Method for manufacturing electrode active material, method for manufacturing secondary battery, and secondary battery

Abstract

The purpose of the present invention is to achieve a method for efficiently producing a reusable electrode active material by regenerating a used active material contained in an electrode of a used secondary battery by a simple process in which the environmental burden is reduced. A method for producing an electrode active material, which is a method for producing a reusable electrode active material by regenerating a used active material contained in an electrode of a used secondary battery, the electrode being provided with a current collector and an electrode mixture containing an active material formed on the current collector, the method is provided with a step (step S1) in which an electrode is immersed in an aqueous alkaline solution and an electrode mixture is peeled off from a current collector, and a step (step S2) in which the peeled-off electrode mixture is neutralized.

Description

Technical Field

[0001] The present invention relates to a method for producing an electrode active material, a method for producing a secondary battery, and a secondary battery. More specifically, it relates to a method for regenerating a used active material contained in an electrode of a used secondary battery to produce a reusable electrode active material, a method for producing a secondary battery using the electrode active material, and a secondary battery having the electrode active material. Background Art

[0002] Used active materials and other battery materials are collected from electrodes of used secondary batteries, and are regenerated and reused.

[0003] Japanese Patent Publication No. 2010-34021 describes a method for recovering battery materials containing oxides from battery waste. The recovery method includes a step of immersing a substrate to which a battery material containing oxides is attached in a solvent that does not substantially dissolve the oxides to peel off the battery material from the substrate and a step of separating the peeled battery material from the substrate. In the publication, N-methyl-2-pyrrolidone, water, dimethyl carbonate, diethyl carbonate, chloroform, etc. are described as solvents. In the publication, it is described that the recovered oxides are calcined at a temperature of 600°C or more and 1100°C or less.

[0004] Japanese Patent Gazette No. 5141970 describes a method for recovering positive electrode active material from the positive electrode of a lithium battery. The lithium battery used as the object of the recovery method has a positive electrode active material layer, which is formed by applying a material including a positive electrode active material dispersed with an aqueous solvent, a conductive material, and a binding material to the surface of a positive electrode collector. The recovery method includes a step of immersing the positive electrode in an alkaline aqueous solution to peel off the positive electrode active material layer from the positive electrode collector, adding an organic solvent to the peeled positive electrode active material layer peeled product to extract the binding material from the peeled product, and a step of separating a supernatant containing a conductive material and a sediment containing a positive electrode active material from the extracted product after the extraction step.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2010-34021

[0008] Patent Document 2: Japanese Patent No. 5141970 Summary of the invention

[0009] Problems to be solved by the invention

[0010] The electrodes of a secondary battery generally include a current collector made of a metal foil or the like and an electrode mixture formed on the current collector. The electrode mixture includes a conductive aid, a binder, and the like in addition to the active material. In the past, the following methods are known as methods for separating the current collector from the electrode mixture: (1) a method of mechanically wiping off the electrode mixture; (2) a method of using a polar solvent to dissolve the binder and peeling the electrode mixture from the current collector; (3) a method of peeling the electrode mixture from the current collector by applying an impact through a pulse wave, and the like.

[0011] However, these methods have the following problems. The method (1) described above may damage the current collector, so that the components of the current collector may be mixed into the electrode mixture. The method (2) described above requires a certain amount of organic polar solvent when using a binder other than a water-soluble resin, which increases the environmental load. The method (3) described above needs to be set as an intermittent method and cannot be used for large-scale treatment.

[0012] An object of the present invention is to provide a method for producing a reusable electrode active material by regenerating a used active material contained in an electrode of a used secondary battery, wherein the electrode active material can be efficiently obtained through a simple process with reduced environmental load.

[0013] Methods for solving problems

[0014] A method for producing an electrode active material according to one embodiment of the present invention is a method for producing a reusable electrode active material by regenerating a used active material contained in an electrode of a used secondary battery, wherein the electrode comprises a current collector and an electrode mixture formed on the current collector and comprising the active material, and the method for producing the electrode active material comprises the steps of immersing the electrode in an alkaline aqueous solution and stripping the electrode mixture from the current collector and the step of neutralizing the stripped electrode mixture.

[0015] A method for producing a secondary battery according to one embodiment of the present invention includes a step of producing an electrode using the electrode active material produced by the above-described method for producing an electrode active material.

[0016] A secondary battery according to one embodiment of the present invention includes an electrode including an electrode active material produced by the above-described method for producing an electrode active material.

[0017] Effects of the Invention

[0018] According to the present invention, a used active material contained in an electrode of a used secondary battery can be regenerated by a simple process with reduced environmental load, thereby efficiently producing a reusable electrode active material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flowchart of a method for producing an electrode active material according to a first embodiment of the present invention.

