SE2251077A1

SE2251077A1 - A method of manufacturing a secondary cell electrode

Info

Publication number: SE2251077A1
Application number: SE2251077A
Authority: SE
Inventors: Michael Koma
Original assignee: Northvolt Ab
Priority date: 2022-09-16
Filing date: 2022-09-16
Publication date: 2024-03-17
Also published as: WO2024056881A1

Abstract

ABSTRACT The present disclosure relates to methods of making electrodes for secondary cells, electrodes made by these methods, as well as methods of making secondary cells and cells made by these methods. The methods involve using a laser to remove excess electrode coating material prior to mitigate issues associated with a high edge, i.e. excess material at the edge of the electrode coating in tab-less electrodes.

Description

FIELD OF THE INVENTION The invention relates to electrodes for secondary cells, particularly a method of manufacturing such electrodes. The invention also relates to secondary cells which comprise said electrodes and a method of manufacturing the secondary cells.

BACKGROUND In addressing climate change, there is an increasing demand for rechargeable batteries to enable greater electrification of transportation and allow for greater dependence on renewable energy, among other reasons. Currently, lithium-ion batteries are becoming increasingly popular. They represent a type of rechargeable battery in which lithium ions move from a negative electrode to a positive electrode during discharge, and in the opposite direction when charging.

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

Jellyrolls, or Swiss rolls, may be used in the secondary cells. A jellyroll is a type of electrode assembly having a structure in which a positive electrode and a negative electrode, each having a long conductive sheet or foil coated with an active material, are wound with a separator interposed in-between. The wound assembly therefore has a cylindrical or “roll' shape. The roll is then placed into a casing or can. In some secondary cells, the roll is then soaked in electrolyte before the can is sealed. However, a solid electrolyte may also be used; in which case, the separator is not required.

Jellyroll secondary cells may be tab-less cells.

In tab-less cells, the conductive sheets commonly have an exposed (i.e., uncoated) part protruding from one side of the cylinder. The exposed part is connected to a terminal of the cell to allow the flow of an electrical current from the jelly roll via the terminal. To create an appropriate surface to connect a terminal to, the exposed part can be folded and/or pressed to form a surface with good contact properties while also aiming to minimize the risk of a short circuit.

When manufacturing electrodes for a tab-less cell, it is important to ensure the proper alignment of the active material to ensure that it is not present on the exposed part of the conductive sheet while retaining maximum overlap between the active materials of the anode and cathode. An excess of coating on the exposed part of the conductive sheet is referred to as a high edge. A high edge may lead to: - an imbalance between electrodes which could reduce the expected life of the cell; - risk of a short circuit when the conductive sheet is folded in order to connect it to the terminal; and/or - issues when folding the conductive sheet leading to the provision of a surface with sub-optimal contact properties.

SUMMARY OF THE INVENTION An object of the present invention is to manufacture electrodes so that the edge of the coated part is more accurately, precisely and/or reliably formed, thereby avoiding the issues associated with a high edge.

According to a first aspect of the invention, there is provided a method of manufacturing an electrode for a secondary cell, the method comprising the steps of: (a) providing a conductive sheet and an electrode coating covering a coated part of the conductive sheet, the conductive sheet further comprising an exposed part; (b)using a laser ablation process to remove an excess portion of the electrode coating from the conductive sheet, thereby enlarging the exposed part of the conductive sheet; wherein the conductive sheet and the electrode coating form the electrode.

In some embodiments, step (a) comprises: applying an electrode coating material to the conductive sheet to form a conductive sheet and an electrode coating material covering a coated part of the conductive sheet; processing the electrode coating material by rolling and/or calendaring; and optionally drying the electrode coating material.

In some embodiments, step (b) comprises the use of: a raster engraving process; and or a vector engraving process.

In some embodiments, step (b) comprises ablating the excess portion of the coating such that it is ejected and urged towards a venting device under a negative airflow.

In some embodiments, the laser is arranged such that it has sufficient power to ablate the electrode coating without damaging the conductive sheet.

