GB2604115A - Battery module - Google Patents

Abstract

A battery module for automotive use having a stack comprising a plurality of electrically interconnected pouch cells 4 interleaved with generally planar, relatively stiff, heat transfer fins 2. The battery module also has a pair of non-planar clamp plates 8 located at each end of the stack. The inner faces of the clamp plates are arranged to apply even pressure across the surface area of the stack. A resilient retaining member (6, Figures 3A, 4C) is wrapped around the stack and the clamp plates, in order to apply a compressive force. The clamp plates may be generally flat on their inner faces and may be thicker near the middle in order to distribute the compressive force away from the edges of the clamp plates. The clamp plates may have an arcuate outer profile. The fins may be provided with stand-offs outside the region of the pouch cells. The standoffs may be formed by relatively stiff bushes 16 placed between the fins. The stand-offs may be separated by resilient components 14 so that the fins can move, to a limited degree, back and forth between the clamping plates as the cells expand and contract during charge and discharge.

Description

Battery Module This invention relates to battery modules for storing electrical energy. Such modules typically contain many electrically interconnected cells having, for example, lithium ion chemistry.

Background

Batteries for automotive markets typically fall into two categories; a) high power density applications and b) high energy density applications. High power density batteries require efficient cooling as the small chemical conversion losses of each cell add up to significant heat generation at high powers. As battery cells continue to develop, energy densities increase, and re-charging times reduce, so the high energy applications also require improved cooling. In some cases, where the external ambient temperature is low, the batteries will require warming before they can be charged, for example by kinetic energy regeneration under braking.

Problem 1 -Thermal gradient and heat transport time.

Prior-art battery thermal management systems have a thick cooling/heating plate situated horizontally below the module, containing water/glycol coolant, and also have either an aluminium cell case or aluminium fins to conduct heat away from the active material inside.

An example of the fins is described in JP2009009889A. Typically in this arrangement, the cells are cylindrical cells with their axes aligned vertically. Aluminium cooling fins extend vertically from the base plate between the cells and are in thermal contact with the base plate.

This results in poor cooling of the cell, because of the thermal gradient down towards the cooling plate (hotter at the top than the bottom) and heat transport time which means that the cells can be significantly warmer than an average temperature, during transient events and see a significant temperature difference across a cell. This temperature difference leads to thermal fatigue of the active material, which in use, is expanded more at one end of the cell than the other due to the temperature difference and the coefficient of thermal expansion.

Thermal fatigue leads to cracks in the active material which then becomes inactive once isolated by cracks, hence thermal fatigue directly reduces battery capacity with cyclic use. This is known as cyclic aging.

Other alternatives in the prior art include the use of direct contacting dielectric oil as a cooling medium. However, the specific heat capacity of the oil is lower than water/glycol mix, resulting in a greater temperature increase in the coolant, compared to water/glycol, for the same heat input and hence a poorer cooling efficiency.

Problem 2 -Even pressure on the cell surface Pouch cells, which are a form of battery cell housed in a soft laminate pouch, require a compressive force perpendicular to the planar surface in order to stop delamination during expansion and contraction of the cell stack, during charge/discharge cycles. If the clamping force is too high, the life will be shortened as the separator thickness is reduced with compression which degrades function. If the pressure is too low, the life will be shortened by delaminafion of the active materials. In short, failure to supply the correct force will reduce cell life.

Problem 3 -Expansion and contraction of cells.

With reference to Figure 1, pouch cells change shape as the lithium ions migrate from anode to cathode and back again during charging and discharging, because the lithium ions cause expansion of the crystal lattice upon intercalation. As the chart shows, there can be growth by as much as.05 millimetres between a 0% and a 100% state of charge. This results in pouch cells becoming thicker or thinner as their state of charge varies. In addition, as cells age, not all ions de-intercalate, meaning that the cells gain thickness with age. Typically this can increase the cell thickness by 5-10% over the product life, depending on their chemistry. As examples, some pouch cells grow by 10% thickness between 0% and 100% state of charge and an additional 10% from beginning to end of life, giving a total of 20%. The particular pouch cells described below are 4.85-5.19mm thick. Pouch cells in general vary from 4mm to 12mm thick.

This then presents the problem of how to securely fix the cells to the surrounding vehicle structures whilst they are expanding and contracting, whilst at the same time keeping the clamping force within the target range, to ensure a good service life.

