FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
AND
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See section 10; rule 13)
TITLE OF THE INVENTION
A COOLING PLATE FOR A BATTERY MODULE AND METHOD OF MAKING THE SAME
APPLICANT
TATA MOTORS LIMITED
Of Bombay House, 24 Homi Mody Street,
Mumbai 400001, Maharashtra, India;
An Indian Company;
&
TATA MOTORS EUROPEAN TECHNICAL CENTRE PLC
of 18 Grosvenor Place, London, SW1X 7HS, United Kingdom;
Nationality: United Kingdom
INVENTORS
LEWIS, John David and BROWN, Mark Christopher
both are of Tata Motors European Technical Centre plc,
Commercial Department, International Automotive Research Centre,
University of Warwick, Coventry, CV4 7AL, United Kingdom;
Nationality: United Kingdom
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner
in which it is to be performed.

TECHNICAL FIELD
The present disclosure relates to a method of making a cooling plate for a battery module, to a battery module, and to a vehicle comprising a battery module.
BACKGROUND
Large battery packs such as used in electric vehicle traction applications are typically made up of a number of battery modules. Each module consists of a plurality of battery cells connected in such a way as to provide the module voltage and capacity required. Modules are then connected together to form a high voltage (HV) battery pack providing overall pack voltage and energy requirements.
Such batteries typically include some form of cooling means, often in the form of one or more cooling plates embodying channels through which a fluid coolant flows. Conventional cooling plates are manufactured by forming the cooling channel(s) by pressing or indenting metal plates, after which said plates are joined by welding, brazing or mechanical fasteners to form an enclosed labyrinthine channel.
A drawback of conventional cooling plates produced in the manner described above is that they require hard tooling to manufacture. This requirement for hard tooling makes it difficult and expensive to evaluate different configurations of cooling channels for a range of battery configurations / applications. Accordingly, the design and manufacturing process is constrained.
A further disadvantage of conventional cooling plates is that the pressing process produces protrusions on the outer face(s) of the plates which correspond with the channels formed on the inner surface(s) thereof. Consequently, the pattern of the cooling channels on the inner surface of the plate may be reproduced through the bulk material of the plate to create an unwanted pattern on the outer surface(s) of the plate. These protrusions, or raised areas, can impair the cooling performance of the plate by reducing the area of the battery cell in physical contact with the plate, which in turn degrades the conduction of thermal energy between the battery cell and the cooling plate.

The protrusions, or raised areas, can also damage the battery cell(s) in contact with the cooling plate by creating localised areas of high pressure on the battery cells. Said areas of localised high pressure can cause unwanted electrical contact between the plurality of interleaved electrodes within the cell, thereby leading to short-circuits and premature failure of the cell.
It is against this backdrop that the present invention has been conceived. At least in certain embodiments, the present invention provides a method of making an improved cooling plate for a battery module.
SUMMARY OF THE INVENTION
Aspects of the present invention relate to a method of making a cooling plate for a battery module, to a battery module, and to a vehicle comprising a battery module.
According to a further aspect of the present invention there is provided a method of fabricating a cooling plate for a battery module comprising:
taking a first planar substrate and selectively etching material from a first face thereof to form a first fluid passageway therein;
juxtaposing a second planar substrate in a face to face arrangement with the first face of the first substrate;
joining the two substrates each to the other.
The method of the present invention is advantageous in that it provides a cooling plate for battery with planar surfaces on one or both sides formed by joining together the two substrates, for example two aluminium brazing sheets. The complexities of joining together three layers of metal sheet as required in the prior-art are thus avoided.
In one embodiment, the method comprises selectively etching material from a first face of the second substrate to form a second fluid passageway therein and wherein the juxtaposing comprises arranging the first face of the first substrate facing the first face of the second substrate.

