Method for producing electrodes
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- PETROLIAM NASIONAL BHD
- Filing Date
- 2024-07-16
- Publication Date
- 2026-05-27
AI Technical Summary
Current methods for producing lithium-ion battery electrodes require toxic solvents like NMP, leading to high energy consumption and environmental concerns during the drying and solvent recovery stages.
A dry mixing process is used to form a mixture of electrode active material and carbon additives, such as graphene, without solvents, creating a conductive layer on the active material particles through mechanical agitation and air flow.
This method reduces energy consumption, eliminates solvent recovery costs, and enhances electrode conductivity and thermal stability, achieving at least 50% improvement in volume resistivity and improved thermal dissipation.
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Figure MY2024050054_23012025_PF_FP_ABST
Abstract
Description
METHOD FOR PRODUCING ELECTRODESFIELD OF INVENTION
[0001] The present invention generally relates to methods for producing electrodes for electrochemical elements such as batteries.BACKGROUND
[0002] In recent years, there has been a significant increase in demand for lithium-ion batteries owing to their small size, high density and repeated chargeability features. Lithium- ion batteries are widely used as a power supply for various small and large electronic appliances, such as mobile phones, wireless headphones, laptops, handheld tools or devices and are currently being introduced for electric vehicles (EV).
[0003] The current method of manufacturing the electrodes for lithium-ion cells typically includes the use of solvents such as N-Methyl-2-pyrrolidone (NMP) to dissolve a binder and is usually mixed with anode or cathode materials. Dissolving of the binder is required in order to form a slurry that is applied onto a current electrode collector foil prior to drying process. The drying process is essentially the removal of NMP in the coating, but because of its toxicity, the process necessitates recovery and purification stages which usually involve large and costly equipment or machines. Studies have shown that the largest energy consumption steps for making lithium-ion cells are drying and solvent recovery stages, whereby about 47% of total energy is required, due to long-time heating and off-gas cooling steps.
[0004] Accordingly, there is a need to find a more sustainable, cost-effective and environmentally friendly way of producing lithium-ion cells.SUMMARY
[0005] In one aspect, the present invention provides a method for producing an electrode comprising: forming a mixture comprising electrode active material and a carbon additive;wherein the electrode active material is in powder form; dry coating the active material particles with the carbon additive to create a conductive layer on the active material particles; adding a binder to the coated active material particles to bind the material particles together in order to form the electrode; wherein the mixture is formed using a dry mixing process comprising suspending the active material particles by flowing air through the mixture and / or mechanically agitating it in order to allow the carbon additive to be in direct contact with the active material particles via shear, compression and impact forces induced by the mixing; wherein the dry coating includes the carbon additive surrounding the active material particles to create a surrounding conductive layer on the active material particles surface.
[0006] Advantageously, the dry mixing procedure does not require solvents and thus saves cost associated to energy, time and footprint required to remove the solvents due to toxicity.
[0007] In an embodiment, the carbon additive includes graphene.
[0008] In a further embodiment, the carbon additive includes carbon nanotube (CNT) or carbon black (CB).
[0009] In yet a further embodiment, the dry mixing process includes mixing at a speed between 1000 to 7000 rpm with air flow for a duration of 5 to 30 minutes to suspend or agitate active materials. Typically, the dry mixing is carried out for a duration of 15 minutes.
[0010] In another embodiment, the method includes adding a binder subsequent to dry coating the active materials with the carbon additives.
[0011] Advantageously, adding the binder subsequent to dry coating the active materials enhances the coverage with carbon additives and avoid the creation of blockages to pathways for ionic transfer.
[0012] In an embodiment, the binder is selected from a group comprising: PVDF (Poly vinylidene Fluoride) and PTFE (polytetrafluoroethylene).
[0013] In a further embodiment, the mixture comprises 85 to 99% of active materials and 1 to 15% by weight percent of carbon additives, in which the active materials are uniformly coated with the carbon additives.
[0014] In yet a further embodiment, the active materials are prepared by grinding or ball milling to reduce their particle size in powder form.
[0015] In an embodiment, the method further includes adhering the fdm onto a substrate to form the electrode.
[0016] In an embodiment, the method is for producing free-standing dry electrodes for batteries. Typically, the electrodes are for making lithium-ion cells.
[0017] In one embodiment the mixture does not include any solvent or aqueous carriers.
[0018] In one embodiment, the active materials are cathodic or anodic materials. Typically, the cathode active materials include lithium nickel- manganate-cobalt (NMC), and anode materials include graphite.
[0019] In a further aspect, the invention provides an electrode prepared with the method described herein.
[0020] In a further aspect, the present invention provides an electrode comprising an electrode active material and a binder, wherein the active material is coated with graphene by way of a dry coating process.