In some embodiments, either before or after step (b), the method comprises the further step of notching and/or patterning the exposed part. The notching and/or patterning the exposed part may comprise using a laser cutting process or a laser ablation process.

According to a second aspect of the invention, there is provided an electrode for a secondary cell manufactured according to an embodiment of the first aspect of the invention.

According to a third aspect of the invention, there is provided a method of manufacturing a secondary cell, the method comprising the steps of (a) providing a first electrode according to the first aspect of the invention; (b) winding the first electrode and a second electrode about a central axis to form an electrode roll assembly having a first end from which the exposed part extends from; (c)connecting the exposed part of the first electrode to a first current collecting plate such that the connection is electrically conductive.

In some embodiments, step (c) further comprises connecting the exposed part of the second electrode to a second current collecting plate such that the connection is electrically conductive, preferably wherein the first and second current collecting plates are at opposing ends of the central axis of the electrode roll assembly.

In some embodiments, the second electrode is manufactured according to the method of the first aspect.

In some embodiments, the method comprises winding the first and second electrode with a separator positioned therebetween.

According to a fourth aspect of the invention, there is provided a secondary cell manufactured according to an embodiment of the third aspect of the invention.

In some embodiments, the secondary cell is a tab-less secondary cell and the excess portion comprises a high edge.

In some embodiments, the conductive sheet is substantially rectangular, having a length and a width, and the exposed part extends from an edge of the conductive sheet to an edge of the coated part across the length of the conductive sheet.

While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example and will be described in detail. It should be understood, however, that other embodiments, beyond the particular embodiments described, are possible as well. All modifications, equivalents, and alternative embodiments falling within the spirit and scope of the appended claims are covered as well.

The above discussion is not intended to represent every example embodiment or every implementation within the scope of the current or future Claim sets. The figures and Detailed Description that follow also exemplify various example embodiments. Various example embodiments may be more completely understood in consideration of the following Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 schematically illustrates a secondary cell manufactured using a method according to an embodiment of the third aspect of the invention; Figure 2 schematically illustrates an isometric view of a partially wound roll of conductive sheets having an exposed part; Figure 3 schematically illustrates a top view of a conductive sheet with active material coating applied, including a high edge; Figure 4 schematically illustrates a step of using a laser ablation process to remove the high edge shown in Figure 3; Figure 5 schematically illustrates a top view of the conductive sheet of Figure 3 following the laser ablation process shown in Figure 4; and Figure 6 schematically illustrates a tab-less secondary cell manufactured using a method according to another embodiment of the third aspect of the invention.

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

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 a secondary cell 1 (hereinafter also referred to as the cell 1).

Herein, the terms “inner' and “outer' are used with reference to the centre of the cell 1.

The cell 1 comprises a substantially cylindrical casing, also referred to as a can 2, and a cylinder-shaped electrode roll assembly 5, which may also be referred to as a jellyroll or Swiss roll, arranged inside the can 2. In this embodiment of the invention, the can 2 is also filled with a liquid electrolyte (not shown).

Figure 2 shows the electrode roll assembly 5 of Figure 1 in a partially rolled state. The electrode roll assembly 5 comprises first and second conductive sheets 4, 4', each sheet coated with a respective electrode coating 41, 41'. The first conductive sheet 4 and its electrode coating 41 are shown more clearly in Figure 3. The electrode coating 41 on the first conductive sheet 4 may constitute an active part of the positive electrode/cathode of the cell 1. In which case, the electrode coating 41' of the second conductive sheet 4' constitutes an active part of the negative electrode/anode of the cell 1. Alternatively, the anode and cathode may be arranged on the first and second conductive sheet respectively.

The materials of the conductive sheets 4, 4' and the electrode coatings thereon are known in the art. Suitable materials for the conductive sheets 4, 4' include copper (often used for the anode) and aluminium (often used for the cathode).

