Positive electrode active material recovery method

Abstract

The present invention makes it possible to effectively dissolve a binder in a hydrophobic solvent.　A positive electrode active material recovery method according to the present invention includes a lithium recovery step for filtering a cell elution slurry that has been extracted from a lithium ion secondary battery and includes a positive electrode active material and a binder to recover lithium, a substitution step for performing a substitution with a compatible solvent on a positive electrode mixture slurry obtained by the processing at the lithium recovery step and filtering, and a binder removal step for performing a substitution with a hydrophobic solvent on the positive electrode mixture slurry processed at the substitution step and filtering to dissolve the binder in the positive electrode mixture slurry and produce a post-removal slurry from which the binder has been removed.

Description

Method for recovering positive electrode active material

[0001] The present invention relates to a method for recovering a positive electrode active material.

[0002] Some lithium-ion secondary batteries and all-solid-state batteries include a laminated electrode in which a positive electrode plate and a negative electrode plate are stacked with a separator interposed therebetween. The positive electrode active material of the positive electrode composite of these batteries is a ternary positive electrode material (NCM) composed of nickel, cobalt, and manganese. When disposing of lithium-ion secondary batteries, it is desirable to remove the binder from the positive electrode composite and recover the positive electrode active material. Conventionally, a technique for dissolving the binder contained in the positive electrode composite with a solvent and recovering valuable metals has been known (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2014-207192

[0004] However, when the binder of the positive electrode mixture is removed using a hydrophobic solvent, the binder may repel the hydrophobic solvent. The present invention has been made in view of the above-mentioned circumstances, and aims to effectively dissolve the binder using a hydrophobic solvent.

[0005] In order to solve the above-mentioned problems, the present invention provides a method for recovering a positive electrode active material, which includes a lithium recovery step of filtering a cell elution slurry that is removed from a lithium ion secondary battery and contains a positive electrode active material and a binder to recover lithium; a substitution step of substituting a compatible solvent for the positive electrode composite slurry obtained by the lithium recovery step, and filtering the resulting solution; and a binder removal step of substituting a hydrophobic solvent for the positive electrode composite slurry that has been treated by the substitution step, and filtering the resulting solution to dissolve the binder in the positive electrode composite slurry, thereby obtaining a binder-removed slurry.

[0006] In the present invention, the binder can be effectively dissolved by a hydrophobic solvent, and the recycling process for lithium ion secondary batteries can be simplified, reducing the burden on the environment and reducing the recycling costs.

[0007] Fig. 1 is a diagram showing a positive electrode active material recovery device, and Fig. 2 is a flowchart showing a positive electrode active material recovery method.

[0008] 1 is a diagram showing a recovery device 100 for a positive electrode active material. The recovery device 100 includes a main tank 101. The main tank 101 is charged with a positive electrode composite slurry containing a positive electrode composite separated from a lithium ion secondary battery, and a cell elution slurry containing lithium ions eluted into water from the positive electrode composite.

[0009] The positive electrode mixture contains a positive electrode active material and a resin binder. Furthermore, the positive electrode mixture after separation from the lithium-ion secondary battery contains lithium. The positive electrode active material contains valuable metals such as nickel, cobalt, and manganese, and is recovered from used lithium-ion secondary batteries. The positive electrode mixture slurry is a slurry containing the positive electrode active material and the binder.

[0010] A filtration unit 102 is connected to the main tank 101. Opening a first valve 111 connects the main tank 101 to the filtration unit 102, and opening a second valve 112 connects the filtration unit 102 to the main tank 101. The filtration unit 102 filters the mixture of solid and liquid supplied from the main tank 101, performing solid-liquid separation.

[0011] The filtration unit 102 is connected to the lithium recovery unit 103 via a third valve 113, and to the drain tank 104 via a fourth valve 114. By opening the third valve 113 and closing the fourth valve 114, a path is established from the filtration unit 102 to the lithium recovery unit 103. By closing the third valve 113 and opening the fourth valve 114, a path is established from the filtration unit 102 to the drain tank 104.

[0012] The main tank 101 is connected to a water tank 105 , a compatible solvent tank 106 , and a hydrophobic solvent tank 107 .

