Method for manufacturing electrodes, electrodes, and batteries
By coating carbon particles with resin and fiberizing PTFE in the mixture, the method addresses excessive SEI formation, improving cell capacity and reducing costs in liquid-based battery electrodes.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TOYOTA JIDOSHA KK
- Filing Date
- 2023-08-09
- Publication Date
- 2026-07-07
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
Existing methods for manufacturing electrodes in liquid-based batteries, such as those described in Patent Document 1, result in suboptimal cell capacity due to excessive formation of the Solid Electrolyte Interface (SEI) on carbon particles, leading to irreversible capacity loss.
A method involving coating carbon particles with resin, mixing with polytetrafluoroethylene (PTFE), and fiberizing the mixture to form electrodes with partially resin-coated carbon particles and PTFE fibers, which suppresses excessive SEI formation.
The method enhances cell capacity by maintaining a larger surface area of carbon particles exposed and reducing irreversible capacity loss, while also being solvent-free, thus reducing manufacturing costs and environmental impact.
Smart Images
Figure 0007885748000001
Abstract
Description
Technical Field
[0001] The present disclosure relates to a method for manufacturing an electrode, an electrode, and a battery.
Background Art
[0002] In batteries such as lithium-ion secondary batteries, an electrode in which active material particles are fixed to the surface of a current collector such as a metal foil with a binder is used. As a method for manufacturing an electrode, there are a method of applying a composition prepared by mixing active material particles and a binder with a solvent to the surface of a current collector (also referred to as a wet method), and a method of fixing active material particles to a current collector with a binder without using a solvent (also referred to as a dry method).
[0003] As a method for manufacturing an electrode by a dry method, a method of using a resin having a property of being fibrillated (fibered) when a shearing force is applied as a binder has been proposed. For example, Patent Document 1 describes a method of manufacturing an electrode film by fibrillating PTFE in a mixture containing active material particles and polytetrafluoroethylene (PTFE), and then integrating this electrode film with a current collector.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] The electrode obtained by the method described in Patent Document 1 has room for improvement in cell capacity when applied to a battery using an electrolytic solution (also referred to as a liquid-based battery). The problem to be solved by one embodiment of the present disclosure is to provide a method for manufacturing an electrode excellent in cell capacity when applied to a liquid-based battery, an electrode excellent in cell capacity when applied to a liquid-based battery, and a battery including this electrode. [Means for solving the problem]
[0006] The following embodiments are included as means for solving the above problems. <1> A method for manufacturing electrodes used in batteries containing an electrolyte, A step of coating at least a portion of the surface of carbon particles with resin, A step of mixing resin-coated carbon particles with polytetrafluoroethylene to obtain a mixture, A method for producing an electrode, comprising the step of fiberizing the polytetrafluoroethylene in the mixture. <2> The resin coating rate of the carbon particles is 3% or more. <1> A method for manufacturing electrodes as described above. <3> An electrode used in a battery containing an electrolyte, It includes a current collector and an electrode layer, The electrode layer comprises carbon particles whose surface is coated with resin at least partially, and fibrous polytetrafluoroethylene. <4> The resin coating rate of the carbon particles is 3% or more. <3> The electrodes described above. <5> <3> or <4> A battery comprising electrodes and an electrolyte as described above. [Effects of the Invention]
[0007] According to one embodiment of the present disclosure, a method for manufacturing an electrode that is excellent in cell capacity when applied to a liquid-based battery, an electrode that is excellent in cell capacity when applied to a liquid-based battery, and a battery containing this electrode are provided. [Modes for carrying out the invention]
[0008] In this disclosure, a numerical range indicated using "~" means a range that includes the numbers written before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. In the numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the values shown in the examples. In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as their intended purpose is achieved. In this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, unless otherwise specified, the amount of each component refers to the total amount of multiple substances if there are multiple substances corresponding to each component.
[0009] <Method of manufacturing electrodes> The method for manufacturing electrodes disclosed herein is: A method for manufacturing electrodes used in batteries containing an electrolyte, A step of coating at least a portion of the surface of carbon particles with resin, A step of mixing resin-coated carbon particles with polytetrafluoroethylene to obtain a mixture, The method for producing an electrode includes the step of fiberizing the polytetrafluoroethylene in the mixture.
