A method, control system and apparatus for battery pack manufacturing

Abstract

A battery pack manufacturing method comprises providing a plurality of battery cells 212, each battery cell having a terminal 218 on a first side 214, and arranging one or more busbars 220 adjacent to the terminals of the plurality of battery cells. The method then comprises obtaining for each battery cell in a first group of battery cells a position of the one or more busbars adjacent the battery cell, wherein the first group of battery cells comprises at least two neighbouring battery cells of the plurality of battery cells, and determining an average position of the one or more busbars for the first group of battery cells in dependence on the obtained positions. A laser is arranged at a first location based on the average position of the one or more busbars for the first group of battery cells and welding, using the laser 302 at the first location, the one or more busbars to the terminals of each battery cell in the first group of battery cells. A control system for controlling a manufacturing system for a battery pack and the apparatus 300 for battery pack manufacturing are also disclosed and claimed.

Description

TECHNICAL FIELD The present disclosure relates to a battery pack manufacturing method. Aspects of the invention relate to a battery pack manufacturing method, a control system for controlling a manufacturing system for a battery pack and an apparatus for battery pack manufacturing. BACKGROUND It is known to provide a battery pack by connecting several battery cells together in series and / or parallel to provide a desired battery power. In the battery pack, terminals of battery cells may be connected using one or more busbars and there may be many such connections in the battery pack. Battery packs made in this way may be used in electric vehicles. It is known to use laser beam welding to connect the terminals of battery cells to the busbars due to its non-contact nature and fast processing speeds. However, laser beam welding often produces large amounts of spatter. That is, ejection of molten droplets during welding. The spatter reduces the quality of the weld and leads to the formation of the weld defects such as underfills and blow-outs which are responsible for weld failure during use. The spatter also contaminates the welding equipment. Furthermore, the quality of welds formed using laser beam welding is affected by tolerances of the battery cells and busbars. The tolerances of battery cells and busbars cause variation in the position of the connection terminals of battery cells and one or more busbars. As such, there exists a need to improve manufacture of battery packs. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide to a battery pack manufacturing method, a control system for controlling a manufacturing system for a battery pack and an apparatus for battery pack manufacturing as claimed in the appended claims. According to an aspect of the present invention there is provided a battery pack manufacturing method. The method comprises: arranging one or more busbars adjacent to terminals of a plurality of battery cells; obtaining for each battery cell in a first group of battery cells a position of the one or more busbars adjacent the battery cell; wherein the first group of battery cells comprises at least two battery cells; determining an average position of the one or more busbars for the first group of battery cells in dependence on the obtained positions; arranging a laser at a first location based on the average position of the one or more busbars for the first group of battery cells; and welding, using the laser at the first location, the one or more busbars to the terminals of each battery cells in the first group of battery cells. According to an aspect of the present invention there is provided a battery pack manufacturing method. The method comprises: providing a plurality of battery cells, each battery cell having a terminal on a first side; arranging one or more busbars adjacent to the terminals of the plurality of battery cells; obtaining for each battery cell in a first group of battery cells a position of the one or more busbars adjacent the battery cell, wherein the first group of battery cells comprises at least two neighbouring battery cells of the plurality of battery cells; determining an average position of the one or more busbars for the first group of battery cells in dependence on the obtained positions; arranging a laser at a first location based on the average position of the one or more busbars for the first group of battery cells; and welding, using the laser at the first location, the one or more busbars to the terminals of each battery cells in the first group of battery cells. The method may therefore reduce the time required to weld busbars to battery cell terminals when manufacturing the battery pack. The reduction in time is achieved by welding a busbar to multiple battery cell terminals from the first location which is based on an average position of the busbar rather than, for example, re-positioning the laser for each weld. Basing the first location on the average position of the busbar helps to improve weld 1 quality by accounting for tolerances of the battery cells and busbars. The reduction in time is advantageous because it enables a greater number of battery packs to be manufactured in a specific time period thereby improving manufacturing efficiency. In embodiments of either the above-described aspects of the invention, the method may comprise one or more of the following may apply. At the first location the focal plane of the laser may be offset from average position of the one or more busbars for the first group of battery cells by a predetermined amount. Offsetting the focal plane of the laser from the one or more busbars may improve quality of the weld and may reduce the amount of spatter produced during welding. At the first location the focal plane of the laser may be offset from average position of the one or more busbars such that the focal plane is outside of the battery. Offsetting the focal plane so that it is within the outside, rather than inside the battery, may reduce the risk of overpenetration of the weld if the laser is incorrectly aligned (e.g. to close to the battery cell during welding). Overpenetration of the weld can damage the battery cell. Positioning the focal plan in this manna- is particularly advantageous when there are space constraints in a production line which limit the maximum distance between the laser and the terminal of the battery cell. At the first location the focal plane of the laser may be offset from average position of the one or more busbars for the first group of battery cells by between 4 and 9 mm. Offsetting the focal plane of the laser from the one or more busbars by between 4 and 9 mm may further reduce the amount of spatter produced during welding. In an embodiment, obtaining for each battery cell in the first group of battery cells the position of the one or more busbars may comprise obtaining each position simultaneously. Obtaining the positions in this way may further reduces the time required to manufacture of the battery pack. Optionally, each position may be obtained using a separate position sensor. In an embodiment, the first group of battery cells comprises three battery cells. In an embodiment, each battery cell may have a second side opposing the first side. Providing the plurality of battery cells may comprise arranging the plurality of battery cells such that the second side of each of the plurality of battery cells reside within a plane. This may further reduce manufacturing time as position of the one or more busbars may not need to be measured on the second side of the battery pack. Optionally, the second side of each of the plurality of battery cells is positioned against a planar surface of a plate. In an embodiment, obtaining for each battery cell in the first group of battery cells a position of the one or more busbars adjacent the battery cell may comprise obtaining a position of a weld area for each battery cell in a first group of battery cells. The weld area may comprise an area of the one or more busbars to be welded to the terminal of a battery cell. The method may comprise determining an average position of the weld areas for the first group of battery cells in dependence on the obtained positions. The method may comprise arranging a laser at a first location based on the average position of the weld areas for the first group of battery cells. At the first location the focal plane of the laser may be offset from average position of the weld areas for the first group of battery cells by a predetermined amount. In an embodiment, the method may comprise obtaining for each battery cell in a second group of battery cells a position of the one or more busbars whilst welding the one or more busbars to the terminals of each battery cell in the first group of battery cells, wherein the second group of battery cells comprises at least two neighbouring battery cells of the plurality of battery cells. As such, the manufacturing time may therefore be further reduced by welding one group of battery cells whilst obtain the positions of the one or more busbars for a second group of battery cells. In an embodiment, the second group of battery cells comprises three battery cells. Battery cells of the first group may be distinct from those of the second group. Therefore, the second group of battery cells may comprise different battery cells to the first group of battery cells. In an embodiment, obtaining for each battery cell in the second group of battery cells a position of the one or more busbars adjacent the battery cell may comprise obtaining a position of a weld area for each battery cell in a first group of battery cells. The weld area may comprise an area of the one or more busbars to be welded to the terminal of a battery cell. In an embodiment, the method may comprise: determining an average position of the one or more busbars for the second group of battery cells; moving the laser from the first location to a second location based on the average position of the one or more busbars for the second group of battery cells; and welding, using the laser at the second location, the one or more busbars to the terminals of each battery cell in the