Method for producing positive electrode active material

Abstract

The purpose of the present disclosure is to provide a method for producing a positive electrode active material in which performance degradation of capacity characteristics and output characteristics is suppressed. A method for producing a positive electrode active material according to the present invention is provided with: a preparation step for preparing a process leftover material for a positive electrode plate; a lye immersion step for immersing the process leftover material in a lye; and a solid-liquid separation step for performing solid-liquid separation on the lye after the lye immersion step and recovering a solid material. A classification step for classifying the recovered solid material into a fine particle component and a coarse particle component; and a calcination step for calcining the coarse particle component. As a result, the reaction between the solid carbon and the charge carrier in the coarse-grained component can be suppressed during the calcination step, and a positive electrode active material in which deterioration in capacity characteristics and output characteristics is suppressed can be obtained.

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, storage devices are suitable for use as portable power sources for personal computers, portable terminals, etc., and vehicle drive power sources for electric vehicles (BEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.

[0003] Generally, a positive electrode active material is used in the positive electrode of a storage device. In recent years, there has been an increasing demand for a recycling technology that recovers metals (such as lithium, nickel, cobalt, etc.) contained in the positive electrode active material from process scraps of the positive electrode plate and recycles them as materials for storage devices. Furthermore, in the research of the above recycling technology, a technology for directly recovering and regenerating the positive electrode active material without restoring it to the metal level from the positive electrode plate is being developed. As an example of this technology, for example, Japanese Patent Publication No. 2023-521497 discloses a method for recovering an electrode active material, which includes: a stage of crushing and pulverizing a waste electrode containing a waste current collector and an electrode active material, a stage of classifying the crushed and pulverized waste electrode and recovering the electrode active material, and a stage of mixing the electrode active material with an alkali solution and selectively removing aluminum impurities in the electrode active material.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Publication No. 2023-521497 Summary of the Invention

[0007] However, in addition to the positive electrode active material, the positive electrode plate sometimes contains solid carbon. In the technology described in Japanese Patent Publication No. 2023-521497, during classification, solid carbon adheres to the crushed positive electrode current collector (aluminum impurity) and remains in the positive electrode active material (electrode active material). In addition, solid carbon does not dissolve in the alkali solution and remains in the positive electrode active material as an impurity. And according to the research of the present inventors, it is known that when the solid carbon and the positive electrode active material are calcined, the solid carbon reacts with the charge carriers contained in the positive electrode active material, and the capacity characteristics and output characteristics of the obtained positive electrode active material are deteriorated compared with those of a new positive electrode active material (at the stage of being contained in the positive electrode plate).

[0008] The present disclosure has been completed in view of the above circumstances, and provides a method for manufacturing a positive electrode active material in which the deterioration of performance in capacity characteristics and output characteristics is suppressed.

[0009] In view of the above problems, a method for manufacturing a positive electrode active material having the following configuration is provided (hereinafter, also simply referred to as "manufacturing method").

[0010] The method for manufacturing a positive electrode active material disclosed herein includes: a preparation step of preparing scraps of a positive electrode plate, an alkali solution impregnation step of impregnating the above-mentioned scraps into an alkali solution, a solid-liquid separation step of performing solid-liquid separation on the above-mentioned alkali solution after the above-mentioned alkali solution impregnation step and recovering a solid substance, a classification step of classifying the above-mentioned recovered solid substance into a fine particle component and a coarse particle component, and a calcination step of calcining the above-mentioned coarse particle component.

[0011] In the manufacturing method having the above configuration, by performing a classification step on the solid substance obtained through the above-mentioned alkali solution impregnation step and the above-mentioned solid-liquid separation step, solid carbon is removed by physical means. Thereby, it is possible to suppress the reaction between the solid carbon and the charge carriers in the coarse particle component during the calcination step and obtain a positive electrode active material in which the deterioration of the capacity characteristics and the output characteristics is suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic cross-sectional view of the positive electrode plate of the present embodiment along the thickness direction and the width direction.

[0013] Figure 2 is a flowchart for explaining the method for manufacturing a positive electrode active material of the present embodiment.

[0014] Figure 3 is a flowchart for explaining the method for manufacturing a positive electrode active material of a modified example. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] Hereinafter, embodiments of the technology disclosed herein will be described with reference to the drawings. It should be noted that matters other than those specifically mentioned in this specification and matters required for the implementation of the technology disclosed herein can be grasped as design matters of those skilled in the art based on the prior art in the field. The technology disclosed herein can be implemented based on the content disclosed in this specification and the common general knowledge in the art. In addition, the expression "A to B" indicating a range in this specification includes the meaning of A or more and B or less and includes the meanings of "preferably greater than A" and "preferably less than B".

[0016] In this specification, the "electric energy storage device" refers to all devices that can be repeatedly charged and discharged by charge carriers moving between a positive electrode and a negative electrode through an electrolyte. The electric energy storage device is a concept including 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.

[0017] 1. Positive Electrode Plate

[0018] The manufacturing method of the positive electrode active material of the present embodiment manufactures the positive electrode active material by recovering the positive electrode active material from the 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 cited. Hereinafter, the positive electrode plate will be described in detail taking 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 the content described in the above embodiment. Figure 1 is a schematic cross-sectional view of the positive electrode plate of the present embodiment along the thickness direction and the width direction.

[0019] As Figure 1 shown, the positive electrode plate 10 includes a positive electrode current collector 12 and a positive electrode active material layer 14 supported on the positive electrode current collector 12. The positive electrode active material layer 14 is provided on both surfaces of the positive electrode current collector 12 in the illustrated example. However, the positive electrode active material layer 14 may also be provided on a single surface of the positive electrode current collector 12.

