WO2023152388A1

WO2023152388A1 - A current collecting plate, a cylindrical secondary cell and a method of its manufacture

Info

Publication number: WO2023152388A1
Application number: PCT/EP2023/053554
Authority: WO
Inventors: Tetsuya Makino; Kenya Shatani
Original assignee: Northvolt Ab
Priority date: 2022-02-14
Filing date: 2023-02-14
Publication date: 2023-08-17

Abstract

A current collecting plate (6) for provision of electrical connection between a terminal (4, 5) and a conductive sheet electrode roll assembly (3) of a cylindrical secondary cell (1). The current collecting plate comprises an electrically conductive disc (69) having a main extension plane in two dimensions. The electrically conductive disc (69) presents at least one through hole (63) at a position intended to overlap with the conductive sheet electrode roll assembly (3). A portion of a respective closed edge (66) encircling the at least one through hole (63) presents diverging edge normals (67) in the main extension plane. Thereby a respective convex tab (62) is defined in the current collecting plate (6). A corresponding manufacturing method is also disclosed.

Description

A CURRENT COLLECTING PLATE, A CYLINDRICAL SECONDARY CELL AND A METHOD OF ITS MANUFACTURE

Technical field

The present disclosure generally relates to cylindrical secondary cells and manufacturing thereof, and in particular to a current collecting plate and its assembling into the cylindrical secondary cell.

Background

In addressing climate change there is an increasing demand for rechargeable batteries. Rechargeable batteries may for instance 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. To achieve an effective production of rechargeable batteries, the design of the batteries as well as their manufacturing process can be optimized.

A rechargeable battery typically comprises one or more secondary cells, which rechargeable battery in the context of the present disclosure also may be referred to as secondary battery.

In cylindrical secondary cells, a conductive sheet electrode roll assembly is typically provided as the part having energy storing capacity. Typically, an electrically connecting part, e.g. a current collecting plate, is used to connect tabs of the conductive sheet electrode roll assembly to a terminal part accessible from the outside of the cylindrical secondary cell. The mechanical mounting of such electrically connecting parts and the electrical securing of such electrically connecting parts to the tabs of the conductive sheet electrode roll assembly present an abundance of problems related to e.g. mechanical precision, heat and current distribution and ease of handling.

There is thus a need for further improvements in such respects.

It is an object of the disclosure to propose designs of current collecting plates and methods for their mounting in cylindrical secondary cells that improves an efficient assembling thereof.

In general words, according to a first aspect, there is provided a current collecting plate for provision of electrical connection between a terminal and a conductive sheet electrode roll assembly of a cylindrical secondary cell. The current collecting plate comprises an electrically conductive disc having a main extension plane in two dimensions. The electrically conductive disc presents at least one through hole at a position intended to overlap with the conductive sheet electrode roll assembly. A portion of a respective closed edge encircling the at least one through hole presents diverging edge normals in the main extension plane. Thereby a respective convex tab is defined in the current collecting plate.

In a second aspect, a cylindrical secondary cell comprises an electrode roll assembly having a conductive sheet, and a current collecting plate according to the first aspect. At least the convex tab of the current collecting plate is configured to be arranged in direct electrical contact with the conductive sheet.

In a second aspect, a method of manufacturing a cylindrical secondary cell comprises providing of a current collecting plate having at least one through hole in an electrically conductive disc having a main extension plane in two dimensions. A portion of a respective closed edge encircling the at least one through hole presents diverging edge normals in a main extension plane of the current collecting plate. A, respective convex tab is thereby defined in the current collecting plate. An electrode roll assembly having a conductive sheet is provided. The current collecting plate is arranged in direct electrical contact with the conductive sheet for covering an end of the electrode roll assembly. The current collecting plate is attached to the electrode roll assembly at least by the convex tab.

One advantage with the proposed technology is that a more reliable contact between the current collecting plate and the electrode roll assembly can be achieved. Other advantages will be appreciated when reading the detailed description.

Brief description of drawings

The above and other aspects of the present invention will now be described in more detail, with reference to the appended figures.

FIG. 1 illustrates an example of a cylindrical secondary cell.

FIG. 2 illustrates, in cross-section, a first end of an example of a cylindrical secondary cell.

FIG. 3 illustrates, in cross-section, a first end of another example of a cylindrical secondary cell.

