TECHNICAL FIELD

The present disclosure generally pertains to cylindrical secondary cells and more precisely to a lid for such a cell, where the lid comprises a vent feature.

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 a one aspect of the present disclosure, a cylindrical secondary cell lid for a cylindrical secondary cell is provided. The cylindrical secondary cell lid comprises a groove or notch configured to provide an opening in the cylindrical secondary cell lid if a pressure to which the cylindrical secondary cell lid is subjected reaches a threshold value, the groove or notch comprising a center portion that at least partially encircles a center of the cylindrical secondary cell lid, and a radial portion that extends from the center portion towards a circumferential edge of cylindrical secondary cell lid. The groove or notch may be referred to as a vent feature.

Such a grove or notch may provide a particularly safe secondary cell as the threshold pressure may be well defined, and as the opening or vent opening may be sufficiently large to provide an efficient venting.

The vent opening may be sufficiently large to allow an electrode roll that is arranged inside the cylindrical enclosure to pass there through. Thus, should the pressure inside the cell reach a threshold value, the electrode roll may be released or ejected out of the cell through the opening formed in the lid.

According to another aspect, there is provided a cylindrical secondary cell comprising an enclosure with an open end and the above described cylindrical secondary cell lid.

According to a further aspect, there is provided a cylindrical secondary cell comprising an end comprising a groove or notch configured to provide an opening in the cylindrical secondary cell end if a pressure inside the cylindrical secondary cell reaches a threshold value, the groove or notch comprising a center portion that at least partially encircles a center of the cylindrical secondary cell end, and a radial portion that extends from the center portion towards a circumferential edge of the cylindrical secondary cell end.

The lid may be configured to be arranged in direct electrical contact with an electrode roll that is arranged inside the cylindrical enclosure. The lid alone may thus provide an electrical contact between the electrode roll and the cylindrical enclosure. The groove or notch may consist of one center portion and two radial portions.

According to a further aspect of the present disclosure, a battery system comprising the herein described cylindrical secondary cell is provided. According to a further aspect, a vehicle comprising the herein described cylindrical secondary cell is provided. 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 1 shows a cylindrical secondary cell lid,

Figure 2 is a schematic cross-section of a cylindrical secondary cell lid with the cylindrical secondary cell lid of figure 1, and

Figures 3 to 8 disclose alternative embodiments of the cylindrical secondary cell lid 1.

DETAILED DESCRIPTION

Embodiments of the present disclosure will now be described more fully hereinafter. The invention may, however, be embodied in many different forms 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.

Figure 2 shows a cylindrical secondary cell 10 (hereinafter referred to as cell) in a cross- sectional side view. In the exemplified embodiment, the cell 10 is circular cylindrical. The cell 10 comprises a cylindrical enclosure 11, and has a first end (or first enclosure end) 10a, an opposite second end (or second enclosure end) 10b and a sidewall (or enclosure sidewall) 10c that extends between the ends 10a, 10b.

In the exemplified embodiment, the first and second ends 10a, 10b are circular. The sidewall 10c is circular cylindrical. The cell 10, and thus its sidewall 10c, may be elongate and extend along a longitudinal axis (Z-axis in figure 1). The ends 10a, 10b may extend in planes (XY- planes in figure 2) that are perpendicular to the longitudinal axis.

As is illustrated, the first end 10a, or first enclosure end side (top side in figure 2), may be closed and formed in one piece with the sidewall 10c. The second end 10b may be open and a separate cylindrical secondary cell lid 1 (hereinafter referred to as lid) may, as shown, be attached to the cylindrical enclosure 11 at the open end 10b. Thus, the lid 1 may form the second enclosure end side (bottom side in figure 2). Alternatively, both ends sides may be formed by respective lids.

Now, the lid 1 comprises, as is shown in figures 1 and 3 to 8, a groove or notch 2 for providing an opening in the lid 1 if a pressure to which the lid 1 is subjected, i.e. a pressure inside the cell 10, reaches a threshold value. In such a situation, gas and/or other ejecta may be released out of the cell 10 through the opening formed in the lid 1. The opening formed in the lid 1 as a result of the groove or notch 2 breaking may be referred to as a vent opening. The groove or notch 2, may alternatively be referred to as a groove pattern or a notch pattern.

