Cylindrical secondary cell comprising a lid

Abstract

There is disclosed herein a cylindrical secondary cell (2000) comprising a cylindrical casing (234) housing an electrode assembly (232), and a lid (200) for closing an open end (234b) of the cylindrical casing (234). The cylindrical casing (234) comprises a beading groove (210) at the open end (234b). The lid (200) is arranged to rest on the beading groove (210). The outer edge (205) of the lid (200) is tapered so as to comprise a tapered surface (206) adjacent the beading groove (200). There is also disclosed herein a method of manufacturing the cylindrical secondary cell (2000), battery pack including such a cell, and a vehicle including such a battery pack.

Description

[0001] CYLINDRICAL SECONDARY CELL COMPRISING A LID

[0002] Technical Field

[0003] The present disclosure relates to a secondary cell, a battery assembly comprising such a secondary cell, and a vehicle comprising such a battery assembly.

[0004] Background

[0005] In addressing climate change, there is an increasing demand for rechargeable batteries, e.g. to enable electrification of transportation and to supplement renewable energy. Currently, lithium-ion batteries are becoming increasingly popular. They represent a type of rechargeable battery in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging.

[0006] As the demand for rechargeable batteries increases, more and more focus is being placed on production speed and cost. To achieve an effective production of rechargeable batteries, the design of the batteries as well as their manufacturing process can be optimized.

[0007] Summary

[0008] The present disclosure aims to provide improved secondary cells and parts thereof. The improvements may be in energy performance, manufacturing efficiency, decreased amount of material used, and assembly simplification, among others.

[0009] In particular, according to an aspect of the present disclosure, there is provided a cylindrical secondary cell, comprising a cylindrical casing housing an electrode assembly, and a lid for closing an open end of the cylindrical casing.

[0010] The cylindrical casing comprises a beading groove at the open end, and the lid is arranged to rest on the beading grove. The outer edge of the lid is tapered so as to comprise a tapered surface adjacent the beading groove.

[0011] Put another way, the tapered surface is a groove abutment surface, since it is the surface that abuts the groove when the lid is in a mounted position (i.e., resting on the groove). Put another way, the outer edge of the lid comprises a beading groove connection surface, wherein the beading groove connection surface is the surface that is configured to interface with the beading groove. Put yet another way, the outer edge of the lid comprises a resting surface, wherein the resting surface rests on the beading groove when the lid is arranged on the beading groove.

[0012] The lid comprises an inner surface and an outer surface. The inner surface of the lid is configured to face the inside of the cylindrical casing, which may also be referred to as the ‘casing’, in a mounted position. The outer surface of the lid is configured to be facing out of the cylindrical casing in the mounted position. The outer edge of the lid comprising a tapered surface could be expressed as, when moving radially outwards beyond a radial distance, the distance between the inner surface and the outer surface (i.e., the thickness) decreases. In this way, there is a narrowing of the lid towards its outer edge. The radial distance at which this narrowing starts is preferably substantially coincidental with the beading groove.

[0013] The outer edge of the lid comprises a radially outermost portion of the inner surface, a radially outermost portion of the outer surface, and one or more side surfaces, wherein the one or more side surfaces bridge between the inner and the outer surface. The outer edge of the lid comprising a tapered surface could thus be expressed as at least one of the one or more side surfaces beingin contact with the beading groove instead of the radially outermost portion of the inner surface being in contact with the beading groove.

[0014] The tapered surface is preferably slanted to better match the profile of the beading groove where the tapered surface sits / rests on the beading groove. Put another way, the at least one of the one or more side surfaces being slanted would comprise said at least one of the one or more side surface forming an oblique angle with respect to both the radial axis and the axial axes. At least one surface of the at least one or more side surfaces that are slanted are slanted such that an axial outermost part of the surface is also a radially outermost part of the surface. In an example, the inner surface and the outer surface of the lid are substantially circular in its radial extension, and concentric in relation to each other. The radius of the inner surface of the lid may be smaller than the radius of the outer surface of the lid (e.g., as a result of the joining tapered surface). Viewed from one perspective, the tapered surface could in this example be formed by a straight or curved side surface directly connecting the outer surface and the inner surface of the lid. The radius of the inner surface of the lid may instead be larger or equal to the radius of the outer surface of the lid. Viewed from one perspective, the tapered surface in this example could be formed by a curved side surface directly connecting the outer surface and the inner surface of the lid. In any case, the tapered surface could be formed by one or more side surfaces positioned between the inner and the outer surface.

[0015] Tapering allows for a tapered surface (rather than a lower corner) to abut the beading groove, such that the contact of the lid with the beading groove is at an intermediate thickness of the lid. Tapering the outer edge of the lid may thus decrease the axial extension of the lid closure of the cylindrical housing, wherein the lid closure comprises the beading groove and the lid. Tapering thus allows the lid to sit axially further down on the beading groove. Consequently, the lid closure comprising the lid and the beading groove is adapted to have a decreased axial extension by tapering the outer edge of the lid, as compared to when the outer edge of the lid is not tapered.