[0020] Figure 2 This is a flowchart of a method for producing an electrode active material according to a second embodiment of the present invention.

[0021] Figure 3 This is a flowchart of a method for producing an electrode active material according to a third embodiment of the present invention.

[0022] Figure 4 3 is the charge and discharge curve of the electrode sheet prepared in the example during the initial charge and discharge.

[0023] Figure 5 It is the discharge curve measured by changing the discharge rate.

[0024] Figure 6 3 is the charge and discharge curve of the electrode sheet prepared in the example during the initial charge and discharge.

[0025] Figure 7 3 is the charge-discharge curve of the electrode sheet prepared in the example during the second charge-discharge. DETAILED DESCRIPTION

[0026] The present inventors have studied a method for recovering and regenerating a lithium composite oxide as a spent active material from an electrode of a used lithium ion secondary battery.

[0027] In the past, as a method for stripping an electrode mixture from a current collector, a method for dissolving a binder in the electrode mixture was performed. The inventors of the present invention have studied stripping the electrode mixture from the current collector by slightly dissolving the surface of the current collector instead of dissolving the binder. As a result, it was confirmed that the electrode mixture can be efficiently stripped from the current collector by immersing the electrode in an alkaline aqueous solution.

[0028] On the other hand, it is known that if the electrode mixture is immersed in an alkaline aqueous solution, then even after replacing with a neutral dispersion medium, the dissolution rate of the lithium from the active material also becomes larger. If the amount of the lithium in the active material decreases, the crystal structure changes, and even if regeneration is carried out afterwards, it is sometimes impossible to reuse as an electrode active material. For this problem, the inventors etc. have found that by neutralizing after the electrode mixture is immersed in an alkaline aqueous solution, the dissolution rate of lithium from the active material can be reduced.

[0029] The present invention has been accomplished based on the above findings. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0030] [Method for producing electrode active material]

[0031] [First embodiment]

[0032] Figure 1 It is a flowchart of the manufacturing method of the electrode active material of the first embodiment of the embodiment of the present invention. The manufacturing method of the electrode active material of this embodiment comprises a process of immersing the electrode in an alkaline aqueous solution to peel off the electrode mixture from the collector (step S1), a process of neutralizing the peeled electrode mixture (step S2), a process of washing the neutralized electrode mixture (step S3), a process of drying the washed electrode mixture (step S4), a process of mixing the electrode mixture and a metal compound to form a mixture (step S5), a primary firing process of firing the mixture at a temperature of 300 to 700°C (step S6), a crushing process of crushing the mixture after the primary firing process (step S7), a secondary firing process of firing the mixture after the crushing process at a temperature above the melting point of the metal compound and below 1000°C (step S8), and a process of classifying the mixture after the secondary firing process (step S9).

[0033] The manufacturing method of the electrode active material of the present embodiment is a method for regenerating the used active material contained in the electrode of the used secondary battery to manufacture a reusable electrode active material. The so-called "used secondary battery" is, for example, a secondary battery that is recycled because its discharge capacity is reduced due to repeated charging and discharging and is no longer suitable for reuse, but is not limited to this. The secondary battery is, for example, a lithium ion secondary battery, but is not limited to this.

[0034] The electrode of the recycled secondary battery has a sheet-shaped collector and an electrode mixture formed on the collector. The collector generally uses a metal foil such as aluminum foil and copper foil, and aluminum foil is particularly preferred. The electrode mixture is a mixture prepared by adding a predetermined additive to an active material. The electrode of the secondary battery is manufactured, for example, as follows: the electrode mixture is dispersed in a solvent to form a paste and applied to the collector, and the solvent is removed by drying.

[0035] Specific examples of the positive electrode active material and the negative electrode active material that can be used in the present invention are described below.

[0036] Examples of positive electrode active materials include LiCoO2 (LCO), LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622) 、 LiNi 0.8 Co0.1 Mn 0.1 O2(NCM811), LiNi 0.8 Co 0.15 Al 0.05 O2(NCA), LiNi 0.5 Mn 1.5 O4, etc. In order to improve the volume energy density, it is preferred to use a positive electrode active material comprising the following lithium composite oxide, wherein the lithium composite oxide is a lithium composite oxide in which the proportion of Ni in the element M in the composition represented by the general formula LiMO2 is more than 50% by atomic ratio. Specifically, NCM523, NCM811 and NCA, etc. are preferably used. In addition, in order to make fast charging and discharging good, it is preferred to use LiMn2O4 with a spinel structure and LiFePO4 (LFP) with an olivine structure.

[0037] As the negative electrode active material, in addition to graphite materials such as natural graphite and artificial graphite; carbon materials such as hard carbon and soft carbon, preferably used are oxides such as lithium titanate, lithium manganate, SiO, elements such as Si and Sn, and alloys thereof.

