Thermal Trigger Primer and Thermosetting Adhesive Multilayer Composition for Separation of EV Battery Pack

Abstract

The method is to separate a battery pack adhered to a substrate by a multi-layer composition, which includes a step of heating the multi-layer composition to a separation temperature above 60°C, where the multi-layer composition includes one or more thermoplastic primer layers having a transition temperature in the range of 60°C to 120°C and one or more thermosetting adhesive layers; and a step of separating one or more layers of the multi-layer composition to separate the battery pack from the substrate, where the substrate has a surface energy of 35 dynes / cm or more. The separation may include the above steps.

Description

Technical Field

[0001] Embodiments relate to methods and systems that include separable battery assemblies manufactured using a thermally separable multilayer adhesive composition.

[0002] Introduction Thermoplastic and thermosetting adhesives are used in a number of industrial applications, including flexible packaging and the attachment of electric vehicle (EV) batteries. In most applications, thermosetting adhesives are selected based on bond strength, substrate compatibility, and long-term durability under operating conditions. However, in many applications, the attached components must be separated for component servicing or replacement. To separate an EV battery bonded to a thermosetting adhesive layer, for example, physical removal methods such as prying, cutting, or laser ablation are typically used. Other approaches involve the use of solvents or acids to remove the thermosetting adhesive, which can pose chemical hazards and provide limited penetration into the adhesive layer. Another concern with common separation methods is their effectiveness in high surface area attachments, including those present in EV battery packs, which can lead to damage to the adhered components.

Summary of the Invention

[0003] The method disclosed herein may include separating a battery cell adhered to a substrate by a multilayer composition, the method including heating the multilayer composition to a separation temperature above 60°C, the multilayer composition including one or more thermoplastic primer layers having a transition temperature in the range of 60°C to 120°C and one or more thermosetting adhesive layers; and separating one or more layers of the multilayer composition to separate the battery cell from the substrate, the substrate having a surface energy of 35 dynes / cm or greater.

Detailed Description of the Invention

[0004] Embodiments relate to a method and system that include a separable battery assembly manufactured using a thermally separable multilayer adhesive composition. In particular, the method includes the separation of one or more components of a composition of a battery assembly that includes a multilayer composition by directed heating from a heat source such as a heat management plate. In some instances, a heat management plate (e.g., a water-cooled plate for an EV battery) can be used to heat the multilayer composition above the transition temperature (e.g., 50 °C to 130 °C) of one or more thermoplastic layers, thereby enabling the thermoplastic primer layer to be automatically or mechanically assisted in separating from an attached surface (e.g., a high surface energy substrate, a thermoset adhesive layer, etc.) while minimizing deformation or damage.

[0005] Electric vehicle battery designs often include one or more battery packs containing multiple battery cells individually bonded to various types of substrates. EV batteries can also include several external features, including several enclosures and substrates, to protect the battery pack and the battery cell arrays. Due to the large surface contact area of the battery components (e.g., about 0.5 m for a pack block 2 to 1.5 m for the entire pack 2 ), and the wide operating temperature range (e.g., -20 °C to 60 °C), thermoset adhesives are often used to provide the bonding strength between the battery and the underlying or overlying substrates and structures. However, the bonding strength of thermoset adhesives makes it difficult to separate the battery pack or the pack substrate without damaging or deforming the bonded components.

[0006] The methods and systems disclosed herein are directed to thermally separable multilayer compositions for separably securing battery components (e.g., battery packs, battery cells) to various types of substrates. The multilayer composition can include one or more thermoplastic primer layers and one or more thermosetting adhesive layers interspersed between two substrates, such as one or more battery cells and a pack substrate (e.g., a battery pack cover, a battery pack bottom, or a thermal management plate). The thermoplastic primer layers disclosed herein can melt or soften at elevated temperatures, which reduces the bond strength of the adhesion of the multilayer composition and allows for the separation of one or more of the constituent layers.

