Lid closure for a secondary cell

Abstract

A current collector disc (300) with a central axis (A) for a cylindrical secondary cell (100) is provided. The current collector disc (300) comprises peripheral lid contact portion (304), extending in a lid contact plane (PL), an electrode contact portion (302), extending in an electrode contact plane (PE), said electrode contact plane (PE) being displaced in a first direction from the lid contact plane (PL), and a connecting portion (306), connecting the lid contact portion (304) and the electrode contact portion (302). The connecting portion (306) comprises at least a flange (306a) extending along a flange axis (B) in a longitudinal section comprising the central axis (A), said flange axis (B) extending in a flange angle (α) in relation to the central axis (A), wherein the flange angle (α) is 0 to 40 degrees.

Description

[0001] LID CLOSURE FOR A SECONDARY CELL

[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] 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] In particular, according to an aspect of the present disclosure, the cell comprises a current collector disc with a central axis for a secondary cell, wherein the current collector comprises an electrode contact portion, a lid contact portion, and a connecting portion joining the electrode contact portion and the lid contact portion, wherein the connecting portion is stiff in the axial direction. The lid contact portion is a peripheral lid contact portion, extending in a lid contact plane. The electrode contact portion extends in an electrode contact plane. The electrode contact plane is displaced in a first direction from the lid contact plane. The connecting portion connects the lid contact portion and the electrode contact portion.

[0011] The stiff connecting portion makes sure that the lid contacting portion and the electrode contact portion are maintained in flush connection with the lid and the electrode, respectively, thereby providing good connection even if the current collector disc has an axial extension.

[0012] In one embodiment the connecting portion comprises at least a flange extending along a flange axis in a longitudinal section comprising the central axis, wherein the flange axis extends in a flange angle in relation to the central axis, wherein the flange angle is 0 to 40 degrees, such as 10 to 40 degrees, such as 20 to 35 degrees, such as 25 to 35 degrees. A low flange angle stiffens the current collector disc, but a too low flange angle may affect logistics and manufacturing negatively. Therefore, a flange angle of 20 to 35 degrees is preferred. The number of flanges of the at least one flange may be 2 to 8, such as 3 to 6. When the connecting portion comprises a plurality of flanges, there will be spatial gaps between the flanges. In this way the connecting portion may take of pressure differences within the cell without displacing certain parts of the lid contact portion and / or the electrode contact portion. Thus, a good contact between the lid contact portion and the electrode contact portion with the lid and electrode, respectively, may be maintained.

[0013] 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. The lid contact portion preferably contacts the lid at a peripheral part of the lid, i.e. not sections of the lid being positioned centrally of the periphery of the lid. Hence, the configuration of the central regions may not be impacted by the contact with the current collector. For example, the current collector can avoid interfering with the vent or the electrolyte filling hole, and the lid contact portion can be dimensioned according to thermal and / or electrical considerations without further consideration of the dimensions of the central regions, and vice versa.

[0014] Preferably, the current collector disc is configured not to contact the cylindrical casing. For example, the connecting portion, the lid contact portion and / or the electrode contact portion may be sized and / or arranged such that, even at an extreme axial compression of the connecting portion, the lid contact portion is kept from moving laterally and radially outwards, which in turn results in the casing not contacting the current collector disc.

[0015] The contacting of the lid contact portion with 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.

[0016] In one embodiment the lid contact portion is annular. In this way spatial integrity of the lid contact portion may be maintained, and a certain rotational play for the lid contact portion during manufacturing may be allowed.

[0017] In embodiments the electrode contact portion comprises a plurality of tongues. In this way local flexibility of the electrode contact portion is improved. The number of tongues in the plurality of tongues may be 2 to 8, such as 3 to 5. Each of the at least one flange may connect to at least one of the plurality of tongues.

[0018] In embodiments the electrode contact portion comprises a plurality of spokes. The number of spokes of the plurality of spokes may be 4 to 16, such as 6 to 10. The plurality of spokes may connect centrally in a central plate, which may be provided with a centrum hole. The central axis may run through the centrum hole. In this way the spatial integrity may be maintained in the current collector disc, including good contact with the electrode.

