Method for manufacturing positive electrode active material for lithium ion secondary battery, and method for manufacturing lithium ion secondary battery

Abstract

The purpose of the present invention is to provide: a method for manufacturing a positive electrode active material, which has characteristics equivalent to those of a new positive electrode active material, from a recovered positive electrode active material; and a method for manufacturing a lithium ion secondary battery using the regenerated positive electrode active material.　In order to achieve the purpose, a method for manufacturing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention, with which a new positive electrode active material is manufactured from a positive electrode active material that is recovered from a lithium ion secondary battery, includes: a pulverization step S002 for pulverizing the recovered positive electrode active material so as to obtain a pulverized powder 1; an aggregation step S003 for obtaining an aggregated powder 2 from the pulverized powder 1 of the positive electrode active material; a lithium replenishment material mixing step S004 for mixing a lithium replenishment material 3, which is composed of a lithium compound, with the aggregated powder so as to obtain a mixed powder 4; and a firing step S005 for firing the mixed powder 4.

Description

Method for manufacturing positive electrode active material for lithium ion secondary battery, and method for manufacturing lithium ion secondary battery

[0001] The present invention relates to a method for producing a new positive electrode active material from a positive electrode active material recovered from a lithium ion secondary battery, and to a method for producing a lithium ion secondary battery using this positive electrode active material.

[0002] Demand for lithium-ion secondary batteries is expected to increase rapidly for hybrid and electric vehicle applications. As demand for lithium-ion secondary batteries expands, the number of lithium-ion secondary batteries reaching the end of their product lifespan will also increase. However, lithium-ion secondary batteries use various metallic materials, including lithium (Li) and nickel (Ni), as their cathode active materials, and the environmental impacts of their mining and refining processes have become a social issue.

[0003] Therefore, it has been proposed to recycle metal materials from lithium-ion secondary batteries that have reached the end of their product life. For example, a method has been proposed in which a positive electrode active material for a lithium-ion secondary battery is produced by regenerating the positive electrode active material for the lithium-ion secondary battery by supplementing the positive electrode active material recovered from waste batteries with hydroxides or carbonates of metals such as lithium, followed by pulverization and calcination (see, for example, Non-Patent Document 1).

[0004] Xiaopin Fan, et al. “A green, efficient, closed-loop direct regeneration technology for reconstructing of the LiNi0.5Co0.2Mn0.3O2 cathode material from spent lithium-ion batteries” Journal of Hazardous Materials. 410 (2021) 124610.

[0005] However, it has been found that the particle properties of the recycled positive electrode active material are not as good as those of a positive electrode active material obtained by a normal manufacturing process. Therefore, it is difficult to obtain a positive electrode active material having particle properties similar to those of a new material by the method disclosed in the aforementioned literature.

[0006] Therefore, an object of the present invention is to provide a method for producing a positive electrode active material that obtains a positive electrode active material having properties equivalent to those of a new positive electrode active material from recovered positive electrode active material, and a method for producing a lithium ion secondary battery that uses the produced positive electrode active material.

[0007] In order to achieve the above object, one embodiment of the present invention is a method for producing a positive electrode active material for a lithium ion secondary battery, in which a new positive electrode active material is produced from a recovered positive electrode active material, the method comprising: a grinding step of grinding the recovered positive electrode active material to obtain a ground powder; an agglomeration step of obtaining an agglomerated powder from the ground powder; a lithium supplement mixing step of mixing a lithium supplement containing a lithium compound with the agglomerated powder to obtain a mixed powder; and a firing step of firing the mixed powder.

[0008] Preferably, the pulverization step includes producing a slurry containing the recovered cathode active material, pulverizing the recovered cathode active material contained in the slurry to obtain a slurry containing the pulverized powder, and the aggregating step includes drying the slurry containing the pulverized powder to obtain an agglomerated powder in which the pulverized powder is agglomerated. Preferably, the lithium supplement includes lithium carbonate or lithium hydroxide.

[0009] Furthermore, it is preferable that the method further comprises a transition metal supplement mixing step of supplementing and mixing the recovered cathode active material with a transition metal supplement containing the transition metal so that the nickel content of the transition metals contained in the new cathode active material is 50 mol % or more. The transition metal supplement is preferably adjusted in terms of the content of each transition metal contained in the transition metal supplement depending on the difference between the composition ratio of the transition metals contained in the new cathode active material and the composition ratio of the transition metals contained in the recovered cathode active material, and the transition metal supplement mixing step preferably supplements a transition metal supplement having an adjusted nickel content so that the nickel content of the new cathode active material is higher than that of the recovered cathode active material.

[0010] In order to achieve the above object, a method for manufacturing a lithium ion secondary battery, which is one embodiment of the present invention, includes a positive electrode formation step of manufacturing a positive electrode using a positive electrode active material manufactured by the above-described method for manufacturing a positive electrode active material for a lithium ion secondary battery, and a battery cell formation step of forming a battery cell by filling an electrolyte between the positive electrode and the negative electrode.

[0011] According to the present invention, even if the cathode active material is recovered, it is possible to provide a cathode active material having properties equivalent to those of a new cathode active material, and it is also possible to obtain a lithium ion secondary battery having equivalent battery properties.

