Method for treating positive electrode of non-aqueous electrolyte secondary battery

Abstract

To provide a treatment method of positive electrodes of nonaqueous electrolyte secondary batteries capable of reducing phosphorous (P) in a metal material at low cost, and a recovering method of valuable metals from metal composite oxides capable of recovering valuable metals in which impurities are reduced at a low cost.SOLUTION: A method for treating a positive electrode of a non-aqueous electrolyte secondary battery is a treatment method of a positive electrode of a non-aqueous electrolyte secondary battery comprising a foil containing Al and an active material as a metal composite oxide containing Ni and / or Co, wherein the processing method includes an addition step S11 of adding an oxide containing Ni and / or Co as an oxidizing agent to the positive electrode, and a melting step S12 of melting the positive electrode to which the oxidant is added to oxidize and remove P contained in the positive electrode to obtain a metal material containing Ni and / or Co.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for treating a positive electrode of a non-aqueous electrolyte secondary battery and a method for recovering valuable metals from a metal composite oxide. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, are used as power sources in hybrid and electric vehicles, and demand for them has been rapidly increasing in recent years. As demand for non-aqueous electrolyte secondary batteries increases, the amount of used non-aqueous electrolyte secondary batteries, defective non-aqueous electrolyte secondary batteries, and process waste generated during manufacturing is also on the rise. Valuable materials such as nickel (Ni) and cobalt (Co) are contained in the electrodes of non-aqueous electrolyte secondary batteries, particularly the positive electrodes. To efficiently utilize resources, metallic materials containing valuable materials such as Ni and Co are recovered from non-aqueous electrolyte secondary batteries. The electrolyte used in lithium-ion secondary batteries is typically a mixture of a non-aqueous solvent and lithium hexafluorophosphate (LiPF6). The recovered metallic materials contain phosphorus (P) as an impurity, and methods for reducing the P content in the metallic materials have been proposed.

[0003] For example, Patent Document 1 describes a method for recovering valuable metals from waste lithium-ion batteries, in which waste lithium-ion batteries are melted, slag is separated from the resulting molten material, and a metal material containing valuables is recovered. Thereafter, calcium oxide (CaO) is added to the metal material while oxygen is blown into the metal material, thereby carrying out a dephosphorization step to oxidize and remove P from the metal material.

[0004] Patent Document 2 describes a method for recovering valuable metals from waste lithium-ion batteries, in which CaO is added as a flux to crushed battery material, and the crushed material is melted together with the flux, thereby incorporating P into the flux and separating it as slag, thereby reducing the P content in the metal material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-091826 [Patent Document 2] International Publication No. 2020 / 013294 Summary of the Invention [Problem to be solved by the invention]

[0006] The recovery method described in Patent Document 1 requires a dephosphorization step, which increases the recycling cost. Furthermore, the recovery methods described in Patent Documents 1 and 2 cannot sufficiently reduce the P content in the metal material.

[0007] Therefore, an object of the present invention is to provide a method for treating the positive electrode of a non-aqueous electrolyte secondary battery that can reduce phosphorus (P) in a metal material at low cost, and a method for recovering valuable metals from metal composite oxides that can recover valuable metals with reduced impurities at low cost. [Means for solving the problem]

[0008] The method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to the present invention is a method for treating a positive electrode of a nonaqueous electrolyte secondary battery equipped with a positive electrode having an Al-containing foil and an active material as a metal composite oxide containing Ni and / or Co, and includes the steps of: adding an oxide containing Ni and / or Co as an oxidizing agent to the positive electrode; and melting the positive electrode to which the oxidizing agent has been added to oxidize and remove P contained in the positive electrode, thereby obtaining a metal material containing Ni and / or Co.

[0009] The method for recovering valuable metals from a metal composite oxide according to the present invention is a method for recovering valuable metals from a metal composite oxide containing valuable metals, and includes the following steps: a reducing agent addition step of adding a reducing agent to the metal composite oxide that reduces the valuable metal in the metal composite oxide; an oxidizing agent addition step of adding an oxide containing the valuable metal as an oxidizing agent to the metal composite oxide to which the reducing agent has been added; a melting step of melting the metal composite oxide to which the reducing agent and the oxidizing agent have been added, thereby reducing the valuable metal in the metal composite oxide and oxidizing impurities contained in the metal composite oxide to obtain a molten material containing the valuable metal and the oxide; and a separation step of separating the oxide from the molten material to obtain the valuable metal. [Effects of the Invention]

[0010] According to the present invention, an oxide containing Ni and / or Co is added as an oxidizing agent to a positive electrode, and the positive electrode to which the oxidizing agent has been added is melted, thereby making it possible to reduce phosphorus (P) in a metal material at low cost.