[0019] In some aspects of the present disclosure, the cell further comprises a lid for closing an open end of the cylindrical casing. The lid comprises a first region extending in a first plane, a second region surrounding the first region and extending in a second plane displaced in a first direction from the first plane, and a third region surrounding the second region and extending in a third plane displaced in the first direction from the second plane. The first region comprises an electrolyte filling hole, and the second region comprises a vent configured to vent gases from the cylindrical casing. Each region may define a surface, and preferably the surface is substantially flat in the plane. In some examples, ‘surrounding’ may mean entirely surrounding (i.e. , enclosing), or at least partially surrounding.

[0020] The first region and the second region may be joined by a surface that extends substantially axially, such that a ‘step’ is formed between the first region and the second region. The interface between regions may also have some radial extension, depending on the implementation, that bridges between the planes in which the regions extend. The interface may be preferably configured so as to maintain a substantially constant material thickness, thereby reducing the risk of creating weaker or stronger seams on the lid that could lead to unexpected points of failure.

[0021] Viewed from one perspective, a lid according to aspects of the present disclosure has a ‘stepped’ profile, having at least two steps down towards the radial center of the lid, the lid being substantially circular in its radial extension so as to correspond to the open end of the cylindrical casing that the lid is configured to close.

[0022] In some examples, one, two, or preferably each of the first, second, and third regions is circular. Further, in preferred examples, each of the first, second, and third regions is concentric with each other. In this way, the lid may be substantially rotationally symmetric and thus the construction of the lid and cell may be simplified, e.g., by mitigating a requirement for rotational alignment between components during manufacture. Further to this effect, the electrolyte filling hole is preferably arranged centrally in the first region. 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 is in a substantially similar position for each cell.

[0023] The electrolyte filling hole 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.

[0024] The vent on the second region may be configured as a thinning, partial perforation, or other weakening in the second region of the lid. More than one vent may be formed on the second region, in some examples. For example, a plurality of vents may be arranged with a circular symmetry in the second region.

[0025] In a particular example, the vent is formed as a grooved thinning formed on the outer and inner surfaces of the second region, in an open shape of a semicircle, arc, rounded triangle, or other open shape. Hence, when there is a build-up of gas pressure inside the cell, the weakened portion may break or rupture, and a portion of the lid defined within the open shape may partially lift, being anchored to the lid via a non-weakened portion at the opening of the open shape, and the gasses may escape through this rupture.

[0026] In another example, the vent is formed as a groove only on an outer surface of the second region of the lid. The profile of the groove may be formed of two substantially trapezoidal shapes, wherein a first trapezoidal shape comprises one part of a groove further towards the outer surface, and a second trapezoidal shape extends further into the lid from the outer surface, thereby forming a ‘sub-groove’ within the groove. The second trapezoidal shape is preferably smaller than the first trapezoidal shape and arranged centrally thereon.

[0027] According to such an example, the reliability of vent rupture may be improved by focusing the location of the rupture on the sub-groove, and the manufacturing of the vent may be simplified as it can be formed only on the outer surface of the lid or only on the inside surface of the lid.

[0028] The present disclosure may be implemented in any suitable cylindrical cell application, such as a conventional ‘2170’ configuration (21 mm in diameter, 70 mm in length), or in a larger format ‘4695’ configuration (i.e., 46 mm in diameter, 95 mm in length), or in variations thereof. Preferred embodiments of the present disclosure may be more similar to the ‘4695’ configuration, e.g., 4680, 46105, etc.

[0029] The radii of the first, second, and third regions may be configured to achieve an improved structural rigidity, simplified manufacture, and / or enhanced specialized functionality, as discussed elsewhere herein.

[0030] The first region may have an outer radius between 5 mm and 10 mm, preferably between 5 and 7 mm, and most preferably 6 mm. The second region may have an outer radius between 10 mm and 17 mm, preferably between 12 and 15 mm, and most preferably 14 mm. The third region may have an outer radius between 15 mm and 22 mm, preferably between 16 and 20 mm, and most preferably 17.5 mm.

[0031] In preferred embodiments, the third region defines an end surface in the third plane that is the axially outermost surface of the cylindrical secondary cell. Hence, the cell may be rested on a surface by being placed down on the end having the lid, and thereby the third region provides a resting surface.

[0032] The axial distances between the first, second, third may be configured to achieve an improved structural rigidity, simplified manufacture, and / or enhanced specialized functionality, as discussed elsewhere herein. For example, the first plane may be axially spaced from the third plane by 1.2 to 2.5 mm, preferably 1 .5 to 2.2 mm, and most preferably 1 .85 mm.