The groove or notch 2 (hereinafter groove) forms a breakable portion and may be a thinning (see figure 2) of the lid material that is configured to break before other parts of the lid 1 (and the cylindrical enclosure 11). In the current embodiments, the groove 2 (or groove pattern) is arranged in flat portions of the lid 1, i.e., in portions of the lid that extend in a plane (XY-plane in figures 1 and 2) that is perpendicular to the longitudinal axis of the cell 10. Said plane may be referred to as a first plane pl or groove plane (indicted in figure 2). The lid 1 may, as is shown, form an outer surface of the cell 10.

The groove 2 comprises a center portion 2c and a radial portion 2r. As is illustrated, the center portion 2c at least partly encircles a center, or midpoint, of the lid 1. As is also illustrated, the radial portion 2r extends from the center portion 2c towards the circumferential edge of lid 1. The radial portion 2r may be straight. The radial portion may extend essentially all the way to the circumferential edge of lid 1. Typically, the radial portion extends from the center portion 2c and ends at a distance from the circumferential edge of lid 1. Said distance may correspond to 1 to 10 percent of the lid radius, or typically 2 to 6 percent of the lid radius.

Should the pressure within the cell 10 increase, the lid 1 is expected to typically first break at the center portion 2c of the groove 2. The center portion 2c may encircle a relatively large area, such that the pressure generates a relatively large force on the center portion 2c. For example, the radius of the center portion may be 30 to 40 percent of the lid radius. Further, the center portion 2c may encircle an area that is positioned immediately adjacent an electrolyte channel or void (not shown) formed through the below-described electrode roll 20. In an axial view, the center portion 2c may at least partially encircle said electrolyte channel or void. The center portion 2c may thus ensure that the groove 2 breaks at the desired threshold pressure, such that the vent opening is reliably formed.

As the radial portion 2r extends from the center portion 2c, the break or rupture that started at the center portion 2c is expected to propagate along the radial portion 2r. The radial portion 2r may thus ensure that a sufficiently large, and thus reliable, vent opening is formed. The center portion 2c and the radial portion 2r may be configured such that breaking the radial portion 2r may be facilitated or initiated by the center portion 2c breaking. For example, the center portion 2c may be connected to the radial portion 2r. The groove pattern 2 that comprises the center portion 2c and the radial portion 2r may be continuous.

As is illustrated in figure 4, a propagation of the rupture from the center portion 2c to the radial portion 2r may be facilitated by the connection between the center portion 2c and the radial portion 2r being rounded. In other words, there may be an in-plane smooth (or rounded) transition from the center portion 2c to the radial portion 2r.

Even though a connection between a center portion 2c and a radial portion 2r is believed beneficial, a rupture may propagate from a center portion 2c to a radial portion 2r also should the portions be adjacent rather than connected. By adjacent is meant that there is a distance between the center portion 2c and the radial portion 2r. Said distance may be small. The distance may for example correspond to approximately 1 to 2 percent of the lid 1 diameter.

Figure 1 illustrates a lid 1 that comprises a circular center portion 2c. In this embodiment, the center portion 2c is a complete circle. Six radial portions 2r extend from the center portion 2c. The radial portions 2r are all connected to the center portion 2c. The radial portions 2r are angularly equidistantly distributed. The angle between each radial portion is thus 60 degrees. The groove pattern 2 of figure 1 essentially resembles a sun emoji. Figure 1 further illustrates six below-described recessed contact portions 3.

Figure 3 illustrates an embodiment similar to the one of figure 1 but without recessed contact portions 3. Figure 4 illustrates an embodiment where the groove 2 (or groove pattern) consists of one arcshaped center portion 2c and two radial portions 2r. The center portion 2c extends around approximately 300 degrees of the 360 degrees lid circumference. In other embodiments, the center portion 2c may extend around for example 200, 240 or 300 degrees.

In figure 4, the center portion 2c comprises a first end 2cl and a second end 2c2. Thus, these ends 2cl, 2c2 are the ends of the arc-shaped center portion 2c. The first end 2cl is connected to a first one 2rl of the two radial portions 2r. The second end 2c2 is connected to a second one 2r2 of the two radial portions 2r. As is shown, the transitions between the respective ends 2cl, 2c2 and the corresponding radial portions 2rl, 2r2 may be rounded.

