LITHIUM RECOVERY METHOD

Description

CROSS-REFERENCE TO RELATED APPLICATION

Priority is claimed on Japanese Patent Application No. 2024-228320, filed Dec. 25, 2024, the content of which is incorporated herein by reference.

BACKGROUND

Field of the Invention

The present invention relates to a lithium recovery method.

Description of Related Art

In recent years, research and development has been conducted on so-called all-solid-state batteries, which use solid electrolytes instead of liquid electrolytes. Since all-solid-state batteries do not use organic solvents, they are expected to offer improved safety and the like. In addition, as with traditional batteries, developments of recycling technologies are also in progress for all-solid-state batteries from the perspective of efficient resource utilization (see, for example, Japanese Unexamined Patent Application, First Publication No. 2024-98840).

SUMMARY

As described in Japanese Unexamined Patent Application, First Publication No. 2024-98840, for recycling an all-solid-state battery, treatment is performed by deactivating and then immersing the battery in water, and a solid electrolyte and lithium are dissolved and separated from solid components such as a positive electrode active material. Then, lithium is recovered from the separation solution in which lithium is dissolved. As one of methods for recovering lithium from a separation solution, electrodialysis can be exemplified. In electrodialysis, if the separation solution contains high concentrations of metal ions such as aluminum, copper, and nickel, these metal ions prevent an increase in purity of the lithium extract and accelerate deterioration of a separation membrane used in electrodialysis. Accordingly, it is required to remove metal ions from the separation solution before electrodialysis is performed.

Since copper and nickel precipitate as hydroxides in the alkaline region, they can be removed by precipitation. Since aluminum precipitates as hydroxide in the neutral region, it can be removed by solid-liquid separation. To separate aluminum as hydroxide, the pH of the separation solution, which is strongly alkaline, is required to be lowered to the neutral region. However, when an attempt to quickly lower the pH of the separation solution is performed by, for example, adding hydrochloric acid to the separation solution, localized areas of high acid concentration may be generated in the separation solution, and thus toxic hydrogen sulfide gas may be generated.

Aspects of the present application provide a lithium recovery method that can separate metals becoming impurities in recovery of lithium ions without generating hydrogen sulfide gas. In addition, aspects of the present application contribute to a significant reduction in waste generation.

The present invention has the following aspects.

[1] A lithium recovery method from a used lithium-ion secondary battery including an electrode body having a positive electrode, a sulfide solid electrolyte, and a negative electrode, the method including: dissolving a solid electrolyte and a lithium compound contained in a deactivated lithium-ion secondary battery in pure water to obtain a dispersion liquid; recovering a separation solution by performing solid-liquid separation on the dispersion liquid; performing an oxidation treatment on the separation solution to generate an acidic component in the separation solution and adjusting a pH of the separation solution; recovering a recovery stock solution by performing solid-liquid separation on the separation solution after the oxidation treatment; and extracting a lithium hydroxide aqueous solution from the recovery stock solution through electrodialysis using a cation exchange membrane.

[2] The lithium recovery method according to [1], wherein the oxidation treatment includes a first oxidation of adjusting the pH of the separation solution to 7 to 12, and a second oxidation of adjusting the pH of the separation solution to 6 to 8.

[3] The lithium recovery method according to [1] or [2], wherein the oxidation treatment includes any of leaving the separation solution in air, aerating the separation solution with air or an oxidizing gas, and heating the separation solution.

[4] The lithium recovery method according to any one of [1] to [3] further including removing impurity anions from the lithium hydroxide aqueous solution using an anion exchange resin.

According to the aspects of the present invention, a lithium recovery method that can separate metals becoming impurities in recovery of lithium ions without generating hydrogen sulfide gas can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a lithium recovery method according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing a lithium recovery device according to one embodiment of the present invention.

FIG. 3 is a diagram showing the results of measuring a pH of a LiOH·H₂O solution and saturation solubilities of copper and nickel in the LiOH·H₂O solution in Experimental Example 1.