[0033] The second plane is between the first and third planes. Thus, it will be understood that the second region, comprising a vent for venting gases, is axially recessed from the third region, hence providing a protection for the vent. The electrolyte filling hole may be closed by a sealing cap after the internal of the cell has been filled with electrolyte, through the electrolyte filling hole. The sealing cap may be formed as a rivet, a screw, or the like, and may have some axial extension above the first plane of the first region when installed into the electrolyte filling hole. Hence, in preferred aspects, and to reliably ensure that the third region provides a stable resting surface, the spacing between the first plane and the third plane may be configured to be equal to or greater than the axial protrusion of the sealing cap. In this way, the sealing cap may not risk disturbing the balance of the cell when the cell is placed into an installation (e.g., a module) or placed onto a surface.

[0034] Preferably, the lid is welded directly to the cylindrical casing (which may also be referred to as simply the ‘casing’ herein). For example, an axially outermost lip of the casing may be bent or folded over a periphery of the lid and welded thereto. In some examples, a beading groove may be formed at the open end of the casing, and the lid may rest on the beading groove. In a particular example, the lid further comprises a fourth region surrounding the third region adapted to attach to the cylindrical casing to thereby close the open end of the cylindrical casing with the lid. Preferably, the lid is attached to the casing without the introduction of any gasket, e.g., using welding such as laser welding.

[0035] 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.

[0036] The fourth region extends in a fourth plane axially between the first plane and the third plane. In this way, the third region may form a protruding lip relative to the second and fourth regions, which may advantageously serve as a ‘pick-up’ feature, i.e., allowing appropriately configured tools to grip onto the lip. In another example where the fourth region or another region extends axially beyond the third region, it will be appreciated that this other region may preferably be configured to form a flat surface for resting the cell on and / or configured with a ‘pick-up’ feature, as discussed above in connection with the third region.

[0037] 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.

[0038] 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.

[0039] Brief Description of the Drawings

[0040] 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:

[0041] Figure 1 schematically shows a longitudinal sectional view of an example secondary cell;

[0042] Figure 2A schematically shows a longitudinal sectional view of a portion of a secondary cell having a lid closure according to an example implementation of the present disclosure;

[0043] Figure 2B shows a magnified section of the lid closure shown in figure 2A;

[0044] Figure 2C shows a top view of the lid closure shown in figure 2A;

[0045] Figure 2D schematically shows a longitudinal sectional view of a portion of a secondary cell having a lid closure according to an example implementation of the present disclosure; Figures 3A and 3B show alternative groove profiles for a vent, according to example implementations of the present disclosure;

[0046] Figure 4 schematically shows a current collector disc according to an example implementation of the present disclosure;

[0047] Figure 5 schematically shows a current collector disc according to an example implementation of the present disclosure;

[0048] Figure 6 shows a battery pack according to an aspect of the present disclosure; and

[0049] Figure 7 shows a vehicle according to an aspect of the present disclosure.

[0050] Detailed Description

[0051] 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.

[0052] 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.

[0053] Figure 1 schematically shows a cross-sectional view of a cylindrical secondary cell 100.

[0054] The cylindrical secondary cell 100 (also referred to as simply the ‘cell 100’) comprises an electrode assembly (or ‘roll’) 102 housed in a cylindrical casing 104. The electrode roll 102 may be formed of an anode sheet, a cathode sheet, and a separator sheet arranged there between to thereby enable a storage of electrical energy. Cathode tabs 102a may extend from a first end of the electrode roll 102 and anode tabs 102b may extend from the other end, or vice versa. The cathode tabs 102a and anode tabs provide connective surfaces to which current collectors 106 can be connected. As used here, the "tabs" 102a and 102b can be uncoated portions of the electrode foil extending from the electrode roll 102, rather than additional tabs connected to the electrode roll 102. Hence, the illustrated cell 100 may be referred to as a ‘tabless’ cell due to the absence of ‘additional’ tabs.

[0055] The cylindrical casing 104 extends along an axis between a first end 104t, which may be referred to as a ‘top end 104t’, and a second end, which may be referred to as a ‘bottom end 104b’. It will be appreciated that the labels ‘top’ and ‘bottom’ are arbitrary, and correspond to the illustration, but may aid in the understanding of the present disclosure.

[0056] The bottom end 104b is an open end of the casing 104 closed by a lid 200. The closure of the casing 104 may comprise a clamped closure or a welded closure, depending on the implementation.

