Assembly of battery components using an adhesive layer

Abstract

A method of bonding a stack 200 of prismatic battery cells 1 to a cooling plate 2 within a vehicle battery module comprises dispensing a two-component adhesive composition onto a bonding face of the cell stack or the cooling plate as a continuous bead in a zigzag pattern. The bonding face on which the adhesive has been dispensed is compressed against the other bonding face until the adhesive composition forms a coalesced adhesive layer 6 with an average thickness of 0.5 to 3 mm, before curing takes place. The two-component adhesive has a viscosity between 220-290 Pa.s and a flow rate between 5.5-7.5 cm3 / s. The compression step takes place at a velocity between 12-18 mm / min and a compressive stress between 0.011-0.114 MPa. The final adhesive layer has a tensile strength of at least 0.5 MPa at 25°C and is formed within 55-60 minutes of dispensing the two-component adhesive. A battery module comprising a stack of enclosed prismatic battery cells 1 adhered to a cooling plate 2 by a continuous thermally conductive adhesive layer, and an adhesive layer 6 for bonding a cell stack of a traction battery of an electric vehicle to a cooling plate are also disclosed.

Description

TECHNICAL FIELD The present disclosure relates to a method of bonding a stack of battery cells to a cooling plate. In particular, but not exclusively, the invention relates to a method of bonding a stack of prismatic battery cells to a cooling plate within a vehicle battery module. Aspects of the invention relate to a method of bonding a cell stack to a cooling plate, a battery module comprising a stack of enclosed prismatic battery cells adhered to a cooling plate by a continuous layer of a thermally conductive adhesive material, and an adhesive layer for bonding a cell stack of a traction battery of an electric vehicle to a cooling plate and positioned between the cooling plate and the cell stack. BACKGROUND Battery-powered vehicles now constitute the most rapidly expanding sector of the automotive industry, spurring a surge in innovation within vehicle battery technology. As manufacturers strive to meet the increasing demand for battery-powered vehicles, they are placing a strong emphasis on enhancing the efficiency and thermal management of battery cells within the modules. In electric vehicles, there are mainly two types of batteries commonly used: traction batteries and auxiliary batteries. Traction batteries are the primary power source for electric vehicles. These batteries are typically high-capacity and designed for sustained discharging and recharging cycles. Lithium-ion batteries are the most common type of traction battery used in electric vehicles. Electric vehicles also include auxiliary batteries, which serve various secondary functions, such as powering onboard electronics, lights, and accessories. Traction batteries are typically made up of individual lithium-ion battery cells. Several battery cells can be configured by connecting them in either series or parallel, allowing for the creation of a larger battery assembly or a stack of battery cells capable of delivering high voltage and high current. The battery cells can be packaged together with various mechanical and electrical couplings between the battery cells to form the assembly. There are different types of battery cells, for instance flat, curved, rounded, and cylindrical variations. Additionally, prismatic or pouch-shaped batteries can be arranged in a stacked configuration to improve space usage and reduce the overall footprint of the assembly. During the charging and discharging processes, the battery cells generate heat. The accumulation of heat within the battery assembly can significantly impact the performance of these battery cells. The need to manage heat generated during charging and discharging processes has led to the integration of cooling systems within battery modules. These cooling systems can take the form of heat sinks, fluid heat exchangers, which function by circulating air over the cells, or they may employ liquid cooling mechanisms. A specific example of a cooling system is the cooling plate. The cooling plate, functioning as a heat sink, may typically have a large surface and is made of a thermally conductive material, such as metal, which allows it to efficiently absorb and spread out the heat. As the battery cells produce heat, this thermal energy flows from the cells into the cooling plate. The cooling plate then serves as a pathway for the heat to spread over a larger surface area. Therefore, a thermal connection must be established between the battery cells and the cooling plate. To facilitate this thermal connection, the bonding gap between the cooling plate and the battery stack is typically filled with a Thermal Interface Material (TIM). TIMs are designed to transfer heat from one surface to another. Thermal Interface Material (TIM) is a substance or compound that is applied between two surfaces to enhance the thermal coupling between them. Its primary purpose is to fill in the microscopic gaps and imperfections between the two surfaces, typically a heat-generating component (like a CPU or GPU) and a heatsink or heat spreader. Thermal Interface Materials (TIMs) are engineered with a primary focus on improving heat transfer rather than providing structural support between two components. As a result, they are generally designed with properties that prioritize thermal conductivity over mechanical strength. One alternative for attaching the cooling plates to the battery cell stack is the use of mechanical fasteners, such as screws, bolts, or clamps. These fasteners are tightened to create a strong and reliable connection between the cooling plate and the battery stack. However, using mechanical fasteners can lead to a complex assembly and the assembly time can be longer compared to other attachment methods like adhesive bonding. The utilization of adhesives or adhesive compositions as an alternative to mechanical fasteners for attaching cooling plates to battery stacks necessitates the careful selection of an adhesive that is not only thermally conductive but also mechanically strong. While the primary role of the adhesives, such as TIM is to facilitate effective heat dissipation from the battery to the cooling plate, it is equally important to choose an adhesive that can provide a robust mechanical bond. This is important to withstand operational stresses and ensure the long-term integrity of the bond. Alongside selecting an adhesive with the right thermal and mechanical properties, it is desirable to manage how the adhesive is applied, ensuring the adhesive is dispensed precisely and cures effectively to avoid issues like air entrapment, which can compromise the overall efficacy and durability of the bond. In any adhesive bonding process, precise dispensing of adhesive composition presents challenges, including the need for accurate selection and control of adhesive flow rates, dispensing patterns, the dispensing of the correct volume of the adhesive in an accurate and repeatable manner and enabling appropriate curing times to ensure reliable and durable bonds. Accurate control over these aspects of the adhesive application process is important because of the risks associated with air entrapment, as air entrapment may lead to adhesive failure. Air entrapment refers to the presence of air bubbles or air voids within the adhesive after it has been applied and cured. When adhesive is applied between two surfaces and then compressed, any air that is trapped and not able to escape forms these air voids. The process of compression reduces the routes available for the air to escape, leading to the formation of the air voids. This is problematic for several reasons. Firstly, the air voids reduce the mechanical strength of the bond, as the adhesive layer is not uniform and continuous due to the presence of these voids. Also, the air is a poor conductor of heat, leading to reduced thermal conductivity of the adhesive layer. Further, these air voids can create hot spots or uneven cooling across the battery stack, potentially leading to thermal runaway or reduced battery life. There is a need for a bonding method between a battery cell stack and a cooling plate that substantially eliminates, or at least reduces, the entrapment of air within the adhesive, ensuring or promoting a void-free bond. There is also a need fora bonding method to join the battery cell stack and the cooling plate that relatively quickly and evenly dispenses adhesive in a predefined pattern while achieving highly uniform and reproducible bonding results. There is a need for adhesive that can quickly establish a strong bond within a very short time after application whilst still meeting good heat transfer criteria. