Battery cell pad for electric vehicle secondary battery and method of manufacturing the same

Abstract

This invention relates to a cell pad for secondary batteries and its preparation method. Specifically, this invention relates to a cell pad for secondary batteries and its preparation method, wherein the cell pad is disposed between the cells of a secondary battery to prevent thermal runaway occurring in a uniaxial cell from spreading to other cells.

Description

Technical Field

[0001] This invention relates to a battery cell pad for secondary batteries and its preparation method. Specifically, this invention relates to a battery cell pad for electric vehicles, disposed between secondary battery cells, and used to prevent thermal runaway occurring in one cell from spreading to another, as well as its preparation method. Background Technology

[0002] Generally speaking, secondary batteries for electric vehicles can be divided into three types according to the shape of their outer casing materials. These are cylindrical secondary batteries with electrode assemblies housed in a metal can, pouch secondary batteries with electrode assemblies housed in a pouch casing, and secondary batteries with battery materials encapsulated in a square aluminum can casing.

[0003] Because multiple (12 cells) battery cells are tightly stacked together, if some battery cells experience thermal runaway, the thermal runaway will spread to adjacent battery cells in a short period of time, which may lead to accidents such as fires or explosions in battery cells with a larger capacity than individual battery cells, such as battery modules or battery packs.

[0004] In particular, when thermal runaway occurs, a single battery cell can generate an ultra-high temperature zone of approximately 600°C to 900°C. This high temperature can ignite surrounding flammable materials (solid electrolyte interphase (SEI), decomposition → cathode electrolyte → anodic decomposition → short circuit → electrolyte ignition → thermal runaway), further increasing the risk of fire. Furthermore, if thermal runaway occurs in one battery cell due to manufacturing defects or misuse of the battery pack, the runaway may spread to adjacent cells.

[0005] In the past, electric vehicle battery packs used to employ buffer pads made of polyurethane foam or silicone foam between uniaxial battery cells and other adjacent battery cells to prevent thermal runaway phenomena occurring in a uniaxial battery cell from spreading to other battery cells, thus delaying and preventing the spread of thermal runaway phenomena.

[0006] However, while the aforementioned polyurethane and silicone foams possess a cushioning function that expands and contracts with pressure (surface pressure), they suffer from the problem of losing their viscoelastic properties at high temperatures (200°C). In particular, because these foams decompose in a temperature range (approximately 200°C) lower than the high-temperature region where thermal runaway occurs in the battery, they cannot provide the required thermal runaway delay effect.

[0007] To address these issues, Korean Patent Publication No. 10-2023-0132800, entitled "Insulating Multilayer Sheet Material, Preparation Method Thereof, and Article Using Thereof," proposes a multilayer sheet structure improved by adding silicone paper, glass fiber, etc., to foam. However, its cost-effectiveness and its function as a buffer pad and thermal runaway prevention pad are insufficient.

[0008] Furthermore, Korean Patent Publication No. 10-2022-0013603 discloses a "thermal runaway prevention pad and a battery cell housing structure including the thermal runaway prevention pad," wherein the thermal runaway prevention pad includes a first buffer made of elastic material, a fire extinguishing component for spraying extinguishing agent, and a second buffer. Additionally, Korean Registered Patent Nos. 10-2425374, 10-2023-0132800, and 10-2669747, as well as US Patent Publication No. US2024 / 0145843, disclose related technologies. Summary of the Invention

[0009] The present invention aims to provide a cell pad for secondary batteries and a method for preparing the same, which can delay thermal runaway that may occur due to misuse or damage to electric vehicle batteries.

[0010] Solution for solving the problem

[0011] The above objective is achieved by a cell pad for a secondary battery, which includes a polymer foam, a carbon fiber composite attached to both sides of the polymer foam, and an adhesive layer located between the polymer foam and the carbon fiber composite layer.

[0012] Preferably, the carbon fiber composite can be prepared by coating a quasi-non-combustible slurry containing an intumescent flame-retardant composition onto a carbon fiber nonwoven fabric.

[0013] Preferably, the polymer foam can be prepared by mixing an intumescent flame retardant composition, fumed silica and a foaming agent into a rubber selected from the group consisting of silicone rubber, thermoplastic elastomer and EPDM rubber and then compressing it.

