FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; rule 13)
TITLE OF THE INVENTION BIMETALLIC BUSBAR FOR BATTERY ASSEMBLY
APPLICANT
TATA MOTORS LIMITED, an Indian company
having its registered office at Bombay House,
24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001 Maharashtra, India
INVENTORS
Mr. John David Lewis, Mr. Robinson Stonely
and Mr. Valerie Anne Self
All are British Nationals
of Tata Motors European Technical Centre pic
4th Floor International Automotive Research Centre
University of Warwick
Coventry, CV4 7AL
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to bimetallic busbars for battery assemblies and particularly, but not exclusively, to bimetallic busbars for interconnecting the positive and negative terminals of cells in a battery assembly to achieve a variety of battery cell configurations and to provide compatible joint interfaces between the busbars and the cell terminals. Aspects of the invention relate to a busbar, to a battery assembly or module, to a product and to a vehicle.
BACKGROUND OF THE INVENTION
Large battery packs used in many applications such as electric, hybrid or plug-in hybrid vehicles generally consist of a plurality of battery cells which are electrically interconnected to provide the voltage and energy capacity required for the specific application. For large battery packs comprising several hundred individual cells it is desirable to use a cost effective interconnection system which is also capable of providing the required reliability.
The battery cells may be of cylindrical, rectangular or pouch configuration. The rectangular or pouch configuration is often preferred because its geometry allows more cells to be accommodated within a given volume and can thus provide a greater energy density. The pouch cells consist of a flexible polymer case which contains electrodes and electrolyte and two foil terminal tabs which extend from one side of the case. Due to the cell chemistry and internal electrode construction, the positive cell terminal (cathode) is often comprised of aluminium or nickel coated aluminium and the negative terminal (anode) is often comprised of copper or nickel coated copper. This is not essential, however, and other arrangements are possible, including arrangements wherein the positive cell terminal is copper and the negative cell terminal is aluminium.

Individual cells can be electrically connected in a parallel and/or series circuit configuration to provide the voltage and energy requirements for a particular application. The cells are usually interconnected using conductive members referred to as busbars. The busbars are made from metals with good electrical conductivity, for example copper, brass or aluminium etc. Various processes can be used for attaching the battery terminal to busbars. For large battery packs welding processes such as resistance, ultrasonic or laser welding or micro TIG can be used to provide a more cost effective, automatable and reliable method of assembly.
The present application have identified that the selection of me 6us6ar materia/ and" a process to form interconnections with the cell terminals should take into account the metallurgy of the joint interfaces, particularly with regard to the positive and negative cell terminals being different Materials. Inappropriate joint metallurgies could result in poor interconnection integrity and subsequent reliability problems.
Patent publication US20100105258 discloses an interconnecting device for battery cell assemblies. The interconnecting device couples a first set of electrodes at a first polarity in series with a second set of electrodes at a second polarity in a battery module while providing a substantially equal current flow through electrical contact members of the interconnect device, The first and second electrical contact members are constructed from a conductive material such as nickel-plated copper.
The above prior art requires a complex manufacturing process, which involves bending the material through an angle of 180° which may affect its structural integrity.
Patent publication WO2010081085 discloses bimetallic busbar jumpers and associated welding methods for battery Systems. The battery system comprises a plurality of battery cells arranged in a Sequence, each cell having a first and a second voltage terminal. The first voltage terminals of the plurality are arranged in