[0020] As Figure 1 such, a positive electrode active material layer non-forming 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-forming portion 12a is a portion where the positive electrode current collector 12 is exposed and has a function as a current collecting portion.

[0021] As the positive electrode current collector 12, a known positive electrode current collector used in a conventional power storage device can be used. As an example thereof, from the viewpoint of good conductivity, an aluminum sheet or foil can be cited. From the viewpoint of easily dissolving the positive electrode current collector in the alkali solution in the subsequent alkali solution impregnation step, an aluminum foil is preferably used as the positive electrode current collector 12.

[0022] The size of the positive electrode current collector 12 can be appropriately changed according to the capacity and size of the power storage device, and thus is not particularly limited. When an aluminum foil is used as the positive electrode current collector 12, its thickness is not particularly limited and can be, for example, 5 μm to 35 μm.

[0023] 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 (such as lithium, etc.). When lithium ions are used as charge carriers, as an example of the above positive electrode active material, lithium transition metal composite oxides such as 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, and lithium nickel cobalt manganese-based composite oxides can be cited. In addition, 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 cited.

[0024] It should be noted that in this specification, the term "lithium nickel cobalt manganese composite oxide" refers to an oxide that contains one or more additional elements in addition to the oxide composed of Li, Ni, Co, Mn, and O as constituent elements. Examples of the above-mentioned additional elements include transition metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, Sn, etc., and typical metal elements. In addition, the additional element can also be a metalloid element such as B, C, Si, P, etc., or a non-metal element such as S, F, Cl, Br, I, etc. The same applies to the above-mentioned lithium nickel-based composite oxide, lithium cobalt-based composite oxide, lithium manganese-based composite oxide, lithium nickel manganese-based composite oxide, lithium manganese cobalt-based composite oxide, lithium nickel cobalt-based composite oxide, etc.

[0025] The positive electrode active material can be, for example, in the form of primary particles or secondary particles. It should be noted that in this specification, the term "primary particle" refers to the smallest unit of the particles constituting the positive electrode active material. Specifically, it refers to the smallest unit judged based on the geometric shape in appearance. In addition, in this specification, the aggregate of the above-mentioned primary particles is called "secondary particle". The secondary particle can be, for example, a form in which 2 to 100 primary particles are aggregated.

[0026] The D50 particle size (average particle size) of the positive electrode active material is not particularly limited. Typically, in terms of primary particle units, it is 0.05 μm to 25 μm, for example, 1 μm to 20 μm, and preferably 3 μm to 15 μm. It should be noted that in this specification, the "D50 particle size" refers to the particle size corresponding to a cumulative frequency of 50% by volume from the side of fine particles with a small particle size in the volume-based particle size distribution based on the laser diffraction / scattering method. Similarly, the "D10 particle size" in this specification refers to the particle size corresponding to a cumulative frequency of 10% by volume from the side of fine particles with a small particle size in the volume-based particle size distribution based on the laser diffraction / scattering method. Thus, the D50 particle size and D10 particle size can be obtained from a well-known laser diffraction / scattering type particle size distribution.

[0027] The positive electrode active material layer 14 can also contain optional components as needed in addition to the positive electrode active material. Examples of the above-mentioned optional components include a conductive material, a binder, etc.

[0028] 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, from the viewpoint of particularly excellent conductivity, carbon black can be preferably used. Specific examples of the above-mentioned carbon black include acetylene black, furnace black, Ketjen black, thermal cracking carbon black, etc.

[0029] The D50 particle size of the conductive material is typically smaller than that of the positive electrode active material. Without particular limitation, typically, it is 1 to 200 nm, and for example, it can be in the range of 10 to 100 nm.

[0030] As the binder, since a polymer that can be dissolved or dispersed in the solvent used can be used, there is no particular limitation. For example, polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc. can be used.

[0031] Above, as an example of the object to be recycled in the manufacturing method of 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 the method that takes the positive electrode plate 10 used in the lithium ion secondary battery having the above-described configuration as the object to be recycled.

[0032] 2. Manufacturing method of positive electrode active material

[0033] Hereinafter, the manufacturing method of the positive electrode active material of the present embodiment will be described. Figure 2 It is a flowchart for explaining the manufacturing method of the positive electrode active material of the present embodiment.

[0034] As Figure 2 shown, the manufacturing method of the positive electrode active material of the present embodiment includes: a preparation step S10, an alkali solution impregnation step S20, a solid-liquid separation step S30, a classification step S40, and a calcination step S50. In addition, the manufacturing method disclosed herein may further include other steps at any stage, and the manufacturing processes other than this are the same as those in the past. Hereinafter, each step will be described.

[0035] (1) Preparation step S10

[0036] In the preparation step S10, the process scraps of the positive electrode plate are prepared. It should be noted that the "process scraps of the positive electrode plate" in this specification include the positive electrode plate in which charge carriers have never entered or exited in the positive electrode active material. That is, the scraps of the positive electrode plate generated in the manufacture of the power storage device, the positive electrode plate that has become a defective product, the positive electrode plate taken out from the battery assembly that has become a defective product before charge and discharge, etc. are all included in the "process scraps of the positive electrode plate". In the present embodiment, the scraps of the positive electrode plate are prepared. It should be noted that the detailed content of the positive electrode plate has been described, so the repeated description is omitted.

[0037] (2) Alkali solution impregnation step S20

[0038] In the alkali solution impregnation step S20, the positive electrode plate prepared in the preparation step S10 is impregnated in the alkali solution. As a result, the positive current collector (aluminum) in the positive electrode plate dissolves 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 in the form of a solid substance in the alkali solution.

