Method for cutting a coated electrode by laser

Abstract

There is disclosed herein a method for preparing an electrode for a sodiumion secondary cell comprising the steps of providing an aluminium sheet configured to act as a current collector in the electrode; applying an electrode coating comprising an active electrode material on the aluminium sheet to form a coated aluminium sheet, and directing a laser beam onto the electrode coating of the coated aluminium sheet to thereby cut the coated aluminium sheet to a desired electrode shape.

Description

[0001] The present disclosure relates to a method for preparing an electrode, an electrode, a secondary battery cell, a vehicle and a battery system.Background

[0002] There is an increasing demand for electric vehicles, and storage possibilities of energy. Current technologies use lithium-ion batteries, which comprises of nowadays expensive lithium only sourced from a few places in the world such as China and South America. Lithium is not abundant and with increasing demand in batteries, the lithium inventory will become depleted. Lithium-ion batteries may have a major market share of rechargeable batteries, but alternatives such as sodium ion batteries represent an attractive alternative to lithium-ion batteries. Sodium-ion batteries contain sodium, which is an abundant and accesible material. Sodium ion batteries are shown an increasing interest in order diversify the battery industry in view of raw materials but also show good storing capacity of energy.

[0003] As the world’s resources are finite, the use of them is important.Recycling of materials and improving performance and lifetime of batteries is key for improving the pace of electrification and use of renewable energy, in order to faster decrease the industrialized world’s dependency on petroleum and natural gas.

[0004] In order to provide a sufficient supply to the battery demand, batteries consisting of abundant and easy to source materials are needed. Thus, there is a need for new batteries and components thereof to overcome the problems with conventional products and to provide new batteries with improved performance.Summary

[0005] The present disclosure aims to provide improved secondary cells and parts thereof. The improvements may be in energy performance, manufacturing efficiency, decreased amount of material used, and assembly simplification, among others.

[0006] In particular, according to an aspect of the present disclosure, there is provided a method for preparing an electrode for a sodium-ion secondary cell comprising the steps of providing an aluminium sheet configured to act as a current collector in the electrode; applying an electrode coating comprising an active electrode material on the aluminium sheet to form a coated aluminium sheet, and directing a laser beam onto the electrode coating of the coated aluminium sheet to thereby cut the coated aluminium sheet to a desired electrode shape.

[0007] When the electrode is configured to be an anode in the secondary cell, the active electrode material comprises Hard carbon. Hard carbon refers to a solid form of carbon that cannot be converted to graphite by heat-treatment. It may be produced by heating carbonaceous precursors to approximately 1000 °C in the absence of oxygen.

[0008] When the electrode is configured to be a cathode in the secondary cell, the active electrode material comprises Prussian blue analogue. The Prussian blue analogue. Prussian blue analogue (PBA) may exist in a hydrated; i.e. hydrous phase, and in a dehydrated; i.e. anhydrous phase, in which the water has been removed. The Prussian blue analogue is preferably applied on the aluminium sheet in its hydrated phase. The Prussian blue analogue of the present invention comprises sodium as a charge carrier.

[0009] Hard carbon anodes and Prussian blue analogue cathodes are known to be utilized in the art of sodium ion-batteries, as described in e.g.WO2023 / 066805 A1.

[0010] In the production of sodium ion batteries, the electrode active material is applied on the metal sheet configured to act as a current collector to form a coated metal sheet, which is then cut to a desired electrode shape. Hard carbon and Prussian Blue analogue electrodes are known to be brittle.Mechanical cutting (which is typically performed by punching a die through the coated sheet), of such electrodes have therefore proven difficult as the brittleness tend to induce coating delamination, in particular in the edge portion of the formed electrode. This is problematic, in particular since after cutting, the electrodes are dried in order to remove water and to obtain the sought-after electrode properties. During drying, minor cracks and coating delamination may propagate and generate larger coating delamination.

[0011] In an attempt to alleviate this problem, the present inventors have found that the coated aluminium sheets of the present invention can be cut to a desired electrode shape by a laser beam, which is directed onto the coated aluminium sheet. Laser cutting has proven advantageous in that it provides a clean cut with little to no coating delamination, even though the electrode active materials utilized in the present invention are brittle. Laser cutting has been found advantageous in particular when cutting relatively thick electrode coatings, and more particularly when said electrode coatings contains high mass loadings of electrode active materials.