Figure 5 illustrates an embodiment with an arc-shaped center portion 2c and three radial portions 2r. One end 2cl of the center portion is adjacent to a first radial portion 2rl . The other end of the center portion 2c is connected to a second radial portion. Essentially mid-way between the ends of the center portion 2c, the third radial portion is connected.

Figure 6 illustrates an embodiment equal to the one of figure 3, but where the center portion 2c is arc-shaped rather than a complete circle. The ends of the center portion 2c are continuous with a respective radial portion (as is the case in figure 4). The respective connections between the ends of the center portion 2c and the radial portions 2r may be rounded (see figure 4).

Figure 7 illustrates an embodiment where the groove 2 consists of one arc-shaped, or more precisely C-shaped, center portion 2c and three radial portions 2r. The center portion 2c extends around approximately 240 degrees of the lid circumference. The ends of the center portion 2c are continuous with a respective radial portion (the transition may be rounded, see figure 4). Circumferentially mid-way between the ends of the center portion 2c, the third radial portion is connected.

As is illustrated in the above embodiments, the center portion 2c may be located closer to the center of the lid 1 than to the circumferential edge of lid 1, to ensure a large vent opening.

Figure 8 illustrates an embodiment where the groove 2 comprise a center portion 2c comprising three sections, each one connected to two respective radial portions 2r. The ends of the center portion sections are continuous with a respective radial portion 2r (the transition may be rounded, see figure 4). The radially outer ends of the radial sections 2r are connected to one another by circumferential external portion 2e. The groove pattern 2 that comprises the center portion sections and the radial portions 2r is thus continuous.

During assembly, the lid 1 may for example be held or clamped towards the inner surface of the cylindrical enclosure 11 and simultaneously be secured thereto by welding, typically laser welding. In other embodiments (not illustrated), the lid 1 may be attached radially externally to the cylindrical enclosure 11 at the open end 10b. The lid 1 may, as is shown, comprise a flange to facilitate attachment to the cylindrical enclosure 11. There lid need not be welded to the cylindrical enclosure, the attachment between the lid and the enclosure is not a focus of the present disclosure.

Figure 2 illustrates a cell 10 of a type that has both a positive terminal and a negative terminal at one and the same end 10a (the top end in figure 2) of the cell 10. The first end 10a comprises a central terminal through-hole for the positive terminal. The negative terminal is electrically connected to the cylindrical enclosure 11. More precisely, the negative terminal is formed by the top surface of the cylindrical enclosure 11 that surrounds the terminal through-hole. Thus, the entire cylindrical enclosure 11 (apart from the positive terminal at the top end) may be the negative terminal. The lid 1 of the present disclosure may for example be used in the cell 10 of figure 2.

A cell 10 having both terminals at one end may bring advantages as regards electrically connecting the cell to a load. Conductors electrically connecting the terminals to the load may be positioned on the same end, the terminal end (top side in figure 2), of the cell. The opposite end, which may be referred to as the electrolyte-filling end (bottom end in figure 2), of the cell 10 may be dedicated to electrolyte filling and venting. An overpressure may be generated within the cell during operation, in particular upon malfunction of the cell or of the load connected to the cell. Such malfunction may require a release of gas and/or other ejecta out of the cell, and it may be advantageous to direct the released gas and/or other ejecta away from the conductors, i.e. at the end opposite to the terminal end.

A number of cells 10 may be positioned at a low position in an electric vehicle. The cells 10 may be arranged with the terminal ends directed upwards and the electrolyte-filling ends 10b (bottom end in figure 2) directed downwards. Upon malfunction, for example resulting from a faulty electric vehicle charger or a faulty cell 10, a release of gas and/or other ejecta from the electrolyte-filling end(s) will be advantageously directed downwards towards the ground beneath the vehicle. In other applications than vehicles, the electrolyte-filling ends may be directed towards a desired location such that any gas and/or other ejecta will not cause damages or injuries.

As is illustrated in figure 2, the cell 10 may comprise an electrode roll 20. The electrode roll 20 comprises a first and a second rolled conductive sheet 21, 22 and separating means (not shown). The separating means may also be termed separator. The conductive sheets 21, 22 and the separating means are rolled to form a circular cylindrical roll. The conductive sheets 21, 22 are coated with electrode coatings and on assembly of the cell 10, the cylindrical enclosure 11 is filled with an electrolyte. The coatings on the conductive sheets 21, 22 act as cathode and anode, respectively. The cathode, anode and electrolyte provide electrochemical energy storage. This principle is known per se, and the electrode roll 20 is commonly referred to as a jellyroll.

