Square lithium battery outer package blue film double-sided adhesive tape, preparation method and application thereof

Abstract

The present application relates to a kind of square lithium battery outer package blue film double-sided tape and its preparation method and application.Square lithium battery outer package blue film double-sided tape includes: polymer base film, first pressure-sensitive adhesive layer, second pressure-sensitive adhesive layer and release layer;First pressure-sensitive adhesive layer is set to the first surface of polymer base film, for attaching square lithium battery cell outer surface;Second pressure-sensitive adhesive layer is set to the second surface of polymer base film, for attaching heat-insulating flame-retardant buffer layer;At least one of first pressure-sensitive adhesive layer and second pressure-sensitive adhesive layer is flame-retardant polyacrylate pressure-sensitive adhesive layer;Release layer is at least set to the side surface of second pressure-sensitive adhesive layer away from polymer base film;Wherein, release layer includes the covering portion corresponding with glue face and the pull-out portion beyond the edge of glue face, the pull-out portion is used to be pulled out and removed after square lithium battery cell positioning, to make corresponding pressure-sensitive adhesive layer and the object to be bonded object fit.

Description

Technical Field

[0001] This invention relates to the field of lithium battery insulation protection materials, and in particular to a square lithium battery outer blue film double-sided adhesive tape, its preparation method and application. Background Technology

[0002] As the new energy vehicle industry continues to demand higher energy density, safety, and lightweighting from power batteries, the assembly methods of square lithium batteries in battery packs are constantly being optimized. Especially with the development of large-module or module-less technologies such as direct integration of cells into the battery pack and direct integration of cells into the chassis, the utilization rate of internal space in the battery pack is continuously improving, and the arrangement of adjacent cells is becoming more compact. Therefore, the connecting tape between cells not only needs to meet the requirements of adhesion and fixation, but also needs to consider multiple performance aspects such as insulation, flame retardancy, cushioning, assembly accuracy, and lightweighting.

[0003] In current prismatic lithium battery assembly, a common approach is to use a combination of single-sided blue film tape and flame-retardant double-sided tape. Specifically, the outer side of the cell is typically covered with a layer of single-sided blue film tape approximately 120 μm thick, and adjacent cells are then bonded together with heat-insulating and flame-retardant gas gel or other buffer layers using flame-retardant double-sided tape approximately 100 μm thick. For two adjacent cells, the traditional structure typically includes one layer of single-sided blue film tape, one layer of flame-retardant double-sided tape, heat-insulating and flame-retardant gas gel, another layer of flame-retardant double-sided tape, and another layer of single-sided blue film tape. This results in a large number of layers, a complex structure, and the tape material occupies a significant portion of the cell spacing and weight, which is detrimental to improving the volume utilization and lightweighting of the battery pack.

[0004] Meanwhile, in traditional battery cell assembly processes, one side of double-sided tape is usually fixed to the heat-insulating aerogel sheet or buffer layer first, then the release film on the other side is removed, and two square battery cells are directly bonded together. Because the bonding area of ​​the battery cells is relatively large, air bubbles are easily generated during the bonding process; and once the double-sided tape adheres to the surface of the battery cells, the cell position is difficult to readjust, which can easily cause cell misalignment, increase assembly difficulty, and affect the consistency and reliability of battery pack assembly.

[0005] Therefore, there is an urgent need to provide a double-sided blue film tape for packaging square lithium battery packs and its assembly method, which can reduce the number of tape layers and the overall thickness while providing functions such as cell protection, insulation, flame retardancy, bonding and fixing, and buffer layer connection. Furthermore, it can complete the bonding by pulling out the release film after the cell is positioned, thereby reducing the problems of air bubbles and misalignment in the large-area bonding process and improving the assembly accuracy and efficiency of square lithium battery packs. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a double-sided blue film tape for the outer packaging of square lithium batteries, its preparation method, and its application. This invention can reduce the thickness, weight, and process complexity caused by the superposition of traditional single-sided blue film tape and flame-retardant double-sided tape, while improving the positioning accuracy, bonding reliability, and assembly convenience of cell connections in square lithium battery packs, and taking into account the requirements of flame retardancy, insulation, adhesion, and lightweighting.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a double-sided adhesive tape for wrapping a square lithium battery with a blue film, comprising: Polymer base film, first pressure-sensitive adhesive layer, second pressure-sensitive adhesive layer and release layer; The first pressure-sensitive adhesive layer is disposed on the first surface of the polymer base film and is used to attach the outer surface of the square lithium battery cell. The second pressure-sensitive adhesive layer is disposed on the second surface of the polymer base film and is used to attach the heat-insulating and flame-retardant buffer layer; At least one of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer is a flame-retardant polyacrylate pressure-sensitive adhesive layer; The release layer is at least disposed on the side surface of the second pressure-sensitive adhesive layer opposite to the polymer base film; The release layer includes a covering portion corresponding to the adhesive surface and a pull-out portion extending beyond the edge of the adhesive surface. The pull-out portion is used to be pulled out after the square lithium battery cell is positioned, so that the corresponding pressure-sensitive adhesive layer adheres to the object being bonded.

[0008] Preferably, the polymer base film includes: biaxially oriented polypropylene (BOPP) base film, polyethylene terephthalate (PET) base film, or multilayer co-extruded biaxially oriented composite base film.

[0009] More preferably, the multilayer co-extruded biaxially oriented composite base film is a five-layer co-extruded biaxially oriented composite base film, comprising a first polypropylene functional layer, a first polyamide reinforcing layer, a polypropylene core layer, a second polyamide reinforcing layer, and a second polypropylene functional layer stacked sequentially. The first polypropylene functional layer, the polypropylene core layer, and the second polypropylene functional layer each comprise 60-80 parts of homopolymer polypropylene, 10-30 parts of maleic anhydride-grafted polypropylene, and 2-8 parts of additives; the isotacticity of the homopolymer polypropylene is greater than 90%. The first polyamide reinforcing layer and the second polyamide reinforcing layer each comprise 95-100 parts of polyamide and 0-5 parts of an opening agent; the opening agent comprises erucamide.

[0010] Preferably, the flame-retardant polyacrylate pressure-sensitive adhesive layer comprises, by weight parts: 50-80 parts polyacrylate, 0.001-0.5 parts curing agent, 10-30 parts flame retardant, and 5-20 parts tackifying resin. The curing agent includes at least one of a multifunctional epoxy resin or an isocyanate oligomer. The flame retardant includes powder flame retardant and / or liquid phosphate flame retardant; the powder flame retardant includes at least one of: phosphonic acid metal salt, coated ammonium polyphosphate, or metal hydroxide; The liquid phosphate flame retardant includes at least one of bisphenol A bis(diphenyl phosphate) BDP or resorcinol bis(diphenyl phosphate) RDP; The tackifying resin includes at least one of rosin resin or terpene resin.

[0011] More preferably, the first pressure-sensitive adhesive layer is an electrolyte-resistant polyacrylate pressure-sensitive adhesive layer, and the second pressure-sensitive adhesive layer is a flame-retardant polyacrylate pressure-sensitive adhesive layer; The electrolyte-resistant polyacrylate pressure-sensitive adhesive layer comprises: 70-99 parts polyacrylate, 0.001-0.5 parts curing agent, and 5-30 parts tackifying resin.

[0012] Preferably, the thickness of the first pressure-sensitive adhesive layer is 20–40 μm, the thickness of the polymer base film is 30–60 μm, and the thickness of the second pressure-sensitive adhesive layer is 20–40 μm. The release layer includes: a first release film and a second release film, or, only the second release film; The first release film covers the first pressure-sensitive adhesive layer, and the length of the first release film is the same as the adhesive surface length of the first pressure-sensitive adhesive layer; The second release film covers the second pressure-sensitive adhesive layer, and the length of the second release film is more than twice the adhesive surface length of the second pressure-sensitive adhesive layer, preferably 2.5 to 3.5 times; wherein, the second release film includes a covering section covering the second pressure-sensitive adhesive layer and a pull-out section extending beyond the second pressure-sensitive adhesive layer, and the pull-out section is disposed on one side of the second pressure-sensitive adhesive layer after being folded in half.