Electrode coatings are typically formed from electrode coating material comprising an active component, a binder and optionally a conductive component, typically at a weight ratio of about 98:1:1. The electrode coating is therefore typically predominantly active component, which (depending on whether the electrode is an anode or cathode) is usually a material containing lithium or a material capable of taking up lithium. Either way, such material typically has high surface area and is powdered, optionally crystalline, and given cohesive strength by the binder which is usually a polymer.

The active component typically differs for the anode and cathode.

For the cathode, the active component is typically a material containing lithium which can be easily released, such as a lithium transition metal complex, with lithium nickel manganese cobalt oxides (NMC) typically being used.

For the anode, the active component is typically a material capable of taking up lithium, such as graphite.

The two conductive sheets 4, 4' are arranged with a separator positioned therebetween. In particular, the electrode roll assembly 5 comprises first and second separator sheets 6, 6'. The first separator sheet 6 is positioned directly between the two conductive sheets 4, 4' and the second separator sheet 6' is positioned to cover an outer surface of the second conductive sheet 4' so that it separates the outer surface of the second conductive sheet 4' from the inner surface of the first conductive sheet 4 of an adjacent layer of wound sheets.

In other embodiments of the invention, a solid electrolyte may be used. In such embodiments, each separator sheet 6, 6' may be replaced by a sheet of solid electrolyte. Alternatively, solid electrolyte may be applied as a coating to the positive electrode coatings, the negative electrode coatings or the electrode coatings of both electrodes. It should be noted that although aspects of the invention are generally described with respect to secondary cells comprising liquid electrolyte, the various features are equally applicable, mutatis mutandis, to secondary cells comprising solid electrolyte. Also, other designs of known secondary cells are readily combinable with the aspects of the invention, for example other designs of the terminals, can or current collecting plate.

Referring back to Figure 2, the conductive sheets 4, 4' (and the separator sheets 6, 6') are wound in a longitudinal direction L (see Figure 3) into a cylindrical shape to form the electrode roll assembly 5. In other embodiments of the invention, the electrode roll assembly 5 may be wound to have a non-circular cross-section, such as an oval- or obround-shaped cross-section.

The first conductive sheet 4 comprises an exposed part 43 free from electrode coating 41 along a longitudinal edge 4a. Similarly, the second conductive sheet 4' also comprises an exposed part 43' along a longitudinal edge 4a'. However, the first and second conductive sheets 4, 4' are arranged in the electrode roll assembly 5 so that the exposed part 43 of the first conductive sheet 4 is positioned at an opposite end of the electrode roll assembly 5 to the exposed part 43' of the second conductive sheet 4'. The exposed parts 43, 43' provide for physical and electrical connection between each electrode and a respective terminal.

Notches 45 are cut (for example, by laser), or otherwise formed, in each of the exposed parts 43, 43'. More specifically, notches 45 are formed in the longitudinal edge 4a, 4a' of each conductive sheet 4, 4' which is free from coating. Due to the notches 45, flaps 44 are formed in the exposed parts 43, 43'. Hence, each notch 45 separates two consecutive flaps 44. The flaps 44 can be bent inwards towards a winding axis 40 of the electrode roll assembly 5 after the different stacked layers of the cell 1 have been rolled up. The bent flaps 44 form a contact surface 12 that enables improved electrical and physical connection to another component.

The above-described notching process is not always necessary. In other embodiments of the invention the exposed parts 43, 43' may be pressed or crushed to form a contact surface. The direction of press or crush may be coaxial with and towards the centre of the electrode roll assembly 5, for example.

Referring again to Figure 1, the cell 1 further comprises a current collecting plate 7 that is arranged adjacent to one end of the electrode roll assembly 5. In this embodiment of the invention, the current collecting plate 7 is in direct electrical and physical contact with the exposed part 43 of the first conductive sheet 4 of the electrode roll assembly 5, specifically the contact surface 12 (shown in Figure 2). In other words, the current collecting plate 7 is in contact with the exposed part 43 of the positive electrode. Further, the current collecting plate 7 is attached to the exposed part 43 by weld (for example, by laser weld).

