A heat transfer plate for a vehicle battery assembly

Abstract

A vehicle battery assembly heat transfer plate 300 comprises a heat transfer portion 410, and at least one thermal interface material overspill reservoir 420,440 each extending between the heat transfer portion and an edge 430,450 of the vehicle battery assembly heat transfer plate. The thermal interface material may be a filler or adhesive for fixing the heat transfer plate to a battery assembly (200, figure 2). Other aspects of the invention relate to the vehicle battery assembly including the heat transfer plate, a vehicle including the battery assembly or heat transfer plate, and a method of producing the vehicle battery assembly. When the heat transfer plate and battery cell stack are pressed together, the thermal interface material forms a layer therebetween and into the overspill reservoir(s). This prevents or reduces contamination of other parts of the vehicle battery assembly by the thermal interface material. Furthermore, the additional volume of thermal interface material provided at the edge(s) of the plate increases the material available for allowing stretch or flex under high load around the edges of the plate, thereby preventing separation of the plate from the battery cell stack.

Description

TECHNICAL FIELD The present disclosure relates to a vehicle battery assembly heat transfer plate. Aspects of the invention relate to a vehicle battery assembly heat transfer plate, a vehicle battery assembly, a vehicle, and a method in a process of producing a vehicle battery assembly. BACKGROUND It is known to provide a cooling plate in combination with a battery cell. The aim of the cooling plate is to reduce heat in the battery cell, where the cooling plate may be at a temperature lower than that of the battery cell. In recent years, one or more battery cells are being included in types of vehicle, such as hybrid cars or electric vehicles (EVs) including electric cars, electric vans, electric aircraft, electric boats etc. A battery cell stack, or a battery assembly, comprising one or more battery cells (or, more typically, a plurality of battery cells) may be included in an electric vehicle to provide power to at least part of the vehicle, such as a drive mechanism. One or more cooling plates can be provided as part of the battery assembly or can be applied to a battery cell stack, with the aim of cooling the battery cell(s). To assist in cooling, an interface material, or thermal interface material (TIM), may be provided between a cooling plate and battery cell(s). The TIM conducts heat from a battery cell to the cooling plate, thereby contributing to lowering or stabilizing the temperature in the battery cell. The TIM may be applied in a liquid form between the battery cell and the cooling plate. In which case, the TIM is cooled after contact with the battery cell and cooling plate, following a process of pressing the cooling plate onto the battery cell (or vice versa). In this process, excess TIM may be squeezed out from between the cooling plate and the battery to leak onto a surrounding area. The TIM may also have adhesive or bonding properties - for example, once cured the TIM provides a bond between the cooling plate and the battery cell. Such a bond may have some inherent flexibility, allowing some relative movement between the TIM and the cooling plate such as may arise when external forces are applied to the bonded plate and cell. There is a need to provide a vehicle battery assembly heat transfer plate that reduces excess TIM leakage and / or maintains bonding between the plate and the cell(s). 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 Aspects and embodiments of the invention provide a vehicle battery assembly heat transfer plate, a vehicle battery assembly, a vehicle, and a method in a process of producing a vehicle battery assembly, as claimed in the appended claims. According to an aspect of the present invention there is provided a vehicle battery assembly heat transfer plate comprising: a heat transfer portion; and at least one thermal interface material (TIM) overspill reservoir each extending between the heat transfer portion and an edge of the vehicle battery assembly heat transfer plate. According to another aspect of the present invention, there is provided a heat transfer plate comprising a heat transfer portion and an overspill portion. Advantageously, the at least one TIM overspill reservoir receives TIM that spills from between the heat transfer portion and a surface to which the plate is being attached in the vehicle battery assembly. This prevents, or reduces the amount of, TIM spilling on to other parts of the vehicle battery assembly during assembly of the plate in the vehicle battery assembly; thereby mitigating an issue of spilled TIM affecting other components in the vehicle battery assembly. Additionally, the additional volume of TIM provided at the edge(s) of the plate in the at least one TIM overspill reservoir increases the material available for allowing stretch or flex under high load around the edges of the plate (e.g., such as may arise during use of a vehicle comprising the plate or vehicle battery assembly); thereby improving strain sensitivity. That is, the additional volume of TIM at the edges of the plate may mitigate or prevent an issue ofcracking or separation of the joints around the edges of a layer of TIM between the heat transfer portion and the surface to which the plate is attached. In various examples, the heat transfer portion comprises a surface for receiving TIM; and each TIM overspill reservoir extends between the surface of the heat transfer portion to the edge of the plate. Advantageously, TIM received on the surface of the heat transfer portion facilitates heat transfer by the plate. In various examples, each TIM overspill reservoir is at least partly surrounded by at least two sidewalls, each sidewall corresponding to an interface between the heat transfer portion and said TIM overspill reservoir. Advantageously, each TIM overspill reservoir is defined by its respective sidewalls which aid in containing TIM. In various examples, a depth of each