second group of battery cells. Repeated the manufacturing method along plurality of battery cells may provide a continuous process for manufacturing the battery pack. In an embodiment, the first group and the second group of battery cells are neighbouring. As such, the method may be used to weld sequential groups of battery cells. In an embodiment of the method: the laser may be arranged such that the focal plane of the laser is offset from the area by between 4 and 9 mm; the welding may occur at a speed of between 450 and 500 mm / s; the laser may comprise a ring beam surrounding a core beam; and each of the ring beam and the core beam may have a power of between 3.5 and 4 kW. The inventors found that the combination of using a laser having a ring and core beam each of the having a power of between 3.5 and 4 kW, offsetting the focal plane of the laser from the area to be welded by between 4 and 9 mm and welding at a speed of between 450 and 500 mm / s surprisingly allowed a substantially spatter free weld to be formed between the busbar and terminal. Since the method produces a spatter free weld, this improves the quality of the weld, reduces contamination of the area surrounding the weld and reduces the risk of damage to the welding equipment. In an embodiment, the core beam may have a diameter between 0.32 mm to 0.38 mm at the one or more the busbar. Limiting the core beam diameter in this way may further reduce the spatter during welding. In an embodiment, the ring beam may have a diameter between 1.6 and 1.7 mm at the one or more busbars. Limiting the ring beam diameter in this way may further reduce the spatter during welding. Optionally, the one or more busbars may each comprise nickel plated aluminium. Nickel plated aluminium may improve the electrical connection with the terminal. Optionally, the terminals of the plurality of battery cells may comprise aluminium. Aluminium may improve the electrical connection with the busbar. In an embodiment, the one or more busbars may each have a thickness of between 1 mm and 2 mm. This thickness may be advantageous because using thicker busbars may unnecessarily increase the overall weight of the battery pack. In an embodiment, the terminals of the plurality of battery cells may have a thickness of between 3.5 and 4.5 mm. In an embodiment, the welding, using the laser, of one or more busbars to the terminals may comprise forming a lap joint between the one or more busbars and the respective terminal. The busbar and the terminal may be thin metals having different thicknesses and being made of different metals. A lap joint may improve the ease of provide a mechanically sound weld between such components. According to an aspect of the invention, there is provided a control system for controlling a manufacturing system for a battery pack, the battery pack comprising a plurality of battery cells, each battery cell having a terminal. The control system comprising one or more processors collectively configured to: receive for each battery cell in a first group of battery cells position data of a position of the one or more busbars adjacent the battery cell, wherein the first group of battery cells comprises at least two battery cells of the plurality of battery cells; calculate an average position of the one or more busbars for the first group of battery cells; determine a first location in dependence on the average position for the first group of battery cells; output a control signal to move a laser to the first location; and output a control signal to initiate welding, using the laser in the first location, the one or more busbars to the terminals of each battery cells in the first group of battery cells. According to an aspect of the invention, there is provided a control system for controlling a manufacturing system for a battery pack, the battery pack comprising a plurality of battery cells, each battery cell having a terminal on a first side. The control system comprising one or more processors collectively configured to: receive for each battery cell in a first group of battery cells position data of a position of the one or more busbars adjacent the battery cell, wherein the first group of battery cells comprises at least two neighbouring battery cells of the plurality of battery cells; calculate an average position of the one or more busbars for the first group of battery cells; determine a first location in dependence on the average position for the first group of battery cells; output a control signal to move a laser to the first location; and output a control signal to initiate welding, using the laser in the first location, the one or more busbars to the terminals of each battery cells in the first group of battery cells. The control system may therefore reduce the time required to weld busbars to battery cell terminals when manufacturing the battery pack. The reduction in time is achieved by welding a busbar to multiple battery cell terminals from the first location which is based on an average position of the busbar rather than, for example, re-positioning the laser for each weld. Basing the first location on the average position of the busbar helps to improve weld quality by accounting for tolerances of the battery cells and busbars. The reduction in time is advantageous because it enables a greater number of battery packs to be manufactured in a specific time period thereby improving manufacturing efficiency. In embodiments of either the above-described aspects of the invention, the control system may comprise one or more of the following may apply. The control system may comprise one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving an input signal; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to controlling a manufacturing system for a battery pack as described above. At the first location the focal plane of the laser may be offset from average position of the one or more busbars for the first group of battery cells by a predetermined amount. Offsetting the focal plane of the laser from the one or more busbars may improve quality of the weld and may reduce the amount of spatter produced during welding. At the first location the focal plane of the laser may be offset from average position of the one or more busbars such that the focal plane is outside of the battery. Offsetting the focal plane so that it is within the outside, rather than inside the battery, may reduce the risk of overpenetration of the weld if the laser is incorrectly aligned (e.g. to close to the battery cell during welding). Overpenetration of the weld can damage the battery cell. Positioning the focal plan in this manna- is particularly advantageous when there are space constraints in a production line which limit the maximum distance between the laser and the terminal of the battery cell. At the first location the focal plane of the laser may be offset from average position of the one or more busbars for the first group of battery cells by between 4 and 9 mm. Offsetting the focal plane of the laser from the one or more busbars by between 4 and 9 mm may further reduce the amount of spatter produced during welding. In an embodiment, the one or more processors may be collectively configured to: receive the position data for each of the battery cells in the first group of battery cells simultaneously. Obtaining the positions in this way may further reduces the time required to manufacture of the battery pack. Optionally, each position may be obtained using a separate position sensor. In an embodiment, the first group of battery cells comprises three battery cells. In an embodiment, the one or more processors collectively may be configured to receive for each battery cell in the first group of battery cells position data of a weld area, wherein the weld area comprises an area of the one or more busbars to be welded to the terminal of a battery cell. The one or more processors collectively may be configured to calculate an average position of the weld areas for the first group of battery cells. The one or more processors collectively may be configured to determine the first location in dependence on the average position of the weld areas for the first group of battery cells. In an embodiment, the one or more processors may be collectively configured to: receive for each battery cell in a second group of battery cells position data of a position of the one or more busbars adjacent the battery cell whilst outputting the control signal to initiate welding the one or more busbars to the terminals of each battery cells in the first group of battery cells: wherein the second group of battery cells comprises at least two neighbouring battery cells of the plurality of battery cells. As such, the manufacturing time may therefore be further reduced by welding one group of battery cells whilst obtain the positions of the one or more busbars for a second group of battery cells. Battery cells of the first group may be distinct from those of the second group. Therefore, the second group of battery cells may comprise different battery cells to the first group of battery cells. In an embodiment, the second group of battery cells comprises three battery cells. In an embodiment, the one or more processors may be collectively configured to: calculate an average position of the one or more busbars for the first group of battery cells for the second group of battery cells; determine a second location in dependence on the average position for the second group of battery cells; output a control signal to move a laser from the first location to the second location; and output a control signal to initiate welding, using the laser in the second location, the one or more busbars to the terminals of each battery cells in the second group of battery cells. Repeated the manufacturing method along plurality of battery cells may provide a continuous process for manufacturing the battery pack. According to an aspect of the invention, there is provided an apparatus for battery pack manufacturing. The apparatus comprising: a frame for supporting a plurality of battery cells; tooling configured to clamp one or more busbars against the terminals of the plurality of battery cells; a position sensor moveable relative to the frame to obtain positions of the one or more busbars adjacent the battery cells, 5 a laser movable relative to the frame; wherein the