High-permeability tape and preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a high-permeability tape and a preparation method therefor and a use thereof. The tape comprises a porous substrate and an adhesive layer which are laminated; the porous substrate has a thickness of 5-50 μm and an air permeability of 50-450 s / 100 mL, and comprises at least one of a porous separator and a non-woven fabric; the adhesive layer is formed by coating at least one surface of the porous substrate with a thermoplastic coating solution to form a discontinuous adhesive layer; and the thermoplastic coating solution is an aqueous coating solution or a solvent-based coating solution, comprising an olefin-based polymer and optionally a tackifying resin. The initial air permeability of the tape satisfies P1≤2.5×P0, wherein P0 is the air permeability of the porous substrate; the air permeability after high-temperature aging satisfies P2≤4.0×P1; and the air permeability after electrolyte immersion satisfies P3≤1.2×P1. The tape protects an electrode sheet in a hot-pressing process without impeding lithium-ion transport and further protects an electrode against lithium plating in a battery cycling process, thereby prolonging the service life of the battery.

Description

A high-transparency adhesive tape and its preparation method and application Technical Field

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

[0002] During the normal production of lithium batteries, the positive electrode sheets are wound with the separator and negative electrode sheets before undergoing processes such as hot pressing, liquid injection, and chemical formation to form a battery cell. Due to the brittleness of the electrode sheets, the bent amplitude of the electrode sheets at the corners of the battery cell is often large, resulting in high stress. This can cause them to crack after hot pressing and cause the active material to fall off, thus affecting the yield rate and safety of the battery cell. It can also lead to lithium deposition at the corners during battery cycling, and cause deformation of the wound battery cell, which puts the electrode sheets at the corners at risk of breaking, affecting the safety and cycling performance of the battery.

[0003] Applying tape to the electrode in this corresponding position can effectively prevent thermal cracking of the electrode, lithium deposition in the cell corners, deformation, and breakage. Using flexible tape can prevent cracking of the tape substrate. Conventional lithium-ion battery tape is generally electrolyte-resistant, with adhesives such as acrylic pressure-sensitive adhesives and hot-melt adhesives used on substrates such as PET and BOPP films. These tapes have low electrolyte solubility and are impermeable to lithium ions, limiting their use in the corners of the cell.

[0004] Invention CN101017916A discloses a high-safety lithium-ion battery with a protective film attached to the separator. The battery comprises a positive electrode, a negative electrode, a separator, an electrolyte, and a battery casing. Adhesive tape or film is applied to the separator's edges at the start and end of electrode coating. The separator with the tape or film is placed between the positive and negative electrodes. The positive electrode, separator, and negative electrode are wound together to form an electrode assembly, which is then placed in the battery casing. The assembly is then filled, sealed, and subjected to a formation process to produce a lithium-ion battery. The thickness of the tape or film on the separator ranges from 10 μm to 30 μm. The adhesive film is a spray-on polymerized film or a hot-pressed acrylic PP film, which is polymerized by photopolymerization or thermal polymerization at a temperature of less than or equal to 90°C. However, the fully covered PP adhesive layer of 10-30 μm in this invention significantly reduces the lithium ion permeability of the separator, leading to lithium ion accumulation at the electrode corners, causing lithium plating and degrading battery performance.

[0005] Invention CN115651554A discloses a battery separator tape with a dissolvable adhesive layer and its preparation method. The tape comprises a battery separator and an adhesive layer disposed on the surface of the separator. The adhesive forming the adhesive layer comprises the following raw materials in weight percentage: 40-60% solvent-based polyacrylate; 10-30% polyvinyl acetate; 5-15% polystyrene resin; 0.1-0.5% initiator; 0.5-1.0% curing agent; and 0-30% solvent. The adhesive layer of the tape provided by this invention dissolves rapidly in the electrolyte and does not block the normal migration of lithium ions. However, after dissolution, the tape loses its ability to provide support at corners, leading to separator rupture, which can cause a short circuit. It can also form an uneven electric field on the negative electrode surface, promoting lithium deposition.

[0006] Therefore, how to optimize the existing electrolyte-resistant battery tape materials and structures so that the tape can protect the electrode from cracking under stress during hot pressing without affecting the passage of lithium ions, and protect the electrode diaphragm during battery cycling to prevent lithium deposition in the battery, thereby extending the battery life, is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0007] In order to solve the above problems, the present invention provides a high-transparency tape and its preparation method and application, which is particularly suitable for lithium batteries. Without affecting the passage of lithium ions, it can protect the electrode from cracking under stress during the hot pressing process, and can protect the electrode diaphragm to prevent lithium deposition in the battery during the battery cycle.

[0008] In a first aspect, the present invention provides a highly transparent adhesive tape comprising a laminated porous substrate and an adhesive layer;

[0009] The porous substrate has a thickness of 5-50 μm and an air permeability of 50-450 s / 100 ml, and comprises at least one of a porous membrane and a non-woven fabric;

[0010] An adhesive layer is formed by coating a thermoplastic coating liquid on at least one surface of the porous substrate to form a discontinuous adhesive layer; the thermoplastic coating liquid is an aqueous coating liquid or a solvent-based coating liquid, comprising an olefin polymer and an optional tackifying resin;

[0011] The initial air permeability of the tape is P1≤2.5×P0, where P0 is the air permeability of the porous substrate;

[0012] After high temperature aging, the tape air permeability P2≤4×P1;

[0013] After soaking in electrolyte, the tape’s air permeability P3≤1.2×P1.

