WO2025177021A1

WO2025177021A1 - Cell interconnect and manufacturing process

Info

Publication number: WO2025177021A1
Application number: PCT/IB2024/051640
Authority: WO
Inventors: Piyush VIJAYVERGIA; Sikhar BARARI
Original assignee: Innovative Clad Solutions Private Ltd
Current assignee: Innovative Clad Solutions Private Ltd
Priority date: 2024-02-21
Filing date: 2024-02-21
Publication date: 2025-08-28
Anticipated expiration: 2026-08-21

Abstract

Cell interconnect (11) for connecting battery cells (3) in a battery pack (1), each battery cell (3) comprising a cell negative terminal (7) and a cell positive terminal (5). The cell interconnect (11) comprises: - a metal clad component (13) formed of a composite material comprising a conductive layer made of a material having an electrical conductivity greater than or equal to that of nickel metal and a connection layer made of stainless steel, - a plurality of cell connection tabs, each cell connection tab comprising at least one connection pad (21), intended for welding to a cell terminal (5, 7) of a respective battery cell (3). The cell connection tabs consist of nickel or nickel alloy or comprise a three layer composite comprising, successively, a first layer of stainless steel, a second layer of copper or its alloys and a third layer of stainless steel.

Description

Cell Interconnect and Manufacturing Process

The present invention relates to a cell interconnect for connecting battery cells in a battery pack, each battery cell comprising a cell negative terminal and a cell positive terminal.

Cell interconnects are used in battery packs or modules for connecting the individual cells to each other in parallel and series to achieve the desired operating voltage and capacity of the battery pack or module.

There are various types of cell interconnect materials available in the market, in particular Pure Nickel Interconnect, Nickel Plated steel Interconnect, 5-Layer Clad Interconnect, Copper Interconnect, Aluminum Interconnect etc.

In addition, various connection methodologies for connecting the cell interconnect to the battery cells are available, i.e., parallel resistance micro-spot welding, step resistance micro-spot welding, laser welding, laser bonding, ultrasonic welding, wire bonding, mechanical fastening, soldering etc.

Li-ion technology is one of the torch bearers of green future. Li-ion Battery packs use different types of cell form factors, in particular cylindrical, prismatic or pouch, and Cell Chemistry, in particular NMC, NCA, LCO, LTO, LFP etc., to fulfill different application requirements, in particular for Electric mobility, Domestic Energy storage Systems, Solar Energy Storage systems, Industrial energy storage systems, Microgrid systems etc..

Nickel has always been a material of choice for cell interconnects in cylindrical form factor cell connection as it is very easy to carry out resistance micro-spot welding due to material compatibility of nickel to cell terminal material. Nickel has moderate electrical properties in terms of electrical conductivity and resistivity, which are better than steel, but lack in comparison with copper or aluminum. Hence, carrying high current through Nickel interconnects has always been a concern. On the other hand, the cost of nickel in the open market is substantially high and sees a lot of fluctuations.

Industry has already tried to combine nickel with copper by way of laser welding to provide alternate cell interconnect solutions to the market, but in the absence of material optimization and high process cost, the solution is still not widely used.

Material clad combinations such as sigmaclad® described in EP3152049 A1 combine five layers (nickel/stainless/copper/stainless/nickel) in a single composite, which allows resistance micro-spot welding together with the benefit of the electrical conductivity of copper. However, the cell interconnect made from this material is not optimal, as the copper is present through the composite material, even at the portion of the cell interconnect needing resistance welding with the battery cell, which is detrimental for resistance micro- spot welding. In addition, if the thickness of the composite material needs to be increased to allow higher current capacity, the resistance micro-spot welding of such a thicker material becomes even more difficult. Also, the process of manufacturing the five-layer composite is expensive. Therefore, the five-layer clad does not provide a cost effective solution. This poses limitations to the cell interconnects designed using sigmaclad® material.

In view of the limitations of the prior art, one purpose of the invention is to provide a cell interconnect for a battery pack, which allows for a reduced manufacturing cost of the battery pack, allows usage of resistance welding, and at the same time provides flexibility and suitability for usage in complete range of low to high power applications.

For this purpose, the invention relates to a cell interconnect for connecting battery cells in a battery pack, each battery cell comprising a cell negative terminal and a cell positive terminal, the cell interconnect comprising:

- a metal clad component, extending along a longitudinal direction, the metal clad component being formed of a composite material comprising a conductive layer made of a material having an electrical conductivity greater than or equal to the electrical conductivity of nickel metal, and a connection layer made of stainless steel, the conductive layer and the connection layer being bonded to each other; and

- a plurality of cell connection tabs, each cell connection tab comprising at least one connection pad, each connection pad being intended for welding to a cell positive terminal or a cell negative terminal of a respective battery cell of the battery pack, wherein the cell connection tabs consist of nickel or nickel alloy or wherein the cell connection tabs comprise a three layer composite comprising, successively, a first layer of stainless steel, a second layer of copper or its alloys and a third layer of stainless steel, the cell connection tabs being joined to the connection layer of the metal clad component and spaced apart from each other along the longitudinal direction.

The cell interconnect according to the invention may also include one or more of the following features, taken alone or according to any technically possible combination:

- the metal clad component consists of the conductive layer and the connection layer.

- the material of the conductive layer is copper or copper alloy or aluminum or aluminum alloy.

- the cell connection tabs extend along a transversal direction, perpendicular to the longitudinal direction.

- each connection pad extends adjacent said metal clad component along the transversal direction. - each cell connection tab further comprises a connection lug extending the or each connection pad along the transversal direction and abutting against the connection layer of the metal clad component along a direction perpendicular to the longitudinal direction and to the transversal direction.