[0012] It should be noted that aluminium current collectors have previously been seen as a substrate unsuitable for laser cutting, as the aluminium tends to melt and / or reflect the laser beam which causes poor edge quality of the cut surface.

[0013] However, the present inventors have found that a Hard carbon coating can absorb some of the energy of the laser beam at the relevant wavelengths used for laser cutting, leading to that an acceptable edge quality can be obtained in the cut electrode.

[0014] Similarly, a Prussian blue analogue coating has also been found to absorb some of the energy of the laser beam at the relevant wavelengths used for laser cutting. The electrode coating may further comprise a carbon black additive, such as CNT, flake type graphite, or Ketjenblack, in order to increase the absorption at the relevant wavelengths.

[0015] The aluminium sheet is provided so that it can act as a current collector of the formed electrode. Preferably, the aluminium sheet is provided as a foil of aluminium metal or of a suitable aluminium alloy, preferably an aluminium alloy comprising aluminium in an amount of at least 98 atom-%, preferably at least 99 atom-%. Such aluminium alloys include aluminium grades 1050 and 1100.

[0016] Preferably, the electrode coating is applied on both major sides of the aluminium sheet. The coating may be applied by any suitable means known to the skilled person in the art. When the aluminium sheet is coated on both sides, a total thickness of the coated aluminium sheet may be at least 150 microns. Alternatively, the electrode coating is applied only on one major side of the aluminium sheet.

[0017] After the coating has been applied by wet coating or other means known to the skilled person in the art, it is typically calendared such that a uniform coating thickness can be applied.

[0018] In some embodiments, when the electrode is intended to be an anode, the electrode coating is applied such that the mass loading of the electrode coating comprising Hard carbon is at least 5 mg / cm2. The higher the mass loading of the Hard carbon electrode coating, the more brittle and prone to cracking the electrode coating becomes. Mass loadings exceeding 5 mg / cm2 have proven particularly advantageous to cut using laser, as mechanical cutting typically renders unacceptable quality due to coating delamination.

[0019] Mass loading [mg / cm2] is defined as the mass of electrode coating per surface area of the coated aluminium sheet. The mass loading of the electrode coating on a coated aluminium sheet may be determined by cutting a coated aluminium sheet to a well-defined electrode size, weighing the cut coated aluminium sheet, deducting the mass of the aluminium foil (which has a known density and thickness) to obtain the mass of the electrode coating, and dividing the mass of the electrode coating with the surface area of a major side of the cut coated aluminium sheet to obtain a value of the mass loading in mg / cm2. If the coated electrode contains coatings on both major sides of the aluminium foil, the value is divided by 2 to obtain the mass loading for the double-sided coating.

[0020] Preferably, the electrode coating is applied such that the mass loading of the electrode coating comprising Hard carbon is at least 5 mg / cm2, such as of at least 6 mg / cm2, such as of at least 7 mg / cm2, such as of at least 9 mg / cm2, such as of at least 9 mg / cm2, such as of at least 10 mg / cm2, such as of at least 11 mg / cm2, such as of at least 12 mg / cm2, such as of at least 13 mg / cm2, such as of at least 14 mg / cm2, such as of at least 15 mg / cm2.

[0021] The mass loading of the electrode coating comprising Hard carbon may be in the range of from 5-30 mg / cm2.

[0022] In some embodiment, when the electrode is intended to be an anode, the coating is applied such that the coating layer comprises Hard carbon in an amount of at least 90 % by weight of the coating layer. A high amount of electrode active material is necessary in order to obtain acceptable electrochemical performance. In addition to the electrode active material, the electrode coating may comprise various additives, such as binders and conductive additives.

[0023] In some embodiments, when the electrode is intended to be a cathode, the electrode coating is applied such that the electrode coating comprises Prussian blue analogue in an amount of at least 10 mg / cm2.

[0024] The higher the mass loading of the Prussian blue analogue coating, the more brittle and prone to cracking the electrode coating becomes. Mass loadings exceeding 10 mg / cm2 have proven particularly advantageous to cut using laser, as mechanical cutting typically renders unacceptable quality due to coating delamination.