[0013] Secondly, embodiments of the present invention provide a method for preparing the double-sided adhesive tape for the outer blue film of the square lithium battery described in the first aspect above, comprising: Preparation of the second pressure-sensitive adhesive solution; The second pressure-sensitive adhesive liquid is coated onto the second surface of the polymer base film and subjected to heat curing treatment to form a second pressure-sensitive adhesive layer; A release layer is attached to the side of the second pressure-sensitive adhesive layer that is away from the polymer base film to obtain a single-sided coated semi-finished product. Preparation of the first pressure-sensitive adhesive solution; The first pressure-sensitive adhesive liquid is coated onto the first surface of the polymer base film in the single-sided adhesive semi-finished product, and then subjected to heat curing treatment to form the first pressure-sensitive adhesive layer, thereby obtaining the double-sided tape master roll. The double-sided tape master roll is slit and die-cut to form a release layer that covers the second pressure-sensitive adhesive layer and a pull-out portion that extends beyond the edge of the second pressure-sensitive adhesive layer, resulting in a square lithium battery outer blue film double-sided tape.

[0014] Preferably, the preparation of the first pressure-sensitive adhesive includes: adding a curing agent, a flame retardant, a tackifying resin, and an organic solvent to a polyacrylate organic solution, mixing, and dispersing at 1000–1200 rpm for 30–60 minutes to obtain a flame-retardant polyacrylate pressure-sensitive adhesive; or adding a curing agent, a tackifying resin, and an organic solvent to a polyacrylate solution, mixing, and dispersing at 1000–1200 rpm for 30–60 minutes to obtain an electrolyte-resistant polyacrylate pressure-sensitive adhesive; wherein the organic solvent includes at least one of ethyl acetate, butyl acetate, or acetone; and the solid content of the first pressure-sensitive adhesive is 20%–55% by mass. The preparation of the second pressure-sensitive adhesive includes: adding a curing agent, a flame retardant, a tackifying resin, and an organic solvent to a polyacrylate organic solution and mixing them, then dispersing the mixture at 1000–1200 rpm for 30–60 minutes to obtain a flame-retardant polyacrylate pressure-sensitive adhesive; wherein the organic solvent includes at least one of ethyl acetate, butyl acetate, or acetone; the solid content of the second pressure-sensitive adhesive is 20%–55% by mass. The thermosetting process adopts a segmented curing method, which includes: first pre-curing at 50-80℃ for 1-2 minutes; then main curing at 90-120℃ for 2-3 minutes; The die-cutting includes: removing portions of the tape at intervals along the length of the double-sided tape master roll while retaining the release layer, so that the release layer forms a pull-out portion extending beyond the adhesive surface.

[0015] Thirdly, embodiments of the present invention provide an application of the blue double-sided tape for wrapping the square lithium battery as described in the first aspect above, wherein the blue double-sided tape for wrapping the square lithium battery is used for assembling the square lithium battery pack; The square lithium battery pack includes: multiple square lithium battery cells, a heat-insulating and flame-retardant buffer layer, and blue double-sided adhesive tape covering the square lithium battery. The first pressure-sensitive adhesive layer of the blue double-sided adhesive tape covering the square lithium battery is attached to the outer surface of the square lithium battery cell. The heat-insulating and flame-retardant buffer layer is disposed between two adjacent square lithium battery cells. The second pressure-sensitive adhesive layer of the blue double-sided adhesive tape covering the square lithium battery is attached to the heat-insulating and flame-retardant buffer layer, so that two adjacent square lithium battery cells are connected and fixed by the blue double-sided adhesive tape covering the square lithium battery and the heat-insulating and flame-retardant buffer layer.

[0016] Fourthly, embodiments of the present invention provide a method for assembling a square lithium battery pack using the blue film double-sided adhesive tape used for wrapping the square lithium battery as described in the first aspect above, the assembly method comprising: The first pressure-sensitive adhesive layer on the first side of the blue film double-sided tape is attached to the outer surface of the square lithium battery cell. The release film on the second side of the blue double-sided adhesive tape covering the square lithium battery is retained, and a heat-insulating and flame-retardant buffer layer is placed between adjacent square lithium battery cells. Multiple square lithium battery cells are arranged sequentially and their positions are aligned. After aligning the positions, pull out and remove the release film on the second side to expose the second pressure-sensitive adhesive layer; Pressure is applied to adjacent square lithium battery cells to bond and fix the second pressure-sensitive adhesive layer to the heat-insulating and flame-retardant buffer layer.

[0017] The blue double-sided adhesive tape for encasing square lithium batteries provided in this embodiment of the invention enables the square lithium battery to simultaneously achieve attachment to the outer surface of the battery cell and connection of the heat-insulating and flame-retardant buffer layer by setting a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on both sides of the polymer base film. This reduces the problems of multiple layers, large thickness and heavy weight caused by the superposition of traditional single-sided blue film tape and flame-retardant double-sided tape.

[0018] Meanwhile, by providing a release layer with a covering portion and a pull-out portion, this invention allows the tape to be removed and bonded after the battery cell is positioned by pulling out the release layer. This reduces the risk of air bubbles and misalignment during large-area bonding, improving the assembly accuracy and efficiency of the square lithium battery pack. At least one of the first and second pressure-sensitive adhesive layers is a flame-retardant polyacrylate pressure-sensitive adhesive layer, further enhancing the tape's flame-retardant properties and bonding reliability. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a square lithium battery wrapped with blue double-sided adhesive tape according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the assembly structure of a square lithium battery pack using blue double-sided adhesive tape for wrapping a square lithium battery, as provided in an embodiment of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0021] This invention provides a double-sided adhesive tape for wrapping a square lithium battery with a blue film, its preparation method, and its application.

[0022] Figure 1 This is a schematic diagram of the structure of a square lithium battery wrapped with blue double-sided adhesive tape according to an embodiment of the present invention. The following is a description of the structure in conjunction with... Figure 1The technical solution of the present invention will be described below.

[0023] The blue double-sided adhesive tape for the outer casing of a square lithium battery includes: a polymer base film 1, a first pressure-sensitive adhesive layer 2, a second pressure-sensitive adhesive layer 3, and a release layer 4.

[0024] The first pressure-sensitive adhesive layer 2 is disposed on the first surface of the polymer base film 1 for attaching the outer surface of the square lithium battery cell; the second pressure-sensitive adhesive layer 3 is disposed on the second surface of the polymer base film 1 for attaching the heat-insulating and flame-retardant buffer layer; the release layer 4 is disposed at least on the side surface of the second pressure-sensitive adhesive layer 3 facing away from the polymer base film 1; wherein, the release layer 4 includes a covering portion corresponding to the adhesive surface and a pull-out portion extending beyond the edge of the adhesive surface, the pull-out portion being pulled out after the square lithium battery cell is positioned, so that the corresponding pressure-sensitive adhesive layer adheres to the object being bonded.

[0025] The polymer base film 1 includes: biaxially oriented polypropylene (BOPP) base film, polyethylene terephthalate (PET) base film, or multilayer co-extruded biaxially oriented composite base film.

[0026] In the preferred embodiment, a multilayer co-extruded biaxially oriented composite base film is used, more preferably a five-layer co-extruded biaxially oriented composite base film, comprising a first polypropylene functional layer, a first polyamide reinforcing layer, a polypropylene core layer, a second polyamide reinforcing layer, and a second polypropylene functional layer stacked sequentially.

[0027] The first polypropylene functional layer, the polypropylene core layer, and the second polypropylene functional layer each comprise 60-80 parts of homopolymer polypropylene, 10-30 parts of maleic anhydride-grafted polypropylene, and 2-8 parts of additives; the additives may include silica, antioxidants, etc. The isotacticity of the homopolymer polypropylene is greater than 90%. Homopolymer polypropylene is used to provide the basic mechanical properties, insulation properties, and lightweight characteristics of the composite base film. The selection of homopolymer polypropylene with an isotacticity greater than 90% leverages its high molecular chain regularity and crystallinity to improve the temperature resistance, tensile strength, and dimensional stability of the polypropylene functional layers, enabling the five-layer co-extruded biaxially oriented composite base film to maintain its lightweight advantage while possessing good mechanical support and heat resistance stability. Maleic anhydride-grafted polypropylene is used to address the low surface energy of the polypropylene material, improve the interfacial bonding between the polypropylene layer and the polyamide reinforcing layer, and reduce delamination and peeling problems during tape application, bending, or long-term use.

[0028] The first and second polyamide reinforcing layers each comprise 95-100 parts of polyamide and 0-5 parts of an opening agent; the opening agent includes erucamide. The polyamide is used to improve the temperature resistance, tear resistance, and dimensional stability of the five-layer co-extruded biaxially oriented composite base film 10, enabling the composite base film to better adapt to the bonding, bending, and long-term use environment during the insulation wrapping process of power battery cells; the opening agent is used to improve the opening performance during film processing and winding, reducing the risk of interlayer adhesion.

