Laser processing of electrode layers
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- GLOBAL NANO NETWORK LTD
- Filing Date
- 2025-11-28
- Publication Date
- 2026-06-04
Smart Images
Figure GB2025052614_04062026_PF_FP_ABST
Abstract
Description
[0001] LASER PROCESSING OF ELECTRODE LAYERS
[0002] Technical Field
[0003] The present invention relates to manufacturing an electrode for use in electrochemical devices, such as batteries, particularly lithium-ion batteries.
[0004] Background
[0005] Lithium-ion batteries, LIBs, consist of two electrodes (a cathode and an anode) separated by a liquid electrolyte. A porous polymeric film that enables the exchange of ions from one side to the other is interposed between the two electrodes. Conventional LIB electrode manufacturing is carried out using a process known as slurry casting, in which a mixture of active material, binder, and conductive additive is mixed with a solvent and cast onto a substrate. This process is not environmentally friendly and requires high capital investment costs due to the necessity for high-energy drying and recovery of solvents such as N-methyl pyrrolidone, NMP. Similar challenges arise for non-lithium based batteries.
[0006] Using a dry powder deposition process instead of slurry casting would eliminate the need for solvents, significantly reducing process time and cost. This approach is proven in the industrial production of coatings for car bodies, surface protection and finishing, and colour painting applications. However, there are challenges associated with dry powder electrode manufacture for LIBs, such as achieving good adhesion and tortuosity, and obtaining an even dispersion and thickness of the coating.
[0007] A more even dispersion and thickness of a dry powder coating may be achieved by compacting the dry powder following deposition. However, the increased density of the coating may reduce the electrical conductivity of the resulting electrode.
[0008] Summary
[0009] According to a first aspect of the invention, there is provided a method of manufacturing an electrode. The method comprises depositing a powder to form a composite layer on an electrically conductive substrate, the composite layer comprising an active material and particles of binder material for adhering the active material to the electrically
[0010] 38234310-2 conductive substrate; exposing the composite layer to a light source (e.g., laser) to heat the particles of binder material and thereby cause groups of particles of the binder material to coalesce to form droplets on and / or within the composite layer; and solidifying the droplets of binder material.
[0011] In some implementations, the droplets of binder material may not be homogeneous, and may comprise material other than the binder material. One or more of the droplets of binder material may be or comprise a bubble - that is, a droplet of binder material enclosing a central region of a substance other than the binder material. For example, one or more of the droplets may enclose a central region comprising a gas, such as air or argon.
[0012] The droplets of binder material may be formed in the bulk of the composite layer. Alternatively or additionally, the droplets may be formed on the surface of the composite layer.
[0013] The active material is a material which participates in the electrode reaction (halfreaction) of a cell comprising the electrode. The active material may be any suitable material. Optionally, the active material may comprise a lithium-containing material. For example, the active material may comprise a high-voltage spinel material; lithium titanate, LTO; NMC111 , LiNi0.33Mn0.33Co0.33O2; NMC 622, LiNi0.67Mn0.28Co0.05O2; NMC 811, LiNi0.8Mn0.1Co0.1O2; Lithium Nickel Manganese Oxide, LNMO; and / or Lithium Iron Phosphate, LFP. The Lithium Nickel Manganese Oxide may be LiMn1.5Nio.5O4, or any other suitable lithium nickel manganese oxide material. As another example, the active material can comprise a sodium salt, e.g., sodium Prussian blue and its analogues (PBAs).
[0014] The binder material is a material suitable for adhering the active material to the electrically conductive substrate. Any suitable material may be used as the binder material - for example, the binder material may comprise a polymer binder. In particular, the polymer binder may be a carboxymethyl cellulose, CMC, polymer. Alternatively, the polymer binder may be a polyvinylidene difluoride, PVDF, polymer, or another fluorocarbon polymer.
[0015] 38234310-2 In some implementations, the particles of binder material can have a plate-like morphology prior to exposing the composite layer to the light source.
[0016] As used herein, the term “plate-like morphology” refers to particles or grains having two mutually orthogonal dimensions (length and width) that are substantially greater than the third dimension (thickness). Such particles generally possess a flattened, sheet-like, flake-like, or lamellar geometry and may be regular or irregular in their perimeter shape. Particles having a plate-like morphology can, for example, have a length and a width that are each at least 1.2 times greater, at least 1.5 times greater, at least 2 times greater, or at least 5 times greater, than their thickness. In some examples, the particles can have a flake-like shape, characterised by irregular, plate-like structures with rough, faceted surfaces. The particles need not be perfectly flat or planar and may exhibit some degree of curvature, warping, or surface irregularity. The morphology of the particles can be investigated by scanning electron microscopy, for example.
[0017] Compared to binder particles that have a substantially spherical morphology, particles having a plate-like morphology tend to interlock or form bridges within the composite layer, which can significantly influence their packing behaviour and mechanical response to applied forces. This bridging tendency can promote better interfacial contact and active material utilisation after exposure of the composite layer to the light source to heat the particles of binder material, which can thereby improve electrode performance.
[0018] In some implementations, the method can further comprise, prior to depositing, mechanically processing substantially spherical particles of binder material to flatten the particles into the plate-like morphology. For example, mechanically processing the particles of binder material can comprise grinding or milling (e.g., ball milling) the particles of binder material. Preferably, the shear forces on the particles of binder material are controlled to avoid damaging the particles. That is, the particles can be flattened without appreciable fragmentation.
[0019] As one particular example, the particles of binder material can be processed with grinding media, such as metallic (e.g., zirconium) or ceramic spheres, to obtain the platelike morphology. For example, in some implementations, the grinding medium can be substantially spherical, e.g., with a radius in a range from 2 mm to 50 mm. For example,
[0020] 38234310-2 the particles of binder material and the grinding media can be processed using an acoustic mixer.
[0021] Optionally, the composite layer may further comprise particles of an electrically conductive additive (e.g., a carbonaceous conductive additive), to enhance the electrical conductivity of the composite layer. The electrically conductive additive may comprise any suitable material, such as carbon black, carbon nanotubes, CNTs; vapour-grown carbon fibres, VGCFs; and / or graphene.
[0022] In some implementations, the droplets of binder material have a substantially spherical morphology after solidifying.
[0023] In some implementations, the particles of binder material can be heated by the electrically conductive additive following absorption of light from the light source by the electrically conductive additive. For example, the particles of binder material and the active material may be substantially transparent at the wavelengths of light emitted by the light source (e.g., laser), whilst the electrically conductive additive can be a strong absorber at these wavelengths (at least relative to the particles of binder material and active material). The particles of binder material can therefore be heated indirectly via thermal conduction from the electrically conductive additive. Preferably, the electrically conductive additive is homogenously dispersed within the composite layer to facilitate heating of the particles of binder material.
[0024] In some implementations, the heating the particles of binder material to form the droplets causes decomposition of the binder material.
[0025] For example, the decomposition of the binder material can generate a gas (e.g., comprising one or more of carbon dioxide, water, hydrogen fluoride, one or more hydrocarbons, and so on). In some implementations, the gas generated by the decomposition of the binder material in a droplet can cause inflation of the droplet, e.g., to thereby increase the surface area of the droplet and cause the droplet to envelop surrounding active material and / or electrically conductive additive.