[0014] The adhesive layer of the present invention is a discontinuous adhesive layer comprising an olefin polymer. Since the olefin polymer has excellent chemical stability and mechanical strength, it can provide good structural support for it during the battery operation process, while not being corroded by the electrolyte, and the olefin polymer cost is relatively low, which can reduce the overall cost of the battery, so the present invention uses an olefin polymer as the main material of the adhesive layer. However, at the same time, the olefin polymer has a high-temperature self-closing characteristic, which automatically closes the pores under high temperature conditions, causing the permeability of the glue layer to decrease. To eliminate the impact of this characteristic in the adhesive layer, the present invention first utilizes an olefin polymer to form an aqueous or solvent-based thermoplastic coating liquid, and then the coating liquid is arranged on a porous substrate with excellent permeability. After drying, a discontinuous adhesive layer is obtained, and the volume ratio of the water or solvent in the coating liquid is utilized to increase the opening between the glue layers to increase the overall permeability of the tape while ensuring bonding performance and mechanical strength. Secondly, when the present invention uses an aqueous coating liquid, the microsphere-shaped olefin polymer in the aqueous emulsion can maintain its appearance shape under high temperature conditions without blocking the lithium ion transmission channel.

[0015] Preferably, after high temperature aging of the tape (for example, baking at 110°C for 24 hours and then cooling to room temperature for testing), the tape has an air permeability of P2 ≤ 2.5 × P1, and more preferably P2 satisfies: P2 = A h ×P1-B h , where A h The value is 1.2-2.2, B h The value ranges from 0 to 30. After soaking in electrolyte (for example, completely immersed in electrolyte solvent, baked at 85°C for 24 hours, taken out, wiped clean, and left for 20 minutes before testing. The electrolyte solvent contains ethylene carbonate EC 20wt%, ethyl methyl carbonate EMC 50wt% and ethyl propionate EP 30wt%), the tape air permeability P3 satisfies: P3 = A e ×P1+B e , where A e The value is 1.02-1.1, B e The value range is 0-15.

[0016] Preferably, the olefin polymer has a melting point of 60-150° C. and is selected from at least one of polyolefin resin, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-methacrylic acid copolymer, and polyvinylidene fluoride;

[0017] The tackifying resin is selected from at least one of hydrogenated C5, hydrogenated C9 resin, hydrogenated C5 / C9 copolymer resin, hydrogenated DCPD, hydrogenated rosin, and hydrogenated polyterpene resin.

[0018] Preferably, the polyolefin resin is selected from at least one of polypropylene resin, amorphous α-olefin copolymer, ethylene-octene or ethylene-butene copolymer, maleic anhydride grafted polyolefin, acrylic acid grafted polyolefin, methacrylic acid grafted polyolefin, and acrylic acid / methacrylic acid blended modified polyolefin.

[0019] Preferably, the porous substrate comprises a porous membrane with a porosity of 30-60%, selected from at least one of a single-layer PP membrane, a multi-layer PP membrane, a single-layer PE membrane, a multi-layer PE membrane, a PP / PE composite membrane, a PP / PE / PP sandwich membrane, and a PVDF membrane; and / or

[0020] The porous substrate comprises non-woven fabric with a pore size of ≤10 μm, and is selected from at least one of PP non-woven fabric, PE non-woven fabric, PET non-woven fabric, and PTFE non-woven fabric.

[0021] The porous substrate used in this invention has a higher porosity than solid membranes such as PET, PI, and BOPP. These pores allow for easier electrolyte penetration, providing a better ion conduction path, which can reduce internal resistance and increase battery power output. Furthermore, porous substrates such as porous PP and PE have relatively high melting points at high temperatures, which helps maintain the integrity of the separator in the event of battery overheating and reduces the risk of short circuits.

[0022] Preferably, the thermoplastic coating liquid is an aqueous coating liquid, and comprises the following raw materials in parts by weight:

[0023] 98-99.5 parts of aqueous emulsion;

[0024] 0-40 parts of inorganic filler;

[0025] Wetting agent 0-2 parts;

[0026] The solid content of the aqueous emulsion is 1-40%, and emulsion microspheres are dispersed therein. The emulsion microspheres contain the olefin polymer, and the particle size D50 of the emulsion microspheres is 0.2-2 μm.

[0027] The inorganic filler includes at least one of aluminum hydroxide, aluminum oxide, boehmite, zinc oxide, magnesium oxide, and boron nitride, and has a particle size D50 of 0.5-5 μm;

[0028] The wetting agent includes an anionic wetting agent or a nonionic wetting agent. Specifically, the anionic wetting agent includes at least one of alkyl sulfates, alkyl sulfonates, higher fatty acid salts, phosphates, fatty acids, or fatty acid sulfates; the nonionic wetting agent includes at least one of polyoxyethylene alkylphenol ethers, polyoxyethylene fatty alcohol ethers, and EO / PO block copolymers, with an HLB value between 5 and 20, preferably between 7 and 13.

[0029] The aqueous coating liquid used in the present invention utilizes emulsion microsphere drying technology to form a uniform but discontinuous adhesive layer on the surface of the tape. This uniformity helps ensure uniform distribution of the electrolyte and ion transport, thereby improving the overall performance and stability of the battery. At the same time, by adjusting the composition, size and concentration of the emulsion microspheres, the microstructure of the adhesive layer, including porosity and pore size distribution, can be precisely controlled. This control can optimize the permeability of the electrolyte and the transmission speed of ions, which is crucial to improving the charge and discharge efficiency and power density of the battery. And by adding different functional materials to the emulsion, such as conductive materials, flame retardants or self-healing materials, additional functions can be given to the tape without sacrificing air permeability and moisture permeability. This versatility makes battery design more flexible and can meet specific application requirements.

