SE545630C2 - A controlled ventilating terminal part for a cylindrical secondary cell - Google Patents

Abstract

This disclosure presents a terminal part (1) for a cylindrical secondary cell (100) and configured to cooperate with a burst part (10) to be positioned internally with respect to the terminal part (1). The terminal part (1) comprises a central portion (2), an annular outer portion (3), and an annular vent portion (4) arranged between the central portion (2) and the annular outer portion (3), the annular vent portion (4) comprising a number of vent holes (5, 5b) for release of gas and/or other ejecta through the terminal part (1). The terminal part (1) comprises a burst initiator (7) that is configured to abut the vent groove (11) of the burst part (10) to initiate the formation of the vent opening, wherein one burst initiator (7) is arranged to protrude into one vent hole (5b) and at least one vent hole (5) is free from a burst initiator (7). A terminal arrangement (50) is also presented.

Description

TECHNICAL FIELD The present disclosure generally pertains to secondary cells, and more particularly to a ventilating terrninal part and a terrninal arrangement for a cylindrical secondary cell.

BACKGROUND 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.

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.

Another aspect to consider is that the rechargeable batteries must be safe to use. Therefore, rechargeable batteries have at least one vent for releasing gas When the pressure inside the batteries rises above an allowed level.

A rechargeable battery, often referred to as a secondary battery, typically comprises one or more secondary cells electrically connected to each other.

SUMMARY It is in view of the above considerations and others that the embodiments of the present invention have been made. The present disclosure aims at providing highly reliable secondary cells that are efficient in manufacture. The number of components is to be reduced and the assembly thereof is to be simplified.

According to one aspect of the present disclosure, a terminal part for a cylindrical secondary cell is provided. The terminal part is conf1gured to cooperate With a burst part that is to be positioned internally with respect to the terminal part in the cylindrical secondary cell. The burst part coniprises a vent groove or notch conf1gured to provide a vent opening in the burst part if a pressure to which the burst part is subjected reaches a threshold value. The terrninal part con1prises a central portion conf1gured to forrn a terrninal of the cylindrical secondary cell, an annular outer portion for electrical connection to an electrode of the cylindrical secondary cell, and an annular vent portion arranged between the central portion and the annular outer portion, the annular vent portion coniprising a number of vent holes for release of gas and/or other ejecta through the terrninal part. The terrninal part coniprises a burst initiator that is configured to abut the vent groove of the burst part to initiate the forrnation of the vent opening, wherein one burst initiator is arranged to protrude into one vent hole and at least one vent hole is free fron1 a burst initiator.

Since the burst initiator abuts the vent groove, it will facilitate the vent groove rupturing when the pressure to which the burst part is subjected reaches a threshold value. Said pressure is typically the pressure inside the cylindrical secondary cell. The increase in pressure will cause the burst part to deforrn, in other words typically deflect towards an end of the cylindrical secondary cell. The pressure value at which the vent groove of the burst part opens n1ay be a second threshold value. The burst part is gas tight before the vent opening is forrned therein.

When the burst part deforrns, the burst initiator that is arranged on one lateral side of the vent groove, radially externally the vent groove, acts to hinder or counteract the deforrnation. At one side of the vent groove the deforrnation is hindered by the burst initiator, but at the opposite side of the vent groove the deforrnation is not hindered by the burst initiator. Thus, it follows that the shear force experience by the vent groove, which eventually results in the rupture of the vent groove, will increase by virtue of the burst initiator. In other words, the burst initiator acts to locally increase the force that the vent groove is subject to as the pressure increases, such that the vent groove is n1ost prone to rupture at the position where the burst initiator is located.

By the burst initiator abutting the vent groove to initiate the forrnation of the vent opening is n1eant that the burst initiator is positioned axially and radially in the vicinity of the vent groove. As is realised, the burst initiator need not be positioned radially immediately adj acent the vent groove, there n1ay be a certain radial distance, such as 0.5 to 2.5 n1illin1eters or typically 0.5 to 1.5 millimeters between the burst initiator (ultimate end) and the vent groove. Axially, the burst initiator is typically arranged to abut the vent groove even before any deforrnation (deflection) if the burst part. however, a certain axial play (typically below 0.5 millimeters) between the burst initiator and the vent groove is allowed.

