SE545608C2 - A cylindrical secondary cell with a conductive sheet comprising flaps - Google Patents

Abstract

The present disclosure generally pertains to secondary batteries and components thereof. According to a first aspect, the present disclosure relates to a cylindrical secondary cell 1 comprising a conductive sheet 4, and electrode coating 41 formed on sides of the conductive sheet 4. The conductive sheet 4 is wound in a longitudinal direction into a cylindrical shape to form an electrode roll 5. The conductive sheet comprises an exposed part 43 closest to a longitudinal edge 4a of the conductive sheet that is free from electrode coating. The exposed part 43 comprises a plurality of protruding flaps 44 separated by notches 45 extending from the longitudinal edge 4a towards the electrode coating 41 and ending before the electrode coating. The protruding flaps are bent towards a centre of the electrode roll 5 to form a contact surface of the conductive sheet 4. Furthermore, the protruding flaps are spaced from transverse edges 4b, 4c of the conductive sheet with respective distances, whereby end parts of the longitudinal edge are free from protruding flaps 44.

Description

TECHNICAL FIELD The present disclosure generally pertains to secondary batteries and components thereof. More specifically, the disclosure relates to a cylindrical battery comprising a conductive sheet with a Iongitudinal edge comprising flaps spaced from a transverse edge. BACKGROUND ln 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.

A rechargeable battery, also referred to as a secondary battery, comprises one or more secondary cells. Jellyrolls are commonly used in the secondary cells. A jellyroll is a frequently used type of electrode assembly having a structure in which a positive electrode and a negative electrode, each having a long sheet shape and being coated on respective conductive foils, are wound with a separator interposed in-betvveen. Hence, the jellyroll is formed by conductive sheets provided by electrode coating and rolled up into a cylinder. The separator is not needed if a solid electrolyte is used. ln tab-less cells, the conductive sheets commonly have an exposed (i.e. uncoated) part protruding from one side of the cylinder. To create an appropriate surface to connect a terminal to, the exposed part can be folded and thereafter pressed. Hence, the exposed part can be formed, pressed or folded in a way such that a surface with good contact properties is provided, while at the same time short circuit between the electrodes is avoided.

SUMMARY The present disclosure aims at providing highly reliable secondary cells. ln particular, it is an object to provide a conductive sheet shaped such that when folded it provides good contact properties, while at the same time short circuit between the electrodes is avoided.