- each cell connection tab comprises two connection pads extending on opposite sides of the metal clad component along the transversal direction, and connected to each other through the connection lug.

- each cell connection tab is joined to the metal clad component in the area in which the connection lug abuts against the connection layer of the metal clad component, and preferably only in the area in which the connection lug abuts against the connection layer of the metal clad component.

- for each cell connection tab, the connection lug and the or each connection pad are formed in one piece.

- each connection pad has a circular contour.

- the metal clad component has a wave shape comprising alternating crests and troughs, each cell connection tab being located at a crest or a trough of the metal clad component.

- each cell connection tab comprises at most two connection pads.

- the cell interconnect comprises two connection pads, the two connection pads facing each other along the transversal direction.

- the cell connection tabs are joined to the metal clad component by resistance welding, in particular by resistance micro-spot welding.

- the cell connection tabs consist of the three layer composite optionally coated with a corrosion resistant coating formed on the side of the first layer which is not in contact with the second layer and/or on the side of the third layer which is not in contact with the second layer.

- the corrosion resistant coating consists of a corrosion resistant metal chosen among nickel, tin, silver or mixtures or alloys of some or all of these elements.

- the conductive layer and the connection layer are bonded to each other through a cladding process, more particularly through a roll bonding process.

The invention also relates to a battery pack comprising:

- a plurality of battery cells, each battery cell comprising a cell negative terminal and a cell positive terminal;

- at least one cell interconnect as described above, the metal clad component of the cell interconnect extending along the cell negative terminals or along the cell positive terminals of a plurality of battery cells of the battery pack and each connection pad being joined to a respective cell negative terminal or cell positive terminal of a battery cell so as to provide an electrical connection between the battery cells through the cell interconnect.

According to a particular embodiment, the battery pack further comprises at least one cell holder, the cell holder comprising a plurality of through-holes facing the cell negative terminals or the cell positive terminals of the battery cells, the cell interconnect being joined to the cell holder.

The invention also relates to a method of manufacturing a cell interconnect as described above comprising the successive steps of:

- providing the metal clad component;

- providing a plurality of cell connection tabs;

- joining the cell connection tabs to the connection layer of the metal clad component to produce the cell interconnect.

The method of manufacturing a cell interconnect according to the invention may also include one or more of the following features, taken alone or according to any technically possible combination:

- the step of joining the cell connection tabs to the metal clad component is performed by resistance welding, in particular by resistance micro-spot welding.

- the method further comprises, prior to the step of providing the metal clad component, a step of manufacturing the metal clad component, comprising the following successive steps:

- providing a first sheet or strip made of the material of the conductive layer;

- providing a second sheet or strip made of the material of the connection layer;

- bonding of the first strip or sheet to the second strip or sheet to obtain a composite strip or sheet; and

- making the metal clad component from the composite strip or sheet, for example by cutting, blanking, forming or stamping of the composite strip or sheet.

- the method further comprises, prior to the step of providing the cell connection tabs, a step of manufacturing the cell connection tabs comprising the steps of:

- providing a strip or sheet made of a material suitable for the cell connection tab, the material being for example nickel or nickel alloy or a material comprising the three layer composite ; and

- making the cell connection tabs from said strip or sheet, for example by cutting, blanking, forming or stamping of the strip or sheet.

The invention also relates to a method of manufacturing a battery pack comprising the successive steps of:

- providing a plurality of battery cells; - providing a plurality of cell interconnects as described above;

- arranging the cell interconnects such that each metal clad component extends along the cell positive terminals or the cell negative terminals of at least some of battery cells and such that each connection pad faces a respective cell positive terminal or cell negative terminal of a battery cell; and

- welding each connection pad to the respective cell positive terminal or cell negative terminal, in particular through resistance welding, more particularly through resistance micro-spot welding.

According to a particular embodiment, the method of manufacturing a battery pack further comprises, prior to welding the connection pads to the cell positive terminals or cell negative terminals, steps of:

- providing at least one cell holder;

- joining at least one cell interconnect to the cell holder; and

- arranging the cell holder at one of cell negative terminal or cell positive terminal of the battery cells such that each metal clad component extends along the cell negative terminals or cell positive terminals of at least some of battery cells and such that each connection pad faces a respective cell negative terminal or cell positive terminal of a battery cell.

The invention will be better understood upon reading the following description, given only by way of example, and made with reference to the appended drawings, on which:

Figure 1 is a schematic perspective view of a battery pack including cell interconnects according to the invention;

Figure 2 is a bottom view of the battery pack of Figure 1 ;

Figure 3 is the perspective view of a cell of a battery pack ;

Fig 4 is a top view of the cell and shows the positive terminal of the cell;

Fig 5 is a bottom view of the cell and shows the negative terminal of the cell;

Figure 6 is a perspective view of the cell holder;

Figures 7 and 8 are perspective views of a cell interconnect according to the invention - Figure 7 represents a cell interconnect for middle cells and Figure 8 represents a cell interconnect for terminal cells - in the battery pack, the first and last row of parallel cells are termed as terminal cells and the cells in the remaining rows of cells are termed as middle cells;

Figures 9 and 10 are bottom views of the cell interconnect - Figure 9 shows a bottom view of the cell interconnect for middle cells and Figure 10 shows a bottom view of the cell interconnect for terminal cells;

Figure 11 is a bottom view of the clad metal component of the cell interconnect; Figure 12 is a top view of the clad metal component of the cell interconnect;

Figure 13 is a sectional view of the clad metal component of the cell interconnect, taken perpendicular to the longitudinal direction L;

Figure 14 is a top view of the cell connection tab of the middle cell interconnect;

Figure 15 is a top view of the cell connection tab for the terminal cells interconnect; Figures 16 and 17 are the perspective views of cell interconnects joined with the cells - Figure 16 shows the joining of cell interconnects with middle cells and Figure 17 shows the joining of cell interconnects with terminal cells; and

Figure 18 is a schematic view of the current flow within the cell interconnect during parallel gap resistance welding, viewed in cross-section perpendicular to the longitudinal axis of the cell interconnect.