[0007] The thermoplastic primer resins disclosed herein can be separably bonded to one or more of the thermosetting adhesive layer, the pack substrate, and / or the thermal management plate. The thermoplastic primer layer can remain solid and can maintain adhesion performance over the operating temperature for most applications (e.g., less than 50 °C or up to 50 °C maximum), however, it softens and / or melts at a temperature above the glass transition temperature (T g ) or melting temperature (T m ) of the thermoplastic adhesive. The thermoplastic primer layers disclosed herein can have a glass transition temperature (T g ) in the range of 60 °C to 130 °C, 60 °C to 120 °C, 60 °C to 110 °C, or 60 °C to 90 °C.

[0008] A method of separating a battery pack adhered to a substrate by the multilayer composition can include heating the multilayer composition to a "separation temperature" above 60 °C to induce softening or melting of the thermoplastic primer layer, and subsequently separating the battery pack from the substrate by separating one or more layers of the multilayer composition. The separation method can include mechanically separating the primer and / or adhesive layer from the substrate layer by suitable techniques such as prying, wedging, and / or impact. In some cases, gravity or other "passive" techniques can be used to separate one or more layers of the multilayer composition.

[0009] Applying heat to the multilayer composition can involve the use of an external heat source such as an electric heating platform, electric heating pad, electric heating sheet, electric heating blanket, etc., or an internal heat source such as a heat management plate, heat management pad, embedded heating element, etc. Heat management plates are often used to maintain an EV battery within a steady temperature range (e.g., between -20°C and 60°C). During operation, the heat management plate operates to dissipate or supply heat to the EV battery by passive heat transfer (e.g., heat sink) or active heat transfer (e.g., utilizing a flowing fluid or gas). The methods disclosed herein can utilize a heat management plate or other means to directly heat the primer layer and the adhesive layer up to the separation temperature (i.e., above the transition temperature of the thermoplastic primer layer) while minimizing heat transfer from the heat source to the battery pack and subsequent battery damage.

[0010] During heating and separation of the multilayer composition, the method and system can utilize direct heating of the multilayer composition to minimize the measured temperature of the battery pack. When a battery cell is directly bonded to a substrate (e.g., a heat management plate within an EV battery pack), the substrate can function as an internal heat source. When a battery cell is directly joined to a pack substrate (e.g., the bottom or cover of an EV battery pack), the heat source can also be external, such as a heat management platform / pad / blanket that contacts the multilayer composition. In either case, the use of an external or internal heat source causes an initial temperature rise at the contact site (e.g., the thermoplastic primer layer and / or the thermosetting adhesive layer), while limitations in heat transfer result in delayed heating of the spaced components (e.g., the battery cell).

[0011] A series of finite element modeling experiments were conducted on a representative battery assembly containing a battery pack, a multilayer composition, and an external thermal management plate. The experiments showed that while heating by the thermal management plate resulted in local heating within the multilayer composition, the temperature of the adhered battery pack was lower. In particular, when heating was carried out using the thermal management plate at a separation temperature of 100 °C, the temperatures of the thermoplastic primer layer and the thermosetting adhesive layer increased to a maximum of 80 °C in 2 minutes, while the center of the battery pack reached 60 °C in 15 minutes and 80 o °C in 30 minutes. Differential thermal measurements between the battery cells of the battery pack and the multilayer composition indicate that there is a window where the battery pack can be separated from the underlying battery assembly components (e.g., the battery pack bottom, cover, etc. substrates) while the thermoplastic primer layer is softening or melting and before exceeding the processable temperature limit. For example, separation of the battery can occur when the thermoplastic primer layer is at the separation temperature (e.g., 80 °C or higher), while the EV battery remains within its operable upper temperature range, such as within the range of 60 °C to 80 °C or higher.

[0012] The method disclosed herein may include separating the battery pack when the measured battery pack temperature is at least 20 °C, at least 10 °C, or at least 5 °C below the separation temperature. In some cases, the method of separating a battery pack adhered to a substrate by a multilayer composition may include separating the battery pack within 2 - 45 minutes, 2 - 30 minutes, or 2 - 20 minutes after heat is applied to the multilayer composition.

