GB2598955A

GB2598955A - Pouch cell unit

Info

Publication number: GB2598955A
Application number: GB2014945.6A
Authority: GB
Inventors: Y Ting Darren
Original assignee: Cummins Inc
Current assignee: Cummins Inc
Priority date: 2020-09-22
Filing date: 2020-09-22
Publication date: 2022-03-23
Also published as: CN216120407U; GB202014945D0

Abstract

A pouch cell unit 30, 31 comprises at least one pouch cell 32, a cell tray (34, Figures 2-3) which supports the pouch cell, and a busbar 36 for electrically connecting a plurality of pouch cells. The busbar is attached to the cell tray. The busbar may be pre-assembled to the cell tray prior to stacking the pouch cell unit with other pouch cell units. The busbar may be located on the outside of the cell tray. The pouch cell may comprise opposing terminal tabs 44, 45. A first terminal tab may be arranged to be connected to the busbar and a second terminal tab may be arranged to be connected to a busbar in an adjacent pouch cell unit. The first terminal tab may be bent around the busbar. The second terminal tab may be bent away from the pouch cell unit. A pouch cell unit can comprise two pouch cells and a first terminal tab from each pouch cell may be arranged to be connected to the busbar and a second terminal tab from each pouch cell may be arranged to be connected to a busbar in an adjacent pouch cell unit.

Description

POUCH CELL UNIT

The present invention relates to a pouch cell unit, and in particular a pouch cell unit which can be stacked to form a battery module, and to a battery module comprising a plurality of such pouch cell units. The present invention has particular, but not exclusive, application with battery modules for use in battery packs for mobile applications such as electric or hybrid electric vehicles, construction equipment, and so forth, as well as stationary applications.

Electric vehicles and hybrid electric vehicles, such as cars, buses, vans and trucks, typically use battery packs that are designed with a high ampere-hour capacity in order to give power over sustained periods of time. A battery pack comprises a large number of individual electrochemical cells connected in series and parallel to achieve the total voltage and current requirements. To assist in manufacturing, assembly and servicing, the cells in a battery pack may be grouped into modules. The modules may include a support structure and a battery management unit to manage cell charge and discharge.

In order to help with packing efficiency, some known battery modules use pouch cells. Pouch cells are electrochemical cells (typically Lithium-ion) where an internal electrode stack is contained within a flexible package. Current collectors in the cell are welded internally to terminal tabs that protrude through seals to allow external connection. The cells in the module are connected in series and parallel to achieve the target voltage. This is normally achieved by connecting a busbar assembly to the terminal tabs to achieve the required configuration.

For example, US 9,225,035, the subject matter of which is incorporated herein by reference, discloses a battery module comprising a plurality of Lithium-ion pouch type unit cells stacked in a linear array. A slotted flat panel is placed over the unit cells and the cell tabs protrude through the panel. An arrangement of slotted busbars is provided on the flat panel. After the cell tabs have been threaded through the slots, they are bent at right angles to allow them to be attached to the busbars.

Many battery applications require high energy densities in both volume and weight limited packages. As a consequence, battery cells are being packaged in ever-tighter volumes, which requires stringent dimensional control and creative ways to effectively utilize the space that is available in a given application.

Usually, these applications also require high volume production in order to meet demand, which means that designs suitable for high-volume manufacturing are required.

The process of manufacturing known battery modules typically requires the insertion of busbar assemblies into a tight space in a highly controlled manner.

This may add to the cost and complexity of manufacture and may be prone to error given the high level of precision that is usually required. Furthermore, the busbar assemblies may add to the overall size of the battery module.

It would therefore be desirable to provide an arrangement which can facilitate the assembly of a battery module and/or reduce the space requirements.

According to one aspect of the present invention there is provided a pouch cell unit comprising: at least one pouch cell; a cell tray which supports the pouch cell; and a busbar for electrically connecting a plurality of pouch cells, wherein the busbar is attached to the cell tray.

The present invention may provide the advantage that, by providing a pouch cell unit in which a busbar is attached to the cell tray, it may be possible for pouch cells to be connected without an additional step of inserting a separate busbar assembly. This may reduce the assembly time and/or reduce error in the assembly process, in comparison to prior techniques. Furthermore, by avoiding the need for a separate busbar assembly, the space requirements may be reduced.

