Separation method and recycling method for electrode active material for lithium ion secondary battery

Abstract

To provide a method for separating an electrode active material aiming at recycling the electrode active material from a lithium ion secondary battery with a reduced cost and in a safe manner.SOLUTION: A method for separating an electrode active material from a lithium ion secondary battery, comprises a step of stirring and mixing a mixture obtained from an electrode of the lithium ion secondary battery and containing an electrode active material and a binder, in the presence of a grinding aid, wherein the binder contains a fluorine-based resin, and the grinding aid is an inorganic compound containing calcium.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a separation method and a recycling method for an electrode active material for a lithium ion secondary battery. [Background technology]

[0002] Lithium-ion secondary batteries are widely used in many industries, including in communication terminal devices and automotive applications. Because the electrode materials for lithium-ion secondary batteries contain rare metals such as cobalt and manganese, methods for recovering and recycling rare metals from lithium-ion secondary batteries are being investigated.

[0003] A lithium-ion secondary battery includes an electrode in which an electrode mixture layer is formed on a current collector. For example, the positive electrode mixture layer constituting the positive electrode contains a positive electrode active material, a conductive additive, and a binder. Polyvinylidene fluoride (hereinafter referred to as "PVdF") is generally used as the binder.

[0004] As a method for recycling lithium ion secondary batteries, a so-called direct recycling method has been investigated in which the positive electrode active material is recovered as is without isolating the positive electrode active material into its individual elements. Direct recycling requires separating and removing components attached to the positive electrode active material. For example, high-temperature heating is effective for removing the binder, but heating PVdF generates harmful hydrogen fluoride, which is a problem.

[0005] As a method for thermally decomposing PVdF while dealing with the generated hydrogen fluoride, Non-Patent Document 1 discloses a method in which calcium oxide is used as a reaction medium and the PVdF is thermally decomposed at 300°C. Non-Patent Document 1 also discloses a method in which the hydrogen fluoride generated during the heat treatment is converted into calcium fluoride, thereby avoiding the release of hydrogen fluoride. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Mengmeng Wang et al.,ACS Sustainable Chem.Eng.2019,7,12799-12806 Summary of the Invention [Problem to be solved by the invention]

[0007] The method disclosed in Non-Patent Document 1 requires a large-scale device to carry out the heat treatment step, and therefore there is room for improvement in terms of further reducing the installation costs and operating costs of recycling facilities. Furthermore, in the method of Non-Patent Document 1, the generated hydrogen fluoride is converted into calcium fluoride to suppress its release, but a safer recycling method is needed that does not generate harmful hydrogen fluoride in the first place.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a method for separating an electrode active material, which aims to recycle an electrode active material from a lithium ion secondary battery in a cost-reducing and safe manner. A further object of the present invention is to provide a method for recycling an electrode active material for a lithium secondary battery, which method includes the above separation method. [Means for solving the problem]

[0009] [1] A method for separating an electrode active material from a lithium ion secondary battery, the method comprising a step of stirring and mixing a mixture obtained from an electrode of the lithium ion secondary battery, the mixture containing the electrode active material and a binder, in the presence of a grinding aid, wherein the binder contains a fluorine-based resin, and the grinding aid is an inorganic compound containing Ca. [2] The separation method according to [1] or [2], wherein the electrode active material is a positive electrode active material. [3] The separation method according to [1] or [2], wherein the inorganic compound containing Ca is at least one of CaO and CaCO3. [4] The separation method according to any one of [1] to [3], wherein in the stirring and mixing step, the amount of the grinding aid added relative to the total amount of the mixture is 2% by mass or more and 10% by mass or less. [5] A method for recycling an electrode active material for a lithium ion secondary battery, comprising the separation method according to any one of [1] to [4] and a step of recovering the electrode active material for a lithium secondary battery. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a method for separating an electrode active material, which aims to recycle the electrode active material from a lithium ion secondary battery in a safe manner while reducing costs. Furthermore, according to the present invention, there can be provided a method for recycling an electrode active material for a lithium secondary battery, which method includes the above separation method. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Separation method> The present invention relates to a method for separating an electrode active material from a lithium ion secondary battery. The separation method of the present invention corresponds to a pretreatment method in a method for directly recycling a lithium ion secondary battery.

