Electrode manufacturing method

Abstract

To provide an electrode remanufacturing method.SOLUTION: A first electrode is provided that includes a first current collector and a first active material layer. The first current collector and the first active material layer are separated. The first active material layer is processed into a wet powder. The wet powder is molded into a second active material layer. A second electrode is produced by placing the second active material layer on the surface of a second current collector. The first active material layer contains an active material and a binder. The second active material layer contains an active material and a binder.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing electrodes. [Background technology]

[0002] Japanese Patent Publication No. 2014-127417 (Patent Document 1) discloses a method for recovering and reusing the negative electrode active material of a lithium-ion battery. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-127417 [Overview of the project] [Problems that the invention aims to solve]

[0004] Recycling of electrode materials is required because electrode materials may contain rare materials. Generally, electrodes consist of a current collector and an active material layer. The active material layer is attached to the surface of the current collector. The main component of the active material layer is the active material. Conventionally, it has been proposed to remanufacture electrodes by using the active material recovered from the active material layer.

[0005] Generally, the active material layer also includes a binder. The binder adheres firmly to the active material. Separating the active material from the binder may require, for example, a long separation process. In the separation process, the active material may be immersed in a heated solvent. The separation process may alter or degrade the active material.

[0006] Generally, the active material layer is formed by applying a slurry (a dispersion of particles). That is, a slurry is created by dispersing the active material in a solvent. The active material layer can be formed by applying the slurry to the surface of the current collector.

[0007] The binder can firmly bond the active materials together. When the separation of the active materials and the binder is insufficient, the active materials may form coarse aggregates. When a slurry containing coarse aggregates is applied, surface defects (coating defects) such as streaks may frequently occur.

[0008] The purpose of this disclosure is to provide a method for remanufacturing electrodes. [Means for solving the problem]

[0009] The technical configuration and effects of this disclosure are described below. However, the mechanisms of action described herein include assumptions. The mechanisms of action do not limit the technical scope of this disclosure.

[0010] 1. The method for manufacturing electrodes includes the following (a) to (e). (a) Prepare a first electrode including a first current collector and a first active material layer. (b) Separate the first current collector and the first active material layer. (c) The first active material layer is processed into a wet powder. (d) The wet powder is formed into the second active material layer. (e) The second electrode is manufactured by placing the second active material layer on the surface of the second current collector. The first active material layer comprises an active material and a binder, and the second active material layer comprises the active material and the binder.

[0011] In this disclosure, the second electrode is remanufactured using the first active material layer as a raw material. The first active material layer is processed into a wet powder. The first active material layer contains the active material and a binder. That is, the active material and binder are reused together. Therefore, in this disclosure, the separation process between the active material and the binder can be reduced.

[0012] A wet powder is a powder in a wet state. Because it is wet, the particles in a wet powder are adhered to each other. In other words, a wet powder can inherently contain aggregates of the active material. Therefore, in this disclosure, the process of breaking down the aggregates can be simplified.

[0013] For example, in the die coating of a slurry, surface defects such as streaks may occur due to clogging of aggregates at the slurry discharge port. Therefore, when a slurry is used, it is necessary to crush the aggregates. On the other hand, the wet powder can be formed into a sheet. That is, an active material layer is formed by the forming process. In the forming process, the aggregates are processed from a granular form to a film form. The forming process of the wet powder is expected to be less likely to cause surface defects such as streaks compared to the coating of the slurry.

[0014] 2. The wet powder may have a solid content ratio of, for example, 70% or more.

[0015] 3. The above (d) may include forming the wet powder into a sheet by roll forming.

[0016] 4. The first active material layer may further contain a conductive material, and the second active material layer may further contain the conductive material.

[0017] The active material, binder, and conductive material may be reused together.

[0018] Hereinafter, embodiments of the present disclosure (hereinafter may be abbreviated as "the present embodiment"), and examples of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the present example do not limit the technical scope of the present disclosure.