[0013] The multilayer composition may include a high surface energy substrate on which one or more thermoplastic primer layers and / or thermosetting adhesive layers are formed, applied, or deposited. Examples of high surface energy substrates include the surfaces of battery components (e.g., battery packs, or cell frames), the surfaces of substrate packs, the surfaces of thermal management plates, and other surfaces. The battery components disclosed herein may include EV battery packs and substrates including prismatic or pouch cell-based batteries, cylindrical cell batteries, battery packs, etc.

[0014] As used herein, "high surface energy substrate" refers to a substrate having a surface energy of 35 dynes / cm or greater. High surface energy substrates disclosed herein include metals such as aluminum, steel or alloys, zinc, non-metals including glass, polar polymers such as epoxy, polyurethane, or polyester, and coating materials such as epoxy-coated aluminum, polyacrylate-coated aluminum, polyester-liner-coated aluminum. Table 1 includes additional examples of suitable high energy substrates.

[0015]

Table 1

[0016] In some cases, the high surface energy substrate may also be placed in contact with a multilayer composition containing one or more thermoplastic primer layers and / or thermosetting adhesive layers assembled on a second substrate(s). In some cases, the multilayer composition may contain a thermoplastic primer layer in contact with the high surface energy substrate and a thermosetting adhesive in contact with the thermoplastic primer layer. The thermosetting adhesive may also mediate adhesion to a second substrate, such as a heat management plate.

[0017] In another embodiment, the multilayer composition may contain a first thermoplastic primer layer in contact with the high surface energy substrate and a thermosetting adhesive in contact with the first thermoplastic primer layer. The second thermoplastic primer layer may be in contact with the thermosetting resin and may mediate adhesion to the second substrate.

[0018] The multilayer composition may include one or more thermosetting adhesive layers, which may include one or more polyurethanes, epoxies, polyacrylates, polyesters, cross-linked derivatives thereof, etc. The thermosetting adhesive may include a structural adhesive and / or a thermally conductive adhesive having a thermal conductivity in the range of 0.2 W / mK or greater, for example, 0.2 W / mK to 3 W / mK. The thermosetting adhesives disclosed herein can be water-based, solvent-based, or solventless.

[0019] The multilayer compositions disclosed herein may contain one or more thermoplastic primer layers that include one or more thermoplastic polymers. The thermoplastic primer layer may contain maleic anhydride grafted chlorinated polyolefin (MAH-g-CPO) alone or in combination with one or more additional thermoplastic polymers. The maleic anhydride grafted chlorinated polyolefin disclosed herein may have a chlorination degree of 10% - 30% and / or at least 1% of at least one maleic anhydride modified polyolefin. The maleic anhydride grafted chlorinated polyolefin disclosed herein may have a weight average molecular weight of 50,000 Da or more, 60,000 Da or more, or 70,000 or more. The maleic anhydride grafted chlorinated polyolefin may have a weight average molecular weight in the range of 40,000 Da - 100,000 Da, 50,000 Da - 90,000 Da, or 50,000 Da - 80,000 Da.

[0020] The thermoplastic primer layer may contain MAH-g-CPO combined with one or more additional thermoplastic polymers including polyurethane, polyester, polyether, polyacrylate, polycarbonate, maleic anhydride grafted polymers such as maleic anhydride grafted polyolefin (MAH-g-POE), maleic anhydride grafted ethylene-vinyl acetate (MAH-g-EVA), maleic anhydride grafted styrene-ethylene-butylene-styrene (MAH-g-SEBS), etc. The thermoplastic primer layer may include one or more of polyolefin, ethyl vinyl acetate, acrylonitrile-butadiene rubber, butadiene styrene rubber, tackifying resins such as rosin, terpene, and modified terpene, aliphatic, alicyclic, and aromatic resins (such as C5 aliphatic resin, C9 aromatic resin, and C5 / C9 aliphatic / aromatic resin, hydrogenated hydrocarbon resin, terpene-phenol resin, novolac, etc.), organic phase change materials (PCM) such as hydrocarbons, paraffins (such as C n H 2n+2 )), lipids, and liquid crystal materials having phase change characteristics in the temperature range of 60°C - 120°C, etc.