[0012] FIG. 1 is a flowchart showing a method for manufacturing a positive electrode active material for a lithium ion secondary battery in a first embodiment of the present invention. FIG. 2 is a schematic diagram showing a schematic cross-sectional structure of agglomerated powder 2 before a lithium replenishment mixing step S004 in the first embodiment of the present invention. FIG. 3 is a schematic diagram showing a schematic cross-sectional structure of mixed powder 4 after a lithium replenishment mixing step S004 in the first embodiment of the present invention. FIG. 4 is a flowchart showing a method for manufacturing a positive electrode active material for a lithium ion secondary battery in a comparative example. FIG. 5 is a schematic cross-sectional view of agglomerated powder 2, mixed powder 4, and a positive electrode active material after lithium has diffused into agglomerated powder 2 after firing in the first embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of agglomerated powder 22 and a positive electrode active material after lithium has diffused (or melted) into agglomerated powder 22 after firing in the comparative example. FIG. 7 is a flowchart showing a method for manufacturing a positive electrode active material for a lithium ion secondary battery in a second embodiment of the present invention. FIG. 8 is a diagram showing X-ray diffraction patterns obtained from X-ray diffraction (XRD) of the positive electrode active materials of Examples 1 and 2 of the present invention and the comparative example. FIG. 9 is a scanning electron microscope (SEM) photograph of the positive electrode active material in Example 1. 1 is a SEM photograph of a positive electrode active material in Example 2. FIG. 2 is a SEM photograph of a positive electrode active material in Comparative Example.

[0013] (Method for Producing a Positive Electrode Active Material According to a First Embodiment) A method for producing a positive electrode active material according to a first embodiment, which is one aspect of the present invention, will be described.

[0014] The recovered positive electrode active material is used to produce a new positive electrode active material by the method for producing a positive electrode active material for a lithium ion secondary battery according to the first embodiment shown in Fig. 1. Fig. 1 is a flowchart showing the method for producing a positive electrode active material according to the first embodiment. In the following description, Fig. 2, which will be described later, will be used in addition to Fig. 1.

[0015] In the manufacturing method of the positive electrode active material of the first embodiment, as shown in FIG. 1, the recovered positive electrode active material is subjected to a recovered positive electrode active material preparation step S001, a crushing step S002, an agglomeration step S003, a lithium supplement mixing step S004, and a firing step S005.

[0016] First, in the step S001 of preparing recovered positive electrode active material, for example, positive electrode active material is recovered from used battery cells to prepare the positive electrode active material to be recycled. The used battery cells may be defective products generated during battery manufacturing. The recovered positive electrode active material may be recovered from battery cells, or may be recovered from defective positive electrode active material recovered during the manufacturing process or from scrap, such as offcuts of positive electrodes generated during the manufacturing process of lithium-ion secondary batteries. The crystalline structure of the positive electrode active material may be a spinel or layered rock salt structure, but preferably at least a portion of the positive electrode active material has a layered rock salt structure. The recovered positive electrode active material in this embodiment contains lithium (Li) and nickel (Ni). In addition to Li and Ni, it is preferable that the recovered positive electrode active material also contains manganese (Mn) and cobalt (Co). Furthermore, aluminum (Al), titanium (Ti), gallium (Ga), magnesium (Mg), zirconium (Zr), and zinc (Zn) may be contained. Furthermore, it is preferable that the X-ray diffraction pattern obtained by X-ray diffraction (XRD) has a peak at 2θ = 18° or more and 19° or less, and a peak at 2θ = 43° or more and 44° or less after removing the spectrum component of Kα2 line.

[0017] Next, in the pulverization step S002, the recovered positive electrode active material is pulverized until the average particle size reaches a predetermined particle size. For example, pulverization is performed until the average particle size (D50) reaches 1 μm or less. More preferably, pulverization is performed until the average particle size reaches 0.5 μm or less, and even more preferably, until the average particle size reaches 0.3 μm or less. Pulverization to the above average particle size is preferable because it reduces the voids in the positive electrode active material. The positive electrode active material obtained in this manner is referred to as pulverized powder 1. Pulverization can be performed using a media mill such as an attritor, ball mill, or bead mill, or a stirring mixer. To pulverize the recovered positive electrode active material to a size corresponding to an average particle size (D50) of 1 μm or less, pulverization using a media mill is preferred in the pulverization step S002, and a bead mill is more preferred. Furthermore, during pulverization, the recovered positive electrode active material is preferably added to a solvent and mixed to prepare a slurry, and then the pulverization step S002 is performed. This allows for efficient transition to the subsequent aggregation step S003.

[0018] In this specification, the average particle size is defined as the 50% particle size (D50) in a volume-based cumulative distribution curve determined by a laser diffraction particle size distribution analyzer.

[0019] Next, an aggregation step S003 is performed to obtain agglomerated powder 2 from the pulverized powder 1 obtained in the pulverization step S002. In the aggregation step S003, if the pulverization step S002 is performed using a dry method, the pulverized powder 1 containing the recovered positive electrode active material is aggregated simultaneously with the dry pulverization, or a slurry is generated using the pulverized powder 1 and a solvent, and the pulverized powder 1 of the recovered positive electrode active material in the slurry is aggregated. On the other hand, if the pulverization step S002 is performed in a slurry state, the slurry is dried in the aggregation step S003 to aggregate the pulverized powder of the recovered positive electrode active material in the slurry. In this way, an aggregated powder 2 having an average particle size of several μm to several tens of μm is formed. In the aggregation step S003, a granulated aggregated powder 2 may be produced by performing a granulation process in which the slurry containing the pulverized powder 1 is spray-dried using a nozzle-type spray dryer, a disk-type spray dryer, or the like, or by simply drying the slurry to produce aggregated particles in which the particle size of the aggregated powder 2 is not controlled. Furthermore, the pulverized powder 1 does not have to be entirely agglomerated with other particles; some of the pulverized powder 1 may exist alone. As such, it is sufficient to form the agglomerated powder 2 containing the pulverized powder 1 by some method. Preferably, the pulverized powder 1 is subjected to a granulation process to obtain a spherical agglomerated powder 2 with controlled shape and particle size. The average particle size of the agglomerated powder 2 is preferably 1 μm to 30 μm, more preferably 5 μm to 20 μm. When the average particle size of the agglomerated powder 2 is 1 μm or more, the density of a positive electrode manufactured using the resulting positive electrode active material after subsequent firing is increased, and when the average particle size of the agglomerated powder 2 is 5 μm or more, the density is further increased. When the average particle size of the agglomerated powder 2 is 30 μm or less, when the positive electrode active material is used while substantially maintaining the shape of the agglomerated powder 2, the surface of the positive electrode manufactured using the positive electrode active material is smooth, and when the average particle size of the agglomerated powder 2 is 20 μm or less, the surface is even smoother.