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION According to an aspect of the invention for which protection is sought, there is provided a method of bonding a cell stack to a cooling plate, wherein the cell stack is for a traction battery of an electric vehicle and comprises enclosed prismatic cells, the method comprising: i. dispensing a two-component adhesive composition in a continuous zigzag pattern onto a bonding face of the cell stack or a bonding face of the cooling plate; ii. compressing the bonding face of the cell stack, or the bonding face of the cooling plate, on which the two-component adhesive composition is dispensed, against the other of the bonding face or the cell stack, until the adhesive composition forms a coalesced adhesive layer; and iii. curing the adhesive composition to form an adhesive layer. This method advantageously establishes a robust bond between the cell stack and cooling plates, in part by reducing air bubbles in the adhesive, while also ensuring effective thermal conductivity between these two bonding faces, thereby advantageously improving heat transfer properties at the bonding faces. “Zigzag” may be understood to be an undulating pattern such as a sawtooth or other pattern comprising straight lines joined at vertices, a serpentine pattern such as a sine wave comprising a continuous curved line, or a combination thereof. Examples discussed herein relate to zigzag patterns comprising a series of straight lines joined at vertices though other examples comprising at least partly curved lines may be envisaged. According to an aspect of the invention for which protection is sought, there is provided a method of bonding a cell stack to a cooling plate, wherein the cell stack is for a traction battery of an electric vehicle and comprises enclosed prismatic cells, the method comprising: i. providing a two-component adhesive composition having a viscosity in the range of from 220 Pa.s to 290 Pa.s, as determined by ASTM D2196-2015, and a flow rate in the range of from 5.5 cm3 / s to 7.5 cm3 / s, ii. dispensing the adhesive composition onto a bonding face of the cell stack or a bonding face of the cooling plate, respectively, as a continuous bead in a zigzag pattern; iii. compressing the bonding face of the cell stack, or the bonding face of the cooling plate, on which the two-component adhesive composition is dispensed, against the other of the bonding face or the cell stack, at a velocity of from 12 mm / min to 18 mm / min and compressive stress in the range of from 0.011 MPa to 0.114 MPa until the adhesive composition forms a coalesced adhesive layer with an average thickness of 0.5 to 3 mm between the two bonding faces; and iv. curing the thermal adhesive composition, v. forming an adhesive layer having a tensile strength of at least 0.5 MPa at 25°C by within 60 minutes of dispensing the two-component adhesive composition. The velocity may be from 14 mm / min to 16 mm / min, for example, 15 mm / min. Such methods of dispensing and compressing the adhesive composition in the present invention offers an enhanced bonding technique. This technique is designed to establish a robust bond between the cell stack and cooling plates, while also ensuring effective thermal conductivity between these two bonding faces (surfaces). Additionally, it guarantees a curing process that can achieve an adhesive layer with a tensile strength of at least 0.5 MPa, for example 1 MPa, for example 1.3 MPa within 60 min of post-mixing the two components of the adhesive composition, improving both structural integrity and thermal management. The method of the present invention further provides substantially uniform and repeatable bonding of the cooling plate to the stack of prismatic battery cells. Another step in the method may comprise transferring the cell stack bonded to the cooling plate from an adhesive application position to a vehicle mounting position or to a storage position. Advantageously, the bonding process may be integrated into a further manufacturing line, for example being mounted in the vehicle or being moved to storage for later vehicle mounting. The cooling plate may comprise a metal or metal alloy, for example aluminium or an aluminium alloy, so the cooling plate bonding face may also comprise a metal or metal alloy, for example aluminium or an aluminium alloy. In some examples the cooling plate may be formed substantially of metal or metal alloy. The (battery) cells of the stack may be enclosed in a thermoplastic polymer material, for example a polyethylene terephthalate casing, wherein the bonding face of the cell stack is substantially formed from the thermoplastic polymer material, for example from a polyethylene terephthalate. Advantageously the prismatic cells are secured with a mechanically robust wrapper with good heat transfer properties. The cell stack bonding face may be formed by an underside of the cell stack. Each prismatic cell may comprise a dilatation groove positioned on its lower surface 4 to accommodate excess thermally conductive adhesive, for example, during the step of compressing the bonding face of the cell stack, or the bonding face of the cooling plate, on which the two-component adhesive composition is dispensed, against the other of the bonding face or the cell stack. Advantageously, the formation of air voids or trapped air is reduced within the thermally conductive adhesive used for bonding the battery cell stack to the cooling plate. The thermally conductive adhesive may be applied to the stack of battery cells. The thermally conductive adhesive composition may be applied to the cooling plate. The thermally conductive adhesive may be applied to the stack of battery cells and the cooling plate in some examples, for example to coincide on pressing the stack of battery cells and the cooling plate together, and / or to adhere different portions of the stack of battery cells and the cooling plate, In an embodiment, the two-component adhesive composition may be applied to the cooling plate or the stack of battery cells by one or more nozzles. Such a nozzle provides an efficient way to spread a layer of adhesive of constant thickness. Dispensing of the two-component adhesive composition may be carried out by an automated dispenser unit, for example wherein the automated dispensing of the adhesive bead is performed at a constant deposition velocity in the range of from 150 mm / s to 190 mm / s. In an embodiment, the flow rate of the adhesive composition is 6.3 cm3 / s at a constant deposition velocity in the range of from 150 mm / s to 190 mm / s. In an embodiment, the adhesive is a two-component adhesive. The two-component adhesive composition may comprise a reactive resin component and a curing agent, or two reactive components and a catalyst. Once these two components are mixed, the cure reaction starts. Normally the formulations will cure at room temperature although cure rates can be increased by raising the temperature. The reactive resin may comprise an optionally functionalized (meth)acrylic resin, epoxy resin, polyisocyanate resin, and / or a silicone resin. The two-component adhesive composition may comprise a thermally conductive adhesive composition. In some examples there may be one or more additional materials included in the two-component adhesive. The adhesive composition may further comprise at least one filler, such as metal or metal oxide particles, pigments or carbon-based fillers; one or more rheology additives such as a thixotropic agent, one or more diluents, dispersants, surface treatment agents, and / or flame retardants. Provision of the adhesive composition may comprise in-situ mixing of the components. The adhesive may be dispensed in a zigzag pattern, advantageously allowing any trapped airto escape during compression and making the bond stronger and more reliable. In an embodiment, the adhesive layer may attain a tensile strength at or above 1.3 MPa within 60 minutes from dispensing. According to a further aspect of the invention, there is provided a battery module comprising a stack of enclosed (encased) prismatic battery cells adhered to a cooling plate by a continuous layer of a thermally conductive interface adhesive material, the layer having a thermal conductivity of at least 3 W / mK and a tensile strength at or above 1.3 MPa (as determined by the test in Example 2) at room temperature (22 to 25 °C) within 55 minutes to 60 minutes of curing. The two-component adhesive composition may be applied in continuous layer. The continuous layer of a thermally conductive