In other embodiments of the invention, there may be an intermediary component or material connecting the current collecting plate 7 to the exposed part and providing electrical conductivity. Also, the current collecting plate 7 may be attached, directly or indirectly, to the electrode by any other suitable means, such as a different type of weld for example.

In embodiments of the invention in which the exposed part 43 is pressed or crushed, the pressing or crushing action may be carried out using the current collecting plate 7.

The cell 1 has a positive terminal (+) and a negative terminal (-). The can 2 comprises a central terminal through-hole 11 for a terminal part 3 forming part of the positive terminal. The terminal part 3 is in electrical contact with the current collecting plate 7 which is, in turn, in contact with the positive electrode, as described above. The negative terminal is electrically connected to negative electrode via any suitable means. Such a suitable connecting means is not shown in Figure 1 but may comprise a current collecting plate at the other end of the cell to the current collecting plate 7 of the positive electrode, as shown in Figure 6. 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 known to a person skilled in the art and they will not be described herein.

Figure 3 shows a top view of the first conductive sheet 4. However, it is to be understood that the following description of the conductive sheet 4 may also be applied, mutatis mutandis, to the second conductive sheet 4'.

The conductive sheet 4 has a flat rectangular structure that can be wound in a longitudinal direction L (indicated by the arrow) into a cylindrical shape (as shown in Figure 2). The conductive sheet 4 may, for example, be between 50 mm and 120 mm wide and about 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 sheet of Figure 3 (and also Figure 5 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 (the front face in Figure 3) and an outer side 4e (not visible in Figure 3 as it is the back face, which is indicated by the partially dotted reference arrow). The inner side 4d and the outer side 4e are defined relative to the centre of the wound e|ectrode roll assembly 5 (see the winding axis 40 in Figure 2). Furthermore, the conductive sheet 4 has two longitudinal edges 4a, 4f 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 to the wound e|ectrode roll assembly 5.

The inner side 4d (front face) of the e|ectrode sheet 4 will now be described. It shall be appreciated that the outer side 4e (back face) is identical but mirrored. Electrode coating 41 is coated, or formed, on both sides 4d, 4e of the conductive sheet 4 except for an exposed part 43 that is free from any e|ectrode coating 41.

The exposed part 43 includes the longitudinal edge 4a of the conductive sheet 4. As may be seen in Figures 1 and 2, the conductive first conductive sheet 4 is arranged within the e|ectrode roll assembly 5 so that the exposed part 43 extends further at one end of the wound e|ectrode roll assembly 5 than the corresponding edges of the second conductive sheet 4' forming the other e|ectrode and separator sheets 6, 6'. In other words, the exposed part 43 protrudes from the e|ectrode roll assembly 5 so that it may be considered as constituting one end of the wound e|ectrode roll assembly 5.

Electrode coating 41 is applied to cover the entire surfaces of the sides 4d, 4e of the conductive sheet 4 below the longitudinal dashed line, which indicates where the coated part is intended to end and the exposed part 43 intended to start.

The intended size of the exposed part 43 may vary. For example, the exposed part may be intended to extend 0.5 to 20 mm from the longitudinal edge 4a.

However, the e|ectrode coating 41 may comprise an excess quantity of e|ectrode coating material which extends further than intended towards the longitudinal edge 4a such that it impinges on a region of the conductive sheet 4 intended to form part of the exposed part 43. The excess quantity is referred to as a high edge 42.

The e|ectrode coating 41 is typically deposited on the conductive sheet 4 by a suitable methodology such as slot-die coating. The thickness of the e|ectrode coating will vary depending on the type of cell being produced. For instance, thinner coatings will favour faster charge and discharge rates of the cell, whereas thicker coatings will favour high- capacity batteries. Typical thicknesses vary from about 20 um to about 300 um, depending on the desired cell properties.

After deposition, the coating may be processed such as by calendaring or rolling to ensure a correct and even thickness. The coating may also undergo a drying step to remove any residual solvent. These steps necessarily cause some deformation of the electrode coating, which can lead to an uneven high edge, as well as abnormalities in the coating thickness in the regions close to the high edge.