[0016] Decreasing the axial extent of the closing arrangement may allow the overall axial height of the cell to be reduced. Decreasing the axial extent of the closing arrangement while keeping the outer dimensions of the cylindrical secondary cell the same may allow for more space for energy storage components. More space for energy storage components allows for more energy to be stored in the cylindrical secondary cell, which allows for an increase in energy density of the battery.

[0017] The lid may be formed by, e.g., stamping, subtractive manufacturing, additive manufacturing, or a combination thereof. For example, a first lid shape could be stamped from a piece of metal, and subtractive manufacturing could be performed on the first lid shape to create the tapered surface, or the other way around.

[0018] In some examples, the tapered surface comprises a chamfer, a bevel, or a fillet. In such examples, the chamfer edge, the bevel edge, or the fillet edge of the lid can rest on the beading grove when the lid is in a mounted position. As mentioned above, the shape of the tapered surface (i.e. the chamfer edge, the bevel edge, or the fillet edge) may be achieved by, e.g., subtractive manufacturing, additive manufacturing and / or stamping. A chamfer edge, bevel edge, or fillet edge may be relatively easy and cheap to manufacture compared to more complicated tapered surface shapes. A substantially close abutment between the tapered surface and the beading groove may be achieved by using these relatively simple shapes. Moreover, such shapes may advantageously assist in centering the lid in place to rest on the beading groove.

[0019] In some examples, the tapered surface is configured to substantially match the surface of the beading groove. The surface of the beading groove could be described as, e.g., the upper internal face of the beading groove. Matching the tapered surface to the surface of the beading groove may be done by forming (by, e.g., subtractive manufacturing, additive manufacturing and / or stamping) the tapered surface so that it complements the shape of at least a portion of the surface of the beading groove. Matching the tapered surface to the beading groove may allow the tapered surface and the beading groove to substantially fit together. Compared to other shapes of the outer edge of the lid, a tapered surface that matches the surface of the beading groove may allow for the lid to be positioned axially even further down on the beading groove. Further, a tapered surface that matches the surface of the beading groove could allow for a tighter seal, a better electrical connection, and / or for the lid to be more easily guided in place, which could in some examples ease the process of obtaining a preferable position of the lid on the beading groove.

[0020] In preferred embodiments, the edge of the open end of the cylindrical casing is bent over the outer edge of the lid. Put another way, an axially outermost lip of the cylindrical casing is bent or folded over a periphery of the lid. The lid could be positioned between the beading groove and a bent portion of the cylindrical casing. The edge of the open end of the cylindrical casing could then function to keep the lid in position.

[0021] In some examples, the casing is further welded to the lid. For example, an axially outermost lip of the casing may be bent or folded over a periphery of the lid and welded thereto. Preferably, the lid is welded directly to the cylindrical casing. It is further preferable that the lid is attached to the casing without the introduction of any gasket, e.g., using welding such as laser welding. Hence, a substantially watertight or fluid-tight seal can be formed by the lid closure.

[0022] By folding an end of the casing over a periphery of the lid, the casing and the lid may be welded together from a direction above the lid, where ‘above’ is used in a sense of being axially beyond the casing and the lid, although from some perspectives, the end of the cell having the lid may be considered as being the ‘bottom’ of the cell. Although the cell may have no preferred or predefined orientation, for the purposes of illustration in the present disclosure, the end of the cell having the lid may be considered as being the ‘bottom’ of the cell. During manufacture, the cell may be rotated or flipped as required.

[0023] In some embodiments of the present disclosure, the cylindrical secondary cell further comprises a current collector arranged between the lid and the electrode assembly. The current collector could comprise an electrode contact portion, a lid contact portion, and a flexible portion joining the electrode contact portion and the lid contact portion. In such embodiments, the flexible portion extends axially towards the lid and radially outwards such that an axially outermost part of the flexible portion is also a radially outermost part of the flexible portion. Viewed from one perspective, it can be said that the flexible portion extends ‘diagonally’ from a radially inner portion of the current collector towards a radially outer portion of the lid, although the flexible portion may in some cases extend directly along the axial direction.

[0024] The flexible portion may allow for a degree of deviation in the axial direction for the electrode roll and the lid, and / or the flexible portion may allow for a reliable electrical contact with the lid when the lid is pressed against the contact portion of the current collector. By having a lid that is tapered, the current collector may be better mechanically retained, and the electrical contact between the current collector and the lid may thereby be improved. It will be appreciated that the particular construction of the current collector is not determinative of the benefit achieved by the lid pressing more firmly against it.

[0025] The current collector may be configured to electrically connect to an end of the electrode roll (e.g., a cathode side or an anode side) via direct contact to protruding electrode foils or ‘tabs’ that are free from electrode coating. In alternative embodiments, these tabs may be in direct contact with the lid and / or the cell casing. In any event, the lid and / or casing may serve as an electrical terminal for the cell.