interface adhesive material may be substantially free from enclosed air voids, and in some examples, the continuous layer may cover at least 80% of the surface of the cooling plate. The thermally conductive adhesive layer may have an average height of from 1 mm to 3 mm, for example 2 mm. The bead may be deposited as a uniform bead having an essentially (i.e. mostly, subnstantially) crescentshaped cross-section with a width in the range of from 5 mm to 10 mm, for example of from 6 mm to 8 mm. The bead may be deposited with a height in the range of from 5 mm to 8 mm. Advantageously, adhesive layer heights and bead dimensions have been found to provide strong bonding and good thermal conductivity. According to a further aspect of the present invention, there is provided a battery pack comprising a plurality of battery modules as described above. According to a further aspect of the present invention, there is provided a vehicle comprising a battery module as described above. According to a further aspect, there is provided an adhesive layer for bonding a cell stack of a traction battery of an electric vehicle to a cooling plate and positioned between the cooling plate and the cell stack, wherein the adhesive layer is obtained under a compressive stress of from 0.011 MPa to 0.114 MPa by applying a two-component adhesive composition with a post-mixing viscosity in the range of from 220 Pa.s to 290 Pa.s, (as per ASTM D2196-2015) and dispensed in a zigzag pattern at a flow rate in the range of from 5.5 cm3 / s to 7.5 cm3 / s on the cooling plate, wherein the adhesive layer has a tensile strength of at least 0.5 MPa when measured in an environment of 25°C within 60 minutes of dispensing the two-component adhesive composition. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in anyway and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. The above features and advantages of the present invention will be better understood with reference to the accompanying figures and detailed description of embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 illustrates an assembled battery cell stack in accordance with embodiments of the invention. FIG. 2 shows schematically a plurality of prismatic battery cells bonded to a cooling plate in accordance with embodiments of the invention. FIG. 3 shows a graph illustrating results from embodiments of the invention, showing the response of a polyurethane adhesive composition to tensile stress over a period, factoring in the cure time and the impact of the bond gap, at a velocity rate of from 12 mm / min to 18 mm / min. FIG. 4 illustrates a graph that illustrates the tensile strength after 1 hr of cure vs different bond gaps (0.5 mm, 1 mm, 1.5 mm) illustrating results from embodiments of the invention; FIG. 5 illustrates methods according to embodiments of the invention; and FIG. 6 shows a schematic vehicle comprising a battery cell stack according to embodiments of the invention. DETAILED DESCRIPTION In the battery manufacturing industry, the use of adhesive materials is common for bonding components such as battery cells to cooling plates to fora battery module. The precise dispensing of adhesive presents unique challenges, including the need for accurate control of adhesive flow rates, dispensing patterns, elimination of any air voids or air bubbles in the adhesive material, the dispensing of the correct volume of the adhesive in an accurate and repeatable manner and curing times to ensure reliable and durable bonds. When these components, both typically characterized by flat surfaces, are joined together, the process can trap air or gaseous bubbles within the adhesive layer, leading to the formation of air voids. In the context of battery assemblies, if these air voids are not effectively eliminated, they can compromise the integrity of the adhesive bond. This, in turn, can lead to failures in the thermal management system of the battery, impacting overall performance and reliability. In light of these challenges, one of the aims of the present invention is addressing the issue of air entrapment in adhesive layers used in battery assembly processes. This invention ensures a more reliable and effective bonding between battery cells and cooling plates, crucial for improving both the thermal management and the overall performance of battery systems. Further, the proposed method not only focuses on eliminating air voids but also ensures the formation of a strong bond between the components in a specific timeframe. This approach is designed to achieve a predetermined tensile strength of the adhesive layer, further enhancing the bond’s durability and the overall efficacy of the thermal management within the battery module. Accordingly, as shown in FIG. 5,the present invention relates to a method 500 of bonding a cell stack to a cooling plate, wherein the cell stack is for a traction battery of an electric vehicle and comprises enclosed prismatic cells. The method comprises: i. providing 502 a two-component adhesive composition having a viscosity in the range of from 220 Pa.s to 290 Pa.s, as determined by ASTM D2196-2015, and a flow rate in the range of from 5.5 cm3 / s to 7.5 cm3 / s, ii. dispensing 504 the adhesive composition onto a bonding face of the cell stack or a bonding face of the cooling plate, respectively, as a continuous bead in a zigzag pattern; iii. compressing 506 the first surface against the second surface at velocity of from 12 mm / min to 18 mm / min mm / min and compressive stress in the range of from 0.011 MPa to 0.114 MPa until the adhesive composition forms a coalesced adhesive layer with an average thickness of 0.5 -3 mm between the two bonding faces; and iv. curing 508 the thermal adhesive composition, v. forming 510 an adhesive layer having a tensile strength of at least 0.5 MPa at 25°C within 55 to 60 minutes of dispensing the two-component adhesive composition. The present invention also relates to a battery module 100 as shown in FIG. 1, comprising a stack of enclosed prismatic battery cells as shown in FIG. 2, adhered to a cooling plate 2 by a continuous layer of a thermally conductive interface adhesive material 6, the layer having a thermal conductivity of at least 3 W / mK and a tensile strength at or above 1.3 MPa at 25° obtained within 55 to 60 minutes of dispensing the two-component adhesive composition. Upon complete curing at room temperature (22°C -25°C), which can take up to 24 hours, the adhesive layer achieves a tensile strength of at least 2.5 MPa. In another aspect, the present invention relates to an adhesive layer 6 for bonding a cell stack 200 of a traction battery of an electric vehicle to a cooling plate 2 and positioned between the cooling plate 2 and the cell stack 200, wherein the adhesive layer 6 is obtained under a compressive stress of from 0.022 MPa to 0.114 MPa by applying a two-component adhesive composition with a post-mixing viscosity in the range of from 220 Pa.s to 290 Pa.s, (as per ASTM D2196-2015) and dispensed in a zigzag pattern at a flow rate in the range of from 5.5 cm3 / s to 7.5 cm3 / s on the cooling plate, wherein the adhesive layer has a tensile strength of at least 0.5 MPa when measured in an environment of 25°C within 60 minutes of dispensing the two-component adhesive composition. Definitions and Abbreviations As used herein: The term “room temperature” refers to a temperature of 22°C to 25°C. The terms “cure” or “curable” refer to joining polymers chains together by covalent chemical bonds, usually via crosslinking molecules or groups. The term “wetting” refers to the ability of the adhesive to spread out and intimately contact a solid surface. Good wetting occurs when a liquid spreads evenly across a surface. The term “in situ means “on site or “in place . for example, the adhesive composition being applied directly to the surface of the component that it will be bonding, without the need for any intermediate steps or processing. The term “thixotropic” refers to refers to a property of certain fluids or gels that are thick or viscous under static conditions but become less viscous and more fluid when agitated, shaken, or otherwise stressed. The terms “void”, “air void”, “bubble”, “air bubble”, “air gap”, “air pocket” are used herein interchangeably. The terms “cell” and “battery cell,” are used herein interchangeably. The terms as “stack,” “cell stack,” and “battery cell stack,” are used interchangeably herein. The term “work life” of an adhesive refers to the period after mixing (in the case of multi-component adhesives) or after opening (for single-component adhesives) during which the adhesive remains usable and retains its ability to bond effectively. During this time, the