Preferably the cell tray comprises means for securing the busbar to the cell tray. This may help to ensure that the busbar remains attached to the cell tray during assembly. For example, the cell tray may comprise a fastener, which hold the busbar in place using a snap-fit or an interference fit. In one example, the cell tray comprises locating pins which engage with holes on the busbar.

Alternatively or in addition, any other means could be used for securing the busbar to the cell tray, such as screws, bolts, a cantilever snap-fit, heat-staking or adhesive.

Preferably the pouch cell unit is arranged such that the busbar can be pre-assembled to the cell tray prior to stacking the pouch cell unit with other pouch cell units. Thus, the busbar may be pre-assembled to the cell tray prior to stacking the pouch cell unit with other pouch cell units. This may facilitate assembly, by avoiding the need to attach a separate busbar assembly.

Preferably, the busbar is integral with the cell tray. This may facilitate assembly by avoiding the need to deal with two separate parts.

Preferably the busbar is located on an outside of the cell tray. This may facilitate connection of pouch cells to the busbar, by allowing the busbar to be easily accessed.

Preferably the pouch cell comprises terminal tabs (typically a positive terminal tab and a negative terminal tab). In this case a first terminal tab may be arranged to be connected to the busbar and a second terminal tab may be arranged to be connected to a busbar in an adjacent pouch cell unit. This may facilitate connection of a plurality of pouch cells in the appropriate configuration using busbars which are part of the cell trays.

Preferably the first terminal tab is arranged to be connected to an outside surface of the busbar (for example, a side of the busbar which is opposite to that of the pouch cell). This may facilitate connection of the terminal tab to the busbar. For example, where the terminal tab is to be welded to the busbar, this may allow the terminal tab (rather than the busbar) to be presented for welding, which may facilitate the welding process.

In order facilitate connection of the first terminal tab to an outside surface of the busbar, the first terminal tab may be bent around the busbar. For example, the terminal tab may be bent from a direction substantially parallel to a plane of the pouch cell to a direction substantially perpendicular to the plane of the pouch cell. Thus, the terminal tab may be bent through an angle of approximately 90° (for example, greater than 600, 700 or 800 and/or less than 1200, 1100 or 1000).

In one possible arrangement, the cell tray comprises a frame with the pouch cell on the inside of the frame and the busbar on the outside of the frame. In this case the first terminal tab may be bent around the frame and the busbar.

Preferably the second terminal tab is bent away from the pouch cell unit, preferably in the direction of an adjacent pouch cell unit when a plurality of pouch cell units are stacked together. This may allow the second terminal tab to be connected to a busbar in an adjacent pouch cell unit. Likewise, the pouch cell unit may be arranged to receive a terminal tab of a pouch cell in an adjacent pouch cell unit, so that that terminal tab can be connected to the busbar. This may facilitate connection of a plurality of pouch cells in the appropriate configuration.

Preferably at least some of the terminal tabs are pre-bent prior to stacking the pouch cell unit with other pouch cell units. This may facilitate the assembly process by ensuring that the terminal tabs are in the correct positions for connection to the appropriate busbars when a plurality of pouch cell units are stacked together.

The pouch cell may comprise opposing terminal tabs, that is, one terminal tab may be on the opposite side of the pouch cell to the other terminal tab. Such pouch cells tend to have a more uniform temperature distribution and typically have a longer life and better performance than other types of pouch cells, and thus may be preferred. The present invention may facilitate the use of pouch cells with opposing terminal tabs, by providing busbars on the appropriate sides of the cell trays. However, if desired, pouch cells with tabs on the same side or on other sides could be used as well or instead.

In one embodiment, the pouch cell unit comprises two pouch cells. For example, the cell tray may comprise a frame which is arranged to hold the two pouch cells.

In this case, a first terminal tab from each pouch cell may be arranged to be connected to the busbar and a second terminal tab from each pouch cell may be arranged to be connected to a busbar in an adjacent pouch cell. This may facilitate connection of the pouch cells in the appropriate configuration.

A pouch cell unit may be arranged such that two pouch cells in the pouch cell unit have opposing orientations, that is, they may be rotated through 180°with respect to each other such that the positive terminal tab of one pouch cell is at the same end of the pouch cell unit as the negative terminal tab of the other pouch cell, and vice versa. For example: in the case of a pouch cell unit with two pouch cells, the two pouch cells may have opposing orientations. This may allow the two pouch cells in a pouch cell unit to be connected in series. However, when the pouch cell units are stacked together, each pouch cell may be connected in parallel with one or more pouch cells in an adjacent pouch cell unit.