[0021] In some cases, the polarity of the thermoplastic primer layer containing MAH-g-CPO and one or more polar thermoplastic polymers can be adjusted to minimize changes in lap shear strength and cross-tensile strength due to incompatibility with the thermosetting adhesive layer. For example, the thermoplastic primer composition can be modified to include a polar resin (e.g., up to 45 wt%) in order to increase adhesion to polar thermosetting resins such as polyurethane and epoxy.

[0022] The thermoplastic primer layer incorporating multiple polymers can contain the MAH-g-CPO component at a weight percentage (wt%) of 55 wt% or more, 70 wt% or more, or 80 wt% or more. The thermoplastic primer layer can contain MAH-g-CPO at a weight percentage (wt%) in the range of 55 wt% - 100 wt%, 60 wt% - 100 wt%, or 70 wt% - 100 wt%. The thermoplastic primer layer containing a mixture of resins can include MAH-g-CPO and one or more thermoplastic polymer components and / or additives as the balance of MAH-g-CPO at a weight percentage (wt%) in the range of 0 wt% - 45 wt%, 0 wt% - 40 wt%, or 0 wt% - 30 wt%.

[0023] The thermoplastic primer layer can be applied to the adhesive layer and / or the substrate layer as a solid, thin film, hot melt, or powder (e.g., 100 wt% solids). The thermoplastic primer layer can be produced by solvating the MAH-g-CPO resin, optionally together with one or more additional thermoplastic polymers, in a suitable solvent and depositing the resulting solvated resin composition on the substrate or surface. Then, the solvent is evaporated as the thermoplastic primer layer is formed. The suitable solvent may vary depending on the solubility of the selected primer resin or resin mixture and can include aqueous or organic solvents. A mixture of a nonpolar organic solvent and a polar organic solvent can be used. Examples of nonpolar solvents can include cycloalkyl or aromatic species (e.g., methylcyclohexane, toluene, etc.). Examples of polar organic solvents can include methyl ethyl ketone, ethyl acetate, butyl acetate, etc.

[0024] The organic solvent and resin composition may contain one or more primer resins (e.g., solids) in a weight percentage (wt%) in the range of 1 wt% to 35 wt%, 1 wt% to 20 wt%, or 3 wt% to 20 wt%. The organic solvent and resin composition may contain a nonpolar organic solvent in a weight percentage (wt%) in the range of 60 wt% to 99 wt%, 65 wt% to 99 wt%, or 70 wt% to 99 wt%. The organic solvent and resin composition may contain a polar organic solvent in a weight percentage (wt%) in the range of 1 wt% to 40 wt%, 1 wt% to 45 wt%, or 1 wt% to 30 wt%.

[0025] The aqueous resin composition may contain one or more primer resins in a weight percentage (wt%) in the range of 15 wt% to 65 wt%, 20 wt% to 60 wt%, or 30 wt% to 55 wt%. The aqueous solvent and resin composition may contain an aqueous fluid in a weight percentage (wt%) in the range of 35 wt% to 85 wt%, 40 wt% to 80 wt%, or 45 wt% to 70 wt%.

[0026] The thermoplastic primer layer disclosed herein can maintain good bond strength with respect to the bond between the adhesive layer and the substrate. The multilayer composition disclosed herein can have a lap shear strength at room temperature that has a decrease of less than 30% compared to a comparative multilayer composition without a thermoplastic primer layer. The multilayer composition disclosed herein can have a cross-tensile strength at room temperature that has a decrease of less than 30% compared to a comparative multilayer composition without a thermoplastic primer layer.