TIM overspill reservoir is substantially constant between the heat transfer portion and an edge of the plate. Advantageously, defining the depth of each TIM overspill reservoir to be constant may provide a thicker additional volume of TIM at the edges of the plate. In various examples, the depth of each TIM overspill reservoiris predetermined based on an intended minimum thickness of TIM to be received on the heat transfer portion. Advantageously, this supports providing a sufficient layer of TIM between the heat transfer portion and a body to which the plate is attached, with the remaining TIM flowing into each TIM overspill reservoir. In various examples, the heat transfer portion comprises one or more cooling channels. Advantageously, the one or more cooling channels facilitates cooling of a body to which the plate is attached. In various examples, the plate comprises a first body and a second body, the second body stacked on the first body; wherein the heat transfer portion is formed of the second body and a part of the first body disposed above the second body, and the at least one TIM overspill reservoir is formed of the remaining part of the first body, the remaining part of the first body extending from over an edge of the second body. Advantageously, the joining or stacking of the two bodies provides a convenient method for forming the plate. In various examples, the first body and the second body are formed of aluminium. Advantageously, aluminium provides good heat transfer capabilities and strength. In various examples, the depth of the TIM overspill reservoir varies between the heat transfer portion and an edge of the plate. Advantageously, this may ease a manufacturing requirement. In various examples, each TIM overspill reservoir corresponds to a sloped or tapered surface extending from the heat transfer portion to the respective edge of the plate for said TIM overspill reservoir. Advantageously, this may ease a manufacturing requirement. In various examples, a first TIM overspill reservoir of the at least one TIM overspill reservoir is provided at a first edge of the plate, and a second TIM overspill reservoir of the at least one TIM overspill reservoir is provided at a second edge of the plate, the second edge being on an opposite side of the plate to the first edge. Advantageously, this allows for retaining of excess TIM at each of the first and second edges of the plate. In various examples, each TIM overspill reservoir extends substantially along the full length of the respective edge of the plate for said TIM overspill reservoir. Advantageously, this provides the benefits of including a TIM overspill reservoir along substantially the full length of the respective edge of the plate. According to an aspect of the present invention there is provided a vehicle battery assembly comprising: a battery cell stack; the vehicle battery assembly heat transfer plate described above; and a layer of thermal interface material (TIM) provided between the battery cell stack and the plate and in each TIM overspill reservoir; wherein the layer of TIM has substantially uniform thickness between a top of the battery cell stack and the heat transfer portion, and has a greater thickness in each TIM overspill reservoir. Advantageously, with the vehicle battery assembly heat transfer plate separated from the battery cell stack with the layer of TIM, the plate may perform heat transfer for the battery cell stack, such as cooling or heating. Further, the at least one TIM overspill reservoir prevents, or reduces the amount of, TIM spilling on to other parts of the vehicle battery assembly during application of the plate to the battery cell stack with TIM inbetween; thereby mitigating an issue of spilled TIM affecting other components in the vehicle battery assembly. Additionally, the additional volume of TIM provided at the edge(s) of the plate in the at least one TIM overspill reservoir increases the material available for allowing stretch or flex under high load around the edges of the plate (e.g., such as may arise during use of a vehicle comprising the plate or vehicle battery assembly); thereby improving strain sensitivity. That is, the additional volume of TIM at the edges of the plate may mitigate or prevent an issue of cracking or separation of the joints around the edges of a layer of TIM between the heat transfer portion and the battery cell stack. According to an aspect of the present invention there is provided a vehicle comprising the vehicle battery assembly heat transfer plate described above or the vehicle battery assembly described above. Advantageously, this provides the benefits described above in relation to a vehicle including the plate or the vehicle battery assembly, such as reducing manufacturing complexity by preventing spilling of TIM onto other components or improving strain sensitivity around the edges of the plate. In examples, the vehicle is a battery electric vehicle, or a hybrid vehicle. For example, the vehicle is a plug-in hybrid vehicle or a mild hybrid vehicle. The vehicle battery assembly may be a primary or secondary energy source for vehicle propulsion. For example, the vehicle battery assembly is a traction battery of the vehicle. Advantageously, the above described benefits are realised in a such a vehicle. According to an aspect of the present invention, there is provided a method in a process of producing a vehicle battery assembly, the method comprising: applying a force to one or more of a vehicle battery assembly heat transfer plate and a surface of a battery cell stack to press together the vehicle battery assembly heat transfer plate and an opposing surface of the battery cell stack such that thermal interface material (TIM) provided between the vehicle battery assembly heat transfer plate and the opposing surface of the battery cell stack is pressed into a layer therebetween and into at least one TIM overspill reservoir of the vehicle battery assembly heat transfer plate; wherein the vehicle battery assembly heat transfer plate comprises: a heat transfer portion; and the at least one TIM overspill reservoir each extending between the heat transfer portion