[0026] For example, in some implementations, the binder material can comprise a fluorocarbon polymer, such as polyvinylidene difluoride (PVDF) and heating the particles of binder to
[0027] 38234310-2 form the droplets can cause defluorination of the binder material, e.g., by releasing a gas comprising one or more of: hydrogen fluoride (HF), methane or other hydrocarbons (e.g., fluorinated hydrocarbons). Defluorination of the PVDF can reduce the fluorine content of the electrode, e.g., reduce the amount (e.g., mass percentage) of fluorocarbons in the composite layer, which can address environmental concerns or regulations associated with products comprising fluorocarbons.
[0028] In some implementations, each droplet can comprise carbonaceous decomposition products of the binder material that are electrically conductive. For example, the one or more decomposition products can comprise one or more unsaturated carbon structures (e.g., amorphous carbon) that are electrically conductive. In such cases, the one or more decomposition products of the binder material can, for example, have a higher carbon percentage (e.g., by mass or mole fraction) than the binder material as a result of the decomposition.
[0029] In some implementations, the active material can be adhered to the composite layer and / or electrically conductive substrate by the carbonaceous decomposition products of the binder material.
[0030] In some implementations, the droplets can encapsulate particles of the active material (and / or the electrically conductive additive).
[0031] As one particular example, the binder material can comprise polyvinylidene difluoride (PVDF) and the heating the particles of binder material to form the droplets can cause defluorination of the binder material to generate electrically conductive carbon-containing decomposition products (e.g., amorphous carbon, graphite, etc.) The droplets can, for example, undergo expansion, driven thermally by the heating of the binder material and as a result of gas (e.g., HF) evolved during defluorination. In some cases, after solidifying, the droplets can form shells (or bubbles) of carbon, which can, in some examples, encapsulate particles of active material and / or electrically conductive additive.
[0032] Any suitable material may be used to provide the electrically conductive substrate. For example, the electrically conductive substrate may be a metal foil layer, such as an aluminium foil layer or copper foil layer.
[0033] 38234310-2 The droplets may have any shape (e.g. spherical or ellipsoidal).
[0034] Solidifying the droplets of binder material may comprise any suitable process. For example, the dry powder may be removed from the light source, and the droplets allowed to cool and solidify.
[0035] This method may provide any of several advantages.
[0036] Once thermally activated by the light source, the binder particles may continue to flow even after the exposure to the light source has ended and thus coalesce to form droplets (“densification”).
[0037] The redistribution of the binder material may result in the formation of voids in and / or on the composite layer, thereby providing additional pathways for ion transport throughout the composite layer. In this way, the electrical conductivity of the resulting electrode may be enhanced.
[0038] Additionally, the heated polymer binder material may be adhesive, allowing the active material to adhere to the droplets of binder material.
[0039] Accordingly, the electrode may be manufactured using a dry powder deposition process, whilst ensuring adequate dispersion and adhesion of the composite layer and maintaining the electrical properties of the electrode.
[0040] Optionally, exposing the composite layer to the light source may further cause inflation within the binder material to form additional droplets on and / or within the composite layer. In particular, the heat resulting from exposure to the light source may cause local expansion within the binder material, thus forming additional voids within the composite layer. Hence, the inflation within the binder material may provide further pathways for ion transport throughout the composite layer and additional increase in surface area of the composite layer provided with the active material and provide additional enhancement of the electrical conductivity of the electrode.
[0041] 38234310-2 Additionally, expansion within the binder material increases the surface area of the composite layer provided with the active material, further enhancing the electrical conductivity of the electrode.
[0042] Optionally, forming the droplets of binder material may increase the porosity of the composite layer. For example, the porosity of the composite layer may be increased by over 10%. In particular, the porosity of the composite layer may be increased by over 20%. More particularly, the porosity of the composite layer may be increased by over 30%.
[0043] Optionally, exposure of the layer to the light source may be controlled to cause coalescence of the particles of binder material and / or inflation within the binder material over a length scale of less than 2 mm. More particularly, exposure of the layer to the light source may be controlled to cause coalescence of the particles of binder material and / or inflation within the binder material over a length scale of less than 1.5 mm.
[0044] Optionally, the droplets of binder material may have respective length dimensions in a range from 50 pm to 2 mm. The respective length dimensions may include an average length dimension, a shortest length dimension, and / or a longest length dimension of the droplet. In one particular example, the droplets of binder material may have an average maximum length dimension of 80 microns.
[0045] Optionally, the droplets of binder material may be substantially spherical. In another embodiment, the droplets of binder material may be ellipsoidal in shape.
[0046] Optionally, the exposure of the composite layer to the light source can cause viscous flow of the binder material in response to exposure of the composite layer to the light source, assisting in the formation of voids in the composite layer.
[0047] Optionally, exposing the composite layer to a light source to heat the particles of binder material may comprise moving the light source and / or the substrate to expose different regions of the composite layer to the light source. The region may be defined by a size of the light source - for example, a spot size of the light source incident on the composite layer. Optionally, the spot size may correspond to an area of at least 0.05mm2. Optionally, the spot size may correspond to an area of at least 0.08mm2. Optionally, the
[0048] 38234310-2 spot size may correspond to an area of from 0.05mm2to 0.08mm2. Moving the light source and / or the substrate may comprise raster scanning the light source across the substrate.
[0049] Optionally, each region of the composite layer may be exposed to the light source for an exposure time from 50ps to 100ps. In general, the exposure time may be greater than the pulse width used for laser ablation of lithium ion battery materials (i.e. femtosecond, picosecond, or nanosecond laser pulses). The exposure time may be at least 100ns. More particularly, the exposure time may be at least 10ps.
[0050] The exposure time may be less than 0.5s. More particularly, the exposure time may be less than 1 ms. The exposure time may be varied according to the power of the light source.
[0051] Optionally, throughout the exposing of the composite layer to the light source, a power density of the light source at the composite layer may be less than or equal to 1000 W / cm2, in order to reduce the likelihood of damage to the electrically conductive substrate. In particular, the power density may be less than or equal to 875Wcm-2, in order to further reduce the likelihood of damage to the electrically conductive substrate. More particularly, the power density may be less than or equal to 750Wcm-2, in order to further reduce the likelihood of damage to the electrically conductive substrate.
[0052] Optionally, throughout the exposing of the composite layer to the light source, a power density of the light source at the composite layer may be greater than or equal to 50 W / cm2, in order to improve the adhesion between the composite layer and the electrically conductive substrate. In particular, the power density may be greater than or equal to 250Wcm-2, in order to further improve the adhesion between the composite layer and the electrically conductive substrate.
[0053] Optionally, the light source may provide light to the composite layer continuously or in pulses having a temporal width (e.g., full width at half-maximum) greater than or equal to 1 ps.
[0054] 38234310-2 Optionally, the light source may be a laser. The laser may be any suitable laser - for example, a diode laser. The laser may have any suitable central wavelength (for example, 450nm).