a row and a bimetallic busbar comprising two members, one part copper and one part aluminium, joined by ultrasonic welding is placed over them. Each member contains U-shaped channels into which the cell tabs are located. A laser beam is directed at the apex of the channel, melting the busbar at this point, and forming a metallurgical bond between the busbar and the top end of the voltage terminal.
The arrangement according to the above prior art is suitable only for asymmetric configurations of the battery cells. Further the accuracy of the engagement between the busbar U shaped channels and the cell terminals cannot be ascertained during the process of welding.
It is against this background that the present invention has been conceived. Embodiments of the invention are intended to address the above issues and may provide a busbar or a method for reliably interconnecting cells in a battery assembly which allows the use of a common basic design but with differing numbers of cells which can be arranged either asymmetrically or symmetrically and connected in a variety of electrical configurations. Other aims and advantages of the invention will become apparent from the following description, claims and drawings.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a bimetallic busbar for interconnecting the positive and negative terminals of cells in a battery module comprises at least one first finger and at least one second finger, each of the first and second fingers comprising a portion defining, at least in part, an abutting surface for electrical contact with a contacting surface of a respective terminal of a cell, wherein the abutting surface of each of the fingers is, in use, substantially plane parallel with the respective cell terminal and wherein the metallic property of the abutting

surface of each of the fingers is substantially the same as that of the contacting surface of the respective cell terminal.
Aspects of the invention provide a busbar, a battery assembly, a battery-powered product, a method and a vehicle as claimed in the appended claims.
According to another aspect of the invention there is provided a bimetallic busbar for interconnecting the positive and negative terminals of cells in a battery module comprising an intermediate portion, at least two spaced apart fingers, a first finger and a second finger, extending uprightly from the intermediate portion, said first finger has an abutting surface for establishing face contact with a contacting surfaces of said positive terminal of one of said cells and said second finger has an abutting surface for establishing face contact with a contacting surface of said negative terminal of another cell of said battery module, said abutting surface of each of the fingers is aligned in-line with the plane of its corresponding cell terminals, and the metallic property of each of said fingers' abutting surface is essentially the same as its corresponding cell terminal's contacting surface.
According to a further aspect of the present invention there is provided a bimetallic electrically conducting connecting device (busbar) for connecting positive and negative cell terminals of respective battery cells in such a way that the metallic property of each of the surfaces of the busbar that abut to the cell terminals are of essentially the same metallurgy as the corresponding cell terminal and further comprises: an intermediate portion, at least two spaced apart fingers, a first finger and a second finger, extending uprightly from the intermediate portion, the first finger has an abutting surface for establishing face contact with a contacting surface of said positive terminal of one of the cells and the second finger has an abutting surface for establishing face contact with a contacting surface of the negative terminal of another cell of the battery module, the abutting surface of each finger is aligned in-line with the plane of its corresponding cell terminals, and the metallic

property of each of the fingers' abutting surfaces is essentially the same as its corresponding cell terminal's contacting surface.
According to a particular embodiment of the invention, the first finger is disposed offset and oriented in an opposite direction relative to the second finger. In this embodiment, the busbar is arranged to interconnect cell terminals of adjacent batteries disposed in different rows within the battery module, for example a battery module having a configuration wherein the negative cell terminals of each cell are arranged in one row and the positive cell terminals of each cell are arranged in a second row.
According to another embodiment of the invention, the first finger and the second finger are oriented in the same direction, for example to define a U-shape. In this embodiment, the busbar is configured to interconnect cell terminals of adjacent batteries disposed in the same row within the battery module, for example a battery module having a configuration wherein the positive and negative terminals of adjacent batteries are alternatively arranged in same row. In an embodiment, the first and second fingers are fabricated by cutting and/or stamping a bimetallic sheet.
In an embodiment of the invention, the abutting surface of the first finger is mainly copper and is configured to establish face contact with the contacting surface of copper terminal of the cell of the battery module. The abutting surface of second finger is mainly aluminium and is configured to established face contact with the contacting surface of aluminium terminal of another cell of the battery module. The permanent connection between the abutting surfaces of the fingers of the busbars and contacting surface of the cell terminals may be made using a suitable welding process including, but not limited to, laser welding, ultrasonic welding, resistance welding or micro-Tig.