[0012] The separation method of the present invention comprises a step of stirring and mixing a mixture obtained from an electrode of a lithium ion secondary battery and containing an electrode active material and a binder in the presence of a grinding aid.

[0013] To obtain the mixture, the lithium ion secondary battery is disassembled to remove the electrodes, and the current collector and the electrode mixture layer are disassembled. Before disassembling the lithium ion secondary battery, it is preferable to discharge the residual charge of the lithium ion secondary battery as necessary. The discharging step may be carried out by a known method.

[0014] The method for disassembling the current collector and the electrode mixture layer is not particularly limited, and may be performed by a known method. In this embodiment, disassembly is preferably performed by a dry method. Methods for dismantling the current collector and the electrode mixture layer include, for example, applying a shear force to the positive electrode to peel off the current collector, or applying a high voltage pulse as described in JP-A-2022-106024. Dismantling can also be carried out by, for example, the method described in Chiharu Tokoro. et al., “Separation of cathode particles and aluminum current foil in lithium-ion battery by high-voltage pulsed discharge Part I: Experimental investigation.”, Waste Management 125 (2021) 58-66.

[0015] The electrode mixture layer that has been disassembled and recovered is the mixture to be treated in the stirring and mixing step. The mixture contains at least an electrode active material and a binder containing a fluorine-based resin, and may further contain a conductive aid.

[0016] In this embodiment, the mixture is stirred and mixed in the presence of a grinding aid. The mixture may be pre-milled and then stirred and mixed in the presence of a grinding aid, or the recovered mixture may be directly stirred and mixed with a grinding aid without being pre-milled. The mixture is agitated and mixed in the presence of a grinding aid, resulting in grinding of the mixture.

[0017] The stirring and mixing step is carried out in the presence of a grinding aid containing a Ca-containing inorganic compound. The mixture is stirred, mixed and pulverized to expose the electrode active material and binder. The fluorine-based resin contained in the binder has a higher affinity with the grinding aid than the electrode active material, so the ground product obtained as a result of the stirring and mixing step contains both the binder selectively adhering to the grinding aid and the electrode active material itself, and as a result, the electrode active material can be separated into individual particles.

[0018] The separation method of the present embodiment does not require heating to separate the electrode active material, does not require large-scale heating equipment, and can be carried out safely because it does not involve a step of decomposing the fluororesin and does not involve a reaction that generates harmful hydrogen fluoride.

[0019] The inorganic compound containing Ca is not limited as long as it has affinity with the fluorine-based resin contained in the binder, and for example, one or more compounds selected from the group consisting of CaO, Ca(OH)2, CaSO4, CaCO3, and Ca3(PO4)2 can be used. Among these, the inorganic compound containing Ca is more preferably one or more selected from the group consisting of CaO, Ca(OH)2, CaCO3, and Ca3(PO4)2, and further preferably at least one or both of CaO and CaCO3.

[0020] In the stirring and mixing step, the amount of grinding aid added relative to the total amount of the mixture is preferably 1.0% by mass to 15% by mass, more preferably 1.5% by mass to 12% by mass, and preferably 2% by mass to 10% by mass. When the amount of the grinding aid added is equal to or greater than the lower limit, the binder and the grinding aid come into contact with each other more easily, and the binder tends to selectively adhere to the grinding aid. When the amount of the grinding aid added is equal to or less than the upper limit, the structure of the electrode active material is easily maintained, which is preferable.

[0021] The grinding aid is preferably a powder of an inorganic compound containing Ca. The inorganic compound containing Ca contained in the grinding aid is preferably in the form of particles having a particle size of 1 μm or more and 50 μm or less.

[0022] The grinding aid preferably comprises an inorganic compound containing Ca, but may contain other components to the extent that the selective adhesion between the inorganic compound containing Ca and the binder is not inhibited.

[0023] The pulverized material obtained as a result of the stirring and mixing step contains a single electrode active material. For example, the particle diameter of a positive electrode active material is generally several μm to 30 μm. In one embodiment of the present invention, it is preferable to stop the stirring and mixing step when the weight ratio of components with particle diameters of 32 μm or less contained in the pulverized material reaches a steady state.