Prior art battery clamping systems have focused on maintaining a fixed length in the through thickness direction by introducing deformable structures between the cells, such as foam, or deformable heat transfer fluid passages interposed between the cells. An external structure then applies force to the stack of cells and deformable parts, arriving at a fixed length for the whole stack, once pre-load has been applied. When the cells expand or contract, the external structure maintains its length, whilst the change in cell thickness is contained by deformation of the deformable structures, between the cells in the pack, such as those disclosed in JP2011096465A. By their nature, the deformable structures have a stiffness, which according to Hooke's law will vary with extension or compression. This means that prior art designs cause a significant change in clamp load across the cell stack as the cells expand and contract, thus degrading component life.

Problem 4 -Technical complexity equals Cost.

Other heat transfer fluid passage designs, which pass alongside the pouch cells, require tuned stiffness components in order to mitigate the increase in clamping force as the pouch cells expand, which is discussed above. These additional components can add significant cost. JP2009170140A, is a good example of this strategy. This has complex springs inside cooling fins, between the cells.

Problem 5 -Heat transfer fluid supply.

When using heat transfer passages between battery cells to achieve thermal management, the heat transfer to/from the fluid must be even from cell to cell, as otherwise one cell will begin to get hotter, its resistance will increase as a result of its increased temperature and it will then generate more heat for the same current flow, further increasing its temperature.

Thus to avoid this undesirable positive feedback loop, even cooling of the cells is beneficial to help prevent thermal runaway events and to ensure cell longevity. The problem to be overcome is how to ensure that the heat transport to/from each cell is even. Prior art thermal management systems may use a single passage interwoven amongst a large number of cells, meaning that the heat transfer fluid runs in 'series', and thus gets warmer as it passes each cell. In cooling mode, the cells at the end of the heat transfer fluid passage run will thus be significantly warmer than those at the beginning, where the coolant has just exited the vehicle cooling radiator and was at its coolest.

Problem 6 -Maintaining a sealed heat transfer fluid system during expansion and contraction.

Interposing heat transfer passages between the battery cells is a potentially efficient method of managing their temperature, with short heat transfer paths. However, the battery cells vary in thickness with changing state of charge and cyclic age, which means that the distance between heat transfer passages also varies. The difficulty is then to ensure the heat transfer medium is retained within the thermal management fluid circuit, whilst allowing for expansion and contraction of the battery cells, and thus potentially, expansion and contraction of the heat transfer passages themselves.

In some cases, the heat transfer fluid passages are flexible and thus allow for limited movement. In other cases, there are sliding seal arrangements to allow for expansion and contraction of the adjacent cells. Both of these solutions are unsatisfactory and in the case of the sliding seals, are complex and difficult to manufacture.

It is important to note that effective thermal management systems are a significant contributor to battery safety by preventing and/or slowing down thermal runaway and propagation to neighbouring cells.

It is an object of the present invention to overcome at least some of the shortcomings of prior art battery cooling arrangements.

In a first aspect, the invention provides a battery module for automotive use, having a stack comprising a plurality of electrically interconnected pouch cells interleaved with generally planar, relatively stiff, heat transfer fins, the battery module further comprising a pair of non-planar clamp plates located respectively at each end of the stack, which on their inner faces are arranged to apply even pressure across the surface area of the stack, and a resilient retaining member which is wrapped around the stack and the clamp plates, in order to apply a compressive force to the pouch cells, via the clamp plates.

This construction has the advantages that it provides a battery cell assembly, or module, which includes heat transfer fluid passages, or fins, adjacent to the cell walls with maximised contact area, a resilient means of compressing the cells together in order to provide an even pressure at the surface of each cell, and a method of joining the heat transfer fluid passages together such that fluid, such as water, water/glycol or a two phase coolant, can be transported to and from the fins without loss of fluid and the cells can be allowed to expand and contract as state of charge varies and as the cells change thickness with age.

Embodiments of the invention will now be described by way of example, with reference to the drawings in which:-Figure 1 is a chart showing pouch cell growth versus state of charge; Figure 2A is an exploded schematic view of a heat transfer passage or fin; Figure 3A is a schematic isometric view of an assembly of heat transfer passages and cells with resilient bands; Figure 3B is a schematic exploded isometric view of an assembly of heat transfer passages and cells with a top plate removed; Figure 4A is a schematic plan view of a battery module; Figure 4B is a schematic cross section through the battery module of figure 4A along line CC of Figure 4A and showing the heat transfer passages; Figure 4C is a side elevation of Figure 4A; Figure 4D is an end elevation of Figure 4A; Figure 5 is a schematic cross section along line D-D of Figure 4A and showing a collector rail of the battery module; Figure 6 is an enlarged schematic cross section (E) of the collector rail construction of Figure 5; and Figure 7 is a chart showing cell life versus pressure.