[0038] The manufacturing method of the electrode active material of this embodiment can be applied to the manufacturing of either the positive electrode active material or the negative electrode active material. In the case of manufacturing the positive electrode active material, the used positive electrode active material is recovered from the positive electrode of the used secondary battery, and the used positive electrode active material is subjected to a regeneration treatment to prepare a reusable positive electrode active material. In the case of manufacturing the negative electrode active material, the used negative electrode active material is recovered from the negative electrode of the used secondary battery, and the used negative electrode active material is subjected to a regeneration treatment to prepare a reusable negative electrode active material.

[0039] The manufacturing method of the electrode active material of this embodiment is particularly suitable for the case where the recovered active material is a used positive electrode active material. The manufacturing method of the electrode active material of this embodiment is suitable when the recovered active material is a compound containing an alkali metal, especially a lithium composite oxide, wherein the recovered active material is a composite oxide of lithium and a transition metal (Li x MO2, where M represents a transition metal, a part of which may be substituted by a typical element) is more suitable, and it is particularly suitable when the recovered active material is a composite oxide of lithium, nickel, cobalt and manganese.

[0040] In the electrode mixture, in addition to the active material, sometimes also includes a binder and a conductive aid. Binders, for example, use polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polytetrafluoroethylene (PTFE), acrylic resin (acrylic acid-acrylate copolymer, etc.), carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) etc. Conductive aids, for example, use carbon black, graphite powder etc. The manufacturing method of the electrode active material of the present embodiment can be applicable regardless of the type of binder and conductive aid.

[0041] First, an electrode recovered from a used secondary battery is immersed in an alkaline aqueous solution to separate the electrode mixture from the current collector (step S1 ).

[0042] The alkaline aqueous solution is an aqueous solution of an alkaline compound. The alkaline compound is, for example, an alkali metal compound, an alkaline earth metal compound, ammonia and an amine, but is not limited thereto. The alkaline aqueous solution is preferably an aqueous solution of an alkali metal compound and an aqueous solution of an alkaline earth metal compound. In order to make the electrode mixture easier to peel off from the collector, an aqueous solution of sodium hydroxide and an aqueous solution of potassium hydroxide are particularly preferred. In order to reduce the waste amount of rare elements such as lithium, the alkaline aqueous solution can be constructed to not contain lithium compounds such as lithium hydroxide. In addition, an aqueous solution mixed with organic solvents such as alcohols can also be made as required.

[0043] If the pH of the alkaline aqueous solution is too low, the electrode mixture cannot be completely stripped from the collector, and sometimes a stripping residue is produced, so it is preferably more than 12.0, more preferably more than 13.0. On the other hand, for active materials containing Mn, if the pH of the alkaline aqueous solution is too high, the amount of metal dissolved from the active material becomes more, and even if regeneration is carried out thereafter, it is sometimes impossible to reuse as an electrode active material. In addition, the amount of dissolution of the collector is too much, and the collector cannot be recycled as a resource, and the components of the collector are sometimes mixed into the electrode mixture. Therefore, the pH of the alkaline aqueous solution is preferably less than 14.5, more preferably less than 14.0.

[0044] The impregnation time is preferably 1 to 10 minutes. When the impregnation time is too short, it is sometimes impossible to completely strip the electrode mixture from the current collector, resulting in stripping residues. On the other hand, when the impregnation time is too long, the amount of metal dissolved from the active material increases, and even if it is subsequently regenerated, it is sometimes impossible to reuse it as an electrode active material. In addition, the amount of the current collector dissolved is too much, the current collector cannot be recovered as a resource, and the components of the current collector are sometimes mixed into the electrode mixture. The impregnation time is more preferably more than 2 minutes, and more preferably more than 3 minutes. On the other hand, the impregnation time is more preferably less than 8 minutes.

[0045] If the electrode mixture is continuously placed in a liquid, the metal is dissolved from the active material. Therefore, it is preferred that the electrode is immersed in an alkaline aqueous solution for a predetermined time to remove the electrode mixture, and then the alkaline aqueous solution is quickly removed. The removal of the alkaline aqueous solution can be carried out, for example, by decantation or filtration.

[0046] Next, neutralize the electrode mixture stripped (step S2). Specifically, for example, after the electrode mixture is dispersed in a liquid such as water and stirred, it is further stirred while adding acid. The type of acid is not particularly limited, and sulfuric acid, hydrochloric acid, nitric acid and hydrofluoric acid can be used. Alternatively, the electrode mixture can be dispersed in a solution of an acid of a predetermined concentration instead of adding an acid after dispersion. In this process, it is preferred that the pH of the dispersion (a solution in which the electrode mixture is dispersed) is below 7.0. In addition, it is preferred to keep the pH below 7.0 for more than 1 minute. However, in the case where the active material recovered is an oxide, etc., if the pH is too low, concerns about the dissolution of the active material are generated, so the pH of the dispersion is, for example, preferably not below 2.0, more preferably not below 3.0.