[0013] Opening the fifth valve 115 connects the water tank 105 to the main tank 101. Water is stored in the water tank 105, and opening the fifth valve 115 allows water to be supplied to the main tank 101.

[0014] Opening the sixth valve 116 connects the compatible solvent tank 106 to the main tank 101. The compatible solvent tank 106 stores a compatible solvent, and opening the sixth valve 116 allows the compatible solvent to be supplied to the main tank 101. The compatible solvent is a liquid that is easily mixed with both water and the hydrophobic solvent, such as ethanol.

[0015] Opening the seventh valve 117 connects the hydrophobic solvent tank 107 to the main tank 101. A hydrophobic solvent is stored in the hydrophobic solvent tank 107, and opening the seventh valve 117 allows a compatible solvent to be supplied to the main tank 101. The hydrophobic solvent is, for example, anisole. The hydrophobic solvent dissolves the binder contained in the positive electrode mixture.

[0016] The distillation section 108 is connected to the waste liquid tank 104 on the upstream side, and to the water tank 105, the compatible solvent tank 106, and the hydrophobic solvent tank 107 on the downstream side.

[0017] The distillation unit 108 separates the water, compatible solvent, and hydrophobic solvent discharged from the main tank 101 to the waste liquid tank 104 by distillation. Distillation is a method of separating liquids by type by utilizing the difference in boiling points of the liquids. The water from the distillation unit 108 is supplied to the water tank 105, the compatible solvent is supplied to the compatible solvent tank 106, and the hydrophobic solvent is supplied to the hydrophobic solvent tank 107. The distillation unit 108 allows the water, compatible solvent, and hydrophobic solvent to be recycled.

[0018] The recovery section 109 is connected to the main tank 101. By opening the eighth valve 118, the path from the main tank 101 to the recovery section 109 can be connected.

[0019] [2. Operation and Effects] Next, an efficient method for recovering positive electrode active material will be disclosed. Fig. 2 is a flowchart showing the method for recovering positive electrode active material. In a preparation step S1, cell elution slurry is charged into a main tank 101. As described above, the cell elution slurry contains a positive electrode composite slurry that has been separated from a lithium ion secondary battery and mixed with a liquid to form a slurry.

[0020] In the lithium recovery step S2, the cell elution slurry is introduced into filtration unit 102. In filtration unit 102, the positive electrode composite slurry and the aqueous component of the cell elution components are filtered. The aqueous component discharged from filtration unit 102 contains lithium ions, and this aqueous component is stored in lithium recovery unit 103. Lithium is recovered by recovering the liquid stored in lithium recovery unit 103.

[0021] In the substitution step S3, the positive electrode composite slurry is substituted with a compatible solvent, filtered, and repeated until the concentration of the compatible solvent reaches or exceeds a predetermined threshold. Specifically, the compatible solvent is introduced from the compatible solvent tank 106 into the main tank 101, the positive electrode composite slurry is substituted with the compatible solvent, and the positive electrode composite slurry and the compatible solvent are filtered in the filtration unit 102. This process is repeated until the concentration of the compatible solvent reaches or exceeds a predetermined threshold. The compatible solvent discharged from the filtration unit 102 is stored in the drainage tank 104. The predetermined threshold is 90% by mass.

[0022] The compatible solvent is miscible with water, and therefore easily replaces the water contained in the positive electrode composite slurry with the compatible solvent. Reducing the proportion of water contained in the positive electrode composite slurry through this replacement makes it easier for the positive electrode composite slurry and the hydrophobic solvent to mix, and makes it easier for the positive electrode composite slurry and the hydrophobic solvent to react with each other in the subsequent binder removal step S4.

[0023] In the binder removal process S4, the positive electrode composite slurry is repeatedly replaced with a hydrophobic solvent and filtered. This process is also repeated until the concentration of the hydrophobic solvent reaches or exceeds a predetermined threshold. This dissolves the binder in the positive electrode composite slurry. Specifically, the hydrophobic solvent is introduced from the hydrophobic solvent tank 107 into the main tank 101. Next, the positive electrode composite slurry and the hydrophobic solvent are filtered in the filtration unit 102. This process is preferably repeated until the concentration of the hydrophobic solvent reaches or exceeds a threshold. The hydrophobic solvent discharged from the filtration unit 102 is stored in the drainage tank 104. The predetermined threshold is 90% by mass.

