Manufacturing method of cathode active material

Abstract

To provide a manufacturing method of a cathode active material, in which a performance deterioration of an a capacity characteristic and an output characteristic are suppressed.SOLUTION: A manufacturing method of a cathode active material to be disclosed here, comprises: a preparation step of preparing a step end material of a cathode board; an alkaline liquid implantation step of implanting the step end material into an alkaline liquid; a solid liquid separation step of correcting a solid material by performing a solid liquid separation to the alkaline liquid after the alkaline liquid implantation step; a classification step of classifying the solid material to be corrected into a fine part and a rough part; and a sintering step of sintering the rough part. Thus, it is possible to obtain a cathode active material in which a reaction of a solid carbon and an electric charge carrier in the rough part is suppressed in the sintering step and deterioration of a capacity characteristic and an output characteristic is suppressed.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The technology disclosed herein relates to a method for manufacturing a positive electrode active material.

Background Art

[0002] In recent years, energy storage devices have been suitably used for portable power sources such as personal computers and mobile terminals, and power sources for vehicle driving such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] Generally, a positive electrode active material is used for the positive electrode used in an energy storage device. In recent years, there has been an increasing demand for recovery technologies that recover metals (for example, lithium, nickel, cobalt, etc.) contained in the positive electrode active material from end materials of the positive electrode plate process and reuse them as materials for energy storage devices. Furthermore, in the study of the above recovery technologies, the development of a technology for recovering and regenerating the positive electrode active material as it is without returning it to the metal level from the positive electrode plate has been promoted. As an example of such a technology, for example, Patent Document 1 discloses a method for recovering an electrode active material including a step of pulverizing a waste electrode including a waste current collector and an electrode active material, a step of classifying the pulverized waste electrode to recover the electrode active material, and a step of mixing the electrode active material and an alkaline solution to selectively remove aluminum impurities in the electrode active material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, the positive electrode plate may contain solid carbon in addition to the positive electrode active material. In the technique described in Patent Document 1, there is a risk that solid carbon adheres to the positive electrode current collector (aluminum impurity) crushed during classification and remains in the positive electrode active material (electrode active material). Further, solid carbon is not dissolved in the alkaline solution and remains as an impurity in the positive electrode active material. Furthermore, according to the study by the present inventor, when solid carbon and the positive electrode active material are fired, the charge carriers contained in the solid carbon and the positive electrode active material react, and the capacity characteristics and output characteristics of the obtained positive electrode active material deteriorate compared to a new positive electrode active material (at the stage contained in the positive electrode plate).

[0006] In view of such circumstances, the present disclosure has been made, and an object thereof is to provide a method for manufacturing a positive electrode active material that suppresses performance deterioration of capacity characteristics and output characteristics.

Means for Solving the Problems

[0007] For the above problems, a method for manufacturing a positive electrode active material having the following configuration (hereinafter, also simply referred to as "manufacturing method") is provided.

[0008] The method for manufacturing a positive electrode active material disclosed herein includes a preparation step of preparing a process end material of a positive electrode plate, an alkaline solution immersion step of immersing the process end material in an alkaline solution, a solid-liquid separation step of performing solid-liquid separation on the alkaline solution after the alkaline solution immersion step and recovering a solid, and a classification step of classifying the recovered solid into a fine particle fraction and a coarse particle fraction, and a firing step of firing the coarse particle fraction.

[0009] In the manufacturing method having the above configuration, by performing a classification step on the solid obtained through the alkaline solution immersion step and the solid-liquid separation step, solid carbon is physically removed. As a result, it is possible to suppress the reaction between solid carbon and the charge carriers in the coarse particle fraction during the firing step, and to obtain a positive electrode active material in which deterioration of capacity characteristics and output characteristics is suppressed.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

[0011] Hereinafter, embodiments of the technology disclosed herein will be described with reference to the drawings. In addition, matters other than those specifically mentioned in this specification and necessary for carrying out the technology disclosed herein can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be carried out based on the content disclosed in this specification and common general knowledge in the relevant field. In addition, the notation "A to B" indicating a range in this specification includes the meaning of "not less than A and not more than B", and also includes the meaning of "preferably greater than A" and "preferably less than B".

[0012] As used herein, the term "power storage device" generally refers to any device capable of repeatedly charging and discharging by the movement of charge carriers between a positive electrode and a negative electrode through an electrolyte. The power storage device is a concept that includes secondary batteries such as lithium ion secondary batteries and nickel metal hydride batteries, and capacitors such as lithium ion capacitors and electric double layer capacitors.

[0013] 1. Positive electrode plate The method for manufacturing a positive electrode active material according to the present embodiment manufactures the positive electrode active material by recovering the positive electrode active material from a positive electrode plate. As an example of the positive electrode plate here, a positive electrode plate of a lithium ion secondary battery using lithium ions as charge carriers can be mentioned. Hereinafter, the positive electrode plate will be described in detail using the positive electrode plate of a lithium ion secondary battery as an example. However, it is not intended to limit the technology disclosed herein to that described in such embodiments. FIG. 1 is a schematic cross-sectional view of the positive electrode plate according to the present embodiment along the thickness direction and the width direction.

[0014] As shown in FIG. 1, the positive electrode plate 10 includes a positive electrode current collector 12 and a positive electrode active material layer 14 supported by the positive electrode current collector 12. In the illustrated example, the positive electrode active material layer 14 is provided on both surfaces of the positive electrode current collector 12. However, the positive electrode active material layer 14 may be provided on one surface of the positive electrode current collector 12.

[0015] As shown in FIG. 1, a positive electrode active material layer non-formation portion 12a where the positive electrode active material layer 14 is not provided may be provided at one end in the width direction of the positive electrode plate 10. The positive electrode active material layer non-formation portion 12a is a site where the positive electrode current collector 12 is exposed and has a function as a current collection portion.