and an edge of the vehicle battery assembly heat transfer plate; and wherein the layer of TIM has substantially uniform thickness between a top of the opposing surface of the battery cell stack and the heat transfer portion, and has a greater thickness in each TIM overspill reservoir. Advantageously, the at least one TIM overspill reservoir prevents, or reduces the amount of, TIM spilling on to other parts of the vehicle battery assembly during the pressing of the plate onto a surface of the battery cell stack with TIM in-between; thereby mitigating an issue of spilled TIM affecting other components in the vehicle battery assembly. Additionally, the additional volume of TIM provided at the edge(s) of the plate in the at least one TIM overspill reservoir increases the material available for allowing stretch or flex under high load around the edges of the plate (e.g., such as may arise during use of a vehicle comprising the plate or vehicle battery assembly); thereby improving strain sensitivity. That is, the additional volume of TIM at the edges of the plate may mitigate or prevent an issue of cracking or separation of the joints around the edges of a layer of TIM between the heat transfer portion and the battery cell stack. 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. 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: Figure 1 shows a vehicle; Figure 2 shows a schematic of a vehicle battery assembly with a heat transfer plate bonded to a battery cell stack; Figure 3 shows a bottom view of a heat transfer plate; Figures 4Aand 4B show perspective views of cut sections along the lines X-X’ in Figure 3 of a portion of the heat transfer plate, according to different examples of embodiments of the invention; Figure 5A is a schematic illustration of a heat transfer plate bonded to a cell stack with thermal interface material (TIM); Figure 5B is a schematic illustration of a heat transfer plate comprising TIM overspill reservoirs bonded to a cell stack with TIM; and Figure 6 shows a flow chart showing a method of providing a vehicle battery assembly. DETAILED DESCRIPTION A vehicle 100 in accordance with an embodiment of the present disclosure is shown in Figure 1. Figure 2 schematically illustrates a vehicle battery assembly 200 such as may be included in vehicle 100. For example, the vehicle battery assembly 200 is installed on an underside of the vehicle 100. Although the term vehicle battery assembly will be used herein, it will be appreciated that the vehicle battery assembly 200 may also or alternatively be referred to as a vehicle battery unit or a vehicle battery configuration or the like. Vehicle battery assembly 200 includes one or more battery cells. A plurality of battery cells can be referred to as a cell stack, and so a vehicle battery assembly 200 may be considered to comprise one or more cell stacks. A heat transfer plate 300 is shown bonded or otherwise attached to a cell stack in Figure 2. A heat transfer plate 300 as disclosed herein is described as being part of the vehicle battery assembly 200; however, it will be appreciated that the heat transfer plate 300 may be considered separately to the vehicle battery assembly 200 and as being optionally bonded to the vehicle battery assembly 200. Additionally, the heat transfer plate 300 may be bonded to a single battery cell instead of to a plurality of battery cells arranged in a cell stack. In the following, reference to heat transfer between heat transfer plate 300 (or a part thereof) and cell stack (or a part thereof) may generally be considered to be via a layer of TIM between the two. The heat transfer plate 300 and battery assembly 200 in Figure 2 is shown in the orientation the battery may have when installed in the vehicle. In this case, the heat transfer plate is above the cell stack that is bonded below it to the heat transfer plate’s lower surface. Relative orientation terms used herein such as above, below, upper and lower therefore anticipate this arrangement of the battery assembly. However, this is not to be understood as limiting as the battery assembly may have any desired orientation in the vehicle. A layer of thermal interface material (TIM) is provided between the heat transfer plate 300 and the cell stack. The TIM may be formed-in-place thermal interface material; for example, pumpable gap filler or thermally conductive adhesive. The TIM facilitates heat transfer between the heat transfer plate 300 and the cell stack. It will be understood that the TIM may also be provided between battery cells or battery cell stacks in the vehicle battery assembly, such that different depths of TIM may be found under the heat transfer plate 300. The TIM also has the function of providing a bond between the heat transfer plate 300 and the cell stack. The layer of TIM may be between 0.5mm and 2mm thick, approximately, between the top of the cell stack and a surface of the heat transfer plate 300. Figure 3 schematically illustrates the underside of a heat transfer plate 300 according to an embodiment of the present disclosure. Although the term heat transfer plate has been used herein, it will be appreciated that other terms such as cooling plate, heat redistribution plate, thermal transfer unit etc. may be used instead. Figures 4A and 4E3 are enlarged perspective views of a cut section along line X-X’ of Figure 3 through different examples of heat transfer plate 300 and showing the bottom surface of the heat transfer plate 300. Heat transfer plate 300 includes a heat transfer portion 410 having a first, lower surface for contact with battery cells, and at least one TIM overspill reservoir 420, 440, with Figure 3 showing two TIM overspill reservoirs 420, 440. Two examples of different TIM overspill reservoirs (e.g. TIM overspill reservoir 420) are shown in more detail in Figures 4A and 4B, as will be described below. It will be appreciated that an analogous description may be applied to each / any other TIM overspill reservoir in the heat transfer plate 300. Heat transfer portion 410 may be regarded as the part of heat transfer plate 300 which will be mainly responsible for transferring heat from (or to) a cell stack