[0014] Preferably, the aforementioned quasi-non-combustible slurry may contain, for every 100 parts by weight of water-soluble epoxy resin or vinyl acetate copolymer, 80 to 150 parts by weight of an intumescent flame retardant composition, 40 to 60 parts by weight of aluminum hydroxide, 1 to 10 parts by weight of an aqueous solution of montmorillonite, and 1 to 10 parts by weight of a polyoxyethylene (propylene-ethylene) copolymer.

[0015] More preferably, the above-mentioned intumescent flame retardant composition may contain 20 to 40 parts by weight of melamine, 20 to 40 parts by weight of carbamide (urea) and 30 to 50 parts by weight of D-glucol for every 100 parts by weight of ammonium polyphosphate.

[0016] Preferably, the adhesive layer may include an epoxy oil-based flame retardant adhesive or an epoxy water-based flame retardant adhesive.

[0017] Preferably, the carbon fiber nonwoven fabric can be treated with a sizing agent comprising liquid epoxy resin and hydrophilic fumed silica.

[0018] Furthermore, the above objective is achieved through a method for preparing a cell pad for secondary batteries, which includes: a step of treating a carbon fiber nonwoven fabric with a sizing agent; a step of coating the sizing carbon fiber nonwoven fabric with a quasi-non-combustible slurry containing an intumescent flame-retardant composition, followed by drying and curing to form a carbon fiber composite; a step of mixing a rubber selected from the group consisting of silicone rubber, thermoplastic elastomer, and EPDM rubber, an intumescent flame-retardant composition, fumed silica, and a foaming agent, followed by compression molding to prepare a polymer foam; a step of coating both sides of the polymer foam with an epoxy adhesive and attaching the carbon fiber composite to both sides of the polymer foam; and a step of heat-treating the attached polymer foam and the carbon fiber composite to dry and cure them.

[0019] Invention Effects

[0020] Because the battery cell pad for secondary batteries according to the present invention has quasi-non-combustible and thermal insulation properties, it can maintain its shape even at thermal runaway temperatures, thereby preventing and delaying thermal runaway. Furthermore, due to its excellent quasi-non-combustible and thermal insulation properties, the battery cell pad for secondary batteries according to the present invention can be used as fireproof products such as fireproof tents and fireproof curtains, or as a fireproof structural material for building exterior walls, etc. Attached Figure Description

[0021] Figure 1 This is a perspective view showing the structure of the cell pad for a secondary battery according to the present invention.

[0022] Figure 2 This is a perspective view showing that the cell pad for a secondary battery according to the present invention is disposed between the cells located in the battery pack.

[0023] Figure 3 This is a graph showing the test results of the combustion performance of the cell pad for secondary batteries according to the present invention. Detailed Implementation

[0024] All technical terms used in this invention, unless otherwise defined, have the following meanings and conform to the common understanding of those skilled in the art related to this invention. Furthermore, although preferred methods or samples are described in this specification, similar or equivalent methods or samples are also included within the scope of this invention.

[0025] The term “about” means a change of about 30%, 25%, 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% in a reference quantity, level, value, number, frequency, percentage, size, quantity, weight, or length.

[0026] In this specification, unless the context otherwise requires, the words “comprising” and “including” shall be understood to include the steps or components mentioned, or groups of steps or components, but do not exclude the inclusion of any other steps or components, or groups of steps or components.

[0027] Figure 1 The structure of the cell pad according to the present invention is shown. See also Figure 1 The battery cell pad for secondary batteries according to the present invention includes a polymer foam 11, a carbon fiber composite 12 attached to both sides of the polymer foam, and an adhesive layer (not shown) located between the polymer foam and the carbon fiber composite layer.

[0028] The aforementioned polymer foam 11 can be prepared by mixing an intumescent flame retardant composition, a foaming agent, and fumed silica into a rubber selected from the group consisting of silicone rubber, thermoplastic elastomers, and EPDM rubber, and then compressing it. Preferably, for every 100 parts by weight of the rubber (selected from the group consisting of silicone rubber, thermoplastic elastomers, and EPDM rubber), it may contain 100 parts by weight of a flame retardant (FR-IFC, intumescent flame retardant composition) and 40 to 60 parts by weight of fumed silica; additionally, it may contain 1 to 10 parts by weight of a foaming agent, dispersant, crosslinking agent, etc., as additives.

[0029] Polymer foams can be made from various types of rubber, thermoplastic elastomers, polyolefin polymers, etc., and preferably from a rubber selected from the group consisting of silicone rubber, thermoplastic elastomers, and EPDM rubber. Specifically, considering the temperature dependence of the compression set properties (creep, stress relaxation) of one of the main specifications of the battery cell pad, silicone rubber, which has the best heat resistance among rubbers, can be used.