[0039] As a specific example of the alkali solution used in the alkali solution impregnation step S20, an aqueous solution of lithium hydroxide (LiOH), an aqueous solution of sodium hydroxide (NaOH), an aqueous solution of potassium hydroxide (KOH), etc. can be cited. Among them, an aqueous solution of lithium hydroxide or an aqueous solution of sodium hydroxide can be appropriately used as the alkali solution. These aqueous solutions exhibit strong alkalinity. When the above alkali solution is used in the alkali solution impregnation step S20, damage to the positive electrode active material in the positive electrode plate can be inhibited, and the positive current collector can be selectively dissolved.

[0040] The pH of the alkali solution used in the alkali solution impregnation step S20 is preferably pH 12 or higher (more preferably pH 13 or higher). When the pH of the alkali solution is too low, the positive current collector does not dissolve in the alkali solution, and in addition, damage may be caused to the positive electrode active material in the object to be recycled. On the other hand, when the pH of the alkali solution is too high, the dissolution reaction of the positive current collector is significant, and there is a possibility of structural damage to the positive electrode active material. Therefore, the pH of the alkali solution used in the alkali solution impregnation step S20 is preferably pH 14 or lower (more preferably pH 13.5 or lower).

[0041] The temperature of the alkali solution in the alkali solution impregnation step S20 is not particularly limited, and is preferably 20°C or higher (more preferably 30°C or higher, further preferably 40°C or higher). Thereby, the dissolution of the positive current collector in the alkali solution can be promoted, and the time of the alkali solution impregnation step S20 can be shortened. On the other hand, the upper limit value of the temperature of the alkali solution in the alkali solution impregnation step S20 is not particularly limited. For example, it can be 80°C or lower, or 60°C or lower, or 50°C or lower.

[0042] The form of the positive electrode plate during the alkali solution impregnation step S20 is not particularly limited, and it can be directly used in the state at the time of preparation. In addition, it can also be in a state that has been cut according to the scale of the equipment, etc.

[0043] (2) Solid-liquid separation step S30

[0044] In the solid-liquid separation step S30, solid substances are recovered from the alkali solution after the alkali solution impregnation step S20. Thereby, the solid substances containing the positive electrode active material can be separated from the alkali solution in which the positive current collector is dissolved. The method of the solid-liquid separation step S30 can use a conventionally known method. For example, a recovery method based on filtration, centrifugal separation, decantation, etc. can be adopted.

[0045] (3) Classification step S40

[0046] In the classification step S40, the solid material obtained in the solid-liquid separation step S30 is classified into a fine particle component and a coarse particle component. The feature of the technology disclosed herein is the performance of the classification step S40.

[0047] However, in the positive electrode active material layer of the positive electrode plate, in addition to the positive electrode active material, solid carbon is sometimes contained. Typically, solid carbon can be contained as a conductive material. Solid carbon is difficult to be removed in the above-mentioned alkali solution impregnation step S20 and remains in the solid material. In addition, if solid carbon remains in the solid material and undergoes the subsequent calcination step S50, it is possible that solid carbon reacts with the charge carriers in the positive electrode active material, resulting in the detachment of the charge carriers in the positive electrode active material. As a result, the capacity characteristics and output characteristics of the positive electrode active material that may be obtained from the solid material may decrease. Here, the present inventors typically focused on the fact that 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 (fine particle side) with a particle size smaller than that of the positive electrode active material. Moreover, according to the research of the present inventors, it is known that by classifying the solid material before calcination after removing the positive electrode current collector, the solid carbon in the solid component can be classified to the fine particle side and removed by physical means.

[0048] In the classification step S40, conventionally well-known classification methods can be used. For example, a bent tube type air classifier (simultaneous multi-product classifier), a cyclone classifier, etc. can be used. In addition, the classification step S40 can be performed by dry classification or wet classification. As an example of a wet classifier that can be used in the classification step S40, for example, iClassifier (manufactured by SATAKE MultiMix Co., Ltd.) etc. can be cited.

[0049] In the classification step S40, by setting a classification point to adjust the particle sizes of the fine particle component and the coarse particle component, the solid carbon in the solid material can be classified to the fine particle component side. In some preferred embodiments, it is preferred to perform the classification step S40 by setting the classification point such that the D50 particle size of the fine particle component is -30% to +10% of the D10 particle size of the positive electrode active material contained in the positive electrode composite material layer.

[0050] When the classification point is too small, solid carbon in the solid substance cannot be sufficiently removed, and a large amount of solid carbon may remain in the coarse particle component. Therefore, from the viewpoint of appropriately removing solid carbon in the solid substance, the classification point is preferably set such that the D50 particle size of the fine particle component 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 set such that the D50 particle size of the fine particle component is 20% or more of the D10 particle size of the positive electrode active material contained in the positive electrode composite material layer, and further preferably set such that the D50 particle size of the fine particle component is 15% or more of the D10 particle size of the positive electrode active material contained in the positive electrode composite material layer. On the other hand, when the classification point is too large, the proportion of the positive electrode active material in the fine particle component increases, and thus the recovery rate of the positive electrode active material (the weight of the positive electrode active material (calcined body) obtained after the calcination process relative to the weight of the positive electrode active material in the object to be recovered) 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 particle component 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 set such that the D50 particle size of the fine particle component is 0% (i.e., the same as the D10 particle size of the positive electrode active material) or less of the D10 particle size of the positive electrode active material contained in the positive electrode composite material layer, and further preferably set such that the D50 particle size of the fine particle component is 5% or less of the D10 particle size of the positive electrode active material contained in the positive electrode composite material layer.

[0051] The setting method of 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 and the classification edge distance.

[0052] The classification point of the classification step S40 can be classified into 2 points or 3 or more points. In this case, multiple groups can be grouped into a coarse particle component or a fine particle component.

