002] With rapid economic development and advancements in modern science and technology, the replacement cycle for electronic products has shortened, electric vehicles have become more prevalent, and energy storage technology has matured, leading to a growing market demand for lithium batteries. During the production, transportation, and assembly of lithium batteries into modules, they are inevitably subject to collisions, which can affect their safety and stability.

[0003] To prevent cylindrical lithium batteries from failing due to movement of the bare cell relative to the casing during use, it is often necessary to insert a filler tape into the gap between the bare cell and the casing. Currently, a commonly used filler tape is a swelling tape. However, when commercially available swelling tape is applied to the bare cell, due to operational reasons, some gaps remain between the bare cell and the casing, failing to completely fill the gap. This hinders the stability and safety of the battery from shaking, falling, and other hazards, creating a potential safety hazard for the daily use of lithium batteries.

[0004] Based on this, it is necessary to find a swelling tape that can firmly fix the bare battery cell and the shell. Summary of the Invention

[0005] The object of the present invention is to provide a swelling tape and a preparation method thereof, wherein the swelling tape can firmly fix the bare battery cell and the shell, and the preparation method has a simple process, convenient operation, and solves the bulging phenomenon.

[0006] According to a first aspect of the present invention, a swelling tape is provided, comprising an adhesive layer and a swelling layer, wherein the adhesive layer and the swelling layer are directly composited, and a composite surface thereof is in an undulating, wrinkled shape.

[0007] The swelling tape of the present invention creates structural weaknesses in the adhesive layer by varying the thickness of the adhesive layer. When immersed in electrolyte, these weak points are easily dissolved, providing ample space for the swelling layer to swell. After swelling, the swelling layer can directly contact the bare cell through the original weak points of the adhesive layer, more fully filling the gap between the bare cell and the casing, achieving better positioning and thus improving the drop resistance of the lithium battery.

[0008] Preferably, the two back-to-back surfaces of the adhesive layer are the first surface and the second surface, the adhesive layer is compounded with the swelling layer on the first surface, the first surface is an uneven wrinkled surface, and the second surface is a flat plane.

[0009] The second surface of the adhesive layer is used as the adhesive surface. If the adhesive surface is flat, it is easy to operate when the swelling tape is attached to the bare battery cell, and the bare battery cell can be tightly wrapped.

[0010] Preferably, in a cross section in the thickness direction of the swelling tape, the first surface of the adhesive layer forms a plurality of alternating peaks and troughs relative to the second surface, with the second surface being used as a reference, the distance between the top of the peak and the second surface being t1, and the distance between the bottom of the trough and the second surface being t0; t1 > 10 μm, and 0 μm < t0 < 4 μm.

[0011] Preferring the adhesive layer thickness to be within the aforementioned range ensures that when t1 > 10 μm, the swelling layer is thick enough to withstand various extreme environments and vibration shocks without falling off, allowing it to tightly adhere to and wrap around the bare battery cell. The trough region of the adhesive layer represents a structural weakness of the adhesive layer. When the distance between the trough and the second surface satisfies 0 μm < t0 < 4 μm, the adhesive material in the trough region readily dissolves in the electrolyte after the tape is soaked in electrolyte, thereby forming a notch corresponding to the trough region. The swelling material in the swelling layer, after swelling, can extend through the notch and directly contact the bare battery cell, enhancing the positioning and protection of the battery cell, thereby improving the battery's drop resistance and operational safety.

[0012] Preferably, t1 is ≤ 20 μm. Thus, the peak region of the adhesive layer in the swelling tape is not too thick, ensuring that the swelling material in the swelling layer fully fills the gap between the swelling layer and the adhesive layer after swelling and abuts the surface of the battery cell. This not only ensures the compact structure of the swelling tape but also helps the swelling tape effectively position the battery cell.

[0013] Preferably, 0 μm < t0 ≤ 2 μm. When the ratio is within the above range, the adhesive strength and swelling function of the swelling tape are maintained within the applicable range, which can not only keep the adhesive layer in an unbroken state before being immersed in the electrolyte, ensuring the structural stability and ease of use of the tape, but also ensure that the structurally weak areas in the adhesive layer are easily corroded by the electrolyte.

[0014] Preferably, t1 and t0 satisfy (t1-t0) / t0≥7.

[0015] The value t1-t0 is actually the area where the swelling layer extends into the wrinkled surface of the adhesive layer, while t0 is the extent of the structurally weak area of ​​the adhesive layer. When the swelling tape satisfies (t1-t0) / t0 ≥ 7, it ensures that the structurally weak area of ​​the adhesive layer can dissolve in the electrolyte, and that the swelling adhesive in the swelling layer swells sufficiently to fill the wrinkled surface of the adhesive layer. Furthermore, the swelling adhesive can extend from the dissolved weak area of ​​the adhesive layer and directly contact the battery cell, effectively positioning the battery cell.