This may facilitate connection of the pouch cells in the appropriate series/parallel configuration (for example, a 2p, 3p or 4p configuration, or any other appropriate configuration).

In another embodiment, the pouch cell unit comprises three pouch cells. In this case, the pouch cells within a pouch cell unit may have the same orientation. A first terminal tab (for example, a positive terminal tab) from each pouch cell may be arranged to be connected to the busbar and a second terminal tab (for example, a negative terminal tab) from each pouch cell may be arranged to be connected to a busbar in an adjacent pouch cell (or vice versa).

It will be appreciated that pouch cell units with a different number of pouch cells may also be provided as appropriate. For example, a pouch cell unit may comprise one, four, five or some other number of pouch cells. Within the same module, some pouch cell units may have a different number of pouch cells from other pouch cell units. The pouch cells within a pouch cell unit may have the same orientations, or at least one may have a different orientation from at least one other.

In any of the above arrangements, each pouch cell may have terminal tabs which are bent so as to contact an outside surface of a respective busbar. For example, in the case of a pouch cell unit with two pouch cells, the terminal tabs of both pouch cells may be pre-bent prior to stacking the pouch cell unit with other pouch cell units. This may help to ensure that the terminal tabs are in the correct positions for connection to the appropriate busbars once the pouch cell units have been stacked.

Preferably a pouch cell unit comprises a cooling fin between two pouch cells. For example, the cell tray may comprise means, such as a slot, for holding a cooling fine. This may allow a cooling surface to be in contact with each pouch cell, thereby helping to ensure effective cooling. The cooling fin may be arranged for example to contact a cooling plate in a battery pack.

Preferably the pouch cell unit is arranged to be stacked with a plurality of other pouch cell units of a similar type, for example, to form a battery module. In this case the cell tray may be arranged to locate the pouch cell unit with respect to the other pouch cell units. For example, the cell tray may include one or more locating features (such as a protrusion or a recess) which are designed to engage with corresponding locating features on an adjacent cell tray. Thus, the cell tray may be arranged to support and mechanically locate the pouch cell as well as support the busbar.

According to another aspect of the present invention there is provided a battery module comprising a plurality of pouch cell units in any of the forms described above. Preferably the plurality of pouch cell units are stacked together to form the battery module. The battery module may further comprise means for physically holding the plurality of pouch cell units together. For example, the plurality of pouch cell units may be held together using one or more bolts, straps or supports, or any combination thereof.

The battery module may comprise a series connection of a plurality of parallel connected pouch cells. For example, the pouch cells in a pouch cell unit may be connected in series with each other, but in parallel with one or more pouch cells from an adjacent pouch cell unit. Thus, the pouch cells may be connected in a series/parallel configuration, such a 2p, 3p, 4p or 5p configuration. However, other configurations such as a lp configuration, are also possible.

Preferably, the pouch cells comprise terminal tabs which are electrically connected to respective busbars. This may be achieved, for example, by welding, such as laser welding, or any other appropriate technique such as soldering or using screws or bolts.

Preferably at least one of the pouch cell units has a first configuration in which the busbar is located on one side of the battery module and at least one other of the pouch cell units has a second configuration in which the busbar is located on another side (for example, the opposite side) of the battery module. This may facilitate the parallel connection of two or more pouch cells from adjacent pouch cell units. Thus, this arrangement may allow the pouch cells to be connected in the appropriate series/parallel configuration. However, in alternative arrangements, it would also be possible for the busbars to be located on the same side of the battery module.

Preferably at least one of the pouch cell units has a third configuration, and the stack of pouch cell units is terminated with a pouch cell unit with the third configuration. The pouch cell unit with a third configuration may have a pouch cell terminal tab arranged to be connected to a busbar in an adjacent pouch cell unit on one side but not the other, and/or may be arranged to receive a terminal tab from an adjacent pouch cell unit on one side but not the other. The pouch cell unit with a third configuration may be arranged to connect to a terminal of the battery module. This may allow a series/parallel configuration to be appropriately terminated.

Corresponding methods may also be provided. Thus, according to another aspect of the invention there is provided a method of assembling a pouch cell unit comprising at least one pouch cell and a cell tray which supports the pouch cell, the method comprising attaching a busbar to the cell tray.

Preferably the busbar is attached to the cell tray prior to stacking the pouch cell unit with other pouch cell units.

