Electrode manufacturing method

Abstract

A method for manufacturing an electrode, comprising: forming a mixture containing an electrode active material and a carbon additive; the electrode active material being in powder form, forming a mixture containing electrode active material particles and a carbon additive; dry coating the active material with a carbon additive to form a uniform or surrounding conductive layer on the surface of the active material particles; adding a binder to the coated active material 10 to bind the coated active material particles to form a single film of the mixture for forming an electrode, or applying the film onto a substrate, wherein the mixture is formed using a dry mixing process which includes suspending the active material particles by mechanical stirring and / or aeration into the mixture, and the active material particles are in direct contact with the carbon additive via shear force 15, compressive force and impact force generated by the mixing, and the dry coating includes a carbon additive surrounding the active material particles, forming a conductive layer on the surface of the active material particles.

Description

Technical Field

[0005] , ,

[0001] The present invention generally relates to a method for manufacturing an electrode for an electrochemical element such as a battery.

Background Art

[0002] In recent years, due to the characteristics of being small, high-density, and rechargeable, the demand for lithium-ion batteries has been significantly increasing. Lithium-ion batteries are widely used as a power supply for various electronic devices of different sizes, such as mobile phones, wireless headphones, notebook computers, portable tools or devices, etc., and are currently introduced in electric vehicles (EVs).

[0003] The current method for manufacturing electrodes for lithium-ion batteries generally involves dissolving a binder using a solvent such as N-methyl-2-pyrrolidone (NMP), and the dissolved binder is usually mixed with an anode material or a cathode material. Before the drying process, the dissolution of the binder is necessary to form a slurry that is applied to a current electrode collector foil for the electrode. The drying process is essentially the removal of NMP during coating, but since NMP is toxic, this process usually requires a recovery and purification stage involving large and expensive equipment or machinery. According to research, in the manufacture of lithium-ion batteries, the most energy-consuming steps are the drying and solvent recovery stages, and about 47% of the total energy is required due to the long-time heating and off-gas cooling processes.

[0004] Therefore, there is a need to find a more sustainable, cost-effective, and environmentally friendly method for manufacturing lithium-ion batteries.

Summary of the Invention

Problems to be Solved by the Invention

[0005] In one embodiment, the present invention provides a method for manufacturing an electrode, comprising: forming a mixture comprising an electrode active material and a carbon additive; the electrode active material being in powder form; dry coating the active material with the carbon additive to form a surrounding conductive layer on the surface of the active material particles; and adding a binder to the coated active material to bind the material particles together to form an electrode, wherein the mixture is formed using a dry mixing process that includes suspending the active material particles by aeration into the mixture and / or mechanical stirring of the mixture so that the carbon additive can come into direct contact with the active material particles via shear, compressive, and impact forces, and the dry coating comprises a carbon additive surrounding the active material particles to form a conductive layer on the surface of the active material particles.

[0006] Advantageously, the dry mixing procedure does not require a solvent, thus reducing costs associated with energy, time, and the footprint required for solvent removal due to toxicity.

[0007] In one embodiment, the carbon additive includes graphene.

[0008] In further embodiments, the carbon additive includes carbon nanotubes (CNTs) or carbon black (CBs).

[0009] In yet another embodiment, the dry mixing process is carried out at 1000-7000 rpm with an airflow for 5-30 minutes to suspend or agitate the active material particles. Typically, the dry mixing is carried out for 15 minutes.

[0010] In another embodiment, the method includes dry coating the active material with a carbon additive, followed by the addition of a binder.

[0011] Advantageously, adding a binder after dry coating the active material improves the coverage by the carbon additive, thus avoiding the formation of blockages in the pathways for ion transport.

[0012] In one embodiment, the binder is selected from the group including PVDF (polyvinylidene fluoride) and PTFE (polytetrafluoroethylene).

[0013] In further embodiments, the mixture comprises 85–99% active material and 1–15% by weight of a carbon additive, wherein the active material is uniformly coated with the carbon additive.