[0010] Electrodes manufactured by the method disclosed herein exhibit superior cell capacity when applied to liquid-based batteries compared to electrodes formed from a mixture obtained by mixing carbon particles, whose surfaces are not coated with resin, with PTFE. The reason for this is thought to be, for example, as follows. Electrodes fabricated by fiberizing PTFE, which is included as a binder along with carbon particles, have a smaller contact area between the carbon particles and the binder compared to electrodes obtained by other methods (wet method, electrostatic method, etc.), and a larger surface area of the carbon particles is exposed. Therefore, a relatively large amount of a film called SEI (Solid Electrolyte Interface) forms on the surface of the carbon particles during the initial charge and discharge of the battery. While the SEI has functions such as suppressing the decomposition of the electrolyte, excessive formation of the SEI leads to an increase in irreversible capacity (i.e., a decrease in cell capacity) due to the immobilization of lithium ions. In the method of the present disclosure, an electrode is manufactured using carbon particles at least partially coated with a resin on the surface thereof. For this reason, excessive formation of the SEI on the surface of the carbon particles is suppressed, and sufficient cell capacity is maintained.
[0011] According to the method of the present disclosure, an electrode can be manufactured without using a solvent. For this reason, the method of the present disclosure is also advantageous in terms of reducing the manufacturing cost of the electrode, reducing the impact on the environment and living organisms, and the like.
[0012] Hereinafter, the step of coating at least a part of the surface of the carbon particles with a resin is also referred to as "Step 1", the step of mixing the carbon particles coated with the resin and PTFE to obtain a mixture is also referred to as "Step 2", and the step of fibrillating the PTFE in the mixture is also referred to as "Step 3".
[0013] (Step 1) In Step 1, at least a part of the surface of the carbon particles is coated with a resin. The type of carbon particles used in this step is not particularly limited and can be selected from materials generally used as negative electrode active materials.
[0014] Specific examples of the material of the carbon particles include graphite, soft carbon, hard carbon, and the like. The carbon particles may be secondary particles formed by aggregation of a plurality of primary particles. The carbon particles used for manufacturing the electrode may be a single type or two or more types. The volume average particle diameter of the carbon particles is not particularly limited and can be selected, for example, from the range of 5 μm to 30 μm.
[0015] In the present disclosure, the volume average particle diameter of the particles is the value (D50) when the cumulative from the smaller diameter side is 50% in the volume-based particle size distribution measured by the laser diffraction / scattering method.
[0016] The type of resin used for coating the carbon particles in this process is not particularly limited and can be selected from materials commonly used in the manufacture of batteries. Specific examples of the resin include polyvinylidene fluoride, polyethylene, polypropylene, polyethylene terephthalate, cellulose, nitrocellulose, carboxymethyl cellulose, polyethylene oxide, polyepichlorohydrin, polyacrylonitrile, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), polyacrylate, polymethacrylate, and the like. The resin used in this process may be a single type or two or more types. From the viewpoints of adhesive strength, affinity with PTFE, electrolyte resistance, etc., polyvinylidene fluoride (PVdF) is preferred as the resin.
[0017] From the viewpoint of ensuring sufficient cell capacity, the coating rate of the surface of the carbon particles with the resin is preferably 3% or more, more preferably 5% or more, and even more preferably 10% or more. The coating rate of the surface of the carbon particles with the resin may be 60% or less, 50% or less, or 40% or less.
[0018] The coating rate of the surface of the carbon particles with the resin is measured by an image analysis method. Examples of the image analysis method include a method of performing F mapping by EDX (energy dispersive X-ray spectroscopy). Specifically, carbon particles coated with resin are observed with a SEM (scanning electron microscope), and F mapping is performed by EDX. The region X corresponding to the carbon particles and the region Y in the region X where the resin (F) exists are binarized, and the coating rate is calculated by the following formula. Coating rate (%) = (Area of Y / Area of X) × 100
[0019] In this process, the method of coating at least a part of the surface of the carbon particles with the resin is not particularly limited and can be carried out by a known method. For example, a composite treatment may be carried out by kneading the carbon particles and the resin with a mixer or the like to coat at least a part of the surface of the carbon particles with the resin. The amount of resin per 100 parts by mass of carbon particles can be selected from, for example, 1 to 20 parts by mass, or 2 to 10 parts by mass.