[0016] As the positive electrode current collector 12, a known positive electrode current collector used in conventional power storage devices may be used. Examples thereof include an aluminum sheet or foil from the viewpoint of good conductivity. From the viewpoint of easily dissolving the positive electrode current collector in an alkaline solution in the alkaline solution immersion step described later, the positive electrode current collector 12 is preferably an aluminum foil.

[0017] The dimensions of the positive electrode current collector 12 are not particularly limited because they can be appropriately changed according to the capacity and size of the power storage device. When an aluminum foil is used as the positive electrode current collector 12, its thickness is not particularly limited, but can be, for example, 5 μm or more and 35 μm or less.

[0018] The positive electrode active material layer 14 is a composite material layer containing a positive electrode active material and the like. The positive electrode active material is a material capable of reversibly occluding and releasing charge carriers (e.g., lithium, etc.). When lithium ions are used as the charge carriers, examples of such positive electrode active materials include lithium nickel-based composite oxides, lithium cobalt-based composite oxides, lithium manganese-based composite oxides, lithium nickel manganese-based composite oxides, lithium manganese cobalt-based composite oxides, lithium nickel cobalt-based composite oxides, lithium nickel cobalt manganese-based composite oxides, and other lithium transition metal composite oxides. Further, as other examples of the positive electrode active material, lithium transition metal phosphate compounds such as lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate can be mentioned.

[0019] In this specification, the term "lithium nickel cobalt manganese-based composite oxide" includes oxides containing one or more additional elements other than those in addition to the oxides composed of Li, Ni, Co, Mn, and O as constituent elements. Examples of such additional elements include transition metal elements and typical metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, Sn, etc. Further, the additional element may be a semi-metal element such as B, C, Si, P, etc., or a non-metal element such as S, F, Cl, Br, I, etc. This also applies to the above-mentioned lithium nickel-based composite oxides, lithium cobalt-based composite oxides, lithium manganese-based composite oxides, lithium nickel manganese-based composite oxides, lithium manganese cobalt-based composite oxides, lithium nickel cobalt-based composite oxides, etc.

[0020] The positive electrode active material may be, for example, primary particles or in the form of secondary particles. In this specification, the term "primary particle" refers to the smallest unit of the particles constituting the positive electrode active material, specifically, the smallest unit judged from the geometric form in appearance. Further, in this specification, an aggregate of such primary particles is referred to as a "secondary particle". The secondary particle can be, for example, a form in which 2 or more and 100 or less primary particles are aggregated.

[0021] The D50 particle size (average particle size) of the positive electrode active material is not particularly limited, but typically, it is 0.05 μm or more and 25 μm or less in terms of primary particles, for example, 1 μm or more and 20 μm or less, and preferably 3 μm or more and 15 μm or less. In this specification, the "D50 particle size" means the particle size corresponding to 50% by volume of the cumulative frequency from the side of fine particles with a smaller particle size in the volume-based particle size distribution based on the laser diffraction / scattering method. Similarly, the "D10 particle size" in this specification means the particle size corresponding to 10% by volume of the cumulative frequency from the side of fine particles with a smaller particle size in the volume-based particle size distribution based on the laser diffraction / scattering method. Therefore, the D50 particle size and the D10 particle size can be obtained by a known laser diffraction / scattering type particle size distribution.

[0022] The positive electrode active material layer 14 may optionally contain any components in addition to the positive electrode active material. Examples of such optional components include a conductive material, a binder, and the like.

[0023] As the conductive material, for example, solid carbon such as carbon black, coke, activated carbon, graphite (natural graphite and its modified products, artificial graphite), carbon fiber (PAN-based carbon fiber, pitch-based carbon fiber), fullerene, graphene, etc. can be used. Among them, carbon black can be preferably used from the viewpoint of particularly excellent conductivity. Specific examples of such carbon black include acetylene black, furnace black, ketjen black, thermal black, and the like.

[0024] The D50 particle size of the conductive material is typically smaller than the D50 particle size of the positive electrode active material. Although not particularly limited, it is typically 1 to 200 nm, and can be, for example, in the range of 10 to 100 nm.

[0025] As the binder, a polymer that can be dissolved or dispersed in the solvent used can be used, so it is not particularly limited. For example, polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc. can be used.

[0026] As described above, as an example of the object to be recovered in the manufacturing method according to the present embodiment, the positive electrode plate 10 used in the lithium-ion secondary battery has been described. However, the manufacturing method disclosed herein is not limited to only the method of recovering the positive electrode plate 10 used in the lithium-ion secondary battery having the above configuration.

[0027] 2. Manufacturing Method of Positive Electrode Active Material Hereinafter, the manufacturing method of the positive electrode active material according to the present embodiment will be described. FIG. 2 is a flowchart for explaining the manufacturing method of the positive electrode active material according to the present embodiment.

[0028] As shown in FIG. 2, the manufacturing method of the positive electrode active material according to the present embodiment includes a preparation step S10, an alkali solution immersion step S20, a solid-liquid separation step S30, a classification step S40, and a firing step S50. Further, the manufacturing method disclosed herein may further include other steps at any stage, and the other manufacturing processes may be the same as those in the prior art. Hereinafter, each step will be described.

[0029] (1) Preparation Step S10 In the preparation step S10, the process end material of the positive electrode plate is prepared. Note that the "process end material of the positive electrode plate" in this specification includes a positive electrode plate in which charge carriers have never entered or exited in the positive electrode active material. That is, the end material of the positive electrode plate generated during the manufacturing of the power storage device, the positive electrode plate that has become a non-standard product, and the positive electrode plate taken out from the battery assembly that has become a non-standard product before charge and discharge are also included as the "process end material of the positive electrode plate". In the present embodiment, the end material of the positive electrode plate is prepared. Since the details of the positive electrode plate have already been described, duplicate descriptions will be omitted.