[0025] Preferably, the electrode coating is applied such that a mass loading of the electrode coating comprising Prussian blue analogue is at least 10 mg / cm2, such as of at least 10.5 mg / cm2, such as of at least 11 mg / cm2, such as of at least 11.5 mg / cm2, such as of at least 12 mg / cm2, such as of at least 12.5 mg / cm2, such as of at least 13 mg / cm2, such as of at least 13.5 mg / cm2, such as of at least 14 mg / cm2, such as of at least 14.5 mg / cm2, such as of at least 15 mg / cm2, such as of at least 15.5 mg / cm2, such as of at least 16 mg / cm2, such as of at least 16.5 mg / cm2, such as of at least 17 mg / cm2, such as of at least 17.5 mg / cm2, such as of at least 18 mg / cm2, such as of at least 18.5 mg / cm2, such as of at least 19 mg / cm2, such as of at least 19.5 mg / cm2, such as of at least 20 mg / cm2, such as of at least 20.5 mg / cm2, such as of at least 21 mg / cm2, such as of at least 21.5 mg / cm2, such as of at least 22 mg / cm2, such as of at least 22.5 mg / cm2, such as of at least 23 mg / cm2, such as of at least 23.5 mg / cm2, such as of at least 24 mg / cm2, such as of at least 24.5 mg / cm2, such as of at least 25 mg / cm2, such as of at least 25.5 mg / cm2, such as of at least 26 mg / cm2, such as of at least 26.5 mg / cm2, such as of at least 27 mg / cm2, such as of at least 27.5 mg / cm2, such as of at least 28 mg / cm2, such as of at least 28.5 mg / cm2, such as of at least 29 mg / cm2, such as of at least 29.5 mg / cm2, such as of at least 30 mg / cm2, such as of at least 30.5 mg / cm2, such as of at least 31 mg / cm2

[0026] The mass loading of the electrode coating comprising Prussian blue analogue may be in the range of from 10-50 mg / cm2.

[0027] In some embodiments, when the electrode is intended to be a cathode, the coating is applied such that the coating layer comprises Prussian blue analogue in an amount of at least 90 % by weight of the coating layer. A high amount of electrode active material is necessary in order to obtain acceptable electrochemical performance. In addition to the electrode active material, the electrode coating may comprise binders and various additives, such as binders and conductive additives.

[0028] In some embodiments, the Prussian blue analogue is a Prussian Blue analogue having the formula AaMb[M’c(CN)6]d, wherein A is sodium, and 1 < a < 2, wherein M and M’ are transition metals, preferably selected from iron and / or manganese, wherein 0 < b < 2, 1 < c < 2, and 1 < d < 2.

[0029] In some embodiments, the Prussian Blue analogue is Prussian white having the formula AaFe[Fe(CN)6], wherein A is sodium, and wherein 1.8 < a < 2, preferably wherein 1.9 < a < 2.

[0030] In some embodiments, the Prussian blue analogue is in a hydrated state when the electrode coating is applied. Preferably, the Prussian Blue analogue is Prussian white in a hydrated state. After the coated aluminium sheet has been cut into an electrode shape, the electrode is typically dried in order to obtain the sought-after electrode properties. During such drying, water is evaporated from the crystal structure and the hydrated Prussian Blue analogue may undergo a phase-transformation to its anhydrous state. In such embodiments it is particularly important that the obtained electrode has welldefined edges, as small cracks and small amounts of delamination of the coating around the edges of the electrode may propagate during drying and cause delamination of larger portions of the coating. Thus, laser cutting has proven to be particularly advantageous when Prussian blue analogue is in a hydrated state when the electrode coating is applied.

[0031] Upon drying and in contact with air, Prussian white may additionally slowly react into hydrated Prussian Blue, iron (III) hexacyanoferrate (II).Consequently, the electrode coating may contain an upper layer comprising Prussian blue near the upper surface of the electrode coating comprising Prussian white.

[0032] In some embodiments, the electrode coating further comprises a conductive additive selected from the list consisting of carbon nano-tubes, flake type graphite, ketjen black, carbon black, or combinations thereof. The conductive electrode may be present in the electrode coating in an amount of less than 5 % by weight of the coating. Conductive additives are particularly preferred when the electrode coating comprises Prussian blue analogue, as they will increase the absorption of the relevant laser wave lengths.

[0033] In some embodiments, the electrode coating further comprises a binder selected from the list consisting of styrene butadiene rubber (SBR), polyacetylene, sodium lignosulfonate (NaLS), sodium alginate, guar, , sodium carboxymethyl cellulose (Na-CMC), polyacrylic acid (PAA), and sodium polyacrylate (PANa), or any combination thereof. The binder may be present in the electrode coating in an amount of less than 5 % by weight of the coating.

