GB2611813A

GB2611813A - Battery components and methods of assembly

Info

Publication number: GB2611813A
Application number: GB2114841.6A
Authority: GB
Inventors: Jones Steve
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2021-10-18
Filing date: 2021-10-18
Publication date: 2023-04-19
Also published as: GB202114841D0

Abstract

A method of thermally coupling a group of cells 100 to a cooling plate 204 involves applying a layer of a liquid thermal interface material 206 to the cooling plate, for example using a fishtail nozzle. At least one dielectric spacer element 208, such as a dielectric mesh or dielectric beads, is provided within the thermal interface material and may be positioned on the cooling plate before or after applying the thermal interface material. A group of cells is then positioned in proximity to the cooling plate, such that the layer of thermal interface material is compressed against the group of cells. The dielectric spacer element maintains a gap (D, Fig 3C) between each of the cells in the group of cells and the cooling plate preventing the cells from coming into electrical contact with the cooling plate. In a battery module a group of cells is positioned in proximity to a cooling plate and are thermally coupled to the cooling plate by a layer of thermal interface material which contains a dielectric spacer element, for example a nylon scrim, fibreglass mesh or dielectric beads.

Description

Battery Components and Methods of Assembly

TECHNICAL FIELD

The present invention relates generally to a method of thermally coupling a group of cells to a cooling plate. In particular, but not exclusively, the invention relates to methods for thermally coupling cells to a cooling plate within a vehicle battery module for incorporation into a vehicle traction battery. Aspects of the invention relate to a method, to a battery module, to a battery pack, and to a vehicle.

INTRODUCTION

There has recently been increased interest in providing battery-powered vehicles, which has led to developments in vehicle battery, in particular vehicle traction battery, technology. Within vehicle battery modules, cells can be cooled via a cooling plate that is thermally coupled to one end of the cells. It is important to ensure that such a cooling plate is in thermal, but not electrical, contact with the cells. This can be achieved by applying a powder coating of a dielectric material onto the surface of the cooling plate. The coating must be sufficiently thick to ensure that it is not removed by any wear that may occur during use of the vehicle. Such coatings can be expensive to apply, and introduce a significant thermal resistance, which is undesirable.

It is an object of the present invention to at least partially mitigate one or more of the above 20 problems.

SUMMARY OF THE INVENTION

According to an aspect of the invention for which protection is sought, there is provided a method of thermally coupling a group of cells to a cooling plate, the method comprising: applying a layer of thermal interface material to the cooling plate, wherein the thermal interface material is applied in a liquid form and at least one dielectric spacer element is provided within the thermal interface material; and positioning the group of cells in proximity to the cooling plate, such that the layer of thermal interface material is compressed against the group of cells, wherein the dielectric spacer element is arranged to maintain a gap of at least a predetermined distance between each of the cells in the group of cells and the cooling plate. Advantageously, the presence of the dielectric spacer element ensures that the cells cannot come into electrical contact with the cooling plate, even if the thickness of the layer of thermal interface material reduces during the service lifetime of the vehicle. This may enable a dielectric coating on the cooling plate to be omitted, or be made thinner. Such coatings are expensive to apply, and also introduce an undesirable increase in thermal resistance, so it is a significant benefit to reduce or obviate the need for such coatings.

In an alternative aspect, the thermal interface material may be applied to the group of cells rather than the cooling plate. Furthermore, in some embodiments, thermal interface material may be applied to both the cooling plate and the group of cells.

In the context of the present specification, the term "within" means that the dielectric spacer element is at least partially surrounded by the thermal interface material. Furthermore, in some embodiments the dielectric spacer element may not be within the thermal interface material when the dielectric spacer element and thermal interface material are first applied.

Instead, the dielectric spacer element may initially be adjacent to the thermal interface material, and the positioning of the group of cells or another subsequent processing step may compress the dielectric spacer element into the thermal interface material.

In an embodiment, the dielectric spacer element comprises a dielectric mesh. Advantageously, such a mesh may be relatively cheap and lightweight, and the thermal resistance introduced by the mesh may be relatively low. Furthermore, the mesh may introduce a predictable amount of material between each cell and the cooling plate.

The dielectric mesh may be a scrim. In some embodiments, a layer of adhesive may be provided on one side of the scrim, and the scrim may be placed onto the cooling plate with the adhesive in contact with the cooling plate. This may help to ensure that the scrim stays in place during the application of the thermal interface material.