[0024] In the stirring and mixing step, a known stirring type pulverizer or a media stirring type pulverizer can be used. Examples of agitation mills that can be used include pin mills, disc mills, rod mills, ball mills, vibration mills, attritors, and bead mills. As the media agitation type mill, for example, a ball mill, a vibration mill, an attritor, or a bead mill can be used.

[0025] During ball mill mixing, the contact state between the binder and grinding aid can be controlled by adjusting the rotation speed of the ball mill, the amount of media (balls) relative to the raw materials (ball powder ratio), and the mixing time. In other words, adjusting conditions such as increasing the rotation speed of the ball mill, increasing the amount of media relative to the raw materials, and extending the mixing time makes it easier for the binder and grinding aid to come into contact, and the binder will selectively adhere to the grinding aid.

[0026] The diameter of the ball is, for example, 0.1 to 10 mm, or 1 to 10 mm. The ball may be made of glass, agate, alumina, zirconia, stainless steel, chrome steel, tungsten carbide, silicon carbide, or silicon nitride.

[0027] The stirring and mixing step is preferably carried out at room temperature around 20°C. Although the electrode active material can be sufficiently liberated even at room temperature around 20°C, based on the known technology that heating facilitates the progress of chemical reactions, the mixture may be stirred and mixed while heated in order to further promote liberation of the electrode active material.

[0028] Lithium ion secondary batteries that are the subject of the separation method of the present invention are, for example, used lithium ion secondary batteries, non-standard lithium ion secondary batteries generated during the manufacturing process, and secondary batteries for sampling inspection processing for quality control. Further, scraps of electrodes generated during the manufacturing process may also be separated.

[0029] The electrode active material may be either a positive electrode active material or a negative electrode active material. Among these, it is preferable to separate the positive electrode active material, since a fluorine-based resin such as PVdF or polytetrafluoroethylene is generally used as a binder for the positive electrode active material.

[0030] The type of positive electrode active material is not limited, and known positive electrode active materials can be used. Preferably, the positive electrode active material is at least one selected from the group consisting of lithium metal composite compounds having a layered structure or a spinel structure and lithium iron phosphate having an olivine structure. The lithium metal composite compound having a layered structure may be, for example, one or more selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese composite oxide, and lithium nickel cobalt aluminum composite metal oxide. An example of the lithium metal composite compound having a spinel structure is a lithium manganese composite oxide. The lithium iron phosphate having an olivine structure may be coated with a carbon material.

[0031] As the electrode active material, a negative electrode active material can also be used as long as it uses a fluorine-based resin as a binder. Examples of the negative electrode active material include carbon materials, chalcogen compounds, silicon oxides, titanium oxides, vanadium oxides, iron oxides, tin oxides, and tungsten oxides. Examples of carbon materials that can be used as the negative electrode active material include graphite such as natural graphite or artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fiber, and fired organic polymer compounds.

[0032] <Recycling method> One aspect of the present invention is a method for recycling an electrode active material for a lithium ion secondary battery, comprising the separation method of the present invention and a step of recovering the electrode active material for a lithium secondary battery. The separation method of the present invention provides a ground product containing an electrode active material and a deposit in which the binder is selectively adhered to the grinding aid.

[0033] The method for recovering the electrode active material from the obtained pulverized material is not particularly limited, and known methods such as sieving or sorting based on the difference in specific gravity can be used. [Example]

[0034] The present invention will be described in more detail below with reference to specific examples, although the present invention is not limited to the examples shown below.

[0035] Example 1 A conductive paste was prepared by mixing 14 parts by mass of binder liquid (binder amount: 10% by mass) and 14 parts by mass of acetylene black (5% by mass) as a conductive additive for 30 minutes using a mixer with high-speed blades. Here, the binder liquid used was prepared by mixing 8 parts by mass of polyvinylidene fluoride (PVdF) as a binder and 92 parts by mass of N-methyl-2-pyrrolidone (NMP) as a solvent using a mixer with high-speed blades as a mixing device. Into a container for stirring and mixing of a planetary mixer, which is a mixing device, 70 parts by mass (85% by mass) of LiMnO was first added as a positive electrode active material, and then 8 parts by mass of the conductive paste-like material (binder: 10% by mass, conductive additive: 5% by mass) was added and mixed for 100 minutes to obtain a mixture.