FIG. 4 illustrates, in cross-section, a second end of an example of a cylindrical secondary cell.

FIG. 5 illustrates schematically an example of a connection between a current collecting plate and a conductive sheet.

FIG. 6 illustrates schematically another example of a connection between a current collecting plate and a conductive sheet.

FIG. 7 illustrates schematically an example of a connection between a current collecting plate, having a convex tab, and a conductive sheet.

FIG. 8 illustrates schematically another example of a connection between a current collecting plate, having a convex tab, and a conductive sheet.

FIG. 9 is a planar view of an example of a current collecting plate.

FIGS. 10A-10F illustrate different examples of shapes of through holes in a current collecting plate.

FIG. 11 is a flow diagram of steps of an example of a method of manufacturing a cylindrical secondary cell. FIG. 12 is a planar view of another example of a current collecting plate.

FIG. 13 is a planar view of yet another example of a current collecting plate.

FIG. 14 is a planar view of yet another example of a current collecting plate.

FIG. 15 is a planar view of yet another example of a current collecting plate.

Detailed description

The present invention will now be described hereinafter with reference to the accompanying drawings, in which currently preferred, exemplary examples of the invention are illustrated.

Throughout the drawings, the same reference numbers are used for similar or corresponding elements.

For a better understanding of the proposed technology, it may be useful to begin with a brief overview of typical example of a cylindrical secondary cell.

Figure 1 shows a schematic illustration of an example cylindrical secondary cell 1 , hereinafter also referred to as a ’’cell”, that comprises a cylindrical enclosure 2 with a first enclosure end 21 , i.e. the top end in the figure, and an opposite second enclosure end 22. The cylindrical enclosure 2 may also be referred to as a can. The first enclosure end 21 may be formed in one piece with the cylindrical enclosure 2 as illustrated in the figure and the second enclosure end 22 may be formed by a separate second enclosure end lid 24, or vice versa. Both enclosure ends 21 , 22 may in alternative be formed by respective lids.

The illustrated example of cell 1 relates to a cell 1 of a type that has both a positive terminal and a negative terminal at one and the same end of the cylindrical secondary cell 1 , i.e. the top end in the figure. To this end, a first terminal 4 and a second terminal 5 are provided. The first terminal 4 is, for example, the positive terminal and the second terminal 5 is the negative terminal. The polarities can also be reversed. The second terminal 5 is electrically connected to the cylindrical enclosure 2. More precisely, the second terminal 5 is formed by the top surface of the cylindrical enclosure 2 that surrounds the first terminal 4. Thus, the entire cylindrical enclosure 2, apart from the first terminal 4 at the top end, may be the second terminal 5. The first terminal 4 and the second terminal 5 are separated by electrically isolating means 7.

A cylindrical secondary cell 1 having both terminals 4, 5 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, of the cell 1. The opposite end, the electrolytefilling end, of the cell 1 may be dedicated to electrolyte filling and gas venting. In the present disclosure, the electrolyte filling end is not described in detail. An overpressure may be generated within the cell during operation, in particular upon malfunction of the cell 1 or of the load connected to the cell 1 . Such malfunction may require a release of gas and/or electrolyte out of the cell, and it may be advantageous to direct the released gas and/or electrolyte away from the conductors.

It should be noted that the disclosure is not limited to the illustrated example cell 1 . Electrolyte filling and/or gas venting may alternatively or in addition be performed at the end of the cell presenting the terminals. Also, the two terminals may be provided at different ends of the cell.

Figure 2 is a cross-sectional view of the top part of an example cylindrical secondary cell 1 . As above, the cell 1 comprises a first terminal 4. In this example the first terminal 4 is rotationally symmetric around its longitudinal center axis. The first terminal 4 extends through a central terminal through hole 23 of the first enclosure end 21 and has an outer, or first, end and an inner, or second, end. The outer end of the first terminal 4 may form the actual terminal of the cell 1 . The electrically isolating means 7 surrounds at least a portion of the first terminal 4 in order to electrically isolate the first terminal 4 from the can, and when applicable, the second terminal 5. In this example, the first terminal 4 has the shape of a rivet with a head portion, or so-called factory rivet head, and a shaft portion, or rivet shaft. In this example, the electrically isolating means is rotational symmetric. As is illustrated, the electrically isolating means 7 surrounds the rivet shaft. The electrically isolating means may be referred to as a rivet gasket.