[0026] Preferably, the current collector is configured not to contact the cylindrical casing. For example, the flexible portion and / or the contact portion may be sized and / or arranged such that, even at an extreme compression of the flexible portion - which, it will be understood, may cause the contact portion to move radially outwards - the casing is not contacted by the current collector. Such an arrangement may thus ensure that the current collector reliably contacts the lid.

[0027] The lid may be welded to the current collector before, after, or in a combination of before and after the edge of the open end of the cylindrical casing is bent over the outer edge of the lid. The contacting of the lid contact portion and the lid may advantageously provide a reliable welding contact surface for welding from the outside, i.e. , from above the lid (where ‘above’ is used in the same sense as before). Thus, the lid and casing may be welded together from the same direction as the lid and the current collector are welded together, thereby further simplifying the manufacture of the cell. Further, the lid, the casing, and the current collector may be welded together in a single operation.

[0028] In a particular embodiments, the current collector is configured to be axially compressed between the lid and the electrode assembly. The current collector may in this way be better mechanically retained, and the electrical contact between the current collector and the lid may thereby be improved. In some embodiments of the present disclosure, the beading groove comprises an average tangential angle of preferably 5-45 degrees, more preferably 10-30 degrees, or most preferably 15-25 degrees. An average tangential angle of the beading groove may be the average inclination, or average tangential inclination, of the upper internal surface (facing the open end of the casing) of the beading groove, as compared to the radial axis. More specifically the average inclination of the beading groove may be the average inclination, compared to the radial axis, of the portion of the upper internal face of the beading groove configured to abut the lid.

[0029] It will be appreciated that a similar angle may be defined in terms of the tapered surface of the lid. That is, the tapered surface at the outer edge of the lid may comprise an average tangential angle of preferably 5-45 degrees, more preferably 10-30 degrees, or most preferably 15-25 degrees. That is, the tapered surface may subtend such an angle with the radial plane of the cell. If the tapered surface is formed as a chamfer, bevel, or similar angled surface, then the tapered surface may substantially lie in a plane that is angled relative to the radial plane by 5-45 degrees, more preferably 10-30 degrees, or most preferably 15-25 degrees.

[0030] Angling the beading groove / lid (as opposed to having it flat, wherein the surface may be substantially flat between the apex of the groove and the vertical extent of the sidewall) helps to allow the lid to slide along the beading groove and be centred concentrically with the cell casing during the closing process (i.e., the process of putting the lid in a mounted position). The surface being flat may also be expressed as the incline of the surface being parallel to the radial axis. An beading groove having an average tangential angle between 5-45 degrees, 10-30 degrees, or 15-25 degrees may thus result in that the beading groove is slanted inwards, i.e., that the axially outermost part of the beading groove is also a radially outermost part of the beading groove.

[0031] According to an aspect of the present disclosure, there is provided a method of manufacturing a cylindrical secondary cell described above. The method comprises arranging the electrode assembly in the cylindrical casing and forming the beading groove in the cylindrical casing. The method further comprises arranging the lid on the beading groove. The lid is arranged on the beading groove so that the tapered surface at the outer edge of the lid rests on the beading groove. The method additionally comprises folding the edge of the open end of the cylindrical casing over the outer edge of the lid. This, as described above, could hold the lid substantially in place in relation to the cylindrical casing.

[0032] In some cases, it may be desirable to provide a more reliable current path between the lid and the electrode assembly. Thus, according to some examples, the method further comprises arranging a current collector in contact with the electrode assembly. To improve the electrical contact that the current collector provides, the method also comprises arranging the lid and / or folding the edge of the open end of the cylindrical casing so that the current collector is axially compressed between the lid and the electrode assembly. It will be appreciated that the tapered surface discussed above helps the lid to sit lower on the beading groove and hence allows for a greater compression of the current collector and hence a better electrical connection between the current collector and the lid.

[0033] In some embodiments of the present disclosure, the method additionally comprises welding the can to the lid. As mentioned above, the casing may be welded to form a substantially watertight or fluid-tight seal, thereby negating any requirement for a gasket. Hence, the number of components required to seal the cell is reduced and the environmental impact of the cell may be improved, as conventional gaskets can be made of materials that are difficult to recycle with current methods.

[0034] According to further aspects of the present disclosure, there is provided a battery pack and a vehicle comprising the battery pack. The battery pack comprises a plurality of cylindrical secondary cells, wherein at least one of the plurality of cylindrical secondary cells is a cylindrical secondary cell substantially as described above.

[0035] It will be appreciated by those skilled in the art, and through the description of example embodiments of the present disclosure, that further advantages as well as those described above may be provided by a lid closure according to aspects of the present disclosure. These advantages may be compounded through the provision of multiple cells having such a lid closure, such as in a battery pack, or a vehicle containing the battery pack.