[0047] By neutralizing the electrode mixture, the rate of metal dissolution from the recovered active material can be reduced. Nevertheless, the metal will gradually dissolve from the active material in the liquid, so it is preferred to quickly remove the dispersion medium after neutralizing the electrode mixture. The removal of the dispersion medium can be performed, for example, by decantation or filtration.

[0048] Next, the neutralized electrode mixture is cleaned (step S3). Specifically, for example, the electrode mixture is dispersed in water and stirred, and then filtered. Alternatively, ultrasonic treatment may be performed instead of stirring or on the basis of stirring. Alternatively, decantation or centrifugation may be performed instead of filtering. In addition, these operations are preferably repeated multiple times.

[0049] Then, the electrode mixture after cleaning is dried (step S4). The drying conditions (temperature, atmosphere, time, etc.) are not particularly limited, and it is preferably carried out in a manner that the moisture content in the electrode mixture is sufficiently reduced. Generally speaking, the drying temperature is set to a temperature lower than the processing temperature of the temporary calcination process described later, for example, less than 300°C.

[0050] After the electrode mixture is dried, a metal compound is added to the recovered electrode mixture and mixed (step S5). The metal compound added to the electrode mixture is a compound containing the metal element contained in the recovered active material. For example, in the case where the recovered active material is a lithium composite oxide, a lithium compound as a metal compound, more specifically lithium carbonate, lithium hydroxide or its hydrate, etc., is added to the electrode mixture for mixing. Hereinafter, the mixture obtained by mixing the electrode mixture and the metal compound is referred to as a "mixture".

[0051] Part of the metal elements in the active material is irreversibly consumed during the charge and discharge process of the secondary battery. For example, when the positive electrode active material is a lithium composite oxide, part of the lithium is consumed in the SEI coating that forms the negative electrode. Therefore, the used active material contained in the electrode of the used secondary battery becomes a state of insufficient metal elements compared to the initial active material. The metal elements in the used active material are further reduced by dissolving in the process of immersing in the above-mentioned alkaline aqueous solution (step S1) and the cleaning process (step S3).

[0052] In order to restore the composition of the active material to an appropriate state during regeneration, a metal compound containing insufficient metal elements is added. The amount of the added metal compound is preferably determined by measuring the amount of the metal element in the active material of the electrode mixture recovered and supplementing the insufficient part, but a predetermined amount can also be added. The determination of the amount of the metal element in the electrode mixture can be performed using, for example, ICP emission spectrometry. Mixing can be performed, for example, by a ball mill or a jet mill, but is not limited to these.

[0053] After the electrode mixture and the metal compound are fully mixed, the mixture is sintered at a temperature of, for example, 300 to 700°C (primary sintering process (step S6)). Through this primary sintering process, the components (binders, conductive additives) contained in the original electrode mixture other than the active material are removed. If the treatment temperature is too low, the components other than the active material cannot be fully removed. On the other hand, if the treatment temperature is too high, the aggregation of the active material is promoted. The treatment temperature of the primary sintering process is preferably above 450°C, more preferably above 500°C, and further preferably above 550°C. In addition, it is preferably below 650°C.

[0054] The primary firing process is preferably carried out in an oxygen-containing atmosphere. The primary firing process can be carried out, for example, in an atmospheric atmosphere. When the recovered active material contains Ni, it is preferably set to an atmosphere with an oxygen concentration increased compared to the atmospheric atmosphere, or it can be set to an atmosphere with an oxygen concentration of 100%. In order to fully remove the components other than the active material, it is preferably kept at the treatment temperature for more than 1 hour. In order to reduce the residue of adhesives, etc., the holding time at the treatment temperature of the primary firing process is more preferably more than 3 hours, and more preferably more than 5 hours. On the other hand, if the holding time is too long, the efficiency is reduced. The holding time of the primary firing process is preferably less than 12 hours, and more preferably less than 10 hours.

[0055] After the primary firing process is completed, the mixture is crushed (crushing process (step S7)). Since the mixture after the primary firing process is partially agglomerated, it is crushed to increase the surface area. In addition, by crushing in a state where the binder and the like attached to the surface of the recovered active material are removed by the primary firing process, the active material and the metal compound can be mixed more uniformly. Crushing can be performed by, for example, a ball mill or a jet mill, but is not limited to these.