As is shown in figure 2, the terminal part 4 can be in direct electrical and physical contact with the current collecting plate 6. More precisely, the inner end of the terminal part 4 is in direct electrical contact with a center part of the current collecting plate 6. The inner end may be attached, for example welded, for example laser welded, to the current collecting plate 6.

Inside the cylindrical enclosure 2, an electrode roll assembly 3 is contained. The electrode roll assembly 3 comprises a first and a second conductive sheet 31 , 32 and separating means (not shown). The separating means may also be termed separator. The conductive sheets 31 , 32 and the separating means are rolled to form a cylindrical roll, preferably circular, defining a central channel 33. The conductive sheets 31 , 32 are coated with electrode coatings and on assembly of the cell 1 the cylindrical enclosure 2 is filled with an electrolyte. The electrolyte may flow through the central channel 33 or conduit to soak the electrode roll assembly. The coatings on the conductive sheets 31 , 32 act as cathode and anode, respectively. The cathode, anode and electrolyte provide electrochemical energy storage. This principle is known per se. A solid electrolyte solution is also applicable to the solutions described herein.

The sheets 31 , 32 of the electrode roll assembly 3 are axially offset in relation to one another, and each sheet comprises an end section that is not coated with electrode coating. In figure 2, only one end of the electrode roll assembly 3 is shown, and at this end the first conductive sheet 31 protrudes axially from the electrode roll assembly 3. In this way, the upper end of the electrode roll assembly 3 may be efficiently electrically connected to the first terminal 4 of the cell 1 . This design is known per se and commonly referred to as a tabless cell.

As is illustrated in figure 2, the current collecting plate 6 may be arranged at the upper end of the electrode roll assembly 3. The current collecting plate 6 is in direct electrical contact and direct physical contact with the first conductive sheet 31 , more precisely with the non-coated end section of the first conductive sheet 31 . Thus, the current collecting plate 6 provides an electrical connection between the first conductive sheet 31 of the electrode roll assembly 3 and the first terminal 4. In this particular example, the noncoated end section of the first conductive sheet 31 are straight, which means that the electrical and physical contact to the current collecting plate 6 are provided mainly by the edge of the first conductive sheet 31. Alternative examples are discussed further below.

In the example of figure 2, the center part of the current collecting plate 6 is recessed with reference to the more peripheral parts of the current collecting plate 6. This may useful e.g. in positioning the inner end of the terminal part 4 with respect to the current collecting plate 6 during cell assembly. Furthermore, such a recess may also enable a more efficient use of the volume within the top part of the cylindrical enclosure 2.

However, alternative shapes of the current collecting plate 6 may involve other geometrical shapes. As an example, in Figure 3, an example of a cell 1 with a flat current collecting plate 6 is illustrated.

Figure 4 is a cross-sectional view of the bottom part of an example cylindrical secondary cell 1 . The lower end of the second conductive sheet 32 is, in analogy with the first conductive sheet 31 , not coated with electrode coatings. The second conductive sheet 32 also protrudes axially with respect to the first conductive sheet 31 . The current collecting plate 6 in this end of the cell 1 is in direct electrical contact and direct physical contact with the second conductive sheet 32, more precisely with the non-coated end section of the second conductive sheet 32. The outer rim 61 of the current collecting plate 6 is furthermore in mechanical and electrical contact with the cylindrical enclosure 2. Thus, the current collecting plate 6 provides an electrical connection between the second conductive sheet 32 of the electrode roll assembly 3 and the second terminal 5.

In the examples of Figures 2-4, the non-coated end section of the first conductive sheet 31 and the second conductive sheet 32 are straight and the connection to the respective current collecting plate 6 is made by the edges of the first conductive sheet 31 and the second conductive sheet 32, respectively. In such cases the contact area between the first and second conductive sheets 31 , 32 and the current collecting plate 6 is small and the attachment therebetween may require careful considerations. One potential problem may be that the non-coated end section is relatively week in the plane of the current collecting plate 6 and may therefore easily be bent. The non-coated end section may also have slightly different heights and the current collecting plate 6 may not be perfectly planar. Such effects may cooperate to prohibit a reliable contact between the surface of the current collecting plate 6 and the non-coated end sections.

Figure 5 illustrates schematically a case where some of the edges of the first conductive sheet 31 are distorted and therefore do not get in contact with the current collecting plate 6. The entire contact will in this example be constituted just by a few edge portions.