adhesive maintains a workable consistency, viscosity, and bonding properties after curing. The term “adhesive” or “adhesive composition" refers to a substance used to bind materials together by surface attachment, typically providing a strong and lasting bond. As used herein, “polyol” refers to any compound comprising two or more hydroxyl groups: the term is thus intended to encompass diols, triols and compounds containing four or more -OH groups. As used herein the term “fatty” means any compound that contains one or more residues of fatty acids. “Fatty acid” in turn denotes any predominately unbranched, non-cyclic (for example substantially linear) aliphatic carboxylic acid that substantially comprises, or consists of, an aliphatic hydrocarbon chain and at least one carboxyl group, for example a single terminal carboxyl group. Fatty acids may comprise a limited number of other substituents such as hydroxyl and may be saturated, mono-unsaturated or poly-unsaturated. The battery described in the embodiments of the present application may refer to a rechargeable battery. In the following, a lithium-ion battery will be taken as an example to describe the embodiments disclosed in the present application, for example a traction battery. It should be understood that the embodiments disclosed in the present application are applicable to any other suitable types of rechargeable batteries. The battery mentioned in the embodiments disclosed in the present application can be directly or indirectly applied to an appropriate device to power the device. The rechargeable batteries, particularly lithium-ion types such as those as discussed in the application, may be designed to be implemented in electric vehicles, either directly or indirectly. In high-power applications like electric vehicles, the battery system includes three levels: battery cell, battery module and battery pack . The battery module is formed by electrically connecting a certain number of battery cells together by a busbar assembly and putting them into a frame to protect the battery cells from external impact, heat, vibration, etc. The battery modules may be connected in series to create a battery pack. The battery pack is the final state of the battery system mounted into the electric vehicle. The battery pack generally includes a case for packaging one or more battery cells. The case can prevent liquid or other foreign objects from affecting the charging or discharging of the battery cell. The case is generally composed of a cover body and a case shell. FIG. 1 illustrates an assembled battery module 100 comprising a plurality of cell stacks 200 as shown in FIG. 2. The battery cell, or simply referred herein as the cell, is the basic unit in the battery, and may be generally grouped, according to the way of packaging, into: a cylindrical battery cell, a prismatic battery cell 1 or a pouch battery cell. The following will mainly focus on the prismatic battery cell 1, as shown in FIG. 2. It should be understood that the embodiments described below are also applicable to the cylindrical battery cell or the pouch battery cell in certain aspects. A prismatic cell stack 200 refers to an assembly where multiple prismatic cells 1 are aligned and integrated together. These prismatic cells 1 have rectangular shapes and are encased in a hard outer shell, typically made of steel or aluminium. This robust outer shell not only provides structural integrity but also aids in protecting the cell’s internal components. The design of prismatic cells 1 allows for efficient use of space within the battery pack, as their flat surfaces facilitate closer packing without significant wasted space. When these cells are stacked to form a prismatic cell stack 200, the arrangement is done in a manner that improves both energy density and thermal management. The prismatic cells 1 may have an insulation covering the outer shell, such as polyvinyl chloride, polyethylene terephthalate (PET), polypropylene, polyimide films, for example polyethylene terephthalate (PET). The battery or battery module may also include a thermal management component. The thermal management component in a battery system, as described, is designed to regulate and control the temperature of the battery cells. The management and adjustment of the temperature may include heating or cooling the plurality of battery cells 1. For example, in the case of cooling or lowering the temperature of the battery cells 1, the thermal management component is configured to dissipate heat generated by the battery cells 1 during operation, such as during charging and discharging processes. In this case, the thermal management component may also be called a cooling component, a cooling system or a cooling plate 2. The cooling plate 2 typically may consist of a thermally conductive material, such as aluminium or copper, and is designed to have direct thermal contact with the cells 1 or their housing; that is, there is a thermal pathway from the cooling plate to the cells to channel excess heat away from the cells. It may incorporate channels or pathways for a coolant fluid to flow through, which helps in transferring heat away from the cells. This setup ensures that the temperature of the cells 1 remains within an advantageous range, enhancing their performance and safety. The thermal management component, in particular the cooling plate 2 may be attached to the cell stack 200 by means of a thermally conductive adhesive composition 6 to provide a good thermal pathway from cells to cooling plate. The present invention relates to a method of bonding a cell stack 200 to a cooling plate 2, utilizing an adhesive as the bonding agent. The cell stack 200 is for a traction battery of an electric vehicle and comprises a plurality of prismatic cells 1 stacked together to define a substantially rectangular cell stack bonding face 4. The cooling plate 2 comprises a substantially rectangular cooling plate bonding face 5 which corresponds to the bonding face 4 of the cell stack 200; This approach involves the application of adhesive in a specific pattern, i.e., a zigzag pattern which can be executed on either the bonding face 5 of the cooling plate 2 or the bonding face 6 of the battery cell stack 200. The prismatic cells 1 also may be arranged next to each other in a horizontal arrangement, side-by-side, creating a flat, wide assembly forming a cell stack 200, or in a vertical arrangement, where the cells are stacked one on top of the other, rather than being laid out side-by-side. This vertical arrangement may create a taller, narrower assembly compared to the flat, wide structure of the horizontal arrangement. The cell stack 200 may have a top surface 3 and a bottom surface 4 as shown in FIG. 2. In the prismatic cell stack 200 with a side-by-side arrangement, the cooling plate 2 may be typically placed directly underneath the horizontally aligned cells 1 or on the bottom surface 4 of the prismatic cell stack 200. The bottom surface 4 is the surface through which heat is transferred to the cooling plate 2 for dissipation. The bottom surface 4 is formed by the collective alignment of individual prismatic cells 1, each with its own width and length dimensions. The bottom surface 4 of the prismatic battery cell stack 200 is referred herein also as a cell stack bonding face 4. This terminology is used to specifically identify and refer to the lower side 4 of the prismatic cell stack 200 that interfaces with the cooling plate bonding face 5, as shown in FIG. 2. This bottom surface 4 of the cell stack 200 is in direct contact with the cooling plate. The cooling plate is designed to match the dimensions of this bottom surface, ensuring that each cell’s lower surface area is in thermal contact with the plate for effective heat dissipation. Each prismatic cell 1 in the stack has at least two key dimensions - width and length. These prismatic cells 1 are flat, with a rectangular shape. Each prismatic battery cell 1 may also have a lower surface 4 and a central line running along the length of this lower surface 4. The lower surface 4 of each cell is defined by the width (the shorter side of the rectangle) and length (the longer side) of each cell 1. The lower surface 4 of the cell, is the surface where the adhesive 6 may be applied to be bonded with the cooling plate 2. The central line runs lengthwise along the prismatic cell 1, effectively bisecting its width, and creating symmetrical halves on either side. The prismatic battery cells 1 may be placed next to each other in a horizontal layout. This means their lengths are aligned parallel to each other, and theirwidths are positioned adjacent. The side-by-side placement creates