[0036] Brief Description of the Drawings

[0037] One or more embodiments of the present disclosure will be described, by way of example only, and with reference to the following figures, in which:

[0038] Figure 1 schematically shows a cross-sectional view of an example secondary cell;

[0039] Figure 2A schematically shows a cross-sectional view of a portion of a secondary cell having a lid closure according to an example implementation of the present disclosure;

[0040] Figure 2B shows in more detail the lid closure shown in figure 2A;

[0041] Figure 2C shows a top view of the lid closure shown in figure 2A;

[0042] Figure 3 schematically show two cross-sectional views of portions of the open bottom ends of secondary cells;

[0043] Figures 4A, 4B, and 4C schematically show alternative tapering profiles for a lid, according to example implementations of the present disclosure;

[0044] Figure 5 illustrates a method of manufacturing the cylindrical secondary cell, according to an embodiment of the present disclosure;

[0045] Figure 6 shows a battery pack according to an aspect of the present disclosure; and

[0046] Figure 7 shows a vehicle according to an aspect of the present disclosure.

[0047] Detailed Description

[0048] The present disclosure is described in the following by way of a number of illustrative examples. It will be appreciated that these examples are provided for illustration and explanation only and are not intended to be limiting on the scope of the present disclosure. Instead, the scope of the present disclosure is defined by the appended claims.

[0049] Furthermore, although embodiments may be presented individually for the sake of focused discussion of particular features, it will be recognized that the present disclosure also encompasses combinations of the embodiments described herein.

[0050] Figure 1 schematically shows a cross-sectional view of a cylindrical secondary cell 1000.

[0051] The cylindrical secondary cell 1000 (also referred to as simply the ‘cell 1000’) comprises an electrode assembly (or Toll’) 132 housed in a cylindrical casing (or ‘casing’) 134. The electrode roll 132 may be formed of an anode sheet, a cathode sheet, and a separator sheet arranged therebetween to thereby enable a storage of electrical energy. Cathode tabs 132a may extend from a first end of the electrode roll 132 and anode tabs 132b may extend from the other end, or vice versa. The cathode tabs 132a and anode tabs 132b provide connective surfaces to which current collectors 136 and 138 can be connected. As used here, the “tabs” 132a and 132b can be uncoated portions of the electrode foil extending from the electrode roll 132, rather than additional tabs connected to the electrode roll 132. Hence, the illustrated cell 1000 may be referred to as a ‘tabless’ cell due to the absence of ‘additional’ tabs.

[0052] The cylindrical casing 134 extends along an axis between a first end 134t, which may be referred to as a ‘top end 134t’, and a second end, which may be referred to as a ‘bottom end 134b’. It will be appreciated that the labels ‘top’ and ‘bottom’ are arbitrary, and correspond to the illustration of figure 1 , but may aid in the understanding of the present disclosure.

[0053] The bottom end 134b is an open end of the casing 134 closed by a lid 100. The closure of the casing 134 may comprise a clamped or crimped closure or a welded closure, depending on the implementation.

[0054] For example, the casing 134 may further comprise a beading groove (not shown) formed in the side wall 134s. Hence, between the beading groove and the edge of the side wall 134s towards the bottom end 134b of the casing 134, a clamping portion can be formed. Optionally, a lid gasket (not shown) may then be clamped around the lid 100 in the clamping portion to thereby seal the open bottom end 134b of the casing 134. Providing a clamped closure in this way is well known in the art and can provide a reliable waterproof seal for the cell.

[0055] As another example, in which a beading groove may still be formed, the lid 100 may be welded to the casing 134 to thereby seal the casing 134. The lid 100 may be additionally welded to the current collector 138 or, in other examples, the lid 100 may act as a current collector itself and be attached (e.g., welded) to the tabs of the electrode assembly 132. Providing a welded closure in this way may advantageously remove the number of components of the cell 1000 and / or the number of process steps required to manufacture the cell 1000. In preferred embodiments of the present disclosure, the lid 100 is welded to the casing 134 and the current collector 138. This latter example is illustrated in figure 2.

[0056] A cathode current collecting plate 136 is arranged in direct electrical contact with the cathode tabs 132a and an anode current collecting plate 138 is arranged in direct electrical contact with the anode tabs 132b. Here, the labels ‘cathode’ and ‘anode’ may be swapped. Thus, an electrical connection is formed from the cathode tabs 132a to a terminal assembly 142, as the terminal assembly 142 is connected to the current collecting plate 136.

[0057] An electrical connection is also formed from the anode tabs 132b to the lid 100 and / or the casing 134, either directly or through connection of the anode current collecting plate 138 to the casing 134, e.g. in the clamping portion and / or by welding. One or both or the current collectors 136, 138 may be formed as a disc, a plate, or have some other shape.

[0058] A gasket 144 is arranged around the terminal assembly 142 and configured to electrically insulate the terminal assembly 142 from the casing 134. The gasket 144 may additionally form a substantially fluid-tight (i.e., gastight) seal for the opening 134o in the casing 134 through which the terminal assembly 142 is arranged.

