Lithium recovery method

Abstract

This invention provides a lithium recovery method that can suppress the inhibition of recovery due to the generation of sulfur particles, the inhibition of lithium recovery due to the deposition of lithium phosphate, and the decrease in lithium recovery rate. [Solution] A lithium recovery method from a used lithium-ion secondary battery comprising an electrode body having a positive electrode, a sulfide solid electrolyte, and a negative electrode, comprising: a dissolution step of dissolving the solid electrolyte and lithium compound contained in the deactivated lithium-ion secondary battery in pure water to obtain a dispersion; a separation liquid recovery step of recovering the separation liquid by solid-liquid separation of the dispersion liquid; an oxidation step of oxidizing the separation liquid to generate acidic components in the separation liquid and adjust the pH of the separation liquid; an aeration step of aerating the separated liquid after oxidation treatment with air or an oxidizing gas to adjust the pH of the separation liquid; a recovery stock liquid recovery step of recovering the recovery stock liquid by solid-liquid separation of the separated liquid after aeration treatment; and a step of extracting an aqueous lithium hydroxide solution from the recovery stock liquid by electrodialysis using a cation exchange membrane.

Description

[Technical Field]

[0001] This invention relates to a lithium recovery method. [Background technology]

[0002] In recent years, research and development has been conducted on so-called all-solid-state batteries, which use a solid electrolyte instead of a liquid electrolyte. Because all-solid-state batteries do not use organic solvents, improvements in safety are expected. Furthermore, as with conventional batteries, recycling technologies are being developed for all-solid-state batteries to ensure efficient resource utilization (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-98840 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In the recycling of all-solid-state batteries, as described in Patent Document 1, a process is carried out in which the solid electrolyte and lithium are dissolved by immersion in water after deactivation treatment, and separated from solid components such as the positive electrode active material. Then, lithium is recovered from the separated liquid in which the lithium has been dissolved. One method for recovering lithium from the separated liquid is electrodialysis. The separated liquid contains sulfur and phosphorus ions, which are components of the solid electrolyte. These ions react with dissolved oxygen in the alkaline pH range to form S2O3. 2- (thiosulfate ion), PO4 3- It generates (phosphate ions). S2O3 2- (Thiosulfate ions) undergo an oxidation reaction during electrodialysis, resulting in SO4 2- It generates sulfate ions and sulfur particles, leading to poor circulation of the liquid and deterioration of the membrane used in electrodialysis. PO4 3-(Phosphate ions) combine with lithium to form Li3PO4 (lithium phosphate) when reaching the saturation concentration, deteriorating the liquid circulation and reducing the lithium recovery rate.

[0005] S2O3 2- (Thiosulfate ions) need to be removed before electrodialysis because an oxidation reaction proceeds during electrodialysis to generate sulfur fine particles. S2O3 contained in the separation liquid 2- (Thiosulfate ions) is oxidized to generate SO4 2- (Sulfate ions) and sulfur fine particles before electrodialysis, and the sulfur fine particles are removed by filtration or the like. PO4 3- Li3PO4 (lithium phosphate) generated from (phosphate ions) dissolves in a strong acid with a pH of 2 or less. Therefore, by acidifying the separation liquid, which is a strong alkaline liquid, by oxidation of the contained ions, lithium is redissolved to prevent a decrease in the recovery rate. As a method for promoting the oxidation of the separation liquid, forced oxidation by aerating the separation liquid with ozone is desirable. By adjusting the pH of the separation liquid to around 2, more than 90% of the sulfur components contained in the separation liquid are oxidized, suppressing the generation of sulfur fine particles during lithium recovery, and recovering the lithium recovery rate by redissolving Li3PO4 (lithium phosphate).

[0006] The present application aims to provide a lithium recovery method that can suppress the inhibition of recovery by sulfur fine particles, the inhibition of lithium recovery due to the precipitation of lithium phosphate, and the decrease in the lithium recovery rate in order to solve the above problems. And it contributes to a significant reduction in the generation of waste.