[0030] The aforementioned polymer foam can be prepared by mixing an intumescent flame retardant composition, fumed silica, and a foaming agent into a rubber selected from the group consisting of silicone rubber, thermoplastic elastomer, and EPDM rubber, and then by compression molding or continuous foaming.

[0031] The compression molding method described above involves loading the mixture (compound) into a mold, compressing it using a compression press under specific temperature, pressure, and time conditions, and then decompressing (removing pressure) to produce foam. This is known as compression molded foam. According to one embodiment of the invention, it can be prepared by mixing an intumescent flame retardant composition (FR-IFC), fumed silica, and a foaming agent into the rubber, followed by applying a peroxide crosslinking system and compression molding.

[0032] The above-mentioned continuous foaming method is a continuous process in which the above-mentioned mixture (compound) is fed to an extruder, discharged from the extruder die to form an extruded sheet, and then subjected to hot air vulcanization (HAV; curing tunnel) to form foam.

[0033] The aforementioned carbon fiber composite 12 can be prepared by coating a quasi-non-combustible slurry containing an intumescent flame-retardant composition onto a carbon fiber nonwoven fabric. The aforementioned carbon fiber nonwoven fabric is not particularly limited and can be a recycled carbon fiber nonwoven fabric.

[0034] According to embodiments of the present invention, the carbon fiber nonwoven fabric can be treated with a sizing agent before the coating step described above. The sizing agent comprises a liquid epoxy resin and hydrophilic fumed silica. There are no particular limitations on the liquid epoxy resin; known products can be used. The sizing agent can be applied to the surface of the carbon fiber nonwoven fabric using methods such as spraying, blade coating, or slot coating, and then dried and cured. Treating the carbon fiber nonwoven fabric with the sizing agent can improve the adhesion to the quasi-non-combustible sizing agent.

[0035] The above-mentioned coating steps for quasi-non-combustible slurry can be achieved through continuous or discontinuous processes.

[0036] In continuous processes, any of the following methods can be used: roller coating, slot coating, or blade coating, to coat both sides of the sized carbon fiber nonwoven fabric with a quasi-non-combustible slurry, followed by heat treatment to cure it. Another method is to use a rotocure machine to coat the carbon fiber nonwoven fabric with the quasi-non-combustible slurry and then cure it through heat treatment.

[0037] In the above curing step, a drying curing machine can be used. For example, an air-medium dryer, such as a hot air curing tunnel (HACT) or an ultra-high frequency-hot air curing tunnel (UHF-HACT), can be used to bond and cure the carbon fiber nonwoven fabric with the quasi-non-combustible slurry as a matrix resin. The preferred curing temperature is 150°C to 200°C, and the curing time is 2 to 10 minutes. The curing time is a factor that determines the length of the drying curing machine.

[0038] Discontinuous processes can be used for both mass production and small-batch production.

[0039] Specifically, the quasi-non-combustible slurry is coated onto sized carbon fiber nonwoven fabric and dried. Then, it is die-cut according to the size of the battery cell pad and dried and cured using a compression press. This process requires a preforming (die-cutting) machine and a mold for compression curing.

[0040] Regarding the aforementioned quasi-non-combustible slurry, for every 100 parts by weight of water-soluble epoxy resin or vinyl acetate copolymer, it may contain 80 to 150 parts by weight of an intumescent flame retardant composition (FR-IFC), 40 to 60 parts by weight of aluminum hydroxide, 1 to 10 parts by weight of an aqueous solution of montmorillonite (G5 clay (MMT)-nanocomposite), and 1 to 10 parts by weight of a polyoxyethylene (propylene-ethylene) copolymer. The quasi-non-combustible slurry can be prepared using various types of mixers. Dissolvers, ribbon mixers, batch mixers, and planetary mixers can be used; for large-scale production, in-line mixers can also be used. The viscosity of the quasi-non-combustible slurry is a medium viscosity of approximately 50,000 to 100,000 cps, thus allowing for selection based on production volume. The aforementioned montmorillonite aqueous solution is a nanocomposite in which montmorillonite (MMT) is dispersed in deionized water in an exfoliated state. The exfoliated MMT nanocomposite exhibits excellent barrier and flame retardant properties and can provide a flame retardant enhancement effect (synergistic effect). When preparing G5 clay nanocomposite, an inline mixer or an ultrasonic mixer can be used.

