GB2577256A

GB2577256A - Battery assembly

Info

Publication number: GB2577256A
Application number: GB1815183.7A
Authority: GB
Inventors: Cherian George Sunoj; Douglas McLaggan James; Talj Elie
Original assignee: McLaren Automotive Ltd
Current assignee: McLaren Automotive Ltd
Priority date: 2018-09-18
Filing date: 2018-09-18
Publication date: 2020-03-25
Anticipated expiration: 2038-09-18
Also published as: GB2577256B; GB201815183D0

Abstract

A method for assembling a battery module includes inserting cells (7, figure 5) into cell holes (6, figure 4) in a cell tray 43 so that the cells each protrude from the cell tray at each end of the cell. Cells may be inserted into each of the cell holes. The cells may be secured to the tray, for example by an interference fit between the cell tray and the cell or by affixing the cells to the cell tray after they have been inserted into the cell holes. A first casing 3a is then attached to a first side of the cell tray to enclose the cell ends protruding from the first side and a second casing 3b is attached to a second side of the cell tray to enclose the cell ends protruding from the second side. The first and second casings may be attached by welding. The method may further comprise attaching electrical connections between terminals of the cells, this may be by attaching a busbar between the cell terminals. The electrical connections may be attached prior to the attachment of the first and second casings.

Description

BATTERY ASSEMBLY

This invention relates to a method for assembling a battery module.

Electric powered or hybrid vehicles are well known and are becoming increasingly prevalent as the desire to reduce carbon emissions increases. In such vehicles, the power that can be provided by, and the weight of, the battery is vital in determining the performance of the vehicle. The power to weight ratio of the battery is therefore something that vehicle designers are trying to optimise. This can clearly be done either by increasing the power generated for a given weight or by reducing the weight for a given power output, or most likely a combination of the two.

The batteries in electric or hybrid vehicles are typically made up of a plurality of individual battery cells connected together in such a way to allow large amounts of power to be provided to drive the wheels or power other systems in the vehicle. These cells are typically provided in the form of one or more battery modules which can be electrically connected together.

Batteries of this type tend to have a housing into which the cells are inserted. Electrical connections between the cells may be made using conductors that connect to cell terminals. As the cells have been inserted into a housing the cell terminals can tend to be located at one end of the cells to permit connection thereto. After any electrical connections that are required are made, a cover can be placed on the housing to enclose the cells. Such a design of battery can mean that the cells have to be designed in a particular way to be compatible with the housing and method of electrical connection. In addition, it can be difficult to service such batteries once assembled.

It would therefore be desirable if there was an improved method of assembling a battery module.

According to a first aspect of the present invention there is provided a method for assembling a battery module, the method comprising: providing a cell tray defining a plurality of cell holes for holding cells; inserting cells into respective cell holes so that the cells each protrude from the cell tray at each end of the cell; attaching a first casing to a first side of the cell tray to enclose the cell ends protruding from the first side; and attaching a second casing to a second side of the cell tray to enclose the cell ends protruding from the second side.

The cells may each comprise cell terminals, and the method may comprise attaching electrical connections between cell terminals. The cells may have a first cell terminal located on a portion of the cell protruding to the first side of the cell tray, and the method may comprise attaching electrical connections between first cell terminals before attaching the first casing. The method may comprise attaching electrical connections to all of the first cell terminals before attaching the first casing.

The cells may have a second cell terminal located on a portion of the cell protruding to the second side of the cell tray, and the method may comprise attaching electrical connections between second cell terminal before attaching the second casing. The method may comprise attaching electrical connections to all of the second cell terminals before attaching the second casing. The method comprising attaching electrical connections between the cell terminals before attaching the first casing and the second casing. Attaching electrical connections between cell terminals may comprise attaching at least one busbar between cell terminals.

