SE2350367A1

SE2350367A1 - Method for manufacturing an electrode for a secondary cell

Info

Publication number: SE2350367A1
Application number: SE2350367A
Authority: SE
Inventors: Dayama Parth Omprakash; Korde Prasad Mangesh
Original assignee: Northvolt Ab
Priority date: 2023-03-30
Filing date: 2023-03-30
Publication date: 2024-10-01
Also published as: SE547774C2

Abstract

This disclosure relates to a method for manufacturing an electrode for a secondary cell, an electrode manufactured by such a method and a secondary cell comprising such an electrode. The method comprises providing an electrode substrate including an electrically conducting material; using an additive manufacturing process to form an active layer on the electrode substrate, wherein the active layer comprises a plurality of carbonaceous particles; and exposing the carbonaceous particles to a magnetic field configured to orient a majority of the carbonaceous particles in a direction substantially normal to the electrode substrate.

Description

METHOD FOR MANUFACTURING AN ELECTRODE FOR A SECONDARY CELL Field This disclosure relates to a method for manufacturing an electrode for a secondary cell, electrodes manufactured using such methods and secondary cells comprising such electrodes.

Background Rechargeable or secondary batteries (comprising a plurality of rechargeable or secondary cells) find widespread use as electrical power supplies and energy storage systems. For example, in automobiles, batteries formed of a plurality of lithium-ion cells are provided as a means of effective storage and utilization of electric power. The lithium-ion cells represent a type of secondary cell in which lithium ions move from the negative electrode through an electrolyte to the positive electrode during discharge and in a reverse direction during charge.

Electrodes in secondary cells comprise active materials participating in the electrochemical charge and discharge reactions. Commonly, graphite is used as active material in anodes thanks to its abundance and relatively low cost.

However, there is an ever-increasing demand in the industry for improved anodes providing, for instance, increased charging density and reduced charging time.

One method of improving charging density and reducing charging time is to expose the electrodes to laser processing to provide pathways through the active material so that electrolyte soaking and ionic transport is improved. However, laser processing may result in waste of valuable active materials, the formation of dust that may reduce electrode performance, and possible damage to the substrate that supports the active materials.

Summary According to a first aspect of the present disclosure there is provided a method for manufacturing an electrode for a secondary cell, comprising the steps of: a. providing an electrode substrate comprising an electrically conducting material; b. using an additive manufacturing process to form an active layer on the electrode substrate, wherein the active layer comprises a plurality of carbonaceous particles; c. exposing the carbonaceous particles to a magnetic field configured to orient a majority of the carbonaceous particles in a direction substantially normal to the electrode su bstrate.

In one or more embodiments, steps b and c may at least partially overlap such that the majority of carbonaceous particles are oriented in a direction normal to the electrode substrate as the active layer is formed.

In one or more embodiments, the plurality of carbonaceous particles may comprise at least one of graphite or graphene oxide.

In one or more embodiments, the method may further comprise adding a dopant to the plurality of carbonaceous particles.

In one or more embodiments, step b may further comprise forming the active layer to comprise at least one passage extending at least partially through the active layer.

In one or more embodiments, the at least one passage may extend substantially parallel to the normal of the electrode substrate.

In one or more embodiments, the at least one passage may extend at least 50% through the active layer.

In one or more embodiments, the additive manufacturing process may comprise inkjet printing or direct ink writing of the active layer on the electrode substrate.

In one or more embodiments, the active layer formed by inkjet printing or direct ink writing may be fluid when exposed to the magnetic field, thereby enabling the magnetic field to orient the majority of the carbonaceous particles within the active layer such that they are substantially aligned to the normal of the electrode.

In one or more embodiments, the method may further comprise the step of drying the active layer after or while exposing the carbonaceous particles to the magnetic field.

In one or more embodiments, the additive manufacturing process may comprise direct ink writing of the active layer on the electrode substrate and the active layer may comprise an ink comprising graphene oxide particles.

In one or more embodiments, the method may further comprise the step of thermally annealing the active layer to reduce the graphene oxide particles to graphene particles.

According to a second aspect of the present disclosure there is provided an electrode for a secondary cell, manufactured using a method according to any of the preceding claims, the electrode comprising: an electrode substrate comprising an electrically conducting material; and an active layer comprising a plurality of carbonaceous particles, wherein a majority of the carbonaceous particles are oriented in a direction substantially normal to the substrate.