[0014] In yet another embodiment, the active material is prepared by grinding or ball milling to reduce the size of the active material particles to a powder form.

[0015] In one embodiment, the method further includes bonding a film onto a substrate to form electrodes.

[0016] In one embodiment, the method is for manufacturing a self-supporting dry electrode for a battery. Typically, the electrode is used to manufacture a lithium-ion battery.

[0017] In one embodiment, the mixture does not contain any solvent or aqueous carrier.

[0018] In one embodiment, the active material is either a cathode material or an anode material. Typically, the cathode active material contains lithium nickel-manganate-cobalt (NMC), and the anode material contains graphite.

[0019] In a further embodiment, the present invention provides electrodes prepared by the method described herein.

[0020] In a further embodiment, the present invention provides an electrode comprising an electrode active material and a binder, wherein the active material is coated with graphene by a dry coating process.

[0021] Advantageously, the electrodes have low volume resistivity and improved thermal stability. [Brief explanation of the drawing]

[0022] The present invention will be better understood by reference to the following description, in conjunction with the accompanying drawings of this specification:

[0023] [Figure 1] FIG. 1 is a schematic diagram of a method according to an embodiment of the present invention;

[0024] [Figure 2A] FIG. 2A shows a comparison of coating results between the conventional method and the method according to an embodiment of the present invention; [Figure 2B] FIG. 2B shows a comparison of coating results between the conventional method and the method according to an embodiment of the present invention;

[0025] [Figure 3A] FIG. 3A shows the experimental results of a performance test (volume resistivity, sheet resistance, and thermal stability) according to an embodiment of the present invention. [Figure 3B] FIG. 3B shows the experimental results of a performance test (volume resistivity, sheet resistance, and thermal stability) according to an embodiment of the present invention. [Figure 3C] FIG. 3C shows the experimental results of a performance test (volume resistivity, sheet resistance, and thermal stability) according to an embodiment of the present invention. [Figure 3D] FIG. 3D shows the experimental results of a performance test (volume resistivity, sheet resistance, and thermal stability) according to an embodiment of the present invention. [Figure 3E] FIG. 3E shows the experimental results of a performance test (volume resistivity, sheet resistance, and thermal stability) according to an embodiment of the present invention.

Mode for Carrying Out the Invention

[0026] In line with the above summary, several specific and alternative embodiments of the present invention are described below to illustrate its features. However, it will be apparent to those skilled in the art that the invention can be implemented without such specific details. Some details may be omitted in length to avoid obscuring the invention. When referring to identical or similar features common to the figures, a common reference number is used throughout the figures for ease of reference.

[0027] Embodiments of the present invention will be described with reference to the drawings. As will be apparent from this specification, various other embodiments of the present invention are possible, and some details thereof can be modified in various ways, but none will depart from the scope of the invention. Note that the drawings include a schematic description of how a process according to a preferred embodiment may be carried out.

[0028] In one embodiment, the present invention provides a method for manufacturing an electrode for producing a self-supporting dry electrode that can be used in a lithium-ion battery.

[0029] The method includes the steps of forming a mixture containing electrode active material particles and a carbon additive, and dry coating the active material particles with the carbon additive to form a conductive layer suitable for electron transfer and ion transfer when the electrode is used.

[0030] The term "electrode active material" typically refers to a cathode material or anode material that contributes to an electrochemical process involving electrodes, or an electrochemically active material.

[0031] The electrode active material and carbon additives may be added in specific ratios in a single dry mixing step, or they may be added in a multi-step approach in which each carbon additive is added and mixed one at a time in a different order. In this embodiment, the mixture contains 1% to 15% (by weight percentage) of carbon additives and 85% to 99% of active material.

