JP7742078B2 - Method for treating positive electrode of non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a method for treating the positive electrode of a non-aqueous electrolyte secondary battery and a method for recovering valuable metals from metal composite oxides.

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 amounts of used non-aqueous electrolyte secondary batteries, defective non-aqueous electrolyte secondary batteries, and process waste generated during manufacturing processes are 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, metal 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 (LiPF ₆ ). The recovered metal materials contain phosphorus (P) as an impurity, and methods for reducing the P content in the metal materials have been proposed.

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 metal materials containing valuables are recovered. Then, calcium oxide (CaO) is added to the metal materials while oxygen is blown into them, thereby carrying out a dephosphorization process to oxidize and remove the P in the metal materials.

Patent Document 2 describes a method for recovering valuable metals from discarded 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.

JP 2013-091826 A International Publication No. 2020/013294

The recovery method described in Patent Document 1 requires a dephosphorization step, which raises the issue of high recycling costs. Furthermore, the recovery methods described in Patent Documents 1 and 2 are unable to sufficiently reduce the P content in the metal material.

The present invention aims to provide a method for treating the positive electrodes of non-aqueous electrolyte secondary batteries that can reduce phosphorus (P) in metal materials 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.

The method for treating the positive electrode of a nonaqueous electrolyte secondary battery according to the present invention is a method for treating the positive electrode of a nonaqueous electrolyte secondary battery equipped with a positive electrode having an Al-containing foil and an active material in the form of a metal composite oxide containing Ni and/or Co. The method includes an addition step of adding an oxide containing Ni and/or Co as an oxidizing agent to the positive electrode, and 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.

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 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 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 oxide; and a separation step of separating the oxide from the molten material to obtain the valuable metal.

According to the present invention, by adding an oxide containing Ni and/or Co as an oxidizing agent to the positive electrode and then melting the positive electrode to which the oxidizing agent has been added, it is possible to reduce phosphorus (P) in the metal material at low cost.

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

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. 3 is a flowchart illustrating a method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to the present embodiment. 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.

1. Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

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 confirmed 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 an electrolyte such as LiPF ₆ (lithium hexafluorophosphate) described below, and P as an impurity in the positive electrode material.

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 tube shape and contains the electrode assembly and the nonaqueous electrolyte. The lid 16 is provided at the opening of the container body 14 and seals 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 the positive electrode (described below) via a positive electrode lead (not shown). The negative electrode terminal 22 is connected to the negative electrode (described below) via a negative electrode lead (not shown).

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 described above, but may also be a laminated type in which a positive electrode, a negative electrode, and a separator are stacked.

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 binder in the positive electrode active material layer are 0 to 30 mass% and 0 to 20 mass%, respectively, of the positive electrode.

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, for 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.

The binder is a fluorine-based binder containing a fluorine compound such as polyvinylidene fluoride (PVDF). The conductive material is a carbon material such as graphite or carbon black.

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 membrane or nonwoven fabric made of a resin such as polyethylene (PE) or polypropylene (PP).

The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt (electrolyte) that is soluble in the non-aqueous solvent. Examples of non-aqueous solvents that can be used 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 alone or in combination of two or more.

As the electrolyte, for example, an electrolyte containing phosphorus (P), such as LiPF ₆ (lithium hexafluorophosphate), is used. As the electrolyte, LiBF ₄ (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 LiPF ₆ will be described as an example.

As shown in FIG. 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 in the form of 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.

[Preparation process]
In the preparation step S10, the cell container 12 is opened and the removed wound electrode assembly is rewound 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 thereto, 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 be prepared in the preparation step S10. This is because, in the melting step S12 described below, if components other than the positive electrode (such as the cell container 12, separator, and negative electrode) are included, the reduction reaction will be inhibited.

[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 a powder, block, sheet, or other shape can be appropriately selected. 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 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.

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 located above P on 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 located below P on 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 along with P in the melting step S12.