to which the heat transfer plate 300 is bonded. In particular, heat transfer portion 410 comprises a first surface 411 (that is, the bottom surface) for bonding to a cell stack using the TIM. The first surface 411 may be substantially flat or adapted to correspond to a surface (e.g., the top surface) of the cell stack to which the heat transfer plate 300 is to be applied. In various examples, heat transfer portion 410 comprises one or more cooling channels 510. As shown in Figures 4A and 4B, a cooling channel 510 is disposed on the other side of the heat transfer portion 410 with respect to the first surface 411 (that is, its bottom surface). A substance, such as a coolant or heat transfer fluid, is arranged to flow along the cooling channel 510 to affect a temperature ofthe heat transfer portion 410 and so also any bonded cell stack. For example, coolant may enter the heat transfer plate 300 at inlet 460 and flow along the one or more cooling channels 510 to an outlet 470. If the cell stack is to be cooled, the coolant received through inlet 460 will have a lower temperature than the coolant exiting at outlet 470, reflective of heat from the cell stack having been transferred to the coolant as it flows through the one or more cooling channel 510 within the heat transfer portion 410. Multiple coolant channels may be provided on the top surface ofthe heat transfer plate, as shown in Figure 2. Each TIM overspill reservoir 420, 440 is located between the heat transfer portion and an edge 430, 450 of the heat transfer plate 300. In particular, a TIM overspill reservoir 420, 440 may be regarded as a portion of the heat transfer plate 300 extending from the heat transfer portion (e.g., from an edge thereof) to an edge 430, 450 ofthe heat transfer plate 300. To put this another way, where the first surface 411 (that is, the bottom surface) ofthe heat transfer portion 410 is arranged to receive TIM, each TIM overspill reservoir 420, 440 is arranged to extend between the first surface 411 ofthe heat transfer portion 410 to the edge 430, 450 ofthe plate corresponding to said TIM overspill reservoir 420, 440. In some examples, two TIM overspill reservoirs 420, 440 are provided, with one at an opposite edge of the heat transfer plate 300 to the other - such an arrangement is illustrated in Figures 2 and 3. An aim of each TIM overspill reservoir 420, 440 is to contain or otherwise hold excess TIM that flows from the space between the heat transfer portion 410 and a surface to which the heat transfer portion 410 is being bonded, such as a surface of the cell stack. In a more detailed example, in applying the heat transfer plate 300 to the cell stack, an amount of TIM is provided on / across either or both of the first surface 411 of the heat transfer portion 410 and the surface of the cell stack. The first surface 411 of the heat transfer portion 410 and the surface of the cell stack are then pressed together (e.g., through application of a force on an opposite surface of the heat transfer portion 410 and / or the cell stack) until a predetermined distance (or gap / spacing of predetermined width) is provided between a top of the surface of the cell stack (bearing in mind the surface ofthe cell stack may not be flat) and the first surface 411 ofthe heat transfer portion 410. This will result in a layer of TIM having a minimum depth of at least the predetermined distance being provided between the heat transfer portion 410 and the surface ofthe cell stack, due to the TIM being compressed as the first surface 411 ofthe heat transfer portion 410 and the surface ofthe cell stack move together. This pressing ofthe TIM will force the TIM to spread outwards which, in some cases, will cause the TIM to flow towards the edges ofthe heat transfer portion 410. If the TIM overspill reservoir(s) 420, 440 are not present, there is a risk of excess TIM flowing off the edge of the heat transfer plate 300, which could result in excess TIM leaking onto other components (e.g., in the vehicle battery assembly 200) which could be detrimental to the operations of a vehicle 100 comprising the vehicle battery assembly 200. Whereas, by providing at least one TIM overspill reservoir 420, 440 in the heat transfer plate 300, excess TIM will instead flow into each TIM overspill reservoir 420, 440 to be contained therein without flowing off the edge ofthe heat transfer plate 300. That is, each TIM overspill reservoir 420, 440 may at least mitigate leakage of excess TIM from a corresponding edge 430, 450 ofthe plate 300. Another aim of the TIM overspill reservoir(s) 420, 440 is to prevent or mitigate an issue of cracking or separation of the joints around the edges of the layer of TIM between the heat transfer portion 410 (i.e., the first surface 411 thereof) and the surface ofthe cell stack, or even an issue of at least partial separation ofthe heat transfer plate 300 from the cell stack. In more detail, with reference to Figures 5A and 5B, consider a vehicle comprising a battery assembly which includes a heat transfer plate bonded to a cell stack via a layer of TIM. Figure 5A illustrates a case where a heat transfer plate 65 does not include any TIM overspill reservoir(s). As a result, at an edge 67 ofthe heat transfer plate 65, the layer of TIM 63 (or an edge thereof) between the heat transfer plate 65 and the cell stack 61 is relatively exposed. While the vehicle is in-use, forces are applied to the layer of TIM 63. For example, during extreme load events, such as when the vehicle is passing over rough terrain, the layer of TIM 63 will be stressed, particularly at the edges. Overtime, this can result in cracking or peeling ofthe layer of TIM 63 around the edges and, eventually, throughout the layer of TIM 63 itself. This has the effect of causing the layer of TIM 63 to lose contact with either, or both, of the heat transfer plate 65 and the cell stack 61, reducing the efficiency of the heat transfer of the heat transfer plate 65. Further, the bonding between the heat transfer plate 65 and the cell stack 61 may deteriorate around the edge 67 of the heat transfer plate 65. In contrast, Figure 5B illustrates a case where a heat transfer