[0024] The binder removal step S4 yields a positive electrode mixture slurry from which the binder has been removed. Hereinafter, the positive electrode mixture slurry from which the binder has been removed will be referred to as a "removed slurry" as appropriate. The "removed slurry" refers to a slurry containing a positive electrode active material and a hydrophobic solvent or a compatible solvent. By performing the binder removal step S4 after the substitution step S3, the binder can be effectively removed even if the binder is an aqueous binder that easily repels hydrophobic solvents, such as styrene butadiene rubber. Furthermore, by performing a wet step of recovering lithium ions (lithium recovery step S2), the binder can be removed using a hydrophobic solvent even if the positive electrode mixture slurry is mixed with water.

[0025] In the hydrophilization step S5, the removed slurry is replaced with a compatible solvent and filtered repeatedly. This is also repeated until the concentration of the compatible solvent reaches a predetermined threshold value or higher. This allows the hydrophobic solvent remaining in the binder removal step S4 to be removed from the removed slurry. The predetermined threshold value is 90% by mass.

[0026] In the water substitution step S6, water is introduced from the water tank 105 into the main tank 101. Water is introduced into the removed slurry, thereby removing the compatible solvent remaining in the hydrophilization step S5 from the removed slurry. This results in a concentrated slurry. The concentrated slurry is a slurry containing a positive electrode active material and water at a predetermined concentration or higher. The concentrated slurry is an example of a slurry treated in the water substitution step. In the water substitution step S6, the removed slurry is substituted with water and filtered, and this is repeated until the water concentration reaches a predetermined threshold value or higher. The predetermined threshold value is 90% by mass. The concentrations of the compatible solvent, hydrophobic solvent, and water are measured using known concentration measurement methods.

[0027] In the recovery step S7, the concentrated slurry that has been treated in the water substitution step S6 is recovered from the main tank 101 to the recovery section 109.

[0028] According to this embodiment, the substitution step S3 is provided between the lithium recovery step S2 and the binder removal step S4, so that the binder can be effectively dissolved by the hydrophobic solvent.

[0029] According to the present embodiment, the positive electrode active material is recovered in a non-destructive state through steps S1 to S7, and therefore, by adding a binder, a conductive material, or the like, it can be used as is as a positive electrode composite for a lithium ion secondary battery.

[0030] According to this embodiment, the cathode composite slurry separated from the lithium ion secondary battery at the time of disposal can be recycled effectively by passing through steps S1 to S7 to recover the cathode composite for a new lithium ion secondary battery. Note that although 90% by mass is exemplified as the predetermined concentration, it is not limited thereto.

[0031] [Configurations Supported by the Above-described Embodiments] The above-described embodiments support the following configurations.

[0032] (Configuration 1) A method for recovering a positive electrode active material, comprising: a lithium recovery step of filtering a cell eluate slurry, which is removed from a lithium ion secondary battery and contains a positive electrode active material and a binder, to recover lithium; a substitution step of substituting a compatible solvent for the positive electrode composite slurry obtained in the lithium recovery step and filtering the resulting slurry; and a binder removal step of substituting a hydrophobic solvent for the positive electrode composite slurry treated in the substitution step and filtering the resulting slurry to dissolve the binder in the positive electrode composite slurry and obtain a binder-removed slurry. According to Configuration 1, the substitution step is provided between the lithium recovery step and the binder removal step, thereby enabling the binder to be effectively dissolved by the hydrophobic solvent.

[0033] (Configuration 2) The method for recovering a positive electrode active material according to Configuration 1, wherein the replacing step is a step of replacing with the compatible solvent and filtering until the concentration of the compatible solvent reaches or exceeds a predetermined threshold. According to Configuration 2, it is possible to further improve the ease of mixing the positive electrode mixture slurry and the hydrophobic solvent.