The burst initiator of the present terrninal part brings the advantage that the pressure at which the vent opening is forrned in the burst part is more predictable.

In prior art cylindrical secondary cells there exist solutions for venting gas and/or other ej ecta through a terrninal part or a similar component. However, the required initiation pressure as well as the fluid dynamics, e.g. venting flow velocity, shape and direction may be largely stochastic. In other words, the fluid dynamics of the flow of ej ecta ventilated from prior art cylindrical secondary cells, in case of an intemal overpressure, is not well predeterrnined. Therefore, the reaction forces of the flow that affect the cylindrical secondary cell are also not well predeterrnined.

By providing a burst initiator in some, but not all, vent holes of the terrninal part an uneven flow may be obtained. For example, there may be a stronger flow through the (single) or those (plural) vent holes that is/ are provided with burst initiator(s), as compared to the vent holes that are not provided with any burst initiator. This additional advantage of the present terrninal part may lead to better predeterrnined reaction forces, which may be beneficial for complying with so-called proj ectile tests that may require the cylindrical secondary cells not moving during heat exposure. The reaction forces may be uneven such that the cylindrical secondary cell is less likely to move away (fly away like a projectile) as a result of the reaction forces. For example, the reaction force may cause the cylindrical secondary cell to spin, essentially at one place, and thus not move away.

The total area of the vent holes of the terrninal part may be relatively large and may correspond to 10 to 30 percent of the area of the terrninal part.

According to a second aspect of the present disclosure, a terrninal arrangement for a cylindrical secondary cell is provided. The terrninal arrangement comprises a terrninal part comprising a central portion configured to form a terrninal of the cylindrical secondary cell, an annular outer portion for electrical connection to an electrode of the cylindrical secondary cell, and an annular vent portion arranged between the central portion and the annular outer portion, the annular vent portion comprising a number of vent holes for release of gas and/or other ej ecta through the terrninal part. The terrninal arrangement further comprises a burst part positioned intemally with respect to the terrninal part and comprising a vent groove conf1gured to provide a vent opening in the burst part if a pressure to which the burst part is subjected reaches a threshold value. The terrninal arrangement comprises a burst initiator that is configured to abut the vent groove of the burst part to initiate the forrnation of the vent opening, wherein one burst initiator is arranged to protrude into one vent hole and at least one vent hole is free from a burst initiator. The burst initiator may be comprised in the terrninal part. The burst initiator may be an integral portion of, i.e. forrned in one piece with, the terrninal part.

The idea behind terrninal part described herein may be applicable to secondary cells more generally, as a vent arrangement. Thus, in a general aspect, the present disclosure concems a vent arrangement for a secondary cell, the vent arrangement comprising a burst part comprising a groove or notch configured to burst if a pressure to which the burst part is subjected reaches a threshold value, and a downstream part to be arranged downstream the burst part and comprising a burst initiator as described herein. The burst initiator supports the burst part on one lateral side of the groove or notch only. The downstream part may comprise a plurality of vent holes out of which only some may be provide with a burst initiator.

Advantages associated with the present disclosure, and additional conceivable features, will become clear from the following description of embodiments and examples.

BRIEF DESCRIPTION OF THE DRAWINGS The embodiments disclosed herein are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings. Like reference numerals refer to corresponding parts throughout the drawings, in which Figure l is an isometric view of a terrninal part for a cylindrical secondary cell, Figure 2 is an isometric view of a burst part for a cylindrical secondary cell, Figure 3 is a plan view of the terrninal part of figure l, Figure 4 is an axial cross-section of a first end of a cylindrical secondary cell and discloses a terrninal arrangement comprising the parts of figures l and 2, Figure 5 is an axial cross-section of a second end of the cylindrical secondary cell of figure 4, Figure 6 shows the terminal arrangement of figure 4 before completion, and also schematically illustrates a ruptured burst part, and Figures 7 to 11 show the terrninal arrangement of figures 4 and 6 in exploded View.