[0030] (2) Alkali Solution Immersion Step S20 In the alkali solution immersion step S20, the positive electrode plate prepared in the preparation step S10 is immersed in an alkali solution. As a result, among the positive electrode plate, the positive electrode current collector (aluminum) is dissolved in the alkali solution. On the other hand, since the positive electrode active material layer of the positive electrode plate does not dissolve in the alkali solution, it precipitates as a solid in the alkali solution.

[0031] Specific examples of the alkaline solution used in the alkaline solution immersion step S20 include an aqueous solution of lithium hydroxide (LiOH), an aqueous solution of sodium hydroxide (NaOH), an aqueous solution of potassium hydroxide (KOH), and the like. Among them, an aqueous solution of lithium hydroxide and an aqueous solution of sodium hydroxide can be preferably adopted as the alkaline solution. These aqueous solutions exhibit strong alkalinity. When such an alkaline solution is used in the alkaline solution immersion step S20, the damage to the positive electrode active material in the positive electrode plate can be suppressed while selectively dissolving the positive electrode current collector.

[0032] The pH of the alkaline solution used in the alkaline solution immersion step S20 is preferably pH 12 or higher (more preferably pH 13 or higher). If the pH of the alkaline solution is too low, the positive electrode current collector may not be dissolved in the alkaline solution, and there is a risk of damaging the positive electrode active material in the material to be recovered. On the other hand, if the pH of the alkaline solution is too high, the dissolution reaction of the positive electrode current collector is significant, and there is a possibility of causing structural damage to the positive electrode active material. Therefore, the pH of the alkaline solution used in the alkaline solution immersion step S20 is preferably pH 14 or lower (more preferably pH 13.5 or lower).

[0033] The temperature of the alkaline solution in the alkaline solution immersion step S20 is not particularly limited, but it is preferably 20°C or higher (more preferably 30°C or higher, even more preferably 40°C or higher). Thereby, the dissolution of the positive electrode current collector in the alkaline solution is promoted, and the time of the alkaline solution immersion step S20 can be shortened. On the other hand, the upper limit value of the temperature of the alkaline solution in the alkaline solution immersion step S20 is not particularly limited, and may be, for example, 80°C or lower, 60°C or lower, or 50°C or lower.

[0034] The state of the positive electrode plate during the alkaline solution immersion step S20 is not particularly limited, and it may be used as it is in the state at the time of preparation. Also, depending on the scale of the equipment, etc., it may be in a cut state.

[0035] (2) Solid-liquid separation step S30 In the solid-liquid separation step S30, solids are recovered from the alkaline solution after the alkaline solution immersion step S20. Thereby, solids containing the positive electrode active material can be separated from the alkaline solution in which the positive electrode current collector has dissolved. As the method of the solid-liquid separation step S30, a conventionally known method can be used, and for example, a recovery method such as filtration, centrifugation, decantation, etc. can be adopted.

[0036] (3) Classification step S40 In the classification step S40, the solids obtained in the solid-liquid separation step S30 are classified into fine particles and coarse particles. The technology disclosed herein is characterized by performing the classification step S40.

[0037] Incidentally, the positive electrode active material layer of the positive electrode plate may contain solid carbon in addition to the positive electrode active material. Solid carbon can typically be included as a conductive material. Solid carbon is difficult to be removed in the above-described alkaline solution immersion step S20 and remains in the solids. Further, if the firing step S50 described later is performed with solid carbon remaining in the solids, there is a risk that solid carbon reacts with the charge carriers in the positive electrode active material and the charge carriers in the positive electrode active material are desorbed. As a result, there is a risk that the capacity characteristics and output characteristics of the positive electrode active material obtained from the solids are deteriorated. Here, the inventor focused on the fact that typically the D50 particle size of solid carbon is smaller than the D50 particle size of the positive electrode active material. In other words, the particle size distribution of solid carbon is shifted to the side with smaller particle size (fine particle side) than the particle size distribution of the positive electrode active material. And, through the study of the inventor, it was found that by classifying the solids after the removal of the positive electrode current collector and before firing, the solid carbon in the solid content can be classified to the fine particle side and physically removed.

[0038] In the classification step S40, conventionally known classification means can be used. For example, an elbow jet classifier (simultaneous multi-product classifier), a cyclone classifier, etc. can be used. Further, the classification step S40 may be dry classification or may be performed by wet classification. As an example of a wet classifier that can be used in the classification step S40, for example, an i Classifier (manufactured by Satake Multimix Co., Ltd.) can be mentioned.

[0039] In the classification step S40, by setting the classification point and adjusting the particle sizes of the fine particles and the coarse particles, the solid carbon in the solid matter can be classified to the fine particle side. In some preferred embodiments, it is preferable to perform the classification step S40 by setting the classification point such that the D50 particle size of the fine particles is -30% to +10% of the D10 particle size of the positive electrode active material contained in the positive electrode composite material layer.

[0040] If the classification point is too small, the solid carbon in the solid matter cannot be sufficiently removed, and there is a risk that a large amount of solid carbon remains in the coarse particles. Therefore, from the viewpoint of preferably removing the solid carbon in the solid matter, the classification point is preferably set such that the D50 particle size of the fine particles is -30% or more of the D10 particle size of the positive electrode active material contained in the positive electrode composite material layer, more preferably -20% or more, and even more preferably -15% or more. On the other hand, if the classification point is too large, the proportion of the positive electrode active material in the fine particles increases, so the recovery rate of the positive electrode active material (the weight of the positive electrode active material (sintered body) obtained after the firing step with respect to the weight of the positive electrode active material in the recovery target) decreases. Therefore, from the viewpoint of increasing the recovery rate of the positive electrode active material, the classification point is preferably set such that the D50 particle size of the fine particles is +10% or less of the D10 particle size of the positive electrode active material contained in the positive electrode composite material layer, more preferably 0% (i.e., the same as the D10 particle size of the positive electrode active material) or less, and even more preferably -5% or less. The method for setting the classification point can be set according to the classifier used in the classification step S40. For example, it can be set by adjusting the mesh size of the sieve or the classification edge distance.