The following is a description of an example of a battery thermal management system using the present invention.

With reference to Figures 2 and 3, for pouch cell applications, cooling/heating passages 2 are placed between the cells 4, directly in contact with the highest surface area cell face, enabling a heat exchange between the cell and the fluid held inside the heat transfer passages. In the preferred embodiment, the heat transfer passages are arranged horizontally, with layers of cells arranged also horizontally and adjacent in the vertical direction. The cells are interconnected at each end using electrical interconnectors 28, in a chosen electrical circuit configuration. The general construction is that of a laminate construction with alternate battery cell and heat transfer passages. Some of the newer cells are produced in a long, thin format, with one electrode at each end. For modules using these, the fins and cells may be arranged vertically rather than horizontally. This also helps with purging air during the first fill with coolant, as long as the outlet is higher than the inlet.

The heat transfer passages 2 are formed from two generally planar components 30 which have opposed raised edges, so that when they are brought together, they form a sealed generally planar volume between them. In use, this volume can be filled with coolant, and the whole assembly placed between layers of battery cells 4. The volume may be supported with a plurality of spacers 33, of similar thickness to the assembled interior distance between the top and bottom plates 30 (they are planar discs in this example) These may, during manufacture, be aligned using a template 32, having apertures 36 in the positions in which the spacers should be located, which may be removed before the upper and lower parts of the heat transfer passage 30 are sealed together. By placing these spacers between the plates 30, away from the raised edges, the plates 30 remain substantially undeflected when the pouch cells that will be between them, change dimension. This prevents the heat transfer passage being crushed by expansion of the pouch cells. By leaving space between the spacers 33, minimal impact is made on flow of coolant within the heat transfer passage.

In use, coolant flow through the heat transfer passage 2 is achieved by providing a respective coolant inlet 38 and outlet 40 in the generally planar components 30. In the example shown in Figure 2A, and replicated in the other figures, each of the top and bottom plates has diametrically opposite circular apertures which are aligned so that when the top and bottom plates are brought together, a through-hole is created in each diametrically opposite corner. Additionally, an annular spacer is located at each of these through holes, and this has radial apertures 35 formed in it so that coolant can flow from inside the inlet/outlet apertures 38,40 through the annular material of the spacer 34, and into the larger volume of the heat transfer passage 2. Figure 2B portrays an enlarged view of spacer 34. Other arrangements, are possible, and the general principle is that coolant can enter the volume between the top and bottom plates 30 at one position and that an exit is provided generally on the opposite edge, thus promoting coolant flow F throughout the whole volume formed between the top and bottom plates 30.

The sealing between the top and bottom plates 30 raised lips may be done using adhesive or welding techniques, or they may be sealed using a gasket and clamping forces. Thus once assembled, the heat transfer passages form a generally incompressible and stiff, hollow component through which coolant may flow. Several different manufacturing options are described in more detail below.

With this laminar construction of pouch cell 4 alternating with heat transfer passage 2, the heat-flow path is short, <1mm, so that the cell faces are held very close to the fluid temperature and heat transport times are short, meaning low transient temperature fluctuations. The fluid is typically water/glycol, so a low temperature rise results from the heat transport to/from the cells. The transfer passages 2 run across the high surface area face of the pouch cells and hence there is low thermal gradient in the through thickness direction of each cell resulting in lowered differential thermal expansion of the cell and reduced aging due to thermal fatigue cracks in the electrode material.

The high-volume manufacture of the heat transfer passages 2 preferably relies on known forming techniques such as coil-fed die stamping, hence costs are low. In low volumes, laser-cut flat sheets can be formed with a 'gasket' style sheet providing the 'stand-off' to ensure a passage is formed. Equally, thermally conductive plastic materials may be vacuum formed in high volumes at low cost, or laser cut in low volumes at low cost.