Inserting cells into respective cell holes may comprise securing the cells to the cell tray. Securing the cells to the cell tray may comprise inserting cells into respective cell holes until an interference fit is achieved between the cell tray surrounding the cell hole and the cell inserted into the respective cell hole. Securing the cells to the cell tray may comprise affixing the cells to the cell tray once inserted into respective cell holes.

Inserting cells into respective cell holes may comprise inserting cells into each of the cell holes. Attaching the first casing may comprise welding the first casing to the cell tray. Attaching the second casing may comprise welding the second casing to the cell tray. The cell holes may extend through the cell tray along a first direction, the first casing may be attached to the first side of the cell tray substantially in the first direction, and the second casing may be attached to the second side of the cell tray substantially opposite to the first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings: Figure 1 shows a battery.

Figure 2 shows a battery module from the front.

Figure 3 shows a battery module from the back.

Figure 4 shows a cell tray.

Figure 5 shows a cell tray holding cells.

Figure 6 shows the busbars and flexible printed circuit of a battery module.

Figure 7 shows the cells, busbars and module terminals of a battery module.

Figure 8 shows a flow diagram of the battery module assembly process.

Figure 9 shows a schematic diagram of part of the battery module assembly process.

Figure 10 shows a schematic diagram of another part of the battery module assembly process.

Figure 11 shows a schematic diagram of a further part of the battery module assembly process.

DETAILED DESCRIPTION OF THE DRAWINGS

The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art.

The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

Battery overview Figure 1 shows a battery 1 which may comprise a number of identical battery modules 2. The battery modules may be arranged in a row. The battery may comprise any number of battery modules 2. In the example depicted in Figure 1, one battery module 2 is shown for clarity, but in a preferred example there may be thirteen modules.

The battery may be installed in a vehicle. Figure 1 shows the battery 1 fixed to a battery floor la. The battery floor 1a may be structurally integral to the vehicle in which the battery is installed. For example, the battery floor may be a load bearing component of a vehicle chassis. The battery floor la may be configured to removably fitted to the vehicle so that the battery 1 can be removed from the vehicle. For example, for maintenance or replacement of the battery 1.

The battery 1 may further comprise a battery control unit 12 which protrudes from the row of battery modules. The battery control unit 12 may be electrically connected to a one or more module control units 12a. Each battery module 2 may comprise an attached module control unit 12a. The battery control unit 12 may control each battery module control unit 12a. Each battery module control unit 12a may control the activity of the respective attached battery module. Each battery module control unit 12a may receive information concerning the operation of the respective attached battery module. The battery module control units 12a may process that information and feed that information to battery control unit 12.

The battery modules and battery control unit 12 may be enclosed by the battery floor la and a battery housing lb. Figure 2 shows a battery module 2 with a trapezoidal prism shape. The battery module depicted in Figure 2 comprises a cell tray 4 and a two-pad housing 3a, 3b. In Figure 2, the battery module 2 and the cell tray 4 share a common longitudinal axis.

Cell tray An exemplary cell tray 4 is shown in Figure 4. The cell tray depicted in Figure 4 comprises cell holes 6 for holding cells (not shown). Each cell hole 6 may extend through the cell tray in a direction perpendicular to the longitudinal axis of the cell tray. The cell tray may be formed of electrically insulating material.

The cell tray may further comprise a fixing hole 5 configured to receive a fixing element (not shown) for securing the cell tray 4, and hence the battery module 2, to the battery floor (not shown).

Figure 4 shows the cell tray 4 comprising two fixings 9, each fixing comprising a tab 9a, the tab forming a connection hole 9b. Both fixings are generally positioned in the same plane as the cell tray. Each connection hole 9b may extend through its respective tab 9a in a direction parallel to the direction in which the cell holes 6 extend through the cell tray 4. The cell tray may comprise more than two fixings. The cell tray may comprise a single fixing. Fixings on multiple battery modules may receive one or more common elements so that the battery modules can be secured to one another.