[0041] The classification point in the classification step S40 may be two points, or may be classified into three or more points. In that case, a plurality of groups may be grouped together as coarse particles or fine particles.

[0042] In some preferred embodiments, the D50 particle size of the positive electrode active material contained in the positive electrode plate is 0.05 to 25 μm (more preferably 1 μm to 20 μm), and the D50 particle size of the solid carbon contained in the fine particle fraction is 1 to 200 nm (more preferably 10 to 100 nm). Thereby, the solid carbon in the solid content can be preferably removed in the classification step S40.

[0043] It is preferable to perform a drying treatment on the solid matter before subjecting it to the classification step S40. By performing the drying treatment, the moisture contained in the solid matter is removed, so that the solid matter can be efficiently classified in the classification step S40. The drying step can be performed by a conventionally known method, such as natural drying, heat drying, blowing drying, vacuum drying, etc. Also, the drying temperature only needs to be able to remove the moisture contained in the solid matter, and typically is preferably generally 100°C or higher, for example 110 to 250°C.

[0044] Note that the classification step S40 is not a step intended to completely remove the solid carbon from the solid matter. In the classification step S40, it is sufficient if 80% or more, 90% or more, or 95% or more of the solid carbon contained in the solid matter can be removed.

[0045] (4) Firing step S50 In the firing step S50, the coarse particle fraction obtained by the classification step S40 is fired (heated). Thereby, while removing the binder component (for example, fluorine (F), etc.) remaining in the coarse particle fraction, the crystal growth of the positive electrode active material in the coarse particle fraction can be promoted. Also, a part of the solid carbon may remain in the coarse particle fraction. Such solid carbon can also be removed in the firing step S50. Also, in the technology disclosed herein, the solid carbon contained in the solid content is removed by the classification step S40. Therefore, during the firing step S50, the reaction between the solid carbon and the charge carriers in the coarse particle fraction can be suppressed.

[0046] When the total mass of the coarse particle fraction subjected to the firing step S50 is 100 mass%, the C content in the coarse particle fraction is preferably 3 mass% or less (more preferably 2 mass% or less, still more preferably 1 mass% or less, and still more preferably 0.5 mass% or less). It can be said that the lower the C content in the coarse particle fraction, the more preferably the solid carbon is removed from the solid matter. In other words, the lower the C content in the coarse particle fraction, the more the reaction between the charge carriers and the solid carbon in the coarse particle fraction during firing is suppressed, and the desorption of the charge carriers in the positive electrode active material contained in the coarse particle fraction can be reduced. Therefore, a positive electrode active material with suppressed deterioration of the initial capacity and output characteristics can be obtained. The "C content (mass%)" in this specification can be determined by a carbon sulfur analyzer.

[0047] When the total mass of the coarse particle fraction subjected to the firing step S50 is 100 mass%, the Na content in the coarse particle fraction is preferably 0.1 mass% or less (more preferably 0.07 mass% or less, still more preferably 0.04 mass% or less). Na is difficult to remove in the firing step S50 and may be mixed as an impurity into the positive electrode active material after production. This may reduce the performance of the power storage device. Therefore, from the viewpoint of suppressing the reduction in the performance of the power storage device, the lower the Na content in the coarse particle fraction, the more preferable. The "Na content (mass%)" in this specification can be determined by ICP (Inductively Coupled Plasma) analysis.

[0048] The firing temperature in the firing step S50 (more specifically, the temperature inside the heating furnace) is preferably, for example, 600°C or higher, more preferably 700°C or higher, and even more preferably 750°C or higher. If the firing temperature is too low (lower than 600°C), the binder component (such as F) in the coarse particle fraction may remain, and there is a risk that the output performance of the positive electrode active material after production will decrease. On the other hand, if the firing temperature is too high (higher than 1000°C), the crystal growth of the positive electrode active material in the coarse particle fraction may proceed too much, and there is a risk that the output performance of the positive electrode active material will decrease. Therefore, the firing temperature in the firing step S50 is preferably, for example, 1000°C or lower, more preferably 900°C or lower, and even more preferably 850°C or lower. Thus, in some preferred embodiments, it is preferable to perform the firing step S50 in a temperature range of 600°C to 1000°C, and more preferably in a temperature range of 700°C to 900°C. Thereby, while optimizing the crystal growth of the positive electrode active material in the coarse particle fraction during firing of the coarse particle fraction, the binder component (such as F) in the coarse particle fraction can be preferably removed.

[0049] The firing step S50 can be carried out in a conventionally known heating furnace. Also, the firing atmosphere in the firing step S50 is preferably an oxygen-containing atmosphere, for example, an oxygen atmosphere or an air atmosphere. The oxygen concentration in the oxygen-containing atmosphere is preferably 10 vol% or higher, and more preferably 18 - 100 vol%.

[0050] The firing time in the firing step S50 is not particularly limited because it varies depending on the amount to be recovered and the like. The firing time in the firing step S50 is preferably, for example, 1 hour to 12 hours, and more preferably 2 hours to 8 hours.