[0016] Preferably, the thickness of the swelling tape is 30 to 120 μm.

[0017] Limiting the thickness of the swelling tape to between 30 and 120 μm not only ensures the swelling layer has sufficient swelling capacity to fill the gap between the bare cell and the casing, but also ensures a secure bond between the adhesive layer and the swelling layer, preventing the battery from loosening during a drop and improving its drop resistance. This also reduces the amount of adhesive used, meeting most battery swelling requirements on the market.

[0018] Preferably, the adhesive layer comprises an adhesive, and the raw materials of the adhesive include styrene-isoprene-styrene block copolymer (SIS block copolymer), tackifying resin, naphthenic oil and antioxidant;

[0019] Preferably, the raw materials of the adhesive are 38-47% SIS block copolymer, 39-48% tackifying resin, 19-24% naphthenic oil and 0.5-2.5% antioxidant, calculated by weight;

[0020] Preferably, the raw materials of the adhesive are 40% SIS block copolymer, 40% tackifying resin, 19% naphthenic oil and 1% antioxidant, calculated by weight;

[0021] Preferably, the swelling layer is an oriented polystyrene film.

[0022] The swelling layer and the adhesive layer made from this raw material formula are both resistant to high temperatures. The swelling layer will not shrink at high temperatures after being soaked in electrolyte, thus avoiding the risk of electrolyte leakage due to shrinkage.

[0023] According to another aspect of the present invention, a method for preparing the above-mentioned swelling tape is provided, comprising the following operations: S1. separately extruding an adhesive melt and a polystyrene melt, wherein the extrusion mode of the adhesive melt and / or the polystyrene melt is variable speed extrusion, wherein the adhesive melt is used to form an adhesive layer, and the polystyrene melt is used to form a swelling layer; S2. simultaneously conveying the adhesive melt and the polystyrene melt to a co-extrusion die, and preparing the swelling tape by co-extrusion, casting, and transverse and / or longitudinal stretching.

[0024] The present invention utilizes a coextrusion process to produce the aforementioned swellable adhesive tape. This simple process allows for the production of a swellable tape with excellent uniformity and consistency. Furthermore, the coextrusion process shortens the cycle time, reduces energy consumption, and is simple and easy to operate, resulting in excellent interlayer adhesion between the swellable layer and the adhesive layer. Furthermore, the coextrusion process reduces waste, eliminates the use of organic solvents, and reduces environmental pollution. By adjusting the extrusion method of the polystyrene melt and the adhesive melt, this method can produce the aforementioned swellable adhesive tape with excellent swelling effect and positioning capability through a simple process.

[0025] Preferably, the feeding method of the glue melt into the co-extrusion die is pulse feeding.

[0026] The pulse feeding method can better control the rate at which the glue melt enters the co-extrusion die, and the pulse feeding is highly flexible, easy to flexibly adjust the glue layer thickness, and has high production efficiency.

[0027] Preferably, S3 is also included, and S3 includes the following operations: performing thickness detection on the swollen tape obtained in S2, detecting the thickness of the adhesive layer in the formed swollen tape, and dynamically adjusting the extrusion speed of the adhesive melt and / or the polystyrene melt according to the measured thickness of the adhesive layer, so as to control the thickness of the adhesive layer in the subsequently formed swollen tape within a preset range.

[0028] When it is detected that t0 in the prepared swelling tape is about to be less than the preset range value, the extrusion rate of the adhesive melt is increased and / or the extrusion rate of the polystyrene melt is reduced, so as to ensure that the adhesive layer in the prepared swelling tape is not interrupted and the swelling tape is tightly adhered to the bare battery cell; when it is detected that t1 in the prepared swelling tape is about to exceed the preset range, the extrusion rate of the adhesive melt is reduced and / or the extrusion rate of the polystyrene melt is increased to ensure that the thickness of the swelling layer in the swelling tape is sufficient to fill the swelling space for the swelling layer to swell after swelling, so that the gap between the shell and the bare battery cell is filled.

[0029] Preferably, the polystyrene melt includes polystyrene and nano-silica, and the polystyrene includes high-impact polystyrene; calculated by mass percentage, the content of polystyrene in the polystyrene melt is 86-90wt%, the content of high-impact polystyrene in the polystyrene melt is 5-8wt%, and the content of nano-silica in the polystyrene melt is 0.9-2.3wt%.

[0030] By combining the formula and adding a certain amount of nano-silicon dioxide, the polystyrene network structure contains stable SiO bonds, which makes it have good thermal stability and not easy to break at high temperatures. When the adhesive melt is pulsed, the composite surface of the two can be deformed accordingly with the change of the adhesive melt injection amount, thereby forming a wrinkled composite surface, but it will not cause chaotic disturbance due to the pulsed injection, and ultimately the product will present a clear wrinkled composite surface.