FIG. 4 is a diagram showing the results of adjusting a pH of a sulfide solid electrolyte solution in Experimental Example 1 by leaving the sulfide solid electrolyte solution in air, aerating the sulfide solid electrolyte solution with air, aerating the sulfide solid electrolyte solution with ozone, or heating the sulfide solid electrolyte solution to 80° C.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described in detail below, but the following description is merely an example of the embodiment of the present invention, and the present invention is not limited to these details and can be modified and implemented within the scope of the present invention.

[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 including an electrode body having a positive electrode, a sulfide solid electrolyte, and a negative electrode.

The lithium recovery method according to one embodiment of the present invention includes a dissolution process of dissolving a solid electrolyte and a lithium compound contained in a deactivated lithium-ion secondary battery in pure water to obtain a dispersion liquid, a separation solution recovery process of performing solid-liquid separation on the dispersion liquid to recover a separation solution, an oxidation process of performing an oxidation treatment on the separation solution to generate an acidic component in the separation solution and adjusting a pH of the separation solution, a recovery stock solution recovery process of performing solid-liquid separation on the separation solution after the oxidation treatment to recover a recovery stock solution, and a process of extracting a lithium hydroxide aqueous solution from the recovery stock solution through electrodialysis using a cation exchange membrane.

FIG. 1 is a flowchart of the lithium recovery method of the present embodiment.

“Dissolution Process”

In the dissolution step S1, after the used lithium-ion secondary battery is deactivated, treatment target members of the deactivated lithium-ion secondary battery are stirred in the pure water, and the solid electrolyte and the lithium compound included in the treatment target members are dissolved in the pure water to prepare the dispersion liquid. The treatment target members are members constituting the deactivated lithium-ion secondary battery.

An deactivation treatment of the used lithium-ion secondary batteries can be performed using a known method (see, for example, Japanese Unexamined Patent Application, First Publication No. 2023-124857, International Publication No. WO 2021/201151, or the like).

The treatment target members include a positive electrode active material, positive electrode materials other than the positive electrode active material (a conductive additive, a binder, and the like), copper from a negative electrode current collector, sulfur and phosphorus derived from an electrolyte, current collector tabs, and current collectors. 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 fragments of a desired size, a filtrate, a separation solution after the extraction, or a mixture of these to prepare a dispersion liquid. The obtained dispersion liquid contains, as solid components, the positive electrode active material, positive electrode materials other than the positive electrode active material, a current collector tab, the current collector, and the like.

The positive electrode active material is not particularly limited and may be any material known as a positive electrode active material for lithium-ion secondary batteries. Examples of the positive electrode active material include ternary positive electrode materials such as LiCoO₂, LiNiO₂, and NCM (Li(Ni_xCo_yMn_z)O₂, (0<x<1, 0<y<1, 0<z<1, and x+y+z=1)), layered positive electrode active material particles such as LiVO₂ and LiCrO₂, spinel-type positive electrode active materials such as LiMn₂O₄, Li(Ni_0.25Mn_0.75)₂O₄, LiCoMnO₄, and Li₂NiMn₃O₈, olivine-type positive electrode active materials such as LiCoPO₄, LiMnPO₄, and LiFePO₄, and the like.

Pure water is used in the dissolution step S1 because natural water, tap water, and other sources contain, as minerals, alkali metals and alkaline earth metals such as sodium, potassium, calcium, and magnesium, which impair separation properties of the cation exchange membrane. Alkali metals and alkaline earth metals contaminate the recovered lithium.

In the dissolution step S1, since the dispersion liquid contains the solid electrolyte containing lithium, a pH of the dispersion liquid is 11 or more and 14 or less. To achieve a lithium recovery rate of 80% or higher, the dispersion liquid is required to contain at least 0.4 mol/L, preferably at least 0.7 mol/L of lithium dissolved therein.