In an embodiment, the method comprises positioning the dielectric mesh onto the cooling plate prior to the step of applying a layer of thermal interface material to the cooling plate. Alternatively, the method comprises positioning the dielectric mesh onto the cooling plate after the step of applying a layer of thermal interface material to the cooling plate.

In an embodiment, the dielectric mesh has a spacing of 2-20mm, preferably 5-15mm.

Advantageously, such a spacing ensures that the mesh provides an adequate number of strands between each cell and the cooling plate, especially when cylindrical cells of the size typically used in automotive traction batteries, such as 21700 cells, are used.

In an embodiment, the dielectric mesh is formed from threads having a thickness of 0.1-1mm, preferably 0.2-0.6mm. Advantageously, such threads provide sufficient spacing to ensure that little or no current flows from the cells to the cooling plate.

In an embodiment, the dielectric mesh is a nylon or fibreglass mesh. Such meshes are widely available and provide good dielectric properties. Alternative materials that would also be suitable include Polypropylene, Polyester, PEEK (polyether ether ketone), PTFE, or PET.

In an embodiment, the spacer element comprises a plurality of dielectric beads dispersed within the thermal interface material.

In an embodiment, the dielectric beads have a diameter of 0.1-1mm, preferably 0.2-0.6mm. Advantageously, such beads provide sufficient spacing to ensure that little or no current flows from the cells to the cooling plate.

In an embodiment, the layer of thermal interface material is applied to the cooling plate by one or more fishtail nozzles. Such a nozzle provides an efficient way to spread a layer of thermal interface material of constant thickness. In some embodiments, a single pass of the fishtail nozzle may be adequate, whereas in other embodiments two or more passes may be required.

According to a further aspect of the invention for which protection is sought, there is provided a battery module comprising a group of cells and a cooling plate, wherein the group of cells are positioned in proximity to the cooling plate and are thermally coupled to the cooling plate by a layer of thermal interface material, wherein at least one dielectric spacer element is provided in the layer of thermal interface material, the spacer element being arranged to maintain a gap of at least a predetermined distance between each of the cells in the group of cells and the cooling plate. Advantageously, the presence of the dielectric spacer element ensures that the cells cannot come into electrical contact with the cooling plate, even if the thickness of the layer of thermal interface material reduces during the service lifetime of the vehicle. This may enable a dielectric coating on the cooling plate to be omitted, or be made thinner. Such coatings are expensive to apply, and also introduce an undesirable increase in thermal resistance, so it is a significant benefit to reduce or obviate the need for such coatings.

In an embodiment, the dielectric spacer element comprises a dielectric mesh. The dielectric mesh may have a spacing of 2-20mm, preferably 5-15mm. The dielectric mesh may be formed from threads having a thickness of 0.1-1mm, preferably 0.2-0.6mm. The dielectric mesh may by a nylon or fibreglass mesh. Alternative materials that would also be suitable include Polypropylene, Polyester, PEEK (polyether ether ketone), PTFE, or PET.

In an embodiment, the spacer element comprises a plurality of dielectric beads dispersed within the thermal interface material. The beads may have a diameter of 0.1-1mm, preferably 0.2-0.6mm.

According to a further aspect of the invention for which protection is sought, there is provided a battery pack comprising a plurality of battery modules as described above.

According to a further aspect of the invention for which protection is sought, there is provided a vehicle comprising a battery pack or a battery module as described above.

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 any way 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.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which: Figures 1A-C show different views of a cylindrical cell that may be used in a vehicle battery module (PRIOR ART); Figure 2 shows a battery module in an embodiment of the present invention; Figure 3 shows a cross section through a portion of a battery module in an embodiment of the present invention; Figure 4 shows a flow chart illustrating a method of thermally coupling a group of cells to a cooling plate in an embodiment of the present invention; and Figure 5 shows a vehicle in an embodiment of the present invention.

DETAILED DESCRIPTION

Figures 1A-C show different views of a conventional cylindrical cell 100. Cylindrical cells 100 are widely available in a variety of different sizes. For example, in traction batteries for vehicles cells having a diameter D of 21mm and a length L of 70mm are often used. Such cells are typically referred to as 21700 cells (the first two numbers referring to the diameter D, in mm, and the last three numbers referring to the length L, in tenths of mm). However, it will be understood that other sizes of cell may also be used in embodiments of the present invention.