In one or more embodiments, the carbonaceous particles may comprise at least one of graphite or graphene oxide.

In one or more embodiments, the carbonaceous particles may be doped with a dopant.

In one or more embodiments, the electrode may have an electrode density of 1.4 to 1.7 g/cm3.

In one or more embodiments, the active layer may have a thickness of from 10 to 120 um.

In one or more embodiments, the active layer may comprise at least one passage extending at least partially through the active layer.

According to a third aspect of the present disclosure there is provided a secondary cell comprising an electrode according to the second aspect of this disclosure or any one of its embodiments.

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 Drawinas One or more embodiments will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 shows a cross-section of an example embodiment of an electrode according to an aspect of this disclosure; Figure 2 shows an example embodiment of a method according to an aspect of this disclosure; Figure 3 shows a cross-section illustrating the orientation of a particle in relation to a substrate; and Figure 4 shows a cross-section of a further example embodiment of an electrode according to an aspect of this disclosure, in which the active layer comprises at least one passage.

Detailed Description Known electrodes for a secondary cell comprise an active layer coating an electrode substrate comprising an electrically conducting material. The morphology of the active layer has turned out to be an important factor affecting the electrochemical performance of the electrode. The inventors have realized that by orienting particles within the active layer such that they are aligned to the normal of the substrate, such that a majority of the particles have a similar orientation with respect to each other, a beneficial effect is observed with respect to the ion diffusion coefficient, i.e., the speed with which ions in the electrolyte can move into and out from the active layer. Put differently, by increasing the ordering of particles in the active layer, the tortuosity and ionic resistance of the material is reduced. As a result, charging and discharging speed is improved. Further, the improved ordering of the particles increases intercalation efficiency and allows the particles to be more densely packed, resulting in an electrode having increased energy density.

Figure 1 illustrates an electrode 100 comprising an electrode substrate 110 formed of an electrically conducting material such as, for example, a copper or aluminium foil. The electrode substrate 110 is at least partially coated with an electrochemically active layer 120 configured to intercalate lithium ions to store electrical charge during charging of the battery cell. The electrode 100 may form the anode of a secondary cell.

The term “electrochemically active layer" is to be understood as referring to a layer comprising electrochemical species which can be oxidized or reduced in a system which enables a cell to produce electric energy during discharge. The electrochemically active layer 120, also referred to as “active layer", may form a continuous layer covering at least a major part of the surface of the substrate.

The active layer 120 comprises a plurality of carbonaceous particles 122 suspended in a binder 123 which may, for example, comprise at least one of styrene butadiene copolymer (SBR), carboxymethyl cellulose (CMC), polyacrylates or polyvinylidene fluoride (PVDF).

The term “carbonaceous” is to be understood as describing a substance or material rich in carbon, such as containing or comprising at least 60 wt% (such as at least 70 wt%, such as at least 80 wt%, such as at least 90 wt%, such as at least 95 wt%, such as at least 99%) carbon.

Thus, carbonaceous particles according to the present disclosure may, for example, comprise or consist of graphite or graphene. Further, the carbonaceous particles may be graphite or graphene particles.

Carbonaceous particles according to the present disclosure may, for example, comprise or consist of graphite. Further, the carbonaceous particles may be graphite particles.

Carbonaceous particles according to the present disclosure may, for example, comprise or consist of graphene. Further, the carbonaceous particles may be graphene particles.

In other examples, the carbonaceous particles may comprise or consist of silicon coated with a carbon-based material, such as graphite or graphene.

In further examples, the active layer 120 may comprise silicon-containing particles (not shown) in addition to carbonaceous particles. The term “silicon-containing” is to be understood as describing a substance or material rich in silicon, such as containing or comprising at least 60 wt% (such as at least 70 wt%, such as at least 80 wt%, such as at least 90 wt%, such as at least 95 wt%, such as at least 99%) silicon.

The silicon-containing particles may be silicon particles.

In some examples, the silicon-containing particles may be spherical in shape or in the form of silicon nanowires.

In examples wherein the active layer 120 comprises silicon-containing particles, the quantity of silicon in the active layer may be limited to a maximum level. For example, the active layer 120 may comprise at most 40 wt% (such as at most 30 wt%, such as at most 20 wt%, such as at most 10 wt%) silicon.