[0041] In addition, the above-mentioned intumescent flame retardant composition may contain 20 to 40 parts by weight of melamine, 20 to 40 parts by weight of carbamide (urea), and 30 to 50 parts by weight of D-glucol for every 100 parts by weight of ammonium polyphosphate. The intumescent flame retardant composition (FR-IFC) is an intumescent flame retardant system that forms a carbon barrier on the substrate surface, effectively blocking the supply of oxygen and providing nitrogen, thereby achieving an excellent flame retardant layer.

[0042] The polymer foam and carbon fiber composite prepared by the method described above can be interfacially bonded with an adhesive to prepare a battery cell pad.

[0043] The adhesives mentioned above can be epoxy oil-based flame retardant adhesives or epoxy water-based flame retardant adhesives.

[0044] The aforementioned epoxy-based oil-based flame-retardant adhesives may include one or more epoxy resins, aluminum hydroxide, ammonium polyphosphate, melamine, dicyandiamide, and a latent curing agent. The aforementioned epoxy resins may be BGE modified epoxy resin, CTBN modified epoxy resin, or mixtures thereof. The aforementioned ammonium polyphosphate may be used for intumescent barrier applications, and a latent curing agent (dicyandiamide) may be used to extend the pot life.

[0045] The aforementioned epoxy-based waterborne flame-retardant adhesive contains an equal weight of water-soluble epoxy resin and the aforementioned intumescent flame-retardant composition (FR-IFC), and may also contain a latent curing agent (imidazolium-based, EH5019S) and other additives. The aforementioned waterborne flame-retardant adhesive can improve the flame retardancy of the battery cell pad by including the intumescent flame-retardant composition (FR-IFC).

[0046] The interface-bonded cell pads can be heat-treated using a drying and curing machine to ultimately produce cell pads for secondary batteries. For example, drying and curing can be performed using a hot air curing tunnel (HACT) or an ultra-high frequency-hot air curing tunnel (UHF-HACT) machine, or continuously using a drum vulcanizing machine.

[0047] According to one embodiment of the present invention, a method for preparing a cell pad for a secondary battery is provided, comprising: a step of treating a carbon fiber nonwoven fabric with a sizing agent; a step of coating the sizing carbon fiber nonwoven fabric with a quasi-non-combustible slurry containing an intumescent flame-retardant composition, followed by drying and curing to form a carbon fiber composite; a step of preparing a polymer foam by mixing a rubber selected from the group consisting of silicone rubber, thermoplastic elastomer, and EPDM rubber with an intumescent flame-retardant composition, fumed silica, and a foaming agent to form a compound, followed by compression molding; a step of coating both sides of the polymer foam with an epoxy adhesive and attaching the carbon fiber composite to both sides of the polymer foam; and a step of heat-treating the attached polymer foam and carbon fiber composite to dry and cure them.

[0048] The battery cell pad prepared according to the present invention exhibits flame-retardant properties that meet the KSF ISO 5660-1 (combustion performance test) and KSF 2271 (gas toxicity test for building decoration materials) standards, and is classified as quasi-non-combustible.

[0049] The present invention will be described in detail through the following embodiments, but the scope of the invention is not limited to these embodiments.

[0050] Example

[0051] Prepare a sizing agent with the composition shown in Table 1 below, apply it to both sides of the recycled carbon fiber nonwoven fabric by spraying, and then dry and cure it. Prepare a quasi-non-combustible sizing coating solution with the composition shown in Table 3 below, and apply it to both sides of the sizing-treated carbon fiber nonwoven fabric. After heat treatment, a carbon fiber composite is formed. Prepare an epoxy adhesive with the compositions shown in Tables 7 and 8 below. Apply the water-based epoxy adhesive from Table 8 to both sides of the polymer foam prepared with the composition from Table 9, and then interfacially bond the carbon fiber nonwoven fabric to the polymer foam. After drying and curing, a battery cell pad is formed.

[0052] Table 1

[0053]

[0054] The above-mentioned IL (ionic liquid) silica has the composition shown in Table 2 below.

[0055] Table 2

[0056]

[0057] The quasi-non-combustible slurry coating solution can be prepared using the compositions shown in Tables 3 and 4 below. The composition in Table 4 was used in this embodiment.

[0058] Table 3

[0059]

[0060] Table 4

[0061]

[0062] The above-mentioned G5 clay (MMT)-nanocompoiste has the composition shown in Table 5 below.