According to a first aspect, the present disclosure relates to a cylindrical secondary cell comprising a conductive sheet, and electrode coating formed on sides of the conductive sheet. The conductive sheet is wound in a longitudinal direction into a cylindrical shape to form an electrode roll. The conductive sheet comprises an exposed part, closest to a longitudinal edge of the conductive sheet, that is free from electrode coating. The exposed part comprises a plurality of protruding flaps separated by notches extending from the longitudinal edge towards the electrode coating and ending before the electrode coating. The protruding flaps are bent towards a centre of the electrode roll to form a contact surface of the conductive sheet. Furthermore, the protruding flaps are spaced from transverse edges of the conductive sheet with respective distances, whereby end parts of the longitudinal edge, closest to the transverse edges, are free from protruding flaps. By leaving end parts of the longitudinal edge free from flaps, a good contact surface is provided by the bent flaps. Furthermore, a risk that the contact surface formed by the flaps extends towards the can wall, or towards a centre hole of the electrode role, during succeeding pressing of the contact surface, is reduced. lt is also avoided that a centre hole of the electrode roll is covered by flaps, which would be problematic as the centre hole is sometimes used to fill electrolyte and also to access parts of the cell in the assembly process. When winding the electrode roll there is usually less tension in the sheet at the outer end of the roll. Because of this, it is harder to control the winding, whereby there is a risk that flaps at the outer end part (relative the centre of the roll) bend in unpredictable ways. Therefore, an advantage of not having flaps at the outer end part is that it is avoided that flaps bend in unintended directions. ln conclusion, by letting the end parts of the longitudinal edge be free from flaps short circuits may be avoided and manufacturing is facilitated. Another advantage of the proposed technique is that the edge of the outermost flap can be used to determine the cutting position when cutting the sheet to a desired size. ln other words, a cutting machine can detect the edge of the outermost flap and use it as a guide for cutting the sheet in a desired length. ln some embodiments, an outer edge of the end parts, relative the electrode coating, is a|igned with inner ends of the notches closest to the electrode coating. Thereby, contact with the electrode sheet is provided along the entire |ongitudina| edge. ln some embodiments, the exposed part extends between zero and 0.5 mm from the electrode coating the end parts that are free from flaps. Thereby, contact with all electrode layers is enabled. Also, such a shape may be formed by laser cutting. ln some embodiments, the exposed part extends at least 0.5 to 2.5 mm from the electrode coating at the end parts that are free from flaps. Thereby, an isolating layer may be applied on an interface between the exposed part and the coating. ln some embodiments, a length of the protruding flaps, in the direction of the notches, becomes gradually longer in the |ongitudina| direction of the conductive sheet starting from an interior transverse edge. An advantage of having shorter flaps at the centre of the roll is that the electric resistance is minimized there. This is because shorter flaps mean a shorter path for the current to travel. An advantage of having longer flaps on the outer parts of the roll is that there is a larger number of flaps overlapping, than if the flaps were consistently shorter. This leads to a thicker layer of foil as the flaps are bent down. A thicker layer is advantageous in the assembly process if a lead disc is to be welded to the flattened surface for current collecting. Also, when the outermost flaps are longer, such a lead disc can be made smaller and still have contact with at least a part of the outermost flaps. This will reduce the cost of the cell. ln some embodiments, the length of one protruding flap is defined as a length at a centre of the flap or as an average length of the flap. Hence, the length of one flap may be defined in different ways. ln some embodiments, outer edges of the protruding flaps are oblique such that they jointly form a continuous |ongitudina| edge. Thereby, manufacturing is facilitated as the edges of the flaps may be formed with one straight cut. ln some embodiments, the protruding flaps are spaced from an interior transverse edge of the conductive sheet by a distance corresponding to a circumference of the innermost winding, or to a circumference of the two innermost windings, of the conductive sheet. Thereby, the centre hole is not covered by flaps. BRIEF DESCRIPTION OF THE DRAWINGS The embodiments disclosed herein are illustrated by way of example, and by not by way of Iimitation, in the figures of the accompanying drawings. Like reference numerals refer to corresponding parts throughout the drawings, in which Fig. 1 illustrates, in cross-section, one end of a cylindrical secondary cell where the proposed technique may be implemented.

Fig. 2 illustrates an isometric view of a rolled up conductive sheets having an exposed part.

Fig. 3A and 3B illustrate a top views of a conductive sheet with electrode coating applied.

Fig. 4A to 4C illustrate example embodiments of an exposed part of the conductive sheet.

DETAILED DESCRIPTION When in the following directions like "up", "down", "left" and "right" are used they always refer to the respective Fig. referenced.

A rechargeable battery, often referred to as a secondary battery, typically comprises one or more secondary cells (herein referred to as simply a cells) electrically connected to each other. Each cell comprises electrode sheets wound to form an electrode roll. The proposed technique is based on the insight that improved contact properties and higher reliability may be achieved by shaping an exposed part that forms a contact plate of the electrode sheet as proposed herein.

Embodiments of the present disclosure will now be described more fully hereinafter, with reference to the figures. The same reference numbers are used throughout the figures. 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 1 illustrates an example cylindrical secondary cell 1 (hereinafter also referred to as cell 1) comprising a cylindrical can 2. Herein, the terms 'inner' and 'outer' are used with reference to the centre of the cell 1. The cylindrical can 2 may also be referred to as an enclosure.

The cylindrical can 2 is filled with an electrolyte. A cylinder-shaped electrode roll 5, typically referred to as a jellyroll, is arranged inside the cylindrical can 2. Ajellyroll is a commonly used type of electrode assembly having a structure in which a positive electrode and a negative electrode each having a longitudinal sheet shape are wound with a separator interposed in-between. The illustrated cell 1 further comprises an electrode lead plate 6 that is arranged at one end of the electrode roll 5. The electrode lead plate 6 is in direct electrical and physical contact with one of the electrodes of the electrode assembly, typically the positive electrode. This connection will be further described in Fig. 2. The electrode lead plate 6 may be attached, for example welded, for example laser welded, to the positive electrode.