DETAILED DESCRIPTION Embodiments of the present disclosure will now be described more fully hereinafter. The invention may, however, be embodied in many different forrns and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those persons skilled in the art.

Figures 1 to 4, 6 and 7 show a terminal part 1 for a cylindrical secondary cell 100. The cylindrical secondary cell 100 is illustrated in the cross-sections of figures 4 and 5. As is particularly clear from figures 1 and 3, the terminal part 1 comprises a central portion 2, an outer portion 3 and a Vent portion 4 arranged between the central portion 2 and the outer portion 3. These radially separate portions 2, 3, 4 of the terminal part 1 may be concentric, as illustrated.

The central portion 2 forrns a terminal of the cylindrical secondary cell 100 (hereinafter referred to as cell) once assembled, see figure 4. By terrninal is herein meant that equipment that is powered by the cell 100 and electrically charges the cell 100 may be connected thereto via the terminal. Electrical connection to the terminal may be established by a connector (not shown) being brought in electrical contact with the terminal. Such a connector may be welded to the terminal, i.e. to the central portion 2. To facilitate establishing the connection, e. g. an automated connection, it may be adVantageous that the central portion 2 is positioned centrally on the terminal part 1. As is shown, the central portion 2 may be essentially circular.

The outer portion 3 is annular and radially surrounds the central portion 2. As is particularly clear from figure 4, the outer portion 3 is, after assembly, electrically connected to an electrode 101 of the cylindrical secondary cell 100. As will be described, the outer portion 3 is electrically connected to the electrode 101 via other components of a terrninal arrangement 50 of the cylindrical secondary cell The vent portion 4 is annular, is radially surrounded by the outer portion 3, and radially surrounds the central portion 2, see figures 1 and 3. The vent portion 4 coniprises a number of vent holes 5 for release (illustrated by upward arrow in figure 1) of gas and/or other ejecta through the terrninal part A burst part 10 to be positioned internally with respect to the terrninal part 1 in the cylindrical secondary cell 100 is shown in figures 2, 4, 6 and 8. The burst part 10, see especially figure 2, coniprises vent groove (or notch) 11 configured to provide an opening in the burst part 10 if a pressure to which the burst part 10 is subjected reaches a second threshold value. As is shown in figures 4 and 6, the burst part 10 is positioned internally the terrninal part 1. The curved, relatively thick arrows of figures 2 and 6 illustrate how the vent groove 11 ruptures. A ruptured vent groove 11 is also illustrated in figure 6 (burst part 10 shown in dashed line).

The vent groove 11 of the burst part 10 is arranged to be positioned radially within the annular vent portion 4 of the terrninal part 1, as is illustrated by the dashed line drawn between figures 1 (terrninal part) and 2 (burst part) and by the dashed line in figure 6. Thus, a release of ej ecta niay flow through the burst opening forrned in the burst part 10 (flow illustrated by hollow, upward arrow in figure 2) and axially straight through the annular vent portion 4 of the terrninal part 1 (flow illustrated by hollow, upward arrow in figure 1), niore precisely through the vent holes 5 of the vent portion The burst part 10 niay essentially have the shape of a bowl, or circular cylinder with one open end and one closed end. In other words, the burst part 10 niay coniprise a circular disc portion 12 (bowl bottoni / closed cylinder end) and a flange portion 13 (bowl or cylinder lateral sidewall), see figure 2. The disc portion 12 niay be convex, such that it protrudes (downward) in the axial direction away from to the flange portion 13, see figure In sonie detail, the disc portion 12 niay protrude axially froni the vent groove 11 to the center, i.e. the curvature of the disc portion 12 niay initiate at the vent groove 11. The center of the disc portion 12 niay be flat, see especially figure 6. In other words, the disc portion 12 niay protrude axially froni the vent groove 11 to the flat center. Thus, the circular disc portion 12 of the burst part 10 niay coniprise an annular outer section and a center, which are aligned with the radial direction of the burst part 10, and an interrnediate annular section that extends at an angle of a few degrees to the radial direction of the burst partAs is best shown in figures 1 and 3, the terminal part 1 comprises a burst initiator 7 that is configured to abut the vent groove 11 of the burst part 10 to initiate the forrnation of the vent opening. Thus, the burst initiator 7 is positioned, sized and shaped to abut the vent groove 11 of the burst part 10 to initiate the forrnation of the vent opening. The size, shape and material characteristic of the burst initiator 7 are thereby selected to be suitable for initiating the forrnation of the vent opening. As is shown, the one burst initiator 7 is arranged to protrude into one vent hole 5b, the leftmost vent hole 5b of the embodiment of figure 1. In the same embodiment, the remaining two vent holes 5 are free from any burst initiator.