[0055] Optionally, exposing the composite layer to a light source to heat the particles of binder material may comprise exposing the composite layer to a light source through a sheet of transparent material covering the composite layer. Any suitable transparent material, such as glass, may be used. This provides a more even heat distribution during and after exposure to the light source, and increases the uniformity of the composite layer.
[0056] Optionally, prior to exposing the composite layer to the light source, the particles of binder material may have respective length dimensions less than or equal to 200 pm. The respective length dimensions may include an average length dimension, a shortest length dimension, and / or a longest length dimension of the particle.
[0057] Optionally, depositing the powder to form the composite layer may comprise spraying the powder onto the electrically conductive substrate. The powder may be sprayed onto the electrically conductive substrate through an electrically-charged nozzle, in order to further increase adhesion between the dry powder and electrically conductive substrate.
[0058] Optionally, the method may further comprise compacting the composite layer prior to exposing the composite layer to the light source. This provides improved dispersion of the dry powder, and improved adhesion of the composite layer to the electrically conductive substrate. The composite layer may be compacted using any suitable method - for example, it may be calendered or pressing. Advantageously, compaction (postdeposition densification of the electrode) may enhance properties of the electrode comprising the composite layer, such as conductivity, homogeneity, mechanical strength, elasticity, and adhesion.
[0059] In particular, compacting the composite layer may comprise (further) flattening (e.g. reducing the sphericity of) the particles of the binder material. Subsequent exposure to the light source may then cause the flattened particles of the binder material to (partially or completely) re-inflate due to local expansion within the binder material, and thereby restore pathways for ion transport lost during the compaction process.
[0060] 38234310-2 Optionally, at least prior to exposing the composite layer to the light source, the thickness of the composite layer may be less than 150 pm to provide effective penetration of the composite layer by the light source. More particularly, the thickness of the composite layer may be less than or equal to 100 pm, in order to further enhance the penetration of the composite layer by the light source.
[0061] Optionally, the powder may be mechanically or ultrasonically processed prior to deposition, e.g., to flatten the binder partices. In particular, the powder may be mechanically or ultrasonically processed to reduce a size of the particles of the active material, a size of the particles of the binder material, and / or a size of the particles of the electrically conductive additive (if present). More particularly, the powder may be mechanically or ultrasonically processed to reduce a size of the particles of the active material, a size of the particles of the binder material, and / or a size of the particles of the electrically conductive additive (if present) to between 50 and 100 microns.
[0062] According to a second aspect of the invention, there is provided an electrode manufactured according to the above-described method.
[0063] According to a third aspect of the invention, there is provided an electrode comprising: an electrically conductive substrate; and a composite layer formed on the electrically conductive substrate, the composite layer comprising an active material and particles of binder material dispersed within the active material, wherein at least a fraction of the particles of the binder material are in the form of solidified droplets of binder material formed by coalescence of particles of the binder material on or within the composite layer.
[0064] In some implementations, the droplets can each comprise carbonaceous decomposition products of the binder material that are electrically conductive. In some implementations, the active material is adhered to the composite layer by carbonaceous decomposition products of the binder material.
[0065] In some examples, substantially all of the binder material can have be replaced by the carbonaceous decomposition products.
[0066] 38234310-2 For example, in one aspect, an electrode can comprise: an electrically conductive substrate; and a composite layer formed on the electrically conductive substrate, the composite layer comprising an active material encapsulated in carbonaceous decomposition products of a binder material (e.g., PVDF). For example, the composite layer can comprise solidified droplets comprising the carbonaceous decomposition products, e.g., formed in situ within the composite layer.
[0067] In some implementations, the carbonaceous decomposition products of the binder material can adhere the active material to the composite layer and / or the electrically conductive substrate. In some implementations, the carbonaceous decomposition products of the binder material are electrically conductive, which can increase the conductivity of the composite layer.
[0068] In some implementations, the droplets of binder material may not be homogeneous, and may comprise material other than the binder material. One or more of the droplets of binder material may be or comprise a bubble - that is, a droplet of binder material enclosing a region of a substance other than the binder material. For example, one or more of the droplets may enclose a region comprising a gas, such as air.
[0069] The droplets of binder material may be formed in the bulk of the composite layer. Alternatively or additionally, the droplets may be formed on the surface of the composite layer.
[0070] The active material is a material which participates in the electrode reaction of a cell comprising the electrode. The active material may be any suitable material. For example, the active material can comprise any intercalation material capable of reversibly storing ions.
[0071] Optionally, the active material may comprise a lithium-containing material. For example, the active material may comprise a high voltage spinel material; lithium titanate, LTO; NMC111 , LiNi0.33Mn0.33Co0.33O2; NMC 811 , LiNi0.8Mn0.1Co0.1O2; NMC 622, LiNi0.67Mn0.28Co0.05O2; Lithium Nickel Manganese Oxide, LNMO; and / or Lithium Iron Phosphate, LFP. The Lithium Nickel Manganese Oxide may be LiMn1.5Nio.5O4, or any other suitable lithium nickel manganese oxide material. As another example, the active
[0072] 38234310-2 material can comprise a sodium salt, e.g., sodium Prussian blue and its analogues (PBAs).
[0073] The binder material is a material suitable for adhering the active material to the electrically conductive substrate. Any suitable material may be used as the binder material - for example, the binder material may comprise a polymer binder, e.g., a fluorocarbon polymer. In particular, the polymer binder may be a carboxymethyl cellulose, CMC, polymer. Alternatively, the polymer binder may be a polyvinylidene difluoride, PVDF, polymer.
[0074] Any suitable material may be used to provide the electrically conductive substrate. For example, the electrically conductive substrate may be a metal foil layer, such as an aluminium foil layer or copper foil layer.
[0075] The droplets may have any shape (e.g. spherical or ellipsoidal). In some examples, multiple droplets can be interconnected, e.g., having a fused morphology.
[0076] This method and the resulting electrode may provide any of several advantages (including those noted above).
[0077] The redistribution of the binder material may result in the formation of voids in and / or on the composite layer, thereby providing additional pathways for ion transport throughout the composite layer. In this way, the electrical conductivity of the resulting electrode may be enhanced.
[0078] Accordingly, the electrode may be manufactured using a dry powder deposition process, whilst ensuring adequate dispersion and adhesion of the composite layer, and maintaining the electrical properties of the electrode.
[0079] Optionally, at least a fraction (or substantially all) of the particles of the binder material are in the form of solidified droplets of binder material, formed by inflation within the binder material, on or within the composite layer.
[0080] In particular, the heat resulting from exposure to the light source may cause local expansion within the binder material, thus forming additional voids within the composite
[0081] 38234310-2 layer. Hence, the droplets formed by inflation within the binder material may provide further pathways for ion transport throughout the composite layer and additional increase in surface area of the composite layer provided with the active material, and provide additional enhancement of the electrical conductivity of the electrode. Flattening the particles of binder material before the light source is applied can enhance this inflation effect.
[0082] Additionally, expansion within the binder material increases the surface area of the composite layer provided with the active material, further enhancing the electrical conductivity of the electrode.