“Separation Solution Recovery Process”

In the separation solution recovery step S2, the solid components contained in the dispersion liquid, such as the positive electrode active material, the positive electrode materials other than the positive electrode active material, the current collector tabs, and the current collectors, are filtered, separated, and removed to recover the separation solution. In this step, water-insoluble solid components of the lithium-ion secondary battery are removed. Examples of the water-insoluble solid components include positive electrode active materials, binders, conductive additives, tabs, electrodes, and the like.

The separation solution obtained in the separation solution recovery step S2 contains, for example, chlorine (Cl), bromine (Br), phosphorus (P), sulfur(S), aluminum (Al), nickel (Ni), copper (Cu), and the like.

“Oxidation Process”

In the oxidation step S3, the separation solution is oxidized to generate the acidic component in the separation solution, thereby adjusting the pH of the separation solution. In the oxidation step S3, the pH of the separation solution is adjusted. The pH of the separation solution is preferably 7 or more and 12 or less. The pH value is adjusted by leaving the separation solution in air, aerating (bubbling) the separation solution with air, aerating (bubbling) the separation solution with an oxidizing gas such as ozone, oxygen gas, or active oxygen gas, or by heating the separation solution. These treatments promote the reaction in which phosphorus (P) in the separation solution becomes PO₄ and the reaction in which sulfur(S) in the separation solution becomes S₂O₃ or SO₄, thereby adjusting the pH of the separation solution. Examples of the active oxygen gas include superoxides, hydroxyl radicals, and the like.

In the treatment of leaving the separation solution in air, for example, the separation solution is left to stand for 10 hours to 100 days.

In the treatment of aerating the separation solution with air, for example, the separation solution is aerated with air for 4 hours to 10 days.

In the treatment of aerating the separation solution with an oxidizing gas, for example, ozone is aerated into the separation solution for 2 hours to 5 hours.

In the treatment of heating the separation solution, for example, the separation solution is heated to a temperature of 40° C. or more to 90° C. or less.

This precipitates hydroxides of copper, nickel, aluminum, and the like.

The oxidation step S3 preferably includes a first oxidation step S4 and a second oxidation step S6.

“First Oxidation Process”

In the first oxidation step S4, the pH of the separation solution obtained in the separation solution recovery step S2 is adjusted to 7 to 12.

The pH of the separation solution is adjusted through the oxidation treatment by utilizing the fact that saturation solubilities of copper and nickel in the separation solution decrease to 10 mg/L in the pH range of 7 to 12, and thus the precipitation of hydroxides of copper, nickel, aluminum, and the like is promoted. The pH of the dispersion liquid immediately after the solid electrolyte has been dissolved reaches around 12, which is due to the dissolution of lithium ions in the lithium-ion secondary battery. Further, due to a sulfide reaction 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 separation solution can reach several hundred mg/L. For that reason, to stabilize an ionic state in the separation solution, the pH of the separation solution is desirably lowered to 10 or less. If the pH of the separation solution falls below 7, dissolved concentrations will increase because copper and nickel are soluble in acid.

The pH of the separation solution can be adjusted using an acidic liquid (such as sulfuric acid or hydrochloric acid), but this is burdensome because it involves the release of hydrogen sulfide, which is a harmful, flammable, and corrosive gas. Since large amounts of phosphorus and sulfur are eluted in the separation solution, it is desirable to oxidize these in the separation solution to bring the pH of the separation solution into a neutral range. For this reason, in the lithium recovery method of the present embodiment, the pH of the separation solution is adjusted without using an acidic liquid by leaving the separation solution in air, aerating (bubbling) the separation solution with air, aerating (bubbling) the separation solution with an oxidizing gas such as ozone, or heating the separation solution.

“Separation Process”

The lithium recovery method of the present embodiment may include a separation step S5. In the separation step S5, solid components (such as aluminum-containing compounds, nickel-containing compounds, and copper-containing compounds) are filtered, separated, and removed from the separation solution that has gone through the first oxidation step S4.

“Second Oxidation Process”

In the second oxidation step S6, the pH of the separation solution obtained in the first separation step S5 is adjusted to 6 to 8.