[0011] According to the present invention, by adding a reducing agent and an oxidizing agent to a metal composite oxide containing a valuable metal, and melting the metal composite oxide to which the reducing agent and the oxidizing agent have been added, valuable metals with reduced impurities can be recovered at low cost. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view of a nonaqueous electrolyte secondary battery used in a method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. [Figure 2] 3 is a flowchart illustrating a method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to the present embodiment. [Figure 3] 1 is a graph showing the recovery rates of Ni, Co, Mn, and Al and the amount of P in the metal material relative to the amount of NiO powder added. DETAILED DESCRIPTION OF THE INVENTION

[0013] 1. Embodiment Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0014] FIG. 1 is a perspective view of a nonaqueous electrolyte secondary battery 10 used in the method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to this embodiment. The nonaqueous electrolyte secondary battery 10 is a used lithium-ion secondary battery used as a power source for automobiles such as electric vehicles and hybrid vehicles. In the following description, the nonaqueous electrolyte secondary battery 10 is a lithium-ion secondary battery. However, the nonaqueous electrolyte secondary battery 10 is not limited to a lithium-ion secondary battery and may be a magnesium-ion secondary battery, a sodium-ion secondary battery, a potassium-ion secondary battery, a calcium-ion secondary battery, or the like. The nonaqueous electrolyte secondary battery 10 is not limited to a used battery and may be an unused nonaqueous electrolyte secondary battery that has been found to be defective after manufacture. Furthermore, the positive electrode to be treated in the method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to this embodiment may be a positive electrode removed from a used nonaqueous electrolyte secondary battery, a positive electrode removed from an unused nonaqueous electrolyte secondary battery, a positive electrode removed from process waste (e.g., defective electrode bodies) in the manufacturing process of a nonaqueous electrolyte secondary battery, or process waste in the manufacturing process of a positive electrode. The positive electrode to be treated contains, for example, phosphorus (P) derived from the electrolyte such as LiPF6 (lithium hexafluorophosphate) described below, and P as an impurity in the positive electrode material.

[0015] The nonaqueous electrolyte secondary battery 10 includes a cell container 12 containing an electrode assembly (not shown) and a nonaqueous electrolyte (not shown). The cell container 12 is made of, for example, an aluminum alloy. The cell container 12 includes a container body 14 and a lid 16. The container body 14 and the lid 16 are laser-welded. The container body 14 is formed in a bottomed rectangular tubular shape and contains the electrode assembly and the nonaqueous electrolyte. The lid 16 is provided at the opening of the container body 14 to seal the container body 14. The lid 16 is provided with a safety valve 18, a positive electrode terminal 20, and a negative electrode terminal 22. The safety valve 18 is used to reduce the pressure inside the nonaqueous electrolyte secondary battery 10. The positive electrode terminal 20 is connected to a positive electrode (described later) via a positive electrode lead (not shown). The negative electrode terminal 22 is connected to a negative electrode (described later) via a negative electrode lead (not shown).

[0016] The electrode assembly includes a positive electrode (not shown) and a negative electrode (not shown) wound with a separator (not shown) interposed therebetween. The electrode assembly is not limited to the wound type as described above, and may be a laminated type in which the positive electrode, negative electrode, and separator are laminated.

[0017] The positive electrode has a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector is a foil containing aluminum (Al) (hereinafter also referred to as Al foil). The mass ratio of the positive electrode current collector in the positive electrode is 5 to 25 mass%. The positive electrode active material layer contains a positive electrode active material, a binder, and a conductive material. The mass ratios of the conductive material and the binder in the positive electrode active material layer are 0 to 30 mass% and 0 to 20 mass%, respectively, of the positive electrode.

[0018] The positive electrode active material can be any metal composite oxide containing nickel (Ni) and / or cobalt (Co). For example, the positive electrode active material can be selected from lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt aluminum composite oxide, lithium nickel cobalt manganese composite oxide, etc. In this embodiment, the positive electrode active material is lithium nickel cobalt manganese composite oxide. Note that, as the positive electrode active material, any magnesium composite oxide can be used in the case of a magnesium ion secondary battery, any sodium composite oxide can be used in the case of a sodium ion secondary battery, any potassium composite oxide can be used in the case of a potassium ion secondary battery, and any calcium composite oxide can be used in the case of a calcium ion secondary battery.

[0019] The binder is a fluorine-based binder containing a fluorine compound such as polyvinylidene fluoride (PVDF), and the conductive material is a carbon material such as graphite or carbon black.

[0020] The negative electrode has a negative electrode current collector and a negative electrode active material layer. For example, the negative electrode current collector is copper (Cu) foil, and the negative electrode active material is graphite. The separator is generally a porous film or nonwoven fabric made of a resin such as polyethylene (PE) or polypropylene (PP).

[0021] The non-aqueous electrolyte solution contains a non-aqueous solvent and a lithium salt (electrolyte) that can be dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include carbonates, such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). These non-aqueous solvents can be used singly or in combination of two or more.