The illustrated cell 1 has a positive terminal and a negative terminal. The can 2 comprises a central terminal through-hole for a terminal part 3 forming the positive terminal. The terminal part 3 is in electrical contact with an electrode lead plate 6. The negative terminal is electrically connected to the cylindrical can 2 (not shown). The cell 1 typically includes a plurality of other components such as vents, connectors and insulating parts etc. There are many ways to design these parts and they will not be described herein. lt should be noted that the aspects of the invention are also applicable to cylindrical secondary cells with solid electrolyte. I such a case there may not be a separator in the jellyroll. Also, other designs of the cylindrical secondary cell are combinable with the aspects of the invention, for example other designs of the terminals, can or electrode lead plate.

Fig. 2 shows an isometric view of an electrode roll 5. The electrode roll 5 normally comprises two conductive sheets 4, both sheets are coated with respective electrode coatings 41 (Fig. 3), arranged with separator sheets 6 in between and wound to form the electrode roll 5. ln case of using a solid electrolyte, the separator sheets may be replaced by a sheet of solid electrolyte. Alternatively, solid electrolyte may be applied as a coating to the either, or all electrode coatings. The conductive sheets 4 (and the separators 6) are wound in a longitudinal direction L (see Fig. 3A) into a cylindrical shape to form the electrode roll 5. ln fig. 2, the electrode roll 5 is shown during the rolling of the conductive sheets 4 and the separators 6. ln the electrode roll 5 of one cell 1, the electrode coating 41 on one of the conductive sheets constitutes an active part of the positive electrode and the electrode coating 41 of the other conductive sheet constitutes an active part of the negative electrode of the cell 1. The materials of the conductive sheets 4 and the electrode coatings thereon are not disclosed herein. Many different material choices known in the art can be used and is up to the implementation.

The conductive sheets 4 comprise exposed parts 43 free from electrode coating 41 along opposite longitudinal edges 4a of the two conductive sheets 4. Hence, each conductive sheet 4 has an exposed part 43 extending along one of its longitudinal edges 4a. The exposed parts 43 provides physical and electrical connections to electrodes. More specifically, a connection to one electrode is provided at one end of the electrode roll and a connection to the other electrode is provided at the other end.

Notches 45 (see Fig. 4A-4C) are cut (for example by laser), or otherwise formed, in the exposed part 43. More specifically, notches are formed in longitudinal edges 4a of the conductive sheet 4 free from coating. ln Fig. 2 these notches are merely schematically shown. Due to the notches 45, flaps 44 (see Fig. 4A-4C) are formed in the longitudinal edges 4a. Hence, each notch 45 separates two consecutive flaps. The flaps 44 can be bent inwards towards a winding axis x of the electrode roll 4 after the different stacked layers of the secondary cell 10 have been rolled up. The bent flaps form a contact surface that enables electrical and physical connection to the electrode plate 6 (Fig. 1).

Fig. 3A shows a top view of a conductive sheet 4 with a Iongitudinal shape that is rolled out. The conductive sheet 4 is a flat rectangular structure that can be wound in a Iongitudinal direction L (indicated by the arrow) into a cylindrical shape. The conductive sheet 4 is for example between 20 mm and 1500 mm wide and 5 meters long. The size of the conductive sheet can be adapted to fit any cylindrical secondary cell measurements. Thus, the rectangular shape of the conductive sheets of Fig. 3A (and also Fig. 3B which is discussed further below) is not proportionally accurate. The conductive sheet 4 comprises two sides (also referred to as side surfaces) 4d and 4e. More specifically, the conductive sheet 4 has an inner side 4d (facing front in Fig. 3A) and an outer side 4e (not visible in Fig. 3A as facing back). The inner side 4d and the outer side 4e are defined relative a centre hole 47 of the wound electrode roll 5, see Fig. 2. Furthermore, the conductive sheet 4 has two Iongitudinal edges 4a and two transverse edges 4b, 4c. More specifically, the conductive sheet 4 has an interior transverse edge 4b and an exterior transverse edge 4c. The interior transverse edge 4b is an innermost edge and the exterior edge 4c is an outermost transverse edge relative the wound electrode roll The inner side 4d (facing front) of the electrode sheet 4 will now be described. lt shall be appreciated that the inner side 4e (facing back) is identical but mirrored. Electrode coating 41 is coated, or formed, on both sides 4d, 4e of the conductive sheet 4 except for at an exposed part 43 that is free from any electrode coating 41. The electrode coating 41 is illustrated by dashed lines. The exposed part 43 is arranged closest to a Iongitudinal edge 4a of the conductive sheet 4. Closest to herein refers to in direct contact with and including the Iongitudinal edge 4a. The Iongitudinal dashed line indicates where the coated part ends and the exposed part 43 starts. The exposed part 43 protrudes longer than the other layers at one end side of the wound electrode roll 5. Hence, the exposed part constitutes one end of the wound electrode roll 5. ln the illustrated example electrode coating 41 is applied to cover the entire surfaces of the sides 4d, 4e of the electrode sheet 4 below the dashed line delimiting the exposed part The exposed part 43 forms an uncoated part of the conductive sheet 4, which is free from electrode coating on both sides 4d, 4e. Hence, the exposed part 43 includes one Iongitudinal edge 4a of the conductive sheet 4 as well as parts of the side surfaces 4d, 4e closest to the longitudinal edge 4a. ln other words, both side surfaces of the exposed part 43, as well as the longitudinal edge 4a joining the sides are completely free from electrode coating. The size of the exposed part 43 varies. For example, the exposed part extends 0.5-3 mm from the longitudinal edge 4a.

