Method for recovering positive electrode active material

Abstract

The present disclosure provides a method for recovering positive electrode active material, which produces high-quality recovered positive electrode active material and has high productivity. The method comprises the following steps: separating and recovering a positive electrode mixture from a positive electrode plate of a battery, wherein the positive electrode plate is formed by laminating the positive electrode mixture containing the positive electrode active material on a positive electrode foil; supplying at least one of ozone and hydrogen peroxide to a slurry containing the positive electrode mixture to oxidize the positive electrode mixture; and separating and recovering the positive electrode active material from the slurry.

Description

Technical Field

[0001] The present disclosure relates to a method for recovering positive electrode active material particles from a battery. Background Art

[0002] Japanese Patent Application Laid-Open No. 2014-203567 discloses a method for recovering the positive electrode active material particles using a solvent after transferring the positive electrode active material layer from a collector foil to an adhesive tape. WO2012 / 072619 discloses a method for recovering lithium from a portion containing LiFePO4. More specifically, the portion containing LiFePO4 is treated with an acid solution in the presence of an oxidizing agent to separate the dissolved lithium ions and precipitate them as salts from the lithium-containing solution. The method describes post-treatment using a wet metallurgical method using dilute sulfuric acid, the introduction of oxygen, ozone, or the addition of hydrogen peroxide, and the temperature range of 80-120°C.

[0003] Japanese Patent Application Laid-Open No. 11-097076 discloses a method of immersing an electrode in an acid solution, separating a current collector and an active material, and recovering valuable metals. Summary of the Invention

[0004] However, according to prior art such as Japanese Patent Application Laid-Open No. 2014-203567, many carbon components such as dispersing materials and / or binding materials (binders) are attached to the surface of the recovered positive electrode active material, making it impossible to recover a positive electrode active material with the same crystallinity as the new positive electrode active material. More specifically, during the charge and discharge of lithium-ion secondary batteries, phosphorus (P) and / or fluorine (F) compounds from salts or additives in the electrolyte form a film on the positive electrode active material and remain on the recovered positive electrode active material.

[0005] In addition, in order to remove the adhesive material (adhesive), there are also technologies that use a large amount of organic solvents or expose to special high-pressure environments. However, these technologies are not suitable for industrial mass production (high cost). Recent life cycle assessment (LCA) calculations have shown that these technologies emit large amounts of CO2.

[0006] Therefore, the present disclosure provides a method for recovering a positive electrode active material, in which the recovered positive electrode active material has good quality and high productivity.

[0007] A method for recovering positive electrode active material according to one embodiment of the present disclosure includes the following steps: separating and recovering a positive electrode mixture from a positive electrode plate of a battery, wherein the positive electrode plate is obtained by laminating a positive electrode mixture containing a positive electrode active material on a positive electrode foil; supplying at least one of ozone and hydrogen peroxide to a slurry containing the positive electrode mixture to oxidize the positive electrode mixture; and separating and recovering the positive electrode active material from the slurry.

[0008] In one embodiment of the present disclosure, when the positive electrode mixture is oxidized, the pH value of the slurry may be controlled to be greater than 9.

[0009] In one embodiment of the present disclosure, the ozone may be supplied by bubbling.

[0010] According to the aspects of the present disclosure, a method for recovering a positive electrode active material can be provided, in which the recovered positive electrode active material has good quality and high productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Hereinafter, features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings, wherein like numerals denote like elements.

[0012] Figure 1 This is an explanatory diagram of the process of recovering the positive electrode active material.

[0013] Figure 2 This is an explanatory diagram showing the difference in the obtained positive electrode active material depending on whether or not the oxidative decomposition step is performed. DETAILED DESCRIPTION

[0014] 1. Battery

[0015] The presently disclosed method for recovering positive electrode active materials is directed to batteries (secondary batteries), for example, sealed non-aqueous electrolyte secondary batteries or all-solid batteries used in vehicles such as hybrid vehicles and electric vehicles, specifically lithium-ion secondary batteries. While the battery configuration is not particularly limited, as is well known, a sealed non-aqueous electrolyte secondary battery having the following structure is exemplified.