[0020] (Process 2) In step 2, the resin-coated carbon particles and PTFE are mixed to obtain a mixture. The mixing method is not particularly limited and can be carried out using known means. The amount of PTFE per 100 parts by mass of carbon particles in the mixture can be selected from, for example, 0.1 parts by mass to 10 parts by mass, or 1 part by mass to 5 parts by mass.
[0021] The PTFE mixed with the carbon particles in step 2 may be in particulate form. The mixture obtained in step 2 does not need to contain a solvent. In step 2, at least a portion of the PTFE may be fibrousized, and a granulated body may be produced in which carbon particles are bound together with the fibrousized PTFE.
[0022] The mixture of resin-coated carbon particles and PTFE may contain a binder other than PTFE. For example, the binder other than PTFE may be selected from the resins used to coat the carbon particles as described above. If the mixture contains a binder other than PTFE, its content may be 20 parts by mass or less, 10 parts by mass or less, or 5% by mass or less per 100 parts by mass of PTFE.
[0023] A mixture of resin-coated carbon particles and PTFE may contain a conductive material. Specific examples of conductive materials include carbon materials such as carbon black (acetylene black, thermal black, furnace black, etc.) and carbon nanotubes. If the mixture contains a conductive material, its content can be selected from the range of 0.1 to 10 parts by mass, or 1 to 5 parts by mass, per 100 parts by mass of carbon particles.
[0024] (Step 3) In step 3, the PTFE in the mixture obtained in step 2 is converted into fibers. The method for fiberizing PTFE is not particularly limited and can be carried out using known means. From the viewpoint of workability when integrating the PEFE fiberized mixture with the current collector, it is preferable in step 3 to fiberize the PTFE and form the mixture into a sheet. One method for fiberizing PTFE and forming the mixture into a sheet is, for example, a rolling process using a roll press.
[0025] The thickness of the molded body obtained by forming the mixture into a sheet is not particularly limited and can be adjusted according to the desired electrode layer thickness. For example, the thickness of the molded body can be selected from a range of 10 μm to 200 μm.
[0026] In step 3, the mixture after the PTFE has been fiberized, preferably in the form of a sheet, is integrated with the current collector to form an electrode. The method for integrating the PTFE fiberized mixture with the current collector is not particularly limited and can be carried out using known means. For example, the mixture and the current collector may be pressed together using a roll press, a flat plate press, or the like. The material of the current collector is not particularly limited and can be selected from known materials such as aluminum, copper, nickel, titanium, and stainless steel.
[0027] <Electrode> The electrodes disclosed herein are An electrode used in a battery containing an electrolyte, It includes a current collector and an electrode layer, The electrode layer is an electrode comprising carbon particles whose surface is coated with resin at least partially, and fibrous polytetrafluoroethylene (PTFE fibers).
[0028] The electrodes of this disclosure exhibit superior cell capacity compared to electrodes containing carbon particles and PTFE fibers whose surfaces are not coated with resin.
[0029] Details and preferred embodiments of the electrodes and materials contained in the electrodes of this disclosure are the same as those of the electrodes manufactured by the electrode manufacturing method described above and the details and preferred embodiments of the materials used.
[0030] The electrode of this disclosure may further include a current collector and components other than the electrode layer containing active material particles and PTFE fibers. For example, the electrode of this disclosure may further include an electrode layer that does not contain PTFE fibers.
[0031] <Battery> The battery of this disclosure includes the electrodes of this disclosure described above and an electrolyte. The battery of this disclosure includes the electrode of this disclosure as the negative electrode.
[0032] There are no particular restrictions on the type of electrolyte contained in the battery; it can be selected from electrolytes commonly used in liquid-type batteries.
[0033] The type of battery described herein is not particularly limited and can be selected from lithium-ion secondary batteries, lead-acid batteries, nickel-metal hydride batteries, nickel-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, silver oxide-zinc batteries, cobalt-titanium lithium secondary batteries, sodium-ion secondary batteries, and other types of batteries. [Examples]
[0034] The present disclosure will be described in more detail below with reference to examples, but the invention of the present disclosure is not limited to these examples.