[0051] The manufacturing method of the positive electrode active material according to the present embodiment has been described above. As described above, it includes a preparation step S10, an alkali solution immersion step S20, a solid-liquid separation step S30, a classification step S40, and a firing step S50. In the manufacturing method according to the present embodiment, particle growth of the positive electrode active material particles is performed in the firing step S50. Therefore, the obtained fired body can be used as the positive electrode active material as it is. The positive electrode active material obtained by the manufacturing method disclosed herein can be handled in the same manner as the conventional positive electrode active material. Further, the obtained positive electrode active material and a new positive electrode active material may be mixed and used.

[0052] 3. Other Embodiments Further, the technology disclosed herein is not limited to the above-described embodiments, and includes other embodiments in which various configurations are changed. Hereinafter, other embodiments of the technology disclosed herein will be described. FIG. 3 is a flowchart for explaining a manufacturing method according to a modification.

[0053] (1-1) Regarding other steps, As shown in FIG. 3, here, in addition to the above-described embodiment, an alkali water washing step S35 and a pulverization step S60 are further included. That is, in the manufacturing method disclosed herein, any step can be added, deleted, or changed as necessary. However, in the technology disclosed herein, it is preferable not to perform pulverization on the solid matter and the coarse particle fraction. By performing pulverization on the solid matter and the coarse particle fraction, the crystal structure of the positive electrode active material may be damaged. In the present specification, "pulverization" refers to an operation of further reducing the particle size of the particles by applying mechanical energy to the particles. Further, "further reducing the particle size of the particles" means, for example, that the D50 particle size of the particles after pulverization is -20% or less with respect to the D50 particle size of the primary particles of the positive electrode active material contained in the positive electrode plate prepared in the preparation step S10.

[0054] (1-2) Alkali water washing step S35 In some preferred embodiments, when an aqueous sodium hydroxide solution is used as the alkaline solution in the alkaline liquid immersion step S20, it is preferably further included an alkaline water washing step S35 of alkaline water washing the solid obtained in the solid-liquid separation step S30. Thereby, the Na content attached to the solid can be preferably removed.

[0055] The alkaline solution used in the alkaline water washing step S35 is not particularly limited, and an aqueous sodium hydroxide solution may be used, or other alkaline solutions may be used. Examples of other alkaline solutions include lithium hydroxide and the like. When an aqueous sodium hydroxide solution is adopted as the alkaline solution used in the alkaline water washing step S35, from the viewpoint of removing the Na content attached to the solid, compared with the aqueous sodium hydroxide solution used in the alkaline liquid immersion step S20, it is preferably diluted by 10 times or more, and more preferably diluted by 100 times or more. On the other hand, if it is diluted more than 1000 times, the pH drops too much, resulting in the desorption of the charge carriers of the positive electrode active material, and thereby there is a risk of deterioration of the performance of the power storage device. From such a viewpoint, compared with the aqueous sodium hydroxide solution used in the alkaline liquid immersion step S20, it is preferably diluted 1000 times or less, more preferably diluted 500 times or less, and particularly preferably diluted 200 times or less.

[0056] The pH of the alkaline solution used in the alkaline water washing step S35 is preferably pH 11 or more (more preferably pH 12 or more). When the pH of the alkaline solution is too low, desorption of the charge carriers of the positive electrode active material may occur, and thereby there is a risk of deterioration of the performance of the power storage device. On the other hand, when the pH of the alkaline solution is too high, the amount of the alkali metal element in the alkaline solution also increases, so that the Na content attached to the solid cannot be sufficiently removed. Therefore, the pH of the alkaline solution used in the alkaline water washing step S35 is preferably pH 14 or less (more preferably pH 13.5 or less, even more preferably pH 13 or less). The pH of the alkaline solution used in the alkaline water washing step S35 is preferably smaller than the pH of the alkaline solution used in the alkaline liquid immersion step S20.

[0057] The number of washing times in the alkali water washing step S35 may be once or multiple times (two or more times), and it is not particularly limited because it can be adjusted according to the Na content or the like adhering to the solid content. Also, the temperature of the alkali solution used in the alkali water washing step S35 is not particularly limited, and can be, for example, 20°C or higher and 80°C or lower.

[0058] However, the above-described alkali water washing step S35 is not essential. For example, when a lithium hydroxide or potassium hydroxide aqueous solution other than a sodium hydroxide aqueous solution is used as the alkali solution in the alkali liquid immersion step S20, the alkali water washing step S35 may be omitted.

[0059] (1-3) Crushing step S60 In some preferred embodiments, a crushing step S60 for crushing the fired body obtained in the firing step S50 can be performed. The fired body obtained in the firing step S50 can be in the form of a particle aggregate (lump) in which a plurality of secondary particles of the positive electrode active material are further aggregated. Here, by performing the crushing step S60, it becomes easier to handle as the positive electrode active material. In this specification, "crushing" refers to an operation of releasing and loosening the connection between the aggregated particles by applying mechanical energy to the particle aggregate. Therefore, it is a different operation from "grinding" in which the particle size is further reduced by applying mechanical energy.

[0060] As the means for the crushing step S60, a conventionally known method can be adopted. For example, a method using a rotary dry sieve, a ball mill, a rotary ball mill, a vibration ball mill, a planetary ball mill, a rotary cutter mill, a sand mill, or the like can be adopted.

[0061] (2) Regarding the object to be recovered For example, in the above-described embodiment, a positive electrode plate was prepared. However, the present invention is not limited thereto, and a positive electrode plate that is an off-spec product of the positive electrode plate may be prepared. Further, at the manufacturing site of the power storage device, after assembling the power storage device assembly and before performing charge and discharge, some defect may occur and the product may become unusable. The positive electrode plate prepared by the manufacturing method disclosed herein may be a positive electrode plate taken out from such a power storage device assembly. That is, the electrode plate prepared by the manufacturing method disclosed herein is not particularly limited to a specific mode. Note that, regarding the configuration of the power storage device assembly other than the positive electrode plate described above, since it does not characterize the technology disclosed herein, the description thereof is omitted.