[0053] In some preferred embodiments, it is preferred that 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 to 20 μm), and the D50 particle size of the solid carbon contained in the fine particle component is 1 to 200 nm (more preferably 10 to 100 nm). Thereby, solid carbon in the solid component can be appropriately removed in the classification step S40.

[0054] It is preferred to perform a drying treatment on the solid substance before the classification step S40. By performing the drying treatment to remove the moisture contained in the solid substance, the solid substance can be efficiently classified in the classification step S40. The drying step can be carried out by using a conventionally known method, such as natural drying, heat drying, air drying, vacuum drying, etc. In addition, the drying temperature only needs to be able to remove the moisture contained in the solid substance. Typically, it is generally 100 °C or higher, for example, preferably 110 to 250 °C.

[0055] It should be noted that the classification step S40 is not a step intended to completely remove solid carbon from solid substances. In the classification step S40, it is sufficient to remove 80% or more of the solid carbon contained in the solid substances, 90% or more can be removed, and 95% or more can be removed.

[0056] (4) Calcination step S50

[0057] In the calcination step S50, the coarse-grained component obtained from the classification step S40 is calcined (heated). Thereby, the binder component (for example, fluorine (F), etc.) remaining in the coarse-grained component can be removed, and the crystal growth of the positive electrode active material in the coarse-grained component can be promoted. In addition, sometimes a part of solid carbon remains in the coarse-grained component. This solid carbon can also be removed by the calcination step S50. In addition, in the technology disclosed herein, the solid carbon contained in the solid component is removed by the classification step S40. Therefore, in the calcination step S50, the reaction between the solid carbon and the charge carriers in the coarse-grained component can be suppressed.

[0058] When the total mass of the coarse-grained component supplied to the calcination step S50 is set to 100% by mass, the content rate of C in the coarse-grained component is preferably 3% by mass or less (more preferably 2% by mass or less, further preferably 1% by mass or less, and further preferably 0.5% by mass or less). The lower the content rate of C in the coarse-grained component, the more appropriately it can be said that the solid carbon has been removed from the solid substance. In other words, the lower the content rate of C in the coarse-grained component, the more the reaction between the charge carriers in the coarse-grained component and the solid carbon during calcination can be suppressed, and the detachment of the charge carriers in the positive electrode active material contained in the coarse-grained component can be reduced. Therefore, a positive electrode active material with suppressed deterioration of the initial capacity and output characteristics can be obtained. It should be noted that the "content rate of C (mass%)" in this specification can be obtained by a carbon-sulfur analyzer.

[0059] When the total mass of the coarse-grained component supplied to the calcination step S50 is set to 100% by mass, the content rate of Na in the coarse-grained component is preferably 0.1% by mass or less (more preferably 0.07% by mass or less, and further preferably 0.04% by mass or less). Na is difficult to remove in the calcination step S50 and may be mixed into the manufactured positive electrode active material as an impurity. Thereby, the performance of the power storage device may be reduced. Therefore, it is preferred from the viewpoint that the lower the content rate of Na in the coarse-grained component, the more the performance reduction of the power storage device is suppressed. It should be noted that the "content rate of Na (mass%)" in this specification can be obtained by ICP (Inductively Coupled Plasma) analysis.

[0060] The calcination temperature in the calcination step S50 (more specifically, the temperature inside the heating furnace) is, for example, preferably 600 °C or higher, more preferably 700 °C or higher, and further preferably 750 °C or higher. When the calcination temperature is too low (lower than 600 °C), the binder components (such as F) in the coarse particle component remain, which may cause a decrease in output performance in the manufactured positive electrode active material. On the other hand, when the calcination temperature is too high (higher than 1000 °C), the crystal growth of the positive electrode active material in the coarse particle component proceeds excessively, which may cause a decrease in the output performance of the positive electrode active material. Therefore, the calcination temperature in the calcination step S50 is, for example, preferably 1000 °C or lower, more preferably 900 °C or lower, and further preferably 850 °C or lower. Therefore, in some preferred embodiments, it is preferred to carry out the calcination step S50 in the temperature range of 600 °C to 1000 °C, and more preferably in the temperature range of 700 °C to 900 °C. Thereby, it is possible to optimize the crystal growth of the positive electrode active material in the coarse particle component during the calcination of the coarse particle component, and appropriately remove the binder components (such as F) in the coarse particle component.

[0061] The calcination step S50 can be carried out using a conventionally well-known heating furnace. In addition, the calcination atmosphere in the calcination step S50 is preferably an oxygen-containing atmosphere, such as an oxygen atmosphere or an air atmosphere. The oxygen concentration of the oxygen-containing atmosphere is preferably 10 vol% or higher, and more preferably 18 - 100 vol%.

[0062] The calcination time in the calcination step S50 varies depending on the amount of the object to be recovered, etc., and thus is not particularly limited. The calcination time in the calcination step S50 is, for example, preferably 1 hour to 12 hours, and more preferably 2 hours to 8 hours.

[0063] The method for manufacturing the positive electrode active material of the present embodiment has been described above. As described above, it includes a preparation step S10, an alkali solution impregnation step S20, a solid-liquid separation step S30, a classification step S40, and a calcination step S50. In the manufacturing method of the present embodiment, particle growth of the positive electrode active material particles is carried out in the calcination step S50. Therefore, the obtained calcined body can be directly used as the positive electrode active material. The positive electrode active material obtained by the manufacturing method disclosed herein can be processed in the same manner as the conventional positive electrode active material. In addition, the obtained positive electrode active material can also be mixed with a new positive electrode active material and used.

[0064] 3. Other Embodiments

[0065] In addition, 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. Figure 3 It is a flowchart for explaining the manufacturing method of the modified example.