With reference to Figures 3A to 4D, a stack of the heat transfer passages 2 and battery cells 4 is then clamped together between top and bottom plates 8, by means of one or more resilient bands 6 acting on the clamping plates 8. The clamping plates 8 preferably have shaped surfaces on the outer faces of the stack, thus ensuring that some of the clamping force from the resilient band(s) 6 is applied towards the centre of the battery cells 4 and away from the edges of the clamping plates 8, ensuring a more even distribution of force application. Further, the shaped surfaces of the clamping plates 8 ensure that the cross-sectional moment of area is highest where the bending moment is highest, which reduces deflection of the clamping plate 8 and ensures that the applied force is distributed evenly across the face of the battery cells 4.

With reference also to Figures 5 and 6, heat transfer fluid enters the structure through a connection to an inlet radial annulus 9 which is interposed between the heat transfer passages/fins 2. The radial annulus 9 leads to a 'collector rail' 10, which in this case is positioned vertically and joins all of the heat transfer passages 2 together, by passing through the inlet apertures 38, in each of the top and bottom plates 30 of the heat transfer passages 2. A similar outlet collector rail 12 and radial annulus 13 is present on the opposite side of the heat transfer fins 2 so to collect and provide an outlet for fluid that has passed through the heat transfer passages 2. Similarly therefore, the collector rail 12 passes through the aligned outlet apertures 40 of each heat transfer passage 2.

With particular reference to Figure 6, between each pair of heat transfer passages 2, the collector rails 10 and 12 are formed by the residual volume within at least one higher stiffness resilient washer/bush element 14 (preferably rubber or another elastomer) and a hollow bush element 16. The bush element may be constructed of metallic materials, such as aluminium, the general principle being that deflection of the bush element 16 is insignificant in relation to the resilient elements 14 and 17, under the applied clamp load. This combination of bush 16, sandwiched between washers 14, forms a flow passage between the inlet/outlet apertures 38, 40 of the heat transfer passages, and also the washers 14 help seal against the outer faces of the heat transfer passages.

External to the heat transfer passage stack, at the top and bottom in a horizontal configuration as shown in these exemplary drawings, the fluid collector rail is formed by the residual volume within a lower stiffness resilient (preferably elastomer) washer/bush element 17 and a clamping bolt 18 and nut 20 which applies a pre-load to the bushes 16 and resilient elements 14 & 17 thereby creating a seal. Each clamping bolt 18 (one for each of the two collector rails 10,12) passes through each of the resilient washers 14 and 17 and the bushes 16 and the respective apertures 38 and 40. The diameter of the clamping bolts 18 are deliberately much smaller than the inner diameter of these other elements, thus providing an annular flow passage around the outside of the bolts 18, and inside the washers 14, 17 and the bushes 16, and which interconnects each of the inlets and outlets of the heat transfer passages 2.

Thus in each case, a collector rail is effectively an annular space around a clamp bolt which is bounded by the bush and washer elements 14, 16 and 17 and the inlet outlets 38 and 40 of the heat transfer passages.

The clamping bolts 18 may have local variations in diameter 22 at locations between the heat transfer passages, to act as restrictions to the fluid flow along the collector rail to help balance the flow through the heat transfer passages 2, and so ensure even flow distribution is achieved through the multitude of heat transfer passages. These elements are preloaded by the clamp bolts 18 and nuts 20. Independently, the pouch cells have pressure applied to them by the top and bottom plates 30, and the resilient bands 6 surrounding the whole stack. The clamping bolts, do not in the preferred embodiment, clamp top and bottom plates 8. These plates 8 are located on the bolts 18 through their location holes 26.

As the pre-load is applied to the clamping bolts 18 by tightening nuts 20, tension is induced in the bolt and compression is induced in the elements between the nuts 20 and respective bolt heads. The resilient elements 14 and 17 deflect under compression and because of their stiffness and Hookes law, offer a restoring force against the compression until full pre-load is achieved on the bolt. Once the pre-load is applied, the resilient elements 14 and 17 all have the same compressive force applied.