An exemplary battery pack 1 as shown in Figures 1 and 2 comprises a plurality of cells 3. As shown in Figures 3 to 5, each cell 3 comprises a cell negative terminal 7 and a cell positive terminal 5.

In the example shown in the drawings, each cell 3 has a cylindrical shape. However, the cells 3 may also have a different cross-sectional shape, depending on the requirements. The cells 3 are for example lithium-ion cylindrical type cells.

The cells 3 are known as such, and will not be described further in the present patent application.

As shown in Figures 1 and 2, the cells 3 are for example arranged in a honeycomb array. In particular, the cells 3 are arranged so as to form several rows of cells 3. In the example shown in Figures 1 and 2, the cells 3 of one row are offset relative to the cells 3 of the adjacent rows of cells 3 so as to extend between the cells 3 of the adjacent rows of cells 3.

The cells 3 are held in place with the help of a cell holder 4, shown more particularly in Figure 6, having through holes 31 for holding the cells 3.

The battery pack 1 further comprises at least one cell interconnect 11. The cell interconnect 1 1 is configured for connecting cells 3 of the battery pack 1 in parallel or in series, depending on the needs.

In the example shown in the drawings, the battery pack 1 comprises a plurality of cell interconnects 1 1 .

As shown more particularly in Figures 7 to 17, the cell interconnect 1 1 according to the invention comprises a clad metal component 13 and a plurality of cell connection tabs 15 joined to the clad metal component 13. The clad metal component 13 extends along a longitudinal direction L. It is intended to extend along the cell negative terminals 7 or along the cell positive terminals 5 of a plurality of cells 3 of the battery pack 1 .

According to the invention, the clad metal component 13 is formed of a composite material comprising a conductive layer 17 and a connection layer 19.

The conductive layer 17 and the connection layer 19 are bonded to each other.

The conductive layer 17 and the connection layer 19 are preferably metallurgically bonded to each other. Metallurgical bonding in particular corresponds to the joining of two or more dissimilar metals without use of any adhesive or joining material. The conductive layer 17 and the connection layer 19 are preferably joined to each other through a cladding process to form a clad material. The conductive layer 17 and the connection layer 19 are for example joined to each other through a roll bonding process.

The conductive layer 17 and the connection layer 19 are superimposed over each other along a direction of superimposition. The conductive layer 17 and the connection layer 19 have the same surface area, taken in a plane normal to the direction of superimposition.

According to the invention, the conductive layer 17 is made of a material having an electrical conductivity equal or greater than the conductivity of nickel metal, i.e. a conductivity equal to or greater than 18% IACS.

Conventionally, a conductivity of 100% IACS is equivalent to a conductivity of 58.108 MS/m at 20°C.

According to a preferred example, the conductive layer 17 is made of copper or a copper alloy or of aluminum or an aluminum alloy.

The copper or its alloys are for example chosen from Oxygen Free Copper (OFC), Electrolytic Tough Pitch (ETP) Copper, Deoxidized High Phosphorus (DHP) Copper, Precipitation Hardened Copper (PHC), Brass and Bronze.

The aluminum or its alloy for example has a purity of aluminum equal to or more than 99%, and is for example chosen among UNS J91100 alloys and UNS A91050 alloys.

The conductive layer 17 has a thickness that can be customized to the application requirement of electrical and mechanical properties, such as current carrying capacity and mechanical strength. The thickness of the conductive layer 17 is for example between 0.05 mm and 4 mm.

According to the invention, the connection layer 19 is made of a metal or an alloy allowing resistance welding. According to one example, the connection layer 19 is made of stainless steel and preferably of austenitic stainless steel, such as 304, 304L or 316 grade austenitic stainless steel. The connection layer 19 preferably has a thickness greater than or equal to 0.04 mm. The thickness of the connection layer 19 is chosen to allow a good quality of resistance welding with the cell connection tab 15. In addition, the thickness of the connection layer 19 may be adjusted depending on the material thereof to provide increased mechanical strength and cost optimization of the clad metal component 13. For example, in the preferred example in which the connection layer 19 consists of stainless steel and the conductive layer 17 consists of aluminum or copper, the connection layer 19 has a higher mechanical strength as compared to copper or aluminum and at the same time provides economical advantage.

In the example shown in the drawings, the clad metal component 13 consists of the conductive layer 17 and the connection layer 19. The clad metal component 13 thus forms a two-layer laminate.

In the example shown in the drawings, the conductive layer 17 of the clad metal component 13 is not bonded or joined to any additional layer on its face opposite the connection layer 19.

According to an alternative (not shown), the clad metal component 13 is plated or coated with a corrosion protection coating formed on the conductive layer 17. The corrosion protection coating consists of a corrosion protection material, for example chosen among nickel, silver or tin or alloys of these elements. In this embodiment, the corrosion protection coating is not bonded or joined to any additional layer on its face opposite the conductive layer 17.

The corrosion protection coating in particular has a thickness at most a few microns, for example between 0.1 pm and 5 pm, more particularly between 1 pm and 5 pm, when the conductive layer 17 used is copper.