The method may further comprise pre-bending pouch cell terminal tabs to allow them to contact an outside surface of a respective busbar prior to stacking the pouch cell unit with other pouch cell units.

The method may further comprise stacking the pouch cell units and connecting the terminal tabs to the busbars after the pouch cell units have been stacked. The terminal tabs may be connected to the busbars, for example, by welding, such as laser welding or any other appropriate technique.

The invention may provide the advantage that, by pre-assembling the busbar to the cell tray and/or pre-bending the terminal tabs prior to stacking the pouch cell units, the appropriate electrical connections may be made using a relatively simple process and without requiring additional components such as a separate busbar assembly.

Features of one aspect of the invention may be used with any other aspect. Any of the apparatus features may be provided as method features and vice versa.

Preferred features of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an example of a battery pack; Figures 2 and 3 show two configurations of a pouch cell unit in an embodiment of the invention; Figure 4 is a cross section through part of a battery module; Figure 5 shows connections made at the top of a pouch cell unit; Figure 6 shows schematically a connection configuration of pouch cells; Figure 7 is a cross section through part of a battery module; Figure 8 shows steps taken to assembly a battery module; and Figure 9 shows a connection configuration of pouch cells in another embodiment.

Figure 1 shows an example of a battery pack. The battery pack of Figure 1 is designed to be used with electric and hybrid vehicles, particularly in high horsepower applications as buses, trucks, vans, construction equipment, and so forth. However, the principles of the present invention can be used with any type of battery pack for use in any type of application.

Referring to Figure 1, the battery pack 10 comprises a plurality of battery modules 12, a plurality of cooling plates 14, a battery management system 16, a surround frame 18, a top panel 20 and a bottom panel 22. In this example, fifteen battery modules 12 are provided in five rows of three modules. Each row of three battery modules 12 is located on a corresponding cooling plate 14. The cooling plates 14 are hollow to allow the flow of coolant. The battery management system 16 is located at one end of the battery pack. In the assembled state, the top panel 20 and the bottom panel 22 are attached to the top and bottom respectively of the frame 20. The battery modules 12, cooling plates 14 and battery management system 16 are housed inside the frame 18 and panels 20, 22.

A typical battery module comprises a number of battery cells, such as cylindrical, prismatic or pouch cells, connected together. In the case of pouch cells, each cell may be held within a cell tray to form a pouch cell unit. The pouch cell units are stacked together to form the battery module. Compliant elements are provided between the pouch cells to allow expansion. The battery module is surrounded by an enclosure or structure that provides the required rigidity. The pouch cells are electrically connected in series and/or parallel to achieve the target voltage. This is usually achieved by welding the cell terminal tabs to a copper busbar.

In order to assembly such a battery module, the typical order of operations is as follows: 1. Assemble pouch cells to cell trays 2. Stack cell tray subassemblies together 3. Assemble busbar tray and busbars 4. Weld pouch cells.

Thus, in the known techniques, the battery module is first assembled by stacking together the pouch cell units. The cells are then electrically linked by installing busbars, and then welding the cell tabs to the busbars. This process normally involves inserting busbars into a tight space in a highly controlled manner. For example, in the arrangement disclosed in US 9,225,035, the cell terminal tabs (which are substantially parallel to the pouch cells) are first threaded through slots in a flat panel which provides a supporting surface for the busbars. The tabs are then bent at right angles before being attached to the busbars. This requires a high level of precision, and may be prone to error, both of which may add to the cost and complexity of manufacture. This process may also take up valuable manufacturing time which in turn impacts manufacturing volume for a given manufacturing line. Furthermore, the busbars may add to the overall size of the battery module.

In embodiments of the invention, busbars are preassembled to the elements that mechanically locate the pouch cells. The cell tabs are pre-bent into specific shapes to facilitate the welding process. This may allow pouch cells to be easily stacked and subsequently welded without the additional step of insertion of busbars into a tight space in a controlled manner.