As will be well understood by the skilled person, the cell 100 comprises a positive terminal 100P, a negative terminal 100N, and vent means 100V. The positive terminal is provided by a steel end cap 106 in a central region of the first end 104 of the cell, and the negative terminal is provided by a steel cylindrical case 108. The steel cylindrical case 108 covers the second end 102, the entire cylindrical surface between the first and second ends, and a peripheral region 100S of the first end surface. The peripheral region of the first end surface may also be referred to as a "shoulder' region 1005 of the first end surface 104. In commercially-available cells, it is sometimes the case of the end cap that defines the positive terminal 100P on the first end surface 104 and protrudes beyond the shoulder region of the first end surface, although this is not the case in the cell shown in figure 1. This allows a substantially planar connector to be connected to the positive terminal and not the negative terminal. As will be well understood by the skilled person, it is important to avoid direct electrical connections between the positive and negative terminals, as such connections create a short circuit which may damage the cell.

As shown in figure 1, the cell 100 comprises three vent means 100V in the first end surface 104, between the steel end cap 106 that defines the positive terminal 100P and the shoulder region 100S of the steel cylindrical case 108. The vent means 100V are gaps that are covered by a material that will rupture to allow hot gases to escape through the gaps between the end cap 106 and steel cylindrical case 108 in the event of excessive pressure occurring inside the cell, thereby mitigate against the risk of the cell exploding.

Cells 100 may be grouped together within a housing and electrically connected together by a busbar assembly to create a battery module. Furthermore, as will become apparent from the following description, in some embodiments a plurality of cells 100 may be mechanically joined together to form a group of cells, and a battery module may comprise one or more of such groups of cells.

Figure 2 shows part of a battery module 200, with some components omitted or shown in partial cutaway for ease of illustration. The battery module 200 comprises a plurality of cells 100, which are electrically connected to one another by a single-sided busbar assembly 202.

As can be seen from figure 2, the cells are arranged in a closely-packed configuration and all of the cells 100 have their first end surfaces 104 in the same plane and their second end surfaces 102 in the same plane.

Busbar assembly 202 is located adjacent to the first ends 104 of the cells 100 and provides electrical connections to the positive and negative terminals of the cells. The cells 100 are divided into a plurality of different groups 100A-E, with the cells within each group electrically connected to one another in parallel by the busbar assembly 202. Adjacent groups are electrically connected in series by the busbar assembly 202. The provision of a single-sided busbar assembly 202 allows cooling of the cells 100 to be performed by a cooling plate 204 located at the opposite end of the cells to the busbar assembly (i.e. adjacent to the second ends 102 of the cells).

Cooling plate 204 may comprise a plurality of channels (not visible in figure 2) through which coolant can flow. A layer of thermal interface material 206 is provided between the cooling plate 204 and the cells 100. As will be understood by the skilled person, thermal interface material is a material that is thermally, but not electrically, conductive. It is widely used to improve thermal conductivity between adjacent components. Although thermal interface materials in solid form are available, liquid thermal interface materials are preferred in the present context, because at least some air pockets will generally be present at the interfaces of a solid thermal interface material. Such air gaps create additional resistance to heat transfer, and, as they can be randomly distributed, they can cause the cooling of the cells within the module to become highly non-uniform.

The thermal interface material 206 is provided on the cooling plate 204 in a liquid form and is deformed by the cells 100 when they are put in place adjacent to the cooling plate 204. This deformation ensures that the thermal interface material to cover at least the second ends 102 of the cells and the portion of the cooling plate 204 that is adjacent to the cells. In this way, the thermal interface material provides a strong thermal contact between the cells and the cooling plate 204, whilst substantially preventing electrical contact. However, the present inventors have recognised that the thermal interface material 206 alone can be insufficient to prevent electrical contact between the cells and the cooling plate throughout the lifetime of a vehicle. This is because vibrations and shocks to the vehicle can cause the cells 100 to move relative to the cooling plate 204, which can ultimately lead to the layer of thermal interface material becoming thinner and potentially being completely removed in at least some regions, such that the cells are in direct contact with the cooling plate. One solution to this problem is to provide a dielectric coating, for example a powder coating, on the cooling plate 204. The thickness of such a coating must be sufficient that it will not be worn away during the lifetime of the vehicle, even if a cell 100 should come into direct contact with the cooling plate 204 relatively early in the vehicle's operational life. Such a coating is expensive to apply and also introduces a significant thermal resistance, which is undesirable.