Figure 5 shows a number of cells 7 being held in the cell holes 6 of the cell tray 4. The cell tray may be configured to hold any number of cells. In the example depicted in Figure 5 there are forty-eight cells held in respective cell holes 6. Each cell hole may hold one cell.

Resin may be poured into a recessed side of the cell tray. The resin may harden around cells placed in the cell tray so as to secure the cells in the cell tray. Alternatively, each cell 7 may be held in a cell hole 6 by an interference fit between the cell tray 4 surrounding the cell hole and the cell inserted into the respective cell hole.

Each cell hole may extend through the cell tray in a direction perpendicular to the longitudinal axis of the cell tray. In the example cell tray depicted in Figures 4 and 5, each cell hole is cylindrical so as to accommodate cylindrical cells. In other examples, each cell hole may be prismatic so as to accommodate prismatic cells.

The length of each cell may be greater than the length of each cell hole. Each cell 7 comprises a positive terminal and negative terminal. When a cell 7 is inserted into a cell hole 6, a length of the cell 7 comprising the positive terminal of the cell may protrude from the cell hole on one side of the cell tray 4 whilst a length of the cell 7 comprising the negative terminal protrudes from the cell hole on the other side of the cell tray. The portion of the cell 7 comprising the positive terminal and the portion of the cell 7 comprising the negative terminal may protrude from opposite sides of the cell tray. The protruding length of the portion of the cell comprising the cell's positive terminal and the protruding length of the portion of the cell comprising the cell's negative terminal may be equal.

The battery module 2 shown in Figure 2 comprises a two-part module housing 3a, 3b. The housing 3a, 3b may form two enclosed regions which contain the cells 7 held in the cell tray 4. In Figure 2, one part of the module housing 3a encloses the portions of cells protruding on one side of the cell tray. The second part of the module housing 3b encloses the portions of the cells protruding on the opposite side of the cell tray.

In Figures 2 and 3, the exterior faces of the battery module 2 comprise faces of the cell tray 4 and the housing 3a, 3b. Alternatively, the housing 3a, 3b may enclose the entirety of the cell tray. In this case, the exterior faces of the battery module would comprise faces of the housing 3a, 3b.

Cell to cell busbars and flexible printed circuit board Figure 7 shows busbars 10 contacting the terminals of multiple cells to form electrical connections between the multiple cells 7. The busbars 10 are formed of electrically conductive material. The busbars 10 may be formed of metal, for example copper or aluminium.

As above, the cell tray 4 (not shown in Figure 7) fixedly holds cells 7, each cell having a positive terminal and a negative terminal. The busbars 10 may link the cell terminals of any number of cells.

Cells 7 may be arranged in the cell tray 4 so that positive and negative cell terminals protrude from opposite sides of the cell tray. In this way, a current flow path may be created through cells and busbars. For example, the current flow path may "snake" through the battery module. The current flow path may repeatedly intersect the cell tray. The current flow path may repeatedly intersect the longitudinal axis of the battery module. At least some of the cells may be connected in parallel by the busbars 10, meaning that the current flow path passes through multiple cells as the current flow path intersects the cell tray.

Module terminals 13 are shown in Figure 7. The module terminals 13 are positioned on the back of the battery module and may be integral to the cell tray 4 (not shown in Figure 7). Module terminals 13 of neighbouring battery modules may be electrically connected, for example, by module to module busbars. The module terminals 13 allow a supply of current to and/or from the cells 7 of the battery module 2.

The busbars 10 may be integrated with a flexible printed circuit board (not shown in Figure 7). Figure 6 shows the flexible printed circuit board 11 of a battery module. A portion of the flexible printed circuit board 11 is located in the region enclosed by the module housing and another portion of the flexible printed circuit board 11 is wrapped around the exterior faces of both parts of the two-part module housing 3a, 3b, also shown in Figures 2 and 3.