[0036] To 30 g of the mixture, 1.5 g of a grinding aid was added, and the mixture was stirred and mixed under the following conditions. (Stirring and mixing conditions) Equipment: Powder Lab, manufactured by Nippon Coke & Engineering Co., Ltd. Folder: Attritor folder made of SUS304, capacity 188mL Media: φ10 zirconia ball, 40 mL (39 pieces) Atmosphere: Air Sample amount: 30g of mixture, 1.5g of grinding aid added. Mixing time: 30 minutes. Rotation speed of the device: 800 rpm

[0037] Powdered CaCO3 was used as a grinding aid. The 80% particle size of CaCO3 was 23 μm. The 80% particle size of CaCO3 was calculated from the particle size distribution measured by a laser diffraction scattering method (SALD-MS30, manufactured by Shimadzu Corporation). Hereinafter, the 80% particle size was measured in the same manner.

[0038] After stirring and mixing under the above conditions, the resulting pulverized material was sieved to separate powder with a particle size of 32 μm or less. The particle size of the positive electrode active material is generally several μm to 30 μm, and sieved powder of 32 μm or less was considered to be the positive electrode active material.

[0039] In Example 1, 75.34 mass % of powder having a particle size of 32 μm or less was separated.

[0040] <Example 2> The separation method was carried out in the same manner as in Example 1, except that the stirring and mixing time was changed to 15 minutes.

[0041] In Example 2, 75.48 mass % of powder having a particle size of 32 μm or less was separated.

[0042] Example 3 The separation method was carried out in the same manner as in Example 1, except that 1.5 g of powdered Ca(OH)2 (80% particle size: 26 μm) was used as a grinding aid.

[0043] In Example 4, 75.34 mass % of powder having a particle size of 32 μm or less was separated.

[0044] Example 4 The separation method was carried out in the same manner as in Example 1, except that 0.5 g of powdered Ca(OH)2 (80% particle size 26 μm) was used as a grinding aid and the stirring and mixing time was changed to 15 minutes.

[0045] In Example 4, 75.25 mass % of powder having a particle size of 32 μm or less was separated.

[0046] <Example 5> The separation method was carried out in the same manner as in Example 1, except that 1.5 g of powdered Ca(OH)2 (80% particle size 26 μm) was used as a grinding aid and the stirring and mixing time was changed to 15 minutes.

[0047] In Example 5, 79.65 mass % of powder having a particle size of 32 μm or less was separated.

[0048] Example 6 The separation method was carried out in the same manner as in Example 1, except that 3.0 g of powdered Ca(OH)2 (80% particle size 26 μm) was used as a grinding aid and the stirring and mixing time was changed to 15 minutes.

[0049] In Example 6, 75.48 mass % of powder having a particle size of 32 μm or less was separated.

[0050] <Comparative Example 1> The process was carried out in the same manner as in Example 1, except that no grinding aid was used.

[0051] In Comparative Example 1, 56.85 mass % of powder having a particle size of 32 μm or less was separated.

[0052] As shown by the above results, the separation method of the present invention was able to separate approximately 20% by mass or more of the positive electrode active material compared to when no grinding aid was used or when a grinding aid not containing a Ca-containing inorganic compound was used.

[0053] The present invention can be carried out without requiring large-scale heating equipment. Furthermore, since there is no heating step, the fluororesin does not decompose and harmful hydrogen fluoride is not produced.

Claims

1. A method for separating an electrode active material from a lithium ion secondary battery, comprising: The method includes a step of stirring and mixing a mixture obtained from an electrode of a lithium ion secondary battery, the mixture including an electrode active material and a binder, in the presence of a grinding aid; the binder contains a fluorine-based resin, The separation method, wherein the grinding aid is an inorganic compound containing Ca.

2. The separation method according to claim 1 , wherein the electrode active material is a positive electrode active material.

3. The inorganic compounds containing Ca include CaO and CaCO ３ The separation method according to claim 1 or 2, wherein the separation method is at least one of the following.

4. In the stirring and mixing step, The separation method according to claim 1 or 2, wherein the amount of the grinding aid added is 2% by mass or more and 10% by mass or less relative to the total amount of the mixture.

5. The separation method according to claim 1 or 2; and recovering the electrode active material for the lithium secondary battery.