SE547876C2

SE547876C2 - Terminal assembly for a secondary cell

Info

Publication number: SE547876C2
Application number: SE2351242A
Authority: SE
Inventors: Kelvin Yuen; Michael Shaughnessy; Rakshith Bellary; Santhosh Sadhasivam
Original assignee: Northvolt Ab
Priority date: 2023-10-30
Filing date: 2023-10-30
Publication date: 2025-12-16
Also published as: SE2351242A1

Abstract

There is disclosed herein a terminal assembly (4) for a cylindrical secondary cell comprising a head portion (4c) configured to form an external terminal for the cylindrical secondary cell, and a shaft portion (4d) configured to axially extend into an opening of a casing of the cylindrical secondary cell. The shaft portion comprises a contact portion (4b) having a contact surface (4i) for contacting a current collector, and a deformable section (4h) arranged radially around the contact portion, configured to deform radially outwards to thereby secure the terminal assembly in the opening of the casing. A gap (4g) is formed radially between the contact portion and the deformable section, configured to allow radially outward deformation of the one or more deformable sections such that, in a deformed state, the contact portion extends axially further from the head portion than the deformable section.

Description

[0001] TERMINAL ASSEMBLY FOR A SECONDARY CELL

[0003] Technical Field

[0005] The present disclosure relates to a terminal assembly for a secondary cell, a secondary cell comprising the terminal assembly, and a method of manufacturing such a secondary cell.

[0007] Background

[0009] 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.

[0011] 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.

[0013] Summary

[0015] 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.

[0017] In particular, according to an aspect of the present disclosure, there is provided a terminal assembly for a cylindrical secondary cell comprising a head portion configured to form an external terminal for the cylindrical secondary cell, and a shaft portion configured to axially extend into an opening of a casing of the cylindrical secondary cell.

[0018] The shaft portion comprises a contact portion having a contact surface for electrically contacting a current collector of the cylindrical secondary cell, and one or more deformable sections arranged radially around the contact portion, configured to deform radially outwards to thereby secure the terminal assembly in the opening of the casing. The deformable section(s) may first extend axially, and may be deformed so as to extend radially outwards. The deformation may preferably result in the extension of the deformable section(s) substantially perpendicular to the head portion. In this way, the deformable section(s) may achieve an improved seal of the opening in the casing.

[0020] A gap is formed radially between the contact portion and the one or more deformable sections. The gap is configured, e.g., in its shaping and/or dimensions, to allow radially outward deformation of the one or more deformable sections such that, in a deformed state, the contact portion extends axially further from the head portion that the one or more deformable sections.

[0021] Hence, with a current collector of the cell may be reliably brought into contact with the contact portion first, i.e., without first contacting the deformable section(s). Indeed, an air gap may advantageously be formed between the deformable section(s) and the current collector, when the cell is manufactured. Thus, the terminal assembly can be more reliably electrically connected and/or attached (e.g., by welding) to the current collector.

[0023] The terminal assembly may be formed substantially as a rivet, such that the deformation of the one or more deformable sections may be achieved by a riveting process, in a manner understood by those skilled in the art. It will be appreciated that the riveting process may comprise a compression of at least the deformable section(s) with a shaped tool.

[0025] The gap advantageously separates the contact portion from the circumferential deformable section(s), such that the deformable section(s) may be deformed substantially independently of the contact portion. For example, the contact portion may be formed as a central cylindrical part, and the deformable portion may be formed as a peripheral cylindrical part that is concentric with the central contact portion, and extends (in the undeformed state) axially away from the head portion more than the contact portion. The gap extends axially towards the head portion by at least (or between) 0.2 to 1 millimeters and/or extends radially between the contact portion and the one or more deformable sections by at least (or between) 0.5 to 3 millimeters. In this way, a reliable deformation of the deformable portion(s) can be achieved, such that the contact portion extends further into the cylindrical cell than the deformed deformable portion(s).