[0031] Preferably, the polystyrene melt comprises styrene-butadiene copolymer, acrylonitrile-styrene copolymer and expandable polystyrene; calculated by mass percentage, the total mass of the styrene-butadiene copolymer, acrylonitrile-styrene copolymer and expandable polystyrene in the polystyrene melt is not less than 31wt%; and, calculated by mass ratio, the styrene-butadiene copolymer: acrylonitrile-styrene copolymer: expandable polystyrene = 40-75:5-15:5-10.

[0032] The addition of acrylonitrile-styrene copolymer to this formulation ensures the resulting polystyrene melt has an appropriate melt index, enabling flexible adjustment of the adhesive layer thickness with pulsed extrusion injection, resulting in high production efficiency. Furthermore, the resulting polystyrene melt blends easily with the adhesive melt when combined, resulting in a distinct, wrinkled composite surface for the resulting swellable tape. Furthermore, the addition of acrylonitrile-styrene copolymer ensures excellent high-temperature resistance after swelling in the electrolyte, preventing the swellable layer from shrinking at elevated temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic cross-sectional view of a swelling tape is provided for the present invention;

[0034] Figure 2 A schematic diagram of a cylindrical lithium battery to which the swelling tape of the present invention is applied;

[0035] Figure 3 Schematic diagram of the cross section of the swelling tape prepared in Comparative Examples 1 and 2;

[0036] Figure 4 Schematic diagram of a cylindrical lithium battery using the swelling tape prepared in Comparative Examples 1 and 2;

[0037] In the above drawings, the corresponding relationship between the reference numerals is: 1. adhesive layer, 2. swelling layer, 3. bare cell, 4. shell. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0039] Example 1

[0040] The raw material formula for preparing the swelling layer 2 in this embodiment is as follows: 88 wt% general-purpose polystyrene (GPPS) particles, 6 wt% high-impact polystyrene (HIPS) particles, 2 wt% nano-silica, and 4 wt% additives; the raw materials for preparing the adhesive layer 1 are 40% SIS block copolymer, 40% tackifying resin, 19% naphthenic oil, and 1% antioxidant.

[0041] Prepare the raw materials for the swelling layer 2 and the adhesive layer 1 according to the raw material formula used in this embodiment, add the required materials into their respective hoppers according to the formula ratio and mix them evenly, and prepare the swelling tape according to the following steps:

[0042] S1. The adhesive layer raw materials and the swelling layer raw materials, prepared and mixed according to the above-mentioned formula, are introduced into separate conveying pipes of the co-extrusion equipment. The adhesive layer raw materials are melted to form an adhesive melt; the swelling layer raw materials are melted to form a polystyrene melt. A pulse extrusion valve is provided in the conveying pipes for the adhesive melt and the polystyrene melt. By controlling the pulse frequency of the pulse extrusion valve for the adhesive melt and / or the polystyrene melt, the thickness of the adhesive layer 1 in the swelling tape can be varied, thereby achieving variable speed extrusion. The resulting swelling tape is directly composited with the adhesive layer 1 and the swelling layer 2, with the composite surface exhibiting an undulating, wrinkled appearance.

[0043] S2. The base film melt and the first adhesive melt are combined to form a first melt, which is then transferred to a coextrusion die. The first melt is extruded through the coextrusion die head of the coextrusion die to form a film at a film discharge speed of 45 m / min. The film is cast and cooled, and then cooled and shaped to obtain a swelling tape.

[0044] S3. The thickness of the swollen tape produced in S2 is measured. Based on the values ​​of t1 and t0 of the adhesive layer 1 in the formed swollen tape, the pulse frequency of the pulse extrusion valve for the adhesive melt and / or polystyrene melt in S1 is dynamically adjusted to control the thickness of the adhesive layer 1 in the subsequently formed swollen tape within a preset range. In a cross-section of the swollen tape in the thickness direction, the two opposing surfaces of the adhesive layer 1 are designated as the first surface and the second surface. The adhesive layer 1 is bonded to the swollen layer 2 on the first surface. The first surface of the adhesive layer 1 forms a plurality of alternating peaks and troughs relative to the second surface. With the second surface as a reference, the distance from the top of the peak to the second surface is t1, and the distance from the bottom of the trough to the second surface is t0. In the swollen tape produced in this embodiment, the maximum value of t1 is 20 μm, and the minimum value of t0 is 1 μm.