[0029] The thickness ratio of the first polypropylene functional layer, the first polyamide reinforcing layer, the polypropylene core layer, the second polyamide reinforcing layer, and the second polypropylene functional layer is 1–3:1–3:2–8:1–3:1–3. By adopting a five-layer co-extrusion structure combining the polypropylene functional layer and the polyamide reinforcing layer, the lightweight advantages of polypropylene materials can be maintained while the polyamide reinforcing layer can improve the temperature resistance, dimensional stability, and tear resistance of the composite base film, thereby addressing the problem of insufficient temperature resistance in ordinary biaxially oriented polypropylene (BOPP) base films.

[0030] Of course, the multilayer co-extruded biaxially oriented composite base film can also be a topology based on the above five-layer structure to achieve a multilayer co-extruded biaxially oriented composite base film with more layers.

[0031] At least one of the first pressure-sensitive adhesive layer 2 and the second pressure-sensitive adhesive layer 3 is a flame-retardant polyacrylate pressure-sensitive adhesive layer; in one embodiment, both the first pressure-sensitive adhesive layer 2 and the second pressure-sensitive adhesive layer 3 are flame-retardant polyacrylate pressure-sensitive adhesive layers, and in another embodiment, the first pressure-sensitive adhesive layer 2 is an electrolyte-resistant polyacrylate pressure-sensitive adhesive layer, and the second pressure-sensitive adhesive layer 3 is a flame-retardant polyacrylate pressure-sensitive adhesive layer.

[0032] According to the mass fractions, the flame-retardant polyacrylate pressure-sensitive adhesive layer comprises: 50-80 parts polyacrylate, 0.001-0.5 parts curing agent, 10-30 parts flame retardant, and 5-20 parts tackifying resin; the electrolyte-resistant polyacrylate pressure-sensitive adhesive layer comprises: 70-99 parts polyacrylate, 0.001-0.5 parts curing agent, and 5-30 parts tackifying resin.

[0033] The curing agent includes at least one of a multifunctional epoxy resin or an isocyanate oligomer; the organic solvent includes at least one of ethyl acetate, butyl acetate, or acetone; the flame retardant includes a powder flame retardant and / or a liquid phosphate flame retardant; the powder flame retardant includes at least one of a phosphonic acid metal salt, coated ammonium polyphosphate, or a metal hydroxide, wherein the phosphonic acid metal salt includes aluminum phosphonate, and the coated ammonium polyphosphate, also known as microencapsulated APP, is a modified flame retardant in which ammonium polyphosphate (APP) particles are encapsulated by polymeric materials or inorganic substances. The liquid phosphate flame retardant includes at least one of bisphenol A bis(diphenyl phosphate) (BDP) or resorcinol bis(diphenyl phosphate) (RDP); the tackifying resin includes at least one of rosin resin or a terpene resin.

[0034] Polyacrylate, as the main film-forming component of the pressure-sensitive adhesive layer, provides the basic adhesive properties, flexibility, and fit of the pressure-sensitive adhesive layer. The curing agent is used to cross-link with the active groups in the polyacrylate, improving the cohesive strength, heat resistance, and adhesive stability of the pressure-sensitive adhesive layer. The organic solvent is used to adjust the solid content and coating viscosity of the adhesive solution, so that the adhesive solution can be uniformly coated on the surface of the polymer base film 1. The tackifying resin is used to improve the adhesion of the pressure-sensitive adhesive layer to the outer surface of the square lithium battery cell or the heat-insulating and flame-retardant buffer layer. The flame retardant is used to impart flame-retardant properties to the flame-retardant polyacrylate pressure-sensitive adhesive layer, so that the tape can achieve both adhesion and flame-retardant protection when used for packaging square lithium batteries.

[0035] In one specific embodiment, the thickness of the first pressure-sensitive adhesive layer 2 is 20–40 μm, the thickness of the polymer base film 1 is 30–60 μm, and the thickness of the second pressure-sensitive adhesive layer 3 is 20–40 μm.

[0036] Release layer 4 includes a first release film and a second release film, or only the second release film.

[0037] In embodiments that include only the second release film, the release layer 4 is a dual-silicone release film, and the release layer 4 is disposed on the side surface of the second pressure-sensitive adhesive layer 3 opposite to the polymer base film 1; the length of the release layer 4 is 2.5 to 3.5 times the adhesive surface length of the second pressure-sensitive adhesive layer 3; the release layer 4 includes a covering portion 41 covering the second pressure-sensitive adhesive layer 3 and a pull-out portion 42 extending beyond the adhesive surface edge of the second pressure-sensitive adhesive layer 3, and the pull-out portion 42 is disposed on one side of the second pressure-sensitive adhesive layer 3 after being folded in half.

[0038] Dual-sided silicone release film is used to protect the pressure-sensitive adhesive layer during tape winding, transportation, and storage, preventing contamination or unintended adhesion. Because both surfaces of the dual-sided silicone release film have release properties, in the tape winding state, it not only covers the second pressure-sensitive adhesive layer 3 but also isolates the first and second pressure-sensitive adhesive layers 2 and 3 in adjacent winding layers, thus enabling stable winding and unwinding of the double-sided tape.

[0039] The pull-out part 42 is used by the operator to pull out the cover part 41 after the square lithium battery cell and the heat-insulating and flame-retardant buffer layer are aligned, thereby exposing the second pressure-sensitive adhesive layer 3 and fixing it to the heat-insulating and flame-retardant buffer layer. With this structure, multiple square lithium battery cells can be arranged and positioned first, and then the release layer 4 can be removed for bonding. This avoids the problems of air bubbles easily generated and difficulty in adjusting the position after bonding when directly bonding large areas in the traditional way, thus improving the assembly accuracy and bonding reliability of the square lithium battery pack.

[0040] In an embodiment where the release layer 4 includes a first release film and a second release film; the first release film covers the first pressure-sensitive adhesive layer 2, and the length of the first release film is the same as the adhesive surface length of the first pressure-sensitive adhesive layer 2; the second release film covers the second pressure-sensitive adhesive layer 3, and the length of the second release film is 2.5 to 3.5 times the adhesive surface length of the second pressure-sensitive adhesive layer 3; wherein, the second release film includes a covering section covering the second pressure-sensitive adhesive layer 3 and a pull-out section extending beyond the second pressure-sensitive adhesive layer 3, the pull-out section being folded and disposed on one side of the second pressure-sensitive adhesive layer 3.

[0041] The first release film protects the first pressure-sensitive adhesive layer 2 before use and is removed before it is attached to the outer surface of the square lithium battery cell. The second release film protects the second pressure-sensitive adhesive layer 3 and is removed by pulling after the square lithium battery cell and the heat-insulating and flame-retardant buffer layer are positioned. Because the second release film has a pull-out section that extends beyond the edge of the adhesive surface of the second pressure-sensitive adhesive layer 3, the operator can pull out this pull-out section from the gap between the cells after the cells are arranged, so that the second pressure-sensitive adhesive layer 3 can be attached to the heat-insulating and flame-retardant buffer layer after positioning, thereby reducing bonding bubbles and positional misalignment.

[0042] This invention also provides a method for preparing a blue film double-sided adhesive tape for wrapping a square lithium battery, comprising the following steps.

[0043] First, a second pressure-sensitive adhesive solution is prepared. Specifically, the curing agent, organic solvent, flame retardant, and tackifying resin used to form the second pressure-sensitive adhesive layer are added to a polyacrylate organic solution and mixed. The mixture is then dispersed in a high-speed disperser at room temperature at a speed of 1000–1200 rpm for 30–60 minutes to obtain the second pressure-sensitive adhesive solution. The solid content (mass fraction) of the second pressure-sensitive adhesive solution is preferably 20%–55%.

[0044] Then, the second pressure-sensitive adhesive is coated onto the second surface of the polymer base film. The coating method can be precision coating, with a coating speed of 15–50 m / min and a coating thickness of 20–40 μm. After coating, the polymer base film coated with the second pressure-sensitive adhesive is placed in a hot air circulating oven for thermosetting, allowing the second pressure-sensitive adhesive to cure and form a second pressure-sensitive adhesive layer. The process parameters for thermosetting can be a curing temperature of 50–120℃ and a curing time of 2–10 minutes; preferably, a segmented curing method can also be used, specifically including: pre-curing at 50–80℃ for 0–2 minutes, and then main curing at 90–120℃ for 2–4 minutes. After curing, it is cooled to room temperature by cooling rollers.