Means for Solving the Problems

[0007] To achieve the above object, the present invention provides the following means. [1] A method for recovering lithium from a used lithium-ion secondary battery including an electrode body having a positive electrode, a sulfide solid electrolyte, and a negative electrode, A dissolution step involves dissolving the solid electrolyte and lithium compound contained in a deactivated lithium-ion secondary battery in pure water to obtain a dispersion. A separation liquid recovery step is performed to separate the dispersion liquid into solid and liquid components and recover the separated liquid, An oxidation step is performed to oxidize the separated liquid to generate acidic components in the separated liquid and adjust the pH of the separated liquid. An aeration step is performed in which the separated liquid after oxidation treatment is aerated with air or an oxidizing gas to adjust the pH of the separated liquid. A recovery liquid stock recovery process involves solid-liquid separation of the separated liquid after aeration treatment to recover the recovery liquid stock, A lithium recovery method comprising the step of extracting an aqueous lithium hydroxide solution from the recovered stock solution by electrodialysis using a cation exchange membrane.

[0008] According to the above embodiment, by oxidizing the separated liquid to generate acidic components in the separated liquid and adjusting the pH of the separated liquid, and then further aerating the separated liquid with air or an oxidizing gas, it is possible to suppress the inhibition of recovery due to the generation of sulfur particles, redissolve acid-soluble Li3PO4 (lithium phosphate), and suppress the inhibition of lithium recovery due to the precipitation of lithium phosphate and the decrease in the lithium recovery rate.

[0009] [2] The lithium recovery method according to [1], wherein in the oxidation step the pH of the separated liquid is adjusted to 7 to 12, and in the aeration step the pH of the separated liquid is adjusted to 2 or less.

[0010] According to the above embodiment, by utilizing the fact that the saturated dissolution amount of copper and nickel in the separated liquid decreases to 10 mg / L between pH 7 and 12, the pH of the separated liquid can be adjusted by oxidation treatment, thereby promoting the precipitation of hydroxides such as copper, nickel, and aluminum. Furthermore, oxidation treatment can promote the precipitation of HS contained in the separated liquid. - (Hydrogen sulfide ion), S2O3 2-By sulfating thiosulfate ions, sulfur fine particles are precipitated before electrodialysis and then removed by filtration or the like to suppress the inhibition of recovery. By strongly oxidizing the separation liquid (pH 2-5), acid-soluble Li3PO4 (lithium phosphate) is redissolved, and the inhibition of lithium recovery due to the precipitation of lithium phosphate and the decrease in the lithium recovery rate can be suppressed.

[0011] [3] Further, the lithium recovery method according to [1] or [2], which includes a step of removing impurity anions from the lithium hydroxide aqueous solution using an anion exchange resin.

[0012] According to the above aspect, the lithium hydroxide aqueous solution is brought into contact with an anion exchange resin to remove chlorine (Cl), bromine (Br), sulfate ions (SO4 2- ) etc. contained in trace amounts (ppm order) in the lithium hydroxide aqueous solution. [Advantages of the Invention]

[0013] According to the present invention, it is possible to provide a lithium recovery method that can suppress the inhibition of recovery due to the generation of sulfur fine particles, the inhibition of lithium recovery due to the precipitation of lithium phosphate, and the decrease in the lithium recovery rate. [Brief Description of the Drawings]

[0014] [Figure 1] It is a flowchart of the lithium recovery method according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view schematically showing a lithium recovery device according to an embodiment of the present invention. [Embodiments for Carrying Out the Invention]

[0015] Hereinafter, embodiments of the present invention will be described in detail. However, the following description is an example of the embodiments of the present invention, and the present invention is not limited to these contents and can be implemented with modifications within the scope of the gist.

[0016] [Lithium Recovery Method] A lithium recovery method according to one embodiment of the present invention is a method for recovering lithium from a used lithium-ion secondary battery that comprises an electrode body having a positive electrode, a sulfide solid electrolyte, and a negative electrode.