[0045] The structure of the swollen tape obtained in this embodiment is as follows Figure 1As shown, the swelling tape includes an adhesive layer 1 and a swelling layer 2. The adhesive layer 1 and the swelling layer 2 are directly laminated, and the composite surface of the two is uneven and wrinkled. The two back-to-back surfaces of the adhesive layer 1 are the first surface and the second surface. The adhesive layer 1 is laminated with the swelling layer 2 on the first surface. The first surface is an uneven and wrinkled surface, and the second surface is a flat surface. A schematic diagram of a cylindrical lithium battery using the swelling tape prepared in this embodiment is shown in FIG. Figure 2 As shown, the second surface of the adhesive layer 1 in the swelling tape serves as an adhesive surface for contact with the bare battery cell 3, while the first surface of the adhesive layer 1 is composited with the swelling layer 2. The surface of the swelling layer 2 not composited with the adhesive layer 1 is provided with a housing 4. The composite surface of the adhesive layer 1 and the swelling layer 2 in the swelling tape exhibits an undulating, wrinkled shape, thereby forming a structural weak point in the adhesive layer 1. In the swelling tape of this embodiment, during use, the structural weak point of the adhesive layer 1 can be dissolved in the electrolyte. After swelling, the swelling layer 2 can extend through the gap left by the dissolution of the original structural weak point in the adhesive layer 1 and directly abut the bare battery cell 3, stably filling the gap between the bare battery cell 3 and the housing 4 and preventing it from moving.

[0046] Comparative Example 1

[0047] This comparative example prepared a swelling tape using the method for preparing a swelling tape provided in Example 1. The differences between this comparative example and Example 1 are that the thickness of the adhesive layer 1 and the swelling layer 2 in the resulting swelling tape are uniform, the combined surface of the adhesive layer 1 and the swelling layer 2 is flat, and the thickness of the adhesive layer 1 in the resulting swelling tape is 20 μm. Specifically, the adhesive melt and the polystyrene melt were extruded at a constant speed, i.e., the pulse extrusion valve was not operated. All other raw materials and preparation methods were identical to those in Example 1.

[0048] The swelling tape prepared is as follows Figure 3 As shown, the two back-to-back surfaces of the adhesive layer 1 are the first surface and the second surface. The first surface of the adhesive layer 1 is composited with the swelling layer 2, and the composite surface of the two is a flat plane. The schematic diagram of the cylindrical lithium battery using the swelling tape prepared in this comparative example is shown in FIG. Figure 4 As shown, the second surface of the adhesive layer 1 in the swelling tape serves as an adhesive surface for bonding with the bare battery cell 3 , and the surface of the swelling layer 2 that is not bonded with the adhesive layer 1 is provided with a shell 4 .

[0049] Comparative Example 2

[0050] This comparative example prepared a swelling tape using the method for preparing a swelling tape provided in Example 1. The differences between this comparative example and Example 1 are that the thickness of the adhesive layer 1 and the swelling layer 2 in the resulting swelling tape are uniform, the combined surface of the adhesive layer 1 and the swelling layer 2 is flat, and the thickness of the adhesive layer 1 in the resulting swelling tape is 1 μm. Specifically, the adhesive melt and the polystyrene melt were extruded at a constant speed, i.e., the pulse extrusion valve was not operated. All other raw materials and preparation methods were identical to those in Example 1.

[0051] The swelling tape prepared is as follows Figure 3 As shown, the two back-to-back surfaces of the adhesive layer 1 are the first surface and the second surface. The first surface of the adhesive layer 1 is composited with the swelling layer 2, and the composite surface of the two is a flat plane. The schematic diagram of the cylindrical lithium battery using the swelling tape prepared in this comparative example is shown in FIG. Figure 4 As shown, the second surface of the adhesive layer 1 in the swelling tape serves as an adhesive surface for bonding with the bare battery cell 3 , and the surface of the swelling layer 2 that is not bonded with the adhesive layer 1 is provided with a shell 4 .

[0052] Example 2

[0053] Experimental group 2-1

[0054] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This experimental group differed from Example 1 in that the thickness of the adhesive layer 1 of the resulting swellable tape was different: specifically, the maximum value t1 was 10 μm, and the minimum value t0 was 2 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0055] Experimental group 2-2

[0056] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This experimental group differed from Example 1 in the thickness of the adhesive layer 1 of the resulting swellable tape. Specifically, the maximum value t1 was 15 μm, and the minimum value t0 was 2 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0057] Experimental groups 2-3

[0058] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This experimental group differed from Example 1 in the thickness of the adhesive layer 1 of the resulting swellable tape; specifically, the minimum value of t0 was 2 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0059] Experimental groups 2-4

[0060] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This group differed from Example 1 in that the thickness of the adhesive layer 1 of the resulting swellable tape was different: specifically, the maximum value t1 was 25 μm, and the minimum value t0 was 2 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0061] Experimental groups 2-5