plate 300 comprises at least one TIM overspill reservoir 420, 440 in accordance with embodiments of the present disclosure. As illustrated in Figure 5B, this has the effect of containing an amount of TIM 610 around the edge 620 of the heat transfer plate 300. This amount of TIM 610 is provided by the pressing of the heat transfer plate 300 onto TIM deposited on the cell stack to bond the two, causing excess TIM to flow into the at least one TIM overspill reservoir 420, 440. It will be appreciated that an amount of TIM around the edge of the heat transfer plate 300 which includes the TIM overspill reservoir(s) 420, 440 is greater than an amount of TIM around the edge of the heat transfer plate 65 which does not include any TIM overspill reservoir(s), due to the excess TIM contained in the TIM overspill reservoir(s). This additional amount of TIM means that, while the vehicle is in-use, the layer of TIM 630 between the heat transfer plate 300 and the cell stack will be protected by the TIM in the TIM overspill reservoir(s) 420, 440. The TIM in the TIM overspill reservoir(s) 420, 440 will lessen the effects of extreme load events on the layer of TIM 630, thereby mitigating or even preventing an issue ofcracking or peeling in the layer of TIM 630. According to various examples, a TIM overspill reservoir 420, 440 is formed as an increase in the bond depth (e.g., the depth of a bond between the plate 300 and a surface to which the plate 300 will be bonded, such as a surface of a cell stack. This increase in the bond depth may be achieved by a step, a taper or a curve. In Figure 4A, the increase in bond depth is achieved with a step 423. That is, as illustrated in Figure 4A, a difference in height or thickness between a first surface 520 of TIM overspill reservoir 420 and an adjacent body, compared with the height or thickness between the first surface 411 of the heat transfer portion 410 and the adjacent body is equal to the thickness of the plate 560 forming the heat transfer portion 410. Furthermore, height or thickness between the first surface 520 of the TIM overspill reservoir and an adjacent body is substantially the same across the first surface 520 of the TIM overspill reservoir. That is, the depth of the TIM overspill reservoir 420 is substantially constant across the first surface of the TIM overspill reservoir 420. The first surface 520 is arranged to face in substantially the same direction as the first surface 411 of the heat transfer portion 410. Figures 3 and 4A illustrate, for TIM overspill reservoir 420 (although the same considerations may apply to another TIM overspill reservoir, such as TIM overspill reservoir 440), a first sidewall 421, extending substantially from the edge 430 of the plate 300 inwards, a second sidewall 423, extending substantially parallel the edge 430 of the plate 300, and a third sidewall 425, extending substantially from the edge 430 of the plate 300 inwards. The first sidewall 421 and the third sidewall 425 may be substantially parallel to one another, or may extend inwards at different angles from the edge 430 of the heat transfer plate 300. These three sidewalls surround the first surface 520 of the TIM overspill reservoir 420, and may be considered to define a reservoir for holding or receiving excess TIM (e.g., as may flow from between the heat transfer portion 410 and an adjacent body (the cell stack) during pressing of the cell stack and heat transfer plate together). The sidewalls 421, 423, 425 correspond to an interface between the heat transfer portion 410 and the TIM overspill reservoir 420. The length of one or more of the first sidewall 421, the second sidewall 423 and the third sidewall 425 may be predetermined or otherwise be set to define a target space (or minimum space) based on an expected amount of excess TIM that may be extruded from between the first surface 411 of the heat transfer portion and the top of the cell stack. That is, TIM in a TIM overspill reservoir 420,440 can be expected to be less efficient (in terms of heat transfer) than TIM in the layer between the heat transfer plate 300 and the cell stack, for example due to the TIM overspill reservoir(s) 420, 440 extending beyond the edges of the cell stack or being located away from the cooling channels) 510. As such, it is beneficial to reduce, or even minimise, the amount of TIM that will be received in the TIM overspill reservoir(s) 420, 440, while still ensuring that there is some excess TIM (to ensure complete coverage between the heat transfer portion 410 and the cell stack) but that the excess is held within the TIM overspill reservoirs) 420, 440 instead of leaking off an edge of the plate 300. As illustrated in Figure 4B, in a different example, a TIM overspill reservoir 420, 440 has a first surface 530 which tapers from an edge 523 of the heat transfer portion 410 to a respective edge 430, 450 of the plate 300. In other words, a difference in height or thickness between a first surface 530 of TIM overspill reservoir 420 and the first surface 411 of the heat transfer portion 410 may change or vary across the first surface 530 of the TIM overspill reservoir 420. To put another way: at the edge 523 of the heat transfer portion 410, which edge may be substantially parallel to an edge 430 of the plate 300, the first surface 530 of the TIM overspill reservoir 420 is substantially flat or planar but as the first surface 530 of the TIM overspill reservoir 420 extends towards the edge 430 of the plate 300, the first surface 530 of the TIM overspill reservoir 420 gradually thins away to the edge 430 of the plate 300. As such, a depth of the TIM overspill reservoir 420 is greater at the edge 430 of the plate 300 compared to at a position adjacent to the edge of the heat transfer portion 410. In a case where the first surface 530 of the TIM overspill reservoir 420 tapers or thins from the edge 523 of the first surface 411 of the heat transfer portion 410 to the corresponding edge 430 of the plate 300, the TIM overspill reservoir 420 may be at least partly surrounded by one or more sidewall. For example, two sidewalls 540 may extend along edges of the TIM overspill reservoir 420 