laser is configured to weld the one or more busbars to the terminals of each battery cell in a first group of battery cells from a single location; and wherein first group of battery cells comprises at least two battery cells of the plurality of battery cells. According to an aspect of the invention, there is provided an apparatus for battery pack manufacturing. The apparatus comprising: a frame for supporting a plurality of battery cells such that a terminal on a first side of each battery cell is arranged on a first side of the frame; tooling configured to clamp one or more busbars against the terminals of the plurality of battery cells; a position sensor moveable relative to the frame in a first direction along the first side ofthe frame to obtain positions of the one or more busbars adjacent the battery cells, a laser movable relative to the frame in at least the first direction and a second direction substantially perpendicular to the first side of the frame to weld the one or more busbars to the plurality of battery cells, wherein the laser is configured to weld the one or more busbars to the terminals of each battery cell in a first group of battery cells from a single location; and wherein first group of battery cells comprises at least two neighbouring battery cells of the plurality of battery cells. The apparatus may therefore reduce the time required to weld busbars to battery cell terminals when manufacturing the battery pack. The reduction in time is achieved by welding a busbar to multiple battery cell terminals from the first location which is based on an average position of the busbar rather than, for example, re-positioning the laser for each weld. Basing the first location on the average position of the busbar helps to improve weld quality by accounting for tolerances of the battery cells and busbars. The reduction in time is advantageous because it enables a greater number of battery packs to be manufactured in a specific time period thereby improving manufacturing efficiency. In embodiments of either the above-described aspects of the invention, the apparatus may comprise one or more of the following may apply. In an embodiment, the position sensor may be offset from the laser in the first direction such that the position sensor is configured to obtain positions the one or more busbars adjacent the battery cells in a second group of battery cells whilst the laser welds the one or more busbars to the terminals ofthe first group of battery cells. As such, the manufacturing time may therefore be further reduced by welding one group of battery cells whilst obtain the positions of the one or more busbars for a second group of battery cells. The second group of battery cells may comprise at least two neighbouring battery cells of the plurality of battery cells. Battery cells of the first group may be distinct from those of the second group. Therefore, the second group of battery cells may comprise different battery cells to the first group of battery cells. In an embodiment, the apparatus may comprise a plurality of position sensors, each ofthe plurality of position sensors being offset from one another in the first direction such that the plurality of position sensors are configured to simultaneously obtain the positions for more than one ofthe plurality of battery cells. Obtaining the positions in this way may further reduces the time required to manufacture of the battery pack. In an embodiment, the apparatus may comprise three position sensors. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 schematically shows a perspective view of a cell stack for a battery pack; Figure 2 schematically shows an apparatus for manufacturing a cell stack for a battery pack; Figure 3 shows a first flow chart showing a method according to an embodiment of the invention; and Figure 4 shows a section of a cell stack for a battery pack; Figure 5 schematically shows an apparatus for manufacturing a cell stack for a battery pack according to an embodiment of the invention; Figure 6 shows a second flowchart showing a method according to an embodiment of the invention; and Figure 7 schematically shows control system according to an embodiment of the invention; and DETAILED DESCRIPTION Figure 1 shows an example of a cell stack 10. A battery pack may be formed from one or more cell stacks 10. The battery pack may be for use in an electric vehicle. As such, the battery pack may be a traction battery pack. The number of cells stacks 10 in the battery pack may vary depending on the requirements of the vehicle. Multiple cells stacks 10 may be combined by any suitable means to form the battery pack. The cell stack 10 comprises a plurality of battery cells 12. Each battery cell 12 having a first side 14 and a second side 16. The number of battery cells 12 in the cell stack 10 may vary depending on the requirements of the vehicle. The invention is not limited to the number of battery cells 12 shown in the Figures. In the cell stack 10, the battery cells 12 are arranged so that the first sides 14 of the battery cells 12 are on one side of the cell stack 10 and the second sides 16 of the battery cells 12 are on the other side of the cell stack 10. The first sides 14 of the plurality battery cells 12 may substantially reside within a plane. However, there maybe some variation in the positions of the first side 14 due to tolerances of each battery cell 12. In a similar manner, the second sides 16 of the battery cells 12 may be substantially in the same plane as one another. As shown in Figure 1, the first side 14 of each battery cell 12 comprises a terminal 18. The terminals 18 may comprise aluminium. Each terminal 18 may have a thickness of between 3.5 and 4.5 mm. Each terminal 18 is connected to a busbar 20. Multiple terminals 18 may be connected to the same busbar 20. The busbar 20 may comprise nickel plated aluminium or the busbar may comprise a pure aluminium busbar. Each busbar 20 may have a thickness of between 1 mm and 2 mm. This thickness may be advantageous because using thicker busbars may unnecessarily increase the overall weight of the battery pack comprising one or more cell stacks 10. As shown in Figure 1, the cell stack 10 may comprise more than one busbar 20. As such, the terminals 18 of all of the plurality of battery cells 12 may not be connected to the same busbar 20. In the example shown in Figure 1, the terminals 18 of four battery cells 12 are connected to a first busbar 20a and the terminals 18 of two battery cells 12 are connected to a second busbar 20b. In alternative examples of the cell stack 10, the terminals 18 of all of the plurality of battery cells 12 may be connected to the same busbar 20. As such, in certain examples, the cell stack 10 may comprise one or more busbars 20. The cell stack 10 may comprise busbars 20 of any suitable shape. Suitable shapes include but are not limited to substantially rectangular busbars and L-shaped busbars. The cell stack 10 may comprise one or more busbars 20 of one or more different shapes. As shown in Figure 1, the first busbar 20a is substantially rectangular in shape. The second busbar 20b is substantially L-shaped. Whilst not shown, the second side 16 of each battery cells 12 may also comprise a terminal. The terminals on the second side 16 of the battery cells 12 may also be connected to one or more busbars 20 in the same way as described for the first side 14 of the battery cells 12. During manufacture of the cell stack 10, the one or more busbars 20 are connected to terminals 18 of the plurality of battery cells 12 using laser beam welding. The laser beam used in the welding comprises a core beam and a ring beam. Using a laser having a core beam and a ring beam may improve the stability of the weld, reduce spatter during welding, reduce porosity of the weld and improve uniform the weld. Figure 2 shows an example of an apparatus 100 for laser beam welding. The apparatus 100 comprises a laser 102. The laser 102 is configured to produce a laser beam comprising a ring beam surrounding a core beam. In a non-limiting example, the laser 102 may have a wavelength of between 1068 nm and 1080 nm. The laser 102 may be a fibre laser. The laser 102 comprises a control unit 104, a laser oscillator 106 and a scan head 108. The control unit 104 is configured to control the laser oscillator 106. The laser oscillator 106 is configured to generate a laser beam 109. In the embodiment shown in Figure 2, the laser oscillator 106 is configured to generate a laser beam 109 having a ring beam 112 and a core beam 110. The core beam 110 may positioned at the centre of the core beam 110. In the laser 102, the laser beam 109 generated by the laser oscillator 106 is configured to pass through the scan head 108. As shown in Figure 2, the scan head 108 may comprise a first aperture 114 for receiving the laser beam 109 from the laser oscillator 106. The scan head 108 may comprise a collimator 116 and a beam splitter 118. The collimator 116 and beam splitter 118 may be positioned so that a laser beam 109 entering the scan head 108 passes through the collimator 116 and then through the beam splitter 118. The collimator 116 may have a length of 140 mm. The scan head 108 may comprise one or more mirrors 120 to direct the laser beam 109 from the first aperture 114 to a second aperture 122 where the laser beam 109 exits the scan head 108. The laser 102 may comprise a cover glass covering 123 the second aperture 122. The scan head 108 may comprise a focusing lens 124. The focusing lens 124 may be positioned by the second aperture 122. As such, the laser beam 109 passes through the focusing lens 124 prior to exiting the scan head 108. The focusing lens 124 defines the focal plane of the laser 102. The focusing lens 124 may have a focal length of 400 mm. In the apparatus 100 shown in Figure 2, the laser 102 may be configured such that the diameter of the ring beam 112 as it exits the laser oscillator 106 maybe 600 pm and the diameter of the core beam 110 as it exits the laser oscillator 106 maybe 100 pm. Diameter of the core beam 110 in the focal plane of the laser may be 0.3 mm. Diameter of the ring beam 112 in the focal plane of the laser may be 1.6 mm. However, the ring and core beams 110 are not limited to these diameters when either exiting the oscillator or at the focal plane. In alternative non-limiting examples, the ring beam 112 may