In another embodiment, the first fluid passageway etched in the first substrate is configured to have a spatial arrangement which is a mirror image of a spatial arrangement of the second fluid passageway etched in the second substrate. Optionally, the first fluid passageway etched in the first substrate has substantially the same dimensions, and / or size, and / or shape as the second fluid passageway etched in the second substrate, albeit in this embodiment the two fluid passageways have respective spatial arrangements or patterns which are mirror images of one another.
In a further embodiment, the method comprises aligning the first and second fluid passageways in registration each with other. By way of explanation, the first and second fluid passageways may be arranged such that features of the first fluid passageway such as edges and corners are substantially spatially aligned with corresponding features of the second fluid passageway. This alignment process may be performed prior to joining the two substrates together so as to form a single fluid passageway after joining the two substrates together.
Preferably, at least one of the substrates is thermally conductive. Accordingly, at least one of the substrates may be selected from the group comprising a metal, a metal alloy, and a ceramic.
In one embodiment, the etching process comprises one or more selected from the group including chemical etching, plasma etching, and ion beam milling.
The joining of the two substrates may comprise one or more selected from the group including adhesive bonding, diffusion bonding, brazing, welding, and mechanical joining using mechanical fasteners.
Optionally, the first fluid passageway comprises a labyrinth having a spatial arrangement comprising at least one of a serpentine, a geometric, a spiral, and an arcuate configuration.
Optionally, the spatial arrangement or pattern of the fluid passageway may be generated by photolithography. This is beneficial because there is no limitation on design complexity and labyrinth geometries can be tailored to provide optimum cooling flow without being

constrained by hard / fixed tooling or the need for assembly fixtures as seen with conventional construction processes. Because no hard tooling is required it is relatively easy to iterate designs during the product development phase to achieve optimum coolant flow within the cooling plate.
According to another aspect of the present invention, there is provided a cooling plate for a battery module fabricated according to the method of the foregoing aspect.
According to a yet further aspect of the present invention, there is provided a method of fabricating a battery module comprising:
taking at least one cooling plate according to the abovementioned aspect and arranging at least one battery cell in thermal communication therewith.
In one embodiment, the method of fabricating the battery module comprises arranging a plurality of battery cells in thermal communication with the at least one cooling plate. Optionally, the method comprises arranging a plurality of battery cells in thermal communication with each face of the cooling plate. The method according to this aspect of the invention may comprise arranging at least one battery cell in thermal communication with a plurality of cooling plates in the battery; optionally arranging a plurality of battery cells in thermal communication with a plurality of cooling plates comprised within the battery.
Certain embodiments of the foregoing method are beneficial in that they maximise use of the available cooling plate surface area. This is advantageous in that fewer cooling components are required, thereby saving space, weight and cost. It also simplifies battery pack assembly by minimising the number of fluid connections which are traditionally a potential source of unreliability.
It therefore follows that it is desirable for a plurality of battery cells to share a common cooling plate by arranging battery cells on both sides so that the planar faces of the cells are in direct thermal contact with the surfaces of the cooling plate.

According to another aspect of the present invention, there is now provided a battery module fabricated according to the method of the foregoing aspect.
According to another aspect of the present invention, there is now provided a battery module for an electric vehicle comprising:
at least one battery cell arranged in thermal communication with at least one cooling plate, the cooling plate comprising two planar substrates joined to one another in a face to face arrangement;
wherein the cooling plate has a fluid passageway etched in to a joined internal face of at least one of the substrates..
In a further aspect of the present invention, there is now provided a traction battery for a vehicle comprising a plurality of battery modules according to the aspect of the invention described above.
According to a yet further aspect of the present invention, there is provided a vehicle comprising a traction battery according to the abovementioned aspect of the present invention.
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
One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