[0066] (1-1) Other processes

[0067] As Figure 3 shown, here, in addition to the above-described embodiments, it further includes an alkali water washing process S35 and a disintegration process S60. That is, in the manufacturing method disclosed herein, any process can be added, deleted, or changed as needed. However, in the technology disclosed herein, it is preferred not to pulverize the solid substance and the coarse particle component. By pulverizing the solid substance and the coarse particle component, it is possible to damage the crystal structure of the positive electrode active material. It should be noted that "pulverization" in this specification refers to an operation of further reducing the particle size of the particle by applying mechanical energy to the particle. In addition, "making the particle size of the particle smaller" means that, for example, the D50 particle size of the pulverized particle is -20% or less relative to the D50 particle size of the primary particles of the positive electrode active material included in the positive electrode plate prepared in the preparation process S10.

[0068] (1-2) Alkali water washing process S35

[0069] In some preferred embodiments, when using an aqueous sodium hydroxide solution as the alkali solution in the alkali solution impregnation process S20, it is preferably further included an alkali water washing process S35 for alkali water washing the solid substance obtained in the solid-liquid separation process S30. Thereby, it is possible to appropriately remove the Na component attached to the solid substance.

[0070] The alkali solution used in the alkali water washing process S35 is not particularly limited, and it can be carried out in an aqueous sodium hydroxide solution, or other alkali solutions can be used. As other alkali solutions, for example, lithium hydroxide, etc. can be cited. When using an aqueous sodium hydroxide solution as the alkali solution used in the alkali water washing process S35, from the viewpoint of removing the Na component attached to the solid substance, the concentration of the aqueous sodium hydroxide solution is preferably diluted by 10 times or more, preferably diluted by 100 times or more, relative to the aqueous sodium hydroxide solution used in the alkali solution impregnation process S20. On the other hand, if the dilution exceeds 1000 times, the pH drops too much, so that the charge carriers of the positive electrode active material are detached, and thus the performance of the power storage device may deteriorate. From the above viewpoints, relative to the aqueous sodium hydroxide solution used in the alkali solution impregnation process S20, it is preferably diluted to 1000 times or less, more preferably diluted to 500 times or less, and particularly diluted to 200 times or less.

[0071] The pH of the alkaline solution used in the alkaline water washing step S35 is preferably 11 or higher (more preferably 12 or higher). When the pH of the alkaline solution is too low, detachment of the charge carriers of the positive electrode active material occurs, which may lead to 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 alkali metal elements in the alkaline solution also increases, so that the Na component attached to the solid material cannot be sufficiently removed. Therefore, the pH of the alkaline solution used in the alkaline water washing step S35 is preferably 14 or lower (more preferably 13.5 or lower, still more preferably 13 or lower). The pH of the alkaline solution used in the alkaline water washing step S35 is preferably less than the pH of the alkaline solution used in the alkaline solution impregnation step S20.

[0072] The number of washing times in the alkaline water washing step S35 can be 1 time or multiple times (2 times or more), and there is no particular limitation since it can be adjusted according to the Na component etc. attached to the solid component. In addition, the temperature of the alkaline solution used in the alkaline water washing step S35 is not particularly limited, and for example, it can be 20°C or higher and can be 80°C or lower.

[0073] Among them, the above-mentioned alkaline water washing step S35 is not essential. For example, when using an alkaline solution other than an aqueous sodium hydroxide solution (such as lithium hydroxide, potassium hydroxide, etc.) in the alkaline solution impregnation step S20, the alkaline water washing step S35 can be omitted.

[0074] (1 - 3) Disintegration step S60

[0075] In some preferred embodiments, a disintegration step S60 of disintegrating the calcined body obtained in the calcination step S50 can be performed. The calcined body obtained in the calcination step S50 can be in the form of a particle aggregate (block) in which a plurality of secondary particles of the positive electrode active material are further aggregated. Here, by performing the disintegration step S60, the operation of manufacturing the positive electrode active material becomes easier. In this specification, "disintegration" refers to an operation of separating the aggregation of the aggregated particles from each other by applying mechanical energy to the particle aggregate. Therefore, it is a different operation from "grinding" in which the particle size becomes smaller by applying mechanical energy.

[0076] The method of the disintegration step S60 can adopt a conventionally known method. For example, a method using a rotary dry sieve, a ball mill, a Ro-Tap type ball mill, a vibration type ball mill, a planetary ball mill, a rotary cutter mill, a sand mill, etc. can be adopted.

[0077] (2) Object to be recovered

[0078] For example, in the above-described embodiment, a positive electrode plate was prepared. However, it is not limited thereto, and a positive electrode plate that is a defective product of the positive electrode plate may also be prepared. In addition, there are cases where a certain defect occurs after assembling the power storage device assembly at the manufacturing site of the power storage device and before charging and discharging, and the product cannot be used. The positive electrode plate prepared by the manufacturing method disclosed herein may also 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 manner. It should be noted that regarding the configuration of the power storage device assembly and the configuration other than the above positive electrode plate, since it is not information characterizing the technology disclosed herein, the description thereof is omitted.

[0079] It should be noted that the positive electrode plate prepared in the preparation step S10 may also be in a state after attaching an electrolyte (for example, a state taken out from a power storage device). In the case of preparing a positive electrode plate after attaching an electrolyte, it may be in a state where the electrolyte is attached, or the electrolyte attached to the positive electrode plate may be rinsed. From the viewpoint of operation efficiency, the positive electrode plate prepared in the preparation step is preferably in a state before attaching the electrolyte.

[0080] [Test Example]

[0081] Hereinafter, test examples related to the technology disclosed herein will be described. It should be noted that the content of the test examples described below is not intended to limit the technology disclosed herein.