[0030] Preferably, the aqueous emulsion further comprises 0.01-10 wt% of an emulsifier, and optionally an auxiliary emulsifier and a defoaming agent;

[0031] The emulsifier is at least one selected from C8-C18 higher fatty acid salts, alkyl sulfates, alkyl sulfonates, phosphates, polyoxyethylene fatty alcohol ethers, polyoxyethylene alkylphenol ethers with an EO segment ≤ 20, and EO / PO block copolymers with an EO+PO segment of 20-80;

[0032] The auxiliary emulsifier is selected from C2-C5 short-chain alcohols or polyglycerol esters. The auxiliary emulsifier is evaporated when the aqueous emulsion is prepared, and substantially no residue remains in the aqueous coating liquid and the final adhesive layer.

[0033] The defoaming agent is selected from one or more of polysiloxane defoaming agents, silicone emulsion defoaming agents, polyether defoaming agents, polyether modified silicon defoaming agents, and higher alcohol defoaming agents.

[0034] The aqueous coating liquid can be prepared by mixing the raw materials described above and referring to existing emulsion preparation techniques. The aqueous emulsion containing dispersed emulsion microspheres can be prepared using processes such as hot melt, granulation dispersion, and phase inversion. The particle size of the emulsion microspheres can be controlled by controlling the type and amount of emulsifiers, co-emulsifiers, and solvents, as well as process parameters such as heating temperature, high-speed dispersion / shear rate, pressure, and time. Subsequently, inorganic fillers, colorants, wetting agents, and other components can be added as needed to produce the aqueous coating liquid.

[0035] Preferably, the thermoplastic coating liquid is a solvent-based coating liquid, comprising the olefin polymer and a solvent and an optional inorganic filler, the concentration of the olefin polymer is 5-20wt%, and the solvent-based coating liquid forms the discontinuous adhesive layer by spraying. Wherein, the solvent is selected from at least one of an aromatic hydrocarbon solvent, a ketone solvent, and an aliphatic hydrocarbon solvent. The mass concentration of the inorganic filler in the coating liquid is 0-30wt%, including at least one of aluminum hydroxide, aluminum oxide, boehmite, zinc oxide, magnesium oxide, and boron nitride, and the particle size D50 is 0.5-5μm. Different from the water-based coating liquid, which can be coated in a variety of ways, the uniform solvent-based coating liquid needs to be sprayed to form discontinuous droplets, and then the solvent evaporates to leave a uniform but discontinuous solute to obtain the adhesive layer.

[0036] Preferably, the adhesive tape further comprises at least one release layer, the release layer being located on the surface of the porous substrate facing away from the adhesive layer and / or on the surface of the adhesive layer facing away from the porous substrate. A release agent may be applied to the surface of the porous substrate facing away from the adhesive layer to form the release layer, and a release film may be provided on the surface of the adhesive layer facing away from the porous substrate.

[0037] In a second aspect, the present invention provides a method for preparing the aforementioned high-transparency adhesive tape, comprising the following steps:

[0038] Step 1: preparing a thermoplastic coating liquid containing an olefin polymer;

[0039] Step 2: Apply the coating solution to at least one surface of the porous substrate with a coating amount of 0.01-80 g / m 2 ;

[0040] Step 3: Drying the coating liquid to obtain the high-transparency adhesive tape.

[0041] The drying method in step 3 is preferably drying in a drying tunnel, with the drying tunnel temperature controlled at 30-150° C., preferably 50-120° C.; and the drying time is 10-300 s, preferably 60-180 s.

[0042] In a third aspect, the present invention also provides the use of the aforementioned highly transparent tape for lithium battery pole piece protection, negative electrode bonding, pole ear protection, and winding tailing, which is bonded to the joint position by cold pressing or hot pressing. When in use, the tape with a release layer can be directly bonded to the joint position by cold pressing, while the tape without a release layer can activate the pressure sensitivity of the adhesive layer by a hot pressing process, and the tape is attached to the position to be joined, such as the position with a large bending amplitude during the winding of the pole piece. The hot pressing temperature is 70-160°C. In the subsequent shaping process, it can effectively prevent the pole piece from cracking and improve the qualified rate of the battery product. The high air permeability of the tape as a whole does not block the transmission of lithium ions. In addition, during the battery cycle, it reduces the problems of lithium deposition, deformation and fracture at the corners of the battery cell. In addition, it can also be used for pole piece (edge) protection, pole ear protection, winding tail, etc.

[0043] The present invention has at least the following beneficial effects:

[0044] (1) The present invention coats a polyolefin polymer in the form of a thermoplastic coating liquid onto a breathable porous substrate, and dries it to obtain a uniform but discontinuously distributed adhesive layer. The adhesive tape prepared in this way uses a porous substrate with a relatively high porosity and a discontinuously distributed adhesive layer. On the basis of ensuring sufficient bonding performance and mechanical strength, it achieves the technical effect of good overall air permeability and high lithium ion permeability without affecting the lithium ion transmission in the battery.

[0045] (2) The present invention adopts coating of a water-based coating liquid or spraying of a solvent-based coating liquid to finally obtain a uniform discontinuous adhesive layer, which can effectively avoid the problem that ordinary polyolefin polymers easily exhibit self-closing characteristics at high temperatures, resulting in reduced air permeability, and reduces the impact on the overall air permeability and ion permeability of the tape.

[0046] (3) The highly permeable tape prepared by the present invention can promote the uniform distribution of electrolyte around the edges and corners of the battery, which helps ensure that all parts of the battery are fully wetted, thereby improving the ion transmission efficiency and enhancing the battery's charge and discharge performance. At the same time, it can reduce the problem of local overheating caused by uneven electrolyte distribution. Uniform electrolyte distribution helps avoid local temperature increases, thereby reducing the risk of thermal runaway and improving the overall safety of the battery.