[0056] It should be noted that, as in the second embodiment described later, the processing temperature in the drying step (step S4) for drying the electrode mixture may be increased to the processing temperature in the primary firing step (step S6), and the drying and primary firing steps (step S7) may be performed in one step. Figure 2 In step S10)), the electrode mixture is dried and the binder and the like attached to the surface of the recovered active material are removed.

[0057] Next, the mixture after the crushing process is calcined at a temperature above the melting point of the metal compound and below 1000°C (secondary calcination process (step S8)). Through this secondary calcination process, the metal element of the metal compound is doped into the active material, and the composition of the active material is regenerated to an appropriate state. If the treatment temperature is too low, the metal element will not diffuse sufficiently, and the composition of the active material will not be regenerated to an appropriate state. On the other hand, if the treatment temperature is too high, the agglomeration of the active material will be promoted. The treatment temperature of the secondary calcination process is more preferably above 800°C, further preferably above 850°C, and below 950°C. It should be noted that the treatment temperature of the secondary calcination process can be appropriately adjusted according to the type of metal compound (Li salt, etc.) used. For example, in the case where the metal compound is lithium carbonate (melting point: 723°C), it is preferred to set the treatment temperature to above 800°C, which is higher than its melting point, but in the case of using lithium hydroxide, since the melting point is as low as 445°C, the treatment temperature can be lower than the above temperature.

[0058] In addition, in LiNi 0.8 Co 0.15 Al 0.05 O2、LiNi 0.8 Co 0.1 Mn 0.1 In the case of active materials whose structure may be destroyed during calcination at high temperature, such as O2, it is preferred to use a compound with a low melting point such as lithium hydroxide and perform a secondary calcination process at a lower treatment temperature. As low melting point salts, lithium formate, lithium oxalate, etc. can be exemplified, and they can be used alone or mixed with high melting point salts such as lithium carbonate.

[0059] The secondary calcination process is preferably carried out in an oxygen-containing atmosphere. The secondary calcination process can be carried out, for example, in an atmospheric atmosphere. When the recovered active material contains Ni, it is preferably set to an atmosphere with an oxygen concentration increased compared to the atmospheric atmosphere, or it can be set to an atmosphere with an oxygen concentration of 100%. In order to allow the metal elements to diffuse fully, it is preferably maintained at the treatment temperature for more than 10 hours. The holding time at the treatment temperature of the secondary calcination process is more preferably more than 12 hours, and more preferably more than 15 hours. On the other hand, if the holding time is too long, the efficiency is reduced. The holding time of the secondary calcination process is preferably less than 48 hours, and more preferably less than 24 hours.

[0060] It should be noted that, as in the third embodiment described later, the treatment temperature in the primary calcination step (step S6) of the mixture of the electrode mixture and the metal compound may be increased to the treatment temperature in the secondary calcination step (step S8) (for example, above the melting point of the metal compound and below 1000° C.), and the mixture may be calcined in one step (the combined calcination step ( Figure 3 In step S13)), the binder and the like attached to the surface of the recovered active material are removed and the metal element of the metal compound is doped into the active material.

[0061] Finally, the mixture after the secondary calcination step is classified (step S9). For example, coarse particles are removed by sieving. It should be noted that, as required, a step of crushing the mixture can also be provided before classification.

[0062] Through the above steps, a recyclable electrode active material is manufactured. The manufactured electrode active material can be used as an electrode material for a secondary battery in the same manner as a new electrode active material.

[0063] [Second embodiment]

[0064] Figure 2 1 is a flow chart of a method for producing an electrode active material according to a second embodiment of the present invention. Figure 1 ) is replaced by a drying and primary firing step (step S10), a crushing step (step S11) and a mixing step (step S12).

[0065] In the drying and primary calcining step (step S10), the drying step (step S4 ( Figure 1 )) the treatment temperature is raised to the primary firing step (step S6 ( Figure 1)) is performed at a treatment temperature (e.g., 300 to 700° C.) to dry the electrode mixture and remove the binder and the like attached to the surface of the recovered active material in one step.

[0066] The processing temperature of the drying and primary firing steps can be increased to the processing temperature of the primary firing step (for example, 300-700°C) at one time. In addition, it can also be temporarily maintained at the drying temperature (for example, below 300°C) and then increased to the processing temperature of the primary firing step.

[0067] In this embodiment (second embodiment), the crushing step (step S7 ( Figure 1 )) Similarly, after the electrode mixture processed in the drying and primary calcination steps (step S10) is crushed (step S11), a metal compound is added to the crushed electrode mixture and mixed (step S12). It should be noted that the crushing step (step S11) can also be omitted.

[0068] [Third Embodiment]

[0069] Figure 3 1 is a flow chart of a method for producing an electrode active material according to a third embodiment of the present invention. The method for producing an electrode active material is as follows: Figure 1 ) is obtained by replacing the steps S6 to S8 (primary firing step, crushing step and secondary firing step) with a combined firing step (step S13).