[0062] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This group differed from Example 1 in that the thickness of the adhesive layer 1 of the resulting swellable tape was different: specifically, the maximum value t1 was 30 μm, and the minimum value t0 was 2 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0063] Experimental groups 2-6

[0064] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This group differed from Example 1 in that the thickness of the adhesive layer 1 of the resulting swellable tape was different: specifically, the maximum value t1 was 20 μm, and the minimum value t0 was 3 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0065] Experimental groups 2-7

[0066] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This group differed from Example 1 in the thickness of the adhesive layer 1 of the resulting swellable tape. Specifically, the maximum value t1 was 4 μm, and the minimum value was 1 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0067] Experimental groups 2-8

[0068] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This group differed from Example 1 in the thickness of the adhesive layer 1 of the resulting swellable tape. Specifically, the maximum value t1 was 6 μm, and the minimum value was 1 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0069] Experimental groups 2-9

[0070] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This group differed from Example 1 in the thickness of the adhesive layer 1 of the resulting swellable tape. Specifically, the maximum value t1 was 8 μm, and the minimum value was 1 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0071] Experimental groups 2-10

[0072] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This experimental group differed from Example 1 in that the thickness of the adhesive layer 1 of the resulting swellable tape was different: specifically, the maximum value t1 was 20 μm, and the minimum value t0 was 4 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0073] Experimental groups 2-11

[0074] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This group differed from Example 1 in that the thickness of the adhesive layer 1 of the resulting swellable tape was different: specifically, the maximum value t1 was 20 μm, and the minimum value t0 was 6 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0075] Experimental groups 2-12

[0076] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This experimental group differed from Example 1 in that the thickness of the adhesive layer 1 of the resulting swellable tape was different: specifically, the maximum value t1 was 8 μm, and the minimum value t0 was 4 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0077] Experimental groups 2-13

[0078] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This group differed from Example 1 in the thickness of the adhesive layer 1 of the resulting swellable tape. Specifically, the maximum value t1 was 8 μm, and the minimum value t0 was 6 μm. The remaining raw materials, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0079] Test Example 1

[0080] 1. Test subjects: The swelling tapes prepared in Example 1, Comparative Example 1, Comparative Example 2, and Experimental Group 2 were used as test subjects.

[0081] 2. Test items:

[0082] According to the evaluation criteria shown in Table 1, the test results of the following test items were obtained.

[0083] (1) Shape of the adhesive layer 1 and the swollen layer 2 after swelling

[0084] like Figure 2 or Figure 4As shown, the test object was attached to a bare cell and soaked in electrolyte to swell. The cell was then stored at room temperature for one day and then disassembled to remove the bare cell. The shape formed by the adhesive layer 1 and the swelling layer 2 was evaluated by assessing the condition of the swollen tape attached to the bare cell.

[0085] (2) Evaluation of the ability of the swelling tape to fill gaps (ability to prevent bare cells from moving)

[0086] like Figure 2 or Figure 4 As shown, the test object was bonded to a bare battery cell and soaked in electrolyte to swell. The tape was then stored at room temperature for one day to evaluate its gap-filling ability. This test example used methods for evaluating residual vibration and residual impact to evaluate the gap-filling ability of the tape.

[0087] The residual vibration assessment method is based on the UN38.3 vibration test: a reciprocating logarithmically swept sine vibration from 7Hz to 200Hz is performed within 15 minutes, and 12 vibrations in three directions are performed within 3 hours. If no battery power is detected after the assessment, the terminal is considered disconnected by movement.

[0088] The method for evaluating residual impact is: adding a battery to an octagonal cylinder and rotating it. When no power from the battery is detected within a fixed time, it is determined that the terminal is disconnected by movement.

[0089] (3) Shape of adhesive layer 1 and swelling layer 2 after vibration test

[0090] After the test object completes the test (2), it is disassembled to remove the bare battery cell, and the shape of the adhesive layer 1 and the swelling layer 2 after the vibration test is evaluated by evaluating the condition of the swelling tape attached to the bare battery cell.

[0091] Table 1. Evaluation criteria for the three test items in this test case

[0092]

[0093]

[0094] 3. Test results: The product dimensions of the test objects and their calculation results are shown in Table 2, and the test results are shown in Table 3.

[0095] According to the test results in Table 3, the swelling tapes of Example 1 and Example 2 have better shape and gap filling ability than those of Comparative Example 1 and Comparative Example 2. Figure 1 and Figure 2As shown, the swelling tapes prepared in Example 1 and Example 2 include an adhesive layer 1 and a swelling layer 2. The adhesive layer 1 is directly compounded with the swelling layer 2, and the composite surface of the two is in an undulating, wrinkled shape. This special structure causes structural weak points on the adhesive layer 1 by setting the thickness of the adhesive layer 1 to vary unevenly. When immersed in electrolyte, the structural weak points of the adhesive layer 1 are easily dissolved in the electrolyte, providing more sufficient swelling space for the swelling layer 2. After swelling, the swelling layer 2 can directly contact the bare cell 3 from the original structural weak points of the adhesive layer 1, so that the gap between the bare cell 3 and the shell 4 can be more fully filled to achieve a better positioning effect, thereby improving the drop resistance of the lithium battery.