These abnormalities at the high edge 42 are undesirable because it may lead to an imbalance between electrodes if one electrode has a relatively large high edge 42 and the other electrode has a relatively small high edge 42, or none at all. Moreover, unevenness in the thickness (i.e. the dimension through the plane of the foil, typically measured by beta gauge) of electrode coating at the high edge will also lead to an imbalance between the electrodes, resulting in differing electrode capacity across its The high edge 42 could also increase the risk of a short circuit when the conductive sheet 4, surface area. The imbalance could reduce the expected life of the cell 1. specifically the exposed part 43, is folded in order to connect it to the terminal. The high edge 42 may also cause issues when folding the exposed part 43, leading to the provision of a surface with sub-optimal contact properties.

To avoid the issues associated with the high edge 42, it may be removed using a laser ablation process. Such laser removal can advantageously result in a very even edge to the electrode coating 41, ensuring an even thickness of the electrode coating across its entire area, and a constant width of active material across the length of the coated area. The even thickness arises due to the tapered area present after calendaring/rolling being removed, to leave a step structure at the edge of the electrode coating. The even width arises due to the high accuracy in edge formation from the laser ablation. This gives rise to cells having improved properties such as improved capacity, improved lifetime, improved connection of the electrode to the current collecting plate, and reduced risk of failure. The laser ablation process may involve a type of laser engraving, in which a laser beam is directed at the high edge 42 to vaporise the excess coating material so that it may then be removed as loose debris from the conductive sheet 4.

To remove an entire high edge 42 from a conductive sheet, the laser beam must move relative to the conductive sheet 4. This may be achieved by: - holding the conductive sheet 4 stationary and moving a laser relative to it; - using a stationary laser and moving the conductive sheet 4 relative to it; or - using a stationary laser while also holding the conductive sheet 4 stationary and using moveable mirrors to adjust the direction of the laser beam.

In Figure 4, a laser ablation apparatus 20 that comprises movable mirrors is being used to remove the high edge 42 from the conductive sheet 4.

In particular, a static laser 21 emits a laser beam 22 along an emission axis running parallel to the conductive sheet 4, which is held stationary. A first mirror 23 is movable with a single degree of freedom represented by x. More specifically, the first mirror is movable along the emission axis and is angled to reflect the beam 22 so that it continues in a direction normal to the emission axis and also parallel to the conductive sheet 4. Once the laser beam 22 has been reflected by first mirror 23, it may be considered as travelling along a reflection axis.

A second mirror 24 is movable with two degrees of freedom. With respect to a first degree of freedom (x), the movement of the second mirror 24 is coupled to the movement of the first mirror 23 so that the two mirrors remain in alignment and the second mirror 24 remains in alignment with the reflection axis. The second degree of freedom (y) allows the second mirror 24 to move along the reflection axis.

The second mirror 24 is angled to reflect the laser beam 22 so that it continues in a direction normal to both the emission axis and the reflection axis, towards the conductive sheet. Once the laser beam 22 has been reflected by second mirror 23, it may be considered as travelling along a focusing axis. The laser beam 22 then passes through a focusing lens 25 which is coupled to the second mirror 24 so that it remains aligned with the second mirror and the focusing axis.

In use, the first and second mirrors 23, 24 are moved target the laser beam towards the high edge 42.

The focusing lens 25 is calibrated to increase the intensity of the laser beam 22 at the point that it contacts the high edge 42.

In some embodiments of the invention, the laser beam 22 may be controlled to direct most of its energy at a fixed penetration depth into the material of the high edge 42.

In this manner, only a particular depth of high edge material is removed when the 11 engraving takes place. Therefore, this setup is preferred for a high edge which is known to have a consistent depth.