[0020] The pulverized powder 1 constituting this agglomerated powder 2 is made of a positive electrode active material recovered from, for example, a used lithium-ion secondary battery. Therefore, as the battery cell from which the recovered positive electrode active material was recovered is repeatedly charged and discharged, the lithium content of the positive electrode active material in the pulverized powder 1 becomes lower than that before use. Therefore, in the first embodiment, in order to replenish (make up) the deficient lithium, a lithium supplement material 3 made of a lithium compound is mixed with the agglomerated powder 2 after the agglomeration step S003. Thus, in the lithium supplement material mixing step S004, the lithium supplement material 3 is mixed with the agglomerated powder 2, and the lithium supplement material 3 is wrapped around the agglomerated powder 2 to obtain a mixed powder 4.

[0021] The lithium supplement 3 is preferably a powder made of lithium carbonate or lithium hydroxide. The lithium supplement 3 may contain, in addition to the lithium compound, other metal elements necessary for the positive electrode active material. The average particle size of the primary particles of the lithium supplement 3 is preferably smaller than the average particle size of the secondary particles of the agglomerated powder 2, and is more preferably 1 μm or less. If the average particle size of the primary particles of the lithium supplement 3 is 1 μm or less, the lithium supplement 3 is easily dissolved during the firing process, and as a result, it is easily diffused into the agglomerated powder 2.

[0022] Figure 2A shows a schematic diagram of the cross-sectional structure of agglomerated powder 2 before the lithium supplement mixing step S004, and Figure 2B shows a schematic diagram of mixed powder 4 after the lithium supplement mixing step S004. As shown in Figures 2A and 2B, mixed powder 4 after the lithium supplement mixing step has a structure in which lithium supplement material 3 adheres around agglomerated powder 2 while roughly maintaining the shape of agglomerated powder 2 before the lithium supplement mixing step S004. Note that the pulverized powder 1, agglomerated powder 2, lithium supplement material 3 and mixed powder 4 of the present invention are not limited to the shapes shown in the figures.

[0023] The agglomerated powder 2 and the lithium replenisher 3 can be mixed using a V-type mixer, a stirring mixer, an attritor, or a media mill such as a ball mill or a bead mill. A stirring method in which the agglomerated powder 2 and the lithium replenisher 3 are stirred inside a container may be used, but a container rotation method in which the contents of the container are stirred by rotating the container containing the agglomerated powder 2 and the lithium replenisher 3 is preferred. In either case, it is sufficient to be able to coat the agglomerated powder 2 with the lithium replenisher 3 without destroying its shape.

[0024] Next, the firing step S005 is performed to fire the mixed powder 4. An electric furnace or a gas furnace is used in this firing step S005. The pre-fired mixed powder is fired, for example, while being left stationary in a firing sagger. It is preferable to deposit the pre-fired mixed powder in an oxygen-containing state by, for example, sieving it once in an air atmosphere or an atmosphere with a higher oxygen content than air, and then allowing it to fall freely, so that the pre-fired mixed powder contains a large amount of oxygen between each particle. After depositing the pre-fired mixed powder in the sagger, the pre-fired mixed powder is fired in an oxygen-containing gas atmosphere while being left stationary, thereby producing a positive electrode active material. It is preferable to leave the pre-fired mixed powder stationary in a dry atmosphere before firing, which makes it possible to suppress caking of the mixed powder. This makes it possible to suppress the reduction in the flow of oxygen gas that occurs when the mixed powder caking. Furthermore, forming groove-like irregularities or depressions in the pre-fired mixed powder placed on the firing sagger facilitates the passage of oxygen-containing gas through the lower portion of the pre-fired mixed powder during firing. This promotes oxidation of the pre-fired mixed powder at the bottom of the firing sagger, resulting in more uniform firing of the pre-fired mixed powder at the top and bottom of the firing sagger. In addition, the present invention can also employ a furnace that rotates the pre-fired mixed powder during firing, such as a rotary kiln. The firing atmosphere preferably contains 20% or more oxygen by volume. When the Ni content is 80 atomic % or more of all metal elements excluding Li, the oxygen concentration is preferably 90% or more. The firing step S023 may be performed at 700°C to 900°C to obtain a positive electrode active material with a layered rock salt structure or a spinel crystal structure. In addition, since a positive electrode active material with a layered rock salt structure is likely to have a high initial capacity, it is preferable to set the firing temperature at which a positive electrode active material with a layered rock salt structure is obtained. When obtaining a positive electrode active material with a layered rock salt structure, the process may include a pre-firing step maintained at 450°C or higher and 730°C or lower, and a main firing step maintained at a temperature higher than the firing temperature in the pre-firing step and 700°C or higher and 900°C or lower, and preferably includes a subsequent annealing step of the positive electrode active material at a temperature lower than the firing temperature in the main firing step.

[0025] By this firing step S005, lithium diffuses (or melts) from the lithium supplement material 3 in the mixed powder 4 into the agglomerated powder 2 inside the mixed powder 4, and crystallization also progresses between the agglomerated powders 2, resulting in a granular positive electrode active material exhibiting a layered rock salt structure. At this time, components other than lithium in the lithium supplement material 3 (for example, hydroxyl groups in the case of lithium hydroxide, or carbonate in the case of lithium carbonate) evaporate. In particular, since the lithium component in the powder of lithium hydroxide or lithium carbonate compound is only about 20% overall, the location where the lithium supplement material 3 was present becomes a space.