The oxidizing agent includes at least one material selected from the group consisting of a combination _of positive _electrode active material materials that 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. The positive electrode active material used as the oxidizing agent can be selected from, for example, LiNi composite oxide, LiCo composite oxide, LiNiCo composite oxide, LiNiMn composite oxide, LiNiCoAl composite oxide, LiNiCoMn composite oxide, etc. The oxidizing agent is preferably an oxide containing Ni and/or Co to be recovered. When the recovered metal material is used as a metal material for a nickel-metal hydride battery or a metal material for hydrogen storage, it is preferable that it 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. This is because Ni is the Ni to be recovered itself, and thus Ni can be recovered by reducing NiO. In this embodiment, NiO is used as the oxidizing agent.

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

The lower limit of the amount of oxidizing agent to be added for oxidizing 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 to be added for oxidizing 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 having 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.

Adding a large amount of oxidizing agent does not affect the P removal effect, so 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 reducing agent after the oxidation-reduction reaction between the active material and the Al as 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, as long as it can reduce the metal composite oxide containing Ni and/or Co in the active material. 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)

Furthermore, based on the mass of the positive electrode, the lower limit of the amount of oxidizer 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 oxidizer added is less than 50.0 mass%, the oxidation and removal of P will be insufficient. The greater the amount of oxidizer added, the lower the P content (ppm) in the metal material (described below). The P content in the metal material is 3500 ppm or less when the amount of oxidizer added is 50.0 mass% or more, 3000 ppm or less when the amount of oxidizer added is 58.3 mass% or more, and 10 ppm or less when the amount of oxidizer added is 66.7 mass% or more. Since adding a large amount of oxidizer does not affect the P removal effect, there is no particular upper limit to the amount of oxidizer added. However, if the amount of oxidizer added is too large, some Co and/or Ni may be oxidized. Therefore, the upper limit of the amount of oxidizer added to the positive electrode is preferably 83.3 mass%, more preferably 71.7 mass%. The recovery rates for Ni and Co are high, exceeding 90%, up to an oxidant addition amount of 71.7% by mass; once the amount exceeds 71.7% by mass, the recovery rates tend to decrease, but even at an addition amount of 83.3% by mass, a high value of approximately 80% is maintained.

[Melting process]
In the melting step S12, the positive electrode to which the oxidizing agent has been added is melted to obtain a molten material. The melting step S12 will be described using an example in which LiNi _x Co _y Mn _z O ₂ is used as the positive electrode active material. 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 ( _{NixCo y} Mn _z ) is obtained as a metal material containing metals that constitute the metal composite oxide.
_LiNix Co _y Mn _z O ₂ +Al → 1/2Li ₂ O+Ni _x Co _y Mn _z +1/2Al ₂ O ₃
In this embodiment, thermal energy is applied to the positive electrode from an external heating means (e.g., 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 (Al ₂ O ₃ ) into a molten slag state.

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

[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.

2. Function and Effect 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. Because 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.

By adding an oxidizer amount to the positive electrode of 50.0 mass% or more and 83.3 mass% or less, it is possible to more reliably reduce the P content in the metal material and prevent a decrease in the recovery rate of Ni and/or Co. By adding an oxidizer amount of 66.7 mass% or more, the P content in the metal material can be reduced to 10 ppm or less, allowing the recovered metal material to 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 using the recovered metal material directly as an electrode material for nickel metal hydride batteries will not affect the battery characteristics.

3. Examples Experiments conducted to confirm the effects of the present invention will be described below.

A used nonaqueous electrolyte secondary battery was prepared, in which a wound electrode assembly and 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:

<Positive electrode>
Al foil, thickness 15 μm, 20 mass%
Active material (LiNi _1/6 Co _2/3 Mn _1/6 O ₂ ) 72-73% by mass
Binder (PVDF) 3 to 4% by mass
Conductive material 4% by mass
<Nonaqueous electrolyte>
Non-aqueous solvent (DMC:EMC:PC) mass ratio 28:27:28
Electrolyte (LiPF ₆ ) 1M

In the experiment, the prepared nonaqueous electrolyte secondary battery was first discharged, the inside of the cell container 12 was cleaned, the cell container 12 was opened, and the wound electrode assembly was removed and rewound and cut with a shredder to prepare the positive electrode (preparation step S10).