[0017] A lithium recovery method according to one embodiment of the present invention includes: a dissolution step of dissolving a solid electrolyte and lithium compound contained in a deactivated lithium-ion secondary battery in pure water to obtain a dispersion; a separation liquid recovery step of recovering the separation liquid by solid-liquid separation of the dispersion; an oxidation step of oxidizing the separation liquid to generate acidic components in the separation liquid and adjust the pH of the separation liquid; an aeration step of aerating the separation liquid after oxidation treatment with air or an oxidizing gas to adjust the pH of the separation liquid; a recovery stock liquid recovery step of recovering the recovery stock liquid by solid-liquid separation of the separation liquid after aeration treatment; and a step of extracting an aqueous lithium hydroxide solution from the recovery stock liquid by electrodialysis using a cation exchange membrane.

[0018] Figure 1 is a flowchart of the lithium recovery method according to this embodiment.

[0019] "Dissolution process" In the dissolution step S1, after deactivating the used lithium-ion secondary battery, the components of the deactivated lithium-ion secondary battery are stirred in pure water to dissolve the solid electrolyte and lithium compound contained in the components in the pure water and prepare a dispersion. The components to be treated refer to the components that make up the deactivated lithium-ion secondary battery. The deactivation of used lithium-ion secondary batteries can be carried out by known methods (see, for example, Japanese Patent Publication No. 2023-124857, International Publication No. 2021 / 201151, etc.). The processed member contains a positive electrode active material, a positive electrode material other than the positive electrode active material (such as a conductive assistant, a binder, etc.), copper of a negative electrode current collector, sulfur and phosphorus derived from an electrolyte, a current collecting tab, a current collector, etc. For example, a positive electrode including a current collector and a positive electrode active material layer formed on the current collector is crushed and dispersed in a fragment of a desired size, a filtrate, a separated liquid after extraction, or a mixed liquid thereof to prepare a dispersion liquid. The obtained dispersion liquid contains a positive electrode active material, a positive electrode material other than the positive electrode active material, a current collecting tab, a current collector, etc. as solid components.

[0020] The positive electrode active material is not particularly limited and may be a material known as a positive electrode active material of a lithium ion secondary battery. Examples of the positive electrode active material include, for example, LiCoO2, LiNiO2, NCM (Li(Ni x Co y Mn z )O2, (0 < x < 1, 0 < y < 1, 0 < z < 1, x + y + z = 1)) and other ternary system positive electrode materials, layered positive electrode active material particles such as LiVO2, LiCrO2, LiMn2O4, Li(Ni 0.25 Mn 0.75 )2O4, spinel type positive electrode active materials such as LiCoMnO4, Li2NiMn3O8, olivine type positive electrode active materials such as LiCoPO4, LiMnPO4, LiFePO4, etc.

[0021] In the dissolution step S1, the reason for using pure water is that natural water, tap water, etc. contain alkali metals and alkaline earth metals such as sodium, potassium, calcium, magnesium, etc. as mineral components, which impairs the separability of the cation exchange membrane. The alkali metals and alkaline earth metals become contaminants of the recovered lithium.

[0022] In the dissolution step S1, since the dispersion liquid contains a solid electrolyte containing lithium, the pH of the dispersion liquid becomes 11 or more and 14 or less. In order to achieve a lithium recovery rate of 80% or more, it is necessary that 0.4 mol / L or more, preferably 0.7 mol / L or more of lithium is dissolved in the dispersion liquid.

[0023] "Separation liquid recovery step" In the separation liquid recovery step S2, solid components such as the positive electrode active material, other positive electrode materials, current collector tabs, and current collectors contained in the dispersion are filtered, separated, and removed, and the separation liquid is recovered. Here, non-water-soluble solid components of the lithium-ion secondary battery are removed. Examples of non-water-soluble solid components include the positive electrode active material, binder, conductive additive, tabs, electrodes, etc.