Figure 1a shows a schematic, cross sectional representation of the component parts of a conventional cooling plate known in the art comprising two metal sheets in which a coolant channel has been produced by a mechanical pressing operation;
Figure 1b shows a schematic, cross sectional representation of a conventional cooling plate assembly after brazing the component parts of Figure 1a;
Figure 2a shows schematic, cross sectional representation of the component parts of conventional flat cooling plate known in the art comprising two flat outer metal sheets between which are sandwiched individual components which define the walls of the cooling channels; .
Figure 2b shows a schematic, cross sectional representation of a conventional flat cooling plate assembly after brazing the component parts of Figure 2a;
Figure 3a shows a schematic, cross sectional representation of the component parts of an etched cooling plate prior to brazing according to an embodiment of the present invention;
Figure 3b shows a schematic, cross sectional representation of an etched cooling plate assembly after brazing the component parts of Figure 3a;
Figure 4 illustrates schematically the steps in a process according to an embodiment of the present invention of fabricating the cooling plate of Fig. 3b; and
Figure 5 shows a schematic representation of a vehicle including a battery module comprising an etched cooling plate according to an embodiment of the present invention.
DETAILED DESCRIPTION
By way of general background, traction battery applications generally use lithium ion cells. These are available in a variety of configurations – cylindrical, rectangular (prismatic) and pouch cells. The latter is often preferred because their geometry allows more cells to be accommodated within a given volume and can thus provide a greater energy density. Pouch cells also have large flat surface areas which facilitate cooling.
Battery cells generate heat in normal operation in proportion to the rate of charge / discharge, so provision must be made for cooling. If cells consistently operate at temperatures higher than recommended by the manufacturer this can cause loss of performance (reduced energy storage capacity) and in extreme cases safety may be

compromised. Various arrangements are used to cool cells within battery packs depending on the application. In demanding applications with severe charge / discharge cycles it is desirable that the cells are in direct contact with a cooling plate embodying channels through which a fluid coolant flows. Efficient heat transfer from the cell to the coolant can be achieved by placing the pouch cell in direct face contact with the cooling plate.
Cooling plates typically contain a labyrinth passage or passages through which a coolant fluid can flow. The labyrinth arrangement is designed to provide uniform cooling of the cell(s).
Referring now to the example shown in Figure 1, a convenient method of producing such a cooling plate 1 comprises forming the labyrinth pattern by pressing or indenting 6 metal plates 2. Aluminium or an alloy of aluminium is a suitable choice because it combines the properties of good formability with good thermal conductivity, low density, corrosion resistance and relatively low cost. The indented aluminium plate 2 is then joined to a similar plate 2 and sealed to form an enclosed labyrinthine pattern 10.
The joining process optionally comprises securing the plates 2 to one another by mechanical fasteners using a suitable gasket, or alternatively by welding the plates together. A further alternative and convenient method of producing a cooling plate is to form each half using a composite aluminium brazing sheet comprising two alloys of different melting point (typically aluminium 3000 and 4000 series). These sheets are produced by laminating the alloy layers by rolling under high pressure and temperature. The lower melting alloy 4 can be on one or both sides of the higher melting alloy 2 which forms the core material. By placing the two indented halves of the cooling plate together with the introduction of a suitable flux and, in an inert atmosphere, raising the temperature to above the melting point of the first alloy 4 but below the melting point of the second alloy 2 the two components can be brazed together to form a sealed labyrinth 10 for cooling. Aluminium composite material can be obtained from ALCOA and are commonly used to construct automotive radiators. These types of material are described in US Patent 4489140.