Referring to figures 1 and 2 in conjunction and also to figures 5 and 6, the burst initiator abuts the vent groove 11 of the burst part 10 and will facilitate the groove 11 rupturing when the pressure to which the burst part 10 is subjected reaches the threshold value. The pressure to which the burst part 10 is subjected is the pressure inside the cylindrical secondary cell 100. As is shown, the burst initiator 7 is arranged on one lateral side (left in figures 1 and 2) of the vent groove 11 and hinders or counteract the (upward) deformation of the burst part 10, more precisely its disc portion 12, at one lateral side of the vent groove 11. Thereby, the vent groove 11 is most prone to rupture at the position where the burst initiator 7 is located as compared to the remaining circumference of the vent groove 11. The burst initiator 7 makes pressure at which the vent opening is formed more predictable, and the present the terminal part 1 may therefore be referred to as a controlled ventilating terminal part.

As is illustrated in figures 1 and 3, the burst initiator 7 may be essentially semicircular or U- shaped. The example of figure 1 discloses a semicircular burst initiator 7 whereas the example of figure 3 is better described as U-shaped. In other undepicted embodiments, the burst initiator 7 may be a polygon, such as a triangle pointing towards the vent groove 11. In both figures 1 and 3, the burst initiator 7 comprises a single, tapered distal end. The distal end may be referred to as an ultimate end or free end.

The burst initiator 7 may, as disclosed, extend as a cantilever from the annular outer portion 3 of the terminal part 1. In the current examples, the burst initiator 7 protrudes or extends into approximately the radial middle of the vent hole 5b, as best seen in the plan view of figure The illustrated burst initiator 7 comprises a proximal end that extends from the inner circumference of the annular outer portion 3. As is shown in the example of figure 3, thetransition from the inner circumference to the burst initiator 7 may be rounded to reduce mechanical stress concentrations.

In the current embodiments, the burst initiator 7 is integral with the terrninal part 1, more precisely with the annular outer portion 3 of the terminal part 1. The current terrninal part 1, including the burst initiator, is formed in one piece e. g. by stamping.