If we consider the outermost (top or bottom) heat transfer passages 2, contact force is applied by resilient member 14 on one side and by resilient member 17 on the opposite side. With pre-load only, and because the elements are dimensioned to match the positions caused by of the initial states of the cells, at the chosen preload force, these forces are the same and no bending of the heat transfer passage occurs. However, once the pouch cells gain charge, or begin to age, they will become thicker. This increases the distance between heat transfer passages 2 and unloads the resilient members 14 whilst also increasing the compressive load on resilient members 17. Considering again the top or bottom heat transfer passage, the contact force applied by resilient member 14 is reduced, whilst the contact force applied by resilient member 17 is increased, leading to an unequal force distribution across the heat transfer passage and resulting in bending. By careful calculation of the growth extent, the relative stiffnesses of the resilient members can be determined so as to minimise this effect, and generally speaking the stiffness of the resilient member 17 will be chosen to be less than that of the resilient member 14.

From Figure 6 it can be seen that the distance between any two neighbouring heat transfer passages will increase by the growth of two pouch cells, reducing the deflection on the resilient members 14 and decreasing their compressive load. The distance between the top and bottom heat transfer passages will be increased by the growth of, in this example, ten pouch cells, increasing compressive deflection of the elements 17 and hence increasing the compressive contact force applied by elements 17 to the top and bottom heat transfer passages 2. It is clear that to minimise bending forces on the heat transfer passages 2, the elements 17 should deflect significantly more than elements 14 and hence should be significantly less stiff relative to elements 14, so as to reduce the bending force applied to the heat transfer passage as a result of pouch cell growth.

The relative stiffnesses of the resilient elements ensures that with expansion and contraction of the battery cells, the change in compressive load on each side of the outermost heat transfer passages results in a low differential force, within a target to achieve the desired component fatigue life.

The stiffnesses of the elements 14 and 17 is a function of the material properties and the geometry of the elements. If the material of elements 14 and 17 is the same, and therefore hardness is the same, the stiffness may still be different because the geometry may be different. Stiffness of a bush is k=E"A/L (E=Youngs modulus, A = cross sectional area perpendicular to extension direction, L = length in extension direction). In the preferred embodiment, the materials used for the elements 14 and 17 are the same, and therefore the hardness is the same, but the stiffness is varied by using different geometries.

Between the heads of the bolts 18 and nuts 20, and the lower stiffness resilient elastomer bush 17, a washer 24, with relatively lower coefficient of friction against the bolt head and relatively higher coefficient of friction against the bush 17, is placed. Similarly another washer 24 is placed between the lower stiffness resilient elastomer bush and the nuts 20, at the opposite end of the bolt, with the desired effect that the tightening of the fastener does not result in the twisting of the lower stiffness resilient bush elements, which would otherwise damage and/or change their stiffness characteristics.

Note that the coolant collector rails 10, 12 pass through the clamping plates Sand are located within them by means of location holes 26 in the clamp plates 8 acting upon the periphery of the bolts 18 and similarly upon the tightening nuts 20. The two location features between clamp plates 8 and the collector rails 10, 12 act as dowels to secure the cells 4 and heat transfer passages 2 stack, removing degrees of freedom to move in the plane of the cells.

Without these features, the cell stack may move with small amounts of vehicle vibration present during operational service and apply force to the electrical connections causing them to break before the end of the expected service life.

Thus, in the above arrangement, coolant such as water/glycol heat transfer fluid is supplied almost directly to the cell walls, ensuring an even temperature and efficient cooling/heating.

Also, the arrangement transfers heat to/from the cells 4, with fluid flowing perpendicular to the length of the shortest face, so reducing the temperature difference across the battery cell and hence reducing thermal fatigue.

Also, the arrangement allows the cells 4 to be cooled/heated with a short thermal path, so reducing transient temperature spikes during transient load events, increasing safety as the cell is less likely to reach thermal runaway temperatures and reducing thermal fatigue and hence cyclic aging. Thus overcoming problem statement 1.

Also, the arrangement uses resilient bands 6 to apply the force, with a low stiffness, or force to extension ratio, that allows the cells to expand and the stack height to increase by 5-10% without significantly increasing the axial clamp force upon them. This, preferably in conjunction with the chosen stiffnesses of the washers 14, 17 noted above, ensures substantially consistent force application throughout the component life, overcoming problem statement 3.

The clamping plates 8 at the top and bottom of the module are shaped such that not all of the force applied by the resilient bands 6 is applied at the edges of the plate. This provides a more even distribution of the clamping force across the surface. In addition, the shape of the top and bottom clamping plates 8 is such that the section with the greatest bending moment applied has the greatest cross section, which reduces distortion of the plate under the applied clamp load and evens the pressure distribution across the cell face. This overcomes problem statement 2. In the preferred embodiment, these plates 8 have a pitched roof configuration with a generally central high point and a continuous elevation from the edges of the plates.