Brief Description of Drawings

[0019] [Figure 1] FIG. 1 is a schematic flowchart of a method for manufacturing an electrode in the present embodiment. [Figure 2] FIG. 2 is a schematic diagram showing an example of an electrode manufacturing apparatus.

Modes for Carrying Out the Invention

[0021] In this specification, expressions such as "may do" and "may be" are used in a permissive sense ("possibility") rather than in an obligatory sense ("must do").

[0022] In this specification, the order in which steps, actions, and operations included in various methods are performed is not limited to the order in which they are described, unless otherwise specified. For example, multiple steps may be performed simultaneously. For example, multiple steps may be performed one after the other.

[0023] In this specification, numerical ranges such as "m~n%" include upper and lower limits unless otherwise specified. That is, "m~n%" indicates a numerical range of "m% or more and n% or less". Also, "m% or more and n% or less" includes "greater than m% and less than n%". Furthermore, a number arbitrarily selected from within the numerical range may be set as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a number within the numerical range with a number listed in another part of this specification, in a table, in a figure, etc.

[0024] In this specification, all numerical values ​​are modified by the term "approximately." The term "approximately" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximations that may vary depending on how the disclosed technology is used. All numerical values ​​may be expressed with significant figures. Measured values ​​may be the average of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. Generally, the reliability of the average value is expected to improve with a larger number of measurements. Measured values ​​may be rounded to the nearest significant figure. Measured values ​​may include errors, for example, those associated with the detection limit of the measuring device.

[0025] In this specification, when a compound is represented by a stoichiometric formula (e.g., "LiCoO2"), this formula is merely a representative example of the compound. The compound may have a non-stoichiometric composition. For example, when lithium cobaltate is represented as "LiCoO2", unless otherwise specified, lithium cobaltate is not limited to the composition ratio of "Li / Co / O = 1 / 1 / 2", but may contain Li, Co, and O in any composition ratio. Furthermore, doping and substitution with trace elements may also be permitted.

[0026] In this specification, "solid content" refers to the mass fraction of solid components in paints, etc. (e.g., slurry, wet powder, active material layer, etc.). Solutes dissolved in the solvent are considered solid components.

[0027] In this specification, "electrode" is a general term for either a positive or negative electrode. An electrode may be a positive electrode or a negative electrode. Electrodes can be applied to any application. Electrodes may, for example, be used in batteries. In this specification, an electrode for a lithium-ion battery is described as an example.

[0028] In this specification, the D50 of the active material represents a particle size in which the cumulative frequency of the smallest particle size reaches 50% in the volume-based particle size distribution. The volume-based particle size distribution can be measured by laser diffraction scattering.

[0029] In this specification, D50 of a wet powder represents the particle size at which the cumulative frequency of the smallest particle size reaches 50% in the mass-based particle size distribution. The mass-based particle size distribution can be measured in accordance with "JIS Z 8815 General Rules for Sieving Test Methods".

[0030] <Method of manufacturing electrodes> Figure 1 is a schematic flowchart of the electrode manufacturing method in this embodiment. Hereinafter, "electrode manufacturing method in this embodiment" may be abbreviated as "this manufacturing method". This manufacturing method includes "(a) electrode preparation", "(b) active material layer recovery", "(c) wet powder formation", "(d) molding", and "(e) electrode remanufacturing".

[0031] (a) Preparation of electrodes This manufacturing method includes preparing a first electrode comprising a first current collector and a first active material layer. The first electrode can be prepared by any method. For example, the electrode may be recovered by disassembling a battery. This could be a used battery or a new battery. For example, defective products, cutting scraps, etc., generated during the manufacture of the electrode may be recovered as the first electrode.

[0032] The first electrode may have any shape. For example, the first electrode may be in the form of a sheet. The first electrode includes a first current collector and a first active material layer. The first active material layer is disposed on the surface of the first current collector. The first active material layer may be disposed on only one side of the first current collector, or on both the front and back surfaces.