The vent holes 5 of the terminal part 1 provide a relatively large total area, i.e. a vent area, which corresponds to 10 to 30 percent of the area (ir-rz) of the terminal part 1. In one embodiment, the vent area is 13 percent of the area of the terminal part 1. In another embodiment, the vent area is 23 percent of the area of the terminal part 1. Suitable area ranges include 12 to 25 percent, 20 to 25 percent, and 20 to 30 percent. The areas are measured in a plan view of the terminal part 1, i.e. as disclosed in figure As is illustrated, the central portion 2 may be axially distanced from the outer portion 3. Therefore, the vent portion 4 that connects the central portion 2 to the outer portion 3 may extend at an angle, of for example approximately 45 degrees, to the extensions of the central 2 and outer portions 3. When assembled, the central portion 2 and the outer portion 3 are essentially aligned with, typically parallel to, the radial direction of the cylindrical secondary cell 100, whereas the vent portion 4 is generally oriented at an angle to the radial direction of the cylindrical secondary cell 100. The central portion 2 may thus protrude outwards from the outer portion 3. As is illustrated, the central portion 2 may form the axially ultimate (top) part of the cylindrical secondary cell The terminal part 1 (as well as the other components) is only schematically disclosed in the figures, but may in an actual implementation essentially be of the shape shown in figure 1. The exemplified size ratios of the portions 2, 3, 4, and the sizes of the vent holes 5, need not reflect an actual implementation. It is further noted that figures 4 and 6 illustrate sharp angles between for example the central portion 2 and the vent portion 4, but in an actual implementation these transitions are typically smooth, as shown in figure In the disclosed embodiment, the number of vent holes 5 is three. This disclosure does not exclude other number of vent holes, such as two, four or five vent holes, but three vent holesare considered beneficial. The annular vent portion 4 may then comprise three terminal bridges6 arranged between the vent holes 5, and three terminal bridges 6 may provide sufficient support to the central portion 2 While not substantially obstructing the flow through the vent portion 4. As is disclosed, the vent holes 5 and the terrninal bridges 6 may be equidistantly arranged along the circumference of the annular vent portion In the disclosed embodiment, the vent holes 5 are elongated. By elongated is meant that the vent holes 5 have a larger length, along the circumference of the annular vent portion 4, as compared to their Width, along the radial direction of the annular vent portion 4. Further, the elongated vent holes 5 comprise rounded opposite ends. The vent holes 5 may thus be essentially bean-shaped as seen in a plan view (figure 3).

The terrninal bridges 6 may, as illustrated in figure 3, comprise a Waist and radial inner and outer ends that are Wider than the Waist. Such terrninal bridges 6, Which are rounded at both ends, may be beneficial for supporting the central portion 2 and may reduce any mechanical or electrical stress concentrations. The terrninal bridges 6 mechanically and electrically connect the central portion 2 to the annular outer portion 3. As is illustrated, the terrninal bridges 6 may be dimensioned such that their circumferential extension essentially equals their radial extension.

The terrninal part 1 may be comprised in a terrninal arrangement 50, Which is best illustrated in figure 6. The terrninal arrangement 50 comprises the above-described terrninal part 1 and the burst part 10. Typically, the burst initiator 7 Will be a part of the terrninal part 1, as is shown. However, in undepicted embodiments it is conceivable to provide the burst initiator 7 as a separate component or as part of a separate component of the terrninal arrangement Referring again to figure 6, the terrninal arrangement 50 may further comprise a current interruption device 30, Which may altematively be referred to as a current collector disc. The current interruption device 30, illustrated in figure 10, comprises a central contact portion 31 and a radially separate collecting portion 33. These portions 31, 33 of the current interruption device 30 may be concentric, as is illustrated.

A groove (or notch) 32 may at least partly surround the contact portion 31, such that the contact portion 31 may be separated from the collecting portion 33 by the groove 32 rupturing, in the event that a pressure to which the burst part 10 is subjected reaches a first threshold value. The central contact portion 31 is secured to the center of the burst part 10, eg. by welding.

The in the present embodiment annular collecting portion 33 may be electrically connected to the electrode 101 of the cylindrical secondary cell 100. For example, as is schematically illustrated in figure 4, a conductor 104 in the forrn of a so-called tab may extend from the electrode 101 to the annular collecting portion 33 of the current interruption device As is shown, the annular collecting portion 33 comprises a number of flow holes 35 for release of gas and/or other ej ecta through the current interruption device 30. The flow holes 35 of the annular collecting portion 33 may be similar in shape (essentially bean-shaped) and size to the vent holes 5 of the terrninal part, at least in a plan view.