Unfortunately, short circuits at the end of the electrode roll 5 may cause problems in this field of technology. This may be mitigated by adding an isolating layer 42 at an interface between the electrode coating electrode 41 and the exposed portion 43, as illustrated in Fig. 3B. This isolating layer 42 may be applied after forming the exposed part 43 and thus it may partly cover the notches 45 (in particular their inner ends). The isolating layer 42 prevents electrical contact between the conductive sheet 4 and electrode coating of the other conductive sheet. The need for an isolating layer 42 depends on design of the electrode roll 5, for example depending on alignment of the sheets. Typically, an isolating layer 42 is applied if there is an overlap between the exposed part 43 and electrode coating of the other electrode, which may be the case at the positive electrode (cathode). The isolating layer 42 may be an isolating strap or an additional isolating coating. This isolating coating is different from the electrode coating Figs. 4A to 4C show three different example embodiments of the exposed part 43 of the conductive sheet 4. The proposed technique will first be described with reference to Fig. 4A. The exposed part 43 illustrated in Fig. 4A comprises a plurality of protruding flaps 44, herein also referred to as simply flaps 44, separated by notches 45. As the conductive sheet is many meters long the number of flaps is in reality hundreds, but for simplicity, and better visibility, only a limited number are illustrated in Figs. 4A to 4B. The notches 45 extend from the longitudinal edge 4a towards the electrode coating 41. The notches 45 end before the electrode coating 41. ln other words, the notches do not extend all the way to the electrode coating 41. lf an isolating layer is applied, the isolating layer 42 may cover inner ends of the notches 45. ln other words, they are not in direct contact with the electrode coating. For example, the notches end 2.5, 1.5 or 0.5 mm before the electrode coating 41. As explained above, the protruding flaps 44 are bent towards a centre of the electrode roll 5 to form a contact surface of the conductive sheet 4. The bending angle is for example about 90 degrees. The contact surface is formed by the part of the flaps 44 which are folded to connect to a terminal 3 of the secondary cell 1. The contact surface is formed on the area of the conductive sheet 4 that is free from any electrode coating. The fold may be arranged anywhere along the notches 45 but typically it is desirable to arrange it as close as possible to the electrode coating 41. The contact surface is for example arranged 5 mm or less from the electrode coating 41. ln some embodiments, 4mm or 3mm or less. The flaps 44 may have essentially a consistent width w (in the longitudinal direction L) over their entire length l (in the transverse direction). Cutting the notches with a consistent width w may ease the manufacturing of the notches. ln the illustrated example, the flaps also have an essentially a consistent length l. ln other words, the flaps are rectangular. Alternatively, an end portion of the notches comprises a rounded cut out or is formed with a turn so that the end of the end portion is not directed towards the electrode coating. ln these embodiments, the flaps have an essentially a consistent length l from the end portion to their outer edges 44a relative the electrode coating electrode ln the example of Fig. 4A, all the flaps have the same dimensions, that is same width w and same length l. However, the dimensions of the flaps 44 may also vary.