An alternative is schematically illustrated in Figure 6. Here the non-coated end section 35 of the first conductive sheet 31 is bent, so that at least a part of the non-coated end section 35 becomes essentially parallel to the current collecting plate 6. This design opens up for a larger area that can be utilized for realizing the physical and electrical attachment between the non-coated end section 35 and the current collecting plate 6. However, also here, there is a risk that the bent portions of the non-coated end section 35 are not provided in a perfectly flat plane or that the current collecting plate 6 may not be perfectly planar, which may make the attachment to the current collecting plate 6 difficult.

To reduce such problems with non-flat connection points of the first conductive sheet 31 and the second conductive sheet 32, it would be advantageous to have a current collecting plate 6 that is more flexible. On the other hand, in order to provide a reliable connection to the first terminal 4 and the second terminal 5, respectively, the current collecting plate 6 is preferably relatively stiff. These contradicting features may be provided in one and the same current collecting plate 6 by providing parts of the current collecting plate 6 that are flexible or bendable, while the main parts of the current collecting plate 6 is more rigid. One way to realize this is to cut holes in the current collecting plate 6 that defines a tab 62 in the current collecting plate 6. This is schematically illustrated in Figure 7. The tab 62 can be bent in a direction perpendicular to the main plane of the current collecting plate 6 and thereby increase the possibilities to provide mechanical and electrical contact with the non-coated end sections 35.

Figure 8 illustrates a similar situation, but with the non-coated end section 35 of the first conductive sheet 31 is bent. The tab 62 can be bent in a direction perpendicular to the main plane of the current collecting plate 6 and thereby increase the possibilities to provide mechanical and electrical contact with the non-coated end sections 35.

Figure 9 illustrates an example of a current collecting plate 6 for provision of electrical connection between a terminal and a conductive sheet electrode roll assembly of a cylindrical secondary cell. The current collecting plate 6 comprises an electrically conductive disc 69 having a main extension plane in two dimensions. The electrically conductive disc 69 has a first part area 64 intended to overlap with the conductive sheet electrode roll assembly. The electrically conductive disc 69 may also have a second part area 65 that does not overlap with any conductive sheet electrode roll assembly, e.g. intended to be arranged over a central channel. At positions in the first part area 64 intended to overlap with the conductive sheet electrode roll assembly, the electrically conductive plate 69 presents at least one through hole 63. The through hole 63 is encircled by a closed edge 66. The closed edge 66 encircling the through hole 63 presents edge normal 67 in the main extension plane. The edge normals 67 of a portion of the closed edge 66 are diverging, thereby defining a respective convex tab 62 in the current collecting plate 6.

The convex tab 62 is in other words to a part surrounded by, and defined by, the through hole 63, allowing the convex tab 62 to be bent in a direction perpendicular to the main plane without causing any displacement of the main parts of the current collecting plate 6. These convex tabs can thereby be provided in better physical and electrical contact with the first or second conductive sheets, respectively. In other words, the convex tabs may be viewed as a part of the disc protruding into a through hole.

The convex tab 62 and thereby the through hole 63 may have many different shapes. In the example of Figure 9, the through hole has a horse-shoe shape, giving the convex tab 62 a half-elliptical shape. Figures 10A-10F illustrate other, non-exclusive, examples of hole shapes. In Figure 10A, a bow-shaped through hole 63 is presented. The flexibility of this shape is, however, rather limited. Figure 10B illustrates a through hole 63 providing a much higher flexibility for the convex tab 92. Preferably, the directions of at least two of the diverging edge normals of a same through hole differ by more than 90 degrees, and even more preferably by more than 150 degrees. Figure 10C illustrates a convex tab 62 having a sharp corner. Figure 10D illustrates a convex tab 62 having two sharp comers. Figure 10E illustrates an example, where the convex tab 62 as a whole has a convex shape, while parts of the through hole edge 66, as such present concave shapes. Figure 10F illustrates an example of a through hole 66 presenting a varying hole width along the convex tab 62. One example of a cylindrical secondary cell thereby comprises an electrode roll assembly having a conductive sheet, and a current collecting plate according to the principles illustrated here above. At least the convex tab of the current collecting plate is configured to be arranged in direct electrical contact with the conductive sheet.