[0016] The battery is composed of a rectangular outer case, a flat wound electrode assembly housed in the outer case, a positive electrode terminal member and a negative electrode terminal member supported by the outer case, etc. A non-aqueous electrolyte is retained in the outer case.

[0017] The electrode assembly is obtained by laminating a strip-shaped positive electrode plate and a strip-shaped negative electrode plate with a pair of strip-shaped separators made of porous resin interposed therebetween, winding the layers around an axis, and compressing the layers into a flat shape.

[0018] The positive plate has a strip-shaped positive electrode foil made of aluminum as a core material. A porous positive electrode active material layer is formed on the front and back surfaces of part of the positive electrode foil. The positive electrode active material layer is composed of a positive electrode mixture, and the positive electrode mixture is formed of positive electrode active material particles, conductive material particles and a binding material. In this method, lithium cobalt nickel manganese composite oxide particles can be used as positive electrode active material particles, acetylene black (AB) particles can be used as conductive material particles, and polyvinylidene fluoride (PVdF) can be used as a binding material.

[0019] The negative electrode plate has a strip-shaped negative electrode foil made of copper as a core material. A porous negative electrode active material layer is formed on the front and back surfaces of the negative electrode foil. The negative electrode active material layer is composed of a negative electrode mixture, which is formed from negative electrode active material particles, a binder, and a thickener. In this method, natural graphite particles can be used as the negative electrode active material particles, styrene-butadiene rubber (SBR) can be used as the binder, and carboxymethyl cellulose (CMC) can be used as the thickener.

[0020] 2. Recovery method of positive electrode active material

[0021] The method for recovering a positive electrode active material disclosed herein is a method for recovering a positive electrode active material from such a battery. Figure 1 The flow of a method S10 for recovering a positive electrode active material according to one embodiment is shown. Figure 1 It can be seen that the positive electrode active material recovery method S10 of this embodiment includes steps S11 to S20. Each step will be described below.

[0022] 2.1. Disassembly Step S11 (Step S11)

[0023] The disassembly step S11 is a step for disassembling the discharged battery. Specifically, the battery is placed in a shredder to be pulverized. The degree of pulverization is not particularly limited, and the optimal particle size varies depending on the separation method performed in the subsequent step. However, if the battery can be pulverized to 500 mm, the optimal particle size will be pulverized to 500 mm. 2 Below, preferably 100mm 2 If the size is too large, the recovered product will be in the form of a composite, thus reducing the recovery rate. If the size is too small, the recovered product may be mixed with micronized components with higher specific gravity during airflow separation, thus reducing the quality of the recovered product.

[0024] 2.2. Separation Step S12 (Step S12)

[0025] The separation step S12 is a step of removing heavy components (external case, positive electrode terminal component, and negative electrode terminal component) and light components (separator, insulating film) from the battery miniaturized in the disassembly step S11 to separate the positive and negative electrode plates.

[0026] The separation method is not particularly limited. For dry separation, air flow separation is exemplified, and for wet separation, gravity separation using a liquid is exemplified.

[0027] 2.3. Dissolution Step S13 (Step S13)

[0028] The dissolution step S13 involves immersing the positive and negative electrode plates separated in the separation step S12 in a NaOH aqueous solution with a pH of 10 or higher. This dissolves the aluminum foil (positive electrode foil), separating the positive electrode mixture from the positive electrode plate and forming a slurry. Thus, the dissolution step S13 forms a mixture consisting of the micronized negative electrode plate and the slurried positive electrode mixture.

[0029] Although NaOH aqueous solution is used here, LiOH may be used instead. However, when LiOH is used, Al ions in the waste liquid must be removed separately after step S15 (washing step S15) described later.

[0030] 2.4. Positive Electrode Mixture Slurry Recovery Step S14 (Step S14)

[0031] The positive electrode mixture slurry recovery step S14 separates and recovers the slurry containing the positive electrode mixture from the mixture obtained in the dissolution step S13. Specifically, the negative electrode plates and other undissolved aggregates are separated and removed from the slurry by coarse filtration through a filter with a mesh size of 100 μm to 1000 μm or by gravity separation, thereby recovering the positive electrode mixture slurry.