in a direction substantially perpendicular to the edge 430 of the plate 300 (and the edge of the heat transfer portion 410) with the first surface 530 of the TIM overspill reservoir 420 extending between these two sidewalls. Figure 4B shows one such sidewall 540. Each sidewall may correspond to an interface between the TIM overspill reservoir 420 and the heat transfer portion 410, with a height or extent of each sidewall increasing towards the edge 430 of the plate 300 as the first surface 530 of the TIM overspill reservoir 420 tapers down to the edge 430 of the plate. Such sidewalls may assist in containing excess TIM in the TIM overspill reservoir 420. However, in other cases, no defined sidewalls are present between the TIM overspill reservoir 420 and the heat transfer portion 410. For instance, the TIM overspill reservoir 420 may be formed as a depression in the plate 300 at the corresponding edge 430 of the plate 300, with no definitive edge where the TIM overspill reservoir 420 meets the heat transfer portion 410. That is, all along the interface between the first surface 411 of the heat transfer portion 410 and the first surface 530 of the TIM overspill reservoir 420, the first surface 530 of the TIM overspill reservoir 420 tapers away from the first surface 411 of the heat transfer portion 410 towards the respective edge 430 of the plate 300. In an example, such a TIM overspill reservoir 420 may be formed by squeezing or compressing the edge 430 of the heat transfer plate 300 to form the depression. In an example, the heat transfer plate 300 is formed from two plates or, more generally, from two bodies. This is illustrated in Figure 4A, where a first body 550 and a second body 560 are shown. The second body 560 is arranged under the first body 550. The first body 550 and the second body 560 are joined together. Either or both of the first body 550 and the second body 560 may be formed of aluminium. Both bodies 550, 560 form parts of the heat transfer portion 410, where edges of the second body 560 may correspond to sidewalls around the at least one TIM overspill reservoir 420, 440, such as the first sidewall 421, second sidewall 423 and third sidewall 425. It will be understood that these sidewalls (such as first sidewall 421, second sidewall 423 and third sidewall 425) may be regarded as part of the heat transfer portion 410, part of the corresponding TIM overspill reservoir 420, or more generally as part of the heat transfer plate 300 itself. The first body 550 forms another part of the heat transfer portion 410 (e.g. the remainder of the heat transfer portion 410) and the at least one TIM overspill reservoir 420, 440. As can be seen in Figure 4A, the first body 550 extends beyond some edges of the second body 560, with an extending portion corresponding to TIM overspill reservoir 420. For example, an exposed surface of the first body 550 corresponds to the first surface 520 of the TIM overspill reservoir 420. It will be understood that another extending portion would correspond to another TIM overspill reservoir 440. Figure 4A also illustrates a gap or space between the first body 550 and the second body 560. Such a space may be used for a cooling channel 510 below the first surface 411 of the heat transfer portion 410. The second body 560 may be formed to provide such a gap when joined to the first body 550. The second body 560 may be joined to the first body 550 to provide such an overlap of the first body 550. Such a method of forming the heat transfer plate 300 is suited to a case where a TIM overspill reservoir 420, 440 is formed as a step in the plate 300, as in Figure 4A. For a case as in Figure 4B, where a TIM overspill reservoir 420, 440 is formed to have a first surface 530 inclined away from the interface 523 with the heat transfer portion 410 to the corresponding edge 430, 450 of the plate 300 (i.e., to define a reservoir in the plate 300 for receiving excess TIM), it will be appreciated that a part of the second body 560 may also form part of the at least one TIM overspill reservoir 420, 440. For example, the thickness of the second body is gradually reduced, or the second body 560 is tapered, from the edge 523 of the heat transfer portion 410 to an edge of the second body 560, where the edge of the second body 560 may correspond to the edge 430, 450 of the plate 300 corresponding to the TIM overspill reservoir 420, 440. The second body 560 is then joined to the first body 550. In an example, the edge of the second body 560 is aligned with an edge of the first body 550 such that both correspond to the edge 430, 450 of the plate 300 corresponding to the TIM overspill reservoir 420, 440, with the first surface 530 of the TIM overspill reservoir tapering down to the edge 430, 450 of the plate 300. This reflects the example of Figure 4E3. Alternatively, the first body 550 may be joined to the second body 560 to overlap the topside of the second body 560; e.g., such that part of the first body 550 extends from over the second body 560. In which case, a first surface of the TIM overspill reservoir 420,440 for receiving excess TIM will include both a tapering portion, which tapers away from the first surface 411 of the heat transfer portion 410 and corresponds to the part of the second body 560 forming the TIM overspill reservoir 420, 440, and a flat portion corresponding to a portion of the first body 550 extending from under the second body 560, where the flat portion extends from the edge of the tapering portion to the edge 430, 450 of the plate 300. It will be understood that the ‘flat portion’ is simply a portion of a surface of the first body 550 which is flat relative to the remainder of the surface of the first body 550 (and may be parallel with the first surface 411 of the heat transfer portion 410). In other words, as well as cases where a TIM overspill reservoir is formed as a step in the plate 300 (such as in Figure 4A) and cases where a TIM overspill reservoir is formed as a tapering at the edge of the plate 300 (such as in Figure 4B), some examples of the present disclosure combine both approaches such that a first surface of the TIM overspill reservoir 420, 