[0062] Note that the positive electrode plate prepared in the preparation step S10 may be in a state after the electrolyte has adhered (for example, a state taken out from the power storage device). When preparing a positive electrode plate after the electrolyte has adhered, it may be in a state where the electrolyte remains adhered, or the electrolyte adhered to the positive electrode plate may be washed away. From the viewpoint of work efficiency, it is preferable that the positive electrode plate prepared in the preparation step is in a state before the electrolyte adheres.

[0063] [Test Example] Hereinafter, test examples relating to the technology disclosed herein will be described. Note that the content of the test examples described below is not intended to limit the technology disclosed herein.

[0064] <Manufacture of Positive Electrode Active Material> (Example 1) In this test, a new positive electrode plate (that is, a positive electrode plate from which charge carriers have never been extracted) was prepared as a process end material, and the following steps were performed on the positive electrode plate. Specifically, as the positive electrode plate, a positive electrode current collector (Al foil) having a thickness of 15 μm with a positive electrode active material layer disposed on the surface thereof was prepared. Note that the positive electrode active material layer of the positive electrode plate used in this test was LiNi as the positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3As the positive electrode active material, a material containing O2 (lithium nickel cobalt manganese composite oxide), polyvinylidene fluoride (PVDF) as a binder, and acetylene black (AB) as a conductive material in a mass ratio of AB:PVDF = 85:10:5 was used. Also, a material with a D50 of 5 μm and a D10 of 1 μm for the positive electrode active material contained in the positive electrode active material layer was used. Further, a material with a D50 of 100 nm for the conductive material contained in the positive electrode active material layer was used. During the preparation of the above positive electrode plate, the carbon (C) content of the positive electrode plate was measured by a combustion method, and the fluorine (F) content of the positive electrode plate was measured by ion chromatography. Then, by correlating the obtained carbon content and fluorine content with the mass ratios of the positive electrode active material, AB, and PVDF in the positive electrode active material layer described above, the amount of the positive electrode active material in the positive electrode plate was calculated and defined as the "amount of the positive electrode active material contained in the positive electrode plate at the time of preparation".

[0065] (Alkali liquid immersion process) Next, the prepared positive electrode plate was immersed in an aqueous sodium hydroxide (NaOH) solution (concentration 30 wt%) as an alkali liquid and left standing at 40 °C for 120 minutes to dissolve the Al foil.

[0066] (Solid-liquid separation process) In the solid-liquid separation process, the alkali liquid and the precipitate in the alkali liquid immersion process were separated by suction filtration, and the solid matter was recovered.

[0067] (Alkali water washing process) In the alkali water washing process, the solid matter recovered in the solid-liquid separation process was further washed with an aqueous sodium hydroxide solution (concentration 0.3 wt%) and suction filtered three times repeatedly.

[0068] (Drying treatment) In this test example, drying (hereinafter referred to as "drying treatment") was carried out on the solid content that had been washed and suction filtered three times using a dryer with a set drying temperature of 120 °C.

[0069] (Classification process) In the classification process, the dried solid was classified using an elbow jet classifier (Nippon Steel Mining Co., Ltd.). Specifically, the classification point was set by adjusting the classification edge of the classifier so that the D50 particle size on the fine particle side was -30% of the D10 particle size of the positive electrode active material. Then, two-point classification was performed on the dried solid, which was classified into fine particles and coarse particles. After classification, the coarse particles were recovered and subjected to the firing process.

[0070] (Measurement of Na and C content rates in coarse particles) In this test example, for the coarse particles before being subjected to the firing process, the content rates (mass%) of Na and C in the coarse particles were measured and calculated respectively. The content rate of Na was measured by ICP analysis, and the content rate of C was measured by a carbon and sulfur analyzer. The results are shown in the column of "Content rate before firing" in Table 2.

[0071] (Firing process) In the firing process, the coarse particles obtained in the above classification process were fired under atmospheric conditions at a firing temperature of 600 °C and a firing time of 3 hours. Thereby, a fired body was obtained.

[0072] (Crushing process) In the crushing process, the fired body obtained in the firing process was subjected to a crushing treatment using a rotary dry sieve (Turbo Screener, manufactured by Freund Turbo Co., Ltd.). Thereby, the positive electrode active material according to Example 1 (hereinafter, also referred to as "recovered positive electrode active material") was obtained. After the crushing process, the obtained positive electrode active material was weighed, and the ratio (%) of the amount of the recovered positive electrode active material to the amount of the positive electrode active material contained in the positive electrode plate at the time of preparation was defined as the "positive electrode active material recovery rate". The results are shown in Table 2.

[0073] (Measurement of F and C content rates in the recovered positive electrode active material) Here, the content rates (mass%) of F and C in the recovered positive electrode active material were measured and calculated respectively. The content rate of F was measured by ion chromatography analysis. Also, the content rate of C was measured by a carbon and sulfur analyzer in the same manner as in the classification process. The results are shown in the column of "Content rate of recovered positive electrode active material" in Table 2.

[0074] (Example 2) In Example 2, instead of the aqueous sodium hydroxide solution, an aqueous lithium hydroxide (LiOH) solution (concentration 10 wt%) was used for alkali immersion. After immersion, the solids in the alkali solution were recovered by suction filtration. The obtained solids were dried under the same conditions as in Example 1 without performing alkali washing. Thereafter, the same operations as in Example 1 were performed.

[0075] (Examples 3 to 6) In Examples 3 to 6, the firing process was performed at the firing temperatures shown in Table 1, respectively. Otherwise, it was the same as in Example 2.

[0076] (Example 7) In Example 7, the classification point was set by adjusting the classification edge of the classifier so that the D50 particle size on the fine particle fraction side was -20% of the D10 particle size of the positive electrode active material, and the classification process was performed. Otherwise, it was the same as in Example 4.