[0034] The coating may preferably be applied such that the electrode coating is devoid of fluorinated compounds. Consequently, neither the binder nor the conductive additive should be selected from fluorinated compounds.

[0035] In some embodiments, the electrode coating is applied from an aqueous slurry comprising the electrode active material. The electrode coating is preferably applied such that the electrode active material is substantially evenly distributed in the coating. This could be obtained by mixing the aqueous slurry to make sure that all components are substantially evenly distributed in the slurry.

[0036] In some examples, the laser beam is produced by a laser beam generating means being selected from the list consisting of a carbon-dioxide laser machine, a neodymium laser machine, or a neodymium-yttriumaluminium-garnet laser machine.

[0037] Preferably, the laser is a pulsed fibre laser.

[0038] The nominal wavelength of the laser beam is preferably in the range of 1040 nm to 1100 nm, such as in the range of 1040 nm to 1080 nm, such as in the range of 1050 to 1070 nm, such as about 1064 nm.

[0039] In some embodiments, wherein the laser beam generating means operates at a laser power in the range of 20-500 W, such as in the range of 200-300 W, such as about 250 W. The laser beam generating means should be capable of generating a laser beam which can cut through the coated electrode sheet.

[0040] In some embodiments, the diameter of the narrowest part of the laser beam is less than 30 microns.

[0041] In some embodiments, the step of applying the electrode coating includes calendaring the coated aluminium sheet to improve the adhesion between the electrode coating and the aluminium sheet. After the electrode coating has been applied on the aluminium sheet, the material may be pressed and compacted onto the current collector by e.g. calendaring, for instance by means of a roller press calendar. Accordingly, a consistent thickness and density of the coating may be achieved. Calendaring, if applied, is performed before the laser cutting of the coated electrode sheet.

[0042] In a second aspect of the present invention, there is provided an electrode prepared by the method described in the first aspect.

[0043] In a third aspect, there is provided a secondary sodium-ion cell comprising an electrode as described in the second aspect as anode or cathode. A secondary cell comprises cathode, anode, electrolyte and separator housed in a housing.

[0044] In a fourth aspect, there is provided a vehicle comprising the secondary sodium-ion cell as described in the third aspect.

[0045] In a fourth aspect, there is provided a battery system comprising the secondary sodium-ion cell as described in the third aspect.

[0046] In a sixth aspect, there is provided a method for preparing an electrode for a potassium-ion secondary cell. Anodes prepared by the method of the first aspect are suitable for use also in potassium ion secondary cells. The method of the first aspect can also prepare cathodes for potassium ion secondary cells if the charge carrier sodium of the Prussian blue analogue is replaced by potassium. Thus, in the fifth aspect, the Prussian blue analogue comprises potassium charge carrier.Brief Description of the Drawings

[0047] One or more embodiments of the present disclosure will be described, by way of example only, and with reference to the following figures, in which:

[0048] Figure 1 illustrates a method of a method for preparing an electrode for a sodium-ion secondary cell according to aspects of the present invention.

[0049] Figure 2 schematically shows a step of directing a laser beam onto a coated aluminium sheet to thereby cut the aluminium sheet.Detailed Description

[0050] The present disclosure is described in the following by way of a number of illustrative examples. It will be appreciated that these examples are provided for illustration and explanation only and are not intended to be limiting on the scope of the present disclosure. Instead, the scope of the present disclosure is defined by the appended claims.

[0051] Furthermore, although embodiments be presented individually for the sake of focused discussion of particular features, it will be recognized that the present disclosure also encompasses combinations of the embodiments described herein.

[0052] Figure 1 shows a flowchart of a method 1000 for a for preparing an electrode for a sodium-ion secondary cell according to an aspect of the present invention. Alternatively or additionally, the electrode may be suitable for use in a potassium ion battery.

[0053] The method 1000 comprises a step of providing 1010 an aluminium sheet. The aluminium sheet may be any aluminium metal sheet or aluminium alloy sheet that is suitable for use as a current configured to act as a current collector in the electrode. In the event that the aluminium sheet is an aluminium alloy sheet, the aluminium alloy preferably comprises at least 95 atom-% aluminium. The aluminium sheet is preferably an aluminium alloy comprising at least 98 % atom-% of aluminium, more preferably at least 99 atom-% of aluminium, such as aluminium grade 1050 or aluminium grade 1100. Both aluminium grade 1050 and aluminium grade 1100 comprises at least 99 atom-% of aluminium and minor additions of alloying elements.