[0032] 2.5. Washing Step S15 (Step S15)

[0033] The washing step S15 is a step of filtering the positive electrode mixture slurry obtained in the positive electrode mixture slurry recovery step S14 using filter paper with a pore size of 1 μm (No. 5C) to recover the positive electrode mixture as a solid component.

[0034] The resulting positive electrode mixture is then washed with water to remove any Na and Al ions adhering to it. However, Li ions also escape from the positive electrode mixture during this washing process, so excessive washing is preferred. Washing is preferably performed until the NV (nonvolatile) value reaches approximately 50% by mass. The "NV value" represents the mass ratio of components other than the dispersion medium.

[0035] 2.6. Slurry Formation Step S16 (Step S16)

[0036] The slurrying step S16 is a step for re-slurrying the positive electrode mixture (solid) obtained in the washing step S15. Specifically, the positive electrode mixture is added to water to which 0.1 mol or more of a base has been added. Examples of the base include LiOH. At this point, the slurry preferably has an NV (nonvolatile) value of approximately 50% by mass. The "NV value" represents the mass ratio of components other than the dispersion medium.

[0037] 2.7. Oxidative Decomposition Step S17 (Step S17)

[0038] The oxidative decomposition step S17 is a step of applying an oxidizing means to the slurry obtained in the slurrying step S16. Specifically, at least one of oxidation by supplying ozone and oxidation by supplying hydrogen peroxide can be mentioned.

[0039] Ozone (O3) is supplied from an ozone generator while the slurry is stirred. Hydrogen peroxide is added to the slurry. Furthermore, since ozone and water generate hydrogen peroxide during ozone supply, the supply of ozone and hydrogen peroxide occurs simultaneously.

[0040] In a lithium-ion secondary battery that has been charged and discharged, as described above, a film is formed on the positive electrode active material by a compound of phosphorus (P), fluorine (F) or a carbon (C) compound such as a binding material or a salt or additive of the electrolyte. Even if it is set to an oxidizing atmosphere of, for example, 900°C or above (even if baked), it will not volatilize and remain. In contrast, as shown in this method, by forming an oxidizing environment under wet conditions (in water) with the slurried positive electrode mixture, the film components are directly oxidized and degraded (oxidative decomposition), partially ionized, and thus dissolved in water and can be separated from the positive electrode active material.

[0041] Furthermore, during the above steps, oxidation of the slurry also progresses as oxidation progresses. Therefore, from the perspective of avoiding degradation and dissolution of the positive electrode active material itself caused by oxidation, it is preferable to control the pH value to a range greater than 9. A more preferred pH value is 10 or less. The specific method for achieving this purpose is not particularly limited, and it can be achieved by adjusting the ozone supply amount and the hydrogen peroxide supply amount.

[0042] In particular, when ozone is supplied, ozone reacts with water in the aqueous solution during ozone aeration, partially producing hydrogen peroxide. This causes the pH of the slurry to continue to drop, turning it into an acidic liquid, which may degrade the positive electrode active material. Therefore, by controlling the pH to prevent it from falling below 9, degradation (dissolution) of the positive electrode active material can be suppressed. Therefore, ozone is preferably continuously supplied into the slurry by bubbling from an ozone generator, and the supply amount is adjusted to control the pH.

[0043] This makes it possible to remove film components and carbon components while suppressing degradation and dissolution of the positive electrode active material.

[0044] 2.8. Positive Electrode Active Material Recovery Step S18 (Step S18)

[0045] The positive electrode active material recovery step S18 is a step of separating and recovering the positive electrode active material from the slurry after the oxidative decomposition step S17. The separation is performed by, for example, filtration, using filter paper with a pore size of 1 μm (No. 5C).

[0046] Furthermore, the positive electrode active material obtained in the above step does not need to be washed with water.