[0077] (Example 8) In Example 8, the classification point was set by adjusting the classification edge of the classifier so that the D50 particle size on the fine particle fraction side was -10% of the D10 particle size of the positive electrode active material, and the classification process was performed. Otherwise, it was the same as in Example 4.

[0078] (Example 9) In Example 9, the classification point was set by adjusting the classification edge of the classifier so that the D50 particle size on the fine particle fraction side was 0% (i.e., the same as the D10 particle size) of the D10 particle size of the positive electrode active material, and the classification process was performed. Otherwise, it was the same as in Example 4.

[0079] (Example 10) In Example 10, the classification point was set by adjusting the classification edge of the classifier so that the D50 particle size on the fine particle fraction side was 10% of the D10 particle size of the positive electrode active material, and the classification process was performed. Otherwise, it was the same as in Example 4.

[0080] (Example 11) In Example 11, instead of the aqueous sodium hydroxide solution (concentration 0.3 wt%), the solids were washed with water. Otherwise, it was the same as in Example 1.

[0081] (Example 12) In Example 12, among the operations performed in Example 1, the order of the classification step and the firing step was reversed. That is, after performing the firing step, the classification step was performed on the fired body under the same conditions as in Example 1, and the obtained coarse particles were subjected to a crushing step. Otherwise, it was the same as in Example 1.

[0082] (Example 13) In Example 13, among the operations performed in Example 12, the crushing step was not carried out. That is, the coarse particles obtained by the classification step were directly used as the positive electrode active material according to Example 12 and were subjected to the measurement of the positive electrode active material recovery rate and subsequent evaluation. Otherwise, it was the same as in Example 12.

[0083] (Example 14) In Example 14, first, a positive electrode plate of the same process end material as in Example 1 was prepared, subjected to a crushing treatment using a shredder, and further subjected to a pulverization treatment using a pin mill pulverizer. Then, using an elbow jet classifier, two-point classification was performed on the pulverized positive electrode plate, and it was classified into fine particles and coarse particles. Specifically, the classification edge of the elbow jet classifier was set so that the D50 particle size on the fine particle side was -90% of the D10 particle size of the positive electrode active material. Then, the coarse particles were recovered, and an alkali liquid immersion step, a solid-liquid separation step, an alkali washing step, and a drying step were performed in this order under the same conditions as in Example 1. And for the solid obtained in the drying step, a firing step and a crushing step were performed under the same conditions as in Example 1.

[0084] (Example 15) In Example 15, among the operations performed in Example 1, the classification step was not carried out. That is, the solid obtained after drying was not classified and was directly subjected to the firing step. Otherwise, it was the same as in Example 1.

[0085] (Example 16) In Example 16, among the operations performed in Example 1, the firing step was not carried out. That is, the coarse particles obtained in the classification step were not fired and were directly subjected to the crushing step. Otherwise, it was the same as in Example 1.

[0086] <Fabrication of Evaluation Storage Device> Using the recovered positive electrode active materials obtained in Examples 1 to 16 above, an evaluation storage device was fabricated by the following procedure.

[0087] (Examples 1 to 16) The recovered positive electrode active materials obtained in Examples 1 to 16, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in N-methylpyrrolidone (NMP) at a mass ratio of recovered positive electrode active material:AB:PVDF = 85:10:5 to prepare a paste for forming a positive electrode active material layer. This paste was applied onto a positive electrode current collector (Al foil) with a thickness of 15 μm and dried to fabricate a positive electrode plate.

[0088] Natural graphite as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed in ion-exchanged water at a mass ratio of natural graphite:SBR:CMC = 98:1:1 to prepare a paste for forming a negative electrode active material layer. This paste was applied onto a Cu foil with a thickness of 10 μm and dried to fabricate a negative electrode plate.

[0089] Also, as a separator sheet, a porous polyolefin sheet with a thickness of 20 μm having a three-layer structure of PP / PE / PP was prepared.

[0090] The above positive electrode plate, negative electrode plate, and separator sheet were stacked, electrode terminals were attached, and they were housed in a laminate case. Subsequently, a non-aqueous electrolyte was injected into the laminate case, and the laminate case was hermetically sealed. Note that as the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3 and dissolved with LiPF6 as a supporting salt at a concentration of 1.0 mol / L was used. In this way, evaluation storage devices according to Examples 1 to 16 were obtained.

[0091] (Reference Example) In addition, an evaluation storage device according to a reference example for comparing the recovered positive electrode active material according to Examples 1 to 16 with a new positive electrode active material was fabricated. Specifically, a positive electrode active material that was the same as in Examples 1 to 16 except that it was new was prepared. An evaluation storage device according to the reference example was fabricated in the same manner as the above-described conditions except for using such a positive electrode active material.

[0092] <Activation and Initial Capacity Measurement> Each of the fabricated evaluation storage devices was placed in an environment at 25°C. The activation (first charge) was performed by a constant current-constant voltage method. Each evaluation storage device was charged at a constant current up to 4.2V with a current value of 1 / 3C, and then charged at a constant voltage until the current value reached 1 / 50C to bring it to a fully charged state. Thereafter, each evaluation storage device was discharged at a constant current with a current value of 1 / 3C down to 3.0V. Then, the discharge capacity at this time was measured to obtain the initial capacity. When the initial capacity of the evaluation storage device of the reference example was set to 1, the ratio of the initial capacities of the evaluation storage devices using the positive electrode active materials obtained in Examples 1 to 16 was determined. The results are shown in the column of "Initial Capacity Ratio" in Table 2.