[0022] As the electrolyte, for example, an electrolyte containing phosphorus (P), such as LiPF6 (lithium hexafluorophosphate), is used. As the electrolyte, LiBF4 (lithium tetrafluoroborate), LiTFSA (lithium trifluoromethanesulfonylamide), LiTFSI (lithium bis(trifluoromethane)sulfonimide), etc. may also be used. These electrolytes may be used alone or in combination of two or more. In the following explanation, the case where the electrolyte is LiPF6 will be explained as an example.

[0023] 2, the method for treating the positive electrode of a nonaqueous electrolyte secondary battery 10 includes a positive electrode having an Al-containing foil and an active material as a metal composite oxide containing Ni and / or Co. The method includes a preparation step S10 for preparing the positive electrode, an addition step S11 for adding an oxide containing Ni and / or Co as an oxidizing agent to the positive electrode, a melting step S12 for melting the positive electrode to which the oxidizing agent has been added to oxidize and remove P contained in the positive electrode and obtain a metal material containing Ni and / or Co, and a separation step S13 for separating the molten positive electrode into a metal material containing Ni and / or Co and slag. Each step is described in detail below.

[0024] [Preparation process] In the preparation step S10, the cell container 12 is opened and the removed wound electrode assembly is unwound to prepare a sheet-like positive electrode. The sheet-like positive electrode is then subjected to the next step, the addition step S11. The preparation step S10 may also include a discharging step in which the nonaqueous electrolyte secondary battery 10 is discharged, an internal cell cleaning step in which the inside of the cell container 12 of the discharged nonaqueous electrolyte secondary battery 10 is cleaned with a cleaning solution, and a cutting step in which the sheet-like positive electrode is cut using a shredder or the like. In this embodiment, the positive electrode prepared in the preparation step S10 is a positive electrode removed from a used nonaqueous electrolyte secondary battery 10. However, the present invention is not limited to this, and the positive electrode may be a positive electrode removed from an unused nonaqueous electrolyte secondary battery, a positive electrode removed from process waste in the manufacturing process of a nonaqueous electrolyte secondary battery, or process waste in the manufacturing process of a positive electrode. It is preferable that only a positive electrode is prepared in the preparation step S10. This is because, in the melting step S12 described below, if components other than the positive electrode (cell container 12, separator, negative electrode, etc.) are included, the reduction reaction will be inhibited.

[0025] [Addition process] In the addition step S11, an oxide containing Ni and / or Co is added to the positive electrode as an oxidizing agent. The shape of the oxidizing agent is not particularly limited, and can be appropriately selected from powder, block, sheet, and other shapes. For example, the positive electrode and the oxidizing agent powder can be placed in a bag and shaken to adhere the oxidizing agent powder to the surface of the positive electrode. The positive electrode and the oxidizing agent powder may also be mixed in a mixer such as a blender, Henschel mixer, or Nauta mixer. The positive electrode to which the oxidizing agent has been added is then subjected to the next step, the melting step S12.

[0026] The oxidizing agent must be a substance that oxidizes P but does not easily oxidize the Ni and / or Co to be recovered, and is an oxide containing an element that is more difficult to oxidize than P. "Elements that are more difficult to oxidize than P" are elements that are located above P in the Ellingham diagram, such as Ni and Co. The oxidizing agent must be an oxide containing an element that is more difficult to oxidize than P, but may also contain an element that is more easily oxidized than P. "Elements that are more easily oxidized than P" are elements that are located below P in the Ellingham diagram, such as Li. Even if the oxidizing agent contains an element that is more easily oxidized than P, it will be oxidized and removed together with P in the melting step S12.

[0027] The oxidizing agent includes at least one material selected from the group consisting of a combination of positive electrode active materials, which are NiO, CoO, Co2O3, Co3O4, NiMnCo composite oxide, NiMn composite oxide, MnCo composite oxide, NiCo composite oxide, and composite oxides containing Ni and / or Co. Examples of positive electrode active materials used as the oxidizing agent include LiNi composite oxide, LiCo composite oxide, LiNiCo composite oxide, LiNiMn composite oxide, LiNiCoAl composite oxide, and LiNiCoMn composite oxide. The oxidizing agent is preferably an oxide containing Ni and / or Co, which are the target of recovery. When the recovered metal material is used as a metal material for nickel-metal hydride batteries or a metal material for hydrogen storage, it is preferable that the material does not contain components that could become contaminants for the respective applications. For example, it is preferable that the oxide does not contain metals other than Ni, Co, and Mn. The most preferred oxidizing agent is NiO. Since Ni is the target of recovery, Ni can be recovered by reducing NiO. In this embodiment, NiO is used as the oxidizing agent.

[0028] The amount of oxidizing agent added to the positive electrode is based on the amount that oxidizes all of the excess Al remaining as a reducing agent after the oxidation-reduction reaction between the active material and Al as a reducing agent. By adding an amount of oxidizing agent that oxidizes all of the excess Al as a reducing agent, it is possible to reliably oxidize and remove P.