The protruding flaps 44 facilitate folding without buckling the conductive sheet. However, due to the rolling a circumference of one winding becomes larger for each lap. Hence, a surface formed by flaps of consistent size will not be even, as overlap of the flaps will be larger in the middle of the roll. To smoothen the surface a pressure may be applied to the contact surface after folding the flaps 44, in some embodiments in combination with heating. However, the contact surface may still have an uneven thickness, which may impair contact with the electrode plate 6. There is also a risk that the pressing may cause the contact surface to extend towards a centre hole 47 of the electrode roll 5 and also towards the can walls, which may cause short circuits. The bent flaps 44 closest to the middle of the electrode roll may also complicate rolling and may for example get stuck in a rod inserted in the electrode roll 4 during the rolling. Hence, there is a risk that the flaps 44 cover a centre hole 47 of the electrode roll To overcome this, it is herein proposed to let end parts of the of the longitudinal edge 4a, closest to the transverse edges 4b, 4c, be free from protruding flaps 44. The end parts are the outer ends of the longitudinal edge 4a closest to the transverse edges 4b, 4c. ln other words no flaps 44 are formed closest to the transverse edges 4b, 4c. This is for example done by laser cutting of the corresponding part of the exposed part43. ln other words, the protruding flaps 44 are spaced from transverse edges 4b, 4c of the conductive sheet 4. Stated differently, the longitudinal edge 4a does not have any flaps 44 within respective distances dl,d2 from the transverse edges 4b, 4c. ln other words, the flaps 44 are spaced a first distance dl from the interior transverse edge 4b and a second distance dl from the exterior transverse edge 4c. The first and second distances dl,d2 may be the same or they may be different. ln this way the exposed part 43 will have a more symmetric shape, which may facilitate manufacturing. Also the risk that the contact surface will extend over the centre hole 47 or outside the electrode roll is reduced, while a good contact surface is provided.

A length of the distances dl, dl may differ depending on dimensions of the electrode roll 5, the size of the flaps 44 and the desired properties of the contact surface. For example, the distances dl,d2 correspond to a total width of at least 8, 10 or 11 flaps 43. ln some embodiments the distances dl, dl are at least 30, 40 or at least mm.

For example, it may be desirable not to have any flaps 44 on the innermost windings, as they may be in the way during rolling. ln other words, in some embodiments the protruding flaps 44 are spaced from an interior transverse edge 4b by a distance dl corresponding to a circumference of the innermost winding, or to a circumference of the two innermost windings, of the conductive sheet The end parts that do not have any flaps will typically also extend a little bit from the electrode coating 41. ln other words, the exposed part 43 comprises end parts 43a, 43b, closest to the transverse edges 4b, 4c, that are free from protruding flaps 44. ln other words, in some embodiments, the exposed part 43 extends a distance d3 from the electrode coating 41 at its end parts 43a, 43b. Typically, the end parts 43a, 43b are shaped such that forming the exposed part 43 by cutting along the coating 41 is possible, which means that the end parts extend a tiny bit from the coating 41. Also it may be desirable that there is contact between the contact surface and the conductive sheet 4 along the entire longitudinal edge 5a, i.e. at all electrode layers, which is facilitated if a small part of the conductive sheet 4 is exposed also at the end parts free from flaps 44. For example, the exposed part 43 extends between 0 and 0.5 mm from the electrode coating 41 at end parts 43a, 43b of an exposed part 43 that are free from flaps. lf an isolating layer 42 is applied, a slightly longer distance d3 may be needed on the conductive sheet 4 comprising the isolating part, to enable attaching the isolating layer 42. Hence, in some embodiments, the exposed part 43 extends at least 0.5-2.5 mm from the electrode coating 41 at the end parts 43a, 43b of the exposed part 43 that are free from flaps. lt could also be that the exposed part 43 extends more than 2.mm.

The distance d3 that the exposed part 43 extend at the ends may be the same as a distance between the inner ends of the notches 45 and the electrode coating 41. ln other words, in some embodiments, an outer edge of one or both of the end parts 43a, 43b, relative the electrode coating, is aligned with inner ends of the notches 45 closest to the electrode coating 41 as illustrated by the dash-dotted line in Fig. 4A.

An alternative embodiment will now be described with reference to Fig. 4B. The shape exposed part 43 of this embodiment is the same as in Fig. 4A except that the length l of the flaps 44 varies. ln other words, in these embodiments the flaps 44 have different lengths.