[0026] However, in the manufacturing method of the positive electrode active material for a lithium-ion secondary battery of the first embodiment, the lithium supplement material 3 is almost absent inside the mixed powder 4 before the firing step S005. Therefore, even if particles in the locations where the lithium supplement material 3 was present are lost during the firing step S005, new voids are unlikely to occur in the internal structure because those locations are located outside the mixed powder 4. Therefore, the recycled positive electrode active material has fewer voids and can obtain good particle characteristics. Furthermore, as described above, by making the size of the pulverized powder 1 1 μm or less, the smaller the size, the closer the spacing between the pulverized powders 1 in the aggregated powder 2 becomes, so the recycled positive electrode active material has even fewer voids and can obtain better particle characteristics.

[0027] Furthermore, even if the recovered positive electrode active material has a lithium content lower than the required amount, the positive electrode active material regenerated by the method for producing a positive electrode active material for a lithium ion secondary battery according to the first embodiment will be in a state where lithium is sufficiently replenished, and a lithium ion secondary battery produced using this positive electrode active material will have sufficient charge / discharge characteristics. In addition, since there are few voids, it is estimated that the particle strength will also be high.

[0028] (Method for Manufacturing Lithium-Ion Secondary Battery) Next, a method for manufacturing a lithium-ion secondary battery using the positive electrode active material manufactured by the method for manufacturing a positive electrode active material for a lithium-ion secondary battery according to the first embodiment will be described.

[0029] FIG. 3 is a flowchart showing a method for manufacturing a lithium ion secondary battery according to an embodiment of the present invention.

[0030] The method for manufacturing a lithium ion secondary battery according to the embodiment of the present invention comprises an electrode manufacturing step S010, a battery cell formation step S011, and a chemical formation and charging step S012.

[0031] The electrode manufacturing process S010 is a process for manufacturing a positive electrode generated using the above-described recycled positive electrode active material and a well-known negative electrode. Regarding the electrode manufacturing process S010, the manufacturing of a positive electrode will be mainly described in detail here, but a negative electrode can also be manufactured using a similar process, with only the negative electrode active material being different. It is assumed that a well-known material is used as the negative electrode active material. Therefore, a detailed description of the manufacturing of a negative electrode will be omitted.

[0032] In the electrode manufacturing process S010, a mixture of the recycled positive electrode active material, a conductive material, a binder, and a dispersion medium is applied to a current collector. The mixture is then dried and molded to form a positive electrode. The positive electrode formation process described in the solution to the problem corresponds to the positive electrode formation process described above.

[0033] Next, the battery cell formation step S011 is performed using the positive and negative electrodes produced in the electrode production step S010. In the battery cell formation step S011, a stacked structure of the positive and negative electrodes is formed with at least a separator interposed between the positive and negative electrodes produced in the electrode production step S010, and the outer periphery is covered with an insulator. Then, an electrolyte is filled between the positive and negative electrodes. This results in the formation of a battery cell that can be charged and discharged.

[0034] Next, a chemical formation charging step S012 is performed on the battery cell in which the positive electrode, electrolyte, and negative electrode are stacked. After chemical formation charging, aging is performed to complete the lithium ion secondary battery. The lithium ion secondary battery manufactured by the method for manufacturing a lithium ion secondary battery of this embodiment has good charge / discharge capabilities. Furthermore, since the positive electrode is formed using a positive electrode active material with particle characteristics with few voids, it can also have sufficient durability.

[0035] The effects of the method for producing a positive electrode active material for a lithium ion secondary battery according to the first embodiment will be described below in comparison with a method for producing a positive electrode active material employed in a comparative example described later.

[0036] In the comparative example, a positive electrode active material for a lithium ion secondary battery was produced by the regeneration method shown in Fig. 4. The step S031 of preparing a recovered positive electrode active material in Fig. 4 is the same as the step S001 of preparing a recovered positive electrode active material in the first embodiment, and therefore a description thereof will be omitted.

[0037] Next, in the lithium supplementary material mixing step S032, a lithium supplementary material 12 for supplementing lithium is mixed with the positive electrode active material recovered from the lithium ion secondary battery.

[0038] Next, the pulverization step S033 is the same as the pulverization step S002 in the manufacturing method of the first embodiment except that the lithium replenishment material 12 replenished in the lithium replenishment material mixing step S032 is also pulverized.

[0039] The aggregation step S034 is the same as the aggregation step S003 in the manufacturing method of the first embodiment except that it also includes a newly introduced lithium supplement material 12. The firing step S035 is the same as the firing step in the manufacturing method of the first embodiment.

[0040] The difference between the manufacturing method of the comparative example and the manufacturing method of the first embodiment is that the lithium supplementary material mixing step S032 of mixing the lithium supplementary material with the recovered positive electrode active material is performed before the aggregation step S034.

[0041] 5A and 5B show schematic diagrams of the agglomerated powders 2 and 22 after the aggregating step undergoing a firing step to reach a state after lithium diffusion (or melting). The left diagram in Fig. 5A shows a schematic cross-sectional structure of the agglomerated powder 2 obtained in the aggregating step S003, the center diagram in Fig. 5A shows a schematic cross-sectional structure of the mixed powder 4 when mixed in the lithium supplement mixing step S004, and the right diagram in Fig. 5A shows a schematic cross-sectional structure of the new positive electrode active material after firing the mixed powder 4. Meanwhile, the left diagram in Fig. 5B shows a schematic cross-sectional structure of the agglomerated powder 22 obtained in the aggregating step S034, and the right diagram in Fig. 5B shows a schematic structure of the positive electrode active material obtained by firing the agglomerated powder 22.