Other shapes, such as arcs or a pitch with the ridge not near the centre, could be used to achieve the functional objects mentioned above.

Additionally, the edges of the plates 8 are radiused typically with a value of 0.5mm or greater, in order to ensure that the resilient bands 4 are not damaged during assembly and so that even tension is achieved throughout the band after assembly, as the bands 4 are substantially free to slide over the edges of the plates 8.

Also, the arrangement maintains the stiffness of the heat transfer passages by using force transferring bosses 33 (see Figure 2A) , spaced throughout the heat transfer passages 2 so as to carry the axial force without damage to the passages. This eliminates the need for internal spring components to deal with expansion forces, used in prior art solutions, thus reducing cost and overcoming problem statement 4.

Also, the arrangement configures the heat transfer passages to be fed in parallel, with a common supply and common return for the majority, or all, of the fins/heat transfer passages 2 in each module. The bolts 18 and nuts 20, that clamp the elastomeric sealing devices 14, 17 together, see above, can have locally increased diameters 22 at locations between the heat transfer passages, to restrict the flow beyond each locally increased diameter. The effect of the local restrictions, from the increased diameter portions of the clamping bolts, is to ensure the flow rate is more balanced meaning that each of the multitude of heat transfer passages receives a similar or the same flow rate of heat transfer fluid. The skilled person, will appreciate that the flow rates do not necessarily need to be the same, if for example the battery cell configuration adjacent to a heat transfer plate 2 is different in different parts of the battery module. The change in the diameter of the clamping bolts 20, allows customized flow balancing to be carried out with a very simple configuration, and which can be changed easily by changing the bolt profile. This ensures that the temperature of the outgoing fluid is at a desired differential, such as the same from each heat transfer passage. The temperature difference from cell to cell is also minimised because the parallel circuit flow means that inlet water temperature is the same for each heat transfer fluid passage, thus overcoming problem

statement 5.

Also, the arrangement uses deformable elastomeric seals 14, 17 configured with a high stiffness in locations between the heat transfer fluid passages and a low stiffness in locations external to the heat transfer passage stack (generally at the top and bottom), with a threaded fixing providing clamp force, such that; a) sufficient clamping pressure is achieved to create a seal for the heat transfer fluid, b) the deformable seals can expand and contract as the battery cells expand with change of state of charge and age, c) as the stack of deformable seals is pre-compressed to create a fluid seal, the force upon each side of each heat transfer fluid passage is equal, resulting in no bending of the passage, however as the battery cells expand, the deformable seals 14 interposed between the fins 2 will have their pre-load decreased, whilst the deformable seals 17 external to the fin stack will have their pre-load increased, resulting in a difference in force across the heat transfer passage and hence bending of the heat transfer passage. The relatively low stiffness of the deformable seals 17 located external to the heat transfer passage stack serves to reduce this bending force to a level tolerable for the material and life and duty cycle of the product. This configuration also means that no sliding seals are required. This overcomes problem statement 6.

Figure 7 shows cell life (in cycles) versus applied pressure on the planar face (in Bar), and which underlines with test data, why it is important to provide a structure which takes account of pressure on the cells.

Summary of advantages:-

1. A pouch type battery cell clamping system, where the clamping plate geometry includes features to increase bending stiffness and distribute force from resilient band(s), to give even pressure across the face of the battery cell and so prolong life.

2. A pouch type battery cell clamping system that makes use of at least one resilient band to provide clamp force and which maintains clamping force within a target range as the cells expand and contract, so prolonging battery cell life.

3. A battery cell thermal management system that provides heat transfer fluid passages in contact with the large surface area faces of the battery cell, which retains the fluid within the system whilst allowing the battery cells to expand and contract, but which does not substantially deform the heat transfer passages in response to the varying thickness of the battery cells with changing state of charge or age.

4. A battery cell thermal management system that flows heat transfer fluid across the short face of the cell, such that the thermal gradient on the cell is reduced, hence thermal fatigue and cyclic aging are reduced.

5. A battery cell thermal management system using heat transfer fluid passages interposed between cells, where the global movement of the heat transfer fluid passages is accommodated by resilient deformable sealing elements, such that multiple heat transfer passages can be connected without using sliding sealing devices, so reducing cost and wear.