Figures 2 and 3 show two configurations of a pouch cell unit in an embodiment of the invention. Referring to Figure 2, a pouch cell unit 30 in the first configuration (configuration "A") comprises two pouch cells 32, a cell tray 34, a busbar 36, a cooling fin 38, an expansion pad 40 and locating dowels 42. Each of the pouch cells 32 is an electrochemical cell (typically Lithium-ion) contained in a pouch. The pouch cells 32 comprise terminal tabs 44, 45 that are connected internally to current collectors in the cell and protrude through seals in the pouch. The pouch cells are flat, and the terminal tabs exit the cells in a direction which is parallel to the plane of the cell. In this embodiment, the pouch cells have opposing terminal tabs, with positive terminal tabs 44 are provided at one end of the pouch cell and negative terminal tabs 45 at the other end. The cell tray 34 is made from a plastic polymer material such as a thermoplastic. The busbar 36 is made from a conducting metal such as copper. The cooling fin 38 is made from a thermally conductive material such as aluminium or graphite. The expansion pad 40 is typically made from a thermally insulative foam (for flame barrier purposes in case of a failed cell). It will be appreciated that these materials are given as examples only, and other materials may be used as appropriate.

In the assembled pouch cell unit, the cell tray 34 frames the pouch cells 32 and holds them in place. Each of the pouch cells 32 is of the same type, rotated through 1800. Thus, the positive terminal tab 34 of one of the pouch cells is located at the same end of the cell tray as the negative terminal tab 35 of the other pouch cell. The busbar 36 is held in place by features provided on the top side of the cell tray. The cooling fin 38 is located at the centre of the cell tray, between the two pouch cells 32. The cooling fin 38 includes a tab 46 which is designed to contact a cooling plate (such as the cooling plate 14 shown in Figure 1) in order to conduct heat away from the cells. The expansion pad 40 is located on one side of the pouch cell unit 30. The expansion pad 40 may be fixed to the side of the pouch cell unit, for example, using adhesive. The locating dowels 42 are fitted into holes in the cell tray.

In the configuration shown in Figure 2, the busbar 36 is attached to the top of the cell tray 34. The terminal tabs 44, 45 exit the cells in vertical directions (parallel to the plane of the pouch cell) and are bent into horizontal directions. The terminal tabs 44, 45 at the top of the cells are bent inwards towards the busbar 36 in a manner such that, in the assembled pouch cell unit, they can rest on top of the busbar. On the other hand, the terminal tabs 44, 45 at the bottom of the cells are bent outwards, away from the cell tray. In the assembled state, the terminal tabs 44, 45 at the top of the cells are welded to the top of the busbar 36 along with terminal tabs from adjacent pouch cell units, as will be explained below.

Referring now to Figure 3, a pouch cell unit 31 in the second configuration (configuration "B") comprises two pouch cells 32, a cell tray 34, a busbar 36, a cooling fin 38, an expansion pad 40 and locating dowels 42, as in the first configuration. However, in this configuration, the two pouch cells 32 are each rotated 180° relative to those of Figure 2 (i.e. they have their positive and negative terminal tabs at opposite ends to those of the corresponding pouch cells in Figure 2). Furthermore, the busbar 36 is attached to the bottom of the cell tray 34 rather than the top (i.e. at the opposite end of the cell tray to that of Figure 2). The terminal tabs 44, 45 at the bottom of the cells are bent inwards towards the busbar 36, while the terminal tabs 44, 45 at the top of the cells are bent outwards, away from the cell tray.

In the arrangement of Figures 2 and 3, the cell trays 34 include pins which engage with holes in the busbars 36. The pins are designed with a snap fit, to ensure that the busbars are held in place during assembly. In this example, the cell trays are the same in both configurations, and a busbar is attached to either the top or the bottom of a cell tray as appropriate. However, if desired, different cell trays could be used for the two configurations.

The pouch cell units 30, 31 of Figures 2 and 3 are designed to be stacked together to form a battery module. The busbars 36 are pre-assembled to the cell trays 34 before the pouch cell units are stacked together. In addition, the terminal tabs 44, 45 are pre-bent into the required shape so that they will contact the appropriate busbar when the battery module is assembled.

Figure 4 is a cross section through part of a battery module showing how a plurality of pouch cell units of the types shown in Figures 2 and 3 are stacked together. Referring to Figure 4, the battery module 50 is built by stacking cell tray units 30, 31 with alternating A and B configurations. The locating dowels 42 (not shown in Figure 4) engage with holes in adjacent pouch cell units in order to locate the units with respect to each other.

In the arrangement of Figure 4, the alternating nature of the cell tray units 30, 31 results in the busbars 36 alternating between the top and the bottom of the battery module. In a pouch cell unit 30 with configuration A, the terminal tabs at the top of the cells are connected to the top of the busbar 36 along with terminal tabs from adjacent pouch cells. In a pouch cell unit 31 with configuration B, the terminal tabs at the bottom of the cells are connected to the bottom of the busbar 36 along with terminal tabs from adjacent pouch cells.