[0047] (4) The highly permeable adhesive tape prepared by the present invention helps to reduce the uneven stress during the charge and discharge process and reduce the microscopic damage inside the battery. The uniform distribution of electrolyte and ions reduces the possibility of local overcharge or overdischarge, avoids local lithium plating, and thus prolongs the battery life. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] FIG1 is a schematic structural diagram of a first embodiment of the present invention;

[0049] FIG2 is a schematic structural diagram of a second embodiment of the present invention;

[0050] FIG3 is a schematic structural diagram of a third embodiment of the present invention.

[0051] Reference numerals: 1-porous substrate, 2-adhesive layer, 3-release layer A, 4-release layer B. DETAILED DESCRIPTION

[0052] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0053] The terms used in the embodiments of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The singular forms "a," "an," "the," and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, and unless the context clearly indicates otherwise, "a plurality" generally includes at least two.

[0054] It should also be noted that the terms "include," "comprises," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a product or device comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such product or device. In the absence of further limitations, an element defined by the phrase "comprises a..." does not exclude the presence of other identical elements in the product or device comprising the element.

[0055] A highly permeable lithium battery tape comprises a porous substrate 1 and an adhesive layer 2, as shown in FIG1 , wherein:

[0056] (1) Porous substrate 1: having a thickness of 5-50 μm and an air permeability of 50-450 s / 100 ml, preferably 50-350 s / 100 ml, and comprising at least one of a porous membrane and a non-woven fabric; the porous membrane having a porosity of 30-60% is selected from at least one of a single-layer PP membrane, a multi-layer PP membrane, a single-layer PE membrane, a multi-layer PE membrane, a PP / PE composite membrane, a PP / PE / PP sandwich membrane, and a PVDF membrane; the non-woven fabric having a pore size ≤10 μm is selected from at least one of a PP non-woven fabric, a PE non-woven fabric, a PET non-woven fabric, and a PTFE non-woven fabric.

[0057] (2) Adhesive layer 2: a discontinuous adhesive layer 2 is formed by coating a thermoplastic coating liquid on at least one surface of the porous substrate 1;

[0058] The thermoplastic coating liquid contains an olefin polymer and an optional tackifying resin; wherein the olefin polymer has a melting point of 60-150°C and is selected from at least one of polyolefin resins, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-ethyl acrylate copolymers, ethylene-methyl acrylate copolymers, ethylene-methacrylic acid copolymers, and polyvinylidene fluoride; and the polyolefin resin is selected from at least one of polypropylene resins, amorphous α-olefin copolymers, ethylene-octene or ethylene-butene copolymers, maleic anhydride grafted polyolefins, acrylic acid grafted polyolefins, methacrylic acid grafted polyolefins, and acrylic acid / methacrylic acid blended modified polyolefins.

[0059] The tackifying resin is selected from at least one of hydrogenated C5, hydrogenated C9 resin, hydrogenated C5 / C9 copolymer resin, hydrogenated DCPD, hydrogenated rosin, and hydrogenated polyterpene resin.

[0060] The thermoplastic coating liquid is 1. a water-based coating liquid or 2. a solvent-based coating liquid:

[0061] 1. The aqueous coating liquid comprises the following raw materials in parts by weight:

[0062] 98-99.5 parts of aqueous emulsion;

[0063] 0-40 parts of inorganic filler;

[0064] Wetting agent 0-2 parts;

[0065] The solid content of the aqueous emulsion is 1-40%, and emulsion microspheres are dispersed therein. The emulsion microspheres contain the olefin polymer, and the particle size D50 of the emulsion microspheres is 0.2-2 μm.

[0066] The aqueous emulsion further comprises 0.01-10 wt % of an emulsifier, and optionally an auxiliary emulsifier and a defoaming agent; the emulsifier is selected from at least one of C8-C18 higher fatty acid salts, alkyl sulfates, alkyl sulfonates, phosphate esters, polyoxyethylene fatty alcohol ethers, polyoxyethylene alkylphenol ethers with an EO segment ≤ 20, and EO / PO block copolymers with an EO+PO segment of 20-80; the auxiliary emulsifier is selected from C2-C5 short-chain alcohols or polyglycerol esters; and the defoaming agent is selected from one or more of polysiloxane defoamers, silicone emulsion defoamers, polyether defoamers, polyether-modified silicon defoamers, and higher alcohol defoamers.

[0067] The inorganic filler includes at least one of aluminum hydroxide, aluminum oxide, boehmite, zinc oxide, magnesium oxide, and boron nitride, and has a particle size D50 of 0.5 to 5 μm;

[0068] Wetting agents include anionic wetting agents or nonionic wetting agents. Anionic wetting agents include alkyl sulfates, alkyl sulfonates, higher fatty acid salts, phosphates, fatty acids, or fatty acid sulfates; nonionic wetting agents include one or more of polyoxyethylene alkylphenol ethers, polyoxyethylene fatty alcohol ethers, and EO / PO block copolymers, with an HLB value between 5 and 20, preferably 7 to 13.

[0069] The method for preparing the highly permeable lithium battery tape using the aqueous coating liquid comprises the following steps:

[0070] Step 1: preparing an aqueous coating liquid containing an olefin polymer according to the above raw material composition in parts by weight;

[0071] Step 2: Apply the aqueous coating solution to at least one surface of the porous substrate 1, with a coating amount of 0.01-80 g / m 2 , preferably 0.5-20g / m 2 ; The coating method can be gravure coating, reverse roller coating, wire rod coating, slot coating, air knife coating, curtain coating, spray coating, dip coating, gap coating, etc., wherein the spray coating process does not require the addition of a wetting agent;

[0072] Step 3: Dry the coating liquid, and the solid component ultimately adheres to the surface of the porous substrate 1 in a substantially uniform but discontinuous manner in the form of microspheres or quasi-spherical structures, thereby obtaining the highly permeable lithium battery tape. The drying device is preferably a drying tunnel, with the drying tunnel temperature controlled at 30-150°C, preferably 50-120°C, and the drying time 10-300 seconds, preferably 60-180 seconds.