It is known that aluminum in the separation solution is amphoteric and dissolves in both acid and alkali solutions, but in the neutral pH range, aluminum hydroxide (Al(OH)₃) precipitates and functions as a flocculant. For that reason, to remove aluminum, adjusting the pH of the separation solution to 6-8 to promote the precipitation of aluminum hydroxide is effective. A method for adjusting the pH of the separation solution is the same as in the first oxidation step.

“Recovery Stock Solution Recovery Process”

In the recovery stock solution recovery step S7, solid-liquid separation is performed on the separation solution after the oxidation treatment to recover the recovery stock solution. In the recovery stock solution recovery step S7, solid components (such as aluminum-containing compounds, nickel-containing compounds, and copper-containing compounds) are filtered, separated, and removed from the separation solution that has gone through the oxidation step S3 (the first oxidation step S4 and the second oxidation step S6).

“Extraction Process”

In the extraction step S8, the lithium hydroxide aqueous solution is extracted from the recovery stock solution through the electrodialysis using the cation exchange membrane.

In the extraction step S8, examples of a material for the cation exchange membrane include sodium sulfonate and polyolefins. The lithium hydroxide aqueous solution reaches a pH of 12 or higher as concentration of lithium progresses, while the recovery stock solution serving as a recovery source undergoes strong oxidation to a pH of around 1 as reduction of lithium and oxidation of anionic components progresses, and thus the cation exchange membrane requires a wide pH resistance range.

According to the electrodialysis using the cation exchange membrane, lithium ions contained in the recovery stock solution permeate the cation exchange membrane, and on the permeated side, the lithium ions react with water to form lithium hydroxide. That is, the lithium hydroxide aqueous solution is produced on the permeated side of the cation exchange membrane. As an electrodialysis method, for example, a method of setting constant current processing at 0.3 A and stopping the process when a voltage across electrodes reaches a membrane's withstand voltage limit, which is a trigger can be exemplified. Also, as an electrodialysis method, for example, a method of setting a voltage to be equal to or lower than a membrane's withstand voltage or less for constant voltage processing and stopping the process when a current value becomes a certain value or less can be exemplified.

In the extraction step S8, copper (Cu), nickel (Ni), aluminum (Al), phosphate ions (PO₄³⁻), and the like do not permeate the cation exchange membrane if their concentrations in the recovery stock solution are less than several tens of ppm or less. Chlorine (Cl), bromine (Br), sulfate ions (SO₄²⁻), and the like hardly permeate the cation exchange membrane. For that reason, in the extraction step S8, these substances are separated from lithium.

“Ion Exchange Process”

The lithium recovery method of the present embodiment may also include an ion exchange step S9. In the ion exchange step S9, the lithium hydroxide aqueous solution obtained in the extraction step S8 is brought into contact with an anion exchange resin to remove trace amounts (on the order of ppm) of impurity anions such as chlorine (Cl), bromine (Br), and sulfate ions (SO₄²⁻) contained in the lithium hydroxide aqueous solution.

In the ion exchange step S9, the temperature at which the lithium hydroxide aqueous solution is brought into contact with the anion exchange resin is preferably 10° C. or higher and 40° C. or lower.

Through the above steps, a high-purity lithium hydroxide aqueous solution can be obtained.

According to the lithium recovery method of the present embodiment, lithium can be recovered solely from the solid electrolyte aqueous solution through the electrodialysis using the cation exchange membrane, without the need to add a preparation to adjust the pH.

[Lithium Recovery Device]

A lithium recovery device according to one embodiment of the present invention is a device that recovers lithium from a used lithium-ion secondary battery.

FIG. 2 is a cross-sectional view schematically showing the lithium recovery device of the present embodiment.

A lithium recovery device 1 includes a treatment tank 10, a cation exchange membrane 20, a first electrode 30, a second electrode 40, and a power supply 50.