[0082] <Manufacture of Positive Electrode Active Material>

[0083] (Example 1)

[0084] In this test, a new positive electrode plate (i.e., a positive electrode plate that has never had charge carriers enter or exit) was prepared as process scrap, and the following processes were performed on the above positive electrode plate. Specifically, as the positive electrode plate, a positive electrode plate in which a positive electrode active material layer is disposed on the surface of a positive electrode current collector (Al foil) having a thickness of 15 μm was prepared. It should be noted that the positive electrode active material layer of the positive electrode plate used in this test contains, as a positive electrode active material, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (lithium nickel cobalt manganese composite oxide), polyvinylidene fluoride (PVDF) as a binder, and acetylene black (AB) as a conductive material. In addition, the D50 of the positive electrode active material contained in the positive electrode active material layer is 5 μm, and the D10 is 1 μm. In addition, the D50 of the conductive material contained in the positive electrode active material layer is 100 nm.

[0085] It should be noted that when preparing the above positive electrode plate, the carbon (C) content of the positive electrode plate is measured by the combustion method, and the fluorine (F) content of the positive electrode plate is measured by ion chromatography. Moreover, the mass of the positive electrode active material in the positive electrode plate is calculated by making the obtained carbon content and fluorine content correspond to the mass ratio of the positive electrode active material, AB, and PVDF in the above positive electrode active material layer, and is used as the "mass of the positive electrode active material contained in the positive electrode plate at the time of preparation".

[0086] (Alkali solution impregnation process)

[0087] Next, the prepared positive electrode plate is immersed in an aqueous sodium hydroxide (NaOH) solution (concentration 30 wt%) as an alkali solution, and left standing at 40 °C for 120 minutes to dissolve the Al foil.

[0088] (Solid-liquid separation process)

[0089] In the solid-liquid separation process, the alkali solution and the precipitated solid matter in the alkali solution impregnation process are separated into an alkali solution and solid matter by suction filtration, and the solid matter is recovered.

[0090] (Alkali water washing process)

[0091] In the alkali water washing process, the solid matter recovered in the solid-liquid separation process is further repeatedly washed and suction filtered 3 times with an aqueous sodium hydroxide solution (concentration 0.3 wt%).

[0092] (Drying treatment)

[0093] In this test example, the solid component that has been washed and suction filtered 3 times is dried using a dryer with a drying temperature set at 120 °C (hereinafter referred to as "drying treatment").

[0094] (Classification process)

[0095] In the classification process, the dried solid matter is classified using a bent tube type air classifier (Nippon Steel Mining Co., Ltd.). Specifically, the classification point is set by adjusting the classification edge of the classifier so that the D50 particle size on the fine particle component side is 30% less than the D10 particle size of the positive electrode active material. Then, the dried solid matter is subjected to two-point classification, classified into a fine particle component and a coarse particle component. After classification, the coarse particle component is recovered and supplied to the calcination process.

[0096] (Measurement of Na and C contents in the coarse particle component)

[0097] It should be noted that in this test example, for the coarse particle component before being supplied to the calcination process, the Na and C contents (mass%) in the coarse particle component are measured and calculated respectively. It should be noted that the Na content is measured by ICP analysis, and the C content is measured by a carbon-sulfur analyzer. The results are shown in the "content before calcination" column of Table 2.

[0098] (Calcination process)

[0099] In the calcination process, the coarse particle component obtained in the above classification process is calcined under atmospheric conditions at a calcination temperature of 600 °C and a calcination time of 3 hours. Thus, a calcined body is obtained.

[0100] (Disintegration process)

[0101] In the disintegration process, a rotary dry sieve (TURBO SCREENER, manufactured by FREUND TURBO Co., Ltd.) is used to disintegrate the calcined body obtained in the calcination process. Thus, the positive electrode active material of Example 1 (hereinafter, also referred to as "recovered positive electrode active material") is obtained. After the disintegration process, the obtained positive electrode active material is weighed, and the ratio (%) of the mass of the recovered positive electrode active material to the mass of the positive electrode active material contained in the positive electrode plate at the time of preparation is defined as the "recovery rate of positive electrode active material". The results are shown in Table 2.

[0102] (Determination of the contents of F and C in the recovered positive electrode active material)

[0103] Here, the contents (mass %) of F and C in the recovered positive electrode active material are respectively measured and calculated. It should be noted that the content of F is measured by ion chromatography analysis. In addition, the content of C is measured using a carbon-sulfur analyzer in the same manner as in the classification process. The results are shown in the "content of recovered positive electrode active material" column of Table 2.

[0104] (Example 2)

[0105] In Example 2, an aqueous lithium hydroxide (LiOH) solution (concentration 10 wt%) is used instead of the aqueous sodium hydroxide solution for alkali impregnation. After impregnation, the solid matter in the alkali solution is recovered by suction filtration. The obtained solid matter is not subjected to alkali cleaning and is dried under the same conditions as in Example 1. Except for this, the same operations as in Example 1 are carried out.

[0106] (Examples 3 to 6)

[0107] In Examples 3 to 6, the calcination process is carried out at the calcination temperatures shown in Table 1. Except for this, it is the same as in Example 2.

[0108] (Example 7)

[0109] In Example 7, the classification point is set by adjusting the classification edge of the classifier so that the D50 particle size on the fine particle component side is 20% less than the D10 particle size of the positive electrode active material, and the classification process is carried out. Except for this, it is the same as in Example 4.

[0110] (Example 8)

[0111] In Example 8, the classification point was set by adjusting the classification edge of the classifier in such a way that the D50 particle size on the fine particle component side was 10% less than the D10 particle size of the positive electrode active material, and the classification process was carried out. Otherwise, it was the same as in Example 4.