In other embodiments of the invention, a laser apparatus with a more elaborate focusing mechanism, such as a dynamic auto focus system, may be used in order to handle an irregularly shaped high edge 42 that varies in depth. Such a laser apparatus may adjust its parameters in real time to adapt to the changing characteristics of the high edge 42 across the conductive sheet 4. For example, the depth of the high edge 42 may be monitored with devices tracking changes to ultrasound, infrared, or visible light aimed at the surface to be ablated. These devices, known as pilot beams or pilot lasers (if a laser is used) help guide adjustments made to the focusing lens 25 in order to adaptively focus the laser beam 22 on the surface of the high edge 42 and vaporise the excess electrode coating material more effectively.

The speed at which the laser beam moves relative to the conductive sheet 4 may also be considered when removing the high edge 42. Changing the amount of time that the laser beam 22 is directed at any one point of the high edge 42 may provide variation in the quantity of material removed.

Further, the laser 21 may be operated to emit the laser beam 22 in pulses. By changing the proportion of time (known as "duty-cycle") that the laser 21 is turned on during each pulse, the power delivered to the high edge 42 can be controlled appropriately for the material of the electrode coating 41 and the depth of the high edge 42.

Typically, the laser is arranged such that it has sufficient power to ablate the electrode coating without damaging (or impacting or altering) the conductive sheet.

Laser ablation of materials is well known in the art, and it is well within the remit of the skilled person to select a suitable laser capable of ablating the electrode coating. This is particularly the case due to the high ratio of active material to binder in the electrode coating, which results in the cohesive strength of the electrode coating being relatively low. In embodiments of the invention, the laser 21 may have a power output of up to about 300 W, preferably about 200 W, and may provide an infrared laser beam 22, preferably with a wavelength of about 1064 nm. 12 A suitable pulse width may be between 10 and 500 ns, optionally between 50 and 200 ns, preferably between 90 and 160 ns.

Pulsed emission of the laser beam can also reduce generation of heat in the laser 21 and associated equipment. In some embodiments of the invention, the laser ablation apparatus may also comprise a cooling system (not shown).

The laser ablation apparatus 20 also comprises a venting device 26 configured to remove the vaporised electrode coating material debris from the conductive sheet 4. The venting device may comprise a frustoconical collector, preferably arranged with the large cross section oriented towards the electrode material.

The venting device typically has a negative airflow, such that the debris and surrounding air is urged into the venting device upon being ejected from the surface. The venting device 26 may comprise blowers or a vacuum pump and may prevent or limit potentially noxious fumes and smoke being released from this process.

The incident angle of the laser is preferably arranged such that ejected debris moves away from the electrode coating 41. This ensures that the ejected debris is not deposited on the electrode coating, impacting the performance of the cell. Typically, the incident angle of the laser is arranged to ensure ejected material is urged towards the venting device 26.

Laser ablation machines may operate in vector and raster mode.

Vector engraving follows a line of electrode coating material to be removed.

Raster engraving traces the laser across the surface in a back-and-forth slowly advancing linear pattern that is analogous to a printhead on an inkjet or similar printer. The amount of advance of each line is normally less than the actual dot-size of the laser and the engraved lines overlap just slightly to create a continuity of material removal.

The electrode coating material is typically applied as a slurry and may comprise a solvent. The method of the disclosure therefore may comprise the step of drying the electrode coating, for instance air drying from 60°C to 120°C.

The laser ablation process may be done prior to or after drying the electrode coating. 13 In some embodiments, the laser ablation process occurs prior to drying the electrode coating.

In some embodiments, the laser ablation process occurs after drying the electrode coating (i.e. it is carried out to remove the dried electrode coating).

Figure 5 shows the conductive sheet of Figure 3 following application of the above- described laser ablation process. Essentially, the high edge 42 has been removed and the exposed part 43 is now the intended size so that the issues associated with a high edge during subsequent manufacturing steps and eventual use of the cell may be avoided.

In Figure 6, a cell 101 is shown which is similar to the cell 1 shown in Figure 1 except that the connection of the negative electrode/anode to the negative terminal is shown. The construction of this connection resembles that of the connection between the positive electrode and the positive terminal.