[0033] The first current collector may include, for example, metal foil, metal mesh, or a porous metal body. The first current collector may include, for example, at least one selected from the group consisting of aluminum (Al) foil, Al alloy foil, copper (Cu) foil, Cu alloy foil, titanium (Ti) foil, stainless steel (SUS) foil, nickel (Ni) plated SUS foil, Ni foil, Ni mesh, and a porous Ni body.

[0034] The first active material layer may be a layer formed from a slurry or a layer formed from wet powder. The first active material layer contains an active material and a binder. In this manufacturing method, the active material and the binder can be reused together.

[0035] The active material may be, for example, particulate. The active material may have a D50 of, for example, 0.5 to 50 μm, or may have a D50 of 1 to 10 μm.

[0036] The active material may contain a positive electrode active material. The active material may contain, for example, at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. For example, in "Li(NiCoMn)O2", "(NiCoMn)" indicates that the total of the composition ratios in the parentheses is 1. As long as the total is 1, the amounts of the individual components are arbitrary. Li(NiCoMn)O2 may contain, for example, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, etc. The active material may contain a negative electrode active material. The active material may contain, for example, at least one selected from the group consisting of graphite, soft carbon, hard carbon, silicon, silicon oxide, silicon-based alloy, tin, tin oxide, tin-based alloy, and Li4Ti5O 12 and may contain at least one selected from the group consisting of.

[0037] The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of active material. The binder may contain any components. For example, the binder may contain at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid (PAA), polyamide-imide (PAI), and polyimide (PI).

[0038] The first active material layer may further contain a conductive material, a solid electrolyte, etc. In this manufacturing method, the active material, binder, conductive material, solid electrolyte, etc. may be reused together. That is, in this manufacturing method, the electrode mixture can be reused.

[0039] The amount of conductive material added may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of active material. The conductive material may include, for example, conductive carbon particles, conductive carbon fibers, etc. The conductive material may include, for example, at least one selected from the group consisting of carbon black, vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes. The carbon black may include, for example, at least one selected from the group consisting of acetylene black, Ketjenblack®, furnace black, channel black, and thermal black.

[0040] The amount of solid electrolyte may be, for example, 1 to 100 parts by volume per 100 parts by volume of active material. The solid electrolyte may include, for example, at least one selected from the group consisting of Li2S-P2S5, LiI-Li2S-P2S5, LiBr-Li2S-P2S5, and LiI-LiBr-Li2S-P2S5.

[0041] (b) Recovery of the active material layer This manufacturing method includes separating the first current collector from the first active material layer. This allows the first active material layer to be recovered. The first active material layer can be recovered in any form. For example, the first active material layer may be recovered as a sheet, as flakes, or as powder or granules.

[0042] The first active material layer can be separated from the first current collector by any method. For example, the first active material layer may be peeled off from the first current collector by a scraper or the like. For example, the first active material layer may be peeled off from the first current collector by applying ultrasonic vibration to the first electrode. To facilitate the separation of the first active material layer and the first current collector, for example, a solvent may be sprayed onto the first active material layer. For example, the first electrode may be stored in a high-humidity environment. The first current collector may also be reused.

[0043] (c) Formation of wet powder This manufacturing method includes processing the first active material layer into a wet powder. For example, the wet powder may be formed by mixing the first active material layer with a solvent. The solvent may be selected depending on, for example, the type of binder. The solvent may include at least one selected from the group consisting of, for example, water, N-methyl-2-pyrrolidone (NMP), alcohol (e.g., ethanol, propanol, etc.), and ester (e.g., butyl butyrate, etc.).

[0044] For example, the first active material layer and the solvent may be mixed using a stirring granulator. The wet powder may be crushed or granulated. For example, a planetary mixer or a three-roll mill may be used. One-stage mixing may be performed, or multiple-stage mixing may be performed. For example, the wet powder may be formed by mixing the first active material layer and the solvent in a planetary mixer. The wet powder may be kneaded using a three-roll mill.

[0045] The wet powder may be manufactured to have, for example, a solid content of 70% or more. The wet powder may be manufactured to have, for example, a solid content of 70-90%. The wet powder may be manufactured to have, for example, a solid content of 75-85%.