have a diameter of 150 pm and the core beam 110 may have a diameter of 50 pm or the ring beam 112 may have a diameter of 300 pm and the core beam 110 may have a diameter of 100 pm. The control unit 104 is configured to control the scan head 108. The control unit 104 may be configured to move the position of the scan head 108 so that the laser beam 109 exiting the scan head 108 may be aligned with an area 24 of a busbar 20 to be welded to a terminal 18. The area 24 of the busbar 20 to be welded to the terminal 18 is on an outer surface of the busbar 20 which faces towards the laser 102 during welding. The scan head 108 may be a 2-dimensioanl scan head. That is, the scan head may be able to move in two direction relative to the area 24 to be welded. As shown in Figure 2, the apparatus 100 comprises clamps 126. The clamps 126 may be used to hold a busbar 20 adjacent to a terminal 18 of a battery cell 12. The clamps 126 may hold the busbar 20 in place during welding. One or more support plates 128 may be used to facilitate clamping the busbar 20 to the terminal 18 of the battery cell 12. Figure 3 illustrates a method 1000 according to an embodiment of the invention. The method 1000 is a battery pack manufacturing method. The steps of the method 1000 of the embodiment in Figure 3 may be used to manufacture a cell stack, such as the cell stack 10 illustrated in Figure 1. As described above, a battery pack may comprise one or more cell stacks 10. Therefore, the steps of the method 1000 shown in Figure 3 may be repeated to manufacture a plurality of cell stacks 10. In such embodiments, the battery pack manufacturing method 1000 may comprise manufacturing a plurality of cell stacks, each cell stack being manufactured according to the method steps shown in and described with reference to Figure 3. The method 1000 may be performed using the apparatus 100 of Figure 2. However, method 1000 may be performed using any apparatus 100. According to the invention, the method 1000 may comprise arranging 1002 a busbar 20 adjacent to a terminal 18 of a battery cell 12. The busbar 20 maybe held in place adjacent to the terminal 18. As shown in Figure 2, one or more clamps 126 maybe used to hold the busbar 20 adjacent to the terminal 18. The method 1000 may comprise aligning 1004 a laser with an area 24 of the busbar 20 to be welded to the terminal 18. As such, when the laser 102 is turned on, a laser beam 109 is directed onto the area 24 of the busbar 20 to be welded to the terminal 18. The area 24 of the busbar 20 to be welded to the terminal 18 is on an outer surface 26 of the busbar 20 which faces towards the laser 102 during welding. The scan head 108 of the laser may be moved relative to the busbar 20 and the terminal 18 to align the laser with the area of the busbar 20 to be welded to the terminal 18. The laser 102 maybe aligned with the area 24 of the busbar 20 to be welded to the terminal 18 such that a focal plane of the laser 102 is offset from the area by between 4 mm and 9 mm. The focal plane of the laser 102 may be offset from the area of the busbar 20 to be welded to the terminal 18 in a direction perpendicular to the side of the battery cell 12 on which the terminal 18 is positioned. As described above, diameter of the core beam 110 in the focal plane of the laser 102 may be 0.3 mm and the diameter of the ring beam 112 in the focal plane of the laser 102 may be 1.6 mm. Therefore, the core beam 110 may have a diameter between 0.32 mm to 0.38 mm at the area of the busbar 20 to be welded to the terminal 18. The ring beam 112 may have a diameter between 1.6 and 1.7 mm at the area of the busbar 20 to be welded to the terminal 18. The laser 102 may be aligned such that the focal plane is outside of the battery cell 12. Offsetting the focal plane so that it resides outside, rather than inside the battery cell 12, may reduce the riskof overpenetration of the weld if the laser 102 is incorrectly aligned. For example, if the focal plane is inside the battery cell 12 and the laser 102 is positioned too close to the battery cell 12 during welding this can case overpenetration of the weld. Overpenetration can damage the battery cell 12. Positioning the focal plan outside of the battery cell 12 means that if the laser 102 is positioned too close to the battery cell 12 during welding this can result in under penetration of the weld which may reduce the strength of the weld but would not cause damage to the battery cell 12. Positioning the focal plane outside the battery cell 12 may be advantageous when there are space constraints in a production line which limit the maximum distance between the laser 102 and the terminal 18 of the battery cell 12. The method 1000 may comprise welding 1006, using the laser, the busbar 20 to the terminal 18. The method 1000 may comprise forming a lap joint between the busbar 20 and the terminal 18. However, the invention is not limited to this type of joint. The laser 102 may comprise a ring beam 112 surrounding a core beam 110. In the method 1000, each of the ring beam 112 and the core beam 110 may have a power of between 3.5 and 4 kW. The method 1000 may comprise keyhole laser welding. As such, during welding a metal vapor may be created in addition to the melt pool. The resulting weld may be deeper than it is wide. The resulting weld strength of the connection between the busbar 20 and the terminal 18 may be between 100 and 120 MPa. Welding of the busbar 20 to the terminal 18 may occur at a speed of between 450 and 500 mm / s. Therefore, during welding 1006 the laser beam 109 moves relative to the busbar 20 at a speed of between 450 and 500 mm / s to weld the busbar 20 to the terminal 18. The control unit 104 may be configured to control the scan head 108 to move the laser beam 109 at this speed. The welding 1006 is performed using any suitable weld pattern. In a non-limiting example, a spiral weld pattern may be used. That is, the laser beam 109 is moved through a spiral at a speed of between 450 and 500 mm / s to weld the busbar 20 to the terminal 18. Alternatively a circle or line weld pattern may be used. The method 1000 may improve battery pack manufacture. The inventors found that the combination of using a laser 102 having a ring and core beam 110 each of the having a power of between 3.5 and 4 kW, offsetting the focal plane of the laser 102 from the area 24 to be welded by between 4 and 9 mm and welding at a speed of between 450 and 500 mm / s surprisingly allowed a substantially spatter free weld to be formed between the busbar 20 and terminal 18. Since the method 1000 produces a spatter free weld, this improves the quality of the weld, reduces contamination of the area surrounding the weld and reduces the risk of damage to the welding equipment. Whilst the method 1000 of Figure 3 is described for welding one busbar 20 to the terminal 18 of one battery cell 12, the method 1000 may be repeated to connect one or more busbars 20 to a plurality of battery cells 12. That is, once the method 1000 has been used to weld a busbar 20 to the terminal 18 of a first battery cell 12, the method 1000 may be repeated to weld either the same busbar 20 or a different busbar 20 to the terminal 18 of a second battery cell 12. The second battery cells 12 may be neighbouring (i.e. positioned next to each other and without an intervening battery cell 12). The method 1000 may be repeated for each of the plurality of battery cells 12 to manufacture, for example, the cell stack 10 shown in Figure 1. Each cell stack 10 within a battery pack may be manufactured using the method 1000 of the embodiment shown in Figure 3. Therefore, for each of the terminals 18 of the plurality of battery cells 12, the method 1000 may comprise aligning 1004 the laser 102 with an area of a busbar 20 to be 9 welded to a terminal 18 such that the focal plane of the laser is offset from the area by between 4 and 9 mm, and welding 1006, using the laser, the busbar 20 to the terminal 18, For each of the battery cells 12, the welding is performed with each of the ring beam 112 and the core beam 110 having a power of between 3.5 and 4 kW and occurs at a speed of between 450 and 500 mm / s. As described above, the method 1000 may be used to weld the terminals one or more battery cells to one or more busbars. There may be some variation in the sizes of battery cells and busbars due to manufacturing tolerances. The thickness of a busbar may vary along its length. Different busbars may have different thicknesses to one another. The battery cells may not have the exact same length as each other, where the length (in a direction parallel to the y axis shown in Figure 4) is the distance from one terminal to the other terminal of the cell. The length (in a direction parallel to the y axis shown in Figure 4) of the terminals of each battery cell may vary. The manufacturing tolerances of the battery cells may be + / - 3 mm. Therefore, once the battery cells have been arranged together for manufacture into a cell stack, there may be some variation in the position of the terminals of a plurality of battery cells. A non-limiting example of such variation is shown in Figure 4. Figure 4 shows a part of three battery cells 12. The first sides 14 of the three battery cells 12 are shown in Figure 4 but the second sides of the three battery cells 12 are not. In Figure 4, the terminal 18 of a first battery cell 12a is longer than the terminal 18 of a second battery cell 12b. The terminal 18 of the second battery cell 12b is longer than the terminal 18 of a third battery cell 12c. Figure 4 shows a busbar 20. When the busbar 20 is clamped to the three terminals 18, an area of the busbar 20 to be welded to the terminal 18 of the first battery cell 12a would have a different position along the y-axis to both an area of the busbar 20 to be welded to the terminal 18 of the second battery cell 12b and an area of the busbar to be welded to the terminal 18 of the third battery cell 12c. For example, when the busbar 20 is clamped to the three terminals 18 the busbar may be at an angle i.e. not parallel to the x axis shown in Figure 4. During welding of the battery cells in Figure 4, a laser beam would generally be in a direction parallel with or almost parallel the y axis shown in the Figure. To ensure that the distance between the laser and the area to be welded is such that a high quality weld is achieved the position of