In an embodiment, the bus bar is formed from a bimetallic material comprising one or more of copper, a copper alloy, aluminium and an aluminium alloy. The bimetallic material may comprise a first metallic layer metallurgically bonded to a second metallic layer. The material layers may be arranged such that the first layer fully or partially covers the second layer. For example, the bimetallic busbar may be fabricated from fully or partially copper-clad aluminium.
Alternatively, the bimetallic material may comprise first and second metallic materials which are metallurgically joined end to end or may be, for example, a butt-joined bimetallic sheet. The metallic materials may comprise copper, or one or more copper alloys, and aluminium, or one or more aluminium alloys.
In an embodiment, the busbar is fabricated from copper-clad aluminium material or partially copper-clad aluminium material and each abutting surface is arranged to metalurgically match with the contacting surface of its respective cell terminal.
For example, in one embodiment the abutting surface of the first finger comprises copper, or one or more alloys of copper, so as to be metallurgically similar to the contacting surface of the copper terminal of each of the cells of the battery module. In addition, the second finger comprises aluminium, or one or more alloys of aluminium, so as to be metallurgically similar to the contacting surface of the aluminium terminal of each of the cells of the battery module.
That is to say, the busbar may be formed from a bimetallic material in such a manner that the abutting surface of each finger is of the same or similar metallurgy to the contacting surface of the respective cell terminal in the battery module.
In an embodiment, the base member is fabricated from aluminium material. The first and second fingers are welded or otherwise joined to the aluminium base member to form a substantially permanent electrical and mechanical connection.

In an embodiment, the bimetallic busbar is in the form of a single unit and comprises a pair of the first fingers, a pair of the second fingers and the base member.
In an embodiment, the intermediate portion and/or the fingers are provided with engaging elements on their respective underside to engage with corresponding slots provided in the base member.
In an embodiment, the fingers are adapted to be welded or mechanically joined with respective cell terminals of the battery module.
In an embodiment, the busbar comprises an array of first fingers and a corresponding array of second fingers, wherein the first fingers and the second fingers are disposed on the base member and are oriented in generally the same direction. The busbar is configured to interconnect cell terminals disposed in the same row inside the battery assembly where equal groups of positive and negative terminals are on the same side of the battery assembly.
The bimetallic busbars may be fabricated from a variety of materials including but not restricted to copper or various copper alloys, aluminium or various aluminum alloys or combinations thereof, depending on the configuration of the busbar. For example, when the first fingers and the second fingers are desired to be orientated in opposite directions, the busbar is fabricated in such a way that the surfaces abutting the negative cell terminals are essentially or mainly copper and the surfaces abutting the positive cell terminals are essentially or mainly aluminium. Likewise, when the first fingers and the second fingers are desired to be oriented in the same direction, the busbar is fabricated such that the fingers in contact with the negative cell terminals are essentially or mainly copper and the fingers in contact with the positive cell terminals are essentially or mainly aluminium. It will be understood that the above assumes the positive cell terminal to be aluminium and

the negative cell terminal to be copper which is not always the case. In an arrangement where, for example, the reverse is the true, then the busbar is fabricated such that the fingers in contact with the positive cell terminals are essentially or mainly copper and the fingers in contact with the negative cell terminals are essentially or mainly aluminium.
In an embodiment of the invention the protruding fingers are fabricated by one or more of, without limitation, stamping and cutting, including laser cutting or water jet cutting, and are then welded or otherwise joined to the aluminium base member.
Appreciably, the number of protruding fingers in a busbar can be increased as required to suit the electrical design of the battery module. This can be achieved simply by adapting the base tool design. It will also be recognised that in some embodiments all of the fingers can be produced from a single tool. This reduces the overall tooling costs. Although the example cited is produced in copper and aluminium, it will be understood that other material combinations can be used.
The terms metallic and metallurgical should not be construed as having reference to metals only. The terms metallic and metallurgical as used herein also refer to materials such as alloys, anodized metals, inter-metallic compounds, etc. that exhibit metallic/metallurgical properties. Accordingly, the invention is not limited to busbars fabricated from metals only but also includes busbars fabricated from substances exhibiting metallic/metallurgical properties. Moreover, the terminologies metallic and metallurgical have been used synonymously.
Within the scope of this application it is envisaged that the various aspects, embodiments, examples and alternatives, and in particular the individual features thereof, set out in the preceding paragraphs, in the claims and/or in the following description and drawings may be taken independently or in any combination. For