[0063] Table 5

[0064]

[0065] The above-mentioned intumescent flame-retardant composition (FR-IFC) has the composition shown in Table 6 below.

[0066] Table 6

[0067]

[0068] The composition of oil-based flame-retardant adhesives is shown in Table 7 below.

[0069] Table 7

[0070]

[0071] The composition of water-based flame retardant adhesives is as follows.

[0072] Table 8

[0073]

[0074] The composition of the polymer foam is shown in Table 9 below. The following compositions were mixed and then compressed to prepare the polymer foam.

[0075] Table 9

[0076]

[0077] Experimental Example

[0078] After preparing three test specimens according to the method described in the examples, combustion performance tests were conducted according to KSF ISO 5660-1, and gas toxicity tests of building decoration materials were conducted according to KSF 2271. The results are shown in Table 10 and... Figure 3 As shown in the image.

[0079] Table 10

[0080]

[0081] As shown in Table 10 and Figure 3 As shown, the battery cell pad according to the present invention meets the KSF ISO 5660-1 and KSF 2271 test standards. This confirms that the above-mentioned battery cell pad has quasi-non-flammable properties.

Claims

1. A cell pad for a secondary battery in an electric vehicle, characterized in that, include: The polymer foam, the carbon fiber composite attached to both sides of the polymer foam, and the adhesive layer located between the polymer foam and the carbon fiber composite layer. The carbon fiber composite is prepared by coating a quasi-non-combustible paste containing an intumescent flame-retardant composition onto a carbon fiber nonwoven fabric. The quasi-non-combustible slurry comprises, for every 100 parts by weight of water-soluble epoxy resin or vinyl acetate copolymer, 80 to 150 parts by weight of an intumescent flame retardant composition, 40 to 60 parts by weight of aluminum hydroxide, 1 to 10 parts by weight of an aqueous solution of montmorillonite, and 1 to 10 parts by weight of a polyoxyethylene (propylene-ethylene) copolymer. The intumescent flame retardant composition comprises, for every 100 parts by weight of ammonium polyphosphate, 20 to 40 parts by weight of melamine, 20 to 40 parts by weight of carbamide and 30 to 50 parts by weight of D-glucol.

2. The cell pad for electric vehicle secondary batteries according to claim 1, characterized in that, The polymer foam is prepared by mixing an intumescent flame retardant composition, fumed silica, and a foaming agent into a rubber selected from the group consisting of silicone rubber, thermoplastic elastomer, and EPDM rubber, and then compressing and molding it.

3. The cell pad for electric vehicle secondary batteries according to claim 1, characterized in that, The adhesive layer includes an epoxy oil-based flame-retardant adhesive or an epoxy water-based flame-retardant adhesive.

4. The battery cell pad for an electric vehicle secondary battery according to claim 1, characterized by The carbon fiber nonwoven fabric is treated with a sizing agent comprising liquid epoxy resin and hydrophilic fumed silica.

5. A method for producing an electrode sheet for a secondary battery of an electric vehicle, characterized by comprising the steps of: include: The step of applying a sizing agent to carbon fiber nonwoven fabric; The step of coating a quasi-non-combustible slurry containing an intumescent flame-retardant composition onto the carbon fiber nonwoven fabric that has been treated with a sizing agent, and then drying and curing it to produce a carbon fiber composite. The step of preparing polymer foam by mixing one rubber selected from the group consisting of silicone rubber, thermoplastic elastomer and EPDM rubber, an intumescent flame retardant composition, fumed silica and a foaming agent and then compressing and molding the mixture. The steps include coating both sides of the polymer foam with an epoxy adhesive and attaching the carbon fiber composite to both sides of the polymer foam; as well as, The steps of heat-treating the attached polymer foam and the carbon fiber composite to dry and cure them are as follows: The quasi-non-combustible slurry comprises, for every 100 parts by weight of water-soluble epoxy resin or vinyl acetate copolymer, 80 to 150 parts by weight of an intumescent flame retardant composition, 40 to 60 parts by weight of aluminum hydroxide, 1 to 10 parts by weight of an aqueous solution of montmorillonite, and 1 to 10 parts by weight of a polyoxyethylene (propylene-ethylene) copolymer. The intumescent flame retardant composition comprises, for every 100 parts by weight of ammonium polyphosphate, 20 to 40 parts by weight of melamine, 20 to 40 parts by weight of carbamide and 30 to 50 parts by weight of D-glucol.

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