The treatment tank 10 has a first space 11 and a second space 12, which are separated by the cation exchange membrane 20 provided in the treatment tank 10. An inner surface of the treatment tank 10 in the first space 11, which faces the cation exchange membrane 20 at a distance, is one main surface 10a of the treatment tank 10. An inner surface of the treatment tank 10 in the second space 12, which faces the cation exchange membrane 20 at a distance, is the other main surface 10b of the treatment tank 10.

The treatment tank 10 is a tank for treating the dispersion liquid obtained by dispersing a water-soluble solid electrolyte contained in the treatment target member of the deactivated lithium-ion secondary battery in pure water through electrodialysis.

The cation exchange membrane 20 is disposed in a central portion of the treatment tank 10 in a height direction of the treatment tank 10 to separate the first space 11 and the second space 12 of the treatment tank 10 from each other.

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.

The first electrode 30 is disposed on the one main surface 10a side of the treatment tank 10 in the first space 11.

The second electrode 40 is disposed on the other main surface 10b side of the treatment tank 10 in the second space 12.

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

A lithium recovery method using the lithium recovery device 1 of the present embodiment will be described.

A separation solution that has gone through the dissolution step S1, the separation solution recovery step S2, the oxidation step S3, and the recovery stock solution recovery step S7 of the lithium recovery method in the above-described embodiment is prepared.

In the lithium recovery device 1 of the present embodiment, the extraction step S8 of the lithium recovery method in the above-described embodiment is performed.

The separation solution is injected into the first space 11 of the treatment tank 10, and a dilute lithium hydroxide aqueous solution is injected into the second space 12 of the treatment tank 10 as a recovery solution to ensure conductivity.

In this state, when a voltage is applied to the first electrode 30 and the second electrode 40 from the power supply 50, electrodialysis begins, and lithium ions contained in the separation solution in the first space 11 permeate the cation exchange membrane and move to the recovery 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. That is, a lithium hydroxide aqueous solution is produced in the second space 12. Also, since trace amounts (on the order of ppm) of chlorine (Cl), bromine (Br), and sulfate ions (SO₄²⁻) permeate the cation exchange membrane, the lithium hydroxide aqueous solution contains the trace amounts (on the order of ppm) of chlorine (Cl), bromine (Br), and sulfate ions (SO₄²⁻).

According to the lithium recovery device of the present embodiment, lithium can be recovered solely from the solid electrolyte aqueous solution through the electrodialysis using the cation exchange membrane without adding a preparation to adjust the pH.

Although the 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 present invention described in the claims.

EXAMPLES

The present invention will be further specifically described below with reference to examples, but the present invention is not limited to the following examples.

Experimental Example 1

A pH of a LiOH·H₂O solution and saturation solubilities of copper and nickel in the LiOH·H₂O solution were measured. LiOH·H₂O powder was dissolved in pure water, and 0.5 g of copper hydroxide or nickel hydroxide was added to 25 mL of the solution with a controlled pH, followed by stirring. Then, after 12 hours or more, the solution was filtered through a 0.45 μm filter, and concentrations of copper and nickel in the solution were analyzed using inductively coupled plasma spectroscopy (ICP). The results are shown in FIG. 3.

From the results shown in FIG. 3, it has been found that copper and nickel have low solubility in alkaline solutions, and the saturation solubilities of copper and nickel in the LiOH·H₂O solution decreases to 10 mg/L in the pH range of 7 to 12, resulting in precipitation of copper hydroxide and nickel hydroxide.

In addition, it is known that aluminum is amphoteric and dissolves well in both acid and alkali solutions, but aluminum hydroxide precipitates in the pH range of 6 to 8 and functions as a flocculant.

From the above, by adjusting the pH of the LiOH·H₂O solution and performing solid-liquid separation on the LiOH·H₂O solution, metal components such as copper and nickel contained in the LiOH·H₂O solution can be removed.

Example 1

A pH of a sulfide solid electrolyte solution was adjusted by leaving the sulfide solid electrolyte solution in air, aerating the sulfide solid electrolyte solution with air, aerating the sulfide solid electrolyte solution with ozone, or heating the sulfide solid electrolyte solution to 80° C. The results are shown in FIG. 4.