[0054] The sheet is preferably provided in the shape of a foil, preferably having a well-defined thickness in the range of 10-20 pm.

[0055] Next, the method comprises a step of applying 1020 an electrode coating comprising an active electrode material on the aluminium sheet to form a coated aluminium sheet. The coating may be applied on one major side of the aluminium sheet, but preferably on both major sides of the aluminium sheet. Means for coating a current collector with electrode active material are known to the person skilled in the art. Preferably, the coating is applied by wet coating from a slurry, preferably an aqueous slurry, which comprises the electrode active material and optionally conductive additives and / or binders. Preferably, the slurry is mixed such that the components of the slurry are uniformly distributed in the slurry.

[0056] Preferably, the coating comprises at least 90 % of electrode active material, by weight of the electrode active material.

[0057] If the electrode is intended to be used as an anode in a secondary cell, the active electrode material in the coating comprises Hard carbon. The electrode coating may have a mass loading of at least 5 mg / cm2.

[0058] If the electrode is intended to be used as an anode in a secondary cell, the active electrode material in the coating comprises Prussian blue analogue. The electrode coating may have a mass loading of at least 10 mg / cm2.

[0059] The conductive additives may be selected from carbon black, graphite, graphene, carbon nanotubes (CNT), or any combination thereof, preferably carbon black.

[0060] The conductive additive may be present in the electrode coating in an amount of less than 5 % by weight of the electrode coating.

[0061] The binder may be selected from selected from styrene butadiene rubber (SBR), polyacetylene, sodium lignosulfonate (NaLS), sodium alginate, guar, sodium carboxymethyl cellulose (Na-CMC), polyacrylic acid (PAA), and sodium polyacrylate (PANa), or any combination thereof, preferably said at least one binder is sodium carboxymethyl cellulose (Na-CMC), styrene butadiene rubber (SBR), or a combination thereof.

[0062] The binder may be present in the electrode coating in an amount of less than 5 % by weight of the electrode coating.

[0063] The coated aluminium sheet is preferably calendared to obtain a coating of substantially uniform thickness with good adhesion to the aluminium sheet.

[0064] Next, the method comprises directing 1030 a laser beam onto the electrode coating of the coated aluminium sheet to thereby cut the coated aluminium sheet to a desired electrode shape.

[0065] After the application of an electrode coating, the coated aluminium sheet needs to be cut to a desired electrode shape. The electrodes are typically cut to a substantially quadrangular shape, such as a rectangular shape. According to the present invention, this is done by directing 1030 a laser beam onto the electrode coating of the coated aluminium sheet. The laser beam is the directed such that coated aluminium sheet can be cut to a desired shape, either by controlling and moving the laser beam in relation to a stationary coated aluminium sheet, or by moving the coated aluminium sheet in relation to a stationary laser beam.

[0066] Advantageously, it has been found that the application of a laser beam to cut the coated aluminium sheet into a desired electrode shape can alleviate flaking problems associated with prior art methods, such as mechanical die cutting. Both Hard carbon and Prussian blue analogue coatings are brittle, especially at high mass loadings of electrode active material coatings. Die cutting has typically caused the coatings to flake or notch, especially at the edges, which negatively impacts the electrochemical performance of the electrode. Laser cutting has proven advantageous in that the coated aluminium sheet can be cut to a desired shape with low or no flaking issues even at high mass loadings of electrode active material coatings.

[0067] It shall be noted that aluminium is known to be a relatively poor substrate for laser cutting, due to its low melting point and reflectivity.However, according to the present invention, the aluminium surface is advantageously covered by the electrode coating, which alleviates the known issues. A high mass loading of electrode active material coating is thus also advantageous in that it provides a better coverage of the aluminium substrate. The electrode coatings of the present invention are furthermore advantageous in that they absorb energy from the laser at the selected wavelength.

[0068] The desired shape of the obtained electrode may vary depending on the type of cell the electrode is configured to be used in. Relevant shapes and sizes are known to the person skilled in the art, and include quadrangular, such as rectangular shapes. To allow the current collector to electrically contact the terminals in the cell, the cut electrode preferably comprises an uncoated tab of aluminium sheet.