[0024] The separated liquid obtained in the separated liquid recovery step S2 contains, for example, chlorine (Cl), bromine (Br), phosphorus (P), sulfur (S), aluminum (Al), nickel (Ni), copper (Cu), etc.

[0025] "Oxidation process" In oxidation step S3, the separated liquid is oxidized to generate acidic components and adjust its pH. The pH of the separated liquid is preferably between 7 and 12. The pH value is adjusted by leaving the separated liquid standing in the air, aerating (bubbling) the separated liquid with air, aerating (bubbling) the separated liquid with an oxidizing gas such as ozone, oxygen gas, or active oxygen gas, or by heating the separated liquid. These treatments promote the reaction of phosphorus (P) in the separated liquid to become PO4 and the reaction of sulfur (S) in the separated liquid to become S2O3 or SO4, thereby adjusting the pH of the separated liquid. Active oxygen gases include superoxide, hydroxyl radicals, etc. In processes where the separated liquid is left to stand in the air, for example, the separated liquid is left to stand for more than 10 hours but less than 100 days. In the process of aerating the separated liquid with air, for example, the separated liquid is aerated with air for more than 4 hours but less than 10 days. In the process of aerating the separated liquid with an oxidizing gas, for example, the separated liquid is aerated with ozone for 2 to 5 hours. In the process of heating the separated liquid, for example, the separated liquid is heated to a temperature between 40°C and 90°C. This causes hydroxides such as copper, nickel, and aluminum to precipitate.

[0026] By utilizing the fact that the saturation dissolution amount of copper and nickel in the separated solution decreases to 10 mg / L between pH 7 and 12, the pH of the separated solution is adjusted through oxidation treatment to promote the precipitation of hydroxides such as copper, nickel, and aluminum. The pH of the dispersion immediately after dissolving the solid electrolyte reaches around 12, which is due to the dissolution of lithium ions in the lithium-ion secondary battery. Furthermore, due to sulfide reactions caused by hydrogen sulfide gas generated when the solid electrolyte is dissolved in water, the content of contaminants such as copper, nickel, and aluminum in the separated solution reaches several hundred mg / L. Therefore, it is desirable to lower the pH of the separated solution to 10 or below in order to stabilize the ionic state in the separated solution. If the pH of the separated solution falls below 7, the dissolution concentration of copper and nickel will increase because they are soluble in acid.

[0027] While it is possible to adjust the pH of the separated liquid using acidic liquids (such as sulfuric acid or hydrochloric acid), this process is burdensome because it involves the release of hydrogen sulfide, a harmful, flammable, and corrosive gas. Since large amounts of phosphorus and sulfur are leached into the separated liquid, it is desirable to oxidize these substances in the separated liquid to bring its pH to the neutral range. Therefore, in the lithium recovery method of this embodiment, the pH of the separated liquid is adjusted without using acidic liquids by processes such as letting the separated liquid stand in the air, aerating (bubbling) the separated liquid with air, aerating (bubbling) the separated liquid with an oxidizing gas such as ozone, or heating the separated liquid.

[0028] "Separation process" The lithium recovery method of this embodiment may include a separation step S4. In the separation step S4, solid components (aluminum-containing compounds, nickel-containing compounds, copper-containing compounds, etc.) are separated and removed from the separated liquid after the oxidation step S3 by filtration.

[0029] "Aeration process" In the aeration step S5, the separated liquid obtained in the oxidation step S3 is aerated with air or an oxidizing gas. This further adjusts the pH of the separated liquid. The pH of the separated liquid is preferably 2 or less. The pH value is adjusted by aerating (bubbling) the separated liquid with air or by aerating (bubbling) the separated liquid with an oxidizing gas such as ozone, oxygen gas, or activated oxygen gas. These processes adjust the HS contained in the separated liquid. - (Hydrogen sulfide ion), S2O3 2- By sulfating the thiosulfate ions, the separated solution is strongly oxidized (pH 2 or lower), which redissolves the acid-soluble Li3PO4 (lithium phosphate). This prevents the precipitation of lithium phosphate from hindering lithium recovery and reduces the lithium recovery rate.