[0073] In step 1, the aqueous coating liquid can be prepared according to the above raw material ratios and with reference to existing emulsion preparation technology. The aqueous emulsion containing dispersed emulsion microspheres can be prepared by hot melt method, granulation dispersion method, phase inversion method, etc.

[0074] For example, (1) preparing an aqueous emulsion by hot melt method may include:

[0075] 1) Add the raw materials of the aqueous emulsion into the pressure reactor according to the formula;

[0076] 2) Add deionized water, alkaline substances, solvents, emulsifiers, etc.; pressurize to 1-15MPa, heat to 90-200℃, and shear at high speed;

[0077] 3) Cooling and discharging to obtain aqueous emulsion.

[0078] (2) The granulation dispersion method for preparing aqueous emulsions may include:

[0079] 1) Add the raw materials and solvent into the reactor according to the formula ratio and dissolve them;

[0080] 2) The material is spray-dried by spray equipment to become powder;

[0081] 3) Disperse emulsifiers and other additives and powders in water at high speed to obtain an aqueous emulsion.

[0082] (3) The phase inversion method for preparing aqueous emulsions may include:

[0083] 1) Add the raw materials into the reactor according to the formula ratio; add the solvent into the reactor and fully dissolve at 40-150℃;

[0084] 2) Add emulsifier, alkaline substance and deionized water into the reactor, stir and perform high-speed shearing;

[0085] 3) Remove the solvent molecules through distillation equipment to obtain an aqueous emulsion.

[0086] Furthermore, the particle size of the emulsion microspheres can be controlled by controlling the type and amount of emulsifiers, co-emulsifiers, and solvents, as well as process parameters such as heating temperature, high-speed dispersion / shear rate, pressure, and time. Subsequently, inorganic fillers, colorants, wetting agents, and other components are added as needed to produce a water-based coating solution.

[0087] 2. A solvent-based coating liquid comprising the olefin polymer, a solvent, and an optional inorganic filler, wherein the concentration of the olefin polymer is 5-20 wt %. The solvent-based coating liquid is sprayed to form the discontinuous adhesive layer 2.

[0088] The solvent is selected from at least one of aromatic hydrocarbon solvents, ketone solvents, and aliphatic hydrocarbon solvents. The inorganic filler has a mass concentration of 0-30% in the coating solution and includes at least one of aluminum hydroxide, aluminum oxide, boehmite, zinc oxide, magnesium oxide, and boron nitride, and has a particle size D50 of 0.5-5 μm.

[0089] The method for preparing the highly transparent lithium battery tape using the solvent-based coating liquid comprises the following steps:

[0090] Step 1: preparing a solvent-based coating solution containing an olefin polymer;

[0091] Step 2: Spray the solvent-based coating liquid onto at least one surface of the porous substrate 1, with a spraying amount of 0.01-80 g / m 2 , preferably 0.5-20g / m 2 ;

[0092] Step 3: Dry the coating liquid. As the solvent evaporates, the solute precipitates and adheres to the surface of the porous substrate 1 in a substantially uniform but discontinuous manner, thereby obtaining the highly permeable lithium battery tape. The drying device is preferably a drying tunnel, with the drying tunnel temperature controlled at 30-150°C, preferably 50-120°C, and the drying time at 10-300 seconds, preferably 60-180 seconds.

[0093] (3) An optional release layer is located on the surface of the porous substrate 1 facing away from the adhesive layer 2, and / or on the surface of the adhesive layer 2 facing away from the porous substrate 1. For example, a release agent may be applied to the surface of the porous substrate 1 facing away from the adhesive layer 2 to form a release layer A 3, as shown in FIG2 ; a release film may be provided on the surface of the adhesive layer 2 facing away from the porous substrate 1 to form a release layer B 4, as shown in FIG3 .

[0094] Example 1

[0095] A highly transparent adhesive tape for lithium batteries, comprising a porous substrate and an adhesive layer, wherein

[0096] (1) Porous substrate: A PP membrane with a thickness of 20 μm, an air permeability of 180 s / 100 ml, and a porosity of 50 ± 10% was selected as the substrate;

[0097] (2) Adhesive layer: A discontinuous adhesive layer is formed by coating a thermoplastic coating liquid on one surface of the porous substrate; the thermoplastic coating liquid is an aqueous coating liquid, and comprises the following raw materials in parts by weight:

[0098] 99 parts of aqueous emulsion;

[0099] 1 part wetting agent;

[0100] The aqueous emulsion has a solid content of 3% and contains dispersed emulsion microspheres. The emulsion microspheres comprise an olefin polymer, which is maleic anhydride grafted polypropylene (brand name Polinker PL2480). The particle size D50 of the emulsion microspheres is approximately 0.3 μm and the melting point is approximately 85°C.

[0101] Prepared by the following method:

[0102] Step 1: Prepare the polyolefin thermoplastic coating liquid with the above parameters;

[0103] Step 2: Apply the coating solution to one surface of the porous substrate using a gravure coating method with a coating amount of 0.18 g / m 2 ;

[0104] Step 3: Dry the coating liquid in a drying channel at a drying temperature of 60-80° C. and a drying time of 60 seconds to obtain the highly transparent lithium battery tape.

[0105] Example 2

[0106] The difference between this embodiment and embodiment 1 is that the solid content of the aqueous emulsion used in this embodiment is 8%, and the coating amount of the coating liquid is 0.98g / m 2 .

[0107] Example 3

[0108] The difference between this embodiment and embodiment 1 is that the solid content of the aqueous emulsion used in this embodiment is 20%, and the coating amount of the coating liquid is 16.6 g / m 2 .