[0046] The wet powder may be granular, flakey, clay-like, or otherwise. The properties of the wet powder can be adjusted, for example, by the solid content ratio, mixing conditions, etc.

[0047] The wet powder may be manufactured to have a D50 of, for example, 4 mm or less. The wet powder may be manufactured to have a D50 of, for example, 0.1 to 4 mm, or 0.5 to 2 mm.

[0048] 《(d) Molding》 This manufacturing method includes forming a wet powder into a second active material layer. The second active material layer is in the form of a sheet. Any molding process can be performed in this manufacturing method. For example, the wet powder may be formed into a sheet by roll molding.

[0049] Figure 2 is a schematic diagram showing an example of an electrode manufacturing apparatus. In the electrode manufacturing apparatus 100, electrodes can be manufactured by a roll-to-roll process. Roll forming and roll transfer can be performed in the electrode manufacturing apparatus 100.

[0050] The electrode manufacturing apparatus 100 comprises a first roll 101, a second roll 102, and a third roll 103. Each roll rotates in the direction of the arrow. The rotation axes of each roll are parallel. When the rotation speed of the first roll 101 is ω1, the rotation speed of the second roll 102 is ω2, and the rotation speed of the third roll 103 is ω3, the relationship "ω1 < ω2 < ω3" may be satisfied, for example.

[0051] Gap AB is formed between the first roll 101 and the second roll 102. The wet powder 10 is supplied to gap AB. In gap AB, the wet powder 10 is compacted to form a second active material layer 22 (sheet). The second active material layer 22 contains an active material and a binder. The active material and binder are the same as those contained in the first active material layer. The second active material layer 22 may further contain a conductive material, a solid electrolyte, etc.

[0052] (e) Remanufacturing of electrodes This manufacturing method includes manufacturing a second electrode 20 by placing a second active material layer 22 on the surface of a second current collector 21. A gap BC is formed between a second roll 102 and a third roll 103. The second roll 102 conveys the second active material layer 22 to the gap BC (see Figure 2). The third roll 103 conveys the second current collector 21 to the gap BC. The second current collector 21 may be made of the same material as the first current collector or of a different material.

[0053] In the gap BC, the second active material layer 22 is rubbed against the surface of the second current collector 21. This causes the second active material layer 22 to adhere to the surface of the second current collector 21. The adhesion of the second active material layer 22 to the second current collector 21 creates the second electrode 20. In other words, the electrode is remanufactured.

[0054] After the placement of the second active material layer 22, the second electrode 20 may be dried. The second electrode 20 may be compressed depending on the application. The second electrode 20 may be cut depending on the application. The second electrode 20 may have the same specifications as the first electrode or may have different specifications. [Examples]

[0055] Examples A positive electrode was prepared as the first electrode. The first electrode consisted of a first current collector and a first active material layer. The first current collector foil was an Al foil (thickness = 12 μm). The composition of the first active material layer was "LiFePO4 / CNT / CMC / SBR = 95.5 / 2 / 1.2 / 1.3 (mass ratio)".

[0056] The first active material layer was scraped off the first current collector using a scraper. The first active material layer was then recovered. The solid content of the first active material layer was measured by the dry weight method. A planetary mixer was prepared. The first active material layer and a solvent (deionized water) were added to the mixing tank of the planetary mixer. The first active material layer and the solvent were mixed in the planetary mixer to produce a wet powder. A three-roll mill was prepared. The wet powder was kneaded in the three-roll mill. The solid content of the wet powder was 78%.

[0057] An electrode manufacturing apparatus 100 was prepared (see Figure 2). The wet powder 10 was formed into a second active material layer 22 by roll molding. The second electrode 20 was manufactured by transferring the second active material layer 22 onto a second current collector 21 (Al foil, thickness = 12 μm).

[0058] The surface quality of the second active material layer 22 was confirmed by visual inspection. No surface defects such as streaks were found in the second active material layer 22.