[0083] Optionally, the particles of binder material may be coalesced, and / or inflation within the binder material may occur, over a length scale of less than 2 mm. More particularly, the particles of binder material may be coalesced, and / or inflation within the binder material may occur, over a length scale of less than 1.5 mm. For example, the exposure of the composite layer to the light source can be controlled, such as through control of a dwell time, scan rate, light source spot size, power or wavelength, so that the particles of binder material coalesce and / or inflate over a desired length scale.
[0084] Optionally, the droplets of binder material may have respective length dimensions in a range from 50 pm to 2 mm. The respective length dimensions may include an average length dimension, a shortest length dimension, and / or a longest length dimension of the droplet.
[0085] Optionally, the droplets of binder material may be substantially spherical. In another embodiment, the droplets of binder material may be ellipsoidal in shape.
[0086] Optionally, the composite layer may further comprise particles of an electrically conductive additive, to enhance an electrical conductivity of the composite layer. The electrically conductive additive may comprise any suitable material, such as carbon black, carbon nanotubes, CNTs; vapour-grown carbon fibers, VGCFs; and / or graphene.
[0087] According to a further aspect of the invention, there is provided a battery or electrochemical cell comprising one or more electrodes as described above.
[0088] 38234310-2 Brief description of the drawings
[0089] Examples of the present invention will now be described in detail with reference to the accompanying drawings, in which:
[0090] Figure 1 is a schematic showing an electrostatic deposition apparatus for manufacturing an electrode;
[0091] Figure 2 is a further schematic showing the electrostatic deposition apparatus of Figure 1 ;
[0092] Figure 3 is a schematic showing a light source for manufacturing an electrode;
[0093] Figure 4 is a further schematic showing the light source of Figure 3;
[0094] Figure 5 is a schematic showing an electrode;
[0095] Figures 6(a) and (b) show micrographs of a composite layer following exposure to a light source;
[0096] Figures 7(a) and (b) show micrographs of a comparative example of a composite layer following exposure to a light source;
[0097] Figure 8 shows discharge capacity as a function of cycling rate, measured for a number of electrodes;
[0098] Figure 9 shows a Randles equivalent circuit for the lithium-ion battery half-cells comprising the electrodes of Figure 8;
[0099] Figure 10 shows electrochemical impedance spectra measured for the lithium-ion battery half-cells of Figure 9;
[0100] Figure 11 shows a method of manufacturing an electrode;
[0101] Figures 12(a) and 12(b) show SEM micrographs of particles of binder material that have been flattened by ball milling for 1 hour;
[0102] Figure 13 shows SEM micrographs of droplets encapsulating particles of active material; Figure 14 is a micrograph showing the composite layer with and without laser treatment; Figures 15(a) and 15(b) show SEM micrographs in which multiple droplets are interconnected; and
[0103] Figures 16(a) and 16(b) are SEM micrographs of substantially spherical particles of PVDF following laser treatment.
[0104] Detailed description of the drawings
[0105] Figure 1 shows an electrostatic deposition apparatus 100 for manufacturing an electrode.
[0106] 38234310-2 The electrostatic deposition apparatus 100 comprises an electrostatic spray device 110 located in an enclosure 120, where the enclosure 120 reduces the likelihood of disruption of particle flow due to stray air currents. The enclosure 120 may be configured to provide an inert atmosphere - for example, the enclosure 120 may be an isolator (“glovebox”). The electrostatic spray device 110 comprises a pump 111 and an aperture 113 connected to a powder reservoir 114. In the embodiment of Figure 1 , aperture 113 comprises a nozzle having the form of a metallic needle.
[0107] The electrostatic spray device 110 is configured to allow particles to accumulate on the substrate 210 in use. The substrate 210 is an electrically conductive substrate (current collector), and may comprise aluminium, copper, or any other suitable metal.
[0108] The aperture 113 is connected to a first terminal of power supply 112, and a second terminal of power supply 112 is connected to the substrate 210, to provide a potential difference between the aperture 113 and the substrate 210. In one implementation of the embodiment of Figure 1 , the power supply 112 is configured to provide a DC potential difference of from 8kV to 25kV between aperture 113 and the substrate 210.
[0109] Pump 111 is configured to fluidise the powder 220 for deposition. Any suitable pump may be used as pump 111 , such as a syringe pump or a positive displacement pump. In one implementation of the embodiment of Figure 1 , pump 111 comprises a positive displacement pump to create a Venturi pump, facilitating the fluidisation of the particles to avoid clogging of aperture 113. The pump 111 may be connected to an air supply or nitrogen supply.
[0110] The powder reservoir 114 is configured to hold a supply of powder 220.
[0111] The powder 220 comprises particles of an active material and particles of a binder material. The active material participates in the electrode reaction of a cell comprising the electrode, whilst the binder material is a material suitable for adhering the active material to the electrically conductive substrate 210.
[0112] The active material in powder 220 may be any suitable material. Optionally, the active material may comprise a lithium-containing material. For example, the active material
[0113] 38234310-2 may comprise a high voltage spinel material; lithium titanate, LTO; NMC111 , LiNi0.33Mn0.33Co0.33O2;, NMC 811 , LiNi0.8Mn0.1Co0.1O2; NMC 622, LiNi0.67Mn0.28Co0.05O2; Lithium Nickel Manganese Oxide, LNMO; and / or Lithium Iron Phosphate, LFP.
[0114] The binder material in powder 220 may be any suitable material. For example, the binder material may comprise a polymer binder. In particular, the polymer binder may be a carboxymethyl cellulose, CMC, polymer. Alternatively, the polymer binder may be a polyvinylidene difluoride, PVDF, polymer.
[0115] In the embodiment of Figure 1 , the powder 220 further comprises an electrically conductive additive, to enhance an electrical conductivity of the composite layer, but in variants of the embodiment, the electrically conductive additive may not be present. The electrically conductive additive may comprise carbon black; carbon nanotubes, CNTs, vapour-grown carbon fibres, VGCFs and / or graphene, or any other suitable electrically conductive additive.
[0116] The powder 220 may have any suitable composition. For example, in a first implementation of the embodiment, the active material comprises LTO as an anode material, the binder material comprises CMC, and the electrically conductive additive comprises single-walled carbon nanotubes, SWCNTs. The active material, binder material, and electrically conductive additive are combined at a mass ratio of 90:5:5. In a second implementation of the embodiment, the active material comprises LNMO as a cathode material, the binder material comprises CMC, and the electrically conductive additive comprises C65 carbon black (e.g. where the particles in the carbon black have a surface area of between 20 and 1500 m2 / g). The active material, binder material, and electrically conductive additive are combined at a mass ratio of 90:5:5. In a third implementation of the embodiment, the active material comprises NMC111 (LiNi0.33Mn0.33Co0.33O2), the binder material comprises PVDF, and the electrically conductive additive comprises carbon black. The active material, binder material, and electrically conductive additive are combined at a mass ratio of 90:5:5. In a fourth implementation of the embodiment, the active material comprises lithium cobalt oxide (LCO), the electrically conductive additive comprises a conductive carbon additive, and the binder material comprises PVDF. The active material, binder material, and electrically conductive additive are combined at a mass ratio of 90:5:5. In a fifth implementation of the embodiment, the active material comprises LMNO, the binder material comprises
[0117] 38234310-2 PVDF, and the electrically conductive additive comprises a conductive carbon additive. The active material, binder material, and electrically conductive additive are combined at a mass ratio of 90:5:5.