440 comprises a first portion tapering away from an interface between the TIM overspill reservoir 420, 440 and the heat transfer portion 410 towards the edge 430, 450 of the plate 300, and a second portion extending from the edge of the first portion (i.e., the end of the taper) to the edge 430, 450 of the plate 300. Across the first portion, a depth of the TIM overspill reservoir decreases towards the interface; while across the second portion, a depth of the TIM overspill reservoir is substantially constant. It will be appreciated that, for examples of the present disclosure in which a heat transfer plate 300 comprises a plurality of TIM overspill reservoirs 420, 440, the TIM overspill reservoirs 420, 440 may all be formed in the same way or may be formed in different ways. For example, one TIM overspill reservoir is formed as a step in the plate 300 as illustrated in Figure 4A, and another TIM overspill reservoir is formed as a taper at the edge of the plate 300 as illustrated in Figure 4B. Although a method of forming heat transfer plate 300 using two bodies or plates is described above, it will be appreciated that other methods of manufacturing a heat transfer plate 300 exist. For example, heat transfer plate 300 may be extruded. A method according to an example of the present disclosure is shown in Figure 6. The method is one of providing a vehicle battery assembly 200, and may form part of a process of manufacturing, or producing, a vehicle battery assembly 200. In operation 700, a heat transfer plate 300 (such as according to any of the examples disclosed herein) is arranged relative to a cell stack to which the heat transfer plate 300 is to be attached. For example, the plate 300 is arranged above the cell stack such that a first surface 411 of a heat transfer portion 410 of the plate 300 is positioned above and facing a top surface of the cell stack, where the first surface 411 of the heat transfer portion 410 is for receiving TIM. In operation 710, TIM is deposited between the heat transfer plate 300 and the cell stack. In an example, the TIM may be applied to the top surface of the cell stack, with deposits of TIM spread or patterned across the top surface of the cell stack to promote even spreading in a subsequent pressing operation (see below). It will be appreciated that TIM may additionally or alternatively be applied to the first surface 411 of the heat transfer portion 410, although if suspended above the cell stack this may increase complexity. In operation 720, a distance between the heat transfer plate 300 and the cell stack is reduced until a gap of a predetermined size is provided, or until a minimum space between the plate 300 and the cell stack is reached. For example, a force may be applied to a surface of the heat transfer plate 300 on an opposite side of the plate 300 to the first surface 411 of the heat transfer portion 410, thereby moving the plate 300 towards the cell stack. It will be understood that the cell stack could instead (or additionally) be moved towards the heat transfer plate. Assuming TIM is applied to the top surface of the cell stack and TIM is applied on the corresponding surface of the plate 300 (e.g., on the first surface 411 of the heat transfer portion 410), the movement of the plate 300 towards the cell stack will cause the TIM to be pressed therebetween. This will result in the TIM spreading between the cell stack and the first surface 411 of the heat transfer portion 410. The amount of TIM deposited on the cell stack should be determined such that, when the first surface 411 of the heat transfer portion 410 and the top of the cell stack are the minimum space apart, a continuous layer of TIM is spread between the first surface 411 of the heat transfer portion 410 and the top of the cell stack. Ideally, only TIM should be present between the first surface 411 of the heat transfer portion 410 and the top of the cell stack, to provide better transfer of heat between the two (i.e. improve thermal conductivity). Deposits of TIM near the edge of the heat transfer portion 410 will be spread outwards by the pressing of the plate 300. As a result, excess TIM will flow into the at least one TIM overspill reservoir 420, 440 of the heat transfer plate 300, thereby being received and contained in the TIM overspill reservoir(s) 420, 440. As such, when the first surface 411 of the heat transfer portion 410 and the top of the cell stack are the minimum space apart, there will be a layer of TIM between the two and excess TIM contained in the at least one TIM overspill reservoir 420, 440. In a subsequent operation (not shown in Figure 6), the TIM may be subjected to a curing process to harden or solidify it. Accordingly, suitable thermal conductivity performance between the heat transfer plate 300 and the cell stack is provided via the layer of TIM, while an issue of excess TIM leaking out from between the heat transfer plate 300 and the cell stack is accommodated. Furthermore, while a vehicle 100 comprising the resulting battery assembly 200 is in use, an issue of cracking in the layer of TIM or separation of the heat transfer plate 300 and the cell stack is inhibited. According to an embodiment of the present disclosure, there is provided a vehicle battery assembly heat transfer plate 300. The heat transfer plate 300 comprises a heat transfer portion 410; and at least one thermal interface material (TIM) overspill reservoir 420, 440 each extending between the heat transfer portion 410 and an edge 430,450 of the heat transfer plate 300. According to another embodiment of the present disclosure, there is provided a heat transfer plate 300. The heat transfer plate 300 comprising a heat transfer portion 410; and at least one thermal interface material (TIM) overspill reservoir 420, 440 each extending between the heat transfer portion 410 and an edge 430, 450 of the heat transfer plate 300. 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 vehicle battery assembly heat transfer plate comprising:a heat transfer portion; andat least one thermal interface material overspill reservoir each extending between the heat transfer portion and an edge of the plate.