[0109] Example 4

[0110] The difference between this embodiment and embodiment 1 is that the solid content of the aqueous emulsion used in this embodiment is 30%, and the coating amount of the coating liquid is 26.3g / m 2 .

[0111] Example 5

[0112] The difference between this embodiment and embodiment 3 is that the particle size D50 of the emulsion microspheres in the aqueous emulsion is about 0.5 μm, and the coating amount of the coating liquid is 16.4 g / m 2 .

[0113] Example 6

[0114] The difference between this embodiment and embodiment 3 is that the particle size D50 of the emulsion microspheres in the aqueous emulsion used in this embodiment is about 1.3 μm, and the coating amount of the coating liquid is 17.2 g / m 2 .

[0115] Example 7

[0116] The difference between this embodiment and embodiment 3 is that the particle size D50 of the emulsion microspheres in the aqueous emulsion used in this embodiment is about 1.8 μm, and the coating amount of the coating liquid is 17.3 g / m 2 .

[0117] Example 8

[0118] The difference between this embodiment and embodiment 6 is that the coating amount of the coating liquid in this embodiment is 16.7 g / m 2 , the drying temperature of the drying channel is set to 80-100℃.

[0119] Example 9

[0120] The difference between this embodiment and embodiment 6 is that the coating amount of the coating liquid in this embodiment is 16.7 g / m 2 , the drying time of the drying channel is set to 180s.

[0121] Example 10

[0122] The difference between this embodiment and embodiment 6 is that the coating amount of the coating liquid in this embodiment is 16.9 g / m 2 , the drying time of the drying channel is set to 300s.

[0123] Example 11

[0124] The difference between this embodiment and embodiment 6 is that the olefin polymer contained in the emulsion microspheres in this embodiment is maleic anhydride grafted polypropylene (brand name Polinker PL2400), with a melting point of about 60°C, and the coating amount of the coating liquid is 16.6 g / m 2 .

[0125] Example 12

[0126] The difference between this embodiment and embodiment 6 is that the olefin polymer contained in the emulsion microspheres in this embodiment is maleic anhydride grafted polypropylene (brand name Fusabond P353), with a melting point of 100°C, and the coating amount of the coating liquid is 17.2 g / m 2 .

[0127] Example 13

[0128] The difference between this embodiment and embodiment 6 is that the olefin polymer contained in the emulsion microspheres in this embodiment is maleic anhydride grafted polypropylene (brand Exxelor PO 1015 + Polinker PL2400 mixture), with a melting point of 120°C, and the coating amount of the coating liquid is 17.0 g / m 2 .

[0129] Example 14

[0130] The difference between this embodiment and embodiment 6 is that the olefin polymer contained in the emulsion microspheres in this embodiment is maleic anhydride grafted polypropylene (brand Exxelor PO 1015), with a melting point of about 140°C, and the coating amount of the coating liquid is 16.8 g / m 2 .

[0131] Example 15

[0132] The difference between this embodiment and embodiment 3 is that this embodiment uses a 9 μm PP diaphragm substrate, the air permeability of the substrate is 120s / 100ml, and the coating amount of the coating liquid is 16.5g / m 2 .

[0133] Example 16

[0134] The difference between this embodiment and embodiment 3 is that this embodiment uses a 45 μm PP diaphragm substrate, the substrate air permeability is 280s / 100ml, and the coating amount of the coating liquid is 16.6g / m 2 .

[0135] Example 17

[0136] The difference between this embodiment and embodiment 3 is that this embodiment uses a 20 μm PP non-woven fabric substrate with a pore size of ≤10 μm, an air permeability of the substrate of 220 s / 100 ml, and a coating amount of 16.5 g / m 2 .

[0137] Example 18

[0138] The difference between this embodiment and embodiment 3 is that this embodiment uses a 9 μm PP non-woven fabric substrate with a pore size of ≤10 μm, an air permeability of 130 s / 100 ml, and a coating amount of 16.8 g / m 2 .

[0139] Example 19

[0140] The difference between this embodiment and embodiment 3 is that this embodiment uses a 45 μm PP non-woven fabric substrate with a pore size of ≤10 μm, a substrate air permeability of 300 s / 100 ml, and a coating amount of 16.4 g / m 2 .

[0141] Comparative Example 1

[0142] The difference between Comparative Example 1 and Example 3 is that a 60 μm PP diaphragm substrate is used, the porosity is 50±10%, and the air permeability of the substrate is 370 s / 100 ml.

[0143] Comparative Example 2

[0144] The difference between Comparative Example 2 and Example 3 is that the coating amount of the coating liquid is about 85g / m 2 The drying temperature of the drying channel is set to 80-100℃ and the drying time is 180s.

[0145] Example 20

[0146] The difference between this embodiment and embodiment 6 is that the EVA emulsion microspheres are used in this embodiment. The melting point of EVA (brand UL 15019CC) is about 85°C, and the coating amount of the coating liquid is 16.3g / m 2 .

[0147] Example 21

[0148] A highly transparent adhesive tape for lithium batteries, comprising a porous substrate and an adhesive layer, wherein

[0149] (1) Porous substrate: A PP membrane with a thickness of 20 μm, an air permeability of 180 s / 100 ml, and a porosity of 50 ± 10% was selected as the substrate;

[0150] (2) Adhesive layer: A discontinuous adhesive layer is formed by coating a thermoplastic coating liquid on one surface of the porous substrate; the thermoplastic coating liquid is a NMP solution (solvent-based coating liquid) of PVDF (brand name Solef 11010) with a concentration of 12% and a melting point of 140°C;

[0151] Prepared by the following method:

[0152] Step 1: Prepare the polyolefin thermoplastic coating liquid with the above parameters;

[0153] Step 2: Spray the coating solution onto one surface of the porous substrate with a coating amount of 17.4 g / m 2 ;

[0154] Step 3: Dry the coating liquid in a drying channel at a drying temperature of 100-120° C. and a drying time of 180 seconds to obtain the highly transparent lithium battery tape.