[0118] Before deposition, the powder 220 may be treated to reduce the size of the particles. For example, the powder 220 may be mechanically or ultrasonically processed prior to deposition. In an implementation of the embodiment, each of the materials present (particles of active material, particles of binder material, and particles of electrically conductive additive if present) in the powder 220 is mixed individually with zirconium beads of 2mm in diameter in an ultrasonic mixing apparatus for 1 hour at 60Hz. The materials are then combined, and processed together for another hour at the same settings. In another implementation of the embodiment, the materials of the powder 220 are mixed with mica mortar and pestle and then placed in a Vortex shaker for 30 minutes.
[0119] In use, the power supply 112 is activated to cause the aperture 113 and substrate 210 to acquire opposite electrical charges. The pump 111 is activated, causing the powder 220 in the powder reservoir 114 to become fluidised and to exit the electrostatic spray device 110 via aperture 113. As the particles of powder 220 pass through the aperture 113, they become charged with an electrical charge opposite to substrate 210 and are attracted to substrate 210. The powder 220 is sprayed at a velocity allowing it to be attracted by substrate 210, and accumulates on substrate 210. The deposition may be conducted under an inert atmosphere.
[0120] This leads to the formation of composite layer 230, as shown in Figure 2.
[0121] The electrode of Figure 2 is then compacted, e.g., by calendering or pressing. In one implementation of the embodiment, the electrode is heated inside an oven in the air for one hour at 170°C, then calendered at room temperature, with the rollers for the calendering being heated to between 80°C and 100°C. However, in other implementations, any suitable compaction process may be used.
[0122] Figure 3 shows the electrode of Figure 2 after compaction, being exposed to light source 300. The light source 300 is used to irradiate a first region 231 of the composite layer 230 via a transparent layer 240 which is located between the composite layer 230 and the light source 300 during the processing of the electrode by the light source 300. The
[0123] 38234310-2 transparent layer 240 serves to distribute heat more evenly across the composite layer 230 during processing by the light source 300. In one implementation of the embodiment of Figure 3, transparent layer 240 is a glass slide, but in variants of the embodiment any other suitable transparent material may be used.
[0124] In the embodiment of Figure 3, the light source 300 is a laser. In one implementation, the light source 300 is a double diode blue laser with a wavelength of 450nm. The light source 300 may be configured to produce an optical output of from 0.5 to 15 watts; more particularly, the light source 300 may be configured to produce an optical output of 10 watts. In one implementation, the electrode 200 may be held at 5 cm from the focal lens of the laser beam, with a spot size of 0.08mm2. In another implementation, the electrode may be held at 20 cm from the focal lens of the laser beam, with a spot size of 0.05mm2.
[0125] The operation of the light source 300 is controlled by control unit 400. The control unit may communicate with the light source 300 through serial communication with a data rate of 2 Hz.
[0126] In one implementation of the embodiment of Figure 3, the output power of the light source 300 may be controlled by a duty cycle - that is, the light source 300 may be controlled to be active intermittently rather than continuously. Advantageously, this may allow for a more controlled heat exposure on the electrode. For example, the light source 300 may be controlled with a 5ms duty cycle to provide improved adhesion. In the embodiment of Figure 3, the temperature of the composite layer 230 is monitored by a temperature sensor module 410. The temperature sensor module 410 is a non-contact infrared temperature sensor module. In the embodiment of Figure 3, the temperature sensor module 410 is attached to the light source 300, but in variants of the embodiment temperature sensor module 410 may be provided in any suitable location to measure the temperature of composite layer 230 during processing by the light source 300. For example, the film deposition temperature may be monitored using an MLX90614 noncontact infrared temperature sensor module attached to the laser head, with a temperature range of -70 °C to 380 °C and a resolution of 0.02°C.
[0127] In use, the light source 300 is operated at an optical power calculated to induce melting of the binder particles in composite layer 230 but to avoid damaging the substrate 210. The optical power may be varied according to the thickness of the composite layer.
[0128] 38234310-2 Appropriate values of the optical power of light source 300 according to the thickness of the composite layer 230 may be identified based on the Beer-Lambert law (Equation 1):
[0129] / (z) = Ioe~az
[0130] (1) where l(z) is the intensity I of the beam as a function of depth z, / o is the intensity of the beam at the surface of the composite layer, and a is the absorption coefficient for the composite layer corresponding to the wavelength of the beam.
[0131] For example, for the above-described composite layers and spot sizes, the light source may be operated at an optical power of 6 watts. In another example, for the abovedescribed composite layers and spot sizes, the light source may be operated at an optical power of 7 watts.
[0132] The thickness of the composite layer 230 may be less than 150 pm to provide effective penetration of the composite layer 230 by the light source 300. More particularly, the thickness of the composite layer 230 may be less than or equal to 100 pm, in order to further enhance the penetration of the composite layer 230 by the light source 300.
[0133] The heat generated in composite layer 230 by exposure to the light source raises the binder material above its melting temperature. For example, an instantaneous temperature of the composite layer 230 in the first region 231 may be around 300°C. The binder then begins to melt and flow in first region 231 .
[0134] In one implementation, region 231 may be irradiated for an exposure time of from 50ps to 100ps. In other implementations, region 231 may be irradiated for an exposure time of less than 0.5s. An appropriate exposure time may be identified based on the optical power of the light source 300.
[0135] In the embodiment of Figure 3, the laser processing is performed via the transparent layer 240, but, in variants of the embodiment, the laser processing may be performed without the transparent layer 240.
[0136] Figure 4 is a further schematic showing the light source 300 of Figure 3.
[0137] 38234310-2 The light source 300 and substrate 210 are moved with respect to one another, causing the light source 300 to irradiate a second region 232 of the composite layer which is different from the first region 231. In the embodiment of Figure 3, the light source 300 is configured to raster across the electrode to treat the whole of the composite layer 230. For example, the light source 300 may be controlled to treat an area of 30cm by 20cm, with an average speed of 1.2 seconds per line and a total of 13 lines to cover the area, and an estimated instant temperature per spot size of 300°C. Both the total area treated by the laser and the size of the individual regions 231 , 232 may be varied.
[0138] The irradiation of the second region 232 by the light source, binder particles melted by the irradiation of first region 231 continue to flow (that is, the viscous flow of the binder particles in the region continues over a longer timescale than the exposure time for which the region is irradiated by the light source). This causes particles of the binder material to coalesce to form droplets (“densification”). Additionally, the heat resulting from exposure to the light source 300 causes local expansion within the binder material, thus forming additional voids within the composite layer 230.
[0139] Figure 5 shows the electrode 200 following the processing by light source 300. Following the processing by light source 200, the treated composite layer 230 is allowed to solidify - for example, by removing the electrode 200 from the light source 300 and allowing the binder material to cool and solidify.