[0057] For example, the casing 104 may further comprise a beading groove 104p, as disclosed in Fig. 2D formed in the side wall 104s. Hence, between the beading groove 104p and the edge of the side wall 104s towards the bottom end 104b of the casing 104, a clamping portion can be formed. A lid gasket (not shown) may then be clamped around the lid 200 in the clamping portion to thereby seal the open bottom end 104b of the casing 104. Providing a clamped closure in this way is well known in the art and can provide a reliable waterproof seal for the cell.

[0058] As another example, the lid 200 may be welded to the casing 104 to thereby seal the casing 104. The lid 200 may be additionally welded to a current collector disc 300 or, in other examples, the lid 200 may act as a current collector itself and be attached (e.g., welded) to the tabs of the electrode assembly 102. Providing a welded closure in this way may advantageously remove the number of components of the cell 100 and / or the number of process steps required to manufacture the cell 100. In preferred embodiments of the present disclosure, the lid 200 is welded to the casing 104 and the current collector disc 300.

[0059] The cathode current collector 106 is arranged in direct electrical contact with the cathode tabs 102a and an anode current collecting plate 108 is arranged in direct electrical contact with the anode tabs 102b. Here, the labels ‘cathode’ and ‘anode’ may be swapped. Thus, an electrical connection is formed from the cathode tabs 102a to a terminal assembly 110, as the terminal assembly 110 is connected to the current collector 106.

[0060] An electrical connection is also formed from the anode tabs 102b to the lid 200 and / or the casing 104, either directly or through connection of the anode current collecting plate 108 to the casing 104, e.g. in the clamping portion or by welding. One or both or the current collectors 106, 108 may be formed as a disc, a plate, or have some other shape.

[0061] A gasket 112 is arranged around the terminal assembly 110 and configured to electrically insulate the terminal assembly 110 from the casing 104. The gasket 112 additionally forms a substantially fluid-tight (i.e., gastight) seal for the opening 104o in the casing 104 through which the terminal assembly 102 is arranged.

[0062] At either end of the cell 100, the cell 100 may further comprise a vent for venting gases, for example during a failure of the cell. Moreover, the cell may comprise an additional through-hole in the lid, for filling the cell 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. Example implementations of such a vent and an electrolyte filling hole are discussed in connection with later figures.

[0063] It is seen that a head of the terminal assembly 110 serves as an external terminal of the cell 100, this being a positive terminal in this example, and the casing 104 serves as the negative terminal. Hence, it is seen that both terminals of the cell 100 are accessible at the same side. The top end 104t of the casing 104 comprises a first electrical contact surface extending in a first plane, and the head of the terminal assembly 110, such as a rivet, 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.

[0064] Figures 2A, 2B, and 2C schematically show cross-sectional views of a bottom end portion of the cell 100 shown in figure 1. The illustrated bottom end 104b of the casing 104 is shown upside down in figure 2A, relative to figure 1 , and the configuration of the lid 200, the current collector disc 300, and the casing 104 are shown in more detail in this illustrated example.

[0065] Protruding from the electrode roll 102 are the electrode tabs 102b, which may be uncoated portions of electrode. A current collector disc 300 is arranged in direct electrical contact with the tabs 102b. An example of the current collector disc 300 is disclosed in Fig. 4. Specifically, an electrode contact portion 302 of the current collector disc 300 is in direct electrical contact with the tabs 102b. The electrode contact portion 302 extends in an electrode contact plane PE.

[0066] The lid 200 closes the open bottom end 104b of the casing 104, and the current collector disc 300 is further connected to the lid 200 via a lid contact portion 304. The lid contact portion 304 is annular. The current collector disc 300 has a central axis A. The lid contact portion 304 is arranged at the periphery of the current collector disc 300, i.e. the lid contact portion 304 is a peripheral lid contact portion 304. The lid contact portion 304 extends in a lid contact plane PL. The electrode contact plane PE is displaced in a first direction from the lid contact plane PL.

[0067] A connecting portion 306 connects the lid contact portion 304 and the electrode contact portion 302. The connecting portion 306 comprises a flange 306a. The flange 306a extends along a flange axis B in a longitudinal section. The longitudinal section also comprises the central axis A. The flange axis B extends in a flange angle a in relation to the central axis A. The flange angle a is 0 to 40 degrees, such as 10 to 30 degrees. A low flange angle stiffens the current collector disc, but a too low flange angle may affect logistics and manufacturing negatively. Therefore, a flange angle of 10 to 30 degrees is preferred. The connecting portion 306 may comprise a plurality of flanges 306a, such as 2 to 8 flanges 306a, such as 3 to 6 flanges 306a.