[0045] Subsequently, a release layer is attached to the side of the second pressure-sensitive adhesive layer facing away from the polymer base film, and the layer is then wound up to obtain a single-sided coated semi-finished product. The release layer is preferably a dual-silicone release film; by attaching a dual-silicone release film to the surface of the second pressure-sensitive adhesive layer, the second pressure-sensitive adhesive layer can be protected during winding and subsequent flipping coating processes, and a foundation is provided for subsequent die-cutting to form a pull-out release structure.

[0046] Next, a first pressure-sensitive adhesive solution is prepared. Specifically, the curing agent, organic solvent, and tackifying resin used to form the first pressure-sensitive adhesive layer are added to a polyacrylate solution and mixed, then dispersed in a high-speed disperser at a speed of 1000–1200 rpm for 30–60 minutes to obtain the first pressure-sensitive adhesive solution. When the first pressure-sensitive adhesive layer is also a flame-retardant polyacrylate pressure-sensitive adhesive layer, a flame retardant may also be added to the first pressure-sensitive adhesive solution. The solid content mass fraction of the first pressure-sensitive adhesive solution is preferably 20%–55%.

[0047] Next, the first pressure-sensitive adhesive is coated onto the first surface of the polymer base film in the single-sided coated semi-finished product. The first surface is the side of the polymer base film facing away from the second pressure-sensitive adhesive layer. The coating method can be precision coating, with a coating speed of 15–50 m / min and a coating thickness of 20–40 μm. After coating, the semi-finished product coated with the first pressure-sensitive adhesive is placed in a hot air circulating oven for heat curing, allowing the first pressure-sensitive adhesive to solidify and form the first pressure-sensitive adhesive layer. The heat curing process parameters can be a curing temperature of 50–120℃ and a curing time of 2–10 minutes; preferably, a segmented curing method can also be used, specifically including: pre-curing at 50–80℃ for 0–2 minutes, and then main curing at 90–120℃ for 2–4 minutes. After curing, it is cooled to room temperature by cooling rollers and then wound up to obtain a double-sided adhesive tape master roll.

[0048] Finally, the double-sided tape master roll is slitting and die-cutting. Slitting yields a double-sided tape master roll of a predetermined width. During die-cutting, portions of tape are removed at intervals along the length of the double-sided tape master roll, retaining the release layer. This release layer forms a covering portion over the second pressure-sensitive adhesive layer and a pull-out portion extending beyond the edge of the second pressure-sensitive adhesive layer. In one specific embodiment, on a 500 mm wide double-sided tape master roll, 1500 mm of tape is removed every 500 mm, retaining the release layer. The removed 500 mm * 1500 mm tape is further divided into three 500 mm * 500 mm segments, each applied to a 500 mm * 1500 mm dual-silicone release film. The actual die-cutting size can be adjusted according to the size of the square lithium battery cell. Preferably, the length of the release layer is 2.5 to 3.5 times the adhesive surface length of the second pressure-sensitive adhesive layer; the portion of the release layer that extends beyond the adhesive surface of the second pressure-sensitive adhesive layer forms a pull-out portion, which is folded in half and placed on one side of the second pressure-sensitive adhesive layer, so that the release layer with a length of 0.5 to 1.5 times the adhesive surface is located outside the adhesive surface, so that a pull-out operation can be performed during the assembly of the square lithium battery cell.

[0049] In the above preparation method, the specific composition of each layer of raw materials can be referred to the material composition of the corresponding layer in the aforementioned square lithium battery outer blue film double-sided adhesive tape, and will not be repeated here.

[0050] This invention also provides an application of a blue double-sided adhesive tape for wrapping a square lithium battery. This blue double-sided adhesive tape is used for assembling square lithium battery packs. The assembly structure is as follows: Figure 2 As shown.

[0051] The square lithium battery pack includes multiple square lithium battery cells 20, a heat-insulating and flame-retardant buffer layer 30, and a blue double-sided adhesive tape 10 covering the square lithium batteries. The heat-insulating and flame-retardant buffer layer 30 is made of heat-insulating and flame-retardant gel.

[0052] During assembly, the first pressure-sensitive adhesive layer 2 of the blue double-sided adhesive tape 10 covering the square lithium battery is attached to the outer surface of the square lithium battery cell 20, serving as an outer protective adhesive layer for the outer surface of the cell; the second pressure-sensitive adhesive layer 3 of the blue double-sided adhesive tape 10 covering the square lithium battery has a release layer 4 covering the side of its surface facing away from the polymer base film 1. The release layer 4 is located between the second pressure-sensitive adhesive layer 3 and the heat-insulating and flame-retardant buffer layer 30, and is used to isolate the second pressure-sensitive adhesive layer 3 and the heat-insulating and flame-retardant buffer layer 30 before the square lithium battery cell 20 and the heat-insulating and flame-retardant buffer layer 30 are positioned.

[0053] A heat-insulating and flame-retardant buffer layer 30 is disposed between two adjacent square lithium battery cells 20 to provide heat insulation, flame retardancy, and buffering between the adjacent square lithium battery cells 20. After the adjacent square lithium battery cells 20 and the heat-insulating and flame-retardant buffer layer 30 are aligned, the release layer 4 is removed by pulling to expose the second pressure-sensitive adhesive layer 3; then pressure is applied to the adjacent square lithium battery cells 20 to bond and fix the second pressure-sensitive adhesive layer 3 to the heat-insulating and flame-retardant buffer layer 30.

[0054] Thus, two adjacent square lithium battery cells 20 are connected and fixed by the square lithium battery outer blue film double-sided adhesive tape 10 and the heat-insulating and flame-retardant buffer layer 30. By positioning the release layer 4 between the second pressure-sensitive adhesive layer 3 and the heat-insulating and flame-retardant buffer layer 30 during the assembly positioning stage, it is possible to avoid the second pressure-sensitive adhesive layer 3 being bonded to the heat-insulating and flame-retardant buffer layer 30 before the cell position is adjusted. This helps to reduce bonding bubbles and positional misalignment, and improves the assembly accuracy of the square lithium battery pack.

[0055] This invention also provides a method for assembling a square lithium battery pack by using blue double-sided adhesive tape to wrap a square lithium battery, comprising the following steps.

[0056] First, the first pressure-sensitive adhesive layer on the first side of the blue double-sided adhesive tape covering the square lithium battery is attached to the outer surface of the square lithium battery cell, so that the blue double-sided adhesive tape covering the square lithium battery cell covers or is attached to the outside of the square lithium battery cell. The first pressure-sensitive adhesive layer can be an electrolyte-resistant polyacrylate pressure-sensitive adhesive layer, which is used to reliably bond to the outer surface of the square lithium battery cell.

[0057] Then, the release film on the second side of the blue double-sided adhesive tape covering the square lithium battery is retained, so that the second pressure-sensitive adhesive layer is temporarily covered by the release film and not exposed. A heat-insulating and flame-retardant buffer layer is placed between adjacent square lithium battery cells. The heat-insulating and flame-retardant buffer layer can be an aerogel sheet, flame-retardant foam, or other sheet material with heat insulation, flame retardant, or buffering functions.

[0058] Next, multiple square lithium battery cells are arranged sequentially, and the positions of adjacent square lithium battery cells and the heat-insulating and flame-retardant buffer layers placed between them are aligned. Since the second pressure-sensitive adhesive layer is still covered by the release film at this time, it will not bond to the heat-insulating and flame-retardant buffer layer in advance. Therefore, the position of the square lithium battery cells can be adjusted before bonding.

[0059] After the multiple square lithium battery cells are aligned, the release film on the second side is pulled out to expose the second pressure-sensitive adhesive layer. Since the release film has a pull-out portion that extends beyond the edge of the second pressure-sensitive adhesive layer, it can be removed by pulling out the release film while the square lithium battery cells and the heat-insulating and flame-retardant buffer layer are already positioned.

[0060] Finally, pressure is applied to the adjacent square lithium battery cells to bond and fix the second pressure-sensitive adhesive layer to the heat-insulating and flame-retardant buffer layer, thereby connecting and fixing the adjacent square lithium battery cells through the double-sided adhesive tape of the blue film on the outer shell of the square lithium battery and the heat-insulating and flame-retardant buffer layer.