[0026] It will be appreciated that, here, the gap ‘extending towards the head portion’ may be measured from an axial extreme of the terminal assembly, l.e., an axial extreme of the deformable section(s) when they are not deformed, as this may be the pertinent measurement for the ability of the gap to permit deformation of the deformable section(s).

[0027] The terminal assembly may further comprise a cut-out portion at least in the head portion, thereby forming a recessed welding surface configured to receive a welding laser. Although the portion is referred to as a ‘cut-out’ portion, it will be appreciated that the terminal assembly may be formed by, e.g., casting of metal, such that no material is cut-out to form the ‘cut-out’ portion. In an example, the head portion may be substantially formed as a cylinder or a circular plate, and the cut-out portion may be cylindrical, concentric with the head portion, and extending into the head portion to thereby form the recessed welding surface at the bottom of said cut-out.

[0028] The recessed welding surface may thus advantageously provide an area for directing a welding laser at, from the outside of the cell, such that the welding energy therefrom can be more readily communicated from the welding surface, through the contact portion, and to the contact surface, where the terminal assembly can contact a current collector and be welded thereto.

[0029] The cut-out portion preferably has a radius less than the contact portion and extends through the head portion and into the contact portion. In this way, the terminal assembly uses overall less material, and the ease of communicating welding energy from the welding surface to the contact surface is enhanced.

[0031] In further preferred examples, the material thickness between the welding surface and the contact portion is less than 1 .5 millimeters. In this way, the contact surface, which, as discussed above, will be in reliable contact with a current collector during manufacture of the cell, can be rapidly brought to a welding temperature.

[0032] The gap may extend towards the head portion axially beyond the welding surface, so as to provide a readily deformable part between the wall of the contact portion (the wall being defined by the cut-out and the gap on either side) and the deformable portion(s).

[0034] In some examples, the terminal assembly further comprises a ledge formed in the head portion, around the cut-out portion, configured to receive a cap for covering the recessed welding surface and forming, the external terminal of the cylindrical secondary cell.

[0036] Thus, even if the welding surface is damaged or made unsuitable for reliable electrical connection, or if the welding surface is substantially recessed relative to the rest of the head portion so as to make its access for connection to, e.g., a busbar difficult, the cap can act as an advantageously undamaged connection surface.

[0038] The ledge may be substantially flat, or may be shaped so as to complement a shaping of the cap (e.g., the periphery thereof). For example, the ledge may comprise a step such that the ledge is configured to receive a cap having a stepped profile.

[0040] In further examples, the terminal assembly comprises the cap, wherein the cap has a radius less than the head portion such that a radial interface is formed between the cap and the head portion when the cap is arranged on the ledge. This radial interface may advantageously allow for a welding laser to be directed thereat, to weld the cap to the head portion, rather than, e.g., attempting to penetrate the cap axially with welding energy to weld to the head portion from above. Hence, the welding energy expended during manufacture of the cell can be further reduced.

[0041] The periphery of the cap may be thinned relative to a main body of the cap. For example, the cap may have a cylindrical central region and an annular thinned region arranged around the central region. The thinning may be on one side of the cap, or equally or unequally on both sides of the cap. This thinning may further reduce the welding energy required to weld the cap to the head portion.

[0042] An underside of the head portion, i.e., the side of the head portion that is configured to face the casing of the cylindrical secondary cell when arranged in the opening thereof, may comprise an annular protrusion configured to engage with a gasket. The annular portion may be formed effectively as a ‘tooth’ that ‘bites’ into the gasket between the head portion of the terminal and the casing of the cell, so as to enhance the seal provided by the terminal assembly.

[0043] When manufacturing a secondary cell having a terminal assembly according to the previously described aspect of the present disclosure, the method comprises arranging the shaft portion of the terminal assembly through an opening in the casing of the cylindrical secondary cell, and deforming the one or more deformable sections radially outwards to thereby secure the terminal assembly in the opening of the cylindrical cell.

[0044] As mentioned above, deforming the deformable section(s) may comprise applying a riveting process to the deformable section(s). That is, the shaft portion may be arranged through the opening in the casing of the cell, and then the shaft portion (or at least the deformable section(s)) may be deformed radially outwards.