[0112] (Example 9)

[0113] In Example 9, the classification point was set by adjusting the classification edge of the classifier in such a way that the D50 particle size on the fine particle component side was 0% more than (i.e., the same as) the D10 particle size of the positive electrode active material, and the classification process was carried out. Otherwise, it was the same as in Example 4.

[0114] (Example 10)

[0115] In Example 10, the classification point was set by adjusting the classification edge of the classifier in such a way that the D50 particle size on the fine particle component side was 10% more than the D10 particle size of the positive electrode active material, and the classification process was carried out. Otherwise, it was the same as in Example 4.

[0116] (Example 11)

[0117] In Example 11, the cleaning of the solid material was carried out using water instead of the sodium hydroxide aqueous solution (concentration 0.3 wt%). Otherwise, it was carried out in the same way as in Example 1.

[0118] (Example 12)

[0119] In Example 12, in the operations carried out in Example 1, the order of the classification process and the calcination process was changed. That is, after the calcination process, the calcined body was classified under the same conditions as in Example 1, and the obtained coarse particle component was subjected to a disintegration process. Otherwise, it was carried out in the same way as in Example 1.

[0120] (Example 13)

[0121] In Example 13, in the operations carried out in Example 12, the disintegration process was not carried out. That is, the coarse particle component obtained from the classification process was directly used as the positive electrode active material in Example 12 for the determination of the positive electrode active material recovery rate and subsequent evaluation. Otherwise, it was the same as in Example 12.

[0122] (Example 14)

[0123] In Example 14, first, a positive electrode plate of the same process scraps as in Example 1 was prepared, crushed using a paper shredder, and then pulverized using a needle mill pulverizer. Then, a bent tube type air classifier was used to perform two-point classification on the pulverized positive electrode plate, classifying it into a fine particle component and a coarse particle component. Specifically, the classification edge of the bent tube type air classifier was set such that the D50 particle size on the fine particle component side was 90% less than the D10 particle size of the positive active material. After that, the coarse particle component was recovered, and the alkali solution impregnation process, solid-liquid separation process, alkali cleaning process, and drying process were carried out in the above order under the same conditions as in Example 1. Then, the solid material obtained in the drying process was calcined and disintegrated under the same conditions as in Example 1.

[0124] (Example 15)

[0125] In Example 15, in the operations carried out in Example 1, the classification process was not performed. That is, the solid material obtained after drying was not classified and was directly supplied to the calcination process. Other than that, it was carried out in the same manner as in Example 1.

[0126] (Example 16)

[0127] In Example 16, in the operations carried out in Example 1, the calcination process was not performed. That is, the coarse particle component obtained in the classification process was not calcined and was directly supplied to the disintegration process. Other than that, it was carried out in the same manner as in Example 1.

[0128] <Manufacture of Evaluation Storage Battery Device>

[0129] An evaluation storage battery device was manufactured in the following order using the recovered positive active material obtained in Examples 1 to 16 above.

[0130] (Examples 1 to 16)

[0131] The recovered positive active material obtained in Examples 1 to 16, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in a mass ratio of recovered positive active material:AB:PVDF = 85:10:5 in N-methylpyrrolidone (NMP) to prepare a paste for forming a positive active material layer. This paste was coated on a positive current collector (Al foil) with a thickness of 15 μm and dried to manufacture a positive electrode plate.

[0132] Natural graphite as a negative active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a tackifier were mixed in a mass ratio of natural graphite:SBR:CMC = 98:1:1 in ion-exchanged water to prepare a paste for forming a negative active material layer. This paste was coated on a Cu foil with a thickness of 10 μm and dried to manufacture a negative electrode plate.

[0133] In addition, as the separator, a porous polyolefin sheet having a three-layer structure of PP / PE / PP with a thickness of 20 μm was prepared.

[0134] The above positive electrode plate, negative electrode plate, and separator were overlapped, electrode terminals were installed, and they were housed in a laminated case. Then, a non-aqueous electrolyte was injected into the laminated case, and the laminated case was hermetically sealed. It should be noted that the non-aqueous electrolyte used was a solution obtained by dissolving LiPF6 as a supporting salt at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3. Thus, the power storage devices for evaluation of Examples 1 to 16 were obtained.

[0135] (Reference Example)

[0136] In addition, a power storage device for evaluation of a reference example for comparing the recycled positive electrode active material of Examples 1 to 16 with the new positive electrode active material was produced. Specifically, except that it was new, the positive electrode active material was prepared in the same manner as in Examples 1 to 16. Except for using the above positive electrode active material, a power storage device for evaluation of the reference example was produced under the same conditions as above.

[0137] <Activation and Initial Capacity Measurement>

[0138] Each of the above-produced power storage devices for evaluation was placed in an environment at 25°C. For activation (first charging), in the constant current-constant voltage method, each power storage device for evaluation was charged at a constant current value of 1 / 3C until 4.2V, and then charged at a constant voltage until the current value reached 1 / 50C to reach the full charge state. Then, each power storage device for evaluation was discharged at a constant current value of 1 / 3C until 3.0V. Then, the discharge capacity at this time was measured to obtain the initial capacity. The ratio of the initial capacities of the power storage devices for evaluation obtained by using the positive electrode active materials obtained in Examples 1 to 16 with the initial capacity of the power storage device for evaluation of the reference example set to 1 was obtained. The results are shown in the "Initial Capacity Ratio" column of Table 2.