The cell connection tabs 15 are intended for connection to the cell negative terminals 7 or the cell positive terminals 5 through resistance welding, more particularly resistance micro-spot welding.

The thickness of the cell connection tabs 15 is for example between about 0.1 mm and about 0.3 mm. This thickness allows resistance welding, and more specifically resistance microspot welding.

According to one embodiment of the invention, the cell connection tabs 15 are made from nickel or nickel alloy, for example of 201 grade nickel alloy or 202 grade nickel alloy.

According to an alternative embodiment of the invention, the cell connection tabs 15 comprise a three layer composite.

The three layer composite comprises, successively, a first layer of stainless steel, a second layer of copper or its alloys and a third layer of stainless steel. The material of the second layer is preferably chosen from Oxygen Free Copper (OFC), Electrolytic Tough Pitch (ETP) Copper, Deoxidized High Phosphorus (DHP) Copper, Precipitation Hardened Copper (PHC), Brass and Bronze.

The stainless steel is preferably chosen from austenitic stainless steel grades, such as 304, 304 L, 316.

The first, second and third layers are bonded to each other, more particularly metallurgically bonded to each other. In particular, the first, second and third layers are bonded to each other through a cladding process. For example, the first, second and third layers are bonded to each other through a roll bonding process.

Preferably, the three layer composite consists of the first layer, the second layer and the third layer.

The thickness of each of the first and third layers of the three layer composite is for example between 2.5% and 75% of the total thickness of the three layer composite. The thickness of the second layer is for example between 18% to 95% of the total thickness of the three layer composite.

These relative thicknesses of the three layers of the three layer composite allow to equal or exceed the conductivity of nickel and further provide a sufficient thickness of the stainless steel layer to allow resistance welding.

According to one embodiment, the cell connection tabs 15 consist of the three layer composite.

Optionally, the three layer composite is coated or plated with a corrosion resistant coating on the side of the first layer and/or of the third layer which is not in contact with the second layer.

The corrosion resistant coating comprises, and for example consists of, a corrosion resistant metal, such as nickel, tin, silver or mixtures or alloys of some or all of these elements.

The corrosion resistant coating for example has a thickness between 1 micron and 5 micron.

According to one embodiment, the cell connection tabs 15 consist of the three layer composite and of the corrosion resistant coating.

Since the first and third layer of the three layer composite are made of stainless steel, they already provide significant corrosion resistance. However, the optional corrosion resistant coating may even further improve the corrosion resistance of the cell connection tabs 15, if required by the application. The cell connection tabs 15 are joined to the connection layer 19 of the metal clad component 13, in particular through resistance welding, more particularly resistance microspot welding, of the cell connection tab 15 to the connection layer 19.

As shown in Figures 7 to 10, the connection layer 19 of the clad metal component 13 extends between the conductive layer 17 of the clad metal component 13 and the cell connection tabs 15.

The cell connection tabs 15 are joined to the clad metal component 13 on the side of connection layer 19, in particular through resistance welding, more particularly resistance micro-spot welding.

The cell connection tabs 15 are spaced apart from each other along the longitudinal direction L. The longitudinal direction L is also the direction of arrangement of the cells 3 for parallel connection.

The cell connection tabs 15 are shown more particularly in Figures 9, 10 and 14, 15.

Each cell connection tab 15 comprises one connection lug 23 and at least one connection pad 21.

As shown in Figures 7 to 10, the connection pad 21 extends adjacent to the clad metal component 13 along the transversal direction T, which is also the direction of arrangement of cells 3 for series connection.

In particular, each connection pad 21 comprises, and for example consists of, a cell welding zone 28, a support structure 29, and a fuse section 30.

The cell welding zone 28 corresponds to the area in which the cell connection tab 15 is welded to the cell positive terminal 5 or cell negative terminal 7 of the cell 3. It is more particularly configured for receiving the welding spots during resistance welding of the cell connection tab 15 to the cell positive terminal 5 or cell negative terminal 7.

The shape of the support structure 29 and of the cell welding zone 28 depends on the shape of the cell terminals 5, 7 to which the connection pad 21 is intended to be welded.

In the example shown in Figures 14 and 15, the support structure 29 has a ring-shape. The cell welding zone 28 extends inside the support structure 29 and has a substantially circular shape, concentric with the support structure 29. A semi-annular gap 34 extends between the cell welding zone 28 and the support structure 29.

The support structure 29 is connected to the cell welding zone 28 through the fuse zone 30. The fuse zone 30 forms a bridge extending from the support structure 29 to the cell welding zone 28 across the semi-annular gap 34.

In the example shown in Figures 14 and 15, the cell welding zone 28 comprises an elongated slot 32. The elongated slot 32 more particularly extends along a longitudinal axis of the cell connection tab 15, approximately in the center of the cell welding zone 28. The elongated slot 32 is to facilitate the resistance welding operation. In particular, during resistance welding, one electrode is placed on each side of the elongated slot 32.

As shown in Figures 9 and 10, the connection lug 23 is in surface contact with and abuts against the connection layer 19 of the clad metal component 13.

The connection lug 23 is joined to the connection layer 19 in the area in which it abuts against the connection layer 19. The connection lug 23 is preferably welded, and preferably resistance micro-spot welded, to the connection layer 19.

The cell connection tab 15 is thus connected to the clad metal component 13 through the connection lug 23. More particularly, the cell connection tab 15 is exclusively connected to the clad metal component 13 through the connection lug 23.

In the example shown in the drawings, and as shown more particularly in Figures 14 and 15, the connection lug 23 comprises a clad metal component welding zone 33 and an elongated slot 35.