As mentioned above, due to the rolling, a circumference of one winding becomes larger for each lap. Consequently, the contact surface formed by the flaps 44 may become uneven. ln particular the middle part of the contact surface may be thicker as there will be more overlap of the flaps 44 when bent down. This may be mitigated by letting the flaps be longer at the outer end of the electrode roll 5. More specifically, the length of the flaps may be designed to be successively longer towards the outer end of the electrode roll. ln other words, in some embodiments, a length l of the protruding flaps 44, in the direction of the notches 45, becomes gradually longer in the longitudinal direction L of the conductive sheet 4 starting from an innermost transverse edge 4b. The length may be varied in different ways. For example, the length may be varied stepwise for every flap or for every x:th flap 44, where x may be any of 1, 2, 3, 4, 5 etc. For example there may be 10 flaps with the same length before the length is increased.

Alternatively, the length may be increased stepwise every winding.

A further alternative is to also modify an outer end 44a of the flaps to have a slanted shape. ln this way they will form a continuous shape before they are bent, which mightmake manufacturing by cutting easier. Such a shape may also improve the evenness of the contact surface. ln other words, in some embodiment outer edges 44a of the protruding flaps 44 are oblique such that they jointly form a continuous longitudinal edge 4a.

The length of one flap is typically defined as a length in the middle (along the longitudinal edge 4a) of the flap 44 as illustrated in Fig. 4A. An average length may also be used. ln other words, in some embodiments, the length l of one protruding flap 44 is defined as a length at a centre of the flap or as an average length of the flap.

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. ln 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 (10)

1. Claims Cylindrical secondary cell (1) comprising: a conductive sheet (4), and electrode coating (41) formed on sides (4d, 4e) of the conductive sheet (4), the conductive sheet (4) being wound in a Iongitudinal direction into a cylindrical shape to form an electrode roll (5), wherein the conductive sheet (4) comprises an exposed part (43), closest to a Iongitudinal edge (4a) of the conductive sheet (4), that is free from electrode coating (41), wherein the exposed part (43) comprises a plurality of protruding f|aps (44) separated by notches (45) extending from the Iongitudinal edge (4a) towards the electrode coating (41) and ending before the electrode coating (41 ), wherein the protruding f|aps (44) are bent towards a centre of the electrode roll (5) to form a contact surface of the conductive sheet (4), wherein the protruding f|aps (44) are spaced from transverse edges (4b, 4c) of the conductive sheet (20, 30) with respective distances (dhdz), whereby end parts of the Iongitudinal edge (4a), closest to the transverse edges (4b, 4c), are free from protruding f|aps (44). _ The cylindrical cell (1) of claim 1, wherein an outer edge of the end parts, _,_is aligned with inner ends of the notches (45) closest to the electrode coating (41). The cylindrical cell (1) of claim 1 or 2, wherein the exposed part (43) extends at least 0.5-2.5 mm from the electrode coating (41) at the end parts that are free from f|aps. The cylindrical cell (1) of claim 1 or 2, wherein the exposed part (43) extends between 0 and 0.5 mm from the electrode coating (41) at the end parts that are free from f|aps. The cylindrical cell (1) of any one of the proceeding claims, wherein a length (l) of the protruding f|aps (44), in the direction of the notches (45), becomesgradually longer in the Iongitudinal direction (L) of the conductive sheet (4) starting from an interior transverse edge (4b). _ The cylindrical cell (1) of claim 5, wherein the length (l) of one protruding flap (44) is defined as a length at a centre of the flap or as an average length of the flap. _ The cylindrical cell (1) of claim 5 or 6, wherein outer edges (44a) of the protruding flaps (44) are oblique such that they jointly form a continuous Iongitudinal edge (4a). _ The cylindrical cell (1) of any one of the proceeding claims, wherein the protruding flaps (44) are spaced from an interior transverse edge (4b) by a distance (dl) corresponding to a circumference of the innermost winding, or to a circumference of the two innermost windings, of the conductive sheet (4). _ The cylindrical cell (1) of any one of the proceeding claims, wherein the protruding flaps (44) are spaced from the transverse edges (5b) by distances (dl, dz) corresponding to a total width of at least 8, 10 or 11 flaps (43). 10_The cylindrical cell (1) of any one of the proceeding claims, wherein the protruding flaps (44) are arranged at least 30, 40 or at least mm from the transverse edges (4b, 4c)_ 14