Figure 5 shows in more detail the connections made at the top of a pouch cell unit. Referring to Figure 5, it can be seen that, in a pouch cell unit 30 with configuration A, the terminal tabs at the top of the pouch cells are connected to the top of the busbar 36. The tabs exit the pouch cells in a vertical direction (parallel to the plane of the cell) and are bent around the busbar so that the ends of the tabs are horizontal. The tabs from the pouch cells to the immediate left and right are also connected to the top of the busbar. These pouch cells are contained in adjacent pouch cell units with configuration B. The tabs from these pouch cells are also bent through an angle of 900, in this case using two 45° bends, so that the ends of the tabs are horizontal. The tabs are attached to the busbars using laser welding.

At the bottom of the battery module the pouch cells are connected in a similar manner, with the terminal tabs at the bottom of the pouch cells in a pouch cell unit with configuration B being connected to the bottom of the busbar, together with the tabs from the pouch cells to the immediate left and right.

Figure 6 shows schematically the configuration in which the pouch cells of Figures 2 to 5 are connected. Referring to Figure 6, in a pouch cell unit 30 with configuration A, the negative terminal tab 45 of one pouch cell is connected to the positive terminal tab 44 of the other pouch cell at the busbar 36 at the top of the unit. Similarly, in a pouch cell unit 31 with configuration B, the negative terminal tab of one pouch cell is connected to the positive terminal tab of the other pouch cell at the busbar 36 at the bottom of the unit. Thus, the pouch cells 32 within a pouch cell unit 30, 31 are connected in series. However, each of those pouch cells is connected in parallel with the pouch cell immediately adjacent to it in the adjacent pouch cell unit. Thus, this arrangement allows the pouch cells to be connected in a 2p configuration, that is, a series connection of pairs of parallel cells.

In the arrangement of Figures 2 to 6, a 2p configuration is achieved by connecting pouch cells from adjacent pouch cell units in parallel. In order to terminate the 2p configuration, a further pouch cell unit having a third configuration (configuration "C") is used. This pouch cell unit contains a single pouch cell, which is connected in parallel with the final pouch cell in the stack of pouch cell units with configurations A and B. Figure 7 is a cross section through part of a battery module, showing how a pouch cell unit with configuration C is used to terminate the stack of pouch cell units. Referring to Figure 7, the pouch cell unit 52 with configuration C comprises a cell tray 54 which holds a single pouch cell 32. A busbar 56 is attached to the top of the cell tray. The terminal tab at the top of the pouch cell is connected to the top of the busbar 56. The terminal tab from the immediately adjacent pouch cell (from a pouch cell unit with configuration B) is also connected to the top of the busbar 56. The busbar 56 has a 1C" shape, which allows the tab from the immediately adjacent pouch cell to pass between the legs of the "C". Although not shown in Figure 7, the terminal tab at the bottom of the pouch cell in pouch cell unit 52 is connected to the busbar at the bottom of the adjacent pouch cell unit.

In the arrangement of Figure 7, an electrical terminal 58 is assembled to the pouch cell unit 52. The electrical terminal 58 is electrically connected to the busbar 56. The electrical terminal 58 provides the electrical interface that allows battery modules to be electrically connected together and placed into a battery pack as needed. Also shown in Figure 7 is a bolt 60. The bolt 60 passes through holes in the cell trays. The bolt 60 is used to physically hold the stack of pouch cell units together. A nut 62 is used to secure the bolt in place and apply the appropriate pressure to ensure physical stability of the battery module. A similar nut and bolt is provided at the bottom of the battery module.

It will be appreciated that another pouch cell unit similar to the unit 52 shown in Figure 7 is provided at the other end of the battery module.

Figure 8 shows steps taken to assembly a battery module using the pouch cell units of Figures 2 to 7 in one embodiment. Referring to Figure 8, in step 100 the busbars are first attached to the cell trays. This is done by pressing the busbars onto securing features on the cell trays with click fit or an interference fit. In step 102 the cooling fins are attached to the cell trays. This is done by sliding the cooling fins into slots in the cell trays. There may be some embodiments where cooling fins are not required or are not designed into the assembly, in which case this step may be omitted. In step 104 the pouch cell terminal tabs are pre-bent into the required shapes. This may be done, for example, by clamping the tabs in moulds of the required shape. In step 106 the pouch cells are attached to the cell trays. This may be done, for example, by clamping the pouch cells to the cell tray using cell covers, or by pressing the pouch cells onto securing features on the cell tray, or any other appropriate technique. In step 108 the expansion pads are attached to one of the pouch cells in each pouch cell unit, for example, using adhesive. It will be appreciated that some or all of the above steps may be carried out in a different order if desired, and it may be possible for some of the steps to be omitted.