The clad metal component welding zone 33 corresponds to the area in which the clad metal component welding zone 33 is welded to the clad metal component 13, and more particularly to the connection layer 19 thereof. The clad metal component welding zone 33 is configured for receiving the welding spots during the resistance welding operation. In Figures 9 and 10, circular dots 36 were added on the connection lugs 23 to schematically represent the location of the welding spots connecting the cell connection tabs 15 to the clad metal component 13.

The elongated slot 35 extends more particularly along a longitudinal axis of the cell connection tab 15, approximately in the center of the clad metal component welding zone 33. The lug elongated slot 35 is to facilitate the resistance welding operation. In particular, during resistance welding, one electrode is placed on each side of the spot.

In the example shown in the drawings, each connection lug 23 has a substantially rectangular contour.

In the example shown in the drawings, for at least some of the cell interconnects 1 1 , each cell connection tab 15 comprises two connection pads 21 , located on opposite ends of the clad metal component 13 along the transversal direction T, the connection lug 23 extending between the two connection pads 21 .

More particularly, as shown in Figures 1 and 2 and as shown more specifically in Figures 7, 9 and 14, for the cell interconnects 1 1 for terminal cells, which are intended to be located at the edges of the battery pack 1 , each cell connection tab 15 comprises only one connection pad 21. Indeed, these cell interconnects 1 1 are intended to be arranged adjacent battery cells 3 on only one side thereof. In the example shown in Figures 1 and 2, and as shown more specifically in Figures 8, 10 and 15, for the cell interconnects 11 for middle cells, which are intended to be located between couples of battery cells 3, each cell connection tab 15 comprises two connection pads 21 as described above, each of the connection pads 12 being intended to be welded to the cell positive terminal 5 or cell negative terminal 7 of one of the cells 3 of the couple of cells 3.

Advantageously, each cell connection tab 15 comprises at most two connection pads 21 , for example only one connection pad 21 or two connection pads 21 as described above.

According to one example, each cell connection tab 15 consists of one or two connection pads 21 and a connection lug 23 which extends to the or each connection pad 21.

Preferably, and as shown in the drawings, each cell connection tab 15 is formed in one piece, for example by cutting, stamping, bending and/or forming from an initial strip of a material corresponding to that of the cell connection tab 15, for example nickel or nickel alloy or of a material comprising the three layer composite as described above.

According to an alternative, each cell connection tab 15 is formed in more than one piece. For example, in the embodiment in which the cell connection tab 15 comprises two connection pads 21 , each piece comprises a connection pad 21 and a portion of the connection lug 23.

Each cell connection tab 15 preferably has a constant thickness. In this case, the thickness of the connection lug 23 is equal to the thickness of the connection pad 21 .

The shape of the clad metal component 13 can be customized based on various factors such as the space availability based on the array structure of cells 3, requirements of assembly with other elements of the battery pack 1 , the cross section and the surface area needed for required electrical and mechanical properties, such as current carrying capacity and mechanical strength, ease of manufacturing operations, optimization of material yield losses etc.

In the example shown on the drawings, the clad metal component 13 has a wave shape including alternating troughs 24 and crests 26, each cell connection tab 15 being arranged at a respective trough 24 or crest 26 of the clad metal component 13.

According to an alternative (not shown), the clad metal component 13 has a substantially rectangular outer contour, for example if the battery cells 3 are formed in a rectangular array.

In the assembled battery pack 1 , as shown in Figures 1 and 2, each connection pad 21 is welded to a cell negative terminal 7 or a cell positive terminal 5 of a respective cell 3 at the weld zone 28. The clad metal component 13 extends along the cell negative terminals 7 or cell positive terminals 5 of a plurality of battery cells 3, and for example between couples of cell negative terminals 7 or cell positive terminals 5 of adjacent cells 3. The connection between the connection pads 21 and cell negative terminals 7 or cell positive terminals 5 of the cells 3 is shown more particularly in Figures 16 and 17, which are views including only the cells 3 and one cell interconnect 1 1 , respectively for terminal cells 3 and for middle cells 3.

The battery pack 1 further comprises at least one cell holder 4. In the example shown in the drawings, the battery pack 1 comprises one cell holder 4 at each of the cell negative terminal 7 and cell positive terminals 5 of the cells 3. Each cell holder 4 extends in a plane parallel to the plane of cell terminals 5, 7 of the cells 3. Each cell holder 4 includes, for each cell terminal 5, 7, a through-hole 31 facing a corresponding cell 3, each cell terminal 5, 7 extending through the corresponding through-hole 31 . The through-holes 31 form an array coinciding with the array formed by the cells 3.

The cell holder 4 consists of a non-conducting material, such as, for example molded plastics.

The cell interconnect 11 according to the invention is advantageous.

Indeed, the invention provides the functional properties of nickel metal for ease of resistance welding with the cell terminals 5, 7, which are usually also made of nickel or nickel alloys, and at the same time utilizes the functional advantage of the clad metal component 13 for enhancing thermal and electrical conductivity.

The cell interconnect 11 has a reduced amount of nickel compared to the cell interconnects 1 1 made fully of nickel or with sigmaclad®, and is therefore less costly to manufacture.

In addition, the cell interconnect 1 1 allows resistance welding and at the same time provides improved design flexibility over the prior art, for the reasons explained below.

Since the cell connection tab 15 is only a small portion of the full cell interconnect 1 1 , and has a thickness which can be optimized independently of the rest of the cell interconnect 11 , i.e. the clad metal component 13, the consumption of nickel metal is greatly reduced or eliminated, without compromising the ease of resistance micro-spot welding. The consumption of nickel is even more reduced in the embodiment in which the connection tab 15 is in the form of the three layer composite described above, optionally coated with a thin corrosion resistant coating since, in this case, the connection tab 15 only contains nickel in the optional thin corrosion resistant coating. In addition, the material of the connection pads 21 allows very good weldability to the cell terminals 5, 7 material using resistance micro-spot welding, thus enabling the manufacturing of reliable and good quality battery pack 1 .