[0070] In the combined firing step (step S13), the primary firing step (step S6 ( Figure 1 )) is increased to the secondary firing process (step S8 ( Figure 1 )) of the treatment temperature (for example, above the melting point of the metal compound and below 1000°C), the binder etc. attached to the surface of the recovered active material and the metal element of the metal compound are removed in one process. In this embodiment (third embodiment), the crushing process (step S7 ( Figure 1 )).

[0071] The processing temperature of the combined firing process can be increased to the processing temperature in the secondary firing process (for example, above the melting point of the metal compound and below 1000°C) at one time. In addition, the processing temperature in the primary firing process (for example, 300-700°C) can be temporarily maintained and then increased to the processing temperature in the secondary firing process.

[0072] [Secondary battery and method for manufacturing secondary battery]

[0073] A secondary battery according to an embodiment of the present invention includes an electrode including an electrode active material produced by the above-described method for producing an electrode active material.

[0074] The electrode active material manufactured by the manufacturing method of the above-mentioned electrode active material can be used as a material of the electrode of the secondary battery in the same manner as the electrode active material of the new product, as described above. Therefore, the electrode of the secondary battery of the present embodiment can be manufactured according to a conventional method. Specifically, for example, a paste of the electrode mixture can be prepared by adding a binder, a conductive auxiliary agent and a solvent to the electrode active material, and the paste is applied to the collector and dried to manufacture the electrode.

[0075] In the above, the method for producing an electrode active material, the method for producing a secondary battery, and the secondary battery according to the embodiments of the present invention have been described.

[0076] In the present embodiment, the electrode is immersed in an alkaline aqueous solution, so that the surface of the collector is slightly dissolved, and the electrode mixture is peeled off from the collector. If the electrode mixture is immersed in an alkaline aqueous solution, even after being replaced with a neutral dispersion medium, the dissolution rate of the metal from the active material will also increase. In the manufacturing method of the electrode active material of the present embodiment, the electrode mixture is neutralized after being immersed in an alkaline aqueous solution, thereby reducing the dissolution rate of the metal from the active material. Therefore, according to the present embodiment, it is possible to prevent the crystal structure of the active material from changing during recovery, and through regeneration treatment, it is possible to obtain an electrode active material with excellent properties that can be reused.

[0077] The manufacturing method of the electrode active material of the present embodiment can be applicable regardless of the type of the adhesive of the electrode mixture. In addition, since it is possible not to use an organic solvent or to reduce the usage, it is possible to reduce the environmental load. And then, the collector after the electrode mixture is separated can also be recycled as a resource.

[0078] In the above, as a method for regenerating the electrode active material, a method (steps S5 to S9) of mixing an electrode mixture and a metal compound to form a mixture and performing a two-stage calcination is described. According to this method, the recovered electrode active material can react efficiently with the metal element. In addition, since it is possible not to use an organic solvent or to reduce the amount used, the environmental load can be reduced. Of course, this regeneration method is an example, and the method including the process of immersing the electrode in an alkaline aqueous solution (step S1) and the process of neutralizing the electrode mixture (step S2) can also be combined with other regeneration methods.

[0079] Example

[0080] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0081] The experiment was conducted to recover and regenerate the used active material from the secondary battery after use. The recovered and regenerated electrode active material was LiNi 0.5 Co 0.2 Mn 0.3 O2. This composition is the initial composition. When the secondary battery is recovered after use, if the composition change caused by the dissolution of transition metal elements is ignored, it becomes Li x Ni 0.5 Co 0.2 Mn 0.3 O2 (x<1, for example x=0.84).

[0082] First, an electrode (positive electrode using polyvinylidene fluoride as a binder) recovered from a used secondary battery is immersed in an alkaline aqueous solution or the like to peel the electrode mixture from the aluminum foil current collector. Table 1 shows the results of the test conducted under alternative immersion conditions.

[0083] [Table 1]

[0084]

[0085] As shown in Table 1, the electrode mixture can be stripped from the current collector by immersing the electrode in a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution with a pH of 13.5 to 13.7 for 5 minutes. In the tests No. 1 and No. 2, no treatment other than the immersion step (such as applying force using a scraper to cut off the electrode mixture) is required, and the electrode mixture is naturally stripped in the stripping solution. Therefore, the electrode mixture and the current collector can be easily separated and can be recovered separately.

[0086] On the other hand, in the test No. 3 using an organic solvent (N-methyl-2-pyrrolidone (NMP)) instead of the alkaline aqueous solution, the electrode mixture was not peeled off even after immersion for 30 minutes.