30 g of positive electrode, a predetermined amount of oxidizer, and 11.1 g of CaO powder were placed in a pre-prepared bag and shaken to add the oxidizer and CaO powder to the positive electrode (addition step S11). The positive electrodes to which the oxidizer was added were designated Examples 1 to 10. NiO powder was used as the oxidizer. 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. 30 g of 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 oxidizer was added were designated Comparative Examples 1 and 2.

Experiments were conducted by subjecting the positive electrodes of Examples 1 to 10 and Comparative Examples 1 and 2 to melting step S12.

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, and while nitrogen (N ₂ ) gas was flowing at a flow rate of 5 L/min, the temperature inside the furnace was raised from room temperature to 1550°C and maintained 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 provided around the outer 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.

The positive electrodes of Comparative Examples 1 and 2, which did not contain an oxidizing agent, were placed in a high-frequency induction melting furnace, the air inside the furnace was evacuated to create a vacuum, and the temperature was raised 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 raised 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.

Figure 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. Figure 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. Figure 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 4,500 to 10,000 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 percentage 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. A Hitachi High-Tech Science PS3520UVDDII or SPS3520UVDD was used for all ICP mass spectrometry analyses.

Figure 3 confirms that the P content can be reduced with increasing oxidizer addition amounts. Up to 10 g of oxidizer addition, the Al recovery rate decreases significantly, but the decrease in P content is small. In contrast, when the oxidizer addition amount exceeds 10 g, i.e., when the Al recovery rate falls below 8.0%, the decrease in Al recovery rate slows down, while the P content decreases rapidly. At 15 g or more (Al recovery rate of 1.6% or less), the P content is below 3500 ppm, at 17.5 g or more (Al recovery rate of 0.2% or less), it is below 3000 ppm, and at 20 g or more (Al recovery rate of 0.01% or less), it is below 10 ppm. It was confirmed that melting the positive electrode to which oxidizer had been added can oxidize and remove the P contained in the positive electrode. The Ni and Co recovery rates remained high, exceeding 90%, up to 20 g of oxidizer addition (Al recovery rate of 0.01% or less). The recovery rates of Ni and Co tended to decrease when the amount of oxidizing agent added 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 did not contribute to the oxidation reaction. However, even when the amount of oxidizing agent added 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 completely oxidize the excess Al (20 g) plus 5 g, which is 25% of the amount required to completely oxidize the excess Al. Furthermore, the recovery rate of Mn decreased with increasing the amount of oxidizing agent added. 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 added exceeded 10 g. The order of ease of oxidation shown in the Ellingham diagram is Al, Mn, P, Co, and Ni. In the melting process S12, oxidation removal of P begins even when unoxidized Al and Mn remain, and it can be seen that once the Al and Mn have been sufficiently oxidized and removed, the amount of P is also sufficiently reduced.

When the alumina crucible was disassembled and the metal material was removed, it was confirmed that the color of the slag surface became darker as the amount of NiO powder added increased. It is believed that the precipitation of _MnO2 on the slag surface progressed as the amount of NiO powder added increased.

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

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 (e.g., alumina) is used, the positive electrode may be melted in an air atmosphere.

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

In the melting step S12, the positive electrode is melted using an external heating means in the above embodiment. However, the positive electrode may also 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 (metallic Al) and a positive electrode active material (metal oxide) is reacted, generating high heat while reducing the metal oxide with metallic Al. The positive electrode generates self-heat due to the heat of reaction between the foil and the active material. "Self-heating" means that the temperature of the positive electrode increases due to the heat of reaction between the foil and the active material, even when no thermal energy is applied to the positive electrode from an external heating means (e.g., a high-frequency induction melting furnace).