[0061] The above assembly method allows for the alignment of multiple square lithium battery cells and the heat-insulating and flame-retardant buffer layer. Then, the release film is pulled out and the second pressure-sensitive adhesive layer is bonded and fixed, thereby reducing the risk of bubbles and misalignment during the traditional large-area direct bonding process and improving the assembly accuracy and efficiency of the square lithium battery pack.

[0062] The square lithium battery outer blue film double-sided adhesive tape, its preparation method, and its application provided in this invention have at least the following technical advantages compared to the prior art: First, the blue double-sided adhesive tape for encasing the square lithium battery in this embodiment of the invention includes a polymer base film, a first pressure-sensitive adhesive layer, a second pressure-sensitive adhesive layer, and a release layer. The first pressure-sensitive adhesive layer is used to adhere to the outer surface of the square lithium battery cell, and the second pressure-sensitive adhesive layer is used to adhere the heat-insulating and flame-retardant buffer layer. Thus, this double-sided tape can simultaneously serve as both cell encapsulation protection and inter-cell connection and fixation. Compared to the traditional method of using a combination of single-sided blue film tape and flame-retardant double-sided tape, it reduces the number of tape layers, lowers the overall thickness and weight of the inter-cell bonding structure, and improves the space utilization and lightweighting of the square lithium battery pack. Background art also describes that traditional solutions require one layer of single-sided blue film tape, one layer of flame-retardant double-sided tape, a heat-insulating and flame-retardant gel, another layer of flame-retardant double-sided tape, and another layer of single-sided blue film tape, resulting in a complex structure and significant thickness.

[0063] Secondly, in this embodiment of the invention, at least one of the first and second pressure-sensitive adhesive layers is a flame-retardant polyacrylate pressure-sensitive adhesive layer, which can improve the flame-retardant performance of the tape, enabling the tape to achieve both bonding and fixation while also providing flame-retardant protection. Furthermore, when the first pressure-sensitive adhesive layer is an electrolyte-resistant polyacrylate pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer is a flame-retardant polyacrylate pressure-sensitive adhesive layer, the first pressure-sensitive adhesive layer can improve the bonding reliability and electrolyte resistance stability between the tape and the outer surface of the square lithium battery cell, while the second pressure-sensitive adhesive layer can improve the bonding reliability and flame-retardant performance between the tape and the heat-insulating and flame-retardant buffer layer, thus allowing the two sides of the tape to adapt to different bonding objects and usage environments.

[0064] Furthermore, in this embodiment of the invention, the release layer is at least disposed on the side of the second pressure-sensitive adhesive layer facing away from the polymer base film, and the release layer includes a covering portion covering the second pressure-sensitive adhesive layer and a pull-out portion extending beyond the edge of the adhesive surface. During assembly, the release layer is located between the second pressure-sensitive adhesive layer and the heat-insulating and flame-retardant buffer layer, ensuring that the second pressure-sensitive adhesive layer does not bond prematurely before the battery cell and the heat-insulating and flame-retardant buffer layer are positioned. After multiple square lithium battery cells and the heat-insulating and flame-retardant buffer layer are aligned, the release layer is removed by pulling, exposing the second pressure-sensitive adhesive layer and bonding it to the heat-insulating and flame-retardant buffer layer. Thus, positioning can be performed before bonding, reducing the risk of air bubbles and misalignment during traditional large-area direct bonding processes, and improving the assembly accuracy, bonding consistency, and assembly efficiency of the square lithium battery pack.

[0065] Furthermore, when a dual-silicone release film is used as the release layer, it not only protects the second pressure-sensitive adhesive layer before use, preventing contamination or unintended adhesion, but also isolates the first and second pressure-sensitive adhesive layers in adjacent winding layers during tape winding, enabling stable winding, transportation, storage, and unwinding of the double-sided tape. Subsequent slitting and die-cutting processes form the cover and pull-out sections of the release layer, further improving the ease of handling the tape during the packaging and assembly of square lithium batteries.

[0066] When the polymer base film adopts a multilayer co-extruded biaxially oriented composite base film, especially a five-layer co-extruded biaxially oriented composite base film, the polypropylene functional layer can provide lightweight, insulation, and basic mechanical properties, the polyamide reinforcing layer can improve the temperature resistance, tear resistance, and dimensional stability of the base film, and the maleic anhydride-grafted polypropylene can improve the interfacial bonding between the polypropylene layer and the polyamide reinforcing layer. Therefore, while maintaining the lightweight advantage of the tape, the structural stability and reliability of the tape during battery cell encapsulation, bending, bonding, and long-term use can be improved.

[0067] Therefore, the embodiments of the present invention can improve the flame retardant properties, bonding reliability, assembly positioning accuracy and production operation convenience of the tape while reducing the number of tape layers, thickness and weight in the traditional square lithium battery assembly structure. It is especially suitable for the close arrangement and high-precision assembly of multiple cells in a square lithium battery pack.

[0068] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0069] Example 1 This embodiment provides a square lithium battery outer blue film double-sided adhesive tape, which includes a first pressure-sensitive adhesive layer, a polymer base film, a second pressure-sensitive adhesive layer and a release layer arranged sequentially.

[0070] The first pressure-sensitive adhesive layer is an electrolyte-resistant polyacrylate pressure-sensitive adhesive layer with a thickness of 35 μm, used to attach the outer surface of the square lithium battery cell; the polymer base film is a five-layer co-extruded biaxially oriented composite base film with a thickness of 50 μm; the second pressure-sensitive adhesive layer is a flame-retardant polyacrylate pressure-sensitive adhesive layer with a thickness of 35 μm, used to attach the heat-insulating and flame-retardant buffer layer; the release layer is a dual-silicone release film, disposed on the side of the second pressure-sensitive adhesive layer opposite to the polymer base film.

[0071] The preparation of the five-layer co-extruded biaxially oriented composite base film is as follows: The raw materials for each layer of the five-layer co-extruded biaxially oriented composite base film are prepared according to the following proportions, all in parts by weight: The raw materials for the first polypropylene functional layer include: 70 parts of high isotactic homopolymer polypropylene, 25 parts of maleic anhydride-grafted polypropylene, 2 parts of antioxidant 1010, 1 part of antioxidant 168, and 2 parts of silica anti-blocking agent. The raw materials for the first polyamide reinforcing layer include: 97 parts of polyamide and 3 parts of erucamide. The raw materials for the polypropylene core layer are the same as those for the first polypropylene functional layer. The raw materials for the second polyamide reinforcing layer are the same as those for the first polyamide reinforcing layer. The raw materials for the second polypropylene functional layer are the same as those for the first polypropylene functional layer. The raw materials for the first polypropylene functional layer, the first polyamide reinforcing layer, the polypropylene core layer, the second polyamide reinforcing layer, and the second polypropylene functional layer are added to the corresponding extruders, melted and plasticized at 220℃, and then extruded together through a co-extrusion die to form a composite casting with a five-layer structure. The composite casting was subjected to longitudinal and transverse stretching sequentially, with a longitudinal stretching ratio of 4 times and a transverse stretching ratio of 8 times, to obtain a five-layer co-extruded biaxially oriented composite base film with a thickness of 50 μm. The five-layer co-extruded biaxially oriented composite base film includes a first polypropylene functional layer, a first polyamide reinforcing layer, a polypropylene core layer, a second polyamide reinforcing layer, and a second polypropylene functional layer, which are stacked sequentially.

[0072] The flame-retardant polyacrylate pressure-sensitive adhesive comprises, by weight: 75 parts polyacrylate, 0.05 parts epoxy curing agent N,N,N',N'-tetratetra(epoxyethylenemethyl)-1,3-phenylenediamine, 15 parts aluminum phosphonate, 4.95 parts bisphenol A bis(diphenyl phosphate), and 5 parts rosin tackifying resin.

[0073] The electrolyte-resistant polyacrylate pressure-sensitive adhesive comprises, by weight: 80 parts polyacrylate, 0.5 parts epoxy curing agent, and 20 parts tackifying resin.