[0087] In the case of using polyvinylidene fluoride as a binder of an electrode mixture to make an electrode, NMP is usually used as a solvent when the mixture is coated, so it is customary to also use NMP in the solvent when stripping the electrode mixture from the current collector. In fact, the electrode mixture can be easily stripped using NMP in an unused electrode. However, in the case of a used electrode, as shown in the above results, it is very difficult to use NMP to strip the electrode mixture from the current collector without applying force to cut off the electrode mixture. The reason is uncertain, but it is speculated that due to the chemical reaction accompanying the charge and discharge of the battery, the junction between the current collector (aluminum foil) and polyvinylidene fluoride is transformed and becomes a structure that is not dissolved in NMP. In contrast, according to the method of the present invention, it is easy to strip and recycle the electrode mixture from the current collector.

[0088] It should be noted that in the test No. 4 using lithium hydroxide aqueous solution as the alkaline aqueous solution, peeling residues were produced in a part even after immersion for 30 minutes. In the test No. 5 in which the concentration of sodium hydroxide was changed and the pH was set to 10.0, the electrode mixture did not peel off even after immersion for 30 minutes. In the test No. 6 in which the pH was set to 15.0, the aluminum of the collector was completely dissolved by immersion for 5 minutes. In addition, it can be seen from the test No. 7 that even when the pH is 13.5 to 13.7, the aluminum of the collector is completely dissolved if it is immersed for 30 minutes.

[0089] The above results show that it is preferable to use an alkaline aqueous solution as the stripping solution, and it is particularly preferable to use an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide. The pH is preferably about 13.0 to 14.0, and the immersion time is preferably about 1 to 10 minutes.

[0090] After the electrode mixture is stripped from the current collector of the aluminum foil, the alkaline aqueous solution is removed by decantation. While the electrode mixture is dispersed in water and stirred, a 1M sulfuric acid aqueous solution is added until the pH becomes below 7.0. After keeping the pH below 7.0 for 1 minute, the electrode mixture is separated from the dispersion by filtration. Then, the electrode mixture is washed by repeatedly stirring and filtering in water twice. The washed electrode mixture is dried at 60°C for 5 hours.

[0091] The amount of Li in the dried electrode mixture was determined as Li x Ni 0.5 Co 0.2 Mn 0.3 In order to make x in O2 become 1, 6.2 parts by mass of lithium carbonate is added to 100 parts by mass of the electrode mixture. That is, when the total amount is reacted with the active material in the electrode mixture by a subsequent calcination treatment, lithium carbonate is added in an amount that makes the molar ratio x of Li in the active material 1. It is mixed with a ball mill for 0.5 hours. The mixture is calcined at 600°C in an atmospheric atmosphere for 5 hours. The mixture after the primary calcination is crushed with a ball mill for 0.5 hours. The crushed mixture is calcined at 900°C in an atmospheric atmosphere for 15 hours for a secondary calcination. The mixture after the secondary calcination is sieved to remove coarse particles larger than 100μm to manufacture an electrode active material.

[0092] It should be noted that in order to investigate the effect of introduced oxygen in the secondary sintering process, secondary sintering was carried out in a state where the lid of the crucible containing the mixture was closed: (B1) "with crucible lid" and in a state where the lid of the crucible containing the mixture was opened: (B2) "without crucible lid", thereby producing two electrode active materials (B1 and B2) with different sintering atmospheres.

[0093] Electrodes (electrode sheets) are made from the manufactured electrode active material. In addition, as a comparison, the following electrode active materials are manufactured respectively. That is, except that the firing process is set to only perform one firing and the secondary firing process (step S8) is omitted, the same operation as the electrode active material (B2) is performed to manufacture the electrode active material (A). In addition, lithium carbonate is not added to the recovered active material, and the process of step S5 is omitted. Otherwise, the same operation as the electrode active material (B2) is performed to manufacture the electrode active material (hereinafter referred to as the "fired product"). In addition, until alkali impregnation, neutralization, washing, and drying (the process of steps S1 to S4), the addition and firing of lithium carbonate (the process of steps S5 to S8) are omitted. Otherwise, the same operation as the electrode active material (B2) is performed to manufacture the electrode active material (hereinafter referred to as the "neutralized product"). Furthermore, the neutralization process (step S2) is further omitted from the neutralized product to manufacture the electrode active material (hereinafter referred to as the "alkali treated product"). Electrode sheets are made using the respective electrode active materials.

[0094] Two electrode sheets were prepared according to the types of the above-mentioned electrode active materials, and the charge and discharge curves were measured. Figure 4 The following are the charge and discharge curves of the calcined, neutralized, and alkali-treated electrode sheets during the initial charge and discharge (discharge rate is 0.05C). Figure 5 This is the discharge curve when the discharge rate is set to 0.02C. Figure 4 and Figure 5 As shown, it was confirmed that the alkali-treated product and the neutralized product did not work even at an extremely low rate, while the calcined product was active and could be used even though the Li ratio was not adjusted.