Typically, silicon-containing particles will be present in the active layer at a loading level of from 5 to 40 mg/cmz, such as from 10-35 mg/cmz, often in combination with graphite.

The silicon-containing particles typically have a D50 particle size of from 2 to 20 um, such as from 5 to 15 um.

Typically, when the carbonaceous particle is graphite (and particularly in combination with silicon-containing particles), the D50 particle size of the graphite particles is from 4 to 25 um, such as from 8 to 20 um.

As used herein, D50 particle sizes refer to the D[4,3]50 particle size (i.e. 50th percentile of the volume weighted mean diameter), as measured using laser diffraction such as with a Mastersizer 3000 from Malvern Panalytical Ltd.

Inclusion of silicon in the active layer, within some or all of the carbonaceous particles 122 and/or within separate silicon-containing particles, may improve the energy density of the active layer 120.

The carbonaceous particles 122, or at least a majority thereof, are oriented in a direction substantially normal to the electrode substrate 110. This means that regions of binder 123 running between the carbonaceous particles 122 also run substantially normal to the electrode substrate 110 and allow ions to travel more directly through the active layer 120, either towards or away from the electrode substrate 110. In other words, the tortuous pathways for ionic transport that would be formed by carbonaceous particles distributed in random orientations are replaced by much more direct pathways. The orientation of the carbonaceous particles 122 in a direction substantially normal to the electrode substrate 110 therefore results in reduced ionic resistance of the active layer 120 and improved charging and discharging times for the resultant secondary cell.

References in this disclosure to “a majority of the carbonaceous particles" are to be understood as referring to at least 50% (such as at least 60%, such as at least 70%, such as at least 80%, such as at least 90%) of the carbonaceous particles.

The terms “direction normal to the substrate" or “normal direction” are to be understood as referring to the orthogonal direction to a main plane of extension of the electrode substrate. The normal direction may also be considered as equivalent to a stacking direction of the layers forming a secondary cell.

The electrode 100 may be manufactured using a method 200, shown in Figure 2. The method 200 comprises steps of: 202) providing an electrode substrate 110 comprising an electrically conducting material; 204) using an additive manufacturing process to form an active layer 120 on the electrode substrate 110, wherein the active layer 120 comprises a plurality of carbonaceous particles 122; 206) exposing the carbonaceous particles 122 to a magnetic field configured to orient a majority of the carbonaceous particles 122 in a direction substantially normal to the electrode substrate 1 10.

The magnetic field may be applied to induce a dipole moment causing the carbonaceous particles 122 to rotate and align with the field lines of the magnetic field as the active layer is being formed using an additive manufacturing process. It is realised that this effect may be employed both for elongated particles having a main direction of extension, and planarorflake-shaped particles extending in a main plane of extension. By applying a magnetic field, the particles are forced to rotate such that their main direction of extension, or main plane of extension, aligns with the magnetic field lines.

Figure 1 includes a representation of field lines (shown as broken lines) for a magnetic field suitable for orienting the majority of the carbonaceous particles 122 in a direction normal to the electrode substrate 110. In particular, the field lines of the magnetic field are oriented to pass through the active layer 120 in a direction substantially parallel to the normal N of the substrate 110. 122, ferromagnetic, at least a majority of the carbonaceous particles 122 may become Due to magnetic properties of the carbonaceous particles which may be diamagnetic, paramagnetic or oriented along the field lines of the magnetic field as the active layer 120 is formed via additive manufacturing.

Orienting a majority of the carbonaceous particles 122 in a direction substantially normal to the electrode substrate 110 causes regions of binder 123 between the particles to extend substantially normal to the electrode substrate 110 as well. In other words, tortuous pathways for ionic transport that would be formed by carbonaceous particles distributed in random orientations are replaced by much more direct pathways. Orienting the carbonaceous particles 122 in a direction substantially normal to the electrode substrate 110 therefore results in reduced ionic resistance of the active layer 120 and improved charging and discharging times in the resultant secondary cell.

In some embodiments, a dopant may be added to the carbonaceous particles 122 to improve the magnetic properties. The dopants may be provided to increase the magnetic dipole moment of the particles. Depending on the type of dopant, may be modified into being paramagnetic or ferromagnetic so as to exhibit a stronger interaction with an applied magnetic field.

Figure 3 illustrates the orientation of a carbonaceous particle 122 in relation to the normal N of the substrate 110. The carbonaceous particle 122, which may be an elongated particle or a flake-shaped particle, is to be oriented such that its length L or main plane of extension (e.g., in case of a flake) is substantially aligned with the normal N.