[0155] Example 22

[0156] The difference between this embodiment and Example 21 is that this embodiment uses a 9 μm PP diaphragm substrate with an air permeability of 120s / 100ml.

[0157] Example 23

[0158] The difference between this embodiment and Example 21 is that this embodiment uses a 45 μm PP diaphragm substrate with an air permeability of 280 s / 100 ml.

[0159] Example 24

[0160] The difference between this embodiment and Example 21 is that this embodiment uses a 20 μm PP non-woven fabric substrate with an air permeability of 220s / 100ml.

[0161] Example 25

[0162] The difference between this embodiment and embodiment 21 is that the solvent-based coating liquid used in this embodiment is a methyl isobutyl ketone (MIBK)-methylcyclohexane solution of POE (brand name Vistamaxx 3588FL) with a concentration of 10% and a melting point of about 85°C; the coating amount is 17.1 g / m 2 ; The drying temperature in the drying channel is 60-80℃, and the drying time is 60s.

[0163] Comparative Example 3

[0164] The difference between Comparative Example 3 and Example 21 is that a 60 μm PP diaphragm substrate is used, the porosity is 50±10%, and the air permeability of the substrate is 370 s / 100 ml.

[0165] Comparative Example 4

[0166] The difference between Comparative Example 4 and Example 21 is that the coating amount of the coating liquid is about 85g / m 2 , the drying channel sets the drying temperature to 100-120℃ and the drying time to 300s.

[0167] The coating liquid and process parameters of each embodiment and comparative example are shown in Table 1:

[0168] Table 1

[0169]

[0170]

[0171] Test method:

[0172] (1) Peel strength test method - before soaking

[0173] Test method: Clean the aluminum foil to be tested with isopropyl alcohol and let it dry, cut the tape sample into strips with a width of 24mm and a length of 100mm; align the test surface of the tape strip with the aluminum foil to be tested, and press them together at 95℃ and 0.2Mpa for 1s to avoid bubbles or wrinkles; adhere the back of the aluminum foil (the side without tape) to a stainless steel plate with double-sided tape, start the timer, and cure for 20 minutes; fix one end of the stainless steel plate on the lower fixture of the tensile testing machine and make it perpendicular to the horizontal plane, and reset the equipment; clamp the substrate of the tape strip with the other fixture, and perform a peel test at a speed of 304.8mm / min. Select a section with stable data (not shorter than 80mm) to calculate the peel strength in N / mm.

[0174] (2) Peel strength test method - after soaking

[0175] Test method: Prepare the tape strips according to the method of test (1). After curing, place them in a container containing electrolyte solvent, ensuring that the liquid surface completely immerses the strips. After baking at 85℃ for 24 hours, remove them and wipe off the surface solvent. After standing for 20 minutes, test the peel strength using the method of test 1. The electrolyte solvent contains ethylene carbonate EC 20wt%, ethyl methyl carbonate EMC 50wt% and ethyl propionate EP 30wt%.

[0176] (3) Air permeability test method

[0177] Cut the tape sample into a circular piece with a diameter greater than 10cm or a square piece with a side length greater than 10cm. Turn on the device and press the slider against the top of the slider. Rotate the slider so that the infrared probe is perpendicular to the center axis of the 100ml test area. Place the film to be tested on the test seat and tighten it. When the screen displays "TIMER SEEKING STARTING MARK", press the "RESET" button and release the slider to begin testing. After the test is complete, read the value on the screen in seconds per 100ml.

[0178] (4) High temperature aging air permeability test

[0179] Cut the tape sample into a circle with a diameter of more than 10 cm or a square with a side length of more than 10 cm, bake it at 110℃ for 24 hours, take it out, cool it to room temperature, and test the air permeability according to the test method of test (3).

[0180] (5) Air permeability test after soaking

[0181] Cut the tape sample into a circular piece with a diameter greater than 10 cm or a square piece with a side length greater than 10 cm. Place the tape into a container containing electrolyte solvent, ensuring the liquid surface completely submerges the tape. Bake at 85°C for 24 hours, remove the tape, wipe off the surface solvent, and let it sit for 20 minutes. Then test the air permeability according to the test method in Test 3. The electrolyte solvent contains 20wt% ethylene carbonate (EC), 50wt% ethyl methyl carbonate (EMC), and 30wt% ethyl propionate (EP).

[0182] The test results are shown in Table 2:

[0183] Table 2

[0184]

[0185] After a lot of experimental exploration and optimization, the initial air permeability of the adhesive tape of the present invention is P1≤2.5×P0, where P0 is the air permeability of the porous substrate, which is 50-450s / 100ml, preferably 50-350s / 100ml.

[0186] After high temperature aging of the tape (for example, baking at 110°C for 24 hours, taking it out and cooling it to room temperature for testing), the tape air permeability P2 ≤ 4.0 × P1, preferably P2 ≤ 2.5 × P1, more preferably the tape air permeability P2 satisfies: P2 = A h ×P1-B h , where A h The value is 1.2-2.2, B h The value range is 0-30;

[0187] After the tape is soaked in electrolyte (for example, completely immersed in the electrolyte solvent, baked at 85°C for 24 hours, taken out, wiped clean, and left for 20 minutes before testing, the electrolyte solvent contains ethylene carbonate EC 20wt%, ethyl methyl carbonate EMC 50wt% and ethyl propionate EP 30wt%), the tape air permeability P3 ≤ 1.2 × P1; preferably, the tape air permeability P3 satisfies: P3 = A e ×P1+B e , where A e The value is 1.02-1.1, B e The value range is 0-15.