[0042] In the manufacturing method of the first embodiment, after obtaining the agglomerated powder 2, newly introduced lithium supplement material 3 is mixed to obtain the mixed powder 4. Therefore, the state of the mixed powder 4 after the lithium supplement material mixing step S004 is such that the lithium supplement material 3 is present on the outside of the agglomerated powder 2, as shown in the central diagram of Figure 5A, and there is almost no lithium supplement material 3 inside the agglomerated powder 2.

[0043] On the other hand, in the manufacturing method of the comparative example, the recovered positive electrode active material and lithium supplement material 12 are mixed in a lithium supplement mixing step S032, and then the recovered positive electrode active material and lithium supplement material 12 are pulverized in a pulverization step S033 to obtain agglomerated powder 22. Therefore, as shown in the left diagram of Figure 5B, the state of agglomerated powder 22 after the agglomeration step is such that lithium supplement material 12 is also present inside agglomerated powder 22. In both the first embodiment and the comparative example, a firing step is performed in the above-mentioned manner.

[0044] In the manufacturing method of the first embodiment, the morphology of the positive electrode active material after the firing step S005 is performed to cause diffusion (or melting) of lithium is shown on the right side of Fig. 5A. On the other hand, the morphology of the positive electrode active material in a similar state in the manufacturing method of the comparative example is shown on the right side of Fig. 5B.

[0045] When comparing the state of the positive electrode active material after lithium diffusion in the firing step for the manufacturing method of the first embodiment and the manufacturing method of the comparative example, it is considered that voids 20 occur inside the positive electrode active material in the manufacturing method of the comparative example, as will be described later, but the positive electrode active material obtained by the manufacturing method of the first embodiment has the generation of voids inside the positive electrode active material suppressed, as will be described later.

[0046] In the right diagrams of Figure 5A and 5B, the grain boundaries of the pulverized powder 1 that existed during the aggregation process are shown as pulverized powders 1' and 11', respectively, as if they still exist after the calcination process and lithium has been diffused. However, this is a convenient illustration to make it easier to understand the process of the generation of voids 20. Therefore, the form of the positive electrode active material according to the present invention is not limited to those in which grain boundaries are necessarily present. The original pulverized powders 1 and 11 may also diffuse into each other during the calcination process, and the grain boundaries of the pulverized powders 1 and 11 that existed in the agglomerated powders 2 and 22 may disappear.

[0047] (Method for manufacturing a cathode active material according to a second embodiment) Next, a method for manufacturing a cathode active material for a lithium-ion secondary battery according to a second embodiment of the present invention will be described. In the second embodiment, in order to replenish the transition metal elements that are deficient in the recovered cathode active material, a transition metal replenishment and mixing step is performed before the firing step S005, in which a transition metal replenisher containing the deficient transition metal elements is replenished and mixed with the recovered cathode active material. Note that the transition metal replenisher may contain a transition metal that is not contained in the recovered cathode active material.

[0048] Preferably, a transition metal supplement mixing step S021 is performed before the pulverization step S002. Therefore, a method for producing a positive electrode active material for a lithium ion secondary battery according to the second embodiment will be described with reference to Fig. 6. Note that the same steps as those in Fig. 1 are the same as those in the first embodiment, and therefore will not be described here.

[0049] In the transition metal supplement mixing step S021, a transition metal supplement is mixed with the recovered positive electrode active material in order to supplement a new positive electrode active material with a transition metal that is deficient in the recovered positive electrode active material.

[0050] For example, the transition metal supplement is a new positive electrode active material for lithium ion secondary batteries. １．０ Ni ０．８ Co ０．１ Mn ０．１ O ２When the target composition ratio is (a) or (b), the transition metal supplement contains at least one metal powder of nickel (Ni), cobalt (Co), and manganese (Mn) or a compound powder of oxide, carbonate, or hydroxide salt. This transition metal supplement may be produced by adjusting the blending amount of at least one metal powder of nickel (Ni), cobalt (Co), and manganese (Mn) or a compound powder of oxide, carbonate, or hydroxide salt based on the composition ratio of the recovered positive electrode active material and the planned amount of lithium supplement added in the lithium supplement mixing step S004. If there are multiple types of transition metals that are missing, an alloy powder made of the multiple missing transition metals may be used. Furthermore, mixing a very small amount of lithium compound powder with the transition metal supplement and oxidizing the transition metal supplement by exposing it to the air once may facilitate the pulverization of the transition metal supplement in the subsequent pulverization step S002, while also promoting more uniform crystallization in the firing step S005.

[0051] In the present invention, the transition metal supplement mixing step S021 may be performed before the pulverization step S002, between the pulverization step S002 and the agglomeration step S003, or between the agglomeration step S003 and the lithium supplement mixing step S004. For example, if it is performed between the pulverization step S002 and the agglomeration step S003, the transition metal supplement is added to the pulverized powder 1 and the transition metal supplement mixing step S021 is performed, and after mixing, the agglomeration step S003 is performed. On the other hand, if the transition metal supplement mixing step S021 is performed between the agglomeration step S003 and the lithium supplement mixing step S004, it does not necessarily have to be performed independently of the lithium supplement mixing step S004, and it is preferable that the lithium supplement mixing step S004 is performed so that the transition metal supplement is mixed with the agglomerated powder together with the lithium supplement. Whether the transition metal supplement mixing step is performed independently of the lithium supplement mixing step S004 or simultaneously with the lithium supplement mixing step S004 can be selected depending on the amount of transition metal supplement material to be supplemented. For example, if the amount of transition metal supplement material to be supplemented is very small, it is preferable to perform it together with the lithium supplement mixing step S004. However, if the pulverized powder 1 and the transition metal supplement material are to be uniformly mixed during the aggregation step, it is preferable to perform the transition metal supplement mixing step S021 before the pulverization step S002. By performing the pulverization step S002 after the transition metal supplement mixing step S021, the particle sizes of the pulverized powder 1 of the recovered positive electrode active material and the supplemented transition metal supplement material become sufficiently small, making it easier for the pulverized powder 1 and the transition metal supplement material to be uniformly mixed during the aggregation step.