The busbars 10 shown in Figures 6 and 7 may be integrated with the flexible printed circuit board 11. The busbars 10 may be configured to conduct a high level of current between the cells of the module and the module terminals 13.

The flexible printed circuit board 11 shown in Figure 6 may further comprise sense wires. The sense wires may be configured to conduct a low current signal. The sense wires in the flexible printed circuit board may be attached to voltage sensors. Each voltage sensor may be capable of determining the voltage at a point on the busbar. Each voltage sensor may be capable of determining the voltage being drawn from a cell. Each voltage sensor may be capable of inferring the voltage being drawn from a cell from a measurement taken of the voltage being drawn from a busbar 10. Each sense wire in the flexible printed circuit board may be capable of communicating voltage measurements from a voltage sensor to a module control unit 12a, shown in Figure 1. The module control unit 12a may be capable of adapting the activity of the battery module in response to the voltage measurements provided by the sense wire. Each sense wire may be capable of communicating voltage measurements to the battery control unit. The module control unit 12a may be capable of communicating voltage measurements to the battery control unit. The battery control unit 12, also shown in Figure 1, may be capable of adapting the activity of the battery module in response to the voltage measurements. The battery control unit 12 may be capable of adapting the activity of the battery in response to the voltage measurements.

The sense wires of the flexible printed circuit board 11 may be attached to one or more temperature sensors. A temperature sensor may be capable of determining the temperature of a part of the battery module. Each sense wire may be capable of communicating temperature measurements from a temperature sensor to the module control unit. The module control unit may be capable of adapting the activity of the battery module in response to the temperature measurements provided by the sense wire. Each sense wire may be capable of communicating temperature measurements to the battery control unit. The module control unit may be capable of communicating temperature measurements to the battery control unit. The battery control unit may be capable of adapting the activity of the battery module in response to the temperature measurements. The battery control unit may be capable of adapting the activity of the battery in response to the temperature measurements.

The sense wires may be attached to other types of sensors, for example current sensors, and/or fluid flow sensors.

Figure 6 and 7 also show terminal tabs 60, 61 which each of which connect either a positive or a negative end of the busbar to the respective positive or negative module terminal.

Module cooling It is known to supply coolant to regulate the temperature of batteries. In typical batteries, the coolant is confined within coolant jackets or pipes. In such batteries, cells are cooled in areas of the cell which make contact with the jacket or pipe containing the coolant. This is a slow and inefficient cooling method.

In other typical batteries, coolant is not confined by coolant jackets or pipes, but makes direct contact only with the body/centre portion of each cell. In such batteries, the cell terminals are protected so that coolant does not make contact with the cell terminals. Such contact is avoided as it would typically lead to electrical shorting. This is also an inefficient method because the cell terminals, being electrically connected, are often the hottest parts of the cell and yet they are not directly cooled by the coolant.

By contrast, in the battery module described herein, coolant supplied to the battery module 2 makes direct contact with cell terminals, flexible printed circuit board 11, busbars 10, and cell body. The entirety of the cell and connected conducting parts are bathed in coolant. The coolant used is a dielectric oil. Dielectric oils have insulating properties. Cells drenched in dielectric oil are insulated from one another preventing short circuiting between cells. This is an efficient method of regulating cell temperature. Such efficient cooling enables the cells to operate at a higher power and for longer. This means that fewer and/or smaller cells are required to generate the same power as batteries utilising the previously mentioned cooling methods.

Figure 3 shows a supply coolant conduit portion 14 and a drain coolant conduit portion 15. In the exemplary configuration shown in Figure 3, the supply coolant conduit portion 14 is positioned in a lower position and the drain coolant conduit portion 15 is positioned in an upper position. Such a configuration reduces the risk of air locks occurring during filling. Alternatively, the supply coolant conduit portion may be positioned in an upper position and the drain coolant conduit portion may be positioned in a lower position.