The terms “length” and “main plane of extension” may be understood by observing a particle extending in at least two different directions, of which the extension in a first direction is greater than an extension in a second direction. The extension in the first direction may then be referred to as the length. In other words, the extension of the particle that is longest (i.e., longer than all other extensions) may be considered as the length of that particle.

Substantially planar particles, such as graphite flakes or graphene sheets, may be characterized by their main plane of extension (that is, the largest cross-sectional plane extending through the particle), rather than their length. Accordingly, it would be the main plane of extension that would be oriented so as to be substantially aligned with the normal of the electrode substrate. In such instances, it will be appreciated that the length (i.e., the longest extension of the particle) might not be substantially aligned with the normal of the electrode substrate despite the main plane of extension being substantially aligned with the normal of the electrode substrate. Particles in such an orientation will still be considered substantially aligned with the normal of the electrode substrate. Such planar particles may be oriented parallel to each other as well to further increase the ordering of the particles.

The carbonaceous particles may conform to three-dimensional shapes such as, for instance, ellipsoids and rods. The orientation of three-dimensionally shaped particles may be considered depending on whether the particle extends dominantly in one, two or three directions from a possible three orthogonal directions.

If a particle extends dominantly in one direction (along one axis if modelled in a cartesian coordinate system), the particle may be considered an elongated particle that has a length which may be oriented to substantially align with the normal of the electrode substrate.

If a particle extends dominantly in two directions (along two axes if modelled in a cartesian coordinate system), the particle may be considered a flake-shaped particle that has a main plane of extension which may be oriented to substantially align with the normal of the electrode substrate.

If a particle extends dominantly in all three directions, it may be considered substantially spherical and the alignment of such particles is of minimal concern in the context of this disclosure as the orientation of such particles will have little, if any, bearing on electrode performance. This is because the orientation of a substantially spherical particle will have little to no effect on the tortuosity of pathways through the active layer.

As indicated in Figure 3, the true orientation of a carbonaceous particle 122 (which is not substantially spherical) may deviate slightly from the normal N, forming an angle d with the normal N, and still be considered substantially parallel to the normal N. The angle d may lie in the interval of O° to 45° (such as O° to 35°, such as O° to 25°, such as O° to 15°, such as O° to 5°) to be considered substantially parallel to the normal N.

Accordingly, any references in this disclosure to carbonaceous particles that are “oriented in a direction substantially normal to the electrode substrate" (or equivalent references such as those mentioned in the preceding paragraph) are to be understood as encompassing any carbonaceous particle having a length or main plane of extension that deviates from normal to the electrode substrate by O° to 45° (such as O° to 35°, such as O° to 25°, such as O° to 15°, such as O° to 5°).

Further, any references in this disclosure to method steps “exposing the carbonaceous particles to a magnetic field configured to orient a majority of the carbonaceous particles in a direction substantially normal to the electrode substrate" are to be understood as encompassing a method step of exposing the carbonaceous particles to a magnetic field configured to orient a majority of the carbonaceous particles “towards' a direction substantially normal to the electrode substrate. Orienting a majority of the carbonaceous particles “towards' a direction substantially normal to the electrode substrate is to be understood as encompassing orienting a majority of the carbonaceous particles so that the length or main plane of extension of those particles ultimately deviates from normal to the electrode substrate by O° to 45° to 35°, such as O° to 25°, such as O° to 15°, such as O° to 5°). (such as O° The carbonaceous particles 122 may comprise graphite, such as graphite particles or flakes, which is known to be a diamagnetic material. To increase their response to an applied magnetic field, the particles 122 may be doped with paramagnetic or ferromagnetic particles. The dopant may comprise nanoparticles, for instance comprising Fe3O4. Fe3O4 particles may be attached to the surface of graphite particles by means of van Der Waals forces, and may beneficially turn the graphite particles into paramagnetic particles. The graphite flakes may for example be fine or medium flakes. Fine flakes typically have a D50 particle size in the range of from 1 to 7um and medium flakes typically have a D50 particle size in the range of from 8 to 18um.