the laser in a direction along the y axis may need to be adjusted for each battery cell. The following apparatus may be used in a method of manufacture to account for tolerances of the battery cells and busbars whilst reducing the time required to weld busbars to a plurality of battery cell terminals. Figure 5 shows an apparatus 300 for battery pack manufacturing according to an embodiment of the invention. The apparatus 300 of Figure 5 is not shown to scale. The apparatus 300 may be used to manufacture a battery pack comprising a plurality of battery cells 212 and one or more busbars 220. The plurality of battery cells 212 and one or more busbars 220 may be welded into cell stacks. The battery pack may comprise one or more cell stacks. The battery cells 212 shown in Figure 5 may be to formed into one cell stack. However, the invention is not limited to the number of battery cells 212 or the cells stack shown in Figure 5. The battery cells 212 and busbars 220 are the same as those described above with reference to Figure 1. Reference numerals in Figure 5 for the cell stack correspond to those used in Figure 1 for like features but are transposed by 200. In Figure 5, the plurality of battery cells 212 are arranged along an x axis so that a first battery cell has a different position along the x axis than a second neighbour battery cell positioned next to the first battery cell. The first sides 214 of the battery cells 212 are substantially parallel to one another. Therefore, the x axis is defined as an axis parallel to the first sides 214 of the battery cells 212. In Figure 5, each battery cell 212 extends in a direction parallel to the y axis from a terminal 218 on a first side 214 to a terminal 218 on a second side 216. For ease of reference, in Figure 5 reference numerals are only included for the features of one of the battery cells 212. The apparatus 300 comprises a frame 402 for supporting a plurality of battery cells 212 during manufacture of the battery pack. As shown in the embodiment in Figure 5, the battery cells 212 may be supported by a third side (not shown) of each of the plurality of battery cells 212 resting on the frame 402. The third side may extend between the first and second sides 214, 216 of each battery cell 212 and be substantially perpendicular to the firstand second sides 214, 216 of the battery cell 212. The frame 402 supports the plurality of battery cells 212 such that the terminal 218 on the first side 214 of each battery cell 212 is arranged on a first side 403 of the frame 402. As such, the first sides 214 of the battery cells 212 are on one side of the frame 402. The first side 403 of the frame 402 is parallel to an x axis shown in Figure 5. The battery cells 212 may be arranged so that the first side 214 of each battery cell may be substantially parallel to the first side 403 of the frame 402. The frame 402 may comprise an upstanding plate 404 which may provide a planar surface. The battery cells 212 may be arranged so that a part of the second sides 216 of each of the plurality of battery cells 212 are positioned against (i.e. abuts) the plate 404. This may facilitate arranging the first sides 214 of each battery cell 212 to be substantially parallel to one another. In an alternative embodiment, the plate may be arranged so that a part of the first sides 214 of each of the plurality of battery cells 212 is positioned against (i.e. abuts) the plate. The apparatus 300 comprises tooling 406 configured to clamp one or more busbars 220 against the terminals of the plurality of battery cells 212. The tooling 406 may comprise a block through which a plurality of apertures 408 extend. The tooling 406 may be moveable in a direction towards and away from the frame 402 and the first sides 214 of the plurality of battery cells 212. That is, in a direction parallel to the y axis. Therefore, the tooling 406 may be moved into place to clamp one or more busbars 220 against the terminals 218 of the plurality of battery cells 212. The tooling 406 may be fixed in position to clamp one or more busbars 220 against the terminals 218 of the plurality of battery cells 212. The tooling 406 may be moved and fixed in place using any suitable means known in the art. The embodiment shown in Figure 5, busbars 220 are shown as clamped to the terminals of the battery by the tooling 406. The apparatus 300 comprises a position sensor 410. As shown in the embodiment in Figure 5, the apparatus 300 may comprise three position sensors 410. The position sensors 410 are arranged along the first side 403 of the frame 402 and are separated (i.e. spaced apart) from the first side 403 of the frame 402 in the y direction. The position sensors 410 are moveable in a first direction relative to the frame 402. In Figure 5, the first direction is parallel to the x axis and, consequently, parallel to the first side 403 of the frame 402. The position sensors 410 can therefore be positioned in front of each of the plurality of battery cells 212. As shown in the embodiment in Figure 5, the position sensors 410 may be offset from one another in the y direction. This may allow the three position sensors 410 to obtain positions of the busbars 220 adjacent the three neighbouring battery cells 212 at the same time. As shown in Figure 5, the apparatus 300 may comprise a support 412 configured to support 412 each of the position sensors 410. The support 412 may comprise one or more arms 414 to support 412 the position sensors 410. The support 412 may support the position sensors 410 at a position which is level with the plurality of battery cells 212. The support 412 may be attached to a gantry 416. The support 412 may be movable along the gantry 416 so that the position sensors 410 are moveable relative to the frame 402. The apparatus 300 may comprise a first motor (not shown) for moving the support 412 along the gantry 416. The position sensors 410 are configured to obtain positions of the one or more busbars 220 adjacent the battery cells 212. That is, for each of the battery cells 212 the position sensor can obtain the position of the part of the busbar 220 that is adjacent to the terminal 218 of that battery cell 212. As shown in the apparatus in Figure 5, the position sensors 410 may be configured to obtain the position of the busbar 220 in the second direction that is parallel to the y axis shown in Figure 5. The position may therefore be a position along the y axis. The position sensors 410 may be configured to measure the distance from the position sensor to the busbar adjacent to one of the battery cells 212. As shown in Figure 5, the position sensors 410 may obtain positions of the one or more busbars 220 adjacent the battery cells 212 through the apertures 408 in the tooling 406. Figure 5 shows a measurement 407 signal emitted from each of the sensors 406 to the busbar 420. The measurement signals 407 are shown as passing through the apertures 408 in the tooling 406. In certain embodiments, the position sensors 410 may comprise time of flight sensors. The position sensors 410 may comprise a time of flight laser ranging sensor. Whilst the embodiment of the apparatus 300 shown in Figure 5 comprises three position sensors 410, the invention is not limited to this specific embodiment. In alternative embodiments, the apparatus 300 may comprise one or more position sensors 410. The apparatus 300 comprises a laser 302. The laser 302 comprises the same features as the laser 302 described above in the embodiment shown in Figure 2. Therefore, the description of the features of the laser will not be repeated 302. Reference numerals in Figure 5 for the laser 302 correspond to those used in Figure 2 for like features but are transposed by 200. The laser 302 is for welding the one or more busbars 220 to the terminals of the 11 battery cells 212. As shown in Figure 5, the laser 302 may weld the one or more busbars 220 to the respective the battery cells 212 by directing a laser 302 beam through the apertures 408 in the tooling 406. The laser 302 is movable relative to the frame 402 to weld the one or more busbars 220 to the plurality of battery cells 212. The laser 302 is movable in the first direction parallel to the x axis and the second direction parallel to the y axis. The laser 302 is therefore movable in directions both substantially parallel to and substantially perpendicular to the first side 403 of the frame 402. The support 412 may be configured to support 412 the laser 302. As such, the support 412 may move along the gantry 416 to facilitate movement of the laser 302 in the first direction parallel to the x axis. The support 412 may comprise means for moving the laser 302 in the second direction parallel to the y axis. Any suitable means may be used. For example, the support 412 may comprise one or more rails 418 to which the laser 302 is movably attached. The rails 418 may extend in a direction parallel to the y axis. The support 412 may comprise a second motor (not shown) configured to move the laser 302 along the rails in the second direction. The apparatus 300 may comprise at least one controller (not shown) configured to control the first motor and second motors. The laser 302 is configured to weld one or more busbars 220 to the terminals of multiple battery cells 212 from a single location. That is, from a fixed position on the x and y axes the laser 302 can may be weld one or more busbars 220 to the terminals 218 of multiple battery cells 212. As such, the laser 302 may be configured to rotate so that multiple battery cells 212 can be welded from the single location. Alternatively, the laser 302 may be configured to change the angle at which a laser 302 beam is produced. For example, the laser 302 may be configured to produce a laser 302 beam in a direction parallel to the y axis and in a direction at one or more angles relative to the y axis as shown in Figure 5. Whilst Figure 5 shows three laser 302 beams, this is for illustration only. The laser 302 may be configured to produce one laser 302 beam at a time. As shown in the embodiment of Figure 5, the position sensors 410 may be offset from the laser 302 in the first direction parallel to the x axis. As such, the position sensors 410 may be configured to obtain positions of busbars 220 adjacent battery cells 212 whilst the laser 302 welds the one or more busbars 220 to the terminals 218 of different battery cells 