[0030] "Recovery process for the recovered concentrate" In the recovery concentrate recovery process S6, the separated liquid after oxidation treatment is separated into solid and liquid components to recover the recovery concentrate. In the recovery concentrate recovery process S6, solid components (sulfur particles) are filtered and separated and removed from the separated liquid that has gone through the aeration process S5.

[0031] "Extraction process" In extraction step S7, an aqueous lithium hydroxide solution is extracted from the recovered stock solution by electrodialysis using a cation exchange membrane.

[0032] In extraction step S7, examples of materials for the cation exchange membrane include sodium sulfonate and polyolefin. As lithium concentration progresses in the lithium hydroxide aqueous solution, the pH exceeds 12, and the recovery stock solution undergoes strong oxidation to around pH 1 due to the decrease in lithium and the progression of oxidation of anionic components. Therefore, the cation exchange membrane requires a wide pH tolerance.

[0033] In electrodialysis using a cation exchange membrane, lithium ions contained in the recovered stock solution permeate through the cation exchange membrane, where they react with water to form lithium hydroxide. In other words, an aqueous solution of lithium hydroxide is produced on the side that has permeated the cation exchange membrane. As an example of an electrodialysis method, one could use a constant current treatment of 0.3A, and stop the process when the voltage between electrodes reaches the membrane's breakdown voltage limit. Alternatively, as an example of an electrodialysis method, one could use a constant voltage treatment, where the voltage is set below the membrane's breakdown voltage, and the process stops when the current value falls below a certain value.

[0034] In extraction step S7, copper (Cu), nickel (Ni), aluminum (Al), and phosphate ions (PO4) are extracted. 3- If the concentration of ) etc. in the recovered stock solution is tens of ppm or less, it will not permeate the cation exchange membrane. Chlorine (Cl), bromine (Br), sulfate ions (SO4 2- These substances hardly permeate the cation exchange membrane. Therefore, in extraction step S7, these substances are separated from lithium.

[0035] "Ion exchange process" The lithium recovery method of this embodiment may include an ion exchange step S8. In the ion exchange step S8, the lithium hydroxide aqueous solution obtained in the extraction step S7 is brought into contact with an anion exchange resin to remove trace amounts (on the order of ppm) of chlorine (Cl), bromine (Br), and sulfate ions (SO4) contained in the lithium hydroxide aqueous solution. 2- Removes impurities such as anions.

[0036] In the ion exchange step S8, it is preferable that the temperature at which the lithium hydroxide aqueous solution is brought into contact with the anion exchange resin is between 10°C and 40°C.

[0037] Through the above process, a high-purity aqueous lithium hydroxide solution is obtained.

[0038] According to the lithium recovery method of this embodiment, it is possible to recover lithium alone from a solid electrolyte aqueous solution by electrodialysis using a cation exchange membrane, while suppressing the inhibition of recovery due to the generation of sulfur particles, the inhibition of lithium recovery due to the deposition of lithium phosphate, and the decrease in the lithium recovery rate.

[0039] [Lithium recovery device] A lithium recovery device according to one embodiment of the present invention is a device for recovering lithium from used lithium-ion secondary batteries.

[0040] Figure 2 is a schematic cross-sectional view showing the lithium recovery device of this embodiment.

[0041] The lithium recovery device 1 comprises a processing tank 10, a cation exchange membrane 20, a first electrode 30, a second electrode 40, and a power supply 50.

[0042] The processing tank 10 has a first space 11 and a second space 12 separated by a cation exchange membrane 20 installed inside the processing tank 10. In the first space 11, the inner surface facing the cation exchange membrane 20 at a distance is defined as one main surface 10a of the processing tank 10. In the second space 12, the inner surface facing the cation exchange membrane 20 at a distance is defined as the other main surface 10b of the processing tank 10.