a flat, wide assembly. When the cells 1 are aligned side-by-side, these central lines run parallel to each other across the entire bottom surface 4 of the prismatic battery cell stack 200. Each cell may comprise a dilatation groove (or simply, a groove) positioned on its lower surface 4 to accommodate excess thermally conductive adhesive. This dilatation groove may be located along the central line of each prismatic cell. Typically, in the assembly of prismatic cell stacks 200, a bead of adhesive may be applied along the central line of each prismatic cell, following a specific pattern. In an embodiment, the adhesive 6 may be a two-component adhesive 6 with high thermal conductivity. A two-component adhesive 6, also known as a two-part adhesive 6, is a type of bonding agent that consists of two separate components which must be mixed together before use. These two components typically include a resin or base, i.e., the main component of the adhesive 6, providing the primary bonding properties, and hardener or activator, i.e., a component that reacts with the resin to cause the adhesive 6 to set or cure. Once these two components are mixed, the cure reaction starts. Normally the formulations will cure at room temperature. Room temperature curing adhesives 6 eliminate the need for elevated temperatures during the curing process, reducing the risk of subjecting the battery to damaging heat. Two-component adhesive 6 types may include epoxies, acrylics, silicones and polyurethanes. In an embodiment, the two-component adhesive composition 6 may comprise a first component and a second component, with the first component comprising at least one polyol, selected from the group consisting of fatty alcohols, polyester polyols, polyether polyols, polyether-polyester polyols and polycarbonate polyols; The polyol may have a molecular weight Mw of 300 to 1,200 g / mol, in particular 400 to 1,000 g / mol. Examples of commercially available polyols are, for example, DESMOPHEN 1262 BD from Covestro, or VORANOL WD 2104 Polyol from Dow. The second component may comprise at least one polyisocyanate, a compound with reactive isocyanate groups (NCO). In some embodiments, the polyisocyanate-containing compound may be reaction products of hydroxylterminated polybutadiene with an excess amount of isocyanates. The isocyanates compound may be selected from the groups consisting of 1, 5-naphthylendiisocyanate (NDI) , 2, 4 ‘-or 4, 4‘-diphenylmethandiisocyanate (MDI), isomers oftoluylendiisocyanates (TDI), methylentriphenyltriisocyanate (MIT), hydrated MDI (H12MDI) , tetramethylxylylendiisocyanate (TMXDI) , 1-isocyanatomethyl-3-isocyanato-1, 5, 5-trimethylcyclohexane (IPDI), xylylendiisocyanate (XDI) , hexan-1, 6-diisocyanate (HDI), pentamethylendiisocyanate, dicyclohexylmethandiisocyanate as well as dimers, trimers, oligomers and polymers of the same. (Poly) isocyanate prepolymers can, for example, be obtained by reacting a polybutadiene diol with an excess amount of aromatic isocyanate. The hydroxyl-terminated polybutadiene can be a polybutadiene diol having terminal hydroxyl groups and a number-average molecular weight (Mn) in the range of 1,000 -5,000 g / mol, or 1,200 -4,500 g / mol, or 2,000 -3,000 g / mol, and / or an average hydroxyl (OH) functionality in the range of 1.7 - 3.5, or 1.9-2.6, or 2.2-2.5. The first component may further comprise a crosslinker and thermal conductive fillers. Usually, crosslinkers are low molecular weight molecules used to link the polymer and form a network structure. The crosslinker may be selected from the group consisting of triol polyether polyol, triol polyester polyol and mixtures thereof. Upon mixing these components, a cross-linking reaction occurs, which results in the formation of the polyurethane polymer network. Further, the two-component adhesive composition 6 may comprise one or more further materials such as thermal conductive fillers, pigments, rheology modifiers, drying agents, flame retardants, surface active agents and anti-foaming agents. The thermal conductive filler may be selected from the group consisting of metal oxides, nonmetal oxide, metal nitride, nonmetal nitride, metal hydroxides, metal silicates, metal sulfides and combinations thereof. Suitable metal oxides to be used as the thermal conductive fillers may be selected from the oxides of metals selected from the group consisting of tin, indium, antimony, aluminium, titanium, iron, magnesium, zinc, rare earth metals, alkaline metals, oxides of Mg, Ca, Sr and Ba, mixed metal oxides and mixtures thereof. The primary function of thermal conductive fillers is to enhance the heat dissipation capability of the adhesive. Thus, the two-component adhesive composition 6 is also a thermal adhesive composition 6. The performance of the bonds made from two-component adhesives 6 depends on having the correct ratio of components intimately mixed and applied within the working life of the system. Mix ratios of adhesive components can vary enormously, and the ratios may be in the range from 4:1 to 1 :4, for example from 2:1 to 1 :2, for example 1 :1. It’s important to mix these compounds with adequate shear forces to ensure a uniform mixture. Various mixing tools can be used for effective blending, including static mixers, magnetic stirrer setups, wire whisk devices, augers, batch mixers, planetary mixers, C.W. Brabender or Banbury® style mixers, and high-shear mixing equipment such as blade-style blenders and rotary impellers. The adhesive composition 6 according to the invention may have a viscosity of no more than 1500 Pa s, for example no more than 1,000 Pa s, e.g. 30 to 800 Pa s, or 220 to 700 Pa s,220-290 Pa.s, or 260 to 270 Pa.s, as determined at 25°C (tested by Anton Paar Rheometer, using a PP25 spindle, at the shear rate of 1 s1 according to ASTM D2196-2015). The two component curable compositions may exhibit an initial viscosity - determined immediately after mixing, for example, up to two minutes after mixing - of less than 400 Pa.s, for instance less than 300 Pa.s, at 25°C, for example equal to or less than 290 Pa.s, according to ASTM D2196-2015. In accordance with the broadest process aspects of the present invention, the above described composition may be applied to the material layer(s) and then cured in situ. Before applying the compositions, it is typically recommended to pre-treat the target surfaces to eliminate any foreign substances. This preparatory step, when applicable, can significantly enhance the adhesion of the compositions to these surfaces, such as mechanical etching, chemical etching, solvent cleaning, plasma treatment, or corona treatment. The adhesive composition 6 may be dispensed from a moving dispensing nozzle, which is part of a robotic system, positioned above the surface to be bonded. The dispensing applicator may have a two-component mixing valve, enabling the adhesive components 6 to be mixed and applied in situ. In a preferred embodiment, the thermally conductive adhesives may be liquid. In a preferred embodiment, the thermally conductive adhesive 6 is applied in a zigzag pattern onto the bonding face of either the cooling plate or the stack of cells. The zigzag pattern addresses challenges associated with adhesive bonding, such as the minimization of air entrapment by providing an air escape path. The alternating angles of the zigzag pattern create channels through which air can be pushed out as the adhesive is applied and the surfaces are brought together. This reduces the likelihood of air pockets or bubbles, which are poor conductors of heat and can significantly hinder heat transfer. As the cooling plate and cell stack 200 are compressed together, the thermally conductive adhesive 6 is displaced from the corners (vertices) of the zigzag pattern, effectively spreading and filling the spaces between the line segments to prevent the formation of air gaps or air voids, providing a more uniform adhesive layer without air gaps, that ensures that heat is distributed more evenly across the interface between the cell stack 200 and the cooling plate, improving this way the heat transfer efficiency. The adhesive composition is pushed away from the corners of the zigzag pattern and spreads evenly between the line segments of the zigzag pattern. By doing so, it effectively fills the spaces between these line segments, thereby eliminating the possibility of voids forming. By filling the spaces between these line segments, the total contact area of the bonding surfaces is enhanced, which in turn improves the adhesion strength and the heat transfer, as it ensures more extensive and uniform contact between the surfaces. The zigzag pattern may extend from one side of the bonding face to