[0059] Comparative Example In the comparative example, a method similar to the technology disclosed in Patent Document 1 was attempted. Samples No. 1 to 9 were prepared as the first electrode (see Table 1 below). Samples No. 1 to 9 were positive electrodes. In samples No. 1 to 9, the first active material layer had either the first composition or the second composition. The second composition differed from the first composition in that it did not contain SBR. SBR has a stronger bonding force than CMC. The initial D50 of the active material was 1.3 μm.

[0060] The first active material layer was recovered by immersing the sample in a solvent (deionized water). A separation process was attempted between the first active material layer and the binder. Specifically, ultrasonic vibrations were applied to the first active material layer in the solvent using an ultrasonic homogenizer. The conditions for the separation process are shown in Table 1 below.

[0061] After the separation process, the D50 of the active material was measured using a wet particle size distribution analyzer (product name "MT3300," manufactured by Microtrac-Bel). The dispersion medium was deionized water. The closer the D50 is to the initial value (1.3 μm), the more advanced the separation is considered to be.

[0062] After the D50 measurement, a slurry containing the active material was prepared. The slurry was then coated onto the surface of the second current collector using a die coater. This formed the second active material layer, thus creating the second electrode.

[0063] The surface quality of the second active material layer was confirmed visually. The results are shown in Table 1 below.

[0064] [Table 1]

[0065] In samples No. 1-3, the D50 after separation treatment was high. This suggests that the separation of the active material and binder was insufficient even when ultrasonic vibration was applied in a solvent at 25°C. In samples No. 1-3, surface defects such as streaks frequently occurred during the formation of the second active material layer. This is thought to be because the active material formed coarse aggregates.

[0066] Samples No. 4-6 show lower D50 values ​​after separation compared to samples No. 1-3. This suggests that the higher solvent temperature accelerates the separation process. However, it is believed that a longer processing time is necessary for sufficient separation of the active material and binder (see sample No. 6).

[0067] In compositions No. 7-9 (second composition), the active material and binder separated in a relatively short time. This is thought to be due to the weak bonding force of the binder, which does not contain SBR. However, in the second composition, it is thought that practical peel strength cannot be obtained due to the weak bonding force of the binder.

[0068] These embodiments and examples are illustrative in all respects. These embodiments and examples are not restrictive. The technical scope of this disclosure includes all modifications in the sense and scope equivalent to the claims. For example, it is intended from the outset that any configuration may be extracted from these embodiments and examples and combined in any way. [Explanation of symbols]

[0069] 10 Wet powder, 20 Second electrode, 21 Second current collector, 22 Second active material layer, 100 Electrode manufacturing apparatus, 101 First roll, 102 Second roll, 103 Third roll, AB, BC gap.

Claims

1. (a) Prepare a first electrode including a first current collector and a first active material layer. (b) Separating the first current collector and the first active material layer, (c) Processing the first active material layer into a wet powder, (d) Forming the wet powder into a second active material layer, (e) Manufacturing the second electrode by arranging the second active material layer on the surface of the second current collector, Includes, The first active material layer comprises an active material and a binder. The second active material layer comprises the active material and the binder, The wet powder includes aggregates of the active material, In the aggregate, the binder binds the active materials together. A method for manufacturing electrodes.

2. The aforementioned wet powder has a solid content of 70% or more. The method for manufacturing an electrode according to claim 1.

3. (d) above includes forming the wet powder into a sheet by roll molding, A method for manufacturing an electrode according to claim 1 or claim 2.

4. The first active material layer further contains a conductive material, The second active material layer further comprises the conductive material, A method for manufacturing an electrode according to any one of claims 1 to 3.

5. The wet powder has a D50 of 0.1 to 4 mm. A method for manufacturing an electrode according to any one of claims 1 to 4.

6. The active material is a positive electrode active material, The binder comprises at least one selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene rubber, polyamide-imide, and polyimide. A method for manufacturing an electrode according to any one of claims 1 to 5.

Images