[0027] The method of preparing a separable multilayer composition disclosed herein may include providing a substrate surface, one or more thermoplastic primer layers, and one or more thermosetting adhesive layers. The thermoplastic primer layer and the thermosetting adhesive layer can be manufactured by coating from a solvent composition by solid deposition or using known methods such as roller coating, flow coating, dip coating, spin coating, spray coating, knife coating, and die coating. The multilayer composition disclosed herein may include a thermoplastic primer layer having a thickness in the range of 0.5 μm to 150 μm, 1 μm to 100 μm, or 5 μm to 90 μm.

[0028] Separation of the substrate from the thermoplastic primer layer and / or the thermosetting adhesive layer can include heating the multilayer composition to a temperature of 60 °C or higher and removing at least one of the layers of the multilayer composition. The method of delivering heat can include internal or external heating. The internal heat source can include a thermal management plate, resistive heating or inductive heating, or other contact-type heating elements. The external heat source can include a heating platform, heating plate or table, heating blanket or sheet, heat gun, steam, etc.

[0029] The separation method can include heating the multilayer composition to a temperature of 60 °C or higher and mechanically separating the primer layer and / or the adhesive layer from the substrate layer by suitable techniques such as prying, wedging, and / or impact.

[0030] The system may include a separable electric vehicle battery system, the separable electric vehicle battery system including an electric vehicle battery and a multilayer composition that adheres the battery to a pack substrate, the multilayer composition including one or more thermoplastic primer layers having a transition temperature in the range of 60°C to 120°C and one or more thermosetting adhesive layers, and a heat source that is in contact with the multilayer composition or functions as a layer thereof (e.g., the thermoplastic primer layer or the thermosetting adhesive layer is directly bonded to a heat management plate or other heat source), the pack substrate being one or more of a pack bottom, a pack cover, or a heat source, the heat source being configured to heat the multilayer composition to a separation temperature in the range of 60°C to 120°C to enable separation of the electric vehicle battery.

Example

[0031] The following examples are presented to illustrate embodiments of the present invention and are not intended to limit its scope. All parts and percentages are by weight unless otherwise indicated. The data and descriptive information provided herein are based on approximations. Table 2 lists the materials used in the following examples.

[0032]

Table 2

[0033] Example 1: Separation Method Using a Heat Management Plate In this example, a sample multilayer composition was used to construct a battery assembly to mediate adhesion between a commercially available battery and a heat management plate. The separation characteristics of the bonded battery assembly were then tested using the method disclosed herein of heating the multilayer composition using the heat management plate to soften or melt the adhesive and / or primer layer to facilitate separation.

[0034] The multilayer composition includes the following layers described in Table 3, and its structural elements are as follows: "battery cell" (including a commercially available LiFePO4 EV battery pack (size: length / width / height = 172 mm / 166 mm / 52.1 mm) with a Type-3 Al surface coated with epoxy), "primer layer" (including a MAH-g-CPO-based primer (thickness of about 13 μm)), "adhesive layer" (including a thermosetting polyurethane adhesive (thermal conductivity of 0.3 w / mK and thickness of about 1 mm)), "pack substrate" (including Type-5 Al (5754) coated with epoxy (thickness 2 mm)), "thermal management plate" (including a forced circulation thermal management plate that can be heated up to 100 °C).

[0035] The comparative example (CE) and the example of the present invention (IE) were adhered between the battery pack and the pack substrate with a polyurethane thermosetting adhesive. The thermoplastic primer layer used in the example was produced by solubilizing primer resin particles of 7 parts of MAH-g-CPO and 3 parts of hydrogenated rosin in an 85:5 mixture of methylcyclohexane and methyl ethyl ketone. The resin particles were added to the flask at a solid content of 10 wt%, and heated to 80 °C with stirring until dissolved. Then, before applying the thermosetting adhesive, the primer resin mixture was applied to the battery pack or the pack substrate.