[0043] The treatment tank 10 is a tank that processes a dispersion obtained by dispersing the water-soluble solid electrolyte contained in the components of a deactivated lithium-ion secondary battery to be treated in pure water, using electrodialysis.

[0044] The cation exchange membrane 20 is positioned in the center of the processing tank 10, along the height direction of the processing tank 10, so as to separate the first space 11 and the second space 12 of the processing tank 10. As the cation exchange membrane 20, the same type as that used in the lithium recovery method of the above-described embodiment can be used.

[0045] The first electrode 30 is positioned within the first space 11 on one main surface 10a side of the processing tank 10. The second electrode 40 is positioned within the second space 12 on the other main surface 10b side of the processing tank 10.

[0046] The power supply 50 is connected to the first electrode 30 and the second electrode 40. The power supply 50 applies the voltage required for electrodialysis to the first electrode 30 and the second electrode 40.

[0047] The lithium recovery method using the lithium recovery device 1 of this embodiment will be described. A separated liquid is prepared after going through the dissolution step S1, the separated liquid recovery step S2, the oxidation step S3, the aeration step S5, and the recovered raw liquid recovery step S7 in the lithium recovery method of the above embodiment. In the lithium recovery apparatus 1 of this embodiment, the extraction step S7 of the lithium recovery method of the above-described embodiment is performed.

[0048] The separation liquid is injected into the first space 11 of the processing tank 10, and a dilute lithium hydroxide solution is injected as the recovery liquid into the second space 12 of the processing tank 10 to ensure conductivity. In this state, when a voltage is applied from the power supply 50 to the first electrode 30 and the second electrode 40, electrodialysis begins, and lithium ions contained in the separated liquid in the first space 11 permeate the cation exchange membrane and move to the recovered liquid in the second space 12. The lithium ions that have permeated the cation exchange membrane react with water in the second space 12 to form lithium hydroxide. In other words, an aqueous solution of lithium hydroxide is generated in the second space 12. Note that trace amounts (on the order of ppm) of chlorine (Cl), bromine (Br), and sulfate ions (SO4) are present. 2- Because ) permeates the cation exchange membrane, the lithium hydroxide aqueous solution contains trace amounts (on the order of ppm) of chlorine (Cl), bromine (Br), and sulfate ions (SO4). 2- ) is included.

[0049] According to the lithium recovery apparatus of this embodiment, lithium can be recovered independently from a solid electrolyte aqueous solution by electrodialysis using a cation exchange membrane, without adding a compounding solution to adjust the pH.

[0050] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0051] 1. Lithium recovery device 10 Processing tanks 11 1st space 12 Second space 20 Cation exchange membrane 30 1st electrode 40 2nd electrode 50 power supply

Claims

1. A method for recovering lithium from a used lithium-ion secondary battery, comprising an electrode body having a positive electrode, a sulfide solid electrolyte, and a negative electrode, A dissolution step involves dissolving the solid electrolyte and lithium compound contained in a deactivated lithium-ion secondary battery in pure water to obtain a dispersion. A separation liquid recovery step is performed to separate the dispersion liquid into solid and liquid components and recover the separated liquid, An oxidation step is performed to oxidize the separated liquid to generate acidic components in the separated liquid and adjust the pH of the separated liquid. An aeration step in which the separated liquid after oxidation treatment is aerated with air or an oxidizing gas to adjust the pH of the separated liquid, A recovery liquid stock recovery process involves solid-liquid separation of the separated liquid after aeration treatment to recover the recovery liquid stock, A lithium recovery method comprising the step of extracting an aqueous lithium hydroxide solution from the recovered stock solution by electrodialysis using a cation exchange membrane.

2. The lithium recovery method according to claim 1, wherein in the oxidation step, the pH of the separated liquid is adjusted to 7 to 12, and in the aeration step, the pH of the separated liquid is adjusted to 2 or less.

3. Furthermore, the lithium recovery method according to claim 1, comprising the step of removing impurity anions from the lithium hydroxide aqueous solution using an anion exchange resin.

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