[0029] The lower limit of the amount of oxidizing agent added to oxidize P does not need to be an amount that oxidizes all of the excess Al. This is because oxidation of P begins partially even when Al remains in the recovered metal. Therefore, the lower limit of the amount of oxidizing agent added to oxidize P is an amount that results in an Al recovery rate of 3.0% or less, more preferably 0.2% or less, and even more preferably 0.01% or less, as shown in the following (Equation 1). Al recovery rate (%) = (mass of metal Al after melting) / (mass of metal Al before melting) ...(Formula 1) Here, metallic Al refers to Al with reducing ability and does not include Al in Al oxide. Unless otherwise specified, metallic Al will be referred to simply as Al in this specification. The Al used for reducing the positive electrode active material may be Al foil in the positive electrode, or may be added separately as needed. The mass of metallic Al can be measured, for example, by ICP (Inductively Coupled Plasma) mass spectrometry.

[0030] Since adding a large amount of oxidizing agent does not affect the P removal effect, there is no particular upper limit to the amount of oxidizing agent added. However, adding too much oxidizing agent may oxidize some Co and / or Ni, and the amount of oxidizing agent that does not contribute to the oxidation reaction increases. Therefore, the upper limit of the amount of oxidizing agent added is the amount at which all of the excess Al remaining as a reducing agent after the oxidation-reduction reaction between the active material and Al as a reducing agent is oxidized, plus 25.0%, more preferably 7.6%, of the amount at which all of the excess Al is oxidized. If the amount of oxidizing agent added is less than this amount, the recovery rates of Ni and Co are high, approximately 80% or more for the former and 90% or more for the latter. Note that the amount at which all of the excess Al is oxidized refers to an amount at which the Al recovery rate (%) is 0.01% or less. The reducing agent is not limited to Al foil, and other reducing agents may be used. Furthermore, the type of reducing agent is not limited to Al, and any reducing agent that can reduce the metal composite oxide containing Ni and / or Co in the active material may be used. The amount of reducing agent added is determined in the same manner as in the case of Al. The reducing agent recovery rate is expressed by the following (Equation 2). Reducing agent recovery rate (%) = (mass of reducing agent after melting) / (mass of reducing agent before melting) ...(Formula 2)

[0031] Furthermore, based on the mass of the positive electrode, the lower limit of the amount of oxidizing agent added to the positive electrode is preferably 50.0 mass%, more preferably 58.3 mass%, and even more preferably 66.7 mass%. If the amount of oxidizing agent added is less than 50.0 mass%, the oxidative removal of P will be insufficient. The greater the amount of oxidizing agent added, the lower the P content (ppm) in the metal material (described below). The P content in the metal material will be 3500 ppm or less when the amount of oxidizing agent added is 50.0 mass% or more, 3000 ppm or less when the amount of oxidizing agent added is 58.3 mass% or more, and 10 ppm or less when the amount of oxidizing agent added is 66.7 mass% or more. Since adding a large amount of oxidizing agent does not affect the P removal effect, the upper limit of the amount of oxidizing agent added is not particularly limited. However, if the amount of oxidizing agent added is too large, some Co and / or Ni may be oxidized. Therefore, the upper limit of the amount of oxidizing agent added to the positive electrode is preferably 83.3 mass%, more preferably 71.7 mass%. The recovery rates of Ni and Co were high, exceeding 90%, up to an oxidant addition amount of 71.7% by mass. When the addition amount exceeded 71.7% by mass, the recovery rates tended to decrease, but even at an addition amount of 83.3% by mass, a high value of approximately 80% was maintained.

[0032] [Melting process] In the melting step S12, the positive electrode to which the oxidizing agent has been added is melted to obtain a melt. x Co y Mn z In the melting step S12, the Al foil contained in the positive electrode acts as a reducing agent, and the following reaction occurs: As a result of the reaction, an alloy containing Ni, Co, and Mn (Ni x Co y Mn z ) is obtained. LiNi x Co y Mn z O2+Al → 1 / 2Li2O+Nix Co y Mn z +1 / 2Al2O3 In this embodiment, thermal energy is applied to the positive electrode from an external heating means (for example, a high-frequency induction melting furnace) to melt the positive electrode at, for example, 1500° C. A flux such as CaO may be added to turn alumina (AlO) into a molten slag state.

[0033] The lithium-nickel-cobalt-manganese composite oxide used as the positive electrode active material is reduced by Al foil as a reducing agent. The P contained in the positive electrode is oxidized and removed by NiO as an oxidizing agent. As a result, an alloy containing Ni, Co, and Mn with reduced P content in the metal material can be recovered. Note that Mn is partially oxidized by NiO, resulting in a lower recovery rate than Ni and Co.