[0059] At either end of the cell 1000, the cell 1000 may further comprise a vent for venting gases, for example during a failure of the cell 1000. Moreover, the cell 1000 may comprise an additional through-hole in the lid 100, for filling the cell 1000 with a liquid electrolyte. This through-hole is preferably adapted to be closed from the outside, such as through the use of a blind rivet or a welded cap. Example implementations of such a vent and an electrolyte filling hole in the lid are discussed in connection with figure 2C.

[0060] It is seen that a head of the terminal assembly 142 serves as an external terminal of the cell 1000, this being a positive terminal in this example, and the casing 134 serves as the negative terminal. Hence, it is seen that both terminals of the cell 1000 are accessible at the same side. The top end 134t of the casing 134 comprises a first electrical contact surface extending in a first plane, and the head of the rivet 142 comprises a second electrical contact surface, extending in a second plane axially spaced from the first plane. Accordingly, electrical connections to each of the first and second electrical contact surfaces are advantageously simplified.

[0061] Figures 2A, 2B, and 2C schematically show cross-sectional views of a bottom end portion of a cell 2000, which may be substantially similar in its overall construction to the cell 1000 shown in figure 1. Reference numerals corresponding to those used in figure 1 , but increased by 100, may indicate elements that are the same or substantially similar to those shown in figure 1 . Accordingly, these repeated elements may not be discussed again in detail. However, the illustrated bottom end 234b of the casing 234 (corresponding to the open bottom end 134b shown in figure 1 ) is shown upside down in figure 2A, relative to figure 1 , and the configuration of the lid 200 and the casing 234 are shown in more detail in this illustrated example.

[0062] The cell 2000 comprises an electrode assembly 232 housed in a casing 234, where the casing 234 is cylindrical and comprises a sidewall 234s extending axially and terminating at an open end 234b of the casing 234. The open end 234b of the casing 234 comprises an edge 212. In this illustrated example, the edge 212 is bent, or folded, so as to extend radially inward. The open end 234b of the casing 234 comprises a beading groove 210 formed in the sidewall 234s. The beading groove 210 extends radially inwards. The upper internal surface of the beading groove 210 is further slanted / angled downwards into the cell 2000. That is, the illustrated beading groove has an average tangential angle of preferably 5-45 degrees, more preferably 10-30 degrees, or most preferably 15-25 degrees. A lid 200 closes the open bottom end 234b of the casing 234. The lid 200 comprises an outer surface 202, an inner surface 204, an edge portion 205 and an electrolyte filling hole 246. In this example, the edge portion 205 comprises a tapered surface 206 and a side surface 208. The electrolyte filling hole 246 is sealed by a sealing cap 248, which may be formed as a blind rivet or the like. The electrolyte filling hole 246 is preferably arranged centrally on the lid 200. Hence, an electrolyte filling step, which may be downstream in the manufacturing process from the assembly of the lid onto the casing, may be simplified as it can be ensured that the electrolyte filling hole 246 is in a substantially similar position for each cell.

[0063] The electrolyte filling hole 246 may be circular in shape and may be formed as a through-hole having substantially constant cross-section. The size of the electrolyte filling hole may be configured according to an expected size of an electrolyte filling port.

[0064] In this example, the edge 212 is bent, or folded, over the outer edge of the lid 200. The edge 212 can be welded to the lid 200. An example welding location W is illustrated in figure 2A. The welding can be done e.g., via a welding laser directed from the top down (as illustrated). As shown in the figure, the welding direction W of the weld (e.g., direction of a welding laser) are substantially aligned with the axial extension of the cell 2000, i.e. , the welding is from ‘above’ in respect of the orientation of the figure. Specifically, in this example, the bottom end 234b of the casing 234 comprises an edge 212 extending radially inwards (which may be folded) so that the outermost part of the edge extends in a direction substantially perpendicular to the direction of extension of the casing. There may be more than one weld attaching the edge 212 to the lid 200.

[0065] Figure 2B illustrates a magnified edge portion 205 of the lid 200. Figure 2C illustrates the top view of the lid 200. The reference numerals of figure 2A, 2B and 2C correspond to each other. As shown in figures 2A and 2B, the cylindrical secondary cell 2000 comprises a cylindrical casing 234 housing an electrode assembly 232. The cylindrical casing 234 comprises a beading groove 210 at the open end (or open bottom end) 234. The lid 200 is arranged to rest on the beading groove 210. The outer edge 205 of the lid 200 is tapered so as to comprise a tapered surface 206 that is adjacent to the beading groove 210 when the lid 200 is in a mounted position. The edge portion 205 is tapered to as to comprise a chamfer 206. When the lid 200 is in a mounted position in the cell 2000, the chamfer 206 abuts the beading groove 210.

[0066] As shown in figure 2C, the lid 200 may comprise one or more vents 240 configured to vent gases from the cylindrical casing 234. Figure 2C shows three vents 240 arranged in a radially symmetric fashion around the center of the lid 200. Each vent 240 is formed with a weakened portion 240a, such as a groove, formed as an open shape (i.e., a shape with a different starting and ending point). Between the starting and ending point, a non-weakened part 240b serves as an anchoring part such that, upon a build-up of gas within the cell 2000 above a certain pressure, the weakened portion 240a will rupture and cause the portion of the lid 200 within the open shape to bend or otherwise open, this portion being held without breaking off of the lid 200 by the nonweakened portion 240b.