[0052] The target new cathode active material for lithium-ion secondary batteries may have the same composition as the recovered cathode active material before use, or the composition may be changed depending on the desired performance. For example, in recent years, there has been a trend toward a higher nickel content than other transition metals in Li-Ni-Co-Mn oxide-based cathode active materials. This is because increasing the nickel content is expected to improve charge / discharge capacity.

[0053] Therefore, by increasing the amount of nickel in the transition metal supplement material supplemented in this transition metal supplement mixing step S021, a cathode active material with higher performance than the recovered cathode active material can be obtained. Therefore, in the transition metal supplement mixing step S021 of the second embodiment, it is preferable to supplement and mix the recovered cathode active material with a transition metal supplement material in which the component ratios of various transition metals are adjusted so that the nickel (Ni) content ratio among the transition metals constituting the new cathode active material for lithium ion secondary batteries generated after the baking step S005 is 50 mol % or more. Alternatively, performance can be improved by supplementing the new cathode active material in the transition metal supplement mixing step with a transition metal supplement material in which the Ni content ratio is adjusted so that the Ni content ratio of the new cathode active material is higher than that of the recovered cathode active material. Therefore, it is even more preferable to ensure that the nickel (Ni) content ratio among the transition metals constituting the new cathode active material for lithium ion secondary batteries is 80 mol % or more, as this further improves charge / discharge capacity. Furthermore, to obtain a cathode active material with higher performance than the recovered cathode active material, the composition of transition metals other than nickel may be changed from the recovered cathode active material to obtain a new cathode active material. In this case, it is preferable to adjust the content of each transition metal contained in the transition metal supplement material supplemented in this transition metal supplement mixing step according to the difference between the composition ratio of the transition metals contained in the new cathode active material and the composition ratio of the transition metals contained in the recovered cathode active material, and then supplement the adjusted transition metal supplement material in the transition metal supplement mixing step. For example, if it is desired to obtain a new cathode active material with a reduced content of cobalt, which is more expensive than the recovered cathode active material, it is preferable to use a transition metal supplement in which the ratio of transition metals other than cobalt is higher than the ratio of cobalt contained in the recovered cathode active material, or a transition metal supplement in which the cobalt content is zero and only the other transition metals are contained.

[0054] The first and second embodiments of the method for manufacturing a positive electrode active material for a lithium ion secondary battery and the method for manufacturing a lithium ion secondary battery have been described above with reference to the drawings. However, the technical scope of the present invention is not limited to the above-described embodiments. It is clear that a person skilled in the art can come up with various modified or altered examples within the scope of the technical ideas described in the claims, and it is understood that these examples also naturally fall within the technical scope of the present invention.

[0055] In particular, in the method for manufacturing a positive electrode active material for a lithium-ion secondary battery according to an embodiment of the present invention, the starting positive electrode active material is not limited to a positive electrode active material recovered from a used lithium-ion secondary battery. For example, the starting positive electrode active material may be a positive electrode active material discarded during the manufacture of a lithium-ion secondary battery, or a positive electrode active material discarded due to some defect after undergoing the chemical charging process performed during the manufacture. Therefore, the starting positive electrode active material may be a positive electrode active material recovered from a battery cell that has undergone at least one charging operation, including the chemical charging process, in the form of a battery cell composed of a positive electrode, a negative electrode, and an electrolyte. The starting positive electrode active material may also be a positive electrode active material that has not undergone a charging operation and that has been recovered from a positive electrode scrap generated during the manufacture of a lithium-ion secondary battery, or a positive electrode active material that has not undergone a charging operation and that has undergone some defect during the manufacture of the positive electrode active material.

[0056] The recovered positive electrode active material may contain aluminum (Al), copper (Cu), carbon (C), and the like. It is preferable to provide a removal step for removing these substances from the recovered positive electrode active material. This removal step is preferably performed before or after the pulverization step S002. Furthermore, when the transition metal supplementation and mixing step S021 is performed before the pulverization step S002, as in the second embodiment, it is preferable to perform the removal step before the transition metal supplementation and mixing step S021. Specific removal methods include a method of separating unnecessary substances using specific gravity differences (e.g., centrifugation) and a method of dissolving the desired substances in a solvent using chemicals. In particular, the method of separating using specific gravity differences is preferably employed in the separation step performed after the pulverization step S002. The regeneration method for a positive electrode active material for a lithium ion secondary battery according to the first and second embodiments is a method for manufacturing a positive electrode active material for a lithium ion secondary battery.

[0057] Next, the means for measuring each characteristic value will be described.

[0058] (X-ray diffraction pattern of X-ray diffraction (XRD)) The X-ray diffraction pattern of X-ray diffraction (XRD) in the X-ray powder diffraction measurement of the positive electrode active material was measured using an X-ray diffractometer "X'Pert PRO MPD" (manufactured by PANalyticalsei) under the conditions of a CuKα source, a tube voltage of 45 kV, a tube current of 40 mA, a sampling interval of 0.02° / step, a divergence slit of 0.5°, a scattering slit of 0.5°, a receiving slit of 0.15 mm, and a scanning range of 15°≦2θ≦80°. From the obtained X-ray diffraction pattern, analysis software "HighScorePlus" (manufactured by PANalyticalsei) was used. At that time, Kα2 was removed.