As shown in figure 2, the present invention may obviate the need for a thick dielectric coating on the cooling plate 204 by providing a dielectric mesh 208 embedded in the thermal interface material. The mesh 208 comprises a plurality of thin strands of dielectric material arranged in a square grid. The spacing between adjacent parallel strands of dielectric material is small enough to ensure that the second ends 102 of the cells 100 are not able to pass through the dielectric mesh 208. For example, the spacing may be in the range of 2-20mm, preferably 5- 15mm. Other spacings may also be useful, especially in embodiments where cells significantly larger or smaller than the 21700 cells illustrated in figure 2 are used. It may be useful to provide spacings which are a ratio of the diameter of the cell, such as 50 to 100% of the diameter of the cell. Where cells are not packed immediately adjacent to one another it may be useful to provide spacings which are a ratio of the separation of the centres of the cells, such as 50 to 100% of the separation. 100% separation would require that the mesh is located to ensure that the second ends 102 of the cells 100 are not able to pass through the dielectric mesh 208. The thickness of the strands in the mesh may be 0.1-1mm thick, preferably 0.2-0.6mm thick. The mesh may be made from any suitable dielectric material, for example Nylon, fibreglass, Polypropylene, Polyester, PEEK (polyether ether ketone), PTFE, or PET. In some embodiments, the mesh 208 may be referred to as a scrim, for example a Nylon or fibreglass scrim. In the illustrated embodiment, the dielectric mesh is a Nylon scrim, having a spacing of 10mm between strands in each direction, and a strand thickness of 0.3mm. In some embodiments, the scrim 208 may be provided with adhesive on one side, which may make application of the scrim onto the cooling plate 204 easier, and may help to hold the scrim in place during the application of the thermal interface material 206.

The dielectric mesh 208 helps to prevent contact between the cells and the cooling plate. As the ends of the cells are too large to pass through the gaps in the dielectric mesh, direct contact between the cells and the cooling plate is not possible when the mesh is in place, even if shocks and vibrations during use of the vehicle cause the cells to move towards the cooling plate. The dielectric properties of the mesh and the thermal interface material that fills the gaps between the mesh strands are sufficient to substantially prevent current flowing between the cells and the cooling plate. Although the thermal conductivity of the mesh 208 will typically be lower than that of the surrounding thermal interface material 206, the overall reduction in thermal conductivity is much less than would be caused by a dielectric coating on the cooling plate 204. Furthermore, provision of a mesh 208 is typically significantly cheaper then providing a thick dielectric coating on the cooling plate 204.

Figures 3A-C illustrate the steps of manufacturing a battery module 200 as shown in figure 2. Figure 3A shows a first stage of the manufacture of a battery module 200. A mesh 208 is positioned on top of a cooling plate 204 such that the mesh covers the entire area of the cooling plate that will be adjacent to the ends of the cells when the battery module is completed.

Figure 3B shows a second stage of the manufacture of a battery module 200, in which a layer of liquid thermal interface material 206 is placed on top of the cooling plate 204 and mesh 208 shown in figure 3A. The thermal interface material substantially covers at least the mesh 208 and the portion of the cooling plate 204 that is covered by the mesh 208. The thermal interface material may be applied by a "fish tail" nozzle controlled by a robot arm. In some embodiments the nozzle may be wide enough that a single pass is sufficient to cover the entire surface.

However, it may be necessary for the robot arm to apply the thermal interface material in several adjacent strips to provide the required coverage. In the illustrated embodiment, the thermal interface material is applied in three adjacent strips, preferably with no overlap between adjacent strips.

In figure 3B, the mesh 208 is shown substantially enclosed within the thermal interface material 206. However, it will be understood that a portion of the mesh may be in contact with the cooling plate 204. Furthermore, it will be understood that some small bubbles may form in the thermal interface material, especially in regions close to the strands of the mesh 208. It is desirable to limit the formation of such bubbles, as they may introduce additional thermal resistance between the cells 100 and the cooling plate 204. However, the present inventors have found that the size of the bubbles is generally small enough that the trapped air is absorbed into the liquid thermal interface material. Although the thermal interface material does cure to become a relatively soft solid, the curing process takes several hours, which provides adequate time for bubbles to break up and be absorbed. Accordingly, any bubbles that do become trapped generally do not introduce significant thermal resistance.