Once the individual pouch cell units have been prepared with the busbars pre-assembled to the cell trays and the cell tabs pre-bent into the required shapes, in step 110 the pouch cell units are stacked together to form a battery module. In step 112 the pouch cell units are secured using nuts which attach to bolts running through the stack of pouch cell units. Once the stack of pouch cell units has been physically assembled, in step 114 the various electrical tabs from the pouch cells are electrically connected to the busbars. In a preferred embodiment, this is achieved by laser welding. Finally, in step 116, the electrical terminals of the battery module are connected to the two end pouch cell units in the stack. This may also be achieved by laser welding.

In the arrangement of Figures 2 to 8, the busbars 36 are preassembled to the elements that mechanically locate the pouch cells, namely, the cell trays 34. The cell tabs 44, 45 are pre-bent into specific shapes in order to bring them to the appropriate busbar. These pre-bent shapes are arranged such that the tabs come into contact with the busbars on the outside surfaces of the busbars. This facilitates the welding process, since the relatively thin tabs are presented for welding, rather than the thicker busbars.

The arrangement described above can allow the pouch cells to be easily stacked and subsequently welded without the additional step of insertion of busbars into a tight space in a controlled manner. In particular, in the above arrangement it is not necessary to thread the electrical tabs from the pouch cells through slots in a busbar assembly prior to welding. This may simplify the assembly process and help to avoid errors which may otherwise occur due to the high level of precision that is typically involved.

A further advantage of the above arrangement is that it facilitates the use of pouch cells with opposing terminal tabs. Pouch cells with opposing tabs tend to have a more uniform temperature distribution and thus typically have a longer life and better performance than those with tabs one the same side of the pouch cell.

However, if desired, pouch cells with tabs on the same side could be used. In this case, the busbars would be provided in the appropriate locations with respect to the cell tabs.

The arrangement described above allows the pouch cells to be electrically connected in a 2p configuration using the busbars that are preassembled to the cell trays.

Figure 9 shows schematically an embodiment in which pouch cells are connected in a 3p configuration. Referring to Figure 9, in this embodiment each pouch cell unit 70, 71 comprises three pouch cells 72 held in place by a cell tray (not shown). The pouch cells 72 have opposing terminal tabs, with positive terminal tabs 74 at one end of the pouch cell and negative terminal tabs 75 at the other end. Each pouch cell unit 70, 71 may include a cooling fin, an expansion pad and locating dowels in the manner described above with reference to Figure 2. Each pouch cell unit 70, 71 is also provided with a busbar 76, which is attached to the cell tray at the same end of the pouch cell unit as the positive terminals 74.

In this embodiment, within each pouch cell unit 70, 71, each of the pouch cells 72 has the same orientation, that is, the positive terminal tabs 74 are all located at one end and the negative terminal tabs 75 are all located at the other end. However, the pouch cell units 70, 71 themselves are provided in two different orientations. In a first orientation, a pouch cell unit 70 has the positive terminals 74 and the busbar 76 at the top of the unit, while in a second orientation a pouch cell unit 71 has the positive terminals 74 and the busbar 76 at the bottom of the unit (i.e. at the opposite end to the first orientation). This may be achieved, for example, by rotating successive pouch cell units through 180° with respect to each other.

In the arrangement of Figure 9, in each of the pouch cell units 70, 71, the positive terminal tabs 74 are connected to the busbar 76, together with the negative terminal tabs 75 from an adjacent pouch cell unit. This allows the pouch cells 72 to be connected in a 3p configuration, that is, a series connection of sets of three parallel cells. As in previous embodiments, the terminal tabs 74, 75 are pre-bent into the required configuration before assembly of the module.

In the arrangement shown in Figure 9, the busbars 76 are provided at the same end of a pouch cell unit as the positive terminals 74. Alternatively, it would be possible for the busbars 76 to be provided at the same end of the unit as the negative terminals 75, or for some other combination to be used.