Both coolant conduit portions may extend along the battery module in a direction orthogonal to the longitudinal axis of the battery module. Both coolant conduit portions may extend along the battery module in a direction orthogonal to the direction in which the fixing hole 5 extends through the cell tray 4. Both coolant conduit portions may extend along the battery module in a direction parallel to the direction in which the cell holes 6 extend through the cell tray 4.

As shown in Figure 3, the supply coolant conduit portion 14 is linked to an inlet 16 in the battery module so that coolant may be supplied to a region enclosed by the housing of the battery module. The drain coolant conduit portion 15 is linked to an outlet 17 so that coolant may be drained from a region enclosed by the housing of the battery module. Inlet 16 and outlet 17 are openings formed in the module housing. The coolant may be supplied to one of the two regions enclosed by the housing and be drained from the other of the two regions enclosed by the housing, one region being on an opposite side of the longitudinal axis of the cell tray to the other region. The cell tray 4 may comprise through-holes 35 to 40 for allowing the passing of coolant from a respective one of the said regions to the other of the said regions. The through-holes may be located in the cell tray 4 at the end of the cell tray 4 remote from the inlet 16 and outlet 17. The through-holes may be shaped to promote even fluid flow over the cells.

As shown in Figure 1, battery 1 contains a number of battery modules 2 arranged in a row. When battery modules 2 are positioned in a row, a coolant conduit portion 14 of one battery module aligns with a coolant conduit portion of a neighbouring battery module. The two coolant conduit portions may be connected to one another by a coupler 19, shown in Figure 3. Couplers 19 form liquid tight connections between coolant conduit portions so that coolant may flow from portion to portion. When supply coolant conduit portions 14 of the battery modules in the row of battery modules are connected by couplers 19, they form a supply coolant conduit 14a which extends along the length of the row of battery modules. When drain coolant conduit portions 14 of the battery modules in the row of battery modules are connected by couplers 19, they form a drain coolant conduit 15a which extends along the length of the row of battery modules.

As shown in Figure 1, the longitudinal axes of all the battery modules 2 in the row of battery modules of the battery 1, may be parallel to one another. Both coolant conduits 14a, 15a may extend along the row of battery modules in a direction orthogonal to the longitudinal axes of the battery modules in the row of battery modules. Both coolant conduits may extend along the row of battery modules in a direction orthogonal to the direction in which the fixing hole 5 extends through the cell tray 4 of each battery module. Both coolant conduits may extend along the row of battery modules in a direction parallel to the direction in which the cell holes 6 extend through the cell tray 4 of each battery module.

Inlet 16 and outlet 17 may be configured to allow coolant to enter and leave the battery module 2. Inlet 16 and outlet 17 may further act as passages through which the flexible printed circuit boards 11 pass between the interior and exterior of the battery module, as shown in Figure 3. The inlet 16 and outlet 17 may be the only openings in the two-part housing 3a, 3b of the battery module 2. Figure 3 shows sealant 18 around the inlet 16 and outlet 17. Sealant 18 ensures that coolant inside the battery module does not leak from the battery module into other parts of the battery.

The method of direct cell cooling described herein also has further advantages in the case that excessive pressure builds up inside a cell. Each cell may comprise a cell vent port. In the case that excessive pressure builds up inside the cell, the cell vent port may be activated, allowing fluids within the cell to escape the cell. The cell vent port may be configured to expel cell fluids in the event that pressure within the cell exceeds a threshold. Upon leaving the cell, the fluids are quenched by the surrounding coolant.

Method of battery assembly A method by which the battery module pictured in the figures can be assembled will now be described. The assembly method will be described with reference to Figures 8, 9 and 10.

As shown in step 101, a cell tray 4 is provided. The cell tray 4 may be as pictured in Figure 4. As described herein, the cell tray 4 defines a plurality of cell holes 6 for holding cells 7. The cell holes 6 may extend through the cell tray 4 in a direction perpendicular to the longitudinal axis of the cell tray. The cell holes 6 are unobstructed so that cells 7 can be inserted into the holes 6.