[0047] 2.9. Drying Step S19 (Step S19)

[0048] The drying step S19 is a step of removing moisture from the positive electrode active material obtained in the positive electrode active material recovery step S18 and drying the positive electrode active material. The drying method is not particularly limited, and examples thereof include air flow drying and vacuum drying.

[0049] 2.10.Li Supplementation Process S20 (Process S20)

[0050] The Li replenishing step S20 is a step of replenishing Li when the positive electrode active material obtained by recovering the positive electrode active material is insufficient in Li.

[0051] Therefore, in the above process, the composition of the positive electrode active material obtained in the drying step S19 is quantified by ICP analysis, and it is supplemented when Li is insufficient. As a supplementary means, for example, lithium carbonate (Li2CO3) or lithium hydroxide (LiOH) can be mixed with the obtained positive electrode active material and calcined at a prescribed temperature of 600 to 1000°C in an electric furnace for several hours. Then, the composition of the positive electrode active material obtained after calcination is reconfirmed by ICP analysis, and the crystal structure is confirmed by XRD to prepare a reusable positive electrode active material.

[0052] Figure 2 The XRD measurement results of the positive electrode active material after replenishing Li through this process are shown (surface 104). No. 1 and No. 2 shown with solid lines are examples of the recovery method S10 of the present disclosure (ozone is supplied in the oxidative decomposition step S17). For comparison, the new positive electrode active material is represented by a dotted line as "Ref", and as an example where the oxidative decomposition step S17 was not performed, "C1" and "C2" are shown with a dashed line. The horizontal axis is the diffraction angle 2θ, and the vertical axis is the X-ray diffraction intensity.

[0053] Depend on Figure 2 It can be seen that the positive electrode active materials (No. 1 and No. 2) recovered by the recovery method disclosed herein have restored their crystallinity to the same level as the new positive electrode active material (Ref.) (X-ray diffraction intensity is the same). In contrast, in the example where the oxidative decomposition step S17 was not performed, the crystallinity could not be restored.

[0054] 3. Effects, etc.

[0055] According to the present disclosure, a recycled positive electrode active material can be obtained with good quality (having the same crystal structure as new) that can be directly used in batteries.

[0056] Furthermore, the process for achieving this purpose does not require a reaction layer in a special environment such as an autoclave, so the equipment is simple, the cost can be reduced, and the productivity is high.

[0057] In addition, the present disclosure does not require the use of a dissolving medium such as a solvent that requires time and effort in safety management and disposal management, and does not require the material covering the positive electrode active material to be burned and removed, thereby significantly reducing the generation of CO2, which is also beneficial from an environmental perspective.

[0058] Furthermore, when considering the reuse of positive electrode active materials, there are three options: (1) the reuse of metal raw materials, (2) the reuse of compounds such as metal sulfates as raw materials for positive electrode active materials, and (3) the direct reuse of positive electrode active materials from recovered batteries. (1) and (2) require further processing of the materials obtained through reuse to produce positive electrode active materials, and thus CO2 is further generated in the process. In contrast, in the present disclosure, as shown in (3), the positive electrode active material can be directly obtained, and therefore, from this perspective, CO2 emissions can also be suppressed.

Claims

1. A method for recovering positive electrode active material, characterized in that: The following steps are included: impregnating a positive electrode plate of a battery in a NaOH aqueous solution or a LiOH aqueous solution having a pH value of 10 or higher to dissolve a positive electrode foil, separating a positive electrode mixture from the positive electrode plate, slurrying the mixture, and recovering the positive electrode mixture, wherein the positive electrode plate is obtained by laminating the positive electrode mixture containing the positive electrode active material on the positive electrode foil; supplying at least one of ozone and hydrogen peroxide to a slurry containing the positive electrode mixture to oxidize the positive electrode mixture; and Separating and recovering the positive electrode active material from the slurry, As the positive electrode active material, lithium-cobalt-nickel-manganese composite oxide was used.

2. The method for recovering positive electrode active material according to claim 1, wherein: When the positive electrode mixture is oxidized, the pH value of the slurry is controlled to be greater than 9.

3. The method for recovering positive electrode active material according to claim 1 or 2, characterized in that: The ozone is supplied by bubbling.

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