Preferably, the cylindrical secondary cell further comprises a first terminal forming an external terminal of the cylindrical secondary cell and configured to be arranged in direct electrical contact with a center or a periphery of the current collecting plate.

Figure 11 illustrates a flow diagram of steps of an example of a method of manufacturing a cylindrical secondary cell. In step S2, a current collecting plate having at least one through hole in an electrically conductive disc having a main extension plane in two dimensions is provided. A portion of a respective closed edge encircling the at least one through hole presents diverging edge normals in a main extension plane of the current collecting plate, thereby defining a respective convex tab in the current collecting plate. In step S4, an electrode roll assembly having a conductive sheet is provided. In step S6, the current collecting plate is arranged direct electrical contact with the conductive sheet and covering an end of the electrode roll assembly. In step S8, the current collecting plate is attached to the electrode roll assembly at least by the convex tab.

The attaching may be performed at both ends of the electrode roll assembly, with a respective current collecting plate.

A pressure may be provided between the convex tab and the electrode roll assembly during the attaching. By applying a such a pressure, the convex tab may be bent down towards the ends of the conductive sheet/sheets of the electrode roll assembly and thereby create more or at least more reliable electrical contact therebetween. The attaching may be performed also at areas of the current collecting plate outside the convex tab. Even if the convex tabs are the most probable points of connection, also other parts of the electrically conductive disc of the current collecting plate may contribute to the electrical connection. This may be particularly important in applications where high currents are expected to occur during use, since the current through the current collecting plate then is distributed over a larger area.

The attaching may be performed by laser welding. However, there are also other possible approaches for accomplish the attachment. Spot welding by sending short pulses of high currents may also be used. Different kinds of electrically conductive adhesives may also be used for providing a reliable attachment.

In step S10, the electrode roll assembly and the current collecting plate(s) may be inserted into a cylindrical enclosure. In step S12, an electrolyte is filled into the electrode roll assembly through the at least one through hole. If the electrolyte is solid, it is instead inserted when making the electrode roll assembly. In step S14, the cylindrical enclosure is sealed.

It is not only during the manufacturing that the contact between the electrode roll assembly and the current collecting plate is of interest. During use of the cylindrical secondary cell, the extracted current will flow through the current collecting plate, and the paths of these currents will be determined by e.g. which spots of the current collecting plate that are in electrical contact with the electrode roll assembly. By utilizing convex tabs, as described above, and by attaching the current collecting plate to the electrode roll assembly at these convex tabs, the most reliable paths for electrical currents during use of the cylindrical secondary cell will pass through the convex tabs. This also enables designing the cylindrical secondary cell for being adapted to different electrical conditions. For some types of cell chemistry and electrode roll assembly design, it may be beneficial to have an as low resistance as possible in the current collecting plate. This may e.g. be the case for cells intended for high current uses. It may, in such cases, be of benefit to direct the through holes and the convex tabs in such directions that short conduction paths are created between the conductive sheet and the terminal of the cell. A low internal resistance will thus be the result. In the case of currents to the first terminal, as illustrated schematically in Fig. 12, the paths 70 between the electrode roll assembly contact points and the center of the current collecting plate 6 should be short. This can for instance be provided for by arranging a convex part 68 of the convex tab 62 to be directed away from the center of the current collecting plate 6. This gives a direct path available between the convex tab 62 and the center of the current collecting plate 6, where the first terminal is to be contacted.

Similarly, as illustrated by Figure 13, in the case of currents to the second terminal, the currents are intended to be conducted to the cylindrical enclosure 2 via the outer rim 61 of the current collecting plate 6. The paths 71 between the electrode roll assembly contact points and the outer rim 61 of the current collecting plate 6 should be short. This can for instance be arranged for by arranging a convex part 68 of the convex tab 62 to be directed towards the center of the current collecting plate 6.

For other types of chemical cell chemistry and electrode roll assembly design, it may be beneficial to have an as low resistance as possible in the current collecting plate. This may for instance be the case for cells where high currents are not to be expected or when heating of the cylindrical secondary cell has to be kept small. It may in such cases be of benefit to direct the through holes and the convex tabs in such directions that long conduction paths are created. The heat dissipation from the current may then be spread out over larger parts of the current collecting plate 6. In the case of currents to the first terminal, as illustrated schematically in Fig. 14, the paths 70 between the electrode roll assembly contact points and the center of the current collecting plate 6 should be long. This can for instance be arranged for by arranging a convex part 68 of the convex tab 62 to be directed towards the center of the current collecting plate 6.