[0139] <Output Characteristic Evaluation>

[0140] After each power storage device for evaluation was subjected to an activation treatment, it was prepared to have an SOC of 60% and placed in an environment at -10°C. Each of these power storage devices for evaluation was discharged at a current value of 15C for 2 seconds. The output power (W) was calculated based on the voltage and current values at this time. The ratio of the output powers of the power storage devices for evaluation obtained by using the positive electrode active materials obtained in Examples 1 to 16 with the output power of the power storage device for evaluation of the reference example set to 1 was obtained. The results are shown in the "Output Ratio" column of Table 2.

[0141] [Table 1]

[0142]

[0143] [Table 2]

[0144] Table 2

[0145]

[0146] Based on the results in Tables 1 and 2, it can be seen that when the process scraps of the positive electrode plate are subjected to the alkali solution impregnation process, the solid-liquid separation process, the classification process, and the calcination process, both the initial capacity ratio and the output ratio become higher. In other words, according to the above configuration, a positive electrode active material with suppressed deterioration of the initial capacity performance and the output performance can be obtained.

[0147] The above has described the technology disclosed herein in detail, but they are merely examples and do not limit the scope of the patent claims. The technology described in the scope of the patent claims includes technical solutions that are various deformations and changes of the specific examples exemplified above. That is, the technology disclosed herein includes the manners described in the following items.

[0148] <Item 1>

[0149] A method for manufacturing a positive electrode active material, comprising:

[0150] A preparation process for preparing process scraps of a positive electrode plate;

[0151] An alkali solution impregnation process for impregnating the above-mentioned process scraps in an alkali solution;

[0152] A solid-liquid separation process for performing solid-liquid separation on the alkali solution after the above-mentioned alkali solution impregnation process and recovering the solid substance;

[0153] A classification process for classifying the recovered solid substance into a fine particle component and a coarse particle component; and

[0154] A calcination process for calcining the above-mentioned coarse particle component.

[0155] <Item 2>

[0156] The method for manufacturing a positive electrode active material according to Item 1, wherein when the total mass of the above-mentioned coarse particle component supplied to the above-mentioned calcination process is set to 100% by mass, the content rate of C in the above-mentioned coarse particle component is 3% by mass or less.

[0157] <Item 3>

[0158] The method for manufacturing a positive electrode active material according to Item 1 or 2, wherein when the total mass of the above-mentioned coarse particle component supplied to the above-mentioned calcination process is set to 100% by mass, the content rate of Na in the above-mentioned coarse particle component is 0.1% by mass or less.

[0159] <Item 4>

[0160] The manufacturing method according to any one of Items 1 to 3, wherein the alkaline solution is an aqueous lithium hydroxide solution.

[0161] <Item 5>

[0162] The manufacturing method according to any one of Items 1 to 3, wherein the alkaline solution is an aqueous sodium hydroxide solution.

[0163] It further includes an alkaline water washing step: performing alkaline water washing on the solid substance obtained in the solid-liquid separation step.

[0164] <Item 6>

[0165] The manufacturing method according to any one of Items 1 to 5, wherein the positive electrode plate includes a positive electrode active material layer containing a positive electrode active material and a positive electrode current collector.

[0166] In the particle size distribution based on volume obtained by the laser diffraction scattering method, when the particle size with a cumulative frequency of 10% is defined as the D10 particle size and the particle size with a cumulative frequency of 50% is defined as the D50 particle size,

[0167] The classification step is performed by setting a classification point such that the D50 particle size of the above-mentioned particulate component is -30% to +10% of the D10 particle size of the positive electrode active material contained in the positive electrode active material layer.

[0168] <Item 7>

[0169] The manufacturing method according to any one of Items 1 to 6, wherein the particulate component contains solid carbon.

[0170] The D50 particle size of the positive electrode active material is 0.05 to 25 μm, and

[0171] The D50 particle size of the solid carbon is 1 to 200 nm.

[0172] <Item 8>

[0173] The manufacturing method according to any one of Items 1 to 7, wherein the calcination temperature in the calcination step is 600°C to 1000°C.

[0174] <Item 9>

[0175] The manufacturing method according to any one of Items 1 to 8, wherein it further includes a disintegration step: disintegrating the calcined body after the calcination step.

Claims

1. A method for producing a positive electrode active material, comprising: Preparation process, preparing the process scraps of positive plates; an alkali solution impregnation process, wherein the scraps from the process are impregnated in an alkali solution; a solid-liquid separation step, performing solid-liquid separation on the alkali solution after the alkali solution immersion step and recovering solid matter; A classification step for classifying the recovered solid matter into a fine particle component and a coarse particle component; as well as The calcination step is to calcine the coarse particle component.

2. The method for producing a positive electrode active material according to claim 1, wherein: When the total mass of the coarse particle component subjected to the calcining step is 100 mass %, the content of C in the coarse particle component 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 component subjected to the calcining step is 100 mass %, the content of Na in the coarse particle component is 0.1 mass % or less.

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

5. The production method according to any one of claims 1 to 3, wherein The alkali solution is a sodium hydroxide aqueous solution, The method further comprises an alkaline water washing step: washing the solid matter obtained in the solid-liquid separation step with alkaline water.

6. The production method according to any one of claims 1 to 3, wherein The positive electrode plate comprises 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 with a cumulative frequency of 10% is taken as the D10 particle size and the particle size with a cumulative frequency of 50% is taken as the D50 particle size, the classification point is set in such a way that the D50 particle size of the particulate component is -30% to +10% of the D10 particle size of the positive electrode active material contained in the positive electrode active material layer, and the classification process is performed.

7. The production method according to any one of claims 1 to 3, wherein The particulate component comprises solid carbon, The D50 particle size of the positive electrode active material is 0.05 to 25 μm, and 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 calcination temperature of the calcination step is 600°C to 1000°C.

9. The production method according to any one of claims 1 to 3, wherein The method further comprises a disintegration step of disintegrating the calcined body after the calcination step.

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