[0096] like Figure 3 and Figure 4As shown, the composite surface of the adhesive layer 1 and the swelling layer 2 in the swelling tapes prepared in Comparative Examples 1 and 2 is a flat plane. In the process of attaching the swelling tape to the bare battery cell 3, bubbles are easily generated between the adhesive layer 1 and the bare battery cell 3. Since there is a flat adhesive layer 1 between the swelling layer 2 and the bare battery cell 3, the swelling layer 2 cannot fill the gap between the adhesive layer 1 and the bare battery cell 3. Displacement may occur between the bare battery cell 3 and the shell 4, resulting in a safety hazard. Among them, the thickness of the adhesive layer 1 in the swelling tape prepared in Comparative Example 1 is consistent with the maximum value of t1 in the adhesive layer 1 of Example 1. The adhesive layer 1 in Comparative Example 1 is thicker. When the adhesive layer 1 is soaked in electrolyte, it will not dissolve and break and produce gaps. When attached to the bare battery cell 3, it is inevitably attached to the air due to operation. The swelling layer 2 swells but there is still a gap. At the same time, due to the thick adhesive layer 1, the flexibility of the swelling tape decreases. When attaching the adhesive, there are more gaps between the swelling tape and the bare battery cell 3, and the positioning effect is poor. The thickness of the adhesive layer 1 in Comparative Example 2 is consistent with the minimum value of t0 in the adhesive layer 1 in Example 1. The adhesive layer 1 in Comparative Example 2 is thinner and very easy to dissolve in the electrolyte, but when subjected to extreme use environments or external impacts, the adhesive layer 1 is prone to fall off on a large scale. The swelling of the swelling layer 2 alone is not enough to position the battery, and the bare cell 3 will be significantly displaced. From the data of Example 1 and Example 2 in Table 3, it can be seen that Example 1 and experimental groups 2-1 to 2-6 have better ability to fix the battery. It shows that when the adhesive layer 1 in the swelling tape satisfies t1>10μm, and 0μm<t0<4μm, the thickness of the swelling layer 2 can enable the swelling tape to fill the gap between the bare cell 3 and the outer shell 4 after being soaked in electrolyte, thereby firmly supporting the battery. The troughs of adhesive layer 1 represent structural weaknesses. When the distance between the troughs and the second surface satisfies 0μm < t0 < 4μm, the adhesive material in the troughs readily dissolves in the electrolyte when the tape 1 is immersed in electrolyte, forming a notch corresponding to the trough. The swelling material in swellable layer 2 then swells and extends through the notch, directly contacting the bare battery cells 3 and enhancing the positioning and protection of the cells. In the swellable tapes produced in Experimental Groups 2-7 to 2-9, adhesive layer 1 did not meet the requirement of t1 > 10μm. This means that the adhesive layer at t1 was too thin, dissolving during electrolyte immersion. However, the adhesive layer was not resistant to external impact and, under extreme operating conditions or external impact, was prone to widespread detachment, resulting in reduced battery positioning effectiveness. In the swollen tapes prepared in experimental groups 2-10 to 2-13, the adhesive layer 1 does not satisfy 0 μm<t0<4 μm, indicating that the adhesive at t0 of the adhesive layer 1 is too thick and difficult to be dissolved by the electrolyte to expose the swollen material.

[0097] Example 1 and experimental groups 2-1 to 2-6 all performed well after all three tests. Experimental group 2-6 showed less dissolution at the adhesive layer t0, indicating that when 0 < t0 ≤ 2 μm, structural weaknesses in adhesive layer 1 are more susceptible to dissolution during the electrolyte soaking process. After increasing the number of battery collisions, the swollen tapes in experimental groups 2-4 and 2-5 showed no signs of detachment at t1, and the gaps were fully filled, though small gaps still existed, indicating that adhesive layer 1 with a t1 ≤ 20 μm provides better fixation. After increasing the number of battery collisions, the adhesive layer at position t1 in Experimental Groups 2-1 and 2-2 partially detached, indicating that the adhesive layer 1 in the swelling tape has excellent battery retention when at least one location satisfies the condition (t1-t0) / t0≥7. Here, t1-t0 is the area where the swelling layer 2 extends into the wrinkled surface of the adhesive layer, while t0 is the area of ​​the structurally weak region of the adhesive layer 1. Satisfying (t1-t0) / t0≥7 ensures that the structurally weak region of the adhesive layer 1 can dissolve in the electrolyte, while also ensuring that the swelling adhesive of the swelling layer 2, after swelling, is sufficient to fill the wrinkled surface of the adhesive layer 1 and extend from the dissolved weak region to directly contact the bare battery cell 3, effectively positioning the battery. After increasing the number of battery collisions, the adhesive layer at position t1 in the swelling tapes of Example 1 and Experimental Groups 2-3 did not detach. Furthermore, the swelling base layer was neatly arranged after swelling, with gaps fully filled and a strong bond. Therefore, Example 1 and Experimental Groups 2-3 are the preferred embodiments.