Figure 30 shows a third stage in the manufacture of a battery module 200, in which the cells 100 are placed on top of the thermal interface material at a predetermined distance D from the surface of the cooling plate 204. As can be seen in figure 30, when the cells 100 are separated from the cooling plate 204 by the distance D, the thermal interface material 206 covers the second end surface 102 and extends a small distance up the cylindrical case 108 of the cell. This provides a large contact area, thereby facilitating efficient heat transfer from the cells 100 to the cooling plate 204. As can also be seen in figure 3C, the second end surfaces 102 of the cells 100 are not in contact with the mesh 208. That is to say, the thickness of the strands of the mesh 208 is less than the separation D between the cells 100 and the cooling plate 204. However, the present inventors have recognised that, during use of a vehicle incorporating a battery module 200, vibrations and shocks may cause the separation between the cells and the cooling plate to reduce. However, the presence of the mesh 208 within the thermal interface material ensures that the cells cannot come into direct contact with the cooling plate 204. This prevents the cells from becoming electrically connected to the cooling plate, and may also ensure that any dielectric coating that is present on the surface of the cooling plate 204 is not abraded by the cells 100.

Although not shown in figure 30, it will be understood that a suitable fixture may be provided to ensure that distance D between the cells and the cooling plate is maintained. The cells and cooling plate may be retained in this fixture at least until the thermal interface material has cured. Alternatively, a module housing may include one or more parts that prevent the cells from being pushed too close to the cooling plate 204 during the curing of the thermal interface material 206, in which case a separate fixture may not be required.

As will be apparent from the above description, the mesh 208 maintains a minimum spacing between the cells 100 and the cooling plate 204 and ensures that the cells and cooling plate do not become electrically connected to each other. As such, the mesh 208 may be referred to as a "dielectric spacer element". Alternative dielectric spacer elements may also be employed in embodiments of the present invention, provided the spacer element is at least partially located within the thermal interface material, that it has adequate dielectric properties, and it maintains a non-zero minimum spacing between the cells and the cooling plate. In one embodiment, a plurality of small beads may be mixed into the thermal interface material. The beads may be formed from glass, and be substantially spherical with a diameter of approximately 0.3mm, although it will be understood that other materials, shapes and sizes could also be used. A sufficient number of beads would generally be provided to ensure that at least one bead is present between each cell and the cooling plate. However, in some embodiments the cells may be arranged in one or more groups that are mechanically joined together. In such embodiments, it may be possible to reduce the number of beads, as even if the beads are not present between some of the cells and the cooling plate, contact would still be prevented by the beads between the other cells in the group and the cooling plate (204). It will be understood that the required number of beads may be determined by an appropriate statistical calculation to give the required confidence that an adequate number of beads will be present at all locations for every part that is produced.

It will be understood that the thermal interface material may be applied in any suitable manner, for example using a fish tail nozzle as described above. The beads may be mixed into the thermal interface material prior to the application via the fish tail nozzle, or they may be applied after the thermal interface material has been applied onto the cooling plate but before the cells are in place.

Figure 4 is a flow chart illustrating a method 400 for thermally coupling a group of cells to a cooling plate in an embodiment of the present invention. The method begins at step 402, in which a layer of liquid thermal interface material is applied to the cooling plate, wherein at least one dielectric spacer element is provided within the thermal interface material. In some embodiments, the dielectric spacer element may be provided on top of the cooling plate prior to the application of the layer of thermal interface material. For example, the spacer element may comprise a mesh or scrim which is applied on top of the cooling plate prior to the application of the thermal interface material, and may be partially surrounded by the thermal interface material after it is applied and flows around the mesh or scrim. In some embodiments the method comprises positioning the dielectric mesh (208) onto the cooling plate (204) after the step of applying a layer of thermal interface material (206) to the cooling plate. In this case the dielectric mesh (208) is applied on to or into the layer of thermal interface material (206) which has previously been applied to the cooling plate (204). This method may then assist with placement and partial securing of the dielectric mesh (208) on the cooling plate (204) with the surface tension of the thermal interface material (206) acting to provide a minimal amount of holding force on the dielectric mesh (208).