As shown in step 102, the cell tray 4 is inserted into a jig 30 prior to the cells 7 being inserted into the cell holes 6. The jig 30 may have a shape which means the cell tray 4 is held in a fixed position whilst the cell tray 4 is held in the jig 30. As shown in Figure 9, the jig 30 has a clamp 31 which is configured to releasably hold one end of the cell tray 4 in a fixed position relative to the jig 30. In Figure 9, the clamp 31 holds the end of the cell tray 4 where the module terminals 13 are located. The jig 30 also has threaded holes 32 which are positioned on the jig so that screws 33 can be inserted through the fixing holes 9b located at the opposite end of the cell tray 4 to the module terminals 13 and screwed into the threaded holes 32. The threaded holes 32 and the clamp 31 are positioned so that the cell holes 6 in the cell tray 4 are located over corresponding indentations 34 in the jig 30. These indentations 34 are shaped to receive cells 7. The indentations 34 each have a depth that corresponds to the desired projection of the cells 7 from the cell tray 4 on the side of the cell tray adjacent to the surface of the jig 30. The indentations 34 each have a cross-sectional shape that means the cells are held in the required orientation through the holes in the cell tray 4. The jig may be shaped so that when the cells 7 are inserted into respective cell holes 6 the cells are held at a uniform depth within the cell holes 6. This means that the cells 7 may be held in place protruding from the cell tray 4. The cells 7 may be held in place protruding by an equal amount from each side of the cell tray 4.

As shown in step 103, cells 7 are inserted into respective cell holes 6. The cells 7 are inserted into respective cell holes 6 so that the cells each protrude from the cell tray at each end of the cell. This is as shown in Figure 5. The cells 7 may all be inserted from the same side of the cell tray 4. This will be the case when the jig shown in Figure 9 is used. Alternatively, some cells 7 may be inserted from one side of the cell tray 4 and some cells 7 may be inserted from the other side of the cell tray 4. The cells 7 each have a respective cell terminal located at opposite ends of the cells 7. The polarity of one of the cell terminals on the cell has opposite polarity to the other of the cell terminals on the cell. The cells may be inserted so that the cell terminals presented on one side of the cell tray all have the same polarity. The cells may be inserted so that some of the cell terminals presented on one side of the cell tray have one polarity and some of the cell terminals presented on that side of the cell tray have opposite polarity. The chosen configuration of polarities will be particular to the power requirements of the battery module 2.

As shown in step 104, the polarity of the cells that have been inserted into the cell tray is checked. This can be achieved by lowering a circuit board 35 with contacts for each cell terminal on to the cell tray. The circuit board 35 is connected to a device 36 that tests the polarity of the cells 7.

As shown in step 105, the cells 7 are secured to the cell tray 4. The cells 7 may be secured to the cell tray 4 merely by their insertion into the cell tray 4 if the cell holes 6 of the cell tray 4 are shaped so that they have an interference fit with the perimeter of the cells 7. If the cells are not fully secured merely by their insertion, then cells 7 may be affixed to the cell tray 4. The cells 7 may be affixed to the cell tray 4 by the pouring of resin into the cell tray 4 and then curing of the resin. As shown in Figure 9, the cell tray 4 may comprise a recess 37 into which resin can be poured or injected. The cell holes 6 may be shaped so that whilst they do not provide an interference fit to the cells the clearance between the cell holes 6 and the perimeter of the cells 7 is such that the resin does not flow through the gap between the cell holes 6 and the perimeter of the cells 7. This may be because the resin has a viscosity that is high enough that it is held in the gap between the cell holes 6 and the perimeter of the cells 7 rather than flowing through. A resin injection nozzle 38 is shown in Figure 9E for the supply of resin but any suitable application method may be used.