[0140] The electrode 200 comprises the electrically conductive substrate 210 and the treated composite layer 230. The redistribution of material within composite layer 230 due to viscous flow of the melted binder material and local inflation of the binder material has caused first droplets 235 to form on the surface of the composite layer 230, and second droplets 236 to form within the bulk of composite layer 230. The droplets 235, 236 provide additional pathways for ionic transport within composite layer 230. Additionally, the local inflation increases the surface area of the composite layer 230 provided with the active material, further enhancing the electrical conductivity of the electrode 200.
[0141] Figures 6(a) and (b) show micrographs of a composite layer of an electrode following processing by a light source according to an embodiment. The micrographs were taken using an optical microscope with a 4X lens.
[0142] 38234310-2 In the powder used to form the composite layer of Figure 6, LNMO , carbon black (a C65 carbon black, e.g. where the particles in the carbon black have a surface area of between 20 and 1500 m2 / g)), and CMC were combined at a mass ratio of 90:5:5. Each of the constituent materials of the powder was processed separately by being mixed with zirconium beads in the ultrasonic mixer. Following this, all of the constituent materials of the powder were combined together and mixed with zirconium beads in the ultrasonic mixer, and then placed in a Vortex shaker for 30 minutes.
[0143] Following the processing in the shaker, the powder was deposited on an aluminium substrate using an electrostatic spray gun to form an electrode. The electrostatic deposition apparatus comprised three main components: a high voltage power supply, syringe pump, and an enclosure or spray booth. A metallic needle was connected to the positive lead of the high voltage power supply setup at 8 kV, while the negative lead of the high voltage supply was connected to the aluminium substrate. A syringe pump was utilised to push the powder through the needle. Due to the potential difference between the metallic needle and aluminium substrate, the powder was attracted to the aluminium substrate and accumulated on the aluminium substrate to form the composite layer of the electrode.
[0144] Following this, the electrodes were held at 20 cm from the focal lens of the laser beam for the laser processing. The laser was a double-diode blue laser with a wavelength of 450nm, an optical output of 10 watts, and a spot size of 0.05mm2. The laser's input power was 12V and 3.8A (40W). The heat transfer level to the electrode was controlled with the laser through serial communication with a data rate of 2Hz. The output power was controlled by a duty cycle, not voltage or frequency. The film deposition temperature was also monitored using an MLX90614 non-contact infrared temperature sensor module attached to the laser head, with a temperature range of -70 °C to 380 °C and a resolution of 0.02 °C. The laser was programmed to raster across the electrode to treat the entire area. The area can be programmed into different area sizes. In the embodiment of Figure 6, the raster area set up with the laser was 30cm by 20cm.
[0145] As can be seen in Figure 6(a) and the leftmost part of Figure 6(b), droplets (“bubbles”) may be observed on the surface of the composite layer which has been subject to the
[0146] 38234310-2 laser processing, due to the melting and re-solidifying of the polymer (CMC) binder. The length scales of the droplets range from 100pm to 1 mm.
[0147] On the rightmost part of Figure 6(b), a region of the composite layer which has not yet been exposed to the laser can be seen. No melting of the binder particles in this region has taken place, and therefore no droplets can be observed on the surface of the composite layer in this region.
[0148] Figures 7(a) and (b) show micrographs of a composite layer of a comparative example of an electrode following processing by a light source. The micrographs were taken using an optical microscope with a 4X lens.
[0149] In the powder used to form the composite layer of Figure 7, LNMO, carbon black (a C65 carbon black), and CMC are combined at a mass ratio of 95:5:0 (that is, no binder is present in the powder of Figure 7). Each of the constituent materials of the powder was processed separately by being mixed with zirconium beads in the ultrasonic mixer. Following this, all of the constituent materials of the powder were combined together and mixed with zirconium beads in the ultrasonic mixer and then placed in a Vortex shaker for 30 minutes.
[0150] Following the processing in the shaker, the powder was deposited on an aluminium substrate using an electrostatic spray gun to form an electrode. The electrostatic deposition apparatus comprised three main components: a high voltage power supply, syringe pump, and an enclosure or spray booth. A metallic needle was connected to the positive lead of the high voltage power supply setup at 8 kV, while the negative lead of the high voltage supply was connected to the aluminium substrate. A syringe pump was utilised to push the powder through the needle. Due to the potential difference between the metallic needle and aluminium substrate, the powder was attracted to the aluminium substrate and accumulated on the aluminium substrate to form the composite layer of the electrode.
[0151] Following this, the electrodes were held at 20 cm from the focal lens of the laser beam for the laser processing. The laser was a double-diode blue laser with a wavelength of 450nm, an optical output of 10 watts, and a spot size of 0.05mm2. The laser's input power was 12V and 3.8A (40W). The heat transfer level to the electrode was controlled with the
[0152] 38234310-2 laser through serial communication with a data rate of 2Hz. The output power was controlled by a duty cycle, not voltage or frequency. The film deposition temperature was also monitored using an MLX90614 non-contact infrared temperature sensor module attached to the laser head, with a temperature range of -70 °C to 380 °C and a resolution of 0.02 °C. The laser was programmed to raster across the electrode to treat the entire area. The area can be programmed into different area sizes. In the embodiment of Figure 7, the raster area set up with the laser was 30cm by 20cm.
[0153] Figure 7(a) shows the composite layer after the laser processing. Since no binder was added to the dry powder mix, no droplets can be observed on the composite layer of Figure 7(a) after the laser processing.
[0154] Figure 7(b) shows the interface between the deposited composite layer and the aluminium substrate (current collector). From Figure 7(b), it can be seen that the interface between the part of the composite layer treated by laser processing and the part of the composite layer not treated by laser processing shows a smoother deposition surface than the composite layer comprising the binder and treated by laser processing (Figures 6(a) and (b)).
[0155] Since no binder was added to the dry powder mix, no droplets can be observed on the composite layer of Figure 7(a) or (b) after the laser processing.
[0156] Additionally, it can be observed in Figures 7(a) and (b) that the grooves or lines produced by the laser in conventional selective laser sintering (SLS) methods are not present, showing an even distribution of the dry powder deposition (due to more even heat distribution resulting from the presence of the transparent layer during deposition).
[0157] Figure 8 shows discharge capacity as a function of cycling rate, measured for a number of lithium-ion battery half-cells comprising electrodes according to an embodiment.
[0158] Each of the composite layers for the electrode samples of Figure 8 was formed from a powder comprising LTO mixed with CMC binder and single-walled carbon nanotubes (SWCNTs) at a mass ratio of 90:5:5. In particular, the powder used LTO as an anode material mixed with CMC binder and SWCNTs as a conductive additive at a mass ratio of 90:5:5. The recipes were prepared by mixing each of the components of the dry
[0159] 38234310-2 powder separately with zirconium beads in the ultrasonic mixer, then combining all of the components of the dry powder together and mixing them with zirconium beads in the ultrasonic mixer, and then placing the resulting mixture in a Vortex shaker for 30 minutes.