In particular, the cell 101 comprises a first current collecting plate 7 (equivalent to the current collecting plate 7 shown in Figure 1) and a second current collecting plate 107 arranged adjacent to the electrode roll assembly 5 but at the opposite end to the first current collecting plate 7. The exposed part 43' of the negative electrode extends from the other sheets in the electrode roll assembly 5 and is in direct electrical and physical contact with the second current collecting plate 107. The second current collecting plate 107 may be attached, directly or indirectly, to the negative electrode by any suitable means, as described above in relation to the first current collecting plate 7.

The can 2 further comprises a terminal part 103 forming the negative terminal. The terminal part 3 is in electrical contact with the current collecting plate 107. The cell 101 may also include a plurality of other components such as vents, connectors and insulating parts etc. There are many ways to design these parts known to a person skilled in the art and they will not be described herein.

It is to be understood that either one, or both, of the cell terminals may have a construction similar to that described above and that methods of manufacturing an electrode according to embodiments of the invention may improve the performance, safety and/or reliability of such cells by virtue of one or more high edges being removed. 14 Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Therefore, persons skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the appended claims. As used herein, the terms “comprise/comprises” or “include/includes” do not exclude the presence of other elements or steps. Furthermore, although individual features may be included in different claims (or embodiments), these may possibly advantageously be combined, and the inclusion of different claims (or embodiments) does not imply that a certain combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Finally, reference numerals in the claims are provided merely as a clarifying example and should not be construed as limiting the scope of the claims in any way.

Claims

1. A method of manufacturing an electrode for a secondary cell, the method comprising the steps of: (a) providing a conductive sheet and an electrode coating covering a coated part of the conductive sheet, the conductive sheet further comprising an exposed part; (b) using a laser ablation process to remove an excess portion of the electrode coating from the conductive sheet, thereby enlarging the exposed part of the conductive sheet; wherein the conductive sheet and the electrode coating form the electrode.

2. The method of c|aim 1, wherein the secondary cell is a tab-less secondary cell and the excess portion comprises a high edge.

3. The method of c|aim 1 or c|aim 2, wherein the conductive sheet is substantially rectangular, having a length and a width, and the exposed part extends from an edge of the conductive sheet to an edge of the coated part across the length of the conductive sheet.

4. The method of any preceding c|aim, wherein step (a) comprises: applying an electrode coating material to the conductive sheet to form a conductive sheet and an electrode coating material covering a coated part of the conductive sheet; processing the electrode coating material by rolling and/or calendaring; and optionally drying the electrode coating material.

5. The method of any preceding c|aim, wherein step (b) comprises the use of: a raster engraving process; and or a vector engraving process.

6. The method of any preceding c|aim, wherein step (b) urging material removed from the excess portion towards a venting device under a negative airflow.

7. The method of any preceding c|aim, wherein the laser is arranged such that it has sufficient power to ablate the electrode coating without damaging the conductive sheet.

8. The method of any preceding claim, wherein, either before or after step (b), the method comprises the further step of notching and/or patterning the exposed part.

9. The method of claim 8, wherein notching and/or patterning the exposed part comprises using a laser cutting process or a laser ablation process.

10. An electrode for a secondary cell manufactured according to the method of any preceding claim.

11. A method of manufacturing a secondary cell, the method comprising: (a) providing a first electrode manufactured according to the method of any of claims 1 to 9; (b) winding the first electrode and a second electrode about a central axis to form an electrode roll assembly having a first end from which the exposed part extends from; (c) connecting the exposed part of the first electrode to a first current collecting plate such that the connection is electrically conductive.

12. The method of claim 11, wherein step (c) further comprises connecting the exposed part of the second electrode to a second current collecting plate such that the connection is electrically conductive, preferably wherein the first and second current collecting plates are at opposing ends of the central axis of the electrode roll assembly.

13. The method of claim 11 or claim 12, wherein the second electrode is manufactured according to the method of any of claims 1 to

14. The method of any of claims 11 to 13, wherein step (b) comprises winding the first and second electrode with a separator positioned therebetween.

15. A secondary cell manufactured according to the method of any of claims 11 to 17