212. In the non-limiting embodiment shown in Figure 5, this is achieved by the relative positions at which the position sensors 410 and the laser 302 are attached to the support 412. The apparatus 300 described above and shown in Figure 5 is for welding busbars 220 to the first sides 214 of each of the plurality of battery cells 212. Whilst not shown, the apparatus 300 may also comprise further tooling, a laser, position sensors and a gantry for welding busbars 220 to the second sides 216 of the plurality of battery cells 212. The tooling, laser, position sensors and the gantry for welding busbars to the second sides 216 of the plurality of battery cells 212 may the same as those described above and positioned at the second side 405 of the frame 402. Figure 6 shows a method 2000 according to an embodiment of the invention. The method 2000 is a method 2000 of manufacturing a battery pack. The steps of the method 2000 of the embodiment in Figure 6 may be used to manufacture a cell stack, such as the cell stack 10 illustrated in Figure 1. As described above, a battery pack may comprise one or more cell stacks 10. Therefore, the steps of the method 2000 shown in Figure 6 may be repeated to manufacture a plurality of cell stacks 10. In such embodiments, the battery pack manufacturing method 2000 may comprise manufacturing a plurality of cell stacks, each cell stack being manufactured according to the method steps shown in and described with reference to Figure 6. Whilst the method 2000 will be described with reference to the apparatus 300 of Figure 5, method 2000 may be performed using any suitable apparatus. As will become apparent, the battery pack manufacture method 2000 of Figure 6 incorporate the battery pack manufacture method 1000 of Figure 3. The method 2000 comprises providing 2002 a plurality of battery cells 212, each battery cell 212 having a terminal 218 on the first side 214. The plurality of battery cells 212 may be arranged on the frame 402 of the apparatus 300 of Figure 5. The battery cells 212 may be arranged such that the first sides 214 of the battery cells 212 are substantially parallel to one another. As shown in Figure 5, the first sides 214 may be parallel to the x axis. The step 2002 of providing the plurality of battery cells 212 may comprise arranging the plurality of battery cells 212 such that the second sides 216 of each of the plurality of battery cells 212 reside within a plane. This may be done by positioning the second sides 216 of the plurality of battery cells 212 a planar surface such as the plate 404 of the embodiment shown in Figure 5. The method 2000 comprises arranging 2004 one or more busbars 220 adjacent to the terminals 218 of the plurality of battery cells 212. In the following discussion, only for the ease of understanding one busbar is discussed. However, references to ‘the busbar’ should be understood to mean one or 12 more busbars 220. The busbar 220 may be held in place adjacent to the terminals 218 of the battery cells 212. As shown in Figure 5, tooling 406 maybe used to hold the busbar 220 adjacent to the terminals 218. The tooling 406 may be used to clamp the busbars 220 to the terminals 218. The method 2000 comprises obtaining 2006 for each battery cell 212 in a first group of battery cells a position of the busbar 220 adjacent the battery cell 212. As described above with reference to Figure 4, a position of the busbar 220 adjacent one battery cell 212 differs to a position of the busbar 220 adjacent to a different battery cell 212 due to manufacturing tolerances. The obtained position may be a position of the busbar 220 in the second direction parallel to the y axis shown in Figure 5. Therefore, the obtained position is a position in a direction which is perpendicular to the first side 214 of the battery cells 212. The obtained positions will depend on the tolerances of the battery cells 212 and busbars 220. The first group of battery cells 212 comprises at least two neighbouring battery cells 212 of the plurality of battery cells 212. That is, the first group of battery cells 212 comprises at least two battery cells 212 that are next to each other. The number of positions obtained is the same as the number of battery cells 212 in the first group. The positions may be obtained using one or more position sensors 410. The position of the busbar 220 adjacent to each of the battery cells 212 in the first group may be obtained simultaneously. This may be achieved by each position being obtained using a separate position sensor 410 and having the same number of position sensors 410 as battery cells 212 in the first group. As described above, the apparatus 300 shown in the embodiment of Figure 5 comprises three position sensors 410. Therefore, if the method 2000 is implemented using the embodiment of the apparatus 300 of Figure 5, the first group of battery cells 212 may comprise three neighbouring battery cells 212. That is, three battery cells 212 may be arranged sequentially next to each other. The positions of the busbars 220 adjacent at each of the three battery cells 212 may be obtained simultaneously. The step 2006 of obtaining the positions may comprise obtaining a position of a weld area for each battery cell 212 in the first group of battery cells 212. The weld area may comprise an area of the one or more busbars 220 to be welded to the terminal 218 of a battery cell 212. However, in alternative embodiments, the step of obtaining for each battery cell 212 in the first group of battery cells 212 the position of the one or more busbars 220 adjacent the battery cell 212 may comprise obtaining a position of a reference area for each battery cell 212 in a first group of battery cells 212. The reference area may differ from the weld area. That is, the reference area of the busbar 220 may not ultimately be welded to the terminal 218. Once the positions for the first group of battery cells 212 has been obtained, the method 2000 may comprise obtaining for each battery cell 212 in a second group of battery cells 212 a position of the one or more busbars 220 adjacent to the battery cell 212. As such, the method 2000 may comprise moving the position sensors 410 to align them with the second group of battery cells 212 (i.e. moving the position sensors 410 in the first direction parallel to the x axis). In the same way as the first group, the second group of battery cells 212 comprise at least two neighbouring battery cells 212 of the plurality of battery cells 212. The second group of battery cells 212 may be next to (i.e. neighbouring) the first group of battery cells 212. If the method 2000 is implemented using the embodiment of the apparatus 300 shown in Figure 5, the second group of battery cells 212 may comprise three neighbouring battery cells 212. In certain embodiments, the same busbar 220 may be adjacent to the battery cells 212 in both the first and second groups. In alternative embodiments, different busbars 220 may be adjacent to the battery cells 212 of the first and second groups. The method 2000 comprises determining 2008 an average position of the one or more busbars 220 for the first group of battery cells 212 in dependence on the obtained positions. The average position will be sensitive to the tolerances of the busbars 220 and the battery cells 212. The average position may be a mean of the obtained positions. In embodiments where the position of the weld area is obtained, the step of determining 2008 the average position may comprise determining an average position of the weld areas for the first group of battery cells 212 in dependence on the obtained positions. In the apparatus 300 shown in Figure 5, the position sensors 410 are offset from each other along the y axis. The relative y axis offset may be known and accounted for when determining the average position. The step 2008 of determining the average position may be performed by a control system which is described below in further detail. The method 2000 comprises arranging 2010 a laser 302 at a first location. The step 2010 of arranging the laser 302 at the first location may comprise moving the laser 302 relative to the battery cells 212. The first location is based on the average position of the one or more busbars 220 for the first group of battery cells 212. Therefore, when using the apparatus 300 shown in Figure 5, the first location comprises a y-component indicating a position along the y axis. That is, a distance from the first sides 214 of the battery cells 212 in the first group of battery cells 212. The y-component is based on the average position of the one or more busbars 220 for the first group of battery cells 212. Therefore, the laser 302 may be moved in a second direction parallel to the y axis (i.e. perpendicular to the first sides 214 of the battery cells 212) to arrange the laser 302 at the first location. In this way, the laser 302 is moved to account for tolerances of the busbar and battery cells 212. In embodiments where the position of the weld area is obtained, the first location may be based on the average position of the weld areas for the first group of battery cells 212. The first location may be based on the average position such that at the first location the focal plane of the laser 302 is offset from average position of the one or more busbars 220 for the first group of battery cells 212 by a predetermined amount. In certain embodiments, when the laser 302 is at the first location, the focal plane of the laser 302 may be offset from average position of the one or more busbars 220 for the first group of battery cells 212 by between 4 and 9 mm. In certain embodiments, at the first location the focal plane of the laser 302 may be offset from the average position of the one or more busbars 220 such that the focal plane is outside of the battery. Offsetting the focal in this way may reduce the risk of overpenetration of the weld if the laser 302 is incorrectly aligned (e.g. to close to the battery cell during welding) which can damage the battery cell. In certain embodiments, the first location may also be based on the position of the first group of battery cells 212 relative to the other battery cells 212 within the cell stack. As such, when the laser 302 is at the first location, the laser may be aligned with the first group of battery cells 212. When the using the apparatus 300 shown in Figure 5, the first location