In Figure 9A, the cell tray 4 is shown as it is being inserted into jig 30. In Figure 9B, the cell tray 4 is shown in a side view showing cells 7 inserted into each of the cell holes 6. The differing polarity of the cell terminals on that side of the cell tray 4 is shown by the different shading and shape of the cell terminals. In Figure 9C, the testing of the polarity is shown. In Figure 9D, the jig is shown with a cell support raised. In Figure 9E, the jig is shown with a cell support lowered and resin being injected into the cell tray.

As shown in step 106, once the cells 7 have been secured to the cell tray 4, the cell tray 4 together with the cells 7 can be removed from the jig 30, if used.

As shown in step 107, electrical connections can be attached between cell terminals. The attachment of electrical connections may comprise attaching electrical connections between first cell terminals that are located on a portion of the cell 7 protruding from a first side of the cell tray 4. The attachment of electrical connections may comprise attaching electrical connections between second cell terminals that are located on a potion of the cell 7 protruding from a second side of the cell tray 4. As shown in Figure 10, busbars 10 may be attached to the cells 7. A first set of busbars 39 may be attached to the cell terminals 40 located on one side of the cell tray 4. A second set of busbars 41 may be attached to the cell terminals 42 located on a second side of the cell tray 4. The busbars may be placed over the cells 7 and then attached to the cell terminals. The attachment may be by welding the busbars to the cell terminals. The busbars may be encapsulated in a flexible material so that the position of the busbars is fixed in the plane of the busbars.

In Figure 10A, the busbars and assembled cell tray 4 and cells 7 are shown. In Figure 10B, the positioning of the busbars relative to the cell tray 4 and cells 7 (not shown for clarity) is shown. The busbars can then be attached to the cell terminals. In Figure 10C, the assembled cell tray 4, cells 7 and busbars 39, 41 are shown at 43.

As shown in step 108, a first casing 3a is attached to a first side of the cell tray to enclose the cell ends protruding from the first side of the cell tray 4. The housing parts may also be known as casings. As shown in step 109, a second casing 3b is attached to a second side of the cell tray to enclose the cell ends protruding from the second side of the cell tray 4. When the first and second casings are attached to the cell tray the cells may be enclosed within the battery module. There may be holes in the casings through which, for example, coolant and/or wires can pass. Therefore, the cells being enclosed within the battery module may be taken to mean substantially enclosed within the battery module. The casings may be attached to the cell tray by any suitable means. For instance, the casings may be each be welded to the cell tray or the casings may be adhered to the cell tray. The attachment between the casings and the cell tray may be impervious to fluid so that fluid cannot flow through the join between the casings and the cell tray. The attachment of the first casing and the second casing to the cell tray may cause the casings to substantially fully enclose the cells.

Figure 11 shows the process of attaching the housing parts to the cell tray. Figure 11A shows the assembled cell tray 43 relative to the first housing part 3a and second housing part 3b prior to attachment. The first housing pad 3a is attached from one side of the cell tray assembly 43 and the second housing part 3b is attached from the other side of the cell tray assembly 43. The cell tray, first casing and second casing may be constituted primarily by plastic. The first and second casings 3a, 3b can be attached to the cell tray using laser welding which heats one part to the point that it melts and fuses to the other part. This is shown in Figure 11 B. The first casing 3a may be placed in contact with the cell tray such that it encloses the cell ends. The contact between the first casing 3a and the cell tray 7 is along an edge of the first casing. The first casing is shown as being cup shaped and the contact between the first casing and the cell tray 7 is along the rim of the cup. A laser beam can then be directed at the joint between the cell tray and first casing. One of the cell tray and first casing comprises a material that is configured to absorb energy from the laser beam and thus heat one of the cell tray and the first casing. In the Figure 11, the material is contained within the cell tray along the region where it contacts the first casing. The heating from the material causes one of the cell tray and first casing to melt and fuse to the other thus welding the pieces together. The cell tray and first casing may otherwise be generally opaque to the laser beam without the presence of the material. The material can be any material that absorbs the laser light such as carbon black.