[0067] Figure 3 schematically illustrates two cross-sectional views of portions of the open bottom ends 334b of secondary cells 3000 wherein each cell 3000 may be substantially similar in their overall construction to the cell 1000 shown in figure 1 and / or the cell 2000 shown in figure 2. Similarly to how the reference numerals of figure 1 and figure 2A-C correspond to each other, reference numerals corresponding to those used in figure 1 , but increased by 200, may indicate elements that are the same or substantially similar to those shown in figure 1 , and reference numerals corresponding to those used in figure 2, but increased by 100, may in indicate elements that are the same or substantially similar to those shown in figure 2. Accordingly, these repeated elements may not be discussed again in detail.

[0068] The portions of the open bottom end 334b shown in figure 3 each comprises a lid 300, an electrode assembly 332, a current collector 338, and a sidewall 334s. Protruding from the electrode assembly 332 are electrode tabs 332b, which may be uncoated portions of electrode. The current collector 338 is arranged in direct electrical contact with the tabs 332b. Specifically, an electrode contact portion 338a is in direct electrical contact with the tabs 332b. The current collector 338 is further connected to the lid 300 via a contact portion 338c and a flexible portion 338b connecting the electrode contact portion 338a to the contact portion 338c. As shown in figure 3, the flexible portion 338b extends axially towards the lid 300 and radially outwards such that an axially outermost part of the flexible portion 338b is a radially outermost part of the flexible portion 338b.

[0069] The contact portion 338c of the current collector 338 is shown contacting the inner surface 304 of the lid 300, but not contacting the casing 334. The contacting portion 338 is illustrated adjacent to the sidewalls 334s, but the contacting portion 338 could be connected to any suitable part of the inner surface 304 of the lid 300. The downward pressure of the lid 300 against the contact portion 338c may cause the flexible portion 338b to flex, and the contact portion 338c may, in such cases, slide radially outwards. In preferred embodiments, the flexible portion 338b and the contact portion 338c may be configured (e.g., sized and positioned) to prevent contact with the casing 334 even when substantially depressed by the lid 300, as such contact may cause the lid 300 to be lifted by the current collector 338 and / or the current collector 338 to be pushed into the electrode assembly 332, thereby causing damage.

[0070] The sidewalls 334s comprises an edge 312. As mentioned in relation to figures 2A-C, the edges 312 may be bent, or folded, over the outer edge of the lid 300. This could correspond to reconfiguring the edge 312 from an open position of the edge 312a to a closed position of the edge 312b. As described above, the edges 312 can be welded to the lid 300. Further, the contact portion 338c may be welded W to the lid 300. The contact portion 338c and the lid 300 may be welded when the edge is in an open position 312a, a closed position 312b, or at any position in between. In the case when the edge is substantially in an open position 312a, a first weld may attach the contact portion 338c of the current collector 338 to the lid 300. After repositioning the edge 312 to a closed position 312b, a second weld could attach the casing 334 to the lid 300. Alternatively, or in combination with one or more of the previously mentioned welds, one weld may simultaneously attach the contact portion 338c, the lid 300 and the casing 234 to each other, wherein the casing 234 is preferably attached via the edge 312 when the edge is in a closed position 312b.

[0071] The edge portion 305 of the lid 300 illustrated in the leftmost cross- sectional view of figure 3 comprises a non-tapered edge 307. The edge portion

[0072] 305 of the lid 300 illustrated in the rightmost cross-sectional view of figure 3 comprises a tapered edge comprising a tapered portion (or ‘tapered surface’)

[0073] 306 and a side surface 308. The tapered edge allows for a lid 300 and the beading groove 310 to have a larger overlap in the axial direction as compared to the same case with a non-tapered edge 307. Having a larger overlap of the lid 300 and the beading groove 310 in the axial direction may allow for an enhanced axial compression of the current collector 338. A larger overlapping of the lid 300 and the beading groove 310 in the axial direction may further allow for the closing arrangement comprising the lid 300 and the beading groove 310 to have a reduced axial extension. The distance d shown in figure 3 illustrates the difference in axial extension of a cell 3000 comprising a lid 300 with a non-tapered edge 307 as compared to a cell 3000 comprising a lid 300 with a tapered portion 306.

[0074] Figure 4A-C schematically shows alternative cross-sectional views of edge portions 405 of different example implementations of a lid 400 according to aspects of the present disclosure. The lid 400 of any of figures 4A-C could be used in cylindrical secondary cell, such as the cylindrical secondary cell 100 shown in figure 1 , the cylindrical secondary cell 2000 shown in figures 2A-C, and / or the cylindrical secondary cell 3000 shown in figure 3.