[0068] The electrode contact portion 302 comprises a plurality of tongues 302a. The number of tongues 302a in the plurality of tongues 302a is 2 to 8, such as 3 to 5. Additionally, the electrode contact portion 302 comprises at least one spoke 302b. The number of spokes 302b of the plurality of spokes 302b is 2 to 16, such as 2 to 10, such as 2 to 8. The plurality of spokes 302b connect centrally in a central plate 302c. The spokes 302b are arranged in between the tongues 302a and follow the contours of the tongues 302a. In this way slits 302d. The central plate 302c is provided with a centrum hole 302e. The central axis A runs through the centrum hole 302e. Each of the at least one flange 306a connects to at least one of the plurality of tongues 302a. The spokes 302b may be provided with first weakenings 302f, as disclosed in the embodiment of Fig. 5. The first weakenings 302f may be in the form of grooves or width tapers. The first weakenings 302f aid eject during lid rupture. In addition, the spokes 302b may be provided with second weakenings 302g. The second weakings 302g may also be in the form of grooves or width tapers. The second weakenings 302g are dimensioned to be more robust than the first weakenings 302f. This may be achieved by configuring the first weakenings 302f with smaller dimensions, such as deeper grooves and / or greater width tapers. In this way, the second weakenings 302g serve to bend the spokes 302b outwardly after the first weakenings 302f ruptures.

[0069] The lid 200 comprises a plurality of regions 201 , 202, 203, and 204. Figure 2B shows an enhanced view of the left side of the lid 200 as shown in figure 2A, and figure 2C shows a top view of the lid 200 shown in figure 2A.

[0070] As shown most clearly in figure 2C, in this example, each of the regions 201 , 202, 203, and 204 is circular and concentric with each other. The lid 200 comprises a first region 201 extending in a first plane 204 (the planes 204, 205, 206 being shown most clearly in figure 2B), a second region 202 surrounding the first region 201 and extending in a second plane 205 displaced in a first direction (i.e., upwards, as shown in figure 2B) from the first plane 201, a third region 203 surrounding the second region 202 and extending in a third plane 206 displaced in the first direction from the second plane 202.

[0071] The first region 201 comprises an electrolyte filling hole 246 and the second region 202 comprises a plurality of vents 240 configured to vent gases from the cylindrical casing 234, although in some examples the second region 202 may only comprise one vent 240. As shown in figure 2A, the electrolyte filling hole 246 is sealed by a sealing cap 248, which may be formed as a blind rivet or the like. The distance D3 between the first plane 204 and the third plane 206 may be configured to correspond to the height H of the sealing cap 248 when it is installed in the electrolyte filling hole 246, or the distance D3 may be configured to be greater than the height H of the sealing cap 248.

[0072] It can be seen that the third region 203 forms a flat axially outermost surface, and thus the cell 2000 may be stably and safely rested on the surface formed by the third region 203 without risking damage to the vent 240 or the electrolyte filling hole 246, which are recessed relative thereto, and the height H of the sealing 248 does not risk extending beyond this resting surface, i.e., the surface in the third plane 206.

[0073] The lid 200 further comprises a fourth region 204 around the third region 203, where the fourth region 204 extends in a fourth plane axially spaced in a second direction opposite the first direction from the third region 203.

[0074] In this way, the third region 203 - or, more particularly, the interface surfaces between the third region and second and fourth regions 202, 204 - forms a ‘pick-up’ feature, whereby an appropriately configured tool such as a gripper tool or the like can grip the protrusion formed around the third region 203. It can further be seen that, by spacing the vents 240 from the third region 203, a risk of damage to the vents 240 by a gripper tool can also be mitigated.

[0075] Moreover, by recessing the fourth region 204 relative to the third region 203, the flange at the end 234b of the casing 234 can be arranged thereover and welded thereto, e.g., via a welding laser directed from the top down, as shown in figure 2A. It can be seen that, were the fourth region 204 not recessed relative to the third region 203 in this way, then the first region 201 may extend further into the internal volume of the cell 200, thereby risking a reduction of the energy density of the cell, e.g., as the height of the electrode roll 232 may have had to have been reduced accordingly.