The second casing 3b may be placed in contact with the cell tray such that it encloses the cell ends. The contact between the second casing 3b and the cell tray 7 is along an edge of the second casing. The second casing is shown as being cup shaped and the contact between the second casing 3b and the cell tray 7 is along the rim of the cup. A laser beam can then be directed at the joint between the cell tray and first casing. One of the cell tray and second casing comprises a material that is configured to absorb energy from the laser beam and thus heat one of the cell tray and the first casing. In the Figure 11, the material is contained within the cell tray along the region where it contacts the second casing. The heating from the material causes one of the cell tray and second casing to melt and fuse to the other thus welding the pieces together. The cell tray and second casing may otherwise be generally opaque to the laser beam without the presence of the material.

Figure 11 B shows example directions for the laser beam. Generally, the laser beam passes through the opaque/transmissive layer first before entering the absorbing layer that contains the material that causes heating. Thus, in the case shown in Figure 11 B the laser beam is projected in the direction such that it passes through the casing prior to entering the cell tray 7. The two casings may be assembled around the cell tray prior to welding of both of the casings. Alternatively, one casing may be brought into contact with the cell tray and welded prior to the other casing being brought into contact with the cell tray and being welded.

As shown in Figure 11A, the busbars have wiring attached to them. The wiring may be passed through a hole in the casing prior to the attachment of the casing to the cell tray.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

CLAIMS1. A method for assembling a battery module, the method comprising: providing a cell tray defining a plurality of cell holes for holding cells; inserting cells into respective cell holes so that the cells each protrude from the cell tray at each end of the cell; attaching a first casing to a first side of the cell tray to enclose the cell ends protruding from the first side; and attaching a second casing to a second side of the cell tray to enclose the cell ends protruding from the second side.
2. The method according to claim 1, wherein the cells each comprise cell terminals, and the method comprises attaching electrical connections between cell terminals.
3. The method according to claims 1 or 2, wherein the cells have a first cell terminal located on a portion of the cell protruding to the first side of the cell tray, and the method comprises attaching electrical connections between first cell terminals before attaching the first casing.
4. The method according to claim 3, the method comprising attaching electrical connections to all of the first cell terminals before attaching the first casing.
5. The method according to any preceding claim, wherein the cells have a second cell terminal located on a portion of the cell protruding to the second side of the cell tray, and the method comprises attaching electrical connections between second cell terminal before attaching the second casing.
6. The method according to claim 5, the method comprising attaching electrical connections to all of the second cell terminals before attaching the second casing.
7. The method according to any of claims 2 to 6, the method comprising attaching electrical connections between the cell terminals before attaching the first casing and the second casing.
8. The method according to any of claims 2 to 7, wherein attaching electrical connections between cell terminals comprises attaching at least one busbar between cell terminals.
9. The method according to any preceding claim, wherein inserting cells into respective cell holes comprises securing the cells to the cell tray.
10. The method according to claim 9, wherein securing the cells to the cell tray comprises inserting cells into respective cell holes until an interference fit is achieved between the cell tray surrounding the cell hole and the cell inserted into the respective cell hole.
11. The method according to claim 9, wherein securing the cells to the cell tray comprises affixing the cells to the cell tray once inserted into respective cell holes.
12. The method according to any preceding claim, wherein inserting cells into respective cell holes comprises inserting cells into each of the cell holes.
13. The method according to any preceding claim, wherein attaching the first casing comprises welding the first casing to the cell tray.
14. The method according to any preceding claim, wherein attaching the second casing comprises welding the second casing to the cell tray.
15. The method according to any preceding claim, wherein the cell holes extend through the cell tray along a first direction, the first casing is attached to the first side of the cell tray substantially in the first direction, and the second casing is attached to the second side of the cell tray substantially opposite to the first direction.