Thanks to the structure of the cell interconnect 11 , the invention further allows for an improved design flexibility for reasons which will be explained with reference to Figure 18. In Figure 18, the arrows show the direction of the flow of electrical current.

In the example of Figure 18, the joining is done using a parallel gap resistance welding process, in which the two welding electrodes 41 , 42 are positioned on the same side in the area in which the connection lug 23 overlaps the clad metal component 13. Thus, during the parallel gap resistance welding process, the electrical current flows from one electrode 41 to the cell connection tab 15 and to the connection layer 19 of the clad metal component 13 and back to the other electrode 42, and forms a weld nugget 45 between the cell connection tab 15 and the connection layer 19 of the clad metal component 13. During this welding process, the electrical current does not have to pass through the conductive layer 17 of the clad metal component 13. Thus, the detrimental effect of the conductive layer 17 on resistance welding is avoided. This eliminates any limitation on the thickness of the conductive layer 17, which can therefore be customized to suit the properties, such as the current carrying capacity, the thermal dissipation needs etc., needed of the cell interconnect 1 1 depending on the desired application.

In addition, with the cell interconnect 1 1 according to the invention, the connection between cell terminals 5, 7 and the cell interconnect 11 is done at the cell connection tab 15. Hence, the clad metal component 13, and especially the conductive layer 17, is not involved during this operation, and the conductive layer 17 therefore does not affect the resistance welding aptitude of the cell interconnect 11 to the cell terminals 5, 7.

The layer ratio within the metal clad component 13 may be customized to suit the application’s need for electrical and thermal conductivity. The thickness of the conductive layer 17 will define the thermal and electrical conductivity of the clad metal component 13.

The electrical conductivity of oxygen free copper is considered as 100% IACS and that of aluminum 91100 grade fully annealed is 55% IACS. Similarly, the thermal conductivity of copper is 400 Watt/m.K and that of annealed aluminum of grade 91000 is 222 Watt/m.K.

Therefore, for example, a clad metal component 13 having a conductive layer 17 made of oxygen free copper representing 20% of the total thickness of the clad metal component 13, the electrical conductivity that can be achieved for the clad metal component 13 is 20% IACS and the thermal conductivity that can be achieved for the clad metal component 13 is 80 W/m.K. The results are very similar to nickel 201 having electrical conductivity of 20% IACS and thermal conductivity of 79.3 Watt/m.K. By increasing the layer ratio of conductive layer 17, the conductivity of clad metal component 13 can be increased further to reach close to the thermal conductivity of the metal of the conductive layer 17.

The thickness of the conductive layer 17 may represent up to 97% of the thickness of the clad metal component 13. Therefore, in case the conductive layer 17 used is of oxygen free copper, an electrical conductivity of up to 97% IACS and a thermal conductivity of up to 388 Watts/m.K thermal conductivity can be achieved.

Thus, the clad metal component 13 can be customized to achieve a wide range of electrical and thermal conductivity. Since the thickness and hence cross section of the clad metal component 13 can also be customized independently of the cell connection tab 15, the overall electricity and heat flow in the cell interconnect 1 1 can further be achieved by designing the cross-section area of the clad metal component 13. Thus, the cell interconnect 11 according to the present invention provides a high flexibility in the design of suitable cell interconnects based on application needs.

Therefore, thanks to the good electrical and thermal conductivity of the material of the conductive layer 17 and to the possibility to freely design the thickness and/or cross section area of the conductive layer 17 as per requirement of the desired application, the cell interconnect 11 according to the invention can be easily adapted for use in a wide range of power applications including the high-power applications.

In addition, since all the joining steps, i.e. the joining of clad metal component 13 to the cell connection tab 15 and the joining of cell interconnect 11 to the cell terminals 5, 7 through the cell connection tab 15 can be done using the resistance welding process, overall process and equipment costs are minimized.

Therefore, the overall design reduces the nickel usage, uses cost effective resistance welding, provides higher performance thanks to the conductive layer 17 and provides design flexibility to customize the clad metal component 13 to suit application needs.

In addition to the economic advantage, the reduction of the nickel also results in an improved environmental impact, as nickel is associated with higher CO2 emissions as compared to the clad metal component 13 used in the invention.

Further, the interconnect 1 1 according to the invention is more economical than the five-layer sigmaclad® interconnect and the cross-section, i.e. the thickness and width of the conductive layer 17 can be optimized without any constraint from the resistance micro-spot welding process, as the resistance welding on the clad material is carried out between the connection layer 19 and the cell connection tab 15 to make the cell interconnect or between cell connection tab 15 and the cell terminal 5, 7 for making the cell connections. On the contrary, in the sigmaclad® interconnect, during resistance welding, the current passes through the full thickness of the material, including the copper layer. Therefore, the thickness of the conductive layer cannot be freely adjusted, as increasing the thickness of the conductive layer reduces the ability of the clad material for resistance welding.

The invention further relates to a method of manufacturing the cell interconnect 11 comprising the following steps:

- providing a clad metal component 13 formed of a composite material comprising a conductive layer 17 and a connection layer 19;

- providing a plurality of cell connection tabs 15;

- joining the cell connection tabs 15 to the connection layer 19 of the clad metal component 13 to produce the cell interconnect 11 .