[0021] Advantageously, the electrode has low volume resistivity and improved thermal stability.BRIEF DESCRIPTION OF DRAWINGS
[0022] The invention will be more understood by reference to the description below taken in conjunction with the accompanying drawings herein:
[0023] FIG. 1 provides a schematic diagram of the method in accordance with an embodiment of the present invention;
[0024] FIG. 2A - FIG. 2B show a comparison of coating outcome between the conventional method and the method in accordance with an embodiment of the present invention;
[0025] FIG. 3A - FIG. 3E show the experimental results for performance testing (volume resistivity, sheet resistance and thermal stability) in accordance with an embodiment of the present invention.DETAILED DESCRIPTION
[0026] In line with the above summary, the following description of a number of specific and alternative embodiments is provided to understand the inventive features of the present invention. It shall be apparent to one skilled in the art, however that this invention may be practiced without such specific details. Some of the details may not be described at length so as not to obscure the invention. For ease of reference, common reference numerals will be used throughout the figures when referring to the same or similar features common to the figures.
[0027] Embodiments of the invention are described by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the scope of the present invention. It should be noted that the drawings include schematic description of how the process in accordance with the preferred embodiments can be carried out.
[0028] In one aspect, the present invention provides a method for producing an electrode for making free-standing dry electrodes that can be used in lithium-ion cells.
[0029] The method comprises the steps of forming a mixture comprising electrode active material particles and a carbon additive, and dry coating the active material particles with the carbon additive to create a conductive layer suitable for electronic and ionic transfer when the electrode is in use.
[0030] The term “electrode active materials” generally define cathode or anode materials or electrochemically active materials, that contribute to the electrochemical processes involving electrodes.
[0031] The electrode active materials and carbon additives may be added in specific ratios, in one-step dry mixing or in a multi-step approach whereby each carbon additive is added and mixed one at a time in difference sequences. In this embodiment, the mixture comprises (in weight percentage) 1% to 15% of carbon additives and between 85% to 99% of active materials.
[0032] With reference to FIG. 1, the mixture is formed using a dry mixing process, which includes the steps of mixing at optimised speed with air flow for a predetermined duration to suspend or agitate the active material particles that causes the carbon additives to surround and adhere to the active material particles such that they wrap around the active materials particles creating a conductive coating interface that forms all-around good connection with adjacent active materials. This creates more pathways for electronic conductivity compared to other mixing methods that introduce carbon additives only at localised points and inbetween the active material particles. This then enables more efficient electronic conductivity between the electrode active material particles, hence lower resistivity and higher thermal efficiency. The mixing process can be carried out at 1000 to 7000 rpm for 5 to 30 min with air flow 0 to 15 L / min. The dry mixing method creates direct coating and contact of the active material particles with the carbon additives through shear, compression and impact forces therefore allowing uniformly distributed carbon additive, which could improve the electrode’s electronic conductivity. Alternatively, the mixture may be formed using a wet mixing process where carbon additives are well-dispersed with the active material using a type of liquid, ultimately to obtain dry coated materials. Using the wet mixing process, the coated active materials are subjected to a drying stage which may be conducted with a spray dryer or the like. The drying is conducted at the temperature of vaporization of the liquid and the mixture may require mechanical milling to achieve powder form.
[0033] A binder may be added to the mixture, examples of binders include PVDF (Polyvinylidene Fluoride) and PTFE (polytetrafluoroethylene), subsequent to the drycoating process to prevent interference of dry coating process and enhance coverage active material with the conductive carbon. Further, adding the binder after the dry coating process avoids the creation of blockages to pathways for ionic transfer. The primary role of the binder is to bind the coated active material particles to form a film. This film can be standalone as an electrode or adhered / pressed onto a substrate surface thereby forming the electrode. Suitably, the substrate may be in the form of thin foils or thin sheets or mesh.
[0034] The active materials include ternary cathode materials such as lithium nickel- manganate-cobalt (NMC). Other examples of cathode active materials include lithium cobalt oxide (LiCoOi), lithium manganese oxide (LiM O-O, lithium iron phosphate (LiFePO4 or LFP), and lithium nickel manganese cobalt oxide (LiNiMnCoO or NMC). The carbon additives include graphene, carbon nanotubes (CNT) and / or carbon black (CB). Active materials, especially that are of larger particles may be reduced into powder form by means of grinding or ball milling process.
[0035] In another embodiment, the present invention provides a method for producing an electrode comprising: forming a mixture comprising lithium nickel- manganate -cobalt (NMC) as the electrode active material and a carbon additive; wherein the NMC is in powder form; dry coating the NMC with the carbon additive to create a conductive layer on the NMC particles; adding a binder to the coated NMC to create a standalone film; and applying the film on a substrate to form the electrode; wherein the mixture is formed using a dry mixing process comprising suspending the active material particles with mechanical agitation and / or air flow in order to allow the carbon additive to be in direct contact with the active material particles; wherein the dry coating includes the carbon additive surrounding the active material’s particle to create the conductive layer on the active material particles surface.
[0036] An experimental example of dry coating obtained using a mixture comprising 97% of active materials and 3% carbon additive, specifically graphene, in accordance with the embodiment of the present invention is shown in FIG. 2A, where it appears that the carbon additive is uniformly coated on the active material compared to the outcome using a conventional method in FIG. 2B whereby the carbon additive is between the active particles and only at localised regions.