[0034] [Separation process] In the separation step S13, the molten metal and molten slag are separated due to the difference in specific gravity and then cooled to separate the slag from the metallic material containing Ni, Co, and Mn. The Ni in the recovered metallic material originates from the lithium-nickel-cobalt-manganese composite oxide used as the positive electrode active material and NiO used as the oxidizer. The Co and Mn in the metallic material originate from the lithium-nickel-cobalt-manganese composite oxide used as the positive electrode active material.

[0035] 2. Action and Effects In the method for treating a nonaqueous electrolyte secondary battery according to this embodiment, an oxide containing Ni and / or Co is added as an oxidizing agent to the positive electrode, and the positive electrode to which the oxidizing agent has been added is melted. Since the P contained in the positive electrode is oxidized and removed by the oxidizing agent, a dephosphorization step is not required, and the P content in the metal material can be reduced at low cost. The Ni and / or Co contained in the oxidizing agent can be recovered as the metal material.

[0036] By adding an oxidizing agent in an amount of 50.0 mass% or more to 83.3 mass% or less to the positive electrode, the P content in the metal material can be more reliably reduced and a decrease in the recovery rate of Ni and / or Co can be suppressed. By adding an oxidizing agent in an amount of 66.7 mass% or more, the P content in the metal material can be reduced to 10 ppm or less, and the recovered metal material can be used directly as a metal material for nickel metal hydride batteries or a metal material for hydrogen storage. If the P content in the recovered metal material is 650 ppm or less, it is believed that the battery characteristics will not be affected even if the recovered metal material is used directly as an electrode material for nickel metal hydride batteries.

[0037] 3. Working Example The following describes experiments conducted to confirm the effects of the present invention.

[0038] A used nonaqueous electrolyte secondary battery was prepared in which a wound electrode body and a nonaqueous electrolyte were housed in a cell container 12. The positive electrode and nonaqueous electrolyte contained in the prepared nonaqueous electrolyte secondary battery had the following configurations.

[0039] <Positive electrode> Al foil, thickness 15 μm, 20 mass% Active material (LiNi 1 / 6 Co 2 / 3 Mn 1 / 6 O2) 72~73% by mass Binder (PVDF) 3-4% by mass Conductive material 4% by mass <Nonaqueous electrolyte> Non-aqueous solvent (DMC:EMC:PC) mass ratio 28:27:28 Electrolyte (LiPF6) 1M

[0040] In the experiment, first, the prepared non-aqueous electrolyte secondary battery was discharged, the inside of the cell container 12 was cleaned, the cell container 12 was opened, and the wound electrode body was taken out, rewound, and cut with a shredder to prepare a positive electrode (preparation step S10).

[0041] 30 g of a positive electrode, a predetermined amount of an oxidant, and 11.1 g of CaO powder were placed in a pre-prepared bag and shaken to add the oxidant and CaO powder to the positive electrode (addition step S11). The positive electrodes to which the oxidant was added were designated Examples 1 to 10. NiO powder was used as the oxidant. The amount of NiO powder added was 10.0 g in Examples 1 and 2, 15.0 g in Examples 3 and 4, 17.5 g in Examples 5 and 6, 20.0 g in Examples 7 and 8, and 25.0 g in Examples 9 and 10. The CaO powder was added to turn the alumina into a molten slag state. Furthermore, 30 g of a positive electrode and 8.0 g of CaO powder were placed in a pre-prepared bag and shaken to add only CaO powder to the positive electrode. These positive electrodes to which no oxidant was added were designated Comparative Examples 1 and 2.

[0042] The positive electrodes of Examples 1 to 10 and the positive electrodes of Comparative Examples 1 and 2 were subjected to the melting step S12 to carry out the experiment.

[0043] The positive electrodes of Examples 1 to 10, to which NiO powder was added as an oxidizer, were placed in a high-frequency induction melting furnace. While nitrogen (N) gas was flowing at a flow rate of 5 L / min, the temperature inside the furnace was increased from room temperature to 1550°C and maintained at this temperature for 20 minutes to melt the positive electrodes of Examples 1 to 10. The high-frequency induction melting furnace was composed of an alumina crucible for filling the positive electrodes of Examples 1 to 10, a carbon crucible for accommodating the alumina crucible, and a high-frequency induction coil attached around the periphery of the carbon crucible. After the temperature inside the furnace was lowered to room temperature, the alumina crucible was disassembled and the metal material was removed.

[0044] The positive electrodes of Comparative Examples 1 and 2, which had no oxidizing agent added, were placed in a high-frequency induction melting furnace, the air inside the furnace was evacuated to create a vacuum, and the temperature was increased from room temperature to 300°C and maintained for 90 minutes. Argon (Ar) gas was then introduced into the furnace to create an Ar gas atmosphere, and the temperature inside the furnace was increased to 1550°C and maintained for 20 minutes to melt the positive electrodes of Comparative Examples 1 and 2. After the temperature inside the furnace was lowered to room temperature, the alumina crucible was disassembled and the metal material was removed.