Brazing together two composite aluminium sheets in the manner described potentially provides a convenient method of fabricating cooling plates 2 for lithium ion batteries. However cooling plates produced in this manner are characterised by having one or both sides containing protrusions, or raised areas, on the outer face(s) of the plates which correspond with the channels 6 formed on the inner surface(s) thereof. Consequently, the pattern of the cooling channels 6 on the inner surface of the plate may be reproduced through the bulk material of the plate to create an unwanted pattern on the outer surface(s) of the plate.
Pouch cells consist of a sealed flexible polymer outer case enclosing the electrodes and electrolyte. The electrodes are arranged in a stack with alternating anodes and cathodes separated by porous insulator layers.
Cell manufacturers normally recommend that a uniform positive pressure is applied to the cell. This is in order to prevent separation of the electrode layers within the cell, and is also necessary to maintain good thermal contact with the cooling plate. A convenient method of applying uniform pressure is by using a foam pad with known compression force deflection characteristics.
It follows that it is desirable that the cooling plate should have a flat surface where it is in contact with the face of the cell(s). If the surface comprises protrusions and / or indentations there is risk that non uniform pressure on the cell may cause internal damage to the electrodes or insulating separator potentially risking an internal short circuit.
Cooling plates of the type shown in Fig. 1b produced in the manner previously described above suffer the disadvantage that one or both surfaces will be non-planar and thus risk internal damage to cells.
Figure 2 illustrates an example of an alternative, known technique which results in cooling plate 3 having substantially planar outer surface(s). Referring to Figure 2a, an alternative solution proposes to use three layers of composite aluminium brazing sheet 12, 16, 12 with two flat outer layers 12 and the internal labyrinth 20 being formed by means of a third internal layer 16. The labyrinth 20 geometry that provides the fluid flow path is delineated

by individual aluminium components 16 that need to be accurately placed and retained during the assembly and brazing processes. This adds cost and complexity since the internal inserts 16 need to be individually stamped or laser cut, positioned and retained by some jigging arrangement.
Referring to Figure 3, an embodiment of the present invention proposes an alternative approach comprising the steps of forming a fluid passageway for the cooling labyrinth 30 within metal substrates, in particular in composite aluminium brazing sheets 22, by selectively photo-etching the alloy to form the cooling channels 30. Notwithstanding the fact that photo-etching of metals, including aluminium, to produce precision components is an established process; Applicant believes this to be a novel and inventive application to battery cooling plates.
According to an embodiment of the present invention illustrated in Figure 4, the first stages in the process 7 comprise coating 32 the aluminium brazing sheet 22 (substrate) with photo-resist for example by roller coating or dry film lamination and superimposing 34 a photo-tool with a positive image of the cooling labyrinth. The coated plate 5 is then exposed 36 to ultra-violet light. Exposed areas of photo-resist (corresponding to clear areas of the photo positive) are hardened by the ultra-violet whereas non-exposed areas of resist corresponding to the labyrinth pattern (solid areas of the photopositive) can be subsequently removed 38 (i.e. developed), for example by washing in a proprietary stripper such as supplied by DuPontTM. The developed plate is then submerged 40 in a suitable etchant, for example sodium hydroxide solution. This selectively removes aluminium to a form at least one blind channel 26 forming the labyrinth pattern, the depth of which is controlled by the time and temperature of the etching process 40. On completion, the remaining photo-resist is chemically removed 42. Aluminium sheets 22 with the labyrinth pattern 26 generated in this manner can then be brazed 44 together as previously described to form a cooling plate 5 as shown in the embodiment of Fig. 3b.
This method is advantageous because it provides cooling plates 5 with planar surfaces on both sides formed by brazing together two aluminium brazing sheets 22. The complexities of brazing together three layers of aluminium sheet as described above in the prior-art example of Fig. 2 are thus avoided. Because the labyrinth pattern is generated by