[0095] Next, a comparison was made between an electrode active material (A) that had been calcined only once and electrode active materials (B1 and B2) that had been calcined once and twice.

[0096] In this test, two electrode sheets were prepared according to the type of electrode active material, and the charge and discharge curves were measured. Figure 6 It is the charge and discharge curve of each electrode sheet during the initial charge and discharge. Figure 7 Table 2 shows the efficiency of the first charge and discharge (ratio of the first discharge capacity to the first charge capacity), and Table 3 shows the efficiency of the second charge and discharge (ratio of the second discharge capacity to the second charge capacity).

[0097] [Table 2]

[0098]

[0099] [Table 3]

[0100]

[0101] Depend on Figure 6 As can be seen from Table 2, the efficiency of the first firing can be greatly improved by performing a second firing on the basis of the first firing. Figure 6 As can be seen from Table 3, the efficiency of the second time is higher when the crucible without a lid is used than when the crucible with a lid is used. This shows that it is preferable to perform the calcination step in an atmosphere in which oxygen exists.

[0102] Furthermore, for comparison, except omitting the neutralization step (step S2), the electrode active materials (A) and (B2) are operated in the same manner, and the electrode active materials (C) and (D) are respectively manufactured, and each electrode sheet is manufactured in the same manner as above, and the influence of the neutralization treatment on the characteristics of the electrode active material is investigated. The charge and discharge curves of each electrode are measured, and the discharge capacity and efficiency (the ratio of the initial discharge capacity to the initial charge capacity) during the initial charge and discharge are obtained, and the measured values ​​of each electrode are taken as relative values ​​when the values ​​of the electrode active materials (A) and (B2) subjected to the neutralization treatment are set to 100, respectively, and are shown in Table 4.

[0103] [Table 4]

[0104]

[0105] In the electrode active materials (A) and (B2) which were neutralized after the stripping of the electrode mixture, compared with the electrode active materials (C) and (D) which were not neutralized, the coating dispersion and preservation when the paste of the electrode mixture was prepared were excellent, and the preparation of the electrode was easy. In addition, the discharge capacity and the efficiency of charge and discharge were improved, and it had excellent characteristics as a regeneration active material.

[0106] It is considered that the neutralization treatment reduces the amount of Li eluted from the active material, and the surface structure and surface properties of the active material particles are different, resulting in the above-mentioned difference.

[0107] As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, Various changes are possible within the scope of this invention.

Claims

1. A method for producing an electrode active material, which is a method for regenerating a used active material contained in an electrode of a used secondary battery to produce a reusable electrode active material, wherein the electrode comprises a current collector and an electrode mixture containing the active material formed on the current collector, The manufacturing method comprises: The step of immersing the electrode in an alkaline aqueous solution and peeling the electrode mixture from the current collector, and The step of neutralizing the peeled electrode mixture.

2. The method for producing an electrode active material according to claim 1, further comprising: The step of mixing the electrode mixture with a metal compound to form a mixture, The mixed body is fired at a temperature of 300 to 700° C. a crushing step of crushing the mixed body after the primary firing step, and A secondary calcination step of calcining the mixed body after the crushing step at a temperature not less than the melting point of the metal compound and not more than 1000° C.

3. The method for producing an electrode active material according to claim 1, further comprising: The electrode mixture is dried and fired at a temperature of 300 to 700° C. a step of mixing the electrode mixture after the drying and primary firing steps with a metal compound to form a mixture, and A secondary calcination step of calcining the mixture at a temperature not lower than the melting point of the metal compound and not higher than 1000° C.

4. The method for producing an electrode active material according to claim 1, further comprising: The step of mixing the electrode mixture with a metal compound to form a mixture, and A combined calcining step of calcining the mixture at a temperature not less than the melting point of the metal compound and not more than 1000° C.

5. The method for producing an electrode active material according to claim 1, wherein: The pH of the alkaline aqueous solution is 12.0 or higher.

6. The method for producing an electrode active material according to claim 1, wherein: The immersion time in the alkaline aqueous solution is 1 to 10 minutes.

7. The method for producing an electrode active material according to claim 1, wherein: The alkaline aqueous solution is an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide.

8. The method for producing an electrode active material according to claim 1, wherein: The electrode active material is a lithium composite oxide. 9 . A method for producing a secondary battery, comprising the step of producing an electrode using an electrode active material produced by the method for producing an electrode active material according to claim 1 . 10 . A secondary battery comprising an electrode comprising an electrode active material produced by the method for producing an electrode active material according to claim 1 .

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