[0074] The method for preparing the blue film double-sided adhesive tape for wrapping the square lithium battery in this embodiment includes the following steps: First, according to the formulation of flame-retardant polyacrylate pressure-sensitive adhesive, the above-mentioned parts of epoxy curing agent, aluminum phosphonate, bisphenol A bis(diphenyl phosphate), and rosin tackifying resin are added to 120 parts of ethyl acetate, and then added to a polyacrylate-ethyl acetate solution containing 75 parts of polyacrylate. The mixture is stirred in a reactor to obtain the second pressure-sensitive adhesive solution. According to the formulation of electrolyte-resistant polyacrylate pressure-sensitive adhesive, the above-mentioned parts of epoxy curing agent and rosin tackifying resin are added to 150 parts of ethyl acetate, and then added to a polyacrylate-ethyl acetate solution containing 80 parts of polyacrylate. The mixture is stirred in a reactor to obtain the first pressure-sensitive adhesive solution.

[0075] Then, the second pressure-sensitive adhesive was uniformly coated onto the second surface of the five-layer co-extruded biaxially oriented composite base film using a precision coating method at a speed of 30 m / min and a coating thickness of 35 μm. After coating, the five-layer co-extruded biaxially oriented composite base film coated with the second pressure-sensitive adhesive was placed in a hot air circulating oven for thermosetting at a temperature of 80℃ for 5 minutes. The thermosetting process adopted a segmented curing method, first pre-curing at 60℃ for 1 minute, and then main curing at 100℃ for 3 minutes. After curing, it was cooled to room temperature by cooling rollers to form the second pressure-sensitive adhesive layer. Subsequently, a double silicone release film was attached to the side of the second pressure-sensitive adhesive layer opposite to the five-layer co-extruded biaxially oriented composite base film and then wound up to obtain a single-sided coated semi-finished product.

[0076] Subsequently, the first pressure-sensitive adhesive was uniformly coated onto the first surface of the five-layer co-extruded biaxially oriented composite base film in the single-sided coated semi-finished product using a precision coating method. The coating speed was 30 m / min, and the coating thickness was 35 μm. After coating, the semi-finished product was sent to a hot air circulating oven for thermosetting. The curing temperature was 80℃, and the curing time was 5 minutes. The thermosetting treatment adopted a segmented curing method, first pre-curing at 60℃ for 1 minute, and then main curing at 100℃ for 3 minutes. After curing, it was cooled to room temperature by cooling rollers and then wound up to obtain the double-sided adhesive tape master roll.

[0077] Finally, the double-sided tape master roll is slitting and die-cutting. On the 10 mm wide tape master roll, 150 mm of tape is removed every 50 mm, leaving the dual-silicone release film. This allows the dual-silicone release film to form a covering portion that covers the second pressure-sensitive adhesive layer and a pull-out portion that extends beyond the edge of the second pressure-sensitive adhesive layer. The removed 10 mm * 150 mm tape is further divided into three 10 mm * 50 mm sections and applied to the 10 mm * 150 mm dual-silicone release film, resulting in a square lithium battery outer blue film double-sided tape.

[0078] This embodiment is applicable to the stacked connection of polymer battery packs with a size of 100 mm × 20 mm. In use, the first pressure-sensitive adhesive layer is attached to the battery pack shell and wraps the battery cells, while the second pressure-sensitive adhesive layer retains a release layer with a pull-out portion. A 50 μm ultra-thin flame-retardant foam is placed between the two battery cells. After alignment, the release layer is pulled out sequentially to allow the second pressure-sensitive adhesive layer to adhere to the ultra-thin flame-retardant foam. Pressure is then applied to firmly connect the battery cells before sealing.

[0079] Example 2 This embodiment provides a square lithium battery outer blue film double-sided adhesive tape, which includes a first pressure-sensitive adhesive layer, a polymer base film, a second pressure-sensitive adhesive layer and a release layer arranged sequentially.

[0080] The first pressure-sensitive adhesive layer is an electrolyte-resistant polyacrylate pressure-sensitive adhesive layer with a thickness of 35 μm, used to attach the outer surface of the square lithium battery cell; the polymer base film is a PET substrate with a thickness of 50 μm; the second pressure-sensitive adhesive layer is a flame-retardant polyacrylate pressure-sensitive adhesive layer with a thickness of 35 μm, used to attach the heat-insulating and flame-retardant buffer layer; the release layer is a dual-silicone release film, disposed on the side of the second pressure-sensitive adhesive layer opposite to the polymer base film.

[0081] The flame-retardant polyacrylate pressure-sensitive adhesive comprises the following raw materials in parts by weight: 75 parts polyacrylate, 0.05 parts epoxy curing agent N,N,N',N'-tetratetra(epoxyethylene methyl)-1,3-phenylenediamine, 15 parts aluminum phosphonate, 4.95 parts bisphenol A bis(diphenyl phosphate), and 5 parts rosin tackifying resin.

[0082] The electrolyte-resistant polyacrylate pressure-sensitive adhesive comprises, by weight: 80 parts polyacrylate, 0.5 parts epoxy curing agent, and 20 parts tackifying resin.

[0083] The method for preparing the blue film double-sided adhesive tape for wrapping the square lithium battery in this embodiment includes the following steps: First, according to the formulation of flame-retardant polyacrylate pressure-sensitive adhesive, the above-mentioned parts of epoxy curing agent, aluminum phosphonate, bisphenol A bis(diphenyl phosphate), and rosin tackifying resin are added to 120 parts of ethyl acetate, and then added to a polyacrylate-ethyl acetate solution containing 75 parts of polyacrylate. The mixture is stirred in a reactor to obtain the second pressure-sensitive adhesive solution. According to the formulation of electrolyte-resistant polyacrylate pressure-sensitive adhesive, the above-mentioned parts of epoxy curing agent and rosin tackifying resin are added to 150 parts of ethyl acetate, and then added to a polyacrylate-ethyl acetate solution containing 80 parts of polyacrylate. The mixture is stirred in a reactor to obtain the first pressure-sensitive adhesive solution.

[0084] Then, the second pressure-sensitive adhesive was uniformly coated onto the second surface of the PET substrate using a precision coating method at a speed of 15 m / min and a coating thickness of 35 μm. After coating, the PET substrate coated with the second pressure-sensitive adhesive was placed in a hot air circulating oven for thermosetting at a temperature of 50°C for 1 minute. The thermosetting process employed a segmented curing method, first pre-curing at 80°C for 2 minutes, and then main curing at 120°C for 2 minutes. After curing, the substrate was cooled to room temperature by cooling rollers to form the second pressure-sensitive adhesive layer. Subsequently, a dual-silicone release film was attached to the side of the second pressure-sensitive adhesive layer facing away from the PET substrate and the substrate was wound up to obtain a single-sided coated semi-finished product.

[0085] Next, following the formulation of the electrolyte-resistant polyacrylate pressure-sensitive adhesive, polyacrylate, epoxy curing agent, ethyl acetate and rosin tackifying resin were added to the reaction vessel and stirred to prepare the first pressure-sensitive adhesive solution.

[0086] Subsequently, the first pressure-sensitive adhesive was uniformly coated onto the first surface of the PET substrate in the single-sided coated semi-finished product using a precision coating method at a speed of 15 m / min and a coating thickness of 35 μm. After coating, the semi-finished product was placed in a hot air circulating oven for heat curing at a curing temperature of 50°C for 1 minute. The heat curing process employed a segmented curing method, first pre-curing at 80°C for 2 minutes, and then main curing at 120°C for 2 minutes. After curing, the product was cooled to room temperature by cooling rollers and then wound up to obtain the double-sided adhesive tape master roll.

[0087] Finally, the double-sided tape master roll is slit and die-cut to form a double-silicone release film covering the second pressure-sensitive adhesive layer and a pull-out portion extending beyond the edge of the second pressure-sensitive adhesive layer, resulting in a square lithium battery outer blue film double-sided tape.

[0088] In this embodiment, the first pressure-sensitive adhesive layer is attached to the outer surface of the square lithium battery cell, and the second pressure-sensitive adhesive layer retains a release layer with a pull-out portion. After the square lithium battery cell and the heat-insulating and flame-retardant buffer layer are positioned, the release layer is pulled out to fix the second pressure-sensitive adhesive layer and the heat-insulating and flame-retardant buffer layer together.

[0089] Example 3 This embodiment provides a square lithium battery outer blue film double-sided adhesive tape, which includes a first pressure-sensitive adhesive layer, a polymer base film, a second pressure-sensitive adhesive layer and a release layer arranged sequentially.

[0090] The first pressure-sensitive adhesive layer is an electrolyte-resistant polyacrylate pressure-sensitive adhesive layer with a thickness of 40 μm, used to attach the outer surface of the square lithium battery cell; the polymer base film is a BOPP base film with a thickness of 40 μm; the second pressure-sensitive adhesive layer is a flame-retardant polyacrylate pressure-sensitive adhesive layer with a thickness of 40 μm, used to attach the heat-insulating and flame-retardant buffer layer; the release layer is a dual-silicone release film, disposed on the side of the second pressure-sensitive adhesive layer opposite to the polymer base film.