[0032] Referring to Figure 1, the mixture is formed using a dry mixing process, which includes mixing at an optimized rate with an airflow for a predetermined time, suspending or stirring the active material particles so that the carbon additive surrounds and adheres to them. This causes the carbon additive to wrap around the active material particles, forming a conductive coating interface that creates good connections with adjacent active materials around the entire circumference. Consequently, more electron conduction pathways are formed compared to other mixing methods that introduce the carbon additive only locally and between active material particles. As a result, more efficient electron conduction is possible between electrode active material particles, resulting in lower resistivity and higher thermal efficiency. The mixing process can be carried out at 1000-7000 rpm for 5-30 minutes with an airflow of 0-15 L / min. The dry mixing method allows for uniform dispersion of the carbon additive because it causes direct coating and contact of the active material particles with the carbon additive via shear, compressive, and impact forces, thereby improving the electron conduction of the electrode. Alternatively, a wet mixing process may be used to form the mixture, in which case a certain liquid is used to well disperse the carbon additive with the active material, ultimately obtaining a dry coating material. When a wet mixing process is used, the coating active material is subjected to a drying step that can be carried out using a spray dryer or the like. Drying is performed at the vaporization temperature of the liquid, and mechanical milling may be required to obtain the mixture in powder form.

[0033] To prevent interference with the dry coating process and to improve the coverage of the active material by conductive carbon, a binder (examples of binders include PVDF (polyvinylidene fluoride) and PTFE (polytetrafluoroethylene)) may be added to the mixture after the dry coating process. Furthermore, adding the binder after the dry coating process avoids the formation of blockages in the pathways for ion transfer. The main role of the binder is to bind the coated active material particles together to form a film. This film can be used alone as an electrode, or it can be bonded / pressed onto the surface of a substrate to form an electrode. Preferably, the substrate may be in the form of a thin foil, a thin sheet, or a mesh.

[0034] Active materials include ternary cathode materials such as lithium nickel-manganate-cobalt (NMC). Other examples of cathode active materials include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4 or LFP), and lithium nickel-manganate-cobalt (LiNiMnCoO2 or NMC). Carbon additives include graphene, carbon nanotubes (CNTs), and / or carbon black (CB). Active materials with particularly large particles may be reduced to powder form by grinding or ball milling processes.

[0035] In another embodiment, the present invention provides a method for manufacturing an electrode, comprising forming a mixture comprising lithium nickel-manganate-cobalt (NMC) as an electrode active material and a carbon additive; the NMC being in powder form, dry coating the NMC with the carbon additive to form a conductive layer on the NMC particles; adding a binder to the coated NMC to form a standalone film; and applying the film to a substrate to form an electrode, wherein the mixture is formed using a dry mixing process that includes suspending the active material particles by mechanical stirring and / or aeration in order to bring the carbon additive into direct contact with the active material particles, and the dry coating comprises a carbon additive surrounding the active material particles to form a conductive layer on the surface of the active material particles.

[0036] Figure 2A shows an experimental example of a dry coating obtained according to an embodiment of the present invention using a mixture containing 97% active material and 3% carbon additive, specifically graphene. Compared with the results obtained using a conventional method in Figure 2B, where the carbon additive is present only between and in localized areas of the active particles, Figure 2A clearly shows that the carbon additive is uniformly coated on the active material.

[0037] The electrodes manufactured by the present invention can be used for the manufacture or production of self-supporting dry electrodes without the use of solvents, thereby significantly reducing costs associated with energy (approximately 47% of total energy in conventional methods using solvents), time, and the required factory footprint. Furthermore, the use of graphene as part of the carbon additive suggests that, in addition to improving the conductivity of the electrodes, heat dissipation is enhanced and thermal stability is imparted.

[0038] In another embodiment, the present invention provides a dry electrode manufactured using the method described in the preceding paragraph. Thus, the present invention provides an electrode with improved thermal stability and low volume resistivity, wherein the electrode comprises electrode active material particles and a binder coated with graphene, and the electrode active material particles are coated with graphene by a dry coating process.