[0075] Figures 4A, 4B, and 4C show edge portions 405 comprising a tapered edge in the form of a bevel edge, a fillet edge, and an specially adapted edge, respectively. The bevel edge of figure 4A comprises a tapered portion 406a, which creates a sloping surface between the outer surface 402 and the inner surface 404 of the lid. The tapered portion 406a extends such that an axially outermost part of the tapered portion 406a is also a radially outermost part of the tapered portion 406a.

[0076] The fillet edge of figure 4b comprises an side surface 408 and a tapered portion 406b. The side surface 408 extend significantly along the axial direction from the outer surface 402 towards the axial position of the inner surface 404, without reaching the axial position of the inner surface 404. The tapered portion 406b comprises a convex surface that connects the side surface 408 and the inner surface 404. The length of the side surface 408 affects the slope of the tapered portion 406b.

[0077] The specially adapted edge of figure 4c is adapted to substantially match the surface of the beading groove. The specially adapted edge comprises an side surface 408 and a concave tapered portion 406c. As is the case for the fillet edge, the side surface 408 in this example extend significantly along the axial direction from the outer surface 402 towards the axial position of the inner surface 404, without reaching the axial position of the inner surface 404. The tapered portion 406c comprises a surface that connects the side surface 408 and the inner surface 404. The surface of the tapered portion 406c substantially matches the beading groove, and, more specifically, it matches a portion of the upper internal face of the beading groove. The tapered portion 406c substantially matches the portion of the beading groove it is arranged to rest on such that, when the lid 400 is in a mounted position, the tapered portion 406c is substantially directly in contact with the beading groove.

[0078] Alternative to a side surface 408 (or ‘axial portion 408’) extending from the outer surface 402 towards the lower surface 404 significantly in an axial direction, an edge portion 405 could comprise an outer edge of another shape. For example, the outer edge, i.e. the part of the tapered edge that connects to the outer surface 402, could comprise e.g. a chamfer edge, a bevel edge, a fillet edge, or an specially adapted edge matching the internal edge of the open end of the cylindrical casing. Adapting the shape of the upper edge may be advantageous to, e.g., obtain a better fit of the lid and a better sealing of the cell.

[0079] Figure 5 illustrates a method 500 of manufacturing a cylindrical secondary cell, which may be the cylindrical secondary cell 1000 shown in figure 1 , the cylindrical secondary cell 2000 shown in figures 2A-C, and / or the cylindrical secondary cell 3000 shown in figure 3. The method 500 comprises arranging an electrode assembly in the cylindrical casing 510. In some examples, a current collector may be arranged in contact with the electrode assembly. The method further comprises forming the beading groove in the cylindrical casing 520. The beading groove is preferably formed of sidewalls of the cylindrical casing, near an open end of the cylindrical casing.

[0080] The method 500 further comprises arranging a lid on the beading groove 530. The lid is arranged on the beading groove so that the tapered surface at the outer edge of the lid rests on the beading groove. If a current collector is arranged in contact with the electrode assembly, the lid may be arranged to axially compress a current collector between the lid and the electrode assembly.

[0081] In order to further secure the lid, the method further comprises folding the edge of the open end of the cylindrical casing 540. The edge of the open end of the cylindrical casing is folded over the outer edge of the lid. If a current collector is arranged in contact with the electrode assembly, the edge may be folded so that the current collector gets axially compressed between the lid and the electrode assembly. The lid may further be welded to the casing / can. If a current collector is arranged in contact with the lid, a weld may attach the current collector to the lid. A weld attaching the current collector to the lid may also, but not necessarily, attach the lid to the can.

[0082] The steps 510, 520, 530, 540 of this method 500 are, by the arrows in figure 5, illustrated in a specific order. It will be appreciated that the order of the steps 510, 520, 530, 540 are provided for illustration and explanation only and are not intended to be limiting on the scope of the present disclosure. Where applicable, the steps 510, 520, 530, 540 may be taken in any order. It will also be appreciated that other steps, not illustrated in the figure, may be taken in between the illustrated steps 510, 520, 530, 540.

[0083] Figure 6 shows a perspective view of a battery pack 600 with a portion of its casing (being illustrated in a purely schematic way) cut away to schematically show a plurality of secondary cells 6000 housed therein. The secondary cells 6000 may correspond to the secondary cell 1000, 2000, and / or 3000 described above and may comprise a lid closure substantially as described above.

[0084] The secondary cells 6000 are connected together in series and / or parallel, and in an optionally modular fashion, so as to form a combined electrical storage capacity. In some examples, the cells 6000 have a common orientation such that failure vents of the cells are oriented in a same direction, and such that the terminals of the cells 6000 can be accessed at a same side.

[0085] Figure 7 schematically shows an example vehicle 700 comprising the battery pack 600 shown in figure 6. In this example, the battery pack is arranged at a lower portion of the vehicle 700, which may be an electric or hybrid vehicle. Other uses for the battery pack 600 may comprise a standalone battery pack for powering devices or installations or the like.