the other. The zigzag pattern may be applied in a continuous manner, starting from a first edge region of the bonding face of the cooling plate to an opposing second edge region of the bonding face. The cooling plate may have a substantially rectangular shape that closely matches the bottom surface 4 of the cell stack 200, ensuring a complementary and precise fit. The line segments of the zigzag pattern may run parallel to the longer sides (length) of the rectangular cooling plate. When the cooling plate and the cell stack 200 are pressed together, each angled line segment on the cooling plate aligns with and adheres to the lower surface 4 of each individual prismatic cell in the stack. This ensures that there is one angled line segment corresponding to each cell. Each angled line segment may align with the central line of each cell. Instead of spreading a thin layer of adhesive across the entire surface, the method may include applying small “beads” or lines of adhesive. These beads are like tiny ridges or rows of the material. The adhesive may have a high thermal conductivity between 2 to 3.5 W / mK, determined according to ISO 22007-2-2015. The cooling plate and the cell stack 200 are compressed (by clamping , pressing) at velocity of from 12 mm / min to 18 mm / min mm / min (e.g. from 14 mm / min to 16 mm / min, e.g. 15 mm / min) and until the thermally conductive adhesive composition forms a coalesced adhesive layer with an average thickness of from 0.5 mm to 3 mm between the cell stack bonding face and cooling plate bonding face. The Applicants have surprisingly found, that at this velocity the adhesive spreads evenly between the surfaces without creating excessive pressure that might squeeze out too much adhesive or cause uneven thickness. Even spreading is a fundamental part of the wetting process, where the adhesive covers the entire surface area it is meant to bond with. The compression force used for compressing the two bonding faces is chosen such as to ensure proper contact between the adhesive and the bonding face to which the adhesive is being applied. This compression force helps to spread the adhesive evenly, ensuring it penetrates any surface irregularities and maximizes the contact area. This provides that the adhesive wets the surfaces while starting to cure into a strong, cohesive bond. TABLE 2 shows examples of compression force (N) and compressive stress (MPa)(the compressive force per unit area ) (see column peak stress in TABLE 2). Applicants have tested different adhesive composition, and have surprisingly found that a composition with the viscosity of 220 to 290 Pa.s can be compressed to a bond gap (0.5 mm, 1 mm, 1.5 mm) and can develop the necessary bond strength under a compressive stress (compressive force per surface area) selected in the range of from 0.011 to 0.114 MPa, with a surface area between 314.1593 to 1256.637 mm2, for example 0.021 to 0.114 Mpa with a surface area 1256.637 mm2 and a bond gap in the range of 0.5 to 1 mm, or 0.022 to 0.027 MPa with a surface area of 314.1593 mm2 and a bond gap of 0.5 mm, or 0.089 to 0.114 MPa (surface area 1256.637 mm2) and a bond gap of 0.5 mm, or 0.021 to 0.03 MPa (surface area 1256.637 mm2) and a bond gap of 1 mm, or 0.011 to 0.012 MPa (surface area 1256.637 mm2) and a bond gap of 1.5 mm. FIG. 3 and FIG. 4 both illustrate graphs of time (s) on the horizontal axis vs Force (N) on the vertical axis. FIG. 3 shows tensile force vs cure time for a 0.5mm bond gap, 40mm disc, compressed at 15mm / min velocity. Traces #1, #2, #3 and #4 refer to the tests of those number in TABLE 1. FIG. 4 shows tensile force vs cure time for a 1 hour cure time, 40mm disc, compressed at 15mm / min velocity. Traces #2, #5, #10, #11, #12 and #13 refer to the tests of those number in TABLE 2. Generally the bond strength (e.g. peel strength, tensile strength, overlap shear strength or impact strength) of the adhesive layer continues to build well after the initial cure time enabling the adhesive layer to achieve a tensile strength of at least 2.5 MPa at temperature in the range of from 22°C to 25°C within 24 hours of curing. The thermally conductive adhesive layer formed between the cooling plate and the cell stack may have a tensile strength that exceeds 0.5 MPa within 60 minutes of curing (see FIG. 3 and FIG. 4 , and TABLE 1 and TABLE 2). The thermally conductive adhesive layer formed between the cooling plate and the cell stack may have a tensile strength that exceeds 1 MPa within 60 minutes of curing, as shown in FIG. 3 and FIG. 4, and TABLE 1 and TABLE 2. This enables the cell stack together with the cooling plate to be lifted and inserted into the battery pack, all within a timeframe of 60 minutes following the mixing of the two-component adhesive composition. In an embodiment, the cooling plate bonding face may be formed of metal, such aluminium or aluminium alloy, and the cell stack bonding face may be formed of thermoplastic polymer, for example a polyethylene terephthalate. Therefore, the adhesive must be chemically compatible with both aluminium (or its alloy) and PET. For achieving the desired level of tensile strength within the range of from 30 min to 120 min, for example 60 minutes post-mixing the two components of the adhesive composition, it is necessary to determine an effective flow rate for dispensing the adhesive. This flow rate is crucial to ensure uniform and precise application, directly influencing the curing process and the development of tensile strength. Simultaneously, selecting an adhesive composition with an appropriate viscosity is equally important. The right viscosity not only facilitates efficient application and spreading but also plays a vital role in achieving the necessary bonding characteristics within the specified timeframe. The synergy between the carefully selected flow rate and the viscosity of the adhesive composition is fundamental to meeting the requirement of significant tensile strength development within the 60-minute timeframe. Applicants have found that applying a bead of adhesive in a zigzag pattern at flow rate in the range of from 5.5 to 7.5 cm3 / s, for example 6.3 cm3 / s at 150 to 190 mm / s robot speed and having a viscosity in the range of from 220 to 290 Pa.s, as tested by Anton Paar MC301 Rheometer, with a gap of 500 pm, at 25°C, and a shear rate of 2.4 per second, results in adhesive that within 60 min of post-mixing the two component adhesive, achieves a tensile strength, determined at 25°C, of at least 0.5 MPa, for example of at least 0,9 MPa, for example of at least 1 MPa, for example of at least 1.3 MPa. In a preferred embodiment, the adhesive may have a thickness ranging from 0.5 to 3 mm. Generally, to maximize the heat conduction through the adhesive layer and to minimize the cost, the adhesive should be as thin as possible , while maintaining good contact with the cooling plate. In a preferred embodiment, the two-component adhesive cures at room temperature, or at a temperature no greater than 30°C, for example no greater than 25°C or even no greater than 20°C. The two-component adhesive composition may be mixed and dispensed in situ. In a preferred embodiment the adhesive is applied between a cooling plate made of aluminium and cells being enclosed in polyethylene terephthalate and forming a cell stack bonding face made of polyethylene terephthalate. EXAMPLES The following describes an illustrative and non-limiting examples. FIG. 3 presents a graph that analyses the response of a two-component thermally conductive polyurethane adhesive composition with viscosity in the range of 220 to 290 Pa.s after mixing at room temperature to tensile stress over a period of 30 min to 2hr, all at a velocity rate of from 12 mm / min to 18 mm / min e.g. 15 mm / min. The size of the aluminium disc was 40 mm the bond gap 0.5 mm. For example, series 2 at 1 hr cure time and peak force of 3920 N, had a tensile strength (peak stress) of 3.12 MPa. FIG. 4 shows a graph that illustrates the tensile strength after 1 hour of cure time. The size of the bond gap was (e.g., 0.5 mm, 1 mm, 1.5 mm). The velocity rate was of 15mm / min. The size of the aluminium disc was 40 mm. The material tested was a two-component thermally conductive polyurethane adhesive composition with viscosity in the range of from 220 to 290 Pa.s after mixing at room temperature. The curing of the adhesive composition was also at room temperature. For example, Sample 10 with a 1 mm bond gap exhibited a tensile strength of 2.89 MPa after curing for 1 hour at room temperature (22-25 °C), with a peak force of 3633 N. On a PET surface, the same sample achieved a lower tensile strength of 0.89 MPa and a peak force of 1115 