[0034] (Configuration 3) The method for recovering a positive electrode active material according to Configuration 1 or 2, comprising: a hydrophilization step of replacing the hydrophobic solvent with a compatible solvent and filtering the binder-removed slurry treated in the binder removal step to remove the hydrophobic solvent remaining in the binder removal step from the binder-removed slurry; a water replacement step of adding water to the binder-removed slurry to remove the compatible solvent remaining in the hydrophilization step from the binder-removed slurry; and a recovery step of recovering a positive electrode active material from the slurry treated in the water replacement step. According to Configuration 3, it is possible to recover a slurry containing a positive electrode active material from which the hydrophobic solvent and the compatible solvent have been removed.

[0035] (Configuration 4) The method for recovering a positive electrode active material according to Configuration 3, wherein the hydrophilization step is a step of replacing with water and filtering until the concentration of the water reaches or exceeds a predetermined threshold. According to Configuration 4, the hydrophobic solvent and the compatible solvent can be sufficiently removed.

[0036] (Configuration 5) The method for recovering a positive electrode active material according to Configuration 4, wherein the predetermined threshold is 90 mass %. According to Configuration 5, the hydrophobic solvent and the compatible solvent can be sufficiently removed by confirming that the concentration of water has increased.

[0037] (Configuration 6) The method for recovering a positive electrode active material according to Configuration 1, wherein the binder removal step is a step of replacing the binder with the hydrophobic solvent and filtering the binder until the concentration of the hydrophobic solvent reaches a predetermined threshold value or higher. According to Configuration 6, water can be sufficiently removed. Furthermore, according to Configuration 6, the compatible solvent can be sufficiently removed.

[0038] (Configuration 7) The method for recovering a positive electrode active material according to Configuration 2 or 6, wherein the predetermined concentration is 90% by mass. According to Configuration 7, water can be sufficiently removed by confirming that the concentration of the compatible solvent has increased. Furthermore, according to Configuration 7, the compatible solvent can be sufficiently removed by confirming that the concentration of the hydrophobic solvent has increased.

[0039] 100...recovery device, 101...main tank, 102...filtration section, 103...lithium recovery section, 104...drainage tank, 105...water tank, 106...compatible solvent tank, 107...hydrophobic solvent tank, 108...distillation section, 109...recovery section, 111...first valve, 112...second valve, 113...third valve, 114...fourth valve, 115...fifth valve, 116...sixth valve, 117...seventh valve, 118...eighth valve, S1...preparation step, S2...lithium recovery step, S3...substitution step, S4...binder removal step, S5...hydrophilization step, S6...water substitution step, S7...recovery step.

Claims

1. A method for recovering a positive electrode active material, comprising: a lithium recovery step of filtering a cell eluate slurry, which is removed from a lithium ion secondary battery and contains a positive electrode active material and a binder, to recover lithium; a substitution step of substituting a compatible solvent for the positive electrode mixture slurry obtained by the lithium recovery step, and filtering the resulting solution; and a binder removal step of substituting a hydrophobic solvent for the positive electrode mixture slurry obtained by the substitution step, and filtering the resulting solution to dissolve the binder in the positive electrode mixture slurry, thereby obtaining a binder-removed slurry.

2. The method for recovering a positive electrode active material according to claim 1, wherein the substitution step comprises a step of substituting the compatible solvent and filtering the solution until the concentration of the compatible solvent reaches a predetermined threshold value or more.

3. The method for recovering a positive electrode active material according to claim 1 or 2, comprising: a hydrophilization step of replacing the removed slurry treated in the binder removal step with a compatible solvent and filtering the removed slurry to remove the hydrophobic solvent remaining in the binder removal step from the removed slurry; a water replacement step of adding water to the removed slurry to remove the compatible solvent remaining in the hydrophilization step from the removed slurry; and a recovery step of recovering a positive electrode active material from the slurry treated in the water replacement step.

4. The method for recovering a positive electrode active material according to claim 3, wherein the hydrophilization step comprises the steps of replacing with water and filtering until the concentration of the water reaches a predetermined threshold value or more.

5. The method for recovering a positive electrode active material according to claim 4, wherein the predetermined threshold value is 90 mass %.

6. The method for recovering a positive electrode active material according to claim 1, wherein the binder removal step comprises a step of replacing the binder with the hydrophobic solvent and filtering the binder until the concentration of the hydrophobic solvent reaches a predetermined threshold value or more.

7. The method for recovering a positive electrode active material according to claim 2 or 6, wherein the predetermined concentration is 90 mass %.

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