Similarly, as illustrated by Figure 15, in the case of currents to the second terminal, the currents are intended to be conducted to the cylindrical enclosure 2 via the outer rim 61 of the current collecting plate 6. The paths 71 between the electrode roll assembly contact points and the outer rim 61 of the current collecting plate 6 should be long. This can for instance be arranged for by arranging a convex part 68 of the convex tab 62 to be directed away from the center of the current collecting plate 6.

The design of the through holes, their directions and the distribution over the surfaces of the current collecting plate can thus be used for optimizing and adapting the electrical behavior of the secondary cell during use. In a typical case, the direction of the convex part of the convex tab in the current collecting plate for the first terminal is opposite to the direction of the convex part of the convex tab in the current collecting plate for the second terminal.

It is also understood that it is preferred to use more than one convex tab. In other words, the current collecting plate preferably comprises a multitude of through holes, wherein a portion of a respective closed edge encircling the multitude of through hole presents diverging edge normals in a main extension plane of the current collecting plate.

In order to utilize the current collecting plate in a most efficient manner, the multitude of through holes are preferably evenly angularly spread over the current collecting plate with respect to a center of the current collecting plate.

The use of holes in current collecting plate is, as such, known in prior art. However, the main purpose of such holes has up to now been for allowing an efficient filling of the electrolyte into the electrode roll assembly. The through holes presented here above may also serve this purpose. Provision of a larger total hole area will increase the filling rate for the electrolyte. However, a large hole area will reduce the conducting material for the current collecting plate. It is therefore presently believed that a ratio of a total through hole area to a total area of the current collecting plate preferably is within the interval of 5-20 %. Even more preferably, this a ratio of a total through hole area to a total area of the current collecting plate preferably is within the interval of I Q- 15 %. These properties are presently believed to be of most importance for the current collecting plate closest to the opening in the cylindrical enclosure where the electrolyte is intended to be introduced. In the example of Figure 1 , the current collecting plate close to the lid is of most importance for these issues.

Another related issue is the electrolyte filling properties when utilizing bent non-coated end sections 35 of the first conductive sheet 31 , as illustrated further above. Such bending of the non-coated end sections 35 may cause a reduction in the electrolyte penetration rate since they tend to cover the ends of the channels between the different conductive sheets and the separators. One idea to mitigate such problems might be to cut away some of the noncoated end sections 35 to open additional electrolyte flow paths. In such a case it would also be of benefit if the areas in which the non-coated end sections 35 are removed can be aligned with the through holes of the current collecting plate. However, since it is highly requested that the convex tabs of the current collecting plate do overlap with the non-coated end sections 35, and since the convex tabs and through holes are situated adjacent to each other, the relative positioning of the end section cut-away areas and the convex tabs has preferably to be very accurate. The radial distance may be defined rather accurately both for the current collecting plate and the electrode roll assembly 3. However, the angular position is in general more difficult to determine and is more difficult to maintain during mounting of cylindrically symmetric parts.

In order to assist in gripping and positioning of the current collecting plate during mounting, the current collecting plate has preferably at least one notch 72 in the circumference thereof, as schematically illustrated in Figures 12-15. These notches 72 can be utilized for ensuring an accurate gripping of the current collecting plate. Furthermore, in a particular example, each of the multitude of notches 72 are provided at a predetermined angular position relative a respective one of the through holes 63. In such a way, a gripping tool utilizing the notches 72 will also be angularly aligned with the through holes 63, whereby an accurate mounting is facilitated.

At the second enclosure end 22, a good electrical conduction is preferably created between the cylindrical enclosure 2 and the current collecting plate 6. This may be arranged for by different means. One approach, as is illustrated in Figure 4, is to design the current collecting plate 6 to have an annular flange 61 along the circumference thereof. This annular flange 61 can be adapted to provide a small resilient force against an inwardly curved portion 58 of the cylindrical enclosure 2 at the second enclosure end 22. This spring action serves to ensure a good mechanical and electrical contact between the annular flange 61 and the cylindrical enclosure 2.

The embodiments described above are to be understood as a few illustrative examples of the present invention. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the scope of the present invention. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible. The scope of the present invention is, however, defined by the appended claims.