[0037] The electrode produced with the method of the present invention can be used in the manufacture or production of free-standing dry electrodes without the use of solvents,therefore would significantly save cost associated with energy (about 47% of total energy in conventional methods using solvents), time and factory footprints required. Further, using graphene as part of the carbon additives appears to enhance thermal dissipation and provide thermal stability, in addition to better electrical conductivity for the electrodes.
[0038] In another aspect, the present invention provides a dry electrode produced with the method as described in the preceding paragraphs. Accordingly, the present invention provides an electrode with improved thermal stability and low volume resistivity, the electrode comprising: electrode active material particles coated with graphene and a binder, wherein the electrode active material particles are coated with graphene by way of dry coating process.
[0039] Experiments were conducted to evaluate the performance of the dry graphene -coated ternary cathode materials and results are shown in FIG. 3A to FIG. 3E. It is observed that the dry graphene coated NMC active materials prepared using dry mixing process for a duration of 15 minutes exhibited low volume resistivity and sheet resistance therefore indicating improved conductivity (FIG. 3A, FIG. 3B and FIG. 3C). It is also observed that the formulation or mixture comprising 3% of graphene exhibited at least 50% improvement in volume resistivity.Further, it appears that thermal dissipation of the material comprising graphene is more efficient therefore indicating thermal stability. This is shown in the results from a thermal behaviour test, using differential scanning calorimetry (DSC) analysis, in which the outcome for both mixture without graphene and containing graphene are shown as plotted graphs in FIG. 3D and FIG. 3E respectively. Accordingly, a mixture comprising NMC, carbon nanotubes (CNT) and graphene appears to dissipate heat more efficiently with gradual increase of energy, as shown in FIG. 3E than the product manufactured using a conventional mixture as shown in FIG. 3D. With graphene, the exothermic heat flow of NMC is reduced by about 30% to 1.70 mW and the peak temperature of exothermic reaction is increased by 10°C.
[0040] The dry carbon additive-coated active materials can be used to make free standing dry electrodes without adding solvents in the electrode-making process and would significantly save cost associated with energy. For instance, coating / drying and solvent recovery process alone typically make up about 40-50% of the total cost in manufacturing lithium batteries. Accordingly, with the method of the present invention, at least 20% of thetotal cost can be saved. In addition, dry electrodes will allow thicker electrodes to be made (>300 micron) with higher energy density.
[0041] While the invention has been described as required in terms in preferred embodiments and specific operating ranges and conditions, those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described.
Claims
CLAIMS1. A method for producing an electrode comprising: forming a mixture comprising electrode active material and a carbon additive; wherein the electrode active material is in powder form; dry coating the active material with the carbon additive to create a surrounding conductive layer on the surface of active material particles; adding a binder to the coated active material to bind the coated active material particles and create a film to form the electrode; wherein the mixture is formed using a dry mixing process comprising suspending the active material particles by mechanical agitation and / or flowing air through the mixture such that they are in direct contact with the carbon additive in through shear, compression and impact forces; wherein the dry coating includes the carbon additive surrounding the active material’s particles to create the conductive layer on the active material particles surface.
2. The method according to claim 1, wherein the carbon additive includes graphene.
3. The method according to anyone of claims 1 to 2, wherein the carbon additive includes carbon nanotube (CNT) or carbon black (CB).
4. The method according to claim 1, wherein the binder is selected from a group comprising: PVDF (Polyvinylidene Fluoride) and PTFE (polytetrafluoroethylene).
5. The method according to claim 1, wherein the electrode active material includes anodic or cathodic material.
6. The method according to claim 1, wherein the electrode active material includes lithium nickel- manganate-cobalt (NMC)7. The method according to claim 1, wherein the dry mixing process is carried out at 1000 to 7000 rpm for 5 to 30 minutes with air flow 0-15 L / min to suspend or agitate the active material particles for the carbon additives to surround the active materials.
8. The method according to claim 7, wherein the dry mixing is performed for a duration of 15 minutes.
9. The method according to claim 1, wherein the mixture comprises between 1% 15% of carbon additives and between 85% to 99% of active materials.
10. The method according to claim 9, wherein the mixture comprises 97% of active materials and 3% by weight percent of carbon additives, in which the active material particles are uniformly coated with the carbon additives.
11. The method according to claim 1, wherein the active material particles are prepared by grinding or ball milling to reduce their sizes into powder form.
12. The method according to claim 1, wherein the mixture does not include any solvent or aqueous carriers.
13. The method according to claim 1, wherein the method further includes adhering the fdm onto a substrate to form the electrode.
14. The method according to claim 1, wherein the electrode is for making free standing electrodes for batteries.
15. An electrode comprising prepared in accordance with a method according to claim 1.
16. An electrode comprising: electrode active material particles; a binder; wherein the electrode active material particles are coated with graphene by way of dry coating process