[0045] In some cases, the cylindrical secondary cell as described may be incorporated into a battery pack having a plurality of similar or different secondary cells. Such a battery back may further be incorporated into a vehicle, such as an electric or hybrid vehicle. Thus, the benefits provided by the above-described configuration of the terminal assembly may further benefit the battery pack or vehicle into which they are integrated, especially if a plurality of cells having such a terminal assembly are installed therein.

[0047] Brief Description of the Drawings

[0049] One or more example implementations of the present disclosure will be described, by way of example only, and with reference to the following figures, in which:

[0051] Figure 1A schematically illustrates a cross-sectional view of a terminal assembly according to a first example;

[0053] Figure 1B schematically illustrates a cross-sectional view of a terminal assembly according to a second example;

[0055] Figure 2A schematically illustrates a cross-sectional view of a terminal assembly, according to an example wherein the deformable sections are in the deformed state;

[0057] Figure 2B schematically illustrates a cross-sectional view of a terminal assembly, according to another example wherein the deformable sections are in the deformed state;

[0059] Figure 3A schematically illustrates a cross-sectional view of a cylindrical secondary cell having a terminal assembly similar to that shown in figure 2A, according to an example implementation of the present disclosure; and

[0061] Figure 3B schematically illustrates a close up of part of the terminal assembly and the cylindrical secondary cell of figure 3A.

[0062] Detailed Description

[0064] 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.

[0065] Furthermore, although examples 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 examples described herein.

[0067] Figure 1A schematically illustrates a cross-sectional view of a terminal assembly (or ‘terminal part’) according to a first example. The terminal part 4 in this example is a rivet which comprises a head portion 4c adapted to form an external terminal of a cylindrical secondary cell (not shown). A shaft portion 4d of the terminal part is adapted to extend through a wall of the cylindrical secondary cell.

[0068] The shaft portion 4d has a first end attached to the head portion 4c and a second end arranged to face a current collector (not shown), which may be shaped as a plate, in the cylindrical secondary cell. The shaft portion 4d comprises an outer annular deformable section 4h, which, in this view, appears as two separate sections, arranged, radially and concentrically around a cylindrical contact portion 4b.

[0070] The shaft portion 4d may, in some implementations, comprise a plurality of deformable sections/elements 4h. For example, the annular deformable section 4h shown in figure 1A may be segmented into a number of sections. The deformable elements 4h are configured to deform radially outwards, thus securing the shaft portion 4d to the cylindrical secondary cell, by securing the terminal assembly 4 to the opening of a casing of the cylindrical secondary cell.

[0071] A gap 4g is formed between the contact portion 4b and the deformable section 4h. While the terminal assembly 4 is shown in cross-section, it should be understood that the gap 4g extends radially outwards from the contact portion 4b and the deformable section 4h. The gap 4g allows for the radially outward deformation of the deformable sections 4h. For example, the deformable section may be deformed by a riveting tool or the like, which may be flat or shaped, which may, as a result of the shaping of this gap 4g, cause the deformable section 4h to deform to a point where the deformable section 4h is entirely axially above (i.e., closer to the head portion 4c) the contact surface 4i of the contact portion 4b.

[0073] Figure 1B schematically illustrates a cross-sectional view of a terminal assembly according to that of figure 1A. Figure 1B shows a terminal assembly comprising substantially similarly features as that shown in figure 1A.

[0074] Additionally, a cut-out portion 4k in the head portion 4c is shown. The cut-out portion forms a recessed welding surface 41 configured to receive a welding laser. The cut-out portion is shown as a cylindrical cut-out; however it should be understood that the shape and size of the cut-out 4k may differ depending on the intended use.

[0076] It will be appreciated that, although the term ‘cut-out’ is used here, the terminal assembly 4 may instead be formed through additive means only, e.g., casting or additive manufacturing.

[0078] Figure 2A schematically illustrates a cross-sectional view of a terminal assembly 4, wherein the deformable section 4h is in a deformed state. The terminal assembly 4 comprises a head portion 4c and a shaft portion 4d. Likenumbered components from previous figures are discussed again in detail.