[0069] The laser beam is produced by a laser beam generating means. The properties of the laser beam generating means and the laser beam are discussed in more detail with reference to Figure 2.

[0070] Figure 2 schematically depicts a step of directing a laser beam onto a coated aluminium sheet to thereby cut the aluminium sheet, i.e. step 1030 in Figure 1.

[0071] Figure 2 shows a cross-section of a coated aluminium sheet 200 comprising an aluminium sheet 210 covered by an electrode coating 220 comprising electrode active material on both major sides of the aluminium sheet 210.lt shall be noted that the thickness of the aluminium sheet 210 in relation to the coating 220 is exaggerated in Figure 2.

[0072] The coating 220 is preferably applied with a substantially uniform thickness t, which may be in the range of 70-200 microns. The thickness is preferably applied so that the thickness of the coating 220 is substantially the same on both major sides of the aluminium sheet 210. The electrode preferably has a total thickness T in the range of 150-400 pm. A uniform coating may be obtained by a step of calendaring the coated aluminium sheet 200.

[0073] A laser beam 250 is directed onto the coating 200 to thereby cut the coated aluminium sheet 200. The laser beam 250 is generated by a laser beam generating means 240.

[0074] The laser beam 250 may be applied in pulses, preferably having a pulse frequency in the range of 1-100 kFIz, such as in the range of 1-50 kFIz. The pulse width may be in the range of 4-500 ns, such as in the range of 150-250 ns, such as about 200 ns.

[0075] The laser beam may have a focus width of less than 30 microns.

[0076] In order to obtain the desired electrode shape, the beam 250 is moved on the surface of the coated aluminium sheet 200 in a pattern corresponding to the desired electrode shape. In one alternative, the coated electrode sheet 200 is provided on a translating support structure (not shown) capable of translating the coated aluminium sheet 200 in relation to a stationary laser beam generating means 240.

[0077] In another alternative, the laser beam generating means 240 is provided on a translating support structure (not shown) capable of translating so that the laser beam can be moved in relation to the stationary coated aluminium sheet 200.

[0078] The cutting speed of the laser beam is preferably in the range of 25-1000 mm / s.

[0079] The wavelength of the laser beam is preferably a nominal laser wavelength in the range of 1040-110Onm, such as 1064 nm.

[0080] The beam generating means 240 can be any laser generating apparatus capable of generating a laser beam as described above with a laser power in the range of 20-500 W. Such laser beam generating means include carbon-dioxide laser machines, neodymium laser machines, or neodymium yttrium-aluminium-garnet laser machines. Preferably, the laser machine is a pulse fibered laser machine.

[0081] Preferably, the step of cutting is performed in a cutting chamber 260 which is sealed from the ambient atmosphere by an enclosing wall 265. This is particularly advantageous when the electrode active material comprises a Prussian Blue analogue. During the cutting of coated aluminium sheets 200 comprising Prussian Blue analogues, cyanide containing gases will emit from coating. Inside the cutting chamber there is provided a scrubber 270 capable of sucking in said gases for treatment. The scrubber may preferably be an active carbon scrubber or a wet alkaline scrubber. It may also be a nickel catalyzed oxidation scrubber or a flame stack. The scrubber may be coupled to an exhaust 280 capable of emitting scrubbed gas from the chamber.EXAMPLES

[0082] 1. Cathode material preparation

[0083] Prussian white electrodes were prepared by coating an aluminium foil on both major sides of the foil. The provided coating comprised Prussian white Na2-xFe[Fe(CN)6] mH20 with a Na content above 1.8 as an cathode active material. The coating had the following composition 93 % by weight cathode active material being Prussian white, 3 % by weight of conductive additive being carbon black, and 4 % by weight of binder (being 1% carboxymethyl cellulose, and 3 % by weight of styrene butadiene rubber) based on the combined total weight of cathode active material, conductive agent, and binder present. The coating was applied from an aqueous slurry.

[0084] A first set of coated aluminium sheets for cathodes were prepared. The mass loading of Prussian white electrode coating was 12.5 mg / cm2. The coated aluminium sheets were then calendared to an electrode thickness of 170 pm (aluminium sheet plus coating on both major sides).

[0085] A second set of coated aluminium sheets for cathodes were prepared in a similar manner, but with a mass loading of 21.7 mg / cm2. The coated aluminium sheets were then calendared to an electrode thickness of 285 pm (aluminium sheet plus coating on both major sides).