example, features disclosed in connection with one embodiment are applicable to all embodiments unless such features are incompatible.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Figure la is a schematic view of a bimetallic sheet used for fabrication of a bimetallic busbar according to some embodiments of the invention;
Figure lb is a schematic view of a bimetallic sheet used for fabrication of a bimetallic busbar according to further embodiments of the invention;
Figure lc is a schematic view of a butt-joined sheet used for fabrication of a bimetallic busbar according to still further embodiments of the invention;
Figure 2 shows a schematic view of a bimetallic busbar according to an embodiment of the present invention;
Figure 3 shows a schematic view of a battery module having a bimetallic busbar according to an embodiment of the invention for connecting cell terminals of adjacent cells;
Figure 4a shows a schematic view of a bimetallic sheet used for fabrication of busbars according to an embodiment of the invention.
Figure 4b shows a schematic view of a bimetallic busbar formed from the sheet of Figure 4a;

Figure 5 shows a schematic view of a battery module having the bimetallic busbar of Figure 4b for connecting cell terminals of battery cells in the module;
DETAILED DESCRIPTION
Within the following description like reference numerals indicate like parts. It will however be appreciated that the embodiments shown in, and described with reference to, the drawings are merely illustrative and are not intended to limit the scope of the invention. It will further be appreciated that it is quite possible, indeed often desirable, to introduce a number of variations in the particular embodiment that has been shown in the drawings or to introduce thereto features from other embodiments.
Figure la illustrates schematically a fully copper-clad aluminium sheet (7) which may be used for fabrication of bimetallic busbars (1) as shown in figures 2, respectively. Figure lb, on the other hand, illustrates schematically a partially copper-clad aluminium sheet (107) which may be used for fabrication of a bimetallic busbar (101) as shown in Figure 4b. Figure lc illustrates schematically a sheet in which two different metals, for example copper and aluminium, or alloys thereof, are joined edge-wise by a butt joint.
In the embodiment of Figure la, a top metallic layer of copper (22) extends over the full length of a bottom metallic layer of aluminium (23). In the embodiment of Figure lb, on the other hand, the top metallic layer of copper (222) extends only partly over the length/width of the bottom metallic layer of aluminium (223). The bimetallic sheets (7) and (107) thus have two layers of different materials.
The thickness of the bimetallic sheet (7, 107) may be selected as desired but is typically between 1.0-2.0mm. The relative thicknesses of the respective metallic layers may also be selected as desired but the top metallic layer of copper (22, 222)

is typically approximately 20% of the overall sheet thickness. A person skilled in the art would be able to modify the dimensions according to his requirements and the same will fall within the scope of this invention.
Figure 2 of the accompanying drawings shows a busbar (1) according to one form of the invention which may, for example, be fabricated by cutting or stamping or forming the components from a flat sheet such as those shown in Figure la. The busbar (1) comprises a conducting base member configured in the form of a generally planar intermediate portion (2), a first pair of fingers (3) extending from one end of the intermediate portion (2) and a second pair of fingers (4) extending from the other end of the intermediate portion (2) and in a direction opposite to the first pair of fingers (3). In this embodiment, the intermediate portion (2) constitutes a conducting base member.
Each finger of the first and second pairs of fingers (3, 4) has a substantially reshaped cross section comprising a first portion being generally co-planar with the intermediate portion (2) and a second portion upstanding from the first portion and substantially at right angles thereto. The first pair of fingers (3) are laterally spaced apart from each other and are disposed offset relative to the second pair of fingers (4).
The upstanding portion of each of the first pair of fingers (3) defines, at least in part, an abutting surface (5) for establishing face contact with a contacting surface of a respective negative terminal of a cell of a battery assembly or module (8) (shown in fig. 3). Similarly, the upstanding portion of each of the second pair of fingers (4) defines, at least in part, an abutting surface (5') for establishing face contact with a contacting surface of a respective positive terminal of a cell of the battery assembly or module (8). The arrangement is such that, in use, i.e. when assembled to a battery module, the abutting surfaces (5, 5') of each of the first and second pairs of fingers (3, 4) are oriented in plane parallel with the corresponding