In alternative embodiments, the pouch cells may be connected in other configurations, such as a 4p configuration (4 cells connected in parallel) or a 5p configuration (5 cells connected in parallel) using the appropriate arrangement of pouch cells in a pouch cell unit, and/or additional busbars in the pouch cell units.

For example, a pouch cell unit may contain four or more pouch cells. Within each pouch cell unit, the pouch cells may have the same or different orientations. Furthermore, if desired, a lp configuration (a series connection of all of the cells in the battery module) could be used. In this case, each cell tray may comprise a single pouch cell. Any other appropriate configuration or combination of configurations may also be used.

It will be appreciated that embodiments of the present invention have been described above by way of example only, and modifications in detail will be apparent to the skilled person within the scope of the appended claims.

Claims

CLAIMS1. A pouch cell unit comprising: at least one pouch cell; a cell tray which supports the pouch cell; and a busbar for electrically connecting a plurality of pouch cells, wherein the busbar is attached to the cell tray.
2. A pouch cell unit according to claim 1, wherein the cell tray comprises means for securing the busbar to the cell tray.
3. A pouch cell unit according to claim 1 or 2, wherein the busbar is pre-assembled to the cell tray prior to stacking the pouch cell unit with other pouch cell units.
4. A pouch cell unit according to any of the preceding claims, wherein the busbar is located on an outside of the cell tray.
5. A pouch cell unit according to any of the preceding claims, wherein: the pouch cell comprises terminal tabs; a first terminal tab is arranged to be connected to the busbar; and a second terminal tab is arranged to be connected to a busbar in an adjacent pouch cell unit.
6. A pouch cell unit according to claim 5, wherein the first terminal tab is arranged to be connected to an outside surface of the busbar.
7. A pouch cell unit according to claim 5 or 6, wherein the first terminal tab is bent around the busbar.
8. A pouch cell unit according to any of claims 5 to 7, wherein the second terminal tab is bent away from the pouch cell unit.
9. A pouch cell unit according to any of claims 5 to 8, wherein the pouch cell unit is arranged to receive a terminal tab of a pouch cell in an adjacent pouch cell unit.
10. A pouch cell unit according to any of claims 5 to 9, wherein the terminal tabs are pre-bent prior to stacking the pouch cell unit with other pouch cell units.
11. A pouch cell unit according to any of the preceding claims, wherein the pouch cell comprises opposing terminal tabs.
12. A pouch cell unit according to any of the preceding claims, wherein the pouch cell unit comprises two pouch cells.
13. A pouch cell unit according to claim 12, wherein a first terminal tab from each pouch cell is arranged to be connected to the busbar and a second terminal tab from each pouch cell is arranged to be connected to a busbar in an adjacent pouch cell.
14. A pouch cell unit according to any of the preceding claims, wherein two pouch cells in a pouch cell unit have opposing orientations.
15. A pouch cell unit according to any of the preceding claims, wherein each pouch cell has terminal tabs which are bent so as to contact an outside surface of a respective busbar.
16. A pouch cell unit according to any of the preceding claims, further comprising a cooling fin between two pouch cells in a pouch cell unit.
17. A pouch cell unit according to any of the preceding claims, wherein the pouch cell unit is arranged to be stacked with a plurality of other pouch cell units of a similar type.
18. A pouch cell unit according to claim 17, wherein the cell tray is arranged to locate the pouch cell unit with respect to the other pouch cell units.
19. A battery module comprising a plurality of pouch cell units according to any of the preceding claims.
20. A battery module according to claim 19, wherein the battery module comprises a series connection of a plurality of parallel connected pouch cells.
21. A battery module according to claim 19 or 20, wherein at least one of the pouch cell units has a first configuration in which the busbar is located on one side of the battery module and at least one other of the pouch cell units has a second configuration in which the busbar is located on another side of the battery module.
22. A battery module according to claim 21, wherein the battery module comprises a stack of pouch cell units, at least one of the pouch cell units has a third configuration, and the stack of pouch cell units is terminated with a pouch cell unit with the third configuration.
23. A method of assembling a pouch cell unit comprising at least one pouch cell and a cell tray which supports the pouch cell, the method comprising attaching a busbar to the cell tray.
24. A method according to claim 23, wherein the busbar is attached to the cell tray prior to stacking the pouch cell unit with other pouch cell units.
25. A method according to claim 22 or 23, wherein the pouch cell comprises terminal tabs, the method comprising bending the terminal tabs so as to contact an outside surface of a respective busbar prior to stacking the pouch cell unit with other pouch cell units.