may comprise an x-component indicating a position along the x axis. The x-component is based on the position of the first group of battery cells 212 relative to the other battery cells 212 and indicates how far along the cell stack the first group of battery cells 212 is located. The x-component may be a position on the x axis which is central to the first group of battery cells 212. For example, if the first group of battery cells 212 consists of three battery cells 212, the x-component may coincide with the middle of the three battery cells 212. The x-component of each battery cell 212 for each group of battery cells 212 may be known. For example, the step 2002 of providing a plurality of battery cells 212 may comprise arranging each battery cell 212 or group of battery cells 212 at a known position along the x axis. The step 2010 of arranging the laser 302 at the first location in the apparatus 300 of Figure 5 may therefore comprise moving the laser in the first direction parallel to the x axis and in a second direction parallel to the y axis. The method 2000 comprises welding 2012, using the laser 302 at the first location, the one or more busbars 220 to the terminals 218 of each battery cells 212 in the first group of battery cells 212. As such, from the first location the laser 302 is used to weld the busbar 220 to multiple battery cells 212. The laser 302 may be rotated or the angle of the laser beam maybe changed, for example, to facilitate welding multiple battery cells 212 from a single location. The step of welding 2012 may comprise forming a lap joint between the busbar 220 and the terminal 218 of the respective battery cell 212. The method 2000 may be repeated. Once the one or more busbars 220 have been welded to the first group of battery cells 212. Each step of the method 2000 may be repeated for a second and subsequent groups of battery cells 212. Each of the groups of battery cells 212 may contain the same number of battery cells 212. As described above, the method 2000 may comprise obtaining for each battery cell in a second group of battery cells 212 a position of the one or more busbars 220 adjacent to the battery cell. This step may be performed whilst welding the one or more busbars 220 to the terminals 218 of each battery cells 212 in the first group of battery cells 212. Once the laser 302 has completed the step 2012 of welding for the first group of battery cells 212. The laser 302 may then be arranged at a second location based on the average position of the one or more busbars 220 for the second group of battery cells 212. The embodiment in Figure 5 shows the laser 302 being used for welding a first group of battery cells 212 and the position sensors 410 being used to obtain positions for a second distinct group of battery cells 212. In the embodiment shown in Figure 5, the steps of the method 2000 may be repeated to form a cell stack from the plurality of battery cells 212 shown in Figure 5. The method 2000 may be further repeated to manufacture multiple cell stacks which may be combined to form a battery pack. 14 The above-described method 2000 may reduce the time required to weld busbars 220 to terminals 218 of battery cells 212 when manufacturing a battery pack. The reduction in time is achieved by welding a busbar 220 to multiple battery cell terminals 218 from one location rather than, for example, re-positioning the laser 302 for each weld. Basing the location on the average position of the busbar 220 helps to improve weld quality by accounting for tolerances of the battery cells 212 and busbars 220. The reduction in time is advantageous because it enables a greater number of battery packs to be manufactured in a specific time period thereby improving manufacturing efficiency. The inventors found that the time taken to weld a busbar 220 to a terminal 218 using the above-described method 2000 was 200 ms per weld compared to 500 ms per weld when the laser 302 is re-positioned each time a busbar is welded to a terminal. The method 2000 of the embodiment in Figure 6 may be combined with the method 1000 of the embodiment shown in Figure 3 to further improve the weld quality. Therefore, when implementing the method 2000 of the embodiment shown in Figure 6, the step of 2012 welding may occur at a speed of between 450 and 500 mm / s. The laser 302 may comprise a ring beam surrounding a core beam. Each of the ring beam and the core beam may have a power of between 3.5 and 4 kW. The core beam may have a diameter between 0.32 mm to 0.38 mm at the one or more the busbar. The method 2000 shown in Figure 6 may be implemented using a control system 500 for controlling a manufacturing system for a battery pack. In certain embodiments, the apparatus 300 may comprise the control system 500. The control system 500 comprises one or more controllers 510. The control system 500 as illustrated in Figure 7 comprises one controller 510, although it will be appreciated that this is merely illustrative. The controller 510 comprises processing means or one or more processors 520 and memory means 530. The processing means 520 may be one or more electronic processing devices which operably execute computer-readable instructions. The memory means 530 may be one or more memory devices. The memory means 530 is electrically coupled to the processing means 520. The memory means 530 is configured to store instructions, and the processing means 520 is configured to access the memory means 530 and execute the instructions stored thereon. As described above, the control system 500 comprises one or more processors 520. The one or more processors 520 are collectively configured to receive for each battery cell in the first group of battery cells 212 position data of a position of the one or more busbars 220 adjacent the battery cell and calculate the average position of the one or more busbars 220 for the first group of battery cells 212. The position data may be received from the position sensor or sensors. The one or more processors are collectively configured to determine the first location in dependence on the average position for the first group of battery cells 212 and output a control signal to move a laser 302 to the first location. The control signal causes the laser 302 to move in the y direction, for example, along the rail of the apparatus 300 shown in Figure 5. The control signal may also cause the laser 302 to move in the x direction along the gantry 416. The one or more processors are 520 collectively configured to output a control signal to initiate welding, using the laser 302 in the first location, the one or more busbars 220 to the terminals of each battery cells 212 in the first group of battery cells 212. The control signal to initiate welding may be sent to the control unit of the laser 302 to initiate welding. The controller 510 may therefore comprise an input means 540 and an output means 550. The input means 540 may comprise an electrical input of the controller 510. The output means 550 may comprise an electrical output of the controller 510. The input 540 is arranged to receive the position signal 565 from the position sensor or sensors 410. The position signal 565 is an electrical signal which may be indicative of a position of a busbars 220 adjacent to one of the battery cells 212 along the y axis. The output 550 is arranged to output a control signal 555 to move the laser 302. The output 550 is arranged to output a control signal 575 to initiate welding using the laser 302. The output 550 may also be arranged to output a control signal 585 to move position sensors 410. The control signal 585 to move the position sensors 410 may cause the position sensors 410 to move from being aligned with a group (i.e. the first group) of battery cells 212 to being aligned with a subsequent group (i.e. the second group) of battery cells 212. In embodiments where the position of the weld area is obtained, the one or more processors 520 collectively may be configured to receive for each battery cell 212 in the first group of battery cells 212 position data of a weld area, calculate an average position of the weld areas for the first group of battery cells 212 and determine the first location in dependence on the average position of the weld areas for the first group of battery cells 212. As described above, the method 2000 may be repeated for second and subsequent groups of battery cells 212. Therefore, the one or more processors 520 may be collectively configured to receive for each battery cell 212 in the second group of battery cells 212 position data of a position of the one or more busbars 220 adjacent the battery cell 212 and calculate an average position of the one or more busbars 220 for the second group of battery cells 212. The one or more processors 520 may be collectively configured to determine a second location in dependence on the average position for the second group of battery cells 212 and output a control signal to move a laser 302 from the first location to the second location. The one or more processors 520 may be collectively configured to output a control signal to initiate welding, using the laser 302 in the second location, the one or more busbars 220 to the terminals of each battery cells 212 in the second group of battery cells 212. In embodiments, the one or more processors 520 may be collectively configured to receive for each battery cell 212 in the second group of battery cells 212 position data of a position of the one or more busbars 220 adjacent the battery cell 212 whilst outputting the control signal to initiate welding the one or more busbars 220 to the terminals of each battery cells 212 in the first group of battery cells 212. As such, welding of the first group of battery cells 212 may occur whilst position data for the second group of battery cells 212 is being received. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application. The method 2000 is described above with reference to the apparatus 300 of Figure 5. However, the method is not limited to the apparatus of Figure 5. The method 2000 may be performed using any suitable apparatus. For example, the method 2000 is not limited to being performed using the laser 302 of Figure 5. The method 2000 may be performed using a different type of laser. For example, the method 2000 is not limited to welding with a laser having a ring beam surround a core beam.