The contact portion 31, optionally including the portion of the burst part 10 that is surrounded by the groove 32, may, as is illustrated, be axially distanced from the annular collecting portion 33. In other words, the contact portion 31 may protrude axially from the annular collecting portion Referring in particular to figures 6 and 9, the terrninal arrangement 50 may further comprise a schematically illustrated insulator part 20 that is arranged between the annular collecting portion 33 of the current interruption device 30 and the burst part 10. The insulator part 20 is electrically insulating, and may altematively be referred to as an inner gasket.

The terrninal arrangement 50 may further comprise a sealing part 40 for sealing and electrically insulating the burst part 10 from a cylindrical enclosure of the cylindrical secondary cell 100. See figures 4, 6 and 11. The sealing part 40 is electrically insulating, and may altematively be referred to as an outer gasket.

The sealing part 40 is only schematically illustrated, but may essentially have the shape of a stepped, open circular cylinder, see figures 6 and 11. The sealing part 40 may comprise a first (upper) section 41 of larger diameter and a second (lower) section 42 of smaller diameter. A step 43, shaped as an annular disc, may extend between the first section 41 and the second section The diameter of the first (larger) section 41 of the sealing part 40 may essentially correspond to the diameters of the terminal part 1 and the burst part 10. The diameter of the second (smaller) section 42 may essentially correspond to the diameters of the insulator part 20 and the current interruption device 30, see figures 4 and A first (top) end of the cylindrical secondary cell 100 is illustrated in figure 4 and a second (bottom) end of the cell 100 is illustrated in figure 5. The cell 100 may be of a so-called 2170- type (radius 21 millimeters and height 70 millimeters). As is shown, the cell 100 may comprise a can 110 within which an electrode roll 103 and the terminal arrangement 50 are arranged.

The electrode roll 103 may comprise a first 101 and a second 102 electrode, optionally with a separator sheet arranged between them, that are formed into a roll in a manner known per se. Such an electrode roll 103 is often referred to as a jelly-roll. The first electrode 101 may, as illustrated, be electrically connected to the terminal part 1 and the second electrode 102 may be electrically connected to the can 110. The can 110 may comprise a bottom formed in one piece with the sidewall (figure 4), or the can bottom may be closed by a separate lid (not shown).

The order, or relative positions, of the components of the cell 100 is clear from figures 4, 6 and 7 to 11. Starting from the top (as illustrated, i.e. most downstream as seen in the ej ecta flow direction), the terminal part 1 forms the upperrnost part of the cell 100. The radially outer edge of the terminal part 1 is enclosed by the axial flange 13 of the burst part 10, which flange 13 is bent radially inwards during manufacture. Thus, the terminal part 1 may be attached to, or held by, the burst part 10. The burst part 10 is positioned below the terminal part 1, i.e. intemally the terminal part 1 after assembly.

The insulator part 20 is positioned below the burst part 10 to electrically insulate the burst part 10 from the current interruption device 30. The current interruption device 30 is positioned below the insulator part In the depicted embodiment, the terminal part 1 and the burst part 10 are positioned radially within the first section 41 of the sealing part 40 whereas the insulator part 20 and the current interruption device 30 are positioned radially within the second section 42 of the sealing partAs is apprehended e. g. from figures 1 and 6, the annular outer portion 3, including the burst initiator 7, may extend in parallel in one radial plane. The disc portion 12 of the burst part 10, including the vent groove 11, may extend in a radial plane adjacent the radial plane of the annular outer portion As is illustrated in figure 4, during manufacture an open can end (lateral sidewall) may be deforrned such that, after completion, the terminal arrangement 50 is held in place. The terminal arrangement 50 may be clamped to the can 110 by the deformation of the open can end. Thereby, the terminal arrangement 50 may seal the open end of the can 110. Thus, the terminal arrangement 50 may serve the purposes of sealing the cell 100, providing a (typically positive) terminal, and also provide a vent function.