The method then proceeds to step 404, in which a group of cells is placed in proximity to the cooling plate, such that the layer of thermal interface material is compressed against the group of cells. In this way, the spacer element maintains at least a predetermined distance between each of the cells in the group of cells and the cooling plate. However, it will be understood that the cells may not be in contact with the spacer element at this point, and that the distance between the cells and the cooling plate may be greater than the predetermined distance. In such an embodiment, the spacer element ensures that the distance between the cells and the cooling plate does not subsequently reduce to less than the predetermined distance. The method then ends at step 406.

Figure 5 shows a vehicle 500 incorporating a battery module 520 according to an embodiment of the present invention or a battery pack 510 comprising two or more battery modules 520 according to one or more embodiments of the present invention.

It will be appreciated that embodiments of the present invention can be realised in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs that, when executed, implement embodiments of the present invention. Accordingly, embodiments provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine-readable storage storing such a program. Still further, embodiments of the present invention may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments which fall within the scope of the claims

Claims

CLAIMS1. A method of thermally coupling a group of cells to a cooling plate, the method comprising: applying a layer of thermal interface material to the cooling plate, wherein the thermal interface material is applied in a liquid form and at least one dielectric spacer element is provided within the thermal interface material; and positioning the group of cells in proximity to the cooling plate, such that the layer of thermal interface material is compressed against the group of cells, wherein the dielectric spacer element is arranged to maintain a gap of at least a predetermined distance between each of the cells in the group of cells and the cooling plate.
2. A method as claimed in claim 1, wherein the dielectric spacer element comprises a dielectric mesh.
3. A method as claimed in claim 2, wherein the method comprises positioning the dielectric mesh onto the cooling plate prior to the step of applying a layer of thermal interface material to the cooling plate.
4. A method as claimed in claim 2, wherein the method comprises positioning the dielectric mesh onto the cooling plate after the step of applying a layer of thermal interface material to the cooling plate.
5. A method as claimed in claim 2, claim 3 or claim 4, wherein the dielectric mesh has a spacing of 2-20mm, preferably 5-15mm.
6. A method as claimed in any one of claims 2-5, wherein the dielectric mesh is formed from threads having a thickness of 0.1-1mm, preferably 0.2-0.6mm.
7. A method as claimed in any one of claims 2-6, wherein the dielectric mesh is a nylon or fibreglass mesh.
8. A method as claimed in claim 1, wherein the spacer element comprises a plurality of dielectric beads dispersed within the thermal interface material.
9. A method as claimed in claim 8, wherein the dielectric beads have a diameter of 0.1- 1mm, preferably 0.2-0.6mm.
10. A method as claimed in any preceding claim, wherein the layer of thermal interface material is applied to the cooling plate by one or more fishtail nozzles.
11. A battery module comprising a group of cells and a cooling plate, wherein the group of cells are positioned in proximity to the cooling plate and are thermally coupled to the cooling plate by a layer of thermal interface material, wherein at least one dielectric spacer element is provided in the layer of thermal interface material, the spacer element being arranged to maintain a gap of at least a predetermined distance between each of the cells in the group of cells and the cooling plate.
12. A battery module as claimed in claim 11, wherein the dielectric spacer element comprises a dielectric mesh.
13. A battery module as claimed in claim 12, wherein the dielectric mesh has a spacing of 2-20mm, preferably 5-15mm.
14. A battery module as claimed in claim 12 or claim 13, wherein the dielectric mesh is formed from threads having a thickness of 0.1-1mm, preferably 0.2-0.6mm.
15. A battery module as claimed in any one of claims 12-14, wherein the dielectric mesh is a nylon or fibreglass mesh.
16. A battery module as claimed in claim 11, wherein the spacer element comprises a plurality of dielectric beads dispersed within the thermal interface material.
17. A battery module as claimed in claim 16, wherein the dielectric beads have a diameter of 0.1-1mm, preferably 0.2-0.6mm.
18. A battery pack comprising a plurality of battery modules as claimed in any one of claims 11-17.
19. A vehicle comprising a battery pack as claimed in claim 18 or a battery module as claimed in any one of claims 11-17.