N. Notably, all samples in the test series achieved the target minimum tensile strength of 0.5 MPa. TIM Bond gap (mm) Disc size (mm) Rate (mm / min) Specimen # Cure time Peak force (N) Peak Stress (MPa) 2k Polyurethane Mix ratio 1:1 Viscosity 220-290 Pa.s At 25°C 94 shore A 0.5 0.5 15 1 2h 3888 3.09 2 1h 3920 3.12 3 45 min 267 0.21 4 30 min 102 0.08 11 (PET) 1 h 1389 1.11 1 1 6 (1 min delay) 10s 30 0.02 7 (6min delay) 10s 26 0.02 8 (12min delay) 10s 27 0.02 9 (20min delay) 10s 28 0.02 10 1 h 3633 2.89 12 (PET) 1h 1115 0.89 1.5 1.5 1h 1520 1.21 13 (PET) 1h 1634 1.30 TABLE 1 illustrates a tensile summary table indicating tensile strength vs cure time vs bond gap. TABLE 1 presents a summary table which demonstrates that the adhesive layer achieves a minimum tensile strength of 0.5 MPa after a cure time of 1 hour. This level of strength is maintained consistently across various bond gap sizes - 0.5 mm, 1 mm, and 1.5 mm - as detailed in FIG. 3 and FIG. 4. This level of tensile strength is significant as it meets the minimum requirement for safely lifting the cell stack using the cooling plate. The material tested was a two-component polyurethane adhesive composition, with viscosity of from 220 to 290 Pa.s after mixing at room temperature. The curing of the adhesive composition was also at room temperature. In the test, discs with sizes of 20 mm and 40 mm were used and with surface area of 314.1593 mm2 and 1256.637 mm2 respectively. TIM Bond gap (mm) Disc size (mm) Rate (mm / min) Specimen # Peak force (N) Peak stress (MPa) Peak Stress (kPa) 2k Polyurethane Mix ratio 1:1 Viscosity 220-290 Pa.s At 25°C 94 shore A 0.5 20 15 14 7.0 0.022 22 15 8.4 0.027 27 40 1 112.1 0.089 89 2 128.8 0.103 103 3 137.6 0.110 110 4 135.1 0.107 107 11 (PET) 143.3 0.114 114 1 6 (1 min delay) 38.0 0.030 30 7 (6 min delay) 34.2 0.027 27 8 (12 min delay) 37.3 0.030 30 9 (20 min delay) 36.7 0.029 29 10 37.5 0.030 30 16 26.9 0.021 21 12 (PET) 37.0 0.029 29 1.5 5 14.2 0.011 11 13 (PET) 15.2 0.012 12 TABLE 2 illustrates a tensile summary table indicating compressive force vs bond gap. TABLE 2 shows an embodiment of the present invention. The table illustrates the relationship between compression force and bond gap of the adhesive composition in accordance with the present invention. (PET) indicates that the base plate was wrapped in PET to represent the cell surface. (X min delay) indicates if there was an intentional delay between applying the glue bead and closing joints. FIG. 6 shows a schematic vehicle comprising a battery cell stack according to embodiments of the invention. The material tested was a two-component polyurethane adhesive composition, with viscosity in the range of from 220 to 290 Pa.s after mixing at room temperature. The curing of the adhesive composition was also at room temperature . In the test, aluminium discs with sizes of 20 mm and 40 mm were used and with surface area of 314.1593 mm2 and 1256.637 mm2 respectively. For example, a peak stress 0.022-0.027 MPa was observed when closing a bond gap of 0.5 mm using a 20 mm disc. While when closing a bond gap of 0.5 mm with 40 mm disc, the peak force was in the range of from 0.089 to 0.114 MPa. When closing a bong gap of 1 mm with a 40 mm disc, the peak stress was in the range of from 0.021 to 0.030 MPa. Sample 10 was tested, when closing a bond gap of 1 mm, at velocity 15 mm / min with a disc size of 40 mm , and a peak stress of 0.030 MPa was observed. Further, sample 10 had a tensile strength of 2.89 MPa within 60 min of applying the adhesive composition at 25 °C, as shown in TABLE 1. EXAMPLE 1 Two-component mixing valve applicator was used, namely static mixer ME 13-24T with a system temperature of 35 °C (mixing valve temperature 35 °C) and robot arm KUKA KR201. A two-component polyurethane adhesive composition was used. The first component was selected from polyether polyol and also comprising a crosslinker, and the second component was selected from isocyanate-containing compound and / or a (poly) isocyanate prepolymer. Further, one of the components comprised a thermal conductive filler, being from 82.5 to 85.0 wt. percent based on the total amount of the composition. The two components were mixed by a static mixing system at volume ratio of 1: 1. The mixed material was applied in a form of a bead of adhesive by the robot equipped with a dispenser. The robot path was 2 mm away at both sides from the centre point to give more air evacuate path. The target volume (4+ 1 beads) was 42,4 ± 4 cm3. The bond gap was 1 mm, compression force 1730 N. The viscosity (2.4 s-1) of the adhesive was in the range of from 220 to 290 Pa.s, measuring the viscosity according to ASTM D2196-2015, as tested by Anton Paar MC301 Rheometer, with a gap of 500 pm, at 25°C, and a shear rate of 2.4 / second, and thermal conductivity of 3.0 W / mK, as measured by ASTM D5470. The working time of the adhesive was approximately 20 min. The thermally conductive adhesive composition was a two-component adhesive composition, curable at room temperature (25 °C), with a mixing ratio (resin: hardener) of 1:1. The application parameters were: flow rate of 6.3 cm3 / s and middle point speed of 160 mm / s, triangle point speed of 170 mm / s, offset 18 mm. The width of each cell was approximately 20 mm. The beads were applied off-centre in a zigzag pattern, not directly along the central line of the lower surface of the cell 4 to ensure that the adhesive spreads evenly when pressure is applied and the angle (vertex) formed where two adjacent angled line segments meet was approximately 15 degrees. It was visually observed that the process yielded a result with no air voids present. EXAMPLE 2 Tensile test procedure The tensile strength of an adhesive is a critical measure indicating the maximum load or stress it can withstand per unit area before experiencing failure, which can be calculated using the following formula: a=F / A, where o (sigma) represents the tensile strength, • F is the force applied to the adhesive measured in Newtons (N), and • A is the cross-sectional area over which the force is distributed, measured in square meters (m2). A bead of a two-component thermally conductive adhesive composition, with a main component polyurethane was applied onto a base plate via manual dispense. The viscosity of the mixed adhesive composition was between 220 - 290 Pa.s, as measured by ASTM D2196-2015. An aluminium circular disk (40 mm diameter) was then gradually lowered onto the adhesive bead at a controlled rate of 15 mm / mm until it reached a preliminary bond gap of 2 mm. This position was maintained for approximately 10 seconds, during which time the force exerted was continuously recorded. This step was crucial for ensuring complete wetting out of the adhesive across the joint. Following the initial 10-second period, the disk was further lowered to establish the final bond gap (1.5 mm, 1 mm, 0.5 mm). This final position was held steady fora minimum of another 10 seconds, and during this phase, the compressive force was again recorded, allowing the adhesive to stop its flow. After this stage, the specimen was either left to cure for a predetermined duration or subjected to a tensile test (pulled apart) at a rate of 15 mm / min. This process ensured a controlled and consistent application of the adhesive, critical for evaluating its bonding characteristics and mechanical strength. The test results are shown in FIG. 3 and FIG. 4. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. A method of bonding a cell stack to a cooling plate, wherein the cell stack is for a traction battery of an electric vehicle and comprises enclosed prismatic cells, the method comprising:(i) providing a two-component adhesive composition having a viscosity in the range of from 220 to 290 Pa.s, as determined by ASTM D2196-2015, and a flow rate in the range of from 5.5 to 7.5 cm3 / s,(ii) dispensing the adhesive composition onto a bonding face of the cell stack or a bonding face of the cooling plate, respectively, as a continuous bead in a zigzag pattern;(iii) compressing the bonding face of the cell stack, or the bonding face of the cooling plate, on which the two-component adhesive composition is dispensed, against the other of the bonding face or the cell stack, at a velocity of from 12 mm / min to 18 mm / min and compressive stress in the range of from 0.011 to 0.114 MPa until the adhesive composition forms a coalesced adhesive layer with an average thickness of 0.5 to 3 mm between the two bonding faces; and(iv) curing the thermal adhesive composition,(v) forming an adhesive layer having a tensile strength of at least 0.5 MPa at 25°C by within 55 to 60 minutes of dispensing the two-component adhesive composition.