cell terminals so that they abut substantially face to face and may be electrically joined, for example by welding, over a relatively large contact area. An alternative explanation is that the abutting surface (5, 5') of each of the fingers in the first and second pairs of fingers (3, 4) is aligned in-line with the plane of the corresponding cell terminal.
In the illustrated embodiment, the abutting surface (5) of each of the first pair of fingers (3) is essentially copper or an alloy of copper, to form a substantially vertical copper bonding surface for subsequent joining to the contacting surface a copper terminal of a cell. The abutting surface (5') of each of the second pair of fingers (4) is essentially aluminium, or an alloy of aluminium, to form a substantially vertical aluminium bonding surface for subsequent joining to the contacting surface of an aluminium terminal of a cell. Each of the fingers (3, 4) is provided with weld projections (6) to facilitate resistance welding as the joining process.
Figure 3 shows a schematic view of a battery module (8) comprising a plurality of cells (9) each having respective positive and negative terminals. The cells (9) forming the battery module (8) are arranged in such way that all of the positive cell terminals (10) are disposed in a first row on one side of the module (8) and all of the negative terminals (11) are disposed in a second row on the opposite side of the module (8).
The battery module (8) is provided with a plurality of bimetallic busbars (1) connecting the cell terminals (10, 11). The first busbar (1) is assembled to the battery module (8) with the aluminium bonding surfaces defined by respective abutting surfaces (5') of each of the second pair of fingers (4) of the busbar (1) aligned in face contact with the aluminium (positive) terminals (10) of the first and second cells (13, 14), and the copper bonding surfaces defined by respective abutting surfaces (5) of each of the first pair of fingers (3) of the busbar (1) are

aligned in face contact with the copper (negative) terminals (11) of the third and fourth cells (16, 17) in the battery module (8). Similarly, the second busbar (1) connects the aluminium (positive) terminals (10) of the third and fourth cells (16, 17) to the copper (negative) terminals (11) of the fifth and sixth cells (19, 20) of the battery module (8). This form of interconnection is repeated for all of the cells (9).
It can be seen that the illustrated busbar arrangement effects a series-parallel connection of the battery cells. In particular, the first busbar (1) connects the first pair of cells (first and second cells 13, 14) together in parallel and connects this parallel pair in series to the second pair of cells (third and fourth cells 16, 17), also connected together in parallel. The second busbar (1) connects the second parallel pair of cells (16, 17) in series to the third parallel pair of cells (fifth and sixth cells 19, 20). This busbar arrangement can be adapted to connect in series a plurality of cells connected in parallel. Indeed, any number of cells can be connected in this way by selecting the appropriate number of busbars (1). The number of fingers on each side of the busbar (1) can be varied to connect any number of copper and aluminium terminals (10, 11) according tc, the required configuration.
Figure 4b shows another embodiment of a bimetallic busbar (101) produced by cutting and/or stamping the components from a suitable bimetallic material, for example a partially copper-clad bimetallic; sheet (118) such as that shown in Figure 4a. In the embodiment, the copper layer (119) extends across only part of the width of the bimetallic sheet (118). A butt joined bimetallic sheet, such as that shown in Figure lc, can also be used for fabricating the bimetallic busbar (101).
As in the embodiment of Figure 2r each of the first pair of fingers (103) and each of the second pair of fingers (104) in the embodiment of Figure 4b have a substantially L-shaped cross section comprising a first portion being generally co-planar with the uncut portion of the bimetallic sheet and a second portion upstanding from the first portion and substantially at right angles thereto. In this