[0039] Experiments were conducted to evaluate the performance of dry graphene-coated ternary cathode materials, and the results are shown in Figures 3A to 3E. Dry graphene-coated NMC active materials prepared using a 15-minute dry mixing process showed low volume resistivity and sheet resistance, confirming improved conductivity (Figures 3A, 3B, and 3C). It was also revealed that formulations or mixtures containing 3% graphene showed at least a 50% improvement in volume resistivity. Furthermore, the thermal dissipation of materials containing graphene was found to be more efficient, thus suggesting thermal stability. This is demonstrated by the results of thermal behavior tests using differential scanning calorimetry (DSC) analysis, with the results for both graphene-free and graphene-containing mixtures shown as plotted graphs in Figures 3D and 3E, respectively. Thus, the mixture containing NMC, carbon nanotubes (CNTs), and graphene is suggested to dissipate heat more efficiently as the energy gradually increases, as shown in Figure 3E, compared to products manufactured using conventional mixtures, as shown in Figure 3D. With the use of graphene, the exothermic heat flow of NMC was reduced by approximately 30% to 1.70 mW, and the peak temperature of the exothermic reaction was raised by 10°C.

[0040] Dry carbon additive-coated active materials can be used to manufacture self-supporting dry electrodes without adding solvents in the electrode manufacturing process, and can also significantly reduce energy-related costs. For example, the coating / drying process and solvent recovery process alone typically account for about 40-50% of the total cost in lithium battery manufacturing. Therefore, using the method of the present invention can reduce the total cost by at least 20%. In addition, dry electrodes can be manufactured as thicker electrodes (>300 microns) with higher energy density.

[0041] While the present invention has been described using terminology necessary for preferred embodiments and specific operating ranges and conditions, those skilled in the art will understand that the invention described herein can be modified and altered in ways not specifically described.

Claims

1. A method for manufacturing electrodes, - Forming a mixture containing electrode active material and carbon additive; - The electrode active material is in powder form, and the active material is dry-coated with a carbon additive to form a surrounding conductive layer on the surface of the active material particles; - Adding a binder to the coated active material to bind the coated active material particles together and form a film for forming electrodes. Includes, The mixture is formed using a dry mixing process that includes suspending the active material particles by mechanical stirring and / or aeration into the mixture, and the active material particles are brought into direct contact with the carbon additive via shear, compressive, and impact forces. Dry coating is a method for manufacturing electrodes, which includes a carbon additive surrounding the active material particles to form a conductive layer on the surface of the active material particles.

2. The method according to claim 1, wherein the carbon additive comprises graphene.

3. The method according to claim 1 or 2, wherein the carbon additive comprises carbon nanotubes (CNTs) or carbon black (CB).

4. The method according to claim 1, wherein the binder is selected from the group comprising PVDF (polyvinylidene fluoride) and PTFE (polytetrafluoroethylene).

5. The method according to claim 1, wherein the electrode active material includes an anode material or a cathode material.

6. The method according to claim 1, wherein the electrode active material comprises 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 an air flow rate of 0 to 15 L / min, suspending or stirring the active material particles so that the carbon additive surrounds the active material.

8. The method according to claim 7, wherein dry mixing is performed for 15 minutes.

9. The method according to claim 1, wherein the mixture comprises 1% to 15% of a carbon additive and 85% to 99% of an active material.

10. The method according to claim 9, wherein the mixture comprises 97% active material and 3% by weight of a carbon additive, and the active material particles are uniformly coated with the carbon additive.

11. The method according to claim 1, wherein the active material particles are prepared by grinding or ball milling, and the size of the active material particles is reduced to a powder form.

12. The method according to claim 1, wherein the mixture does not contain any solvent or aqueous carrier.

13. The method according to claim 1, further comprising bonding a film onto a substrate to form electrodes.

14. The method according to claim 1, wherein the electrode is for manufacturing a self-supporting electrode for a battery.

15. An electrode prepared according to the method described in claim 1.

16. Electrode active material particles; binder, Includes, An electrode in which electrode active material particles are coated with graphene by a dry coating process.

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