2. The plate of claim 1, wherein the heat transfer portion comprises a surface for receiving thermal interface material; andwherein each thermal interface material overspill reservoir extends between the surface of the heat transfer portion to the edge of the plate.

3. The plate of any previous claim, wherein each thermal interface material overspill reservoir is at least partly surrounded by at least two sidewalls, each sidewall corresponding to an interface between the heat transfer portion and said thermal interface material overspill reservoir.

4. The plate of any previous claim, wherein a depth of each thermal interface material overspill reservoir is substantially constant between the heat transfer portion and an edge of the plate.

5. The plate of claim 4, wherein the depth of each thermal interface material overspill reservoir is predetermined based on an intended minimum thickness of thermal interface material to be received on the heat transfer portion.

6. The plate of any previous claim, wherein the heat transfer portion comprises one or more cooling channels.

7. The plate of any previous claim, wherein the plate comprises a first body and a second body, the second body stacked on the first body; andwherein the heat transfer portion is formed of the second body and a part of the first body disposed above the second body, and the at least one thermal interface material overspill reservoir is formed of the remaining part of the first body, the remaining part of the first body extending from over an edge of the second body.

8. The plate of claim 7, wherein the first body and the second body are formed of aluminium.

9. The plate of any of claims 1 to 3, wherein the depth of the thermal interface material overspill reservoirvaries between the heat transfer portion and an edge of the plate.

10. The plate of claim 9, wherein each thermal interface material overspill reservoir corresponds to a sloped surface extending from the heat transfer portion to the respective edge of the plate for said thermal interface material overspill reservoir.

11. The plate of any previous claim, wherein a first thermal interface material overspill reservoir of the at least one thermal interface material overspill reservoir is provided at a first edge of the plate, and a second thermal interface material overspill reservoir of the at least one thermal interface material overspill reservoir is provided at a second edge of the plate, the second edge being on an opposite side of the plate to the first edge.

12. The plate of any previous claim, wherein each thermal interface material overspill reservoir extends substantially along the full length of the respective edge of the plate for said thermal interface material overspill reservoir.

13. A vehicle battery assembly comprising:a battery cell stack;a vehicle battery assembly heat transfer plate according to any of claims 1 to 12; anda layer of thermal interface material provided between the battery cell stack and the plate and in each thermal interface material overspill reservoir;wherein the layer of thermal interface material has substantially uniform thickness between a top of the battery cell stack and the heat transfer portion, and has a greater thickness in each thermal interface material overspill reservoir.

14. A vehicle comprising a vehicle battery assembly heat transfer plate according to any of claims 1 to 12 or a vehicle battery assembly according to claim 13.

15. A method in a process of producing a vehicle battery assembly, the method comprising: applying a force to one or more of a vehicle battery assembly heat transfer plate according to any of claims 1 to 12 and a surface of a battery cell stack to press together the plate and an opposing surface of the battery cell stack such that thermal interface material provided between the plate and the opposing surface of the battery cell stack is pressed into a layer therebetween and into the at least one thermal interface material overspill reservoir of the plate;wherein the layer of thermal interface material has substantially uniform thickness between a top of the opposing surface of the battery cell stack and the heat transfer portion, and has a greater thickness in each thermal interface material overspill reservoir.

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