photolithography there is no limitation on design complexity and labyrinth geometries can be tailored to provide optimum cooling flow without being constrained by tooling or need for assembly fixtures as seen with alternative construction processes. Because no hard tooling is required it is relatively easy to iterate designs during the product development phase to achieve optimum coolant flow.
The method 7 of the present embodiment subsequently comprises the step of taking the manufactured cooling plate 5 and integrating the same 46 into a battery module by arranging 48 one or more battery cells in thermal communication with one or more of the external faces of the cooling plate 5.
In one embodiment of the invention, optimum use is made of the available cooling plate surface area by arranging a plurality of battery cells on either, optionally both, faces of the cooling plate 5. This reduces the number of cooling components required in a battery module 50, thereby saving space, weight and cost. It also simplifies battery pack 52 assembly by minimising the number of fluid connections between cooling plates 5 which is a potential source of unreliability. It therefore follows that it is desirable for a plurality of battery cells to share a common cooling plate by arranging cells on both sides so that the planar faces of the cells are in direct contact with the surface of the cooling plate 5.
Referring to Figure 5, a traction battery 52 according to a further embodiment of the present invention may be created comprising at least one battery module 50 (labelled 50-1, 50-2… 50-n in Figure 5) manufactured using the method 7 according to the foregoing embodiment. The traction battery 52 may be incorporated in a vehicle 9. The traction battery 52 is configured to supply electrical energy to one or more electric machine 54 to propel the vehicle 9, as shown schematically in Figure 5. The vehicle 9 in the present embodiment is an automobile, but the invention is not limited in this respect.
Notwithstanding the fact that two etched plates have been described in the forgoing embodiments of the invention, it will be evident to the skilled person that a single etched plate could be used in combination with a non-etched / planar plate.

It will be appreciated that various changes and modifications can be made to the method and resulting etched cooling plate described herein without departing from the scope of the present invention.

WE CLAIM
1. A method of fabricating a cooling plate for a battery module comprising:
taking a first planar substrate and selectively etching material from a first face
thereof to form a first fluid passageway therein;
juxtaposing a second planar substrate in a face to face arrangement with the first face of the first substrate;
joining the two substrates each to the other.
2. A method according to claim 1 comprising selectively etching material from a first face of the second substrate to form a second fluid passageway therein and wherein the juxtaposing comprises arranging the first face of the first substrate facing the first face of the second substrate.
3. A method according to claim 2 wherein the first fluid passageway etched in the first substrate is configured to have a spatial arrangement which is a mirror image of a spatial arrangement of the second fluid passageway etched in the second substrate.
4. A method according to claim 3 comprising aligning the first and second fluid passageways in registration each with other.
5. A method according to any preceding claim wherein at least one of the substrates is thermally conductive.
6. A method according to any preceding claim wherein at least one of the substrates is selected from the group comprising a metal, a metal alloy, and a ceramic.
7. A method according to any preceding claim wherein the etching comprises one or more selected from the group including chemical etching, plasma etching, and ion beam milling.

8. A method according to any preceding claim wherein the joining comprises one or more selected from the group including adhesive bonding, diffusion bonding, brazing, welding, and mechanical joining using mechanical fasteners.
9. A method according to any of the preceding claims wherein the first fluid passageway comprises a labyrinth having a spatial arrangement comprising at least one of a serpentine, a geometric, a spiral, and an arcuate configuration.
10. A cooling plate for a battery module fabricated according to the method of any of the preceding claims.
11. A method of fabricating a battery module comprising:
taking at least one cooling plate according to claim 10 and arranging at least one battery cell in thermal communication therewith.
12. A method according to claim 11 comprising arranging a plurality of battery cells in thermal communication with the at least one cooling plate.
13. A method according to claim 12 comprising arranging a plurality of battery cells in thermal communication with each face of the cooling plate.
14. A method according to any one of claims 11 – 13 comprising arranging at least one battery cell in thermal communication with a plurality of cooling plates.
15. A battery module fabricated according to the method of any of claims 11 – 14.
16. A battery module for an electric vehicle comprising:
at least one battery cell arranged in thermal communication with at least one cooling plate, the cooling plate comprising two planar substrates joined to one another in a face to face arrangement;
wherein the cooling plate has a fluid passageway etched in to a joined internal face of at least one of the substrates.

17. A traction battery comprising a plurality of battery modules according to claim 15 or 16.
18. A vehicle comprising a traction battery according to claim 17.
19. A battery cooling plate substantially as herein described with reference to the accompanying figures.
20. A battery module substantially as herein described with reference to the accompanying figures.
21. A vehicle substantially as herein described with reference to the accompanying figures.