6. A battery cell thermal management system utilising resilient flexible sealing elements external to the stack of heat transfer fluid passages with a lower stiffness in the clamping direction, than the resilient flexible sealing elements interposed between the heat transfer fluid passages.

Claims (15)

1. Claims 1. A battery module for automotive use, having a stack comprising a plurality of electrically interconnected pouch cells interleaved with generally planar, relatively stiff, heat transfer fins, the battery module further comprising a pair of non-planar clamp plates located respectively at each end of the stack, which on their inner faces are arranged to apply even pressure across the surface area of the stack, and a resilient retaining member which is wrapped around the stack and the clamp plates, in order to apply a compressive force to the pouch cells, via the clamp plates.
2. 2. A battery module as claimed in claim 1, wherein the clamp plates, are generally flat on their inner faces and are thicker near the middle of the plane, so that the compressive force from the resilient retaining member is caused to be distributed away from the edges of the clamp plates.
3. 3. A battery module as claimed in claim 1 or claim 2, wherein each clamp plate has an arcuate outer profile.
4. 4. A battery module as claimed in any preceding claim, wherein each clamp plate has two planar surfaces on its outer face joined with a single vertex.
5. 5. A battery module as claimed in any preceding claim, wherein the fins are provided with stand-offs outside the region of the pouch cells, and wherein the standoffs are each separated by resilient components so that the fins can move, to a limited degree, back and forth between the clamp plates, as the dimensions of the pouch cells change during charge and discharge cycles.
6. 6. A battery module as claimed in claim 5, wherein the resilient components have differing stiffnesses.
7. 7. A battery module as claimed in claim 6, wherein the resilient components are less stiff in the outer regions of the stack than in the more central regions, thus causing clamp loads between the clamp plates to be relatively evenly distributed between each layer of pouch cells in the stack.
8. S. A battery module as claimed in any of claims 5 to 7, wherein the standoffs are formed by relatively stiff bushes placed between the fins.
9. 9.
10. 10.
11. 11.
12. 12.
13. 13.
14. 14.
15. 15.A battery module as claimed in any of claims 5 to 8, wherein the standoffs and/or the resilient components are located onto a clamp bolt which passes through each of the fins and both clamp platen, and applies a clamp force to the whole stack.A battery module as claimed in any preceding claim, wherein the fins are hollow and arranged to contain a heat transfer fluid which in use is able to extract, or inject, heat into the battery module, via conduction through the walls of the fins into the adjacent pouch cells.A battery module as claimed in claim 10, wherein the fins are manifolded together so that flow through the fins of the heat transfer fluid can occur in parallel, generally from one side of the module to the other side.A battery module as claimed in claim 9, wherein the fins are manifolded together in a collector rail, the collector rail being formed by an aligned stack of apertures formed in the respective fins, which are sealed together with annular resilient spacers between the apertures having predetermined differing stiffness characteristics, and through which a clamp bolt passes, to create an enclosed, fluid-tight space around the clamp bolt which is in fluid communication with the hollow space within each of the fins.A battery module as claimed in claim 12, wherein the stiffness of the resilient spacers is lower towards the outer edges of the module.A battery module as claimed in claim 12 or claim 13, wherein the clamp bolt has localised variations of diameter to create localised flow restrictions along the collector rail.A battery module as claimed in any of claims 9 to 14 when dependent on claim 9 or claim 12, wherein the stack of fins and cells is retained within the module by location holes in the clamping plates through which the clamping bolt passes thereby acting to locate the coolant collector rails.Table of Drawings Components and Reference Numerals Name Numeral Cooling /Heating Passages/Heat Transfer Passage 2 Battery Cells 4 Resilient Bands 6 Clamping Plates 8 Inlet Radial Annulus 9 Inlet Collector Rail 10 Outlet Collector Rail 12 Outlet Radial Annulus 13 Higher stiffness Resilient Washer Element 14 Bush Element 16 Lower stiffness washer 17 Clamping Bolt 18 Tightening Nut 20 Locally Increased Bolt Diameters 22 Low Friction Washer 24 Clamping plate location holes 26 Electrical Interconnectors 28 Generally Planar Components/Top and Bottom Plate for heat transfer passage 30 Template 32 Spacer/Clamp Force 33 Spacer Internal Flow 34 Spacer Apertures 35 Template Aperture 36 Transfer passage inlet 38 Transfer passage outlet 40 Coolant flow 'F' F