[0093] <Output Characteristic Evaluation> After performing an activation process on each evaluation storage device, it was adjusted to an SOC of 60% and placed in an environment at -10°C. Each of these evaluation storage devices was discharged at a current value of 15C for 2 seconds. The output (W) was calculated based on the voltage and current value at this time. When the output of the evaluation storage device of the reference example was set to 1, the ratio of the outputs of the evaluation storage devices using the positive electrode active materials obtained in Examples 1 to 16 was determined. The results are shown in the column of "Output Ratio" in Table 2.

[0094]

Table 1

[0095]

Table 2

[0096] From the results in Tables 1 and 2, it was found that when the step end material of the positive electrode plate was subjected to an alkali liquid immersion step, a solid-liquid separation step, a classification step, and a firing step, both the initial capacity ratio and the output ratio increased. In other words, according to the above configuration, the positive electrode active material could be obtained while suppressing the deterioration of the initial capacity performance and the output performance.

[0097] Although the technology disclosed herein has been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples exemplified above. That is, the technology disclosed herein includes the forms described in the following items.

[0098] <Item 1> A preparation step of preparing a step end material of a positive electrode plate, An alkali liquid immersion step of immersing the step end material in an alkali liquid, A solid-liquid separation step of performing solid-liquid separation on the alkali liquid after the alkali liquid immersion step and recovering a solid matter, A classification step of classifying the recovered solid matter into a fine particle fraction and a coarse particle fraction, A firing step of firing the coarse particle fraction, and A method for producing a positive electrode active material.

[0099] <Item 2> The method for producing a positive electrode active material according to Item 1, wherein when the total mass of the coarse particle fraction subjected to the firing step is 100 mass%, the content of C in the coarse particle fraction is 3 mass% or less.

[0100] <Item 3> The method for producing a positive electrode active material according to Item 1 or 2, wherein when the total mass of the coarse particle fraction subjected to the firing step is 100 mass%, the content of Na in the coarse particle fraction is 0.1 mass% or less.

[0101] <Item 4> The production method according to any one of Items 1 to 3, wherein the alkali liquid is an aqueous lithium hydroxide solution.

[0102] <Item 5> The above alkali solution is an aqueous sodium hydroxide solution, The manufacturing method according to any one of Items 1 to 3, further including an alkali water washing step of alkali water washing the solid matter obtained in the above solid-liquid separation step.

[0103] <Item 6> The above positive electrode plate includes a positive electrode active material layer containing a positive electrode active material and a positive electrode current collector, In the volume-based particle size distribution obtained by the laser diffraction scattering method, when the particle size at which the cumulative frequency is 10% is defined as the D10 particle size and the particle size at which the cumulative frequency is 50% is defined as the D50 particle size, The classification step is performed by setting a classification point such that the D50 particle size of the above fine particles is -30% to +10% of the D10 particle size of the positive electrode active material contained in the above positive electrode active material layer. The manufacturing method according to any one of Items 1 to 5.

[0104] <Item 7> The above fine particles contain solid carbon, The D50 particle size of the above positive electrode active material is 0.05 to 25 μm, and The manufacturing method according to any one of Items 1 to 6, wherein the D50 particle size of the above solid carbon is 1 to 200 nm.

[0105] <Item 8> The manufacturing method according to any one of Items 1 to 7, wherein the firing temperature in the above firing step is 600°C or higher and 1000°C or lower.

[0106] <Item 9> The manufacturing method according to any one of Items 1 to 8, further including a crushing step of crushing the fired body after the above firing step.

Explanation of Signs

[0107] 10 Positive electrode plate 12 Positive electrode current collector 12a Non-formation part of positive electrode active material layer 14 Positive electrode active material layer

Claims

1. A preparation step of preparing a process end material for a positive electrode plate, An alkali solution immersion step of immersing the process end material in an alkali solution, A solid-liquid separation step of performing solid-liquid separation on the alkali solution after the alkali solution immersion step and recovering a solid substance, A classification step of classifying the recovered solid substance into a fine particle fraction and a coarse particle fraction, A firing step of firing the coarse particle fraction, and A method for producing a positive electrode active material.

2. The method for producing a positive electrode active material according to claim 1, wherein when the total mass of the coarse particle fraction subjected to the firing step is 100 mass%, the content of C in the coarse particle fraction is 3 mass% or less.

3. The method for producing a positive electrode active material according to claim 2, wherein when the total mass of the coarse particle fraction subjected to the firing step is 100 mass%, the content of Na in the coarse particle fraction is 0.1 mass% or less.

4. The production method according to any one of claims 1 to 3, wherein the alkali solution is an aqueous lithium hydroxide solution.

5. The alkali solution is an aqueous sodium hydroxide solution, and The production method according to any one of claims 1 to 3, further including an alkali water washing step of alkali water washing the solid substance obtained in the solid-liquid separation step.

6. The positive electrode plate includes a positive electrode active material layer containing a positive electrode active material and a positive electrode current collector, and In the volume-based particle size distribution obtained by the laser diffraction scattering method, when the particle size at which the cumulative frequency is 10% is defined as the D10 particle size and the particle size at which the cumulative frequency is 50% is defined as the D50 particle size, The classification step is performed by setting a classification point such that the D50 particle size of the fine particle fraction is -30% to +10% of the D10 particle size of the positive electrode active material contained in the positive electrode active material layer. The production method according to any one of claims 1 to 3.

7. The fine particle fraction contains solid carbon, and The D50 particle size of the positive electrode active material is 0.05 to 25 μm, and The production method according to any one of claims 1 to 3, wherein the D50 particle size of the solid carbon is 1 to 200 nm.

8. The production method according to any one of claims 1 to 3, wherein the firing temperature in the firing step is 600°C or higher and 1000°C or lower.

9. The production method according to any one of claims 1 to 3, further including a crushing step of crushing the fired body after the firing step.

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