[0080] In the illustrated example, the deformable section 4h is in the deformed state. The deformable section 4h deforms radially outwardly, shown as an outward bend intended to secure the terminal assembly in an opening in a cylindrical secondary cell. For example, if the opening has a certain radius, the head portion 4c may be sized to be larger than this radius, and the shaft portion 4d may be sized to be smaller than this radius, also taking into account that a gasket may be arranged around the terminal assembly 4 to assist in sealing the opening and electrically isolating the terminal assembly 4 from the casing of the cell.

[0082] When the deformable section 4h is in the deformed state, the contact portion 4b extends axially further from the head portion 4c than the deformable sections 4h. Hence, a reliable connection between the contact portion 4b and a current collector (an example of which is shown in figure 3A) can be ensured.

[0083] When installed in a cylindrical secondary cell, the deformable section 4h of the shaft 4d will be deformed radially outwardly creating a bend.

[0084] Preferably, this bend will cause the deformable section 4h to be substantially perpendicular to the head portion 4c. The contact portion 4b extends past the deformable sections 4h in an axial direction, such that the contact portion 4b can be in reliable contact with a current collector. Additionally, the bend of the deformable sections 4h will create an air space between the current collector of the cylindrical secondary cell and the deformable section 4h when assembled together. A detailed view of this is shown in figure 3B.

[0085] Figure 2A further shows a cap 4m, arranged in a ledge 4n formed in the head portion 4c. The ledge is formed around the cut-out portion 4k in the head portion 4c. The cap 4m covers the recessed welding surface 41 and forms an external terminal.

[0087] Figure 2B schematically illustrates a cross-sectional view of a terminal assembly 4, wherein the deformable section 4h are in the deformed state.

[0088] Figure 2B illustrates all features as shown in figure 2A. Figure 2B further shows a stepped ledge 4n, and wherein the cap 4m has a similarly stepped profile. The stepped profile of the ledge 4n and the cap 4m is shown with one step, however it may comprise more than one step. Further, the periphery of the cap 4m is thinned 4o, such that the periphery of the cap is substantially leveled with the head portion 4c of the terminal assembly 4, while the non-thinned part of the cap 4m is raised from the head portion 4. The cap 4m thus forms an external terminal of the terminal assembly 4 having a raised center and recessed outer periphery, allowing for more versatile electrical connections to be made to this external terminal when installing the cell into a battery pack or the like.

[0090] The cap 4m may be welded to the head portion 4c. It can be seen that the ledge 4n allows a radial interface between the cap 4m and the head portion 4c to be formed. Hence, reliable welding can be performed at this radial interface, which may allow for less welding energy to be expended relative to, for example, penetrative welding through a thickness of the cap 4m. It will be appreciated that the thinning of the cap 4m at its periphery further enhances this effect.

[0092] Figure 3 schematically shows a cross-sectional view of a cylindrical secondary cell 6000 comprising a terminal assembly formed as a rivet 600 extending through an opening 634o in the casing 634, corresponding to the example terminal assembly 4 shown and discussed in relation to e.g. figure 2B. The particulars of the terminal assembly 4 are thus not discussed again in relation to figure 3.

[0094] The cylindrical secondary cell 6000 (also referred to as simply the ‘cell 6000’) comprises an electrode roll 632 housed in a cylindrical casing 634. The electrode roll 632 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 632a may extend from a first end of the electrode roll 632 and anode tabs 632b may extend from the other end, or vice versa. The cathode tabs 632a and anode tabs 632b may provide connective surfaces to which current collector 636 can be connected.

[0096] The cylindrical casing 634 extends along an axis A between a first end 634t, which may be referred to as a ‘top end 634t‘, and a bottom end (not shown) which may be an open end of the casing 634 closed by a lid. The closure of the casing may comprise a clamped closure or a welded closure, depending on the implementation.