The thermite reaction is a highly exothermic reaction, and once it reaches a temperature where the reaction can continue, it proceeds due to self-heating (heat of reaction). One method of 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 as needed. Alternatively, there are methods that use equipment that applies high-temperature heat from an external source, such as an arc melting or high-frequency induction melting furnace. In this case, the positive electrode melts due to self-heating (heat of reaction), and also due to the heat from the arc melting or high-frequency induction melting.

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

The heating process will now be described. The heating device used for the heating process 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 air flow rate inside the heating furnace. The control unit controls the heating unit based on the measurement results of the thermometer, raising the temperature inside the heating furnace at a predetermined heating rate and controlling it to a preset heating temperature. The control unit controls the gas supply unit based on the measurement results of the flow meter, controlling the flow rate of air supplied into the heating furnace. The control unit controls the heating unit and gas supply unit so that the heating temperature and flow rate are maintained for a predetermined period of 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 is used, the heat treatment can be carried out continuously.

The heating process procedure will be explained below. First, a sheet-shaped positive electrode is placed in a heat-resistant container. Next, the heating device is activated, raising the temperature inside the heating furnace until it reaches a preset heating temperature. The container with the positive electrode placed inside the heating furnace is placed inside the heating furnace, and air is supplied into the heating furnace at a specified 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 inside the heating furnace may also be placed before the heating device is activated.

The heat treatment is preferably carried out at a temperature that does not oxidize the foil. If the heating temperature is too high, the Al foil serving as the positive electrode current collector will oxidize. Oxidized Al foil cannot be used as a reducing agent in the melting step S12.

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 in the melting step S12 will generate gases of hydrogen and carbon oxides such as _H2O , _CO2 , and CO, inhibiting the reduction reaction. Gases that inhibit the reduction reaction are called reaction-inhibiting gases. In addition, 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. In addition, the heat treatment is preferably performed at a temperature at which the conductive material is oxidized and removed.

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. However, if the heating temperature is too high, the Al in the positive electrode current collector may act as a reducing agent, causing an unintended reduction reaction, which is dangerous. Heat treatment is more preferably carried out at a temperature of 450°C or higher and 600°C or lower, and even more preferably at a temperature of 500°C or higher and lower than 600°C.

In the heating process, heating is performed at a temperature that does not oxidize the foil, which suppresses the formation of alumina on the surface of the Al foil and promotes the reduction reaction (thermit reaction) in the melting process S12.

By heating the material in the heating step at a temperature that decomposes the binder, the generation of reaction-inhibiting gases during the melting step S12 is suppressed and the reduction reaction (thermit reaction) is promoted.

By heating the material at a temperature between 400°C and 650°C inclusive during the heating process, the occurrence of a thermite reaction during the heating process is suppressed, improving safety. The heating process removes the binder and conductive material, suppressing the generation of reaction-inhibiting gases during the melting process S12. This promotes the reduction reaction (thermit reaction) during the melting process S12.

In the above embodiment, the positive electrode current collector's Al foil was used as the reducing agent, but Al powder, for example, may also be added as the reducing agent.

The present invention is not limited to methods for treating the positive electrodes of nonaqueous electrolyte secondary batteries, but is a technology that can be widely applied to removing impurities that are more easily oxidized than the valuable metals in a metal composite oxide and recovering valuable metals from the metal composite oxide containing the valuable metals. For example, it 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 metals 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 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 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 oxidizing agent have been added to reduce the valuable metal in the metal composite oxide and oxidize 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.

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

Claims (5)

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 ,
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, represented 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) 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 to the positive electrode is 50.0 mass % or more and 83.3 mass % or less. 3. _{The method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to claim 1 or 2 , wherein} the oxidizing agent contains at least one substance selected from the group consisting of combinations of positive electrode active material materials that 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. The nonaqueous electrolyte secondary battery further comprises a nonaqueous electrolyte,
4. The method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to claim 1 , wherein the nonaqueous electrolyte contains an electrolyte containing P. 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.