2. The method according to claim 1, wherein the velocity is from 14 mm / min to 16 mm / min.

3. The method according to claim 2, wherein the bead is deposited as a uniform bead having asubstantially crescent-shaped cross-section with one or more of a width in the range of from 5 to 10 mm, and a height in the range of from 5 to 8 mm.

4. The method according to any preceding claim, wherein the adhesive layer attains a tensile strength at or above 1.3 MPa within 60 minutes from dispensing.

5. The method according to any preceding claim, wherein the cooling plate comprises a metal or metal alloy.

6. The method according to any preceding claim, wherein the two-component adhesive composition comprises a reactive resin component and a curing agent, or two reactive components and a catalyst.

7. The method according to any preceding claim, wherein the reactive resin comprises one or more of: an optionally functionalised (meth)acrylic resin, epoxy resin, polyisocyanate resin, and a silicone resin.

8. The method according to any preceding claim, wherein the battery cells are enclosed in a thermoplastic polymer material, and wherein the bonding face of the cell stack is substantially formed from the thermoplastic polymer material.

9. The method according to any preceding claim, wherein provision of the two-component adhesivecomposition comprises m-situ mixing of the components of the two-component adhesive composition,10. The method according to any preceding claim, wherein dispensing of the two-component adhesive composition is carried out by an automated dispenser unit.

11. The method according to any preceding claim, wherein two-component adhesive composition further comprises at least one filler from:, metal particles, metal oxide particles, pigments, carbon-based fillers, a rheology additive, a thixotropic agent, a diluents, a dispersants, a surface treatment agents, and a flame retardant.

12. A battery module, comprising a stack of enclosed prismatic battery cells adhered to a cooling plate by a continuous layer of a thermally conductive adhesive material, the layer having a thermal conductivity of at least 3 W / mK and a tensile strength at or above 1.3 MPa.

13. The battery module of claim 12, wherein the continuous layer of a thermally conductive interface adhesive material is substantially free from enclosed air voids.

14. A vehicle comprising the battery module according to claim 11 or claim 12.

15. An adhesive layer for bonding a cell stack of a traction battery of an electric vehicle to a cooling plateand positioned between the cooling plate and the cell stack, wherein the adhesive layer is obtained under a compressive stress of from 0.011 to 0.114 MPa by applying a two-component adhesive composition with a post-mixing viscosity in the range of from 220 to 290 Pa.s, (as per ASTM D2196-2015) and dispensed in a zigzag pattern at a flow rate in the range of from 5.5 to 7.5 cm3 / s on the cooling plate, wherein the adhesive layer has a tensile strength of at least 0.5 MPa when measured in an environment of 25°C within 60 minutes of dispensing the two-component adhesive composition.Application No: GB2406109.5Examiner:Contract Unit ExaminerClaims searched: 1-15Date of search: 10 January 2025Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X Y X,Y Y Y X X,E X: 1,2,4-9, 11-15 Y: 3,10 X: 1,2,4- 9, 11-15 Y: 3, 10 3 10 15 1, 12, 15 US2018 / 358666 Al (SIERING SEBASTIAN ET AL) paragraph [0002] - paragraph [0004], paragraph [0024], paragraph [0046] - paragraph [0049]; pages 1, 2, 3C; figures 1, 2, 3C JP2015207541A (HITACHI CONSTRUCTION MACHINERY) the whole document US2019 / 181514 Al (YAMASHITA AKI) figures 1, 10-13, paragraph [0043] WO2023 / 102525 Al (PPG IND OHIO INC) the whole document GB2611813 A (JAGUAR LAND ROVER LTD) the whole document WO2024 / 157602 Al (AESC JAPAN LD) the whole documentCategories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of same category'. before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:24International Classification:Subclass Subgroup Valid From HO IM 0010 / 653 01 / 01 / 2014 B29C 0065 / 00 01 / 01 / 2006 B29C 0065 / 48 01 / 01 / 2006 B29C 0065 / 52 01 / 01 / 2006 HO IM 0010 / 613 01 / 01 / 2014 HO IM 0010 / 625 01 / 01 / 2014 HO IM 0010 / 647 01 / 01 / 2014 HO IM 0010 / 6554 01 / 01 / 2014 HO IM 0050 / 209 01 / 01 / 2021 HO IM 0050 / 244 01 / 01 / 2021 HO IM 0050 / 249 01 / 01 / 2021 HO IM 0010 / 6556 01 / 01 / 2014

Images