[0160] The resulting powder was deposited on an aluminium substrate using a electrostatic spray gun to form an electrode. The electrostatic deposition apparatus comprised three main components: a high voltage power supply, syringe pump, and an enclosure or spray booth. A metallic needle was connected to the positive lead of the high voltage power supply setup at 8 kV, while the negative lead of the high voltage supply was connected to the aluminium substrate. A syringe pump was utilised to push the powder through the needle. Due to the potential difference between the metallic needle and aluminium substrate, the powder was attracted to the aluminium substrate and accumulated on the aluminium substrate to form the composite layer of the electrode
[0161] Following this, each electrode was held at 5 cm from the focal lens of a laser beam. The laser device used was a double diode blue laser with a wavelength of 450nm with an optical output of 15 watts and a spot size of 0.08mm2. The input power required to power the laser was 12V and 3.8A (40W). The heat level transferred to the electrode was controlled through serial communication with the laser with a data rate of 2Hz. The output power was controlled by a duty cycle. The film deposition temperature was monitored using an MLX90614 non-contact infrared temperature sensor module attached to the laser head, with a temperature range of -70 °C to 380 °C and a resolution of 0.02 °C. The raster area set up with the laser was 30cm by 20cm.
[0162] Each region of the electrode sample was irradiated for around 5ms. Sample one (LTO 1) was processed at an optical power of 7W, whereas sample 2 (LTO 2) was processed at an optical power of 6W. The properties of LTO 1 and LTO 2 are summarised in Table 1 below.
[0163] Table 1
[0164] 38234310-2
[0165] The electrode samples LTO 1 and LTO 2 were processed into lithium-ion battery "halfcells" opposite lithium foil, with an electrolyte consisting of 1 M lithium hexafluorophosphate, LiPFe in 1 :1 ethylene carbonate, EC: diethyl carbonate, DEC.
[0166] The resulting half-cells were charged and discharged from 1.0 - 2.5 V vs Li / Li+ at various cycling rates (from C / 5 to 20 C, where C = 1 / t and t is the discharge time of the half-cell in hours), performing five cycles at each rate. Performance was compared with a halfcell comprising a standard slurry cast electrode sample having the same composition as LTO 1 and LTO 2, but not having been subject to laser processing, a lithium foil cathode, and an electrolyte consisting of 1M lithium hexafluorophosphate, LiPFe in 1 :1 ethylene carbonate, EC: diethyl carbonate, DEC.
[0167] The discharge capacity obtained for each half-cell is plotted in mAh / g as a function of cycling rate in Figure 8.
[0168] At low cycling rates (< 2C), the slurry cast sample performed better than LTO 1 and LTO 2. However, the situation was reversed at higher cycling rates, with both LTO 1 and LTO 2 outperforming the slurry cast sample. The lower performance at slow rates suggests that the laser treatment may have damaged the material (hence providing a lower capacity at low cycling rates) but provided a highly conductive electrode (and hence a good high-rate performance).
[0169] This is further supported by the observation that sample 2 (LTO 2) shows better performance at low current loads than sample 1 (LTO 1), which was treated at higher laser power (with LTO 1 performing better than LTO 2 at high cycling rates). The laser power may be selected to achieve a high electrode conductivity, while minimising any material damage. Additionally, the performance of the electrode may be further optimized whilst minimizing material damage by varying the mass loading of the electrode (i.e. the mass of deposited material on the electrode per unit area).
[0170] 38234310-2 Figure 9 shows a Randles equivalent circuit for lithium-ion battery half-cells comprising the electrodes of Figure 8. The Randles equivalent circuit consists of a resistance Ri in series with the parallel combination of (1) double-layer capacitance Cdiand (2) the (series combination of) resistance R2 and the Warburg diffusion element Zw.
[0171] The resistance R1 is an ohmic resistance associated with the electrolyte of the cell (ionic resistance). The resistance R2 is a charge transfer resistance (also referred to as a polarization resistance) associated with the faradaic reaction in the cell. The double-layer capacitance Cdi is a capacitance associated with the electrical double layer between the electrode and electrolyte in the cell (attributed to resistance of the charge transfer or polarisation resistance and the double layer capacitance in parallel). The Warburg diffusion element (also referred to as a Warburg element) is an impedance element associated with diffusion (mass transfer) in the cell.
[0172] Figure 10 shows electrochemical impedance spectroscopy (EIS) spectra measured for the cells LTO 1 and LTO 2. The spectra show the negative of the imaginary part of the impedance Z of the cell, -lm(Z), plotted as a function of the real part of the impedance Z of the cell, Re(Z).
[0173] From the EIS spectra, the following properties of the cell can be measured: (a) the high- frequency intercept (R1) , attributed to the ohmic resistance of the electrolyte of the cell, (b) a depressed semicircle of diameter R2 at medium frequencies, attributed to resistance of the charge transfer or polarization resistance and the double layer capacitance in parallel, and (c) a near-straight line at low frequencies, attributed to the Warburg element Zw.
[0174] Using the equivalent circuit shown in Figure 9, R1 and R2 were calculated from the EIS spectra for both samples (shown in Table 2 below).
[0175] Table 2
[0176] 38234310-2 It was observed that the capacitive R2 values dominated the cell resistance and that cell "LTO 2" had a significantly lower R2 value (91 Q) than "LTO 1" (164 Q). The resistance indicates that the lower laser power (6 W) provided a more conductive electrode and good film-to-substrate adhesion, enhancing the high-rate performance of the cell.
[0177] Figure 11 shows a method of manufacturing an electrode.
[0178] In step S101 of the method, a powder is deposited to form a composite layer on an electrically conductive substrate. The composite layer comprises an active material and particles of binder material for adhering the active material to the electrically conductive substrate.
[0179] In step S102 of the method, the composite layer is exposed to a light source to heat the particles of binder material and thereby cause groups of particles of the binder material to coalesce to form droplets on and / or within the composite layer.
[0180] In step S103 of the method, the droplets of binder material are solidified.
[0181] The method of Figure 11 may be implemented using an electrostatic deposition apparatus and light source according to the embodiment of Figures 1-4, or using any other suitable deposition apparatus and light source.
[0182] Figures 12(a) and 12(b) are SEM micrographs of particles of binder material, in this case PVDF, that have been flattened by ball milling for 1 hour. The SEM micrographs show a change in particle morphology with a flake-like shape, characterised by irregular, platelike structures with rough, faceted surfaces. Unlike the spherical particles of the initial binder material, these flake-shaped particles exhibit a higher aspect ratio and tend to interlock or form bridges, which can significantly influence their packing behaviour and mechanical response. This bridging tendency is particularly relevant during the laser treatment, which can “re-inflate” the particles, thereby increasing their surface area and enhancing electrode performance by promoting better interfacial contact and active material utilisation.
[0183] 38234310-2 Figure 13 shows SEM micrographs of droplets encapsulating particles of active material, in this case, LNMO. The droplets were formed using flattened particles of PVDF, e.g., as shown in Figures 12(a) and 12(b). As can be seen most clearly in the bottom micrographs, a droplet (bubble) formed by thermal decomposition of the PVDF includes the much smaller particles of LNMO, which can be observed as result of the partial closure of the droplet around the LMNO particles. The active material is believed to enter the droplet because of the expansion of the droplet from the initially flattened geometry driven by the laser treatment. In particular, the droplet can form a protective layer around the particles of active material to at least partially encapsulate them and prevent their degradation.