More particularly, the step of joining the cell connection tabs 15 to the connection layer 19 is performed by welding the cell connection tabs 15 to the connection layer 19. Preferably, the step of joining the cell connection tabs 15 to the clad metal component 13 is performed by resistance welding, in particular by parallel resistance welding, for example by resistance micro-spot welding.

The method may include, prior to the step of providing the clad metal component 13, a step of manufacturing the clad metal component 13, comprising the following successive steps:

- providing a first sheet or strip made of the material of the conductive layer 17;

- providing a second sheet or strip made of the material of the connection layer 19;

- bonding the first sheet or strip to the second sheet or strip to obtain a composite metal sheet or strip.

The bonding is in particular carried out via a cladding process, more particularly via a roll bonding process. The roll bonding process for example comprises the following steps:

- activation of the metal surfaces of the first and second metal sheets or strips which are to be bonded;

- superposition of the first and second metal sheets or strips with their activated surfaces facing each other;

- press-rolling the first and second metal sheets or strips together under pressure to obtain a green bonded metal sheet or strip;

- diffusion annealing of the green bonded metal sheet or strip to obtain the composite metal sheet or strip.

The composite metal sheet or strip forms a clad metal.

The composite metal sheet or strip has the properties and behavior of a single composite material. The composite metal sheet or strip is optionally further rolled down, annealed, cleaned and slit to obtain a clad metal sheet or strip having the desired size and properties, in particular chemical and mechanical properties, as well as the desired microstructure and grain size.

The clad metal component 13 is then for example obtained from the clad metal sheet or strip by a process including cutting, for example laser cutting or wire cutting, blanking, forming or stamping.

Preferably, a plurality of clad metal components 13 are made from one clad metal sheet or strip.

Optionally, the clad metal component 13 is plated or coated with a corrosion protection coating formed on the conductive layer 17.

The method may also comprise, prior to the step of providing the cell connection tabs 15, a step of manufacturing the cell connection tabs 15 comprising the steps of:

- providing a strip or sheet made of the material suitable for cell connection tab 15 such as nickel or its alloys or a material comprising the three layer composite described above ; and

- making the cell connection tabs 15 from said strip or sheet.

The step of making a cell connection tab 15 is achieved by using processes such as cutting, for example laser or wire cutting, blanking, stamping, forming etc. However, this step may be carried out by any adapted cutting method known to the skilled person.

The invention also relates to a method of producing a battery pack 1 , comprising the successive steps of:

- providing a plurality of battery cells 3;

- providing a plurality of cell interconnects 1 1 as described above;

- arranging the cell interconnects 1 1 such that each clad metal component 13 extends along the cell negative terminals 7 or cell positive terminals 5 of a plurality of battery cells 3 such that each cell connection tab 15 faces a respective cell negative terminal 7 or cell positive terminal 5 of a battery cell 3; and

- welding the cell connection tabs 15 to the cell negative terminals 7 or cell positive terminals 5, in particular through resistance welding, for example through resistance microspot welding.

Claims

1. Cell interconnect (1 1 ) for connecting battery cells (3) in a battery pack (1 ), each battery cell (3) comprising a cell negative terminal (7) and a cell positive terminal (5), the cell interconnect (1 1 ) comprising:

- a metal clad component (13), extending along a longitudinal direction (L), the metal clad component (13) being formed of a composite material comprising a conductive layer (17) made of a material having an electrical conductivity greater than or equal to the electrical conductivity of nickel metal, and a connection layer (19) made of stainless steel, the conductive layer (17) and the connection layer (19) being bonded to each other; and

- a plurality of cell connection tabs (15), each cell connection tab (15) comprising at least one connection pad (21 ), each connection pad (21 ) being intended for welding to a cell positive terminal (5) or a cell negative terminal (7) of a respective battery cell (3) of the battery pack (1 ), wherein the cell connection tabs (15) consist of nickel or nickel alloy or wherein the cell connection tabs (15) comprise a three layer composite comprising, successively, a first layer of stainless steel, a second layer of copper or its alloys and a third layer of stainless steel, the cell connection tabs (15) being joined to the connection layer (19) of the metal clad component (13) and spaced apart from each other along the longitudinal direction (L).

2. Cell interconnect (1 1 ) according to claim 1 , wherein the metal clad component (13) consists of the conductive layer (17) and the connection layer (19).

3. Cell interconnect (1 1 ) according to any one of claims 1 or 2, wherein the material of the conductive layer (17) is copper or copper alloy or aluminum or aluminum alloy.

4. Cell interconnect (1 1 ) according to any one of claims 1 to 3, wherein the cell connection tabs (15) extend along a transversal direction (T), perpendicular to the longitudinal direction (L).

5. Cell interconnect according to claim 4, wherein each connection pad (21) extends adjacent said metal clad component (13) along the transversal direction (T).

6. Cell interconnect (1 1 ) according to claim 4 or claim 5, wherein each cell connection tab (15) further comprises a connection lug (23) extending the or each connection pad (21 ) along the transversal direction (T) and abutting against the connection layer (19) of the metal clad component (13) along a direction perpendicular to the longitudinal direction (L) and to the transversal direction (T).

7. Cell interconnect (1 1 ) according to claim 6, wherein each cell connection tab (15) comprises two connection pads (21 ) extending on opposite sides of the metal clad component (13) along the transversal direction (T), and connected to each other through the connection lug (23).

8. Cell interconnect (1 1 ) according to claim 6 or claim 7, wherein each cell connection tab (15) is joined to the metal clad component (13) in the area in which the connection lug (23) abuts against the connection layer (19) of the metal clad component (13), and preferably only in the area in which the connection lug (23) abuts against the connection layer (19) of the metal clad component (13).