Referring back to the method 200 shown in Figure 2, the additive manufacturing process of step 204 may comprise inkjet printing or direct ink writing of the active layer 120 on the electrode substrate 110. In such examples, the method 200 may comprise an additional step of drying the active layer 120 after or while exposing the carbonaceous particles 122 to the magnetic field. In some examples, drying of the active layer 120 may be performed by employing a freeze-drying process to solidify the active layer 120 by removing a solvent such as water.

In examples of the method 200 comprising direct ink writing of the active layer 120 on the electrode substrate 110, the active layer may comprise an ink comprising graphite or graphene oxide (GO) particles and a solvent. The solvent may be water such that the ink is an aqueous ink.

The material for forming the active layer 120, which may comprise an ink, may be configured so as to have a viscosity that enables sufficient movement of carbonaceous particles 122 therein for the intended orientation of those particles to occur. Furthermore, the material may be configured to have a viscosity that is also low enough to prevent blockage of the nozzle it is ejected from during the additive manufacturing process and/or high enough to provide the resulting active layer 120 with suitable structural characteristics.

In some examples, the active layer 120 may be formed with a layer-by-layer deposition process. This may involve depositing a first sub-layer of material, comprising the ink, onto the electrode substrate 110. While the material is fluid and exposed to the magnetic field, carbonaceous particles 122 therein will be oriented in a direction substantially normal to the electrode substrate 110. The material forming the first sub-layer may then be allowed to dry (or actively dried) and a subsequent sub-layer may be deposited on top, thereby sandwiching the first sub-layer between the electrode substrate 110 and the subsequent sub-layer. As with the first sub-layer, the material of the subsequent sub-layer may be exposed to the magnetic field while it is fluid so that carbonaceous particles 122 therein are oriented in a direction substantially normal to the electrode substrate 110 before the material dries. This sub-layer deposition may be repeated until an active layer 120 is formed with the desired depth. 11 Layer-by-layer deposition may be particularly beneficial as it may allow a majority of the carbonaceous particles 122 to be oriented in a direction substantially normal to the electrode substrate 110 without the magnetic field causing unwanted travel of the carbonaceous particles through the active layer 120 (either towards or away from the electrode surface) or distortion of the intended shape of the active layer 120.

In examples comprising GO particles, the method 200 may comprise the step of thermally annealing the active layer 110 to reduce the GO particles to graphene particles.

The inclusion of GO particles in the ink may be particularly beneficial for carrying out the method 200 because GO has ferromagnetic characteristics and exposing GO particles to a magnetic field will cause the desired alignment without necessarily requiring an additional dopant. However, GO exhibits low electrical conductivity, so it is necessary to reduce the GO particles to graphene particles to provide the active layer with the required electrical conductivity.

In other examples, the additive manufacturing process of step 204 may comprise alternative additive manufacturing processes to inkjet printing or direct ink writing. For example, a laser-based additive manufacturing process may be used wherein a laser is used to melt, sublime or ablate materials that are to be deposited on the electrode surface 110, optionally in a layer-by-layer process. While the material is molten or in an evaporated, particulate, form, carbonaceous particles 122 may be free to orientate to a direction substantially normal to the electrode substrate 110 due to exposure to the magnetic field. Then as the molten or evaporated material solidifies and/or deposits on the electrode substrate 110 (or the preceding sub-layer), the carbonaceous particles 122 will become fixed in the normal orientation.

Figure 4 shows an electrode 300 which may be similarly configured as the electrode 100 shown in Figure 1 except that a plurality of passages 340 extends through the active layer 120.

The plurality of passages 340 increase the porosity of the active layer 120 and further reduce the tortuosity of pathways through the active layer. Therefore, the passages 340 assist in reducing an ionic resistance of the active layer 120 to enable the electrode 300 to have improved electrochemical performance. The passages also assist in facilitating electrolyte soaking of the active layer 120 to improve the mass and charge 12 transport Characteristics of the electrode 300. In some embodiments, the plurality of passages forms grooves or channels, such as zig-zag grooves, in the active layer.

The passages 340 shown in Figure 4 are conica| penetrations into the active layer 120. It is to be understood that the passages 340 may have other shapes, such as non- conica| penetrations. In some examples, a single passage 340 may extend across the active layer 120 as grooves or channels configured in a spiral, grid or web so as to be evenly distributed across active layer 120. In other examples, a plurality of passages 340 may extend across the active layer 120 as grooves or channels configured in lines (e.g., as “zig-zags', rows, columns or concentric shapes) so as to be evenly distributed across the active layer 120.