Claims

1. A battery pack manufacturing method comprising:providing a plurality of battery cells, each battery cell having a terminal on a first side;arranging one or more busbars adjacent to the terminals of the plurality of battery cells;obtaining for each battery cell in a first group of battery cells a position of the one or more busbars adjacent the battery cell, wherein the first group of battery cells comprises at least two neighbouring battery cells of the plurality of battery cells;determining an average position of the one or more busbars for the first group of battery cells in dependence on the obtained positions;arranging a laser at a first location based on the average position of the one or more busbars for the first group of battery cells; and welding, using the laser at the first location, the one or more busbars to the terminals of each battery cells in the first group of batterycells.

2. A method according to claim 1, wherein at the first location the focal plane of the laser is offset from average position of the one or more busbars for the first group of battery cells by a predetermined amount.

3. A method according to claim 2, wherein at the first location the focal plane of the laser is offset from average position of the one or more busbars such that the focal plane is outside of the battery.

4. A method according to any one of the preceding claims, wherein obtaining for each battery cell in the first group of battery cells the position of the one or more busbars comprises obtaining each position simultaneously.

5. A method according to any one of the preceding claims, wherein each battery cell has a second side opposing the first side; and wherein providing the plurality of battery cells comprises arranging the plurality of battery cells such that the second side of each of the plurality of battery cells reside within a plane.

6. A method according to any one of the preceding claims, comprising:obtaining for each battery cell in a second group of battery cells a position of the one or more busbars (220) whilst welding the one or more busbars to the terminals of each battery cell in the first group of battery cells, wherein the second group of battery cells comprises at least two neighbouring battery cells of the plurality of battery cells.

7. A method according to claim 6 comprising:Determining an average position of the one or more busbars for the second group of battery cells;moving the laser from the first location to a second location based on the average position of the one or more busbars for the second group of battery cells; andwelding, using the laser at the second location, the one or more busbars to the terminals of each battery cell in the second group of battery cells.

8. A method according to claim 7, wherein the first group and the second group of battery cells are neighbouring.

9. A control system for controlling a manufacturing system for a battery pack, the battery pack comprising a plurality of battery cells, eachbattery cell having a terminal on a first side, the control system comprising one or more processors collectively configured to:receive for each battery cell in a first group of battery cells position data of a position of the one or more busbars adjacent the battery cell, wherein the first group of battery cells comprises at least two neighbouring battery cells of the plurality of battery cells;calculate an average position of the one or more busbars for the first group of battery cells;determine a first location in dependence on the average position for the first group of battery cells;output a control signal to move a laser to the first location; and17output a control signal to initiate welding, using the laser in the first location, the one or more busbars to the terminals of each battery cells in the first group of battery cells.

10. A control system according to claim 9, wherein the one or more processors are collectively configured to: receive the position data for each of the battery cells in the first group of battery cells simultaneously.

11. A control system according to claim 9 or 10, wherein the one or more processors are collectively configured to:receive for each battery cell in a second group of battery cells position data of a position of the one or more busbars adjacent the battery cell whilst outputting the control signal to initiate welding the one or more busbars to the terminals of each battery cells in the first group of battery cells;wherein the second group of battery cells comprises at least two neighbouring battery cells of the plurality of battery cells.

12. A control system according to claim 9 to 11, wherein the one or more processors are collectively configured to:Calculate an average position of the one or more busbars for the first group of battery cells for the second group of battery cells;determine a second location in dependence on the average position for the second group of battery cells;output a control signal to move the laser from the first location to the second location; andoutput a control signal to initiate welding, using the laser in the second location, the one or more busbars to the terminals of each battery cells in the second group of battery cells.

13. An apparatus for battery pack manufacturing comprising:a frame for supporting a plurality of battery cells such that a terminal on a first side of each battery cell is arranged on a first side of the frame;tooling configured to clamp one or more busbars against the terminals of the plurality of battery cells;a position sensor moveable relative to the frame in a first direction along the first side (403) of the frame to obtain positions of the one or more busbars adjacent the battery cells,a laser movable relative to the frame in at least the first direction and a second direction substantially perpendicular to the first side of the frame to weld the one or more busbars to the plurality of battery cells;wherein the laser is configured to weld the one or more busbars to the terminals of each battery cell in a first group of battery cells from a single location; andwherein first group of battery cells comprises at least two neighbouring battery cells of the plurality of battery cells.

14. An apparatus according to claim 13, wherein the position sensor is offset from the laser in the first direction such that the position sensor is configured to obtain positions the one or more busbars adjacent the battery cells in a second group of battery cells whilst the laser welds the one or more busbars to the terminals of the first group of battery cells.

15. An apparatus according to claim 13 or 14, comprising a plurality of position sensors, each of the plurality of position sensors being offset from one another in the first direction such that the plurality of position sensors are configured to simultaneously obtain the positions for more than one of the plurality of battery cells.

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