The rolled conductive sheets 21, 22 of the electrode roll 20 may be axially offset in relation to one another, and each conductive sheet may comprise an end section that is not coated with electrode coating. Via the non-coated end sections, the respective ends of the electrode roll may be efficiently electrically connected to a respective assigned terminal of the cell 10. This design is known per se and commonly referred to as a tabless cell.

As is illustrated in figure 2, one 22 of the rolled conductive sheets may be in electrical contact, more precisely in direct electrical contact, with the lid 1. Direct electrical contact may be referred to as physical contact.

As is clear from figures 1, 2 and 7, the lid 1 may be configured to be arranged in direct electrical contact with the rolled conductive sheet 22. Typically, the lid 1 is welded, e.g. laser welded, to the conductive sheet 22. Thus, no additional separate component needs to be arranged to make contact with the rolled conductive sheet 22.

As is shown (figures 1, 2 and 7), the lid 1 may comprise at least one recessed contact portion 3 that is configured to form the direct electrical contact with the rolled conductive sheet 22. Typically, the above-mentioned weld attaching the lid 1 to the rolled conductive sheet 22 is arranged within the at least one recessed contact portion 3.

The lid 1 may comprise a filling opening (not shown) for the above-described electrolyte filling. The filling opening may be arranged in a recessed filling portion 4, illustrated in figure 2. The recessed filling portion 4 may be arranged in, more precisely axially extend or protrude to, the same plane as the recessed contact portion 3. Said plane may be referred to as a second plane p2 or contact plane (indicted in figure 2). The filling opening may be sealed by a sealing element (not shown) such as for example a rivet, such as a blind rivet. If the filling portion 4 is recessed, the sealing element may be countersunk such that it does not protrude beyond the lid 1.

The lid 1 may be generally disc-shaped. The lid 1 may have the general shape of a circular plate. In some more detail, the lid 1 may comprise a circular disc that at the radially outer end comprises the above-described optional flange. The flange may extend from the circular disc in a direction away from the cylindrical enclosure 11 (when the lid 1 is attached to the cylindrical enclosure 11). The flange may however alternatively extend in a direction towards the cylindrical enclosure. The circular disc and the flange may be formed in one integral piece.

The recessed contact portion 3 or portions (figure 1 discloses six recessed contact portions 3 and figure 7 indicated one recessed contact portion 3) may be formed in the circular disc. The recessed contact portions 3 may be equidistantly distributed along the circumference of the lid 1. Each one of the recessed contact portions 3 may be of the same size. The recessed contact portions 3 may have essentially the same extension radially and circumferentially to facilitate welding. In other words, the recessed contact portions may have similar extensions in all direction as seen in the plane (XY-plane in figures 1 and 2) of the lid 1. The smallest extension of the recessed contact portions 3 may be at least 20 percent of the total extension of the lid.

As is illustrated in particular in figure 1, the recessed contact portions 3 may be arranged between the radial portions 2r. This may alternatively be expressed as the radial portions 2r being arranged between the recessed contact portions 3.

The recessed contact portions 3 may, as is shown in figure 2, axially extend or protrude from the first plane pl to the second plane p2. The axial position (contact plane p2) at which the recessed contact portions 3 electrically contact the electrode roll 20 may thus be axially distanced from the axial position of the groove 2 (groove plane pl). Such a design may be beneficial for rupturing the groove 2.

Referring to the figures, the lid 1 may be one-piece. The lid 1 may form a continuous surface that closes the cylindrical enclosure 11. In other words, the lid 1 may be gas-tight.

In figure 2, the material thickness of the cell 10 and the lid 1 has been exaggerated. Figure 2 further illustrates a certain (radial) gap between the cylindrical enclosure 11 and the lid 1. It is to be apprehended that in actual implementations the lid is in direct contact with the cylindrical enclosure before attachment e.g. by welding. Also, during assembly the lid 1 is brought in direct contact with the electrode roll 20, the illustrated (axial) gap between the lid 1 and the electrode roll 20 will thus be closed.

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. For example, a cylindrical secondary cell lid, or a cylindrical secondary cell end, may be provided with the groove or notch described herein without the lid or end comprising the other features of the lid described herein. Such as the recessed contact portions regions or the filling opening.

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.