embodiment, however, each of the fingers in the first and second pairs of fingers (103, 104) extends in the same direction from the uncut portion of the bimetallic sheet which constitutes a conducting base member (120). The respective second portions of each of the fingers in the first and second pairs of fingers (103, 104) are thus substantially vertically oriented and are aligned substantially in parallel to face, and in use align with, the contacting surface of a respective terminal of the cells (109) as shown in Figure 5.
The fingers (103, 104) are generally produced by cutting and/or stamping and the material is positioned within the tooling such that the first fingers (103) are formed from that part of the sheet material which is essentially copper and the second fingers (104) are formed from that part of the sheet material which is essentially aluminium. A second production operation forms the respective second portions of the fingers such that each of the first pair of fingers (103) provides a substantially vertical copper bonding surface (105) for subsequent joining to the copper cell terminals and each of the second pair of fingers (104) provides a substantially vertical aluminium bonding surface (105') for subsequent joining to the aluminium cell terminals. If projection resistance welding is used as the joining process, the weld projections (6) for resistance welding of the cell terminals are provided on the vertical face.
Figure 5 shows an arrangement in which the bimetallic busbar (101) is used to connect cells (109) within a battery module (108). In this embodiment the cells (109) forming the battery module (108) are arranged in such a way that alternate pairs of cells are arranged with opposite polarity. Thus, on one side of the module (108), shown in the exploded view, the first two cells (113, 114) are arranged to have aluminium (positive) cell tabs on that side and the next two cells (116, 117) have copper (negative) cell tabs and so on. Conversely, on the opposite side of the module (108) the first two cells have copper terminals and the next two are aluminium and so on.

The bimetallic busbar (101) is configured such that when it is assembled to the battery module (108) the copper bonding surface (105) of each of the first pair of fingers (103) of the busbar (101) is aligned in face contact with the contacting surface of the copper (negative) terminals of one pair of cells (109), and the aluminium bonding surface (105') of each of the second pair of fingers (104) of the busbar (101) is aligned in face contact with the contacting surface of aluminium (positive) terminals of an adjacent pair of cells (109). In a similar way on the other side of the module (108) another busbar (101') connects the copper (negative) terminals of the adjacent pair of cells to the aluminium (positive) terminals of the next adjacent pair of cells.
It will be appreciated that, due to the opposite polarities of the terminals on the other side of the module (108), the configuration of the busbar (101') is required to be the reverse of the busbar (101), that is to say that each of the first pair of fingers (103) in the busbar (101') provides an aluminium bonding surface (105), while each of the second pair of fingers (104) provides a copper bonding surface (105'). Manufacture of the busbar (101') can readily be achieved, for example in a similar manner to that of busbar (101) but with the fingers being cut and/or stamped from the opposite edge of the bimetallic sheet (118).
In the exploded view of Figure 5, the reference-numbered busbar (101) is the second busbar connected to the module (108) and connects the negative terminals of the second pair of cells (third and fourth cells 116, 117) to the positive terminals of the third pair of cells (fifth and sixth cells 119, 120). Only a portion of the first busbar (101') is shown but it will be understood that this busbar has a reversed configuration compared to that of the second busbar (101), as described above, and is arranged to connect the negative terminals of the first pair of cells (113, 114) to the positive terminals of the second pair of cells (116, 117).