[0045] FIG. 3 shows the results of component analysis of each metallic material obtained by melting the positive electrodes of Examples 1 to 10 and Comparative Examples 1 and 2. FIG. 3 is a graph showing the recovery rates of Ni, Co, Mn, and Al and the amount of P in the metallic material versus the amount of NiO powder added. FIG. 3 plots the average values ​​of measurements (N=2) for Examples with the same amount of NiO powder added, with the amount of NiO powder added (g) on ​​the horizontal axis, the recovery rates (%) of Ni, Co, Mn, and Al on the vertical axis on the left side of the page, and the amount of P in the metallic material (ppm) on the vertical axis on the right side of the page. Note that the amount of P in the positive electrodes of Examples 1 to 10 before melting was approximately 4500 to 10000 ppm. The recovery rates of Ni, Co, Mn, and Al were calculated by dividing the mass of each metal after melting by the mass of each metal before melting. The Ni recovery rate was calculated by dividing the mass of each metal after melting by the sum of the amount of Ni contained in the positive electrode before melting and the amount of Ni in the NiO powder added as an oxidizer. The mass of each metal before melting was measured using ICP (Inductively Coupled Plasma) mass spectrometry. For some samples, the mass was calculated based on the mass% of the positive electrode active material in the positive electrode before melting and the composition of the positive electrode active material. The mass of each metal after melting and the amount of P in the metal material were also measured using ICP mass spectrometry. Both ICP mass spectrometry analyses were performed using a Hitachi High-Tech Science PS3520UVDDII or SPS3520UVDD.

[0046] Figure 3 confirms that the P content can be reduced with increasing oxidant addition. Up to 10 g of oxidant addition, the Al recovery rate significantly decreased, but the decrease in P content was small. In contrast, when the oxidant addition amount exceeded 10 g, i.e., when the Al recovery rate became less than 8.0%, the decrease in Al recovery rate slowed, while the P content rapidly decreased. It was found to be below 3500 ppm at 15 g or more (Al recovery rate of 1.6% or less), below 3000 ppm at 17.5 g or more (Al recovery rate of 0.2% or less), and below 10 ppm at 20 g or more (Al recovery rate of 0.01% or less). It was confirmed that melting the cathode with oxidant addition enabled the oxidation and removal of P contained in the cathode. The Ni and Co recovery rates remained high, exceeding 90%, up to 20 g of oxidant addition (Al recovery rate of 0.01% or less). The Ni and Co recovery rates tended to decrease when the oxidant addition amount exceeded 20 g. This is thought to be due to the partial oxidation of Ni and Co and the increase in the amount of oxidizing agent (NiO powder) that does not contribute to the oxidation reaction. However, even when the amount of oxidizing agent was 25 g, the recovery rates of Ni and Co remained high at approximately 80%. The recovery rate of Al was below 0.01% when 20 g of oxidizing agent was added, which suggests that all of the excess Al had been oxidized at this point. In other words, the amount of oxidizing agent added of 25 g is the amount required to oxidize all of the excess Al (20 g) plus 5 g (25% of the amount required to oxidize all of the excess Al). Furthermore, the recovery rate of Mn decreased with increasing the amount of oxidizing agent. The recovery rate of Mn exhibited a similar behavior to the decrease in the amount of P, decreasing rapidly when the amount of oxidizing agent exceeded 10 g. The order of ease of oxidation shown in the Ellingham diagram is Al, Mn, P, Co, and Ni. In the melting step S12, oxidation removal of P begins even when unoxidized Al and Mn remain, and it can be seen that the amount of P is also sufficiently reduced after Al and Mn have been sufficiently oxidized and removed.

[0047] When the alumina crucible was disassembled and the metal material was removed, it was confirmed that the more NiO powder was added, the darker the color of the slag surface became. It is thought that as the amount of NiO powder added increased, the precipitation of MnO2 on the slag surface progressed.

[0048] From the above, it was confirmed that by adding an oxidizing agent in an amount of 15 g (50.0 mass%) or more and 25 g (83.3 mass%) or less, the P content in the metal material could be reduced to 3500 to 10 ppm while achieving a Ni and Co recovery rate of 80% or more. By adding an oxidizing agent in an amount of 17.5 g (58.3 mass%) or more and 20 g (66.7 mass%) or less, the P content in the metal material could be further reduced to 3000 to 10 ppm, and the Ni and Co recovery rate could be improved to 95% or more. By adding an oxidizing agent in an amount of 20 g (66.7 mass%) or more and 25 g (83.3 mass%) or less, the P content in the metal material could be reduced to 10 ppm or less without reducing the Ni and Co recovery rate, and sufficient dephosphorization was achieved.