Claims

1 . A current collecting plate (6) for provision of electrical connection between a terminal and a conductive sheet electrode roll assembly (3) of a cylindrical secondary cell (1 ), the current collecting plate (6) comprising:

- an electrically conductive disc (69) having a main extension plane in two dimensions; wherein the electrically conductive disc (69) presents at least one through hole (63) at a position intended to overlap with the conductive sheet electrode roll assembly (3); wherein a portion of a respective closed edge (66) encircling the at least one through hole (63) presents diverging edge normals (67) in the main extension plane, thereby defining a respective convex tab (62) in the current collecting plate (6).

2. The current collecting plate according to claim 1 , wherein directions of at least two of the diverging edge normals (67) of a same through hole (63) differ by more than 90 degrees, preferably more than 150 degrees.

3. The current collecting plate according to claim 1 or 2, wherein a convex part (68) of the convex tab (62) is directed away from a center of the current collecting plate (6).

4. The current collecting plate according to claim 1 or 2, wherein a convex part (68) of the convex tab (62) is directed towards a center of the current collecting plate (6).

5. The current collecting plate according to any of the claims 1 to 4, wherein the current collecting plate (6) comprises a multitude of through holes (63), wherein a portion of a respective closed edge (66) encircling the multitude of through holes (63) presents diverging edge normals (67) in a main extension plane of the current collecting plate (6).

6. The current collecting plate according to claim 5, wherein the multitude of through holes (63) are evenly angularly spread over the current collecting plate (6) with respect to a center of the current collecting plate (6).

7. The current collecting plate according to any of the claims 1 to 6, wherein a ratio of a total through hole (63) area to a total area of the current collecting plate (6) is within the interval of 5-20 %, preferably within the interval of 10-15 %.

8. The current collecting plate according to any of the claims 1 to 7, wherein the current collecting plate (6) has an annular flange (61 ) along the circumference of the current collecting plate (6).

9. The current collecting plate according to any of the claims 1 to 8, wherein the current collecting plate (6) has at least one notch (72) in the circumference of the current collecting plate (6).

10. The current collecting plate according to claim 9, wherein the current collecting plate (6) has a multitude of notches (72) in the circumference of the current collecting plate (6), wherein each of the multitude of notches (72) is provided at a predetermined angular position relative a respective one of the through holes (63).

11. A cylindrical secondary cell (1 ) comprising:

- an electrode roll assembly (3) having a conductive sheet (31 , 32); and

- a current collecting plate (6) according to any of the claim 1 to 10; wherein at least the convex tab (62) of the current collecting plate (6) is configured to be arranged in direct electrical contact with the conductive sheet (31 , 32).

12. The cylindrical secondary cell according to claim 11 , further comprising: - a terminal (4, 5) forming an external terminal of the cylindrical secondary cell and configured to be arranged in direct electrical contact with a center or periphery of the current collecting plate (6).

13. A method of manufacturing a cylindrical secondary cell (1 ), the method comprising:

- providing (S2) a current collecting plate (6) having at least one through hole (63) in an electrically conductive disc (69) having a main extension plane in two dimensions, wherein a portion of a respective closed edge (66) encircling the at least one through hole (63) presents diverging edge normals (67) in a main extension plane of the current collecting plate (6), thereby defining a respective convex tab (62) in the current collecting plate (6);

- providing (S4) an electrode roll assembly (3) having a conductive sheet (31 , 32);

- arranging (S6) the current collecting plate (6) in direct electrical contact with the conductive sheet (31 , 32) and covering an end of the electrode roll assembly (3); and

- attaching (S8) the current collecting plate (6) to the electrode roll assembly (3) at least by the convex tab (62).

14. The method according to claim 13, wherein the attaching (S8) is performed at both ends of the electrode roll assembly (3) with a respective current collecting plate (6).

15. The method according to claim 13 or 14, further comprising:

- filling (S12) an electrolyte into the electrode roll assembly (3) through the at least one through hole (62).

16. The method according to any of the claims 13 to 15, wherein the attaching (S8) is performed by laser welding.

17. The method according to any of the claims 13 to 16, wherein the attaching (S8) is performed also by areas of the current collecting plate (6) outside the convex tab (62).

18. The method according to any of the claims 13 to 17, wherein a pressure is provided between the convex tab (62) and the electrode roll assembly (3) during the attaching (S8).