This form of interconnection is repeated for all of the cells within the module and provides an arrangement where each pair of cells is connected in parallel circuit and in series to the next pair and so on, this being electrically identical to the arrangement of Figure 3. This busbar design principle can be adapted to connect two or more cells in a parallel group and to connect the group in series to the next group of two or more cells. A plurality of cells can be grouped to connect negative terminals of the first group of cells to positive terminals of the second group. The positive and negative terminals of alternate groups are arranged in a row. The plurality of fingers on the busbar connects negative terminals of the first group with positive terminals of the second group. The copper terminals of the first group of cells connected to the copper bonding surface of the bimetallic busbar fingers and the aluminium terminals of the second group connected to the aluminium bonding surface of the bimetallic busbar.
In the above-mentioned embodiments of the bimetallic busbars (1, 101, 101'), the fingers (3, 4, 103, 104) may be integrally formed with the intermediate portion (2) and with the conducting base member (120), respectively, to constitute a single unit. The separation and/or spacing of the cells within the module assembly govern the separation/spacing of the fingers (3, 4, 103, 104) in the busbar. When this distance falls below a critical value, it becomes impractical, but not impossible, to form the busbar from a single piece of bimetallic material.
As described above, the busbars (1, 101, 101',) can be produced from a bi-metallic sheet in a variety of configurations such that when assembled into a battery module (8, 108) they provide metallurgically compatible joint interfaces between the abutting surfaces of the fingers of the busbars and the cell terminals. The abutting surface of the first and second pairs of fingers exhibits the same or similar metallurgical property as the contacting surface of its corresponding cell terminals of the battery. Other materials such as metals and alloys exhibit similar metallurgical property and as such will also come within the scope of this

invention. Furthermore, the upstanding or substantially vertical portions defining the abutting surfaces ensure a large contact surface between the busbar and the cell terminals, improving electrical contact and reliability.
Various processes can also be used to form a permanent, reliable connection between the busbar and the battery cell terminals, including laser welding, resistance welding, ultrasonic welding, micro-tig or any other known joining process. It is also possible to produce the bimetallic busbar by butt joining two different metal strips, as shown in Figure lc. The single piece single layer bimetallic busbar will have two portions of different metal to achieve the compatible joint interfaces as explained above.
It will be seen that this concept can be readily extended to increase the number of busbar fingers as required in dependence on the electrical design of the battery module. For example, the electrical arrangement may require the first three or four cells to be arranged in the module with opposite polarity to the next group of three or four cells. This can be achieved simply by adapting the base tool design and it will also be recognised that all of the fingers can be produced from a single tool. The overall design arrangement reduces material and tooling costs and it may be appropriate to use this approach as an alternative to a one-piece busbar in circumstances other than when there is a small separation between cell terminals.
On the other hand, the invention also envisages an arrangement wherein the busbar includes only one first finger, for connection to the positive terminal of the cell, and one second finger, for connection to the negative terminal of an adjacent cell. For example, a busbar comprising one half of the arrangements of Figures 2 or 4 is considered to be novel, inventive and advantageous over the known prior art and such an arrangements are therefore intended to fall within the scope of this application and the following claims.

While the above-described embodiments assume that the positive terminal of the cell is aluminium and the negative terminal of the cell is copper, the invention is applicable to other arrangements, including arrangements where the positive terminal of the cell is copper and the negative terminal of the cell is aluminium and arrangements wherein the terminals are made of different materials which are neither copper or aluminium. In such case, the inventive principles taught herein can be readily applied by the skilled person to conFigure a busbar wherein the materials used for the first and second pairs of fingers are appropriate for the respective cell terminals.
Busbars according to embodiments of the invention may comprise various types of bimetallic material which can be arranged such that the cell tab and adjoining busbar are mainly of the same material. The invention also encompasses metallic coatings that may be applied to the busbar and/or cell terminal for protecting the component against oxidation or for facilitating the welding/joining process. Such coatings may be applied by electro-plating, chemical deposition, dipping, evaporation or any other means.
As already mentioned the foregoing description is illustrative of embodiments of the invention and is not intended to limit its scope, because it will be apparent to persons skilled in the art to devise other alternative embodiments without departing from the broad ambit of the disclosures made herein.