[0091] The flame-retardant polyacrylate pressure-sensitive adhesive comprises the following raw materials in parts by weight: 75 parts polyacrylate, 0.05 parts epoxy curing agent N,N,N',N'-tetratetra(epoxyethylene methyl)-1,3-phenylenediamine, 15 parts aluminum phosphonate, 4.95 parts bisphenol A bis(diphenyl phosphate), and 5 parts rosin tackifying resin.

[0092] The electrolyte-resistant polyacrylate pressure-sensitive adhesive comprises, by weight: 80 parts polyacrylate, 0.5 parts epoxy curing agent, and 20 parts tackifying resin.

[0093] The method for preparing the blue film double-sided adhesive tape for wrapping the square lithium battery in this embodiment includes the following steps: First, according to the formulation of flame-retardant polyacrylate pressure-sensitive adhesive, the above-mentioned parts of epoxy curing agent, aluminum phosphonate, bisphenol A bis(diphenyl phosphate), and rosin tackifying resin are added to 120 parts of ethyl acetate, and then added to a polyacrylate-ethyl acetate solution containing 75 parts of polyacrylate. The mixture is stirred in a reactor to obtain the second pressure-sensitive adhesive solution. According to the formulation of electrolyte-resistant polyacrylate pressure-sensitive adhesive, the above-mentioned parts of epoxy curing agent and rosin tackifying resin are added to 150 parts of ethyl acetate, and then added to a polyacrylate-ethyl acetate solution containing 80 parts of polyacrylate. The mixture is stirred in a reactor to obtain the first pressure-sensitive adhesive solution.

[0094] Then, the second pressure-sensitive adhesive was uniformly coated onto the second surface of the BOPP base film using a precision coating method at a speed of 50 m / min and a coating thickness of 40 μm. After coating, the BOPP base film coated with the second pressure-sensitive adhesive was placed in a hot air circulating oven for thermosetting at a temperature of 50°C for 5 minutes. The thermosetting process employed a segmented curing method, first pre-curing at 50°C for 2 minutes, and then main curing at 120°C for 4 minutes. After curing, the film was cooled to room temperature by cooling rollers to form the second pressure-sensitive adhesive layer. Subsequently, a dual-silicone release film was attached to the side of the second pressure-sensitive adhesive layer facing away from the BOPP base film and the film was wound up to obtain a single-sided coated semi-finished product.

[0095] Subsequently, the first pressure-sensitive adhesive was uniformly coated onto the first surface of the BOPP base film in the single-sided coated semi-finished product using a precision coating method at a speed of 50 m / min and a coating thickness of 40 μm. After coating, the semi-finished product was placed in a hot air circulating oven for heat curing at a temperature of 50℃ for 5 minutes. The heat curing process employed a segmented curing method, first pre-curing at 50℃ for 2 minutes, and then main curing at 120℃ for 4 minutes. After curing, the product was cooled to room temperature by cooling rollers and then wound up to obtain the double-sided adhesive tape master roll.

[0096] Finally, the double-sided tape master roll is slit and die-cut to form a double-silicone release film covering the second pressure-sensitive adhesive layer and a pull-out portion extending beyond the edge of the second pressure-sensitive adhesive layer, resulting in a square lithium battery outer blue film double-sided tape.

[0097] In this embodiment, the first pressure-sensitive adhesive layer is attached to the outer surface of the square lithium battery cell, and the second pressure-sensitive adhesive layer retains a release layer with a pull-out portion. After the square lithium battery cell and the heat-insulating and flame-retardant buffer layer are positioned, the release layer is pulled out to fix the second pressure-sensitive adhesive layer and the heat-insulating and flame-retardant buffer layer together.

[0098] Comparative Example 1 This comparative example provides a traditional square lithium battery pack cell connection structure.

[0099] The traditional square lithium battery pack cell connection structure includes a single-sided blue film tape with a thickness of 120 μm, a flame-retardant double-sided tape with a thickness of 100 μm, a heat-insulating and flame-retardant gel, a flame-retardant double-sided tape with a thickness of 100 μm, and a single-sided blue film tape with a thickness of 120 μm, arranged in sequence.

[0100] In this structure, the single-sided blue film tape is used to cover the outer surface of the square lithium battery cell, and the flame-retardant double-sided tape is used to connect the single-sided blue film tape and the heat-insulating and flame-retardant gel. In this traditional structure, the total thickness of the tape products alone is 440 μm.

[0101] During the assembly process, one side of the flame-retardant double-sided tape is first attached to the heat-insulating and flame-retardant gel, and then the other side of the release film is removed before the square lithium battery cell is directly attached and fixed.

[0102] Comparative Example 2 This comparative example provides a square lithium battery pack cell connection structure using ordinary double-sided adhesive tape.

[0103] This standard double-sided tape includes a polymer base film and standard acrylic pressure-sensitive adhesive layers disposed on both sides of the polymer base film. This standard double-sided tape does not include a flame-retardant polyacrylate pressure-sensitive adhesive layer, nor does it include a release layer with a pull-out portion.

[0104] During the assembly process, one side of the pressure-sensitive adhesive layer of ordinary double-sided tape is attached to the outer surface of the square lithium battery cell or the heat-insulating and flame-retardant buffer layer, and then the release film on the other side is removed and directly bonded and fixed to the corresponding object.

[0105] As shown in Examples 1-3, by respectively setting a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on both sides of the polymer base film, the blue double-sided adhesive tape covering the square lithium battery can simultaneously serve the functions of outer surface protection of the battery cell and connection and fixation of the heat-insulating and flame-retardant buffer layer. Compared with the traditional structure of "two layers of single-sided blue film tape + two layers of flame-retardant double-sided tape" in Comparative Example 1, the present invention can significantly reduce the number of tape layers and the total thickness of the tape.

[0106] Specifically, the total thickness of the tape product in Comparative Example 1 is 440 μm; while the total thickness of the double-sided tape encasing the square lithium battery in Examples 1 and 2 is 120 μm, and the total thickness of the double-sided tape encasing the square lithium battery in Example 3 is also 120 μm. Therefore, this invention, while ensuring the protection and connection of the battery cells, can significantly reduce the cell spacing occupied by the tape structure, which is beneficial to improving the space utilization and weight reduction of the square lithium battery pack. This invention uses a double-sided tape structure of approximately 120 μm, which, compared to the traditional approximately 440 μm tape combination structure, reduces the total thickness by approximately 45% and the weight by more than 40%.

[0107] Meanwhile, Examples 1-3 all include a release layer for covering the second pressure-sensitive adhesive layer. The release layer is formed into a covering portion and a pull-out portion through slitting and die-cutting. During the assembly process of the square lithium battery pack, the first pressure-sensitive adhesive layer can be first attached to the outer surface of the square lithium battery cell, and the positions of multiple square lithium battery cells and the heat-insulating and flame-retardant buffer layer can be aligned while the second pressure-sensitive adhesive layer is still covered by the release layer. Then, the release layer is pulled out to expose the second pressure-sensitive adhesive layer and fix it to the heat-insulating and flame-retardant buffer layer. Compared with the method of directly bonding a large area after removing the release film in Comparative Examples 1 and 2, the present invention can reduce the problems of bubbles and misalignment caused by pre-bonding, and improve the assembly accuracy and bonding reliability of the square lithium battery pack.

[0108] Furthermore, Examples 1 and 3 use a five-layer co-extruded biaxially oriented composite film or BOPP film as the polymer base film, which helps to reduce the weight of the tape; Example 2 uses a PET substrate, which can provide better temperature resistance and dimensional stability. Therefore, this invention can select different types of polymer base films according to the assembly requirements of different square lithium battery packs, and has good applicability in balancing the needs of adhesion and fixation, flame retardant protection, assembly positioning, and lightweighting.