[0188] The present invention selects a porous substrate with good permeability and cooperates with an appropriate adhesive layer to obtain a lithium battery tape with excellent air permeability, air permeability after high-temperature aging, and air permeability after soaking in electrolyte. Without affecting the passage of lithium ions, it can protect the electrode from cracking under stress during the hot pressing process and prevent lithium deposition in the battery during the battery cycle, which is beneficial to improving the safety of battery use and extending the battery life.

[0189] Comparing the compositions and test results of the various examples and comparative examples reveals that while there are numerous options for both the porous substrate and the adhesive layer, both, provided they adhere to the aforementioned pre-selected material selection methods and test results, generally meet the air permeability and adhesion requirements, satisfying the tape's application scenarios. However, while Comparative Examples 1-4 meet the requirements for individual parameters, overall they still fail to achieve the comprehensive properties required for lithium battery tapes.

[0190] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they become aware of the basic inventive concepts. Therefore, the technical solutions of the present invention are intended to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention.

Claims

1. A highly transparent tape, characterized in that: including a laminated porous substrate and an adhesive layer; The porous substrate has a thickness of 5-50 μm and an air permeability of 50-450 s / 100 ml, and comprises at least one of a porous membrane and a non-woven fabric; An adhesive layer is formed by coating a thermoplastic coating liquid on at least one surface of the porous substrate to form a discontinuous adhesive layer; the thermoplastic coating liquid is an aqueous coating liquid or a solvent-based coating liquid, comprising an olefin polymer and an optional tackifying resin; The initial air permeability of the tape is P1≤2.5×P0, where P0 is the air permeability of the porous substrate; After high temperature aging, the tape air permeability P2≤4.0×P1; After soaking in electrolyte, the tape’s air permeability P3≤1.2×P1.

2. The high-transparency adhesive tape according to claim 1, wherein: The olefin polymer has a melting point of 60-150° C. and is selected from at least one of polyolefin resin, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-methacrylic acid copolymer, and polyvinylidene fluoride; The tackifying resin is selected from at least one of hydrogenated C5, hydrogenated C9 resin, hydrogenated C5 / C9 copolymer resin, hydrogenated DCPD, hydrogenated rosin, and hydrogenated polyterpene resin.

3. The high-transparency adhesive tape according to claim 2, wherein: The polyolefin resin is selected from at least one of polypropylene resin, amorphous α-olefin copolymer, ethylene-octene or ethylene-butene copolymer, maleic anhydride grafted polyolefin, acrylic acid grafted polyolefin, methacrylic acid grafted polyolefin, and acrylic acid / methacrylic acid blended modified polyolefin.

4. The highly transparent adhesive tape according to any one of claims 1 to 3, characterized in that: The porous substrate comprises a porous membrane with a porosity of 30-60%, selected from at least one of a single-layer PP membrane, a multi-layer PP membrane, a single-layer PE membrane, a multi-layer PE membrane, a PP / PE composite membrane, a PP / PE / PP sandwich membrane, and a PVDF membrane; and / or The porous substrate comprises non-woven fabric with a pore size of ≤10 μm, and is selected from at least one of PP non-woven fabric, PE non-woven fabric, PET non-woven fabric, and PTFE non-woven fabric.

5. The highly transparent adhesive tape according to claim 4, wherein: The thermoplastic coating liquid is an aqueous coating liquid, and comprises the following raw materials in parts by weight: 98-99.5 parts of aqueous emulsion; 0-40 parts of inorganic filler; Wetting agent 0-2 parts; The solid content of the aqueous emulsion is 1-40%, and emulsion microspheres are dispersed therein. The emulsion microspheres contain the olefin polymer, and the particle size D50 of the emulsion microspheres is 0.2-2 μm. The inorganic filler includes at least one of aluminum hydroxide, aluminum oxide, boehmite, zinc oxide, magnesium oxide, and boron nitride, and has a particle size D50 of 0.5-5 μm; The wetting agent includes anionic wetting agents or nonionic wetting agents.

6. The highly transparent adhesive tape according to claim 5, wherein: The aqueous emulsion further comprises 0.01-10 wt% of an emulsifier, and optionally an auxiliary emulsifier and a defoaming agent; The emulsifier is selected from at least one of C8-C18 higher fatty acid salts, alkyl sulfates, alkyl sulfonates, phosphates, polyoxyethylene fatty alcohol ethers, polyoxyethylene alkylphenol ethers with EO segments ≤ 20, and EO / PO block copolymers with EO+PO segments of 20-80.

7. The highly transparent adhesive tape according to claim 4, wherein: The thermoplastic coating liquid is a solvent-based coating liquid, comprising the olefin polymer, a solvent and an optional inorganic filler, wherein the concentration of the olefin polymer is 5-20 wt %. The solvent-based coating liquid is sprayed to form the discontinuous adhesive layer.

8. The highly transparent adhesive tape according to any one of claims 5 to 7, characterized in that: The porous substrate further comprises at least one release layer, wherein the release layer is laminated on the surface of the porous substrate facing away from the adhesive layer, and / or laminated on the surface of the adhesive layer facing away from the porous substrate.

9. A method for preparing the highly transparent adhesive tape according to any one of claims 1 to 8, characterized in that: The steps include: Step 1: preparing a thermoplastic coating liquid containing an olefin polymer; Step 2: Apply the coating solution to at least one surface of the porous substrate with a coating amount of 0.01-80 g / m 2 ; Step 3: Drying the coating liquid to obtain the high-transparency adhesive tape.

10. Application of the highly transparent adhesive tape according to any one of claims 1 to 8 for lithium battery pole piece protection, negative electrode bonding, tab protection, and winding and finishing, characterized in that: Bonded to the joint by cold or hot pressing.

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