[0049] In the above experiment, a carbon crucible was used, and the positive electrode was melted while flowing N2 gas. However, if a crucible made only of a material that does not easily react with oxygen (such as alumina) is used, the positive electrode may be melted in an air atmosphere.

[0050] 4. Variations The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the invention.

[0051] In the melting step S12, the positive electrode is melted using an external heating means in the above embodiment. However, the positive electrode may be melted by the heat of reaction between the foil and the active material. The "reaction between the foil and the active material" refers to an oxidation-reduction reaction, also known as a thermite reaction, in which a mixture of a positive electrode current collector made of metal Al and a positive electrode active material made of metal oxide is reacted, generating high heat while reducing the metal oxide with the metal Al. The positive electrode generates heat by itself due to the heat of reaction between the foil and the active material. "Self-heating" refers to the rise in the temperature of the positive electrode itself due to the heat of reaction between the foil and the active material, even without the application of thermal energy to the positive electrode from an external heating means (e.g., a high-frequency induction melting furnace).

[0052] The thermite reaction generates a large amount of heat, and once the reaction reaches a sustained temperature, it proceeds due to self-heating (heat of reaction). One method for exciting the thermite reaction is the thermite method, in which a positive electrode is placed in a crucible and ignited. Essentially, the thermite reaction proceeds through this ignition alone, yielding a metallic material containing the metals that make up the metal composite oxide. The thermite method can also use a combustion enhancer, if necessary. Alternatively, there are methods that use devices that apply high-temperature heat externally, such as arc melting or high-frequency induction melting furnaces. In these cases, the positive electrode melts due to self-heating (heat of reaction), and the heat from the arc melting or high-frequency induction melting also melts the positive electrode.

[0053] The method for treating the positive electrode of the nonaqueous electrolyte secondary battery 10 may further include a heating step for performing a heat treatment to heat the positive electrode in addition to the preparation step S10, the addition step S11, the melting step S12, and the separation step S13. The heating step is performed between the preparation step S10 and the addition step S11 or between the addition step S11 and the melting step S12.

[0054] The heating treatment will be described. The heating device used for the heating treatment includes a heating furnace, a heating unit, a thermometer, a gas supply unit, a flow meter, and a control unit. The heating furnace has an internal space for accommodating a positive electrode. The heating unit heats the positive electrode placed in the heating furnace. The thermometer measures the temperature inside the heating furnace. The gas supply unit supplies an oxygen-containing gas (air in this example) into the heating furnace, creating an oxygen-containing atmosphere inside the heating furnace. The flow meter measures the flow rate of air inside the heating furnace. The control unit controls the heating unit based on the measurement result of the thermometer, raising the temperature inside the heating furnace at a predetermined temperature increase rate and controlling it to a preset heating temperature. The control unit controls the gas supply unit based on the measurement result of the flow meter, controlling the flow rate of air supplied into the heating furnace. The control unit controls the heating unit and the gas supply unit so that the heating temperature and flow rate are maintained for a predetermined time. The time during which the heating temperature and flow rate are maintained is referred to as the "maintenance time." Note that the above heating device is an example. Therefore, the configuration of the heating device is not limited to the above configuration and can be designed as appropriate. For example, if a rotary kiln or the like is used, the heat treatment can be carried out continuously.

[0055] The procedure for the heating treatment will be explained. First, a sheet-shaped positive electrode is placed in a heat-resistant container. Next, the heating device is activated to raise the temperature inside the heating furnace to a preset heating temperature. The container with the positive electrode placed in it is placed in the heating furnace, and air is supplied into the heating furnace at a predetermined flow rate. The heating temperature and flow rate are maintained until a preset hold time has elapsed. Note that the container with the positive electrode placed in it may be placed in the heating furnace before the heating device is activated.

[0056] The heat treatment is preferably performed at a temperature at which the foil does not oxidize. If the heating temperature is too high, the Al foil serving as the positive electrode current collector will oxidize. The oxidized Al foil cannot be used as a reducing agent in the melting step S12.

[0057] The heat treatment is preferably performed at a temperature at which the binder is decomposed. If the heating temperature is too low, the binder will not be decomposed sufficiently, and the binder will remain in the positive electrode. If a positive electrode with a remaining binder is subjected to the melting step S12, the thermal decomposition of the binder and subsequent oxidation will generate gases of hydrogen and carbon oxides such as HO, CO, and CO, inhibiting the reduction reaction. Gases that inhibit the reduction reaction are called reaction-inhibiting gases. Furthermore, the generated gases may suddenly expand, damaging the furnace and causing danger. By performing the heat treatment at a temperature at which the binder is decomposed, a positive electrode from which the binder has been removed can be subjected to the melting step S12. Furthermore, the heat treatment is preferably performed at a temperature at which the conductive material is oxidized and removed.