[0184] Figure 14 is a micrograph showing the composite layer with (upper and lefthand side of the image) and without laser treatment (bottom and righthand side of the image). The portion of the composite layer to which the laser treatment has been applied shows the microstructure and droplets formation, whilst the portion without laser treatment remains relative amorphous and lacking in droplets.
[0185] Figures 15(a) and 15(b) show SEM micrographs in which multiple droplets are interconnected to provide conductive pathways through the composite layer.
[0186] Chemical analysis (electron diffraction spectroscopy) of the composite layer before laser treatment indicates that the layer comprises 5-6% fluorine by mass dispersed throughout the layer, which is attributable to the fluorine present in the PVDF binder. After laser treatment, substantially no fluorine was found to be present, indicating decomposition (defluorination) of the PVDF binder particles. It is believed that, at least in some examples, the droplets comprise conductive carbon structures generated as decomposition products of the PVDF binder. As a result of the laser treatment, the binder is therefore able to play a dual role in mechanically stabling the composite layer whilst also increasing the conductivity.
[0187] Figures 16(a) and 16(b) are SEM micrographs of substantially spherical particles of PVDF (i.e. , that have not been flattened, e.g., by ball milling) following laser treatment. No changes in morphology or particle size were detected in this case.
[0188] 38234310-2 It should be understood that any method of the present disclosure could include additional steps, and any device could include additional components. In addition, unless indicated otherwise or technically infeasible, the method steps disclosed herein may be performed in alternative orders, and any order described herein should be considered as exemplary rather than limiting.
[0189] 38234310-2
Claims
CLAIMS:1 . A method of manufacturing an electrode, the method comprising: depositing a powder to form a composite layer on an electrically conductive substrate, the composite layer comprising an active material and particles of binder material for adhering the active material to the electrically conductive substrate; exposing the composite layer to a light source to heat the particles of binder material and thereby cause groups of particles of the binder material to coalesce to form droplets on and / or within the composite layer; and solidifying the droplets of binder material.
2. The method of claim 1 , wherein the particles of binder material have a plate-like morphology prior to exposing the composite layer to the light source.
3. The method of claim 2, further comprising, prior to depositing, mechanically processing substantially spherical particles of binder material to flatten the particles into the plate-like morphology.
4. The method of claim 3, wherein mechanically processing the particles of binder material comprises grinding or milling the particles of binder material.
5. The method of any one of claims 2-4, wherein the droplets of binder material have a substantially spherical morphology after solidifying.
6. The method of any one of the preceding claims, wherein the composite layer further comprises particles of an electrically conductive additive.
7. The method of claim 6, wherein the particles of binder material are heated by the electrically conductive additive following absorption of light from the light source by the electrically conductive additive.
8. The method of any one of the preceding claims, wherein heating the particles of binder material to form the droplets causes decomposition of the binder material.38234310-29. The method of claim 8, wherein the decomposition of the binder material generates a gas.
10. The method of claim 8 or 9, wherein the binder material comprises a fluorocarbon polymer and heating the particles of binder to form the droplets causes defluorination of the binder material.
11. The method of claim 10, wherein the fluorocarbon polymer comprises polyvinylidene difluoride, PVDF.
12. The method of any one of claims 8-11 , wherein each droplet comprises carbonaceous decomposition products of the binder material that are electrically conductive.
13. The method of any one of the preceding claims, wherein the droplets encapsulate particles of the active material.
14. The method of any one of the preceding claims, wherein forming the droplets of binder material increases the porosity of the composite layer.
15. The method of any preceding claim wherein exposure of the layer to the light source is controlled to cause coalescence of the particles of binder material and / or inflation within the binder material over a length scale of less than 2 mm.
16. The method of any preceding claim, wherein the droplets of binder material have respective length dimensions in a range from 50 pm to 2 mm.
17. The method of any preceding claim, wherein exposing the composite layer to a light source to heat the particles of binder material comprises moving the light source and / or the substrate to expose different regions of the composite layer to the light source.
18. The method of any preceding claim, wherein each region of the composite layer is exposed to the light source for an exposure time of from 50ps to 100 ps.38234310-219. The method of any preceding claim, wherein throughout the exposing of the composite layer to the light source, a power density of the light source at the composite layer is less than or equal to 1000 W / cm2.
20. The method of any preceding claim, wherein throughout the exposing of the composite layer to the light source, a power density of the light source at the composite layer is greater than or equal to 50 W / cm2.
21. The method of any preceding claim, wherein the light source provides light to the composite layer continuously or in pulses having a temporal width greater than or equal to 1 ps.
22. The method of any preceding claim, wherein the light source is a laser.
23. The method of any preceding claim, wherein exposing the composite layer to a light source to heat the particles of binder material comprises exposing the composite layer to a light source through a sheet of transparent material covering the composite layer.
24. The method of any preceding claim, wherein prior to exposing the composite layer to the light source, the particles of binder material have respective length dimensions less than or equal to 200 pm.
25. The method of any preceding claim, wherein depositing the powder to form the composite layer comprises spraying the powder onto the electrically conductive substrate.
26. The method of claim 25, wherein the powder is sprayed onto the electrically conductive substrate through an electrically-charged nozzle.
27. The method of any preceding claim, further comprising compacting the composite layer prior to exposing the composite layer to the light source.38234310-228. The method according to any preceding claim, wherein at least prior to exposing the composite layer to the light source, the thickness of the composite layer is less than 150 pm.
29. The method according to any preceding claim, wherein the powder is mechanically or ultrasonically processed prior to deposition.
30. An electrode manufactured according to the method of any preceding claim.31 . An electrode comprising: an electrically conductive substrate; and a composite layer formed on the electrically conductive substrate, the composite layer comprising an active material and particles of binder material dispersed within the active material, wherein at least a fraction of the particles of the binder material are in the form of solidified droplets of binder material formed by coalescence of particles of the binder material on or within the composite layer.
32. The electrode of claim 31 , wherein each droplet comprises carbonaceous decomposition products of the binder material that are electrically conductive.
33. The electrode of claim 31 or 32, wherein the active material is adhered to the composite layer and / or electrically conductive substrate by the carbonaceous decomposition products of the binder material.
34. The electrode according to any one of claims 31 to 33, wherein at least a fraction of the particles of the binder material are in the form of solidified droplets of binder material, formed by inflation within the binder material, on or within the composite layer.
35. The electrode according to any one of claims 31-34, wherein the droplets of binder material have respective length dimensions in a range from 50 pm to 2 mm.
36. An electrode comprising: an electrically conductive substrate; and a composite layer formed on the electrically conductive substrate, the composite layer comprising an active material encapsulated in carbonaceous decomposition products of a binder material.38234310-237. The electrode of claim 36, wherein the carbonaceous decomposition products of the binder material adhere the active material to the composite layer and / or the electrically conductive substrate.
38. The electrode of claim 37, wherein the carbonaceous decomposition products of the binder material are electrically conductive.
39. An electrode according to any one of claims 31 to 38, wherein the active material comprises a lithium-containing material.
40. A battery or electrochemical cell comprising one or more electrodes according to any one of claims 31 to 39.38234310-2