Upon deformation of the can 110, the sealing part 40 is also deforrned. As is apprehended from figures 4 and 6, after the deformation of the can 110 (figure 4), the first section 41 of the sealing part 40, the terminal part 1 and the burst part 10 are clamped axially together by the can 110. It is to be noted that the components are illustrated at some distance from one another in figures 4 and 6. In a real implementation, the deformation of the can 110 continues beyond the illustration of figure 4, until the can 110 tightly clamps the terminal arrangement 50 and the cell 100 is sealed.

Should the pressure inside the cell 100 increase, e.g. as a result of an intemal cell malfunction or an extemal load short-circuit, the pressure will deforrn the burst part 10 such that its central portion moves (upward) in a direction away from the current interruption device 30 (axially away from the electrode roll 103). Since the contact portion 31 of current interruption device 30 is secured to the burst part 10, the contact portion 31 will move axially along with the burst part 10. As is shown e.g. in figure 4, before burst part 10 deformation the disc portion 12 of the burst part 10 and the contact portion 31 of the current interruption device 30 protrude axially toward each other.

After a certain pressure increase, at a first threshold value, the groove 32 of the current interruption device 30 will break such that the collecting portion 33 is separated from the contact portion 31. As a result, the electrode 101 is electrically disconnected from the terminal part 1. When the burst part 10 is deforrned axially toward the upper cell end 100 such that the groove 32 of the current interruption device 30 will break, the burst part 10 may change shapefrom being convex to being concave, such that is protrudes (upward) in the axial direction along with the flange portion 13, see deforrned burst part 10 indicated by a dashed line in figure 6. In some cases, the pressure increase will now stop.

In case the pressure inside the cell 100 increases beyond the first threshold Value to a second, higher, threshold value the vent groove ll of the burst part 10 will break such that the overpressure may be released through the burst part 10, see the right end of the burst part 10 indicated by the dashed line in figure 6. More in detail, the overpressure (ej ecta) will be released (flow) through the flow holes 35 of the current interruption device 30, through the opening formed in the burst part 10 and finally exit the cell 100 through the vent holes 5 of the terminal part 1. The upward arrows in figures 1 and 2 illustrated the flow through the burst part 10 and the terminal part. An additional flow path may be formed through the central opening of the current interruption device 30 formed by the ruptured groove Modifications and other variants of the described embodiments will come to mind to ones skilled in the art having benefit of the teachings presented in the foregoing description and associated drawings. Therefore, it is to be understood that the embodiments are not limited to the specific example embodiments described in this disclosure and that modifications and other variants are intended to be included within the scope of this disclosure.

Furthermore, although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Therefore, persons skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the appended claims. As used herein, the terms "comprise/comprises" or "include/includes" do not exclude the presence of other elements or steps. Furthermore, although individual features may be included in different claims (or embodiments), these may possibly advantageously be combined, and the inclusion of different claims (or embodiments) does not imply that a certain combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Finally, reference numerals in the claims are provided merely as a clarifying example and should not be construed as limiting the scope of the claims in any way.

Claims (15)