[0097] For example, the casing 634 may further comprise a beading groove 634g formed in the side wall 634s. Hence, between the beading groove and the end edge of the side wall towards the bottom end of the casing, a clamping portion can be formed. A lid gasket may then be clamped around the bottom lid in the clamping portion to thereby seal the open bottom end of the casing. Providing a clamped closure in this way is well known in the art and thus can provide a reliable waterproof seal for the cell.

[0098] As another example, the lid may be welded to the casing to thereby seal the casing. The lid may be additionally welded to a current collector, or the lid may act as a current collector itself and be attached (e.g., welded) to the tabs of the electrode assembly 632. Providing a welded closure in this way may advantageously remove the number of components of the cell and/or the number of process steps required to manufacture the cell.

[0099] A cathode current collector 636 is arranged in direct electrical contact with the cathode tabs 632a and an anode current collector (not shown) may be arranged in direct electrical contact with the anode tabs (also not shown). Here, the labels ‘cathode’ and ‘anode’ may be swapped. Thus, an electrical connection is formed from the cathode tabs 632a to the terminal assembly, as the terminal assembly is connected to the current collector 636.

[0100] An electrical connection may also be formed from the anode tabs to the casing 634, either directly or through connection of an anode current collector to the casing 634, e.g. in the clamping portion or by welding. One or both or the current collectors may be formed as a disc, a plate, or have some other shape.

[0101] At either end of the cell, the cell 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 casing and/or 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.

[0102] Thus, it is seen that the cap of the terminal assembly 600 serves as an external terminal of the cell 6000, this being a positive terminal in this example, and the casing 634 serves as the negative terminal. Hence, it is seen that both terminals of the cell 6000 are accessible at the same side. The top end 634t of the casing 634 comprises a first electrical contact surface extending in a first plane, and the head of the rivet 600 comprises a second electrical contact surface, extending in a second plane axially spaced from the first plane.

[0104] Arranged around the terminal assembly 600 is a gasket 642 configured to form a fluid-tight seal for the opening 634o in the top end 634t of the casing 634. The gasket 642 is arranged at least around the hollow shaft of the terminal assembly 600. The gasket 642 further extends between the head of the rivet 600 and the top end 634t of the casing 634 so as to electrically isolate the opposite terminals of the cell 6000 from each other. Thus, it can be seen that gasket 642 serves multiple purposes. The gasket 642 may be preferably formed of a polymer having elastic, resilient, and electrically insulating properties, such as PFA. In preferred examples, including that illustrated in figure 3A, the gasket 642 extends between the cap of the terminal assembly 600 and the casing 634, radially beyond the cap of the terminal assembly 600.

[0106] In some examples, the gasket 642 may be formed of separate parts, each part being specifically configured for a respective purpose. For example, for the part(s) of the gasket 642 around the opening 634o and intended to seal the opening, the gasket 642 may be formed of one material such as PFA. For the part(s) of the gasket 642 between the head of the rivet 600 and the casing 634 and intended to electrically isolate these components from each other, the gasket 642 may be formed from another material such as a PPS polymer.

[0107] The advantageous configuration of the terminal assembly 600 provides an overall lesser material mass between the welding surface and the contact surface, thus aiding in less heat throughout the terminal assembly 600, e.g., from welding. Hence, there is a reduced risk that the gasket 642 and/or the cathode tabs 632a are damaged by an excessively heated terminal assembly 600.

[0109] Figure 3B schematically illustrates a close-up of a part of the terminal assembly 600 and part of the cylindrical secondary cell. Figure 3B aids visualization of the space created between the deformable section 4h in the deformed state, and the current collector 636.

[0111] As shown in Figure 3B the contact portion 4b, extends further than the deformable section 4h in an axial direction, and is in contact with the current collector 636. The radially outward deformation of the deformable section 4h, or in other words outward bend, enables for a space to be created between the current collector 636 and the deformable section 4h, which enables air to flow in said space. Hence, ventilation is assisted and the electrical and welded connection between the terminal assembly 600 and the current collector 636 is not impeded.