[0098] Table 2. Product dimensions and calculation results of the test objects in this test case

[0099] Group <![CDATA[Maximum value of t1]]> <![CDATA[Minimum value of t0]]> <![CDATA[(t1-t0) / t0]]> Example 1 20 1 19 Comparative Example 1 / / / Comparative Example 2 / / / Experimental group 2-1 10 2 4 Experimental group 2-2 15 2 6.5 Experimental groups 2-3 20 2 9 Experimental groups 2-4 25 2 11.5 Experimental groups 2-5 30 2 14 Experimental groups 2-6 20 3 5.67 Experimental groups 2-7 4 1 3 Experimental groups 2-8 6 1 5 Experimental groups 2-9 8 1 7 Experimental groups 2-10 20 4 4 Experimental groups 2-11 20 6 2.33 Experimental groups 2-12 8 4 1 Experimental groups 2-13 8 6 0.33

[0100] Table 3. Performance test results of the test objects in this test case

[0101]

[0102]

[0103] Example 3

[0104] Experimental group 3-1

[0105] This experimental group strictly followed the method for preparing a swelling tape provided in Example 1 to prepare a swelling tape, so that the prepared swelling tape was strictly consistent with that in Example 1.

[0106] Experimental group 3-2

[0107] This experimental group prepared a swelling tape using the method for preparing a swelling tape provided in Example 1. This experimental group differed from Example 1 in that the raw material formulation for forming swelling layer 2 did not contain silica. Specifically, the formulation consisted of 90% general-purpose polystyrene and 6% high-impact polystyrene. The remaining raw material ratios, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0108] Experimental group 3-3

[0109] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This experimental group differed from Example 1 in the raw material formulation for swellable layer 2: 22% styrene butadiene styrene, 10% acrylonitrile styrene, 6% expandable styrene, and 62% general-purpose polystyrene. The remaining raw material ratios, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0110] Experimental groups 3-4

[0111] This experimental group prepared a swellable tape using the method for preparing a swellable tape provided in Example 1. This experimental group differed from Example 1 in the raw material formulation for swellable layer 2: 22% styrene butadiene styrene, 6% expandable styrene, and 72% general-purpose polystyrene. The remaining raw material ratios, preparation method, and amounts of the adhesive melt and polystyrene melt remained identical to those in Example 1.

[0112] Test Example 2

[0113] 1. Test subjects: The swelling tape prepared in Example 3 was used as the test subject.

[0114] 2. Test items: Strictly consistent with test case 1

[0115] 3. Test results: The raw material composition of the swelling layer of the test objects is shown in Table 4, and the test results are shown in Table 5.

[0116] From the data of experimental groups 3-1 to 3-4 in Table 5, it can be seen that the swelling tapes prepared in experimental groups 3-1 to 3-4 are all resistant to high temperatures. The swelling layer 2 thereof will not shrink at high temperatures after being soaked in electrolyte, thus avoiding the risk of electrolyte leakage due to shrinkage.

[0117] Secondly, Experimental Groups 3-1 and 3-2, and Experimental Groups 3-3 and 3-4, use different raw material formulations. Experimental Group 3-1 exhibited superior fixation performance compared to Experimental Group 3-2. In tests measuring the gap-filling capacity of the swelling tape, the resistivity change rate of the battery in Experimental Group 3-1 was within an acceptable range, while the resistivity change of the battery in Experimental Group 3-2 was more pronounced under residual vibration and residual impact. This is presumably due to the inclusion of a certain amount of nano-silica in the raw material formulation used to prepare the swelling layer 2 in Experimental Group 3-1. This stabilizes the SiO bonds within the polystyrene network, imparting excellent thermal stability and resisting breakage at high temperatures. During pulsed injection of the adhesive melt, the composite surface of the two materials deforms accordingly with the amount of adhesive melt injected, thereby forming a wrinkled composite surface. However, this prevents the chaotic disturbances caused by the pulsed injection, ultimately resulting in a clear, wrinkled composite surface in the resulting product.