[0036] The separation test was conducted as follows. Step 1: Samples were prepared according to Table 3 and aged for one week. Step 2: CE1 was placed in an oven at 80 °C for 30 minutes. The remaining samples were placed on a preheated thermal management plate at 100 °C for 5 minutes, and it was ensured that the temperature of the primer layer and the adhesive layer exceeded 80 °C 5 minutes after heat transfer. Step 3: A driver with a length of 21 cm was used to manually perform a separation test between the high-temperature battery cell and the battery substrate. The tip of the driver was placed between the battery pack and the pack substrate to pry open the layers. If the sample could be manually separated within 5 minutes, it was defined as "separable". If the sample could not be manually separated within 5 minutes, it was defined as "non-separable". In order to check the performance at room temperature, a similar test could also be performed on the above samples at room temperature.

[0037]

Table 3

[0038] Sample CE1 is a multilayer composition with a thermosetting 2K PU adhesive without a primer. The battery cell and the multilayer composition were heated under the same conditions in an oven at a separation temperature of 80 °C for 30 minutes. Subsequent attempts to separate the battery cell from the pack substrate failed, indicating that the thermosetting 2k PU adhesive had good bonding with the battery cell and the pack substrate even at high temperature (80 °C). CE2 was the same as CE1 but was heated using a thermal management plate. However, the bonding strength between the thermosetting adhesive, the battery cell, and the pack substrate remained strong after heating, and the separation attempt failed. In the examples of IE1 to IE3 with a thermoplastic primer layer, the thermoplastic primer layer(s) heated to 80 °C (glass transition temperature above 70 °C) was softened or melted to facilitate separation, and separation was possible by manually prying it open.

[0039] While the foregoing is directed to exemplary embodiments, other and further embodiments may be devised without departing from the basic scope thereof, which is determined by the following claims.

Claims

1. A method for separating a battery cell adhered to a substrate by a multilayer composition, comprising: heating the multilayer composition to a separation temperature above 60°C, wherein the multilayer composition comprises one or more thermoplastic primer layers having a transition temperature in the range of 60°C to 120°C and one or more thermosetting adhesive layers; separating one or more layers of the multilayer composition to separate the battery cell from the substrate, wherein the substrate has a surface energy of 35 dyn / cm or more.

2. The method according to claim 1, wherein the heating step comprises heating the multilayer composition using a thermal management plate, pad, or blanket.

3. The method according to claim 1, wherein the heating step comprises heating the multilayer composition using an internal thermal management system such as a water-cooled plate.

4. The method according to claim 1, wherein the one or more thermoplastic primer layers comprise 55 wt% to 100 wt% of maleic anhydride-grafted chlorinated polyolefin.

5. The method according to claim 1, wherein the separating step comprises prying open the multilayer composition.

6. The method according to claim 1, wherein the multilayer composition comprises a thermoplastic primer layer in contact with the substrate.

7. The method according to claim 1, wherein the multilayer composition comprises a thermoplastic primer layer in contact with the battery cell.

8. The method according to claim 1, wherein the battery cell temperature is at least 5°C lower than the separation temperature of the multilayer composition.

9. A separable electric vehicle battery system, comprising: an electric vehicle battery; a multilayer composition for adhering the battery to a pack substrate, the multilayer composition comprising one or more thermoplastic primer layers having a transition temperature in the range of 60°C to 120°C and one or more thermosetting adhesive layers; a heat source in contact with the multilayer composition or being a layer of the multilayer composition; wherein the pack substrate is one or more of a pack bottom, a pack cover, or the heat source; the heat source is configured to heat the multilayer composition to a separation temperature in the range of 60°C to 120°C to enable separation of the electric vehicle battery.

10. The system according to claim 9, wherein the one or more thermoplastic primer layers comprise from 55% to 100% by weight of maleic anhydride-grafted chlorinated polyolefin. **Claim 11** The system according to claim 9, wherein the heat source is a heat management plate.

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