[0086] Mechanical cutting (comparative example)

[0087] Coated aluminium sheets of the first and second set were then cut into electrodes using a mechanical die, by punching the mechanical die through the coated aluminium sheet.

[0088] Edge flaking (i.e. coating delamination from the aluminium sheet) could be observed in all electrodes, by visual inspection. More flaking was observed in the cathodes having a mass loading of 21.7 mg / cm2 than in the cathodes having a mass loading of 12.5 mg / cm2

[0089] Four electrodes having a mass loading of 21.7 mg / cm2 was weighed after mechanical cutting and the average weight was 4.3975 g.

[0090] Laser cutting (inventive example)

[0091] Coated aluminium sheets of the second set were instead cut using laser cutting to a corresponding size as the mechanically cut electrodes. The laser cutting was performed with a pulse fibre laser with a nominal laser wavelength of 1064 nm. Laser power of 100 W. Pulse frequency is set to 20 kHz The pulse width was set to 200 ns. Beam diameter focus was <30pm. Cutting speed was 35 mm / s.

[0092] No edge flaking could be observed in any of the samples, by visual inspection.

[0093] Four electrodes having a mass loading of 21.7 mg / cm2 was weighed after cutting and the average weight was 4.5474 g.

[0094] Thus, the average weight of the mechanically cut electrodes were 96.70 % of the weight of the laser cut electrodes.

[0095] 2. Anode material preparation

[0096] A first set of coated aluminium sheets for anodes were prepared by coating an aluminium foil on both major sides of the foil. The provided coating comprised Hard carbon as a anode active material. The coating had the following composition 92 % by weight anode active material being Hard carbon, 4 % by weight of conductive additive being carbon black, and 4 % by weight of binder (being 1 % by weight of carboxymethyl cellulose, and 3 % by weight of styrene butadiene rubber) based on the combined total weight of anode active material, conductive agent, and binder present. The coating was applied from an aqueous slurry.

[0097] The coated aluminium sheets were then calendared to an electrode thickness of 240 pm (aluminium sheet plus coating on both major sides). The mass loading of the coating was 11 mg / cm2.

[0098] A second set of coated aluminium sheets for anodes were prepared in a similar manner, but they were only coated on one major side in order to investigate the effects of mechanical cutting versus laser cutting on the foil itself. The coated aluminium sheets were then calendared to an electrode thickness of 120 μm (aluminium sheet plus coating on one major side). The mass loading of the coating was 5.8 mg / cm2

[0099] Mechanical cutting (comparative example)

[0100] Coated aluminium sheets of the first and second sets of anodes were then cut into electrodes using a mechanical die, by punching the mechanical die through the coated aluminium sheet.

[0101] Edge flaking (i.e. coating delamination from the aluminium sheet) could be observed in all electrodes, by visual inspection. More flaking was observed in the anodes having a mass loading of 11 mg / cm2 than in the anodes having a mass loading of 5.8 mg / cm2

[0102] In electrodes of the second set, deformation of the aluminium foil along the edges could be observed on the uncoated major side. The deformation is attributed to the pressure exerted by the mechanical die during the punching. This deformation not only promotes flaking but also generates sharp edges that have the potential to facilitate separator penetration when assembling the battery cells risking short circuiting.

[0103] Laser cutting (inventive example)

[0104] Coated aluminium sheets of the first and second sets of anodes were instead cut using laser cutting to a corresponding size as the mechanically cut electrodes. The laser cutting was performed with a pulse fibre laser with a nominal laser wavelength of 1064 nm. Laser power of 65 W. Pulse frequency is set to 20 kHz The pulse width was set to 200 ns. Beam diameter focus was <30μm. Cutting speed 35 mm / s.

[0105] No edge flaking could be observed in any of the samples, by visual inspection.

[0106] No deformation of the aluminium foil along the edges could be observed.

[0107] While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments are shown and described above by way of example in relation to the drawings, with a view to clearly explaining the various advantageous aspects of the present disclosure. It should be understood, however, that the detailed description herein and the drawings attached hereto are not intended to limit the disclosure to the particular form disclosed. Rather, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the following claims.