[0059] (Oil Absorption Measurement) The oil absorption of the positive electrode active material was measured in accordance with JIS K5101-13-1, using NMP (N-methylpyrrolidone) as the solvent. 5.0 g of positive electrode active material was weighed out and placed in a mountain shape on a flat tray. The NMP solvent was sucked up using a plastic dropper (2 ml capacity), and the mass was measured. Next, NMP was added dropwise to the positive electrode active material while kneading with a spatula. The addition and kneading were continued until the positive electrode active material became clay-like overall. When NMP was excessive, it was visible that the droplets were not absorbed by the positive electrode active material and remained on the surface. The amount of NMP added dropwise up to this point was converted per 100 g of positive electrode active material to represent the oil absorption. The oil absorption of a preferred positive electrode active material is 24 ml / 100 g or more and 32 ml / 100 g or less.

[0060] (Residual Li Amount) 0.5 g of the positive electrode active material and 30 ml of pure water were placed in a 50 ml plastic container, and the inside of the plastic container was replaced with argon gas. The container was then stirred for 1 hour to extract the Li component, and the extract was obtained by suction filtration. 15 ml of the obtained extract was diluted with pure water to about 40 ml, and titrated with 0.02 M hydrochloric acid to determine the amount of Li in the extract. ２ CO ３ The amount of the component and LiOH component was analyzed. An automatic titrator (Hiranuma COM-1700A) was used for the titration.

[0061] The titration curve has two stages, and the equivalence point (x) of the first stage represents the reaction of formula (1) and formula (2), and the equivalence point (y) of the second stage represents the reaction of formula (2). ２ CO ３ The number of moles of is the same as the number of moles of HCl in formula (3), so the remaining Li ２ CO ３ The amount of residual LiOH is the amount of titration up to the first equivalence point, but since the amount of titration up to the first equivalence point is also included in the amount of titration up to the first equivalence point, the amount of residual LiOH is calculated by the equation (2), that is, the amount of residual LiOH. ２ CO ３ The amount obtained by subtracting the amount was (2x-y).

[0062] In addition, residual Li ２ CO ３The amount of Li in the remaining LiOH, i.e., the amount of unreacted Li, was calculated. The number of moles of unreacted Li was divided by the number of moles of metal elements other than Li contained in the positive electrode active material, and multiplied by 100 to calculate the unreacted Li ratio. LiOH + HCl → LiCl + H ２ O...(1) Li ２ CO ３ +HCl→LiCl+LiHCO ３ ...(2) LiHCO ３ +HCl→LiCl+CO ２ +H ２ O (3) The amount of residual LiOH in the preferred positive electrode active material is 1.3 mass % or less, and the amount of residual Li ２ CO ３ The amount of unreacted Li is preferably 0.4 mass % or less. The unreacted Li content is preferably 3 mass % or less.

[0063] Next, each example will be described. ０．７０ Ni ０．８０ Co ０．１０ Mn ０．１０ O ２ (hereinafter referred to as simulated positive electrode active material) was used to regenerate a positive electrode active material for a lithium ion secondary battery. [Example 1] A newly regenerated positive electrode active material (hereinafter referred to as regenerated positive electrode active material) was produced from the simulated positive electrode active material by the process shown in Figure 1. Pure water was added to the simulated positive electrode active material, and the material was pulverized by wet pulverization using a bead mill. The pulverized slurry of the simulated positive electrode active material obtained by the pulverization process was agglomerated using a spray dryer to obtain an agglomerated powder with a secondary particle diameter of 10 μm. The agglomerated powder was obtained by adjusting the conditions during spray drying so that it would have an approximately spherical shape. Li １．０４ Ni ０．８０ Co ０．１０ Mn ０．１０ O ２Lithium carbonate weighed out so that the content was 34 mol% relative to Ni, Co, and Mn was added. The amount of lithium carbonate was 34 mol% in terms of molar ratio relative to Ni, Co, and Mn. The powder was mixed in a V-type mixer to prevent the aggregated powder from collapsing, producing a mixed powder. The added lithium carbonate was in powder form, and its average particle size was equivalent to that of the simulated positive electrode active material. The resulting mixed powder was fired in an oxygen atmosphere at 700°C for 10 hours to obtain a regenerated positive electrode active material.

[0064] Example 2 A regenerated positive electrode active material was produced in the same manner as in Example 1, except that the lithium supplement to be mixed with the agglomerated powder was changed from lithium carbonate to lithium hydroxide.

[0065] Comparative Example A regenerated positive electrode active material was produced from the simulated positive electrode active material by the process shown in FIG. １．０４ Ni ０．８０ Co ０．１０ Mn ０．１０ O ２ Lithium carbonate weighed so as to obtain a simulated positive electrode active material was added, and the mixture was wet-pulverized using a bead mill. The pulverized slurry of the simulated positive electrode active material containing lithium carbonate obtained by the pulverization process was agglomerated using a spray dryer to obtain an agglomerated powder with a secondary particle diameter of 10 μm. The spray dryer was controlled in the same manner as in the examples, and an approximately spherical agglomerated powder was obtained. The obtained agglomerated powder was fired in an oxygen atmosphere at 700°C for 10 hours to obtain a regenerated positive electrode active material.

[0066] [Results of Characteristic Measurements for Examples 1 and 2 and Comparative Example] The regenerated positive electrode active materials of Examples 1 and 2 and Comparative Example were subjected to X-ray diffraction pattern measurement, cross-sectional SEM image observation, residual lithium amount, and oil absorption measurement.