[0035] <Example: Fabrication of the negative electrode> The following materials were added to an MP mixer (Nippon Coke Industries Co., Ltd.) in the quantities shown in Table 1, and a composite treatment was performed to coat the surface of the carbon particles with resin under the conditions of 10,000 rpm for 10 minutes. Carbon particles: Graphite (Volume-average particle size: 20 μm) Resin: PVdF
[0036] PTFE was further added to the MP mixer after the compounding process and mixed at 300 rpm for 180 seconds. Then, it was further mixed at 5000 rpm for 500 seconds to form a granule in which carbon particles were bound together with fibrous PTFE.
[0037] A mixture containing granules was rolled using a roll press (linear pressure: 0.4 t / cm) to fibrousize the PTFE and form it into a sheet (thickness: 200 μm). A sheet-like molded body and copper foil (thickness: 8 μm) to be used as a current collector were bonded together using a flat plate press (load: 5t, 160℃).
[0038] Through the above process, a negative electrode was obtained in which a negative electrode layer containing carbon particles and PTFE fibers, with at least a portion of their surface coated with resin, was placed on top of a current collector.
[0039] <Comparative Example: Fabrication of the Negative Electrode> The negative electrode was prepared in the same manner as in Example 1, except that the carbon particle composite treatment was not performed.
[0040] <Evaluation of coverage> Carbon particles after composite processing were observed using a scanning electron microscope (SEM), and F-mapping was performed using an EDX attached to the SEM to calculate the resin coating rate of the carbon particles. The results are shown in Table 1.
[0041] <Evaluation of cell capacity> A small cell was fabricated using the negative electrode prepared in the examples and comparative examples, and the positive electrode prepared by the method described below. As the electrolyte, a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate containing 1.14 M LiPF6 (EC:DMC:EMC = 30:34:36, vol%) was used. The discharge capacity was measured using the fabricated miniature cell by the method described below. The results are shown in Table 1. Measurement method: Perform CCCV (cut-off current: 1 / 20C) in the range of 4.25V to 2.5V with a current value of 0.3C, and calculate the discharge capacity (mAh / g).
[0042] (Fabrication of the positive electrode) A positive electrode was fabricated by coating a paste containing NCM (97.5 parts by mass) as the positive electrode active material, acetylene black (1.5 parts by mass) as the conductive material, and PVdF (1 part by mass) as the binder onto aluminum foil (thickness: 12 μm) as the current collector.
[0043] [Table 1]
[0044] As shown in Table 1, the examples were made from carbon particles and PTFE, with at least a portion of the surface coated with resin. Cell containing the negative electrode This is a comparative example made from carbon particles whose surface is not coated with resin and PTFE. Cell containing the negative electrode It has a larger cell capacity compared to others. These results suggest that coating the surface of carbon particles with resin suppresses the excessive formation of SEI on the surface of carbon particles, thereby contributing to an increase in cell capacity.
Claims
1. A method for manufacturing a negative electrode used in a battery containing an electrolyte, A step of coating at least a portion of the surface of the carbon particles contained in the negative electrode with resin by a compounding process in which the carbon particles and resin are kneaded together, A step of mixing resin-coated carbon particles with polytetrafluoroethylene to obtain a mixture, A step of forming fibers from the polytetrafluoroethylene in the mixture, A method for manufacturing a negative electrode, comprising the step of integrating the fibrous mixture with a current collector.
2. The method for manufacturing a negative electrode according to claim 1, wherein the resin coating rate of the carbon particles is 3% or more.
3. The method for manufacturing a negative electrode according to claim 1, wherein the resin is a thermoplastic resin.
4. A negative electrode used in a battery containing an electrolyte, It includes a current collector and a negative electrode layer, The negative electrode layer comprises carbon particles whose surface is coated with a resin, with a resin coating rate of 10% to 60%, and fibrous polytetrafluoroethylene.
5. The negative electrode according to claim 4, wherein the resin is a thermoplastic resin.
6. A battery comprising a negative electrode according to claim 4 or claim 5 and an electrolyte.