[0058] The heat treatment is preferably carried out at a temperature of 400°C or higher and 650°C or lower. By setting the heating temperature to 400°C or higher and 650°C or lower, the binder is reliably decomposed and oxidation of the Al foil is suppressed. On the other hand, if the heating temperature is too high, the Al of the positive electrode current collector may act as a reducing agent, causing an unintended reduction reaction, which is dangerous. The heat treatment temperature is more preferably 450°C or higher and 600°C or lower, and even more preferably 500°C or higher and lower than 600°C.

[0059] In the heating step, heating is performed at a temperature at which the foil does not oxidize, thereby suppressing the generation of alumina on the surface of the Al foil, and thus promoting the reduction reaction (thermit reaction) in the melting step S12.

[0060] In the heating step, heating is performed at a temperature at which the binder is decomposed, thereby suppressing the generation of reaction-inhibiting gases in the melting step S12 and promoting the reduction reaction (thermit reaction).

[0061] In the heating step, heating is performed at a temperature of 400°C or higher and 650°C or lower, which suppresses the occurrence of the thermite reaction during the heat treatment and improves safety. The heat treatment removes the binder and conductive material, suppressing the generation of reaction-inhibiting gases in the melting step S12. This promotes the reduction reaction (thermit reaction) in the melting step S12.

[0062] In the above embodiment, the positive electrode current collector Al foil is used as the reducing agent, but Al powder, for example, may also be added as the reducing agent.

[0063] The present invention is not limited to a method for treating the positive electrode of a nonaqueous electrolyte secondary battery, but is a technology that can be widely applied to removing impurities that are more easily oxidized than the valuable metal in the metal composite oxide and recovering the valuable metal from the metal composite oxide containing the valuable metal. For example, the present invention may be applied to primary batteries or ores in mineral resources. Furthermore, the impurities are not limited to phosphorus (P), and any impurity that is more easily oxidized than the valuable metal in the metal composite oxide may be used. By using the present invention, it is possible to recover valuable metals from which impurities such as P have been removed. That is, the method for recovering valuable metals from metal composite oxides according to the present invention is a method for recovering valuable metals from metal composite oxides containing valuable metals, and includes a reducing agent addition step of adding a reducing agent to the metal composite oxide that reduces the valuable metal in the metal composite oxide; an oxidizing agent addition step of adding an oxide containing a valuable metal as an oxidizing agent to the metal composite oxide to which the reducing agent has been added; a melting step of melting the metal composite oxide to which the reducing agent and the oxidizing agent have been added, thereby reducing the valuable metal in the metal composite oxide and oxidizing the impurities contained in the metal composite oxide to obtain a molten material containing the valuable metal and the oxide; and a separation step of separating the oxide from the molten material to obtain the valuable metal, thereby making it possible to recover valuable metals with reduced impurities from metal composite oxides at low cost. [Explanation of symbols]

[0064] 10 Nonaqueous electrolyte secondary battery S10 Preparation process S11 Addition process S12 Melting process S13 Separation process

Claims

1. A method for treating a positive electrode of a nonaqueous electrolyte secondary battery having a positive electrode having an Al-containing foil and an active material as a metal composite oxide containing Ni and / or Co, comprising: an addition step of adding an oxide containing Ni and / or Co as an oxidizing agent to the positive electrode; a melting step of melting the positive electrode to which the oxidizing agent has been added to oxidize and remove P contained in the positive electrode, thereby obtaining a metal material containing Ni and / or Co; and The method for treating a positive electrode of a nonaqueous electrolyte secondary battery, wherein the amount of the oxidizing agent added is an amount such that the Al recovery rate, as expressed by the following formula 1, is 3.0% or less. [Formula 1] Al recovery rate (%) = (mass of metal Al after melting) / (mass of metal Al before melting)

2. A method for treating a positive electrode of a non-aqueous electrolyte secondary battery having a positive electrode having a foil containing Al and an active material as a metal composite oxide containing Ni and / or Co, comprising: an addition step of adding an oxide containing Ni and / or Co as an oxidizing agent to the positive electrode; a melting step of melting the positive electrode to which the oxidizing agent has been added to oxidize and remove P contained in the positive electrode, thereby obtaining a metal material containing Ni and / or Co; and The method for treating a positive electrode of a nonaqueous electrolyte secondary battery, wherein the amount of the oxidizing agent added to the positive electrode is 50.0 mass % or more and 83.3 mass % or less.

3. The oxidizing agent is NiO, CoO, Co ２ O ３ , Co ３ O ４ 3. The method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is a combination of a NiMnCo composite oxide, a NiMn composite oxide, a MnCo composite oxide, a NiCo composite oxide, and a composite oxide containing Ni and / or Co.

4. The nonaqueous electrolyte secondary battery further comprises a nonaqueous electrolyte, 4. The method for treating a positive electrode of a non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte contains an electrolyte containing P.

5. 5. The method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to claim 1, further comprising a preparation step of preparing the positive electrode before the addition step.

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