[0086] It will be appreciated that the advantages described above in respect of, e.g., energy density, conferred to the secondary cells according to aspects of the present disclosure, will also be conferred to a battery pack comprising said cells, and any vehicle comprise such a battery pack. Thus, these advantages are not discussed in detail again.

[0087] The present disclosure may be better appreciated through consideration of the following numbered clauses:

[0088] 1 . A cylindrical secondary cell, comprising: a cylindrical casing housing an electrode assembly; and a lid for closing an open end of the cylindrical casing; wherein the cylindrical casing comprises a beading groove at the open end, and the lid is arranged to rest on the beading groove; and wherein the outer edge of the lid is tapered so as to comprise a tapered surface adjacent the beading groove.

[0089] 2. The cylindrical secondary cell according to clausel , wherein the tapered surface comprises a chamfer, a bevel, or a fillet.

[0090] 3. The cylindrical secondary cell according to clause 1 or clause 2, wherein the tapered surface is configured to substantially match the surface of the beading groove.

[0091] 4. The cylindrical secondary cell according to any preceding clause, wherein the edge of the open end of the cylindrical casing is bent over the outer edge of the lid.

[0092] 5. The cylindrical secondary cell according to any preceding clause, wherein the casing is welded to the lid.

[0093] 6. The cylindrical secondary cell according to any preceding clause, further comprising a current collector arranged between the lid and the electrode assembly.

[0094] 7. The cylindrical secondary cell according to clause 6, wherein the current collector is configured to be axially compressed between the lid and the electrode assembly.

[0095] 8. The cylindrical secondary cell according to any preceding clause, wherein the upper internal surface of the beading groove comprises an average tangential angle of 5-45 degrees, preferably 10-30 degrees, or most preferably 15-25 degrees.

[0096] 9. A method of manufacturing the cylindrical secondary cell according to any preceding clause, comprising: arranging the electrode assembly in the cylindrical casing; forming the beading groove in the cylindrical casing; arranging the lid on the beading groove so that the tapered surface at the outer edge of the lid rests on the beading groove; and folding the edge of the open end of the cylindrical casing over the outer edge of the lid. 10. The method according to clause 9, further comprising: arranging a current collector in contact with the electrode assembly; and arranging the lid and / or folding the edge of the open end of the cylindrical casing so that the current collector is axially compressed between the lid and the electrode assembly.

[0097] 11 . The method according to clause 9 or clause 10, further comprising: welding the can to the lid.

[0098] 12. A battery pack comprising a plurality of cylindrical secondary cells, wherein at least one of the plurality of cylindrical secondary cells is a cylindrical secondary cell according to any of clauses 1 to 8.

[0099] 13. A vehicle comprising the battery pack according to clause 12.

[0100] While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments are shown and described above by way of example in relation to the drawings, with a view to clearly explaining the various advantageous aspects of the present disclosure. It should be understood, however, that the detailed description herein and the drawings attached hereto are not intended to limit the disclosure to the particular form disclosed. Rather, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the following claims.

Claims

P A T E N T C L A I M S1 . A cylindrical secondary cell, comprising: a cylindrical casing housing an electrode assembly; and a lid for closing an open end of the cylindrical casing; wherein the cylindrical casing comprises a beading groove at the open end, and the lid is arranged to rest on the beading groove; and wherein the outer edge of the lid is tapered so as to comprise a tapered surface adjacent the beading groove.

2. The cylindrical secondary cell according to claim 1 , wherein the tapered surface comprises a chamfer, a bevel, or a fillet, or wherein the tapered surface is configured to substantially match the surface of the beading groove.

3. The cylindrical secondary cell according to any preceding claim, wherein the edge of the open end of the cylindrical casing is bent over the outer edge of the lid, and / or wherein the casing is welded to the lid.

4. The cylindrical secondary cell according to any preceding claim, further comprising a current collector arranged between the lid and the electrode assembly, preferably wherein the current collector is configured to be axially compressed between the lid and the electrode assembly.

5. The cylindrical secondary cell according to any preceding claim, wherein the upper internal surface of the beading groove comprises an average tangential angle of 5-45 degrees, preferably 10-30 degrees, or most preferably 15-25 degrees.

6. A method of manufacturing the cylindrical secondary cell according to any preceding claim, comprising: arranging the electrode assembly in the cylindrical casing; forming the beading groove in the cylindrical casing;arranging the lid on the beading groove so that the tapered surface at the outer edge of the lid rests on the beading groove; and folding the edge of the open end of the cylindrical casing over the outer edge of the lid.

7. The method according to claim 6, further comprising: arranging a current collector in contact with the electrode assembly; and arranging the lid and / or folding the edge of the open end of the cylindrical casing so that the current collector is axially compressed between the lid and the electrode assembly.

8. The method according to claim 6 or claim 7, further comprising: welding the can to the lid.

9. A battery pack comprising a plurality of cylindrical secondary cells, wherein at least one of the plurality of cylindrical secondary cells is a cylindrical secondary cell according to any of claims 1 to 5.

10. A vehicle comprising the battery pack according to claim 9.

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