Claims

1. A method (1000) for preparing an electrode for a sodium-ion secondary cell comprising the steps ofproviding (1010) an aluminium sheet (210) configured to act as a current collector in the electrode;applying (1020) an electrode coating (220) comprising an active electrode material on the aluminium sheet (210) to form a coated aluminium sheet (200), wherein the active electrode material comprisesHard carbon, if the electrode is configured to be an anode in the secondary cell, and wherein the electrode coating is applied such that the mass loading of the electrode coating is at least 5 mg / cm2, or Prussian blue analogue, if the electrode is configured to be a cathode in the secondary cell, and wherein the electrode coating is applied such that the mass loading of the electrode coating is at least 10 mg / cm2;directing (1030) a laser beam (250) onto the electrode coating (220) of the coated aluminium sheet to thereby cut the coated aluminium sheet to a desired electrode shape.

2. The method according to any one of the preceding claims, wherein the active electrode material comprises Hard carbon.

3. The method according to claim 2, wherein the electrode coating is applied such that the mass loading of the electrode coating is at least 10 mg / cm2.

4. The method according to any one of claims 2 or 3, wherein the coating is applied such that the electrode coating comprises Hard carbon in an amount of at least 90 % by weight of the coating layer.

5. The method according to claim 1, wherein the active electrode material comprises Prussian blue analogue.

6. The method according to claim 5, wherein the electrode coating is applied such that the mass loading of the electrode coating is at least 15 mg / cm2.

7. The method according to any one of claims 5 or 6, wherein the coating is applied such that the electrode coating comprises Prussian blue analogue in an amount of at least 90 % by weight of the coating layer.

8. The method according to any one of claims 5 to 7, wherein the Prussian blue analogue is a Prussian Blue analogue having the formula AaMb[M’c(CN)6]d, wherein A is sodium, and 1 < a < 2, wherein M and M’ are transition metals, preferably selected from iron and / or manganese, wherein 0 < b < 2, 1 < c < 2, and 1 < d < 2.

9. The method according to claim 8, wherein the Prussian Blue analogue is Prussian white having the formula AaFe[Fe(CN)6], wherein A is sodium, and wherein 1.8 < a < 2, preferably wherein 1.9 < a < 2.

10. The method according to any one of claims 8 or 9, wherein the Prussian blue analogue is in a hydrated state when the electrode coating is applied.

11. The method according to any one of the preceding claims, wherein the electrode coating further comprises a conductive additive selected from the list consisting of carbon nano-tubes, flake type graphite, ketjen black, carbon black, or combinations thereof.

12. The method according to any one of the preceding claims, wherein the electrode coating further comprises a binder selected from the list consisting of styrene butadiene rubber (SBR), polyacetylene, sodium lignosulfonate (NaLS), sodium alginate, guar, sodium carboxymethyl cellulose (Na-CMC), polyacrylic acid (PAA), and sodium polyacrylate (PANa), or any combination thereof.

13. The method according to any one of the preceding claims, wherein the electrode coating is applied from an aqueous slurry comprising the electrode active material.

14. The method according to any one of the preceding claims, wherein the electrode coating is applied such that the electrode active material is substantially uniformly distributed in the coating.

15. The method according to any one of the preceding claims, wherein the laser beam is produced by a laser beam generating means (240) being selected from the list consisting of a carbon-dioxide laser machine, a neodymium laser machine, or a neodymium yttrium-aluminium-garnet laser machine.

16. The method according to claim 15, wherein the laser beam generating means operates at a laser power in the range of 20-500 W.

17. The method according to any one of the preceding claims, wherein the diameter of the narrowest part of the laser beam is less than 30 microns.

18. The method according to any one of the preceding claims, wherein the coating is applied on both major sides of the aluminium sheet.

19. The method according to any one of the preceding claims, wherein a thickness of the coated aluminium sheet is at least 150 microns.

20. The method according to any one of the preceding claims, wherein the coating is applied such that the coating layer is devoid of fluorinated compounds.

21. The method according to any one of the preceding claims, wherein the step of applying (1010) the electrode coating further comprises calendaring the coated aluminium sheet to improve the adhesion between the electrode coating and the aluminium sheet.

22. An electrode prepared by the method defined in any one of claims 1-20.

23. A secondary sodium-ion cell comprising an electrode as defined in claim 22 as anode or cathode.

24. A vehicle comprising the secondary sodium-ion cell as defined in claim 23.

25. A battery system comprising the secondary sodium-ion cell as defined in claim 23.