1.Claims 1.A terminal part (1) for a cylindrical secondary cell (100), the terminal part (1) being configured to cooperate With a burst part (10) to be positioned intemally With respect to the terrninal part (1) in the cylindrical secondary cell (100) and comprising a vent groove (11) configured to provide a vent opening in the burst part (10) if a pressure to Which the burst part (10) is subjected reaches a threshold value, the terrninal part (1) comprising - a central portion (2) conf1gured to forrn a terrninal of the cylindrical secondary cell (100), - an annular outer portion (3) for electrical connection to an electrode (101) of the cylindrical secondary cell (100), and - an annular vent portion (4) arranged between the central portion (2) and the annular outer portion (3), the annular vent portion (4) comprising a number of vent holes (5, 5b) for release of gas and/or other ej ecta through the terrninal part (1), Wherein the terrninal part (1) comprises a burst initiator (7) that is conf1gured to abut the vent groove (11) of the burst part (10) to initiate the formation of the vent opening, Wherein one burst initiator (7) is arranged to protrude into one vent hole (5b) and at least one vent hole (5) is free from a burst initiator (7). 2.The terrninal part (1) of claim 1, Wherein the burst initiator (7) is essentially semicircular or U-shaped or polygonal. 3.The terrninal part (1) of claim 1 or 2, Wherein the burst initiator (7) comprises a tapered distal end. 4.The terrninal part (1) of any preceding claim, Wherein the burst initiator (7) extends from the annular outer portion (3) of the terrninal part (1). 5.The terrninal part (1) of claim 4, Wherein the burst initiator (7) protrudes into approximately the radial middle of the vent hole (5b). 6.The terrninal part (1) of any preceding claim, Wherein the burst initiator (7) comprises a proximal end that extends from an inner circumference of the annular outer portion (3), Wherein the transition from the inner circumference to the burst initiator (7) is rounded. 7.The terminal part (1) of any preceding claim, Wherein the burst initiator (7) is integral With the annular outer portion (3). 8.The terrninal part (1) of any preceding claim, Wherein the number of vent holes (5, 5b) is three and one burst initiator (7) is arranged to protrude into one vent hole (5b) and the remaining two vent holes (5) are free from any burst initiator (7). 9.A terrninal arrangement (5 0) for a cylindrical secondary cell (100), the terminal arrangement (50) comprising - a terminal part (1) comprising - a central portion (2) conf1gured to form a terminal of the cylindrical secondary cell (1 00), - an annular outer portion (3) for electrical connection to an electrode (101) of the cylindrical secondary cell (100), and - an annular vent portion (4) arranged between the central portion (2) and the annular outer portion (3), the annular vent portion (4) comprising a number of vent holes (5, 5b) for release of gas and/or other ej ecta through the terminal part (1), the terminal arrangement (5 0) further comprising - a burst part (10) positioned intemally With respect to the terminal part (1) and comprising a vent groove (11) configured to provide a vent opening in the burst part (10) if a pressure to Which the burst part (10) is subjected reaches a threshold Value, Wherein the terminal arrangement (5 0) comprises a burst initiator (7) that is conf1gured to abut the vent groove (11) of the burst part (10) to initiate the formation of the vent opening, Wherein one burst initiator (7) is arranged to protrude into one vent hole (5b) and at least one vent hole (5) is free from a burst initiator (7). 10.The terminal arrangement (50) of claim 9, Wherein the vent groove (11) of the burst part (10) is positioned radially Within the annular vent portion (4) of the terminal part (1). 12. 5 14. The terminal arrangement (50) of claim 9 or 10, Wherein the vent groove (11) of the burst part (10) is positioned substantially radially centrally Within the annular vent portion (4) of the terrninal part (1). The terrninal arrangement (5 0) according to any one of claim 9 to 11 further comprising - a current interruption device (30) comprising - a contact portion (31) conf1gured to be arranged in physical contact With the burst part (10) and at least partly surrounded by a groove (32) configured to rupture if a pressure to Which the burst part (10) is subjected reaches a first threshold value and - an annular collecting portion (33) for electrical connection to the electrode (1 10) of the cylindrical secondary cell (100), the annular collecting portion (33) comprising a number of flow holes (35) for release of gas and/or other ejecta through the current collecting plate (3 0). Wherein the floW holes (35) are substantially radially aligned With the annular vent portion (4). The terrninal arrangement of claim 12, Wherein the Wherein the floW holes (35) of the current interruption device (3 0) are substantially radially aligned With the annular vent portion (4) of the terrninal part (1). The terrninal arrangement (50) of claim 12 or 13 further comprising - an insulator part (20) arranged between the annular collecting portion (33) and the burst part (10), and - a sealing part (40) for providing sealing and electrical insulation the burst part (10) from a cylindrical enclosure (110) of the cylindrical secondary cell (100). A cylindrical secondary cell (100) comprising the terrninal arrangement (5 0) according to of any one of claims 9 to 16