[0067] Fig. 7 shows the X-ray diffraction pattern measurement results for Examples 1 and 2 and the Comparative Example, Fig. 8 shows a cross-sectional SEM image of the positive electrode active material of Example 1, Fig. 9 shows a cross-sectional SEM image of the positive electrode active material of Example 2, and Fig. 10 shows a cross-sectional SEM image of the positive electrode active material of the Comparative Example. Table 1 also shows the residual lithium amount and oil absorption. Note that item (a) in Table 1 shows the amount of residual lithium hydroxide (% by mass), item (b) shows the amount of residual lithium carbonate (% by mass), and item (c) shows the oil absorption (ml / 100g).

[0068]

[0069] FIG. 7 shows X-ray diffraction (XRD) patterns of the recycled positive electrode active materials obtained from Examples 1 and 2 and the Comparative Example. The vertical axis represents the X-ray diffraction light detection intensity, and the vertical axis represents the X-ray reflection diffraction angle. From top to bottom, the graph shows the reflection intensity (a.u.) versus the reflection diffraction angle (2θ) of the X-ray diffraction for Comparative Example (Ref.1), Example 2 (Ex.2), and Example 1 (Ex.1). Also shown are the X-ray diffraction pattern of a simulated positive electrode active material (D.M.) and the measurement results of the reflection intensity versus reflection diffraction angle of the X-ray diffraction for a positive electrode active material (New) produced from various metal raw materials without using the simulated positive electrode active material, but with the same composition as the simulated positive electrode active material. The recycled positive electrode active materials of Examples 1 and 2 and the Comparative Example exhibited peaks at the same angles as the new positive electrode active material, confirming that they had a layered rock salt structure and were recycled into new positive electrode active materials.

[0070] Furthermore, as shown in Table 1, the regenerated positive electrode active materials of Examples 1 and 2 and the Comparative Example had small amounts of residual lithium hydroxide, 0.9% by mass or less, and residual lithium carbonate, 0.3% by mass or less, and it was confirmed that the replenished lithium was replenished to the simulated positive electrode active material and recycled.

[0071] However, excessive voids may reduce the particle strength of the recycled positive electrode active material and reduce the capacity retention rate (lifespan) due to the elimination of coating. The cross-sectional SEM images in Figures 8 to 10 reveal that Examples 1 and 2 have fewer voids than the Comparative Example. Furthermore, Table 1 shows that the oil absorption of Examples 1 and 2 is 31 ml / 100 g or less, less than the 38 ml / 100 g of the Comparative Example. Therefore, a longer lifespan can be expected due to the reduced voids. Furthermore, the positive electrode active materials of Examples 1 and 2 both had an oil absorption of 32 ml / 100 g or less. Therefore, particle performance comparable to that of a positive electrode active material produced from raw materials rather than recycled materials is obtained, and a longer lifespan can be expected compared to the positive electrode active material recycled by the method of the Comparative Example, which is preferable. In particular, Example 1 is preferable because it has a low oil absorption of 30 ml / 100 g or less.

[0072] S001: Preparation step of recovered positive electrode active material, S002: Pulverization step, S003: Aggregation step, S004: Lithium replenishment material mixing step, S005: Firing step, 1: Pulverized powder, 2: Aggregated powder, 3: Lithium replenishment material, 4: Mixed powder, S010: Electrode manufacturing step, S011: Battery cell formation step, S012: Chemical charging step, S021: Transition metal replenishment mixing step, S031: Preparation step of recovered positive electrode active material, S032: Lithium replenishment material mixing step, S033: Pulverization step, S034: Aggregation step, S035: Firing step, 11: Pulverized powder, 12: Lithium replenishment material, 20: Void

Claims

1. A method for producing a positive electrode active material for a lithium ion secondary battery, in which a new positive electrode active material is produced from a recovered positive electrode active material, comprising: a grinding step of grinding the recovered positive electrode active material to obtain a ground powder; an agglomeration step of obtaining an agglomerated powder from the ground powder; a lithium supplement mixing step of mixing a lithium supplement containing a lithium compound with the agglomerated powder to obtain a mixed powder; and a firing step of firing the mixed powder.

2. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1, characterized in that the pulverization step produces a slurry containing the recovered positive electrode active material, pulverizes the recovered positive electrode active material contained in the slurry, and obtains a slurry containing the pulverized powder, and the agglomeration step dries the slurry containing the pulverized powder to obtain the agglomerated powder in which the pulverized powder is agglomerated.

3. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, characterized in that the recovered positive electrode active material has a layered rock salt structure.

4. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, characterized in that the lithium supplementary material contains lithium carbonate.

5. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, wherein the lithium supplementary material contains lithium hydroxide.

6. A method for producing a positive electrode active material for a lithium ion secondary battery as described in claim 1 or 2, characterized in that it further comprises a transition metal supplement mixing process in which a transition metal supplement containing the transition metal is mixed with the recovered positive electrode active material so that the nickel content ratio of the transition metals contained in the new positive electrode active material is 50 mol % or more.

7. A method for producing a positive electrode active material for a lithium ion secondary battery as described in claim 6, characterized in that the content of each transition metal contained in the transition metal supplement is adjusted according to the difference between the composition ratio of the transition metals contained in the new positive electrode active material and the composition ratio of the transition metals contained in the recovered positive electrode active material.

8. A method for producing a positive electrode active material for a lithium ion secondary battery as described in claim 6, wherein the transition metal supplement mixing process supplements the transition metal supplement with an adjusted nickel content so that the nickel content of the new positive electrode active material is higher than that of the recovered positive electrode active material.

9. A method for manufacturing a lithium ion secondary battery, comprising: a positive electrode forming step of manufacturing a positive electrode using a positive electrode active material manufactured by the method for manufacturing a positive electrode active material for a lithium ion secondary battery described in claim 1 or 2; and a battery cell forming step of forming a battery cell by filling an electrolyte between the positive electrode and the negative electrode.

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