[0076] Example welding locations W1 and W2 are shown in figure 2A. A first weld W1 may attached the lid contact portion 304 of the current collector disc 300 to the lid 200, and a second weld W2 may attach the casing 104 to the lid 200. As shown in the figure, the welding direction of both the welds W1 and W2 (e.g., direction of a welding laser) are substantially aligned with the axial extension of the cell 100, i.e., the welding is from ‘above’ in respect of the orientation of the figure. Specifically, in this example, the bottom end 104b of the casing 104 comprises a flange extending radially inwards at substantially 90 degrees (which may be folded), wherein the flange overlaps the first weld W1 between the current collector disc 300 and the lid 200. The second weld W2 is further towards the radial center of the lid 200 and may extend in a circular manner around the flange, the overlap of the flange with the lid 200 being shown as a dashed line in figure 2C. In this way, the first weld W1 is covered by the folded-over flange of the casing 104.

[0077] In some examples, the second weld W2 may be radially further from the center than the first weld W1 , or the second weld W2 may be aligned axially with the first weld W1 , i.e., such that the welds W1 and W2 are on top of each other. In further examples, both the first weld W1 and the second weld W2 may be performed simultaneously (e.g., with welding heat penetrating through the flange, then the lid 200, to the current collector disc 300. However, in preferred examples, the second weld W2 is radially further in than the first weld W1 , thereby protecting the first weld W1 location from corrosion. Moreover, in preferred examples, the first weld W1 and the second weld W2 are at least radially spaced apart from each other (i.e., not overlapping) such that the lid 200, the current collector disc 300, and / or the casing 104 are not excessively heated, which could damage these components or surrounding components.

[0078] As disclosed in Fig. 2D, the second weld W2 may connect the lid 200 to a beading 104p in the casing 104. The casing may anyhow be crimped above the lid 200. Herein, there may be no gasket between the lid 200 and the casing 104.

[0079] In this preferred example, the first region 201 has an outer radius R1 of 6 mm, the second region 202 has an outer radius R2 of 14 mm, the third region 203 has an outer radius R3 of 17.5 mm, and the outer radius of the fourth region 204 substantially defines the outer radius of the cell 2000, which may be 23 mm.

[0080] The transitions between the regions 201 , 202, 203, and 204 are shown in figure 2C as having no radial extension. However, as shown in figures 2A and 2B, it will be understood that these transition portions may have some radial extension, and may comprise straight and / or curved surfaces, depending on the implementation and / or, for example, the means used to manufacture the lid 200.

[0081] Preferably, the transition portions between the regions 201, 202, 203, and 204 are configured to use a minimal amount of material, and such that the material thickness of the lid 200 is consistent throughout (e.g., by including some radius allowance at the bends).

[0082] The lid contact portion 304 of the current collector disc 300 is shown contacting the inner surface of the fourth region 204 of the lid 200, but not contacting the casing 104. The downward pressure of the lid 200 against the lid contact portion 304 may assert an axial pressure on the connecting portion 306, and the lid contact portion 304 may, in such cases, be prohibited from sliding radially outwards, preventing contact with the casing 104 even high axial loads on the cell 100.

[0083] By contacting the lid 200 outside of the first, second, or third regions 201, 202, 203, these regions 201 , 202, 203 may not require configuration to accommodate such contact with the current collector disc 300. Hence, a greater design freedom is afforded to these regions 201, 202, 203 of the lid 200. Moreover, by contacting the lid 200 towards a periphery thereof, wherein the end 104b of the casing 104 is also folded over the periphery, a welding of the casing 104 to the lid 200, and the lid 200 to the current collector disc 300, may be streamlined. Moreover, both of these welding processes may be performed using a laser welding process directed from above (as shown in figure 2A).

[0084] Figure 2C shows three vents 240 arranged in a radially symmetric fashion around the second region 202. 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 100 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 non-weakened portion 240b.

[0085] Figure 3A shows an example profile for the vent 240 shown in figures 2A, 2B, and 2C. The vent 240 is formed as a first groove 240a in the outer surface of the lid 200, and a second groove 240b in the inner surface of the lid 200. Both the grooves 240a and 240b have a substantially trapezoidal shape.

[0086] Figure 3B shows an alternative profile for the vent 240, which may be provided instead of or in addition to the profile shown in figure 3A. That is, in some examples, some vent(s) may be formed with the profile shown in figure 3A, and some may be formed with the profile shown in figure 3B.