[0113] 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

1. 547 876

1. A terminal unit (4, 600) for a cylindrical secondary cell (6000), comprising;

- a main part (4c) designed to form an external terminal for the cylindrical secondary cell (6000); and

- a shaft part (4d) designed to extend axially into an opening (634o) in the housing (634) of the cylindrical secondary cell, in which the shaft part (4d) comprises;

- a contact section (4b) with a contact surface (4i) for electrical contact with a current collector (636) in the cylindrical secondary cell (6000);

- one or more deformable sections (4h) placed radially around the contact section (4b), designed to deform radially outwards to thereby fix the terminal unit (4, 600) in the opening (634o) of the housing (634); and

- a gap (4g) formed radially between the contact section (4b) and the deformable sections (4h), designed to enable deformation radially outwards of the deformable sections (4h), so that the contact section (4b) in the deformed state extends axially further from the main part (4c) than the deformable sections (4h),

characterized by;

547 876

the gap (4g) extends axially towards the main part (4c) by at least 0.2 to 1 millimeter and/or therein the gap (4g) extends radially between the contact section (4b) and the deformable sections (4h) by at least 0.5 to 3 millimeters.

2. The terminal unit (4, 600) according to claim 1, wherein the terminal unit (4, 600) is mainly designed as a rivet (600).

3. The terminal unit (4, 600) conforms to any of the preceding claims, further comprising a chamfered part (4k) at least in the main part (4c), which forms a recessed welding surface (4I) designed to receive a welding laser.

4. The terminal unit (4, 600) according to claim 3, wherein the original faceted part (4k) has a radius smaller than the contact section (4b) and extends through the main part (4c) and into the contact section (4b).

5. The terminal unit (4, 600) according to claim 4, where the material thickness between the welding surface and the contact section (4b) is less than 1.5 millimeters.

6. The terminal unit (4, 600) according to claim 4 or 5, in which the gap (4g) extends axially towards the main part (4c) past the welding surface.

7. The terminal unit (4, 600) according to any of claims 3 to 6, further comprising a ledge (4n) in the main part (4c), around the original faceted part (4k), designed to receive a lock (4m) to cover the recessed welding surface (4I) and form the external terminal for the cylindrical secondary cell (6000).

547 876

8. The terminal unit (4, 600) according to claim 7, in which the landing (4n) includes a step so that the step (4n) is designed to receive a lock (4m) with a step profile.

9. The terminal unit (4, 600) according to claim 7 or 8, further comprising the lock (4m), wherein the lock (4m) has a radius smaller than the main part (4c) so that a radial interface is formed between the lock (4m) and the main part (4c) when the lock (4m) is placed on the landing (4n).

10. The terminal unit (4, 600) according to claim 9, wherein the periphery of the locket (4m) is thinner than the main part of the locket (4m).

11. The terminal unit (4, 600) according to any preceding claim, wherein the underside of the main part (4c), designed to face the housing (634) of the cylindrical secondary cell (6000) when placed in the opening (634o), comprises an annular projection designed to engage a packing (642).

12. A cylindrical secondary cell (6000), comprising;

- a housing (634) with an opening (634o); and

- the terminal unit (4, 600) according to any previous requirement is placed in the opening (634o) of the housing (634) to thereby seal said opening (634o);

wherein the deformable sections (4h) extend radially outward from the shaft part (4d); and

547 876

wherein the contact surface (4b) of the contact section extends axially further from the main part (4c) of the terminal unit (4, 600) than the deformable sections (4h).

13. A manufacturing method for the cylindrical secondary cell (6000) according to claim 12, comprising;

- placement of the shaft part (4d) of the terminal unit (4, 600) through an opening (634o) in the housing (634) of the cylindrical secondary cell (6000); and

- deforming the deformable sections (4h) radially outwards to thereby fix the terminal unit (4, 600) in the opening (634o) of the cylindrical secondary cell (6000).

14. A battery pack comprising several secondary cells, wherein one or more of these secondary cells is a cylindrical secondary cell (6000) according to claim 12.

15. A vehicle including the battery pack according to claim 14.