In some examples, the passages 340 may have a depth D corresponding to from more than 0% and up to 95%, such as from 5% to 95%, such as from 25% to 90%, such as from 50% to 90% of the thickness of the active layer 120. Further, the passages 340 may have a maximum width W (or maximum diameter, if appropriate) of less than 60um, such as from 5 to 60um, such as from 10 to 50um, such as from 10 to 40um, such as from 12 to 35um, such as from 15 to 35um, such as from 15 to 30um.

A layer-by-layer deposition process for the formation of the active layer 120 may assist with the formation of passages 340 having the desired shape, width and depth.

Referring again to the method 200 shown in Figure 2, the method 200 may further comprise calendaring the active layer 120 and the substrate 110 to increase a coating density, or electrode density, of the electrode 100. Calendaring, or compaction, may involve pressing or rolling of the surface of the active layer 120 and may be performed after the magnetic field has been applied to orientate the carbonaceous particles 122. It will be appreciated that the calendaring process may be performed a single time or multiple times during the processing of the electrode.

In some examples, the resultant electrode 100 has an electrode density of from 1.4 to 1.7 g/cm3. The term “electrode density” is to be understood as the volumetric mass density of the active layer.

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 13 “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. 14

Claims

1. A method for manufacturing an electrode for a secondary cell, comprising the steps of: a. providing an electrode substrate comprising an electrically conducting material; b. using an additive manufacturing process to form an active layer on the electrode substrate, wherein the active layer comprises a plurality of carbonaceous particles; c. exposing the carbonaceous particles to a magnetic field configured to orient a majority of the carbonaceous particles in a direction substantially normal to the electrode substrate.

2. The method of Claim 1, wherein steps b and c at least partially overlap such that the majority of carbonaceous particles are oriented in a direction normal to the electrode substrate as the active layer is formed.

3. The method of Claim 1 or Claim 2, wherein the plurality of carbonaceous particles comprise at least one of graphite or graphene oxide.

4. The method of any of the preceding claims, further comprising adding a dopant to the plurality of carbonaceous particles.

5. The method of any of the preceding claims, wherein step b further comprises forming the active layer to comprise at least one passage extending at least partially through the active layer.

6. The method of Claim 5, wherein the at least one passage extends substantially parallel to the normal of the electrode substrate.

7. The method of Claim 5 or Claim 6, wherein the at least one passage extends at least 50% through the active layer.

8. The method of any of the preceding claims, wherein the additive manufacturing process comprises inkjet printing or direct ink writing of the active layer on the electrode substrate.

9. The method of claim 8, wherein the active layer formed by inkjet printing or direct ink writing is fluid when exposed to the magnetic field, thereby enabling the magnetic field to orient the majority of the carbonaceous particles within the active layer such that they are substantially aligned to the normal of the electrode.

10. The method of Claim 8 or claim 9, further comprising the step of drying the active layer after or while exposing the carbonaceous particles to the magnetic field.

11. The method of any one of Claims 8 to 10, wherein the additive manufacturing process comprises direct ink writing of the active layer on the electrode substrate and the active layer comprises an ink comprising graphene oxide particles.

12. The method of Claim 11, further comprising the step of thermally annealing the active layer to reduce the graphene oxide particles to graphene particles.

13. An electrode for a secondary cell, manufactured using a method according to any of the preceding claims, the electrode comprising: an electrode substrate comprising an electrically conducting material; and an active layer comprising a plurality of carbonaceous particles, wherein a majority of the carbonaceous particles are oriented in a direction substantially normal to the su bstrate.

14. The electrode of Claim 13, wherein the carbonaceous particles comprise at least one of graphite or graphene oxide.

15. The electrode of Claim 13 or Claim 14, wherein the carbonaceous particles are doped with a dopant.

16. The electrode of any of Claims 13 to 15, having an electrode density of 1.4 to 1.7 g/cm

17. The electrode of any of Claims 13 to 16, wherein the active layer has a thickness of from 10 to 120 um.

18. The electrode of any of Claims 13 to 17, wherein the active layer comprises at least one passage extending at least partially through the active layer.

19. The electrode of Claim 18, wherein the at least one passage extends substantially parallel to the normal of the electrode substrate.

20. The electrode of Claim 18 or Claim 19, wherein the at least one passage extends at least 50% through the active layer.

21. A secondary cell comprising an electrode according to any one of Claims 13 to 17