9. Cell interconnect (11 ) according to claim 6 to 8, wherein, for each cell connection tab (15), the connection lug (23) and the or each connection pad (21 ) are formed in one piece.

10. Cell interconnect (1 1 ) according to any one of claims 1 to 9, wherein each connection pad (21) has a circular contour.

11 . Cell interconnect (11 ) according to any one of claims 1 to 10, wherein the metal clad component (13) has a wave shape comprising alternating crests (26) and troughs (24), each cell connection tab (15) being located at a crest (26) or a trough (24) of the metal clad component (13).

12. Cell interconnect (1 1 ) according to any one of claims 1 to 1 1 , wherein each cell connection tab (15) comprises at most two connection pads (21 ).

13. Cell interconnect (1 1 ) according to claim 12, wherein the cell interconnect (1 1 ) comprises two connection pads (21 ), the two connection pads (21 ) facing each other along the transversal direction (T).

14. Cell interconnect (1 1 ) according to any one of claims 1 to 13, wherein the cell connection tabs (15) are joined to the metal clad component (13) by resistance welding, in particular by resistance micro-spot welding.

15. Cell interconnect (1 1 ) according to any one of claims 1 to 14, wherein the cell connection tabs (15) consist of the three layer composite optionally coated with a corrosion resistant coating formed on the side of the first layer which is not in contact with the second layer and/or on the side of the third layer which is not in contact with the second layer.

16. Cell interconnect (11 ) according to claim 15, wherein the corrosion resistant coating consists of a corrosion resistant metal chosen among nickel, tin, silver or mixtures or alloys of some or all of these elements.

17. Cell interconnect (11 ) according to any one of the preceding claims, wherein the conductive layer (17) and the connection layer (19) are bonded to each other through a cladding process.

18. Cell interconnect (11 ) according to any one of the preceding claims, wherein the conductive layer (17) and the connection layer (19) are bonded to each other through a roll bonding process.

19. Battery pack (1 ) comprising:

- a plurality of battery cells (3), each battery cell (3) comprising a cell negative terminal (7) and a cell positive terminal (5);

- at least one cell interconnect (1 1 ) according to any one of claims 1 to 16, the metal clad component (13) of the cell interconnect (1 1 ) extending along the cell negative terminals (7) or along the cell positive terminals (5) of a plurality of battery cells (3) of the battery pack (1 ) and each connection pad (21 ) being joined to a respective cell negative terminal (7) or cell positive terminal (5) of a battery cell (3) so as to provide an electrical connection between the battery cells (3) through the cell interconnect (11 ).

20. Battery pack (1 ) according to claim 19, further comprising at least one cell holder (4), the cell holder (4) comprising a plurality of through-holes (31 ) facing the cell negative terminals (7) or the cell positive terminals (5) of the battery cells (3), the cell interconnect (11 ) being joined to the cell holder (4).

21 . Method of manufacturing a cell interconnect (1 1 ) according to any one of claims 1 to 18, comprising the successive steps of:

- providing the metal clad component (13);

- providing a plurality of cell connection tabs (15);

- joining the cell connection tabs (15) to the connection layer (19) of the metal clad component (13) to produce the cell interconnect (1 1 ).

22. Method according to claim 21 , wherein the step of joining the cell connection tabs (15) to the metal clad component (13) is performed by resistance welding, in particular by resistance micro-spot welding.

23. Method according to claim 21 or claim 22, further comprising, prior to the step of providing the metal clad component (13), a step of manufacturing the metal clad component (13), comprising the following successive steps:

- providing a first sheet or strip made of the material of the conductive layer (17);

- providing a second sheet or strip made of the material of the connection layer (19);

- bonding the first strip or sheet to the second strip or sheet to obtain a composite strip or sheet; and

- making the metal clad component (13) from the composite strip or sheet, for example by cutting, blanking, forming or stamping of the composite strip or sheet.

24. Method according to any one of claims 21 to 23, further comprising, prior to the step of providing the cell connection tabs (15), a step of manufacturing the cell connection tabs (15) comprising the steps of:

- providing a strip or sheet made of a material suitable for the cell connection tab (15), the material being for example nickel or nickel alloy or a material comprising the three layer composite ; and

- making the cell connection tabs (15) from said strip or sheet, for example by cutting, blanking, forming or stamping of the strip or sheet.

25. Method of producing a battery pack (1 ), comprising the successive steps of:

- providing a plurality of battery cells (3);

- providing a plurality of cell interconnects (1 1 ) according to any one of claims 1 to 18; - arranging the cell interconnects (11 ) such that each metal clad component (13) extends along the cell positive terminals (5) or the cell negative terminals (7) of at least some of battery cells (3) and such that each connection pad (21 ) faces a respective cell positive terminal (5) or cell negative terminal (7) of a battery cell (3); and

- welding each connection pad (21 ) to the respective cell positive terminal (5) or cell negative terminal (7), in particular through resistance welding, more particularly through resistance micro-spot welding.

26. Method according to claim 25, further comprising, prior to welding the connection pads (21 ) to the cell positive terminals (5) or cell negative terminals (7), steps of:

- providing at least one cell holder (4);

- joining at least one cell interconnect (11 ) to the cell holder (4); and

- arranging the cell holder (4) at one of cell negative terminal (7) or cell positive terminal (5) of the battery cells (3) such that each metal clad component (13) extends along the cell negative terminals (7) or cell positive terminals (5) of at least some of battery cells (3) and such that each connection pad (21 ) faces a respective cell negative terminal (7) or cell positive terminal (5) of a battery cell (3).