WE CLAIM
1. A bimetallic busbar for interconnecting the positive and negative terminals
of cells in a battery module comprising:
at least one first finger and at least one second finger, each of the first and second fingers comprising a portion defining, at least in part, an abutting surface for electrical contact with a contacting surface of a respective terminal of a cell;
wherein the abutting surface of each of the fingers is, in use, substantially plane parallel with the respective cell terminal; and
wherein the metallic property of the abutting surface of each of the fingers is substantially the same as that of the contacting surface of the respective cell terminal.
2. A bimetallic busbar as claimed in claim 1, comprising an intermediate portion electrically interconnecting the first and second fingers, wherein the abutting surface of each finger is defined, at least in part, by a portion upstanding from the intermediate portion to provide, in use, a substantially vertical surface for face to face contact with the respective cell terminal.
3. A bimetallic busbar as claimed in claim 1 or claim 2, wherein the first finger has an abutting surface adapted for electrical contact with a contacting surface of a positive terminal of a respective cell and the second finger has an abutting surface adapted for electrical contact with a contacting surface of a negative terminal of a respective cell.
4. A bimetallic busbar as claimed in any preceding claim, wherein the first finger is disposed offset relative to the second finger and is oriented in a direction substantially opposite thereto thereby to permit interconnection between cell terminals disposed in different rows within the battery module

having a configuration of all negative terminals of the cells arranged in one row and all positive terminals of the cells arranged in a second row.
5. A bimetallic busbar as claimed in any preceding claim, wherein the first finger and the second finger are spaced apart and oriented in substantially the same direction thereby to permit interconnection between cell terminals disposed in the same row within the battery module having a configuration of an array of positive and negative terminals alternately arranged in the same row.
6. A bimetallic busbar as claimed in any preceding claim, wherein the first and second fingers are fabricated by cutting and/or stamping a bimetallic sheet.

7. A bimetallic busbar as claimed in any preceding claim, wherein the abutting surface of the first finger comprises mainly a first electrically conductive material and is configured to contact with the contacting surface of a cell terminal formed of a similar material or having similar metallurgical or electrical properties to the first material, and wherein the abutting surface of second finger comprises mainly a second electrically conductive material, different from the first material, and is configured to contact with the contacting surface of a cell terminal formed of a similar material or having similar metallurgical or electrical properties to the second material.
8. A bimetallic busbar as claimed in any preceding claim, wherein the abutting surface of the first finger is mainly copper and is configured to contact with the contacting surface of a copper terminal of a respective cell of the battery module, and wherein the abutting surface of second finger is mainly aluminium and is configured to contact with the contacting surface of an aluminium terminal of a respective different cell of the battery module.

9. A bimetallic busbar as claimed in any preceding claim fabricated from one
or more of:
copper, or various copper alloys;
aluminium, or various aluminium alloys; and
a combination of copper and aluminium, or alloys thereof.
10. A bimetallic busbar as claimed in any preceding claim fabricated from at
least one of:
a fully copper-clad aluminium material;
a parriatfy copper-clad arami'nium materia/; and
a butt-joined bimetallic sheet.
11. A bimetallic busbar as claimed in any preceding claim, comprising a plurality of first fingers and a plurality of second fingers.
12. A bimetallic busbar as claimed in any preceding claim, comprising a pair of first fingers, arranged in parallel and extending in a first common direction, and a pair of second fingers, arranged in parallel and extending in a second common direction, the first and second common directions being substantially the same or substantially opposite.
13. A battery assembly or module comprising one or more busbars as claimed in any preceding claim.
14. A battery-powered product comprising a battery assembly or module or a busbar as claimed in any preceding claim.

15. An electric or hybrid-electric motor vehicle having a battery assembly or module or a busbar as claimed in any of claims 1 to 13.