[0087] The vent 240 shown in figure 3B comprises a primary groove 240c formed in the outer surface of the lid 200, and a secondary ‘sub-groove’ 240d extending deeper into the outer surface of the lid 200 that the primary groove 240c. No groove is formed in the inner surface of the lid 200, in this example. Both the primary groove 240c and the secondary groove 240d have a substantially trapezoidal shape. The trapezoidal shape of the secondary groove 240d is smaller in height and width than that of the primary groove 240c, and is centered therein.

[0088] The configuration of the grooves 240c, 240d shown in figure 3D may be easier to manufacture than the grooves 240a and 240b shown in figure 3A, may further provide a more reliable venting action.

[0089] Figure 6 shows a perspective view of a battery pack 500 with a portion of its casing (being illustrated in a purely schematic way) cut away to schematically show a plurality of secondary cells 100 housed therein. The secondary cells 100 may correspond to the secondary cell 100 described above and may comprise a lid closure substantially as described above. The secondary cells 100 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 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 (which may be on the same side, as discussed in relation to figure 1) can be accessed at a same side.

[0090] Figure 7 schematically shows an example vehicle 600 comprising the battery pack 500 shown in figure 5. In this example, the battery pack is arranged at a lower portion of the vehicle 600, which may be an electric or hybrid vehicle. Other uses for the battery pack 500 may comprise a standalone battery pack for powering devices or installations or the like.

[0091] 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.

[0092] 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

C L A I M S1. A current collector disc (300) with a central axis (A) for a cylindrical secondary cell (100), said current collector disc (300) comprising: a peripheral lid contact portion (304), extending in a lid contact plane (PL); an electrode contact portion (302), extending in an electrode contact plane (PE), said electrode contact plane (PE) being displaced in a first direction from the lid contact plane (PL); a connecting portion (306), connecting the lid contact portion (304) and the electrode contact portion (302); wherein the connecting portion (306) comprises at least a flange (306a) extending along a flange axis (B) in a longitudinal section comprising the central axis (A), said flange axis (B) extending in a flange angle (a) in relation to the central axis (A), wherein the flange angle (a) is 0 to 40 degrees.

2. The current collector disc (300) according to claim 1 , wherein the flange angle (a) is 20 to 35 degrees.

3. The current collector disc (300) according to claim 1 or 2, wherein the peripheral lid contact portion (304) is annular.

4. The current collector disc (300) according to claim 1 , 2, or 3, wherein the electrode contact portion (302) comprises a plurality of tongues (302a).

5. The current collector disc (300) according to claim 4, wherein the number of tongues (302a) in the plurality of tongues (302a) is 2 to 8.

6. The current collector disc (300) according to any of the preceding claims, wherein the electrode contact portion (302) comprises at least one spoke (302b).

7. The current collector disc (300) according to claim 6, wherein the number of spokes (302b) is 2 to 16.

8. The current collector disc (300) according to any one of claims 6 or 7, wherein the plurality of spokes (302b) connect centrally in a central plate (302c).

9. The current collector disc (300) according to claim 10, wherein the central plate (302c) comprises a centrum hole (302e) and the central axis (A) runs through the centrum hole (302e).

10. The current collector disc (300) according to any of the preceding claims, wherein the connecting portion (306) comprises 2 to 8 flanges (306a).11 . A cylindrical secondary cell (100), comprising: a cylindrical casing (104) housing an electrode assembly (102); a lid (200) for closing an open end of the cylindrical casing (104); a current collector disc (300) in between the electrode assembly (102) and the lid (200).

12. The cylindrical secondary cell (100) according to claim 11 , wherein the lid comprises: a first region extending in a first plane, wherein the first region comprises an electrolyte filling hole; a second region surrounding the first region and extending in a second plane displaced in a first direction from the first plane, wherein the second region comprises a vent configured to vent gases from the cylindrical casing; and a third region surrounding the second region and extending in a third plane displaced in the first direction from the second plane.

13. The cylindrical secondary cell (100) according to claim 11 or 12, wherein the current collector disc (300) does not contact the cylindrical casing.

14. A battery pack (500) comprising a plurality of cylindrical secondary cells (100), wherein at least one of the plurality of cylindrical secondary cells is a cylindrical secondary cell according to any one of claims 11 to 13.

15. A vehicle (600) comprising the battery pack (500) according to claim14.

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