[0109] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A double-sided adhesive tape with blue film for wrapping a square lithium battery, characterized in that, The square lithium battery outer blue film double-sided adhesive tape includes: a polymer base film, a first pressure-sensitive adhesive layer, a second pressure-sensitive adhesive layer, and a release layer; The first pressure-sensitive adhesive layer is disposed on the first surface of the polymer base film and is used to attach the outer surface of the square lithium battery cell. The second pressure-sensitive adhesive layer is disposed on the second surface of the polymer base film and is used to attach the heat-insulating and flame-retardant buffer layer; At least one of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer is a flame-retardant polyacrylate pressure-sensitive adhesive layer; The release layer is at least disposed on the side surface of the second pressure-sensitive adhesive layer opposite to the polymer base film; The release layer includes a covering portion corresponding to the adhesive surface and a pull-out portion extending beyond the edge of the adhesive surface. The pull-out portion is used to be pulled out after the square lithium battery cell is positioned, so that the corresponding pressure-sensitive adhesive layer adheres to the object being bonded.

2. The double-sided adhesive tape with blue film covering the square lithium battery according to claim 1, characterized in that, The polymer base film includes: biaxially oriented polypropylene (BOPP) base film, polyethylene terephthalate (PET) base film, or multilayer co-extruded biaxially oriented composite base film.

3. The double-sided adhesive tape with blue film covering the square lithium battery according to claim 2, characterized in that, The multilayer co-extruded biaxially oriented composite base film is a five-layer co-extruded biaxially oriented composite base film, comprising a first polypropylene functional layer, a first polyamide reinforcing layer, a polypropylene core layer, a second polyamide reinforcing layer, and a second polypropylene functional layer stacked sequentially. The first polypropylene functional layer, the polypropylene core layer, and the second polypropylene functional layer each comprise 60-80 parts of homopolymer polypropylene, 10-30 parts of maleic anhydride-grafted polypropylene, and 2-8 parts of additives; the isotacticity of the homopolymer polypropylene is greater than 90%. The first polyamide reinforcing layer and the second polyamide reinforcing layer each comprise 95-100 parts of polyamide and 0-5 parts of an opening agent; the opening agent comprises erucamide.

4. The double-sided adhesive tape with blue film covering the square lithium battery according to claim 1, characterized in that, According to the mass fractions, the flame-retardant polyacrylate pressure-sensitive adhesive layer comprises: 50-80 parts polyacrylate, 0.001-0.5 parts curing agent, 10-30 parts flame retardant, and 5-20 parts tackifying resin. The curing agent includes at least one of a multifunctional epoxy resin or an isocyanate oligomer. The flame retardant includes powder flame retardant and / or liquid phosphate flame retardant; the powder flame retardant includes at least one of: phosphonic acid metal salt, coated ammonium polyphosphate, or metal hydroxide; The liquid phosphate flame retardant includes at least one of bisphenol A bis(diphenyl phosphate) BDP or resorcinol bis(diphenyl phosphate) RDP; The tackifying resin includes at least one of rosin resin or terpene resin.

5. The double-sided adhesive tape with blue film covering the square lithium battery according to claim 4, characterized in that, The first pressure-sensitive adhesive layer is an electrolyte-resistant polyacrylate pressure-sensitive adhesive layer, and the second pressure-sensitive adhesive layer is a flame-retardant polyacrylate pressure-sensitive adhesive layer; According to the mass fractions, the electrolyte-resistant polyacrylate pressure-sensitive adhesive layer comprises: 70-99 parts polyacrylate, 0.001-0.5 parts curing agent, and 5-30 parts tackifying resin.

6. The double-sided adhesive tape with blue film covering the square lithium battery according to claim 1, characterized in that, The thickness of the first pressure-sensitive adhesive layer is 20–40 μm, the thickness of the polymer base film is 30–60 μm, and the thickness of the second pressure-sensitive adhesive layer is 20–40 μm; The release layer includes: a first release film and a second release film, or, only the second release film; The first release film covers the first pressure-sensitive adhesive layer, and the length of the first release film is the same as the adhesive surface length of the first pressure-sensitive adhesive layer; The second release film covers the second pressure-sensitive adhesive layer, and the length of the second release film is more than twice the adhesive surface length of the second pressure-sensitive adhesive layer, preferably 2.5 to 3.5 times; wherein, the second release film includes a covering section covering the second pressure-sensitive adhesive layer and a pull-out section extending beyond the second pressure-sensitive adhesive layer, and the pull-out section is disposed on one side of the second pressure-sensitive adhesive layer after being folded in half.

7. A method for preparing a double-sided adhesive tape with a blue film coating for a square lithium battery as described in any one of claims 1-6, characterized in that, The preparation method includes: Preparation of the second pressure-sensitive adhesive solution; The second pressure-sensitive adhesive liquid is coated onto the second surface of the polymer base film and subjected to heat curing treatment to form a second pressure-sensitive adhesive layer; A release layer is attached to the side of the second pressure-sensitive adhesive layer that is away from the polymer base film to obtain a single-sided coated semi-finished product. Preparation of the first pressure-sensitive adhesive solution; The first pressure-sensitive adhesive liquid is coated onto the first surface of the polymer base film in the single-sided adhesive semi-finished product, and then subjected to heat curing treatment to form the first pressure-sensitive adhesive layer, thereby obtaining the double-sided tape master roll. The double-sided tape master roll is slit and die-cut to form a release layer that covers the second pressure-sensitive adhesive layer and a pull-out portion that extends beyond the edge of the second pressure-sensitive adhesive layer, resulting in a square lithium battery outer blue film double-sided tape.

8. The preparation method according to claim 7, characterized in that, The preparation of the first pressure-sensitive adhesive includes: adding a curing agent, a flame retardant, a tackifying resin, and an organic solvent to a polyacrylate organic solution, mixing, and dispersing at 1000–1200 rpm for 30–60 minutes to obtain a flame-retardant polyacrylate pressure-sensitive adhesive; or adding a curing agent, a tackifying resin, and an organic solvent to a polyacrylate solution, mixing, and dispersing at 1000–1200 rpm for 30–60 minutes to obtain an electrolyte-resistant polyacrylate pressure-sensitive adhesive; wherein the organic solvent includes at least one of ethyl acetate, butyl acetate, or acetone; the solid content of the first pressure-sensitive adhesive is 20%–55% by mass. The preparation of the second pressure-sensitive adhesive includes: adding a curing agent, a flame retardant, a tackifying resin, and an organic solvent to a polyacrylate organic solution, mixing, and dispersing at 1000–1200 rpm for 30–60 minutes to obtain a flame-retardant polyacrylate pressure-sensitive adhesive; wherein the organic solvent includes at least one of ethyl acetate, butyl acetate, or acetone; the solid content of the second pressure-sensitive adhesive is 20%–55% by mass. The thermosetting process adopts a segmented curing method, which includes: first pre-curing at 50-80℃ for 1-2 minutes; then main curing at 90-120℃ for 2-3 minutes; The die-cutting includes: removing portions of the tape at intervals along the length of the double-sided tape master roll while retaining the release layer, so that the release layer forms a pull-out portion extending beyond the adhesive surface.

9. An application of the blue double-sided adhesive tape for wrapping a square lithium battery as described in claim 1, characterized in that, The square lithium battery is wrapped with blue double-sided adhesive tape for assembling the square lithium battery pack. The square lithium battery pack includes: multiple square lithium battery cells, a heat-insulating and flame-retardant buffer layer, and blue double-sided adhesive tape covering the square lithium battery. The first pressure-sensitive adhesive layer of the blue double-sided adhesive tape covering the square lithium battery is attached to the outer surface of the square lithium battery cell. The heat-insulating and flame-retardant buffer layer is disposed between two adjacent square lithium battery cells. The second pressure-sensitive adhesive layer of the blue double-sided adhesive tape covering the square lithium battery is attached to the heat-insulating and flame-retardant buffer layer, so that two adjacent square lithium battery cells are connected and fixed by the blue double-sided adhesive tape covering the square lithium battery and the heat-insulating and flame-retardant buffer layer.

10. A method for assembling a square lithium battery pack using the blue film double-sided adhesive tape described in claim 1, characterized in that, The assembly method includes: The first pressure-sensitive adhesive layer on the first side of the blue film double-sided tape is attached to the outer surface of the square lithium battery cell. The release film on the second side of the blue double-sided adhesive tape covering the square lithium battery is retained, and a heat-insulating and flame-retardant buffer layer is placed between adjacent square lithium battery cells. Multiple square lithium battery cells are arranged sequentially and their positions are aligned. After aligning the positions, pull out and remove the release film on the second side to expose the second pressure-sensitive adhesive layer; Pressure is applied to adjacent square lithium battery cells to bond and fix the second pressure-sensitive adhesive layer to the heat-insulating and flame-retardant buffer layer.

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