[0118] The swelling tapes in Experimental Group 3-3 exhibited superior overall performance compared to those in Experimental Group 3-4. In tests measuring the gap-filling capacity of the swelling tapes, the resistivity change rate of the batteries in Experimental Group 3-3 remained within an acceptable range, while the resistivity of the batteries in Experimental Group 3-4 increased by more than 10% under residual vibration and residual impact, indicating that the swelling tapes in Experimental Group 3-3 provided better battery buffering performance than the swelling tapes in Experimental Group 3-4. This is presumably due to the inclusion of acrylonitrile-styrene copolymer in the raw material formulation for preparing the swelling layer 2 in Experimental Group 3-3, which resulted in a polystyrene melt with an appropriate melt index, enabling pulse extrusion feeding and flexible adjustment of the thickness of the adhesive layer 1, resulting in high production efficiency. Furthermore, the polystyrene melt produced with this formulation did not mix well with the adhesive melt upon merging, resulting in the resulting swelling tape forming a distinct, wrinkled composite surface. Furthermore, the addition of acrylonitrile-styrene copolymer into the formula can make the swelling layer 2 have good high temperature resistance after swelling in the electrolyte, and the shape of the swelling layer 2 does not shrink in a high temperature environment.

[0119] Therefore, the swelling tape prepared using the raw material formula for preparing the swelling layer 2 in experimental group 3-1 and experimental group 3-3 has excellent battery fixing ability, can fill the gap between the bare battery cell 3 and the shell 4, and increase the battery's shock and impact resistance.

[0120] Table 4. Raw material composition for preparing swelling layer 3 in the test objects of this test example

[0121]

[0122] Table 5. Performance test results of the test objects in this test case

[0123]

[0124] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A swelling tape, characterized in that: The adhesive layer comprises an adhesive and a swelling layer, wherein the adhesive layer comprises an adhesive, and the raw materials of the adhesive comprise styrene-isoprene-styrene block copolymer and a tackifying resin; the swelling layer is an oriented polystyrene film; The adhesive layer is directly laminated with the swelling layer, and the composite surface of the two is in an undulating, wrinkled shape; the two back-to-back surfaces of the adhesive layer are designated as a first surface and a second surface, and the adhesive layer is laminated with the swelling layer through the first surface, the first surface being an undulating, wrinkled surface, and the second surface being a flat surface; in a cross-section in the thickness direction of the swelling tape, the first surface of the adhesive layer forms a plurality of alternating peaks and troughs relative to the second surface, with the second surface being used as a reference, and the distance from the top of the peak to the second surface being t1, and the distance from the bottom of the trough to the second surface being t0; The t1 is greater than 10 μm, and the 0 μm is less than t0 and less than 4 μm.

2. The swelling tape according to claim 1, wherein: The t1 and the t0 satisfy (t1-t0) / t0≥7.

3. The swelling tape according to claim 1, wherein: The thickness of the swelling tape is 30-120 μm.

4. The method for preparing a swelling tape according to any one of claims 1 to 3, wherein: The following operations are included: S1. Separately extruding an adhesive melt and a polystyrene melt, wherein the adhesive melt and / or the polystyrene melt are extruded in a variable speed manner, wherein the adhesive melt is used to form the adhesive layer, and the polystyrene melt is used to form the swelling layer; S2. Simultaneously conveying the adhesive melt and the polystyrene melt to a coextrusion die, and producing the swelling tape by coextrusion, casting, and transverse and / or longitudinal stretching.

5. The preparation method according to claim 4, wherein: S3 is also included, and S3 includes the following operations: The thickness of the swollen tape prepared in S2 is detected, and the thickness of the adhesive layer in the formed swollen tape is detected. The extrusion speed of the adhesive melt and / or the polystyrene melt is dynamically adjusted according to the measured thickness of the adhesive layer, so as to control the thickness of the adhesive layer in the subsequently formed swollen tape within a preset range.

6. The preparation method according to claim 4, wherein: The polystyrene melt comprises polystyrene and nano-silicon dioxide, and the polystyrene comprises high-impact polystyrene; Calculated by mass percentage, the content of the polystyrene in the polystyrene melt is 86-90 wt %, the content of the high-impact polystyrene in the polystyrene melt is 5-8 wt %, and the content of the nano-silicon dioxide in the polystyrene melt is 0.9-2.3 wt %.

7. The preparation method according to claim 4, wherein: The polystyrene melt includes styrene-butadiene copolymer, acrylonitrile-styrene copolymer and expandable polystyrene; Calculated by mass percentage, the total mass of the styrene-butadiene copolymer, the acrylonitrile-styrene copolymer and the expandable polystyrene in the polystyrene melt is not less than 31 wt%; Moreover, calculated according to the mass ratio, styrene-butadiene copolymer: acrylonitrile-styrene copolymer: expandable polystyrene = 40~75:5~15:5~10.

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