From the results shown in FIG. 4, it has been found that heating the sulfide solid electrolyte solution to 80° C. causes a rapid change in the pH of the sulfide solid electrolyte solution. It has been also found that the change in the pH of the solution becomes more gradual in the order of heating the sulfide solid electrolyte solution to 80° C., aerating sulfide solid electrolyte solution with ozone, aerating sulfide solid electrolyte solution with air, and leaving sulfide solid electrolyte solution in air.

Example 2

After deactivating a used lithium-ion secondary battery, treatment target members of the deactivated lithium-ion secondary battery were stirred in pure water to dissolve a positive electrode active material and lithium compounds contained in the treatment target members in pure water, thereby preparing a dispersion liquid.

The obtained dispersion liquid was left at room temperature (25° C.) in air. Table 1 shows the results of inductively coupled plasma (ICP) analysis of the dispersion liquid 3 days after the start of leaving the dispersion liquid, and the pH measurement results of the dispersion liquid. Further, Table 1 shows the results of inductively coupled plasma (ICP) analysis of the dispersion liquid two months after the start of leaving the dispersion liquid, and the pH measurement results of the dispersion liquid.

For the analysis of aluminum in the dispersion liquid, an ICP atomic emission spectrometer ICP-8100 (manufactured by Shimadzu Corporation) was used. For the analysis of copper and nickel, an ICP mass spectrometer 7700x (manufactured by Agilent Technologies) was used.

For measuring the pH of the dispersion liquid, a LAQUA-PH-SE (manufactured by Horiba, Ltd.) was used.

	TABLE 1
	ICP analysis results [mg/L]

Element	Al	Cu	Ni	pH

Three days after start of	75	19	12	12.1
leaving
Two months after start of	1.7	1.4	0.55	9.5
leaving

It has been found that, in the dispersion liquid, as time passes, the oxidation of hydrogen sulfide ions (HS⁻) proceeds slowly, generating sulfate ions (SO₄²⁻), and the oxidation of the dispersion liquid itself progresses, causing the separation solution to become neutralized. When the separation solution is neutralized, hydroxides of multivalent metals having low solubilities precipitate, and an amount of dissolved multivalent metals in the separation solution decreases.

While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.

The present invention has the following aspects.

[1] A lithium recovery method from a used lithium-ion secondary battery including an electrode body having a positive electrode, a sulfide solid electrolyte, and a negative electrode, the method including: dissolving a solid electrolyte and a lithium compound contained in a deactivated lithium-ion secondary battery in pure water to obtain a dispersion liquid; recovering a separation solution by performing solid-liquid separation on the dispersion liquid; performing an oxidation treatment on the separation solution to generate an acidic component in the separation solution and adjusting a pH of the separation solution; recovering a recovery stock solution by performing solid-liquid separation on the separation solution after the oxidation treatment; and extracting a lithium hydroxide aqueous solution from the recovery stock solution through electrodialysis using a cation exchange membrane.

According to the above aspect, by performing the oxidation treatment on the separation solution to generate the acidic component in the separation solution and adjusting the pH of the separation solution, the inclusion of impurity metals is reduced while the generation of hydrogen sulfide is inhibited, and thus lithium can be recovered from a solid electrolyte secondary battery that uses lithium as a charge carrier and includes the sulfide solid electrolyte.

[2] The lithium recovery method according to [1], wherein the oxidation treatment includes a first oxidation of adjusting the pH of the separation solution to 7 to 12, and a second oxidation of adjusting the pH of the separation solution to 6 to 8.

According to the above aspect, by adjusting the pH of the separation solution through the oxidation treatment by utilizing the fact that saturation solubilities of copper and nickel in the separation solution decrease to 10 mg/L in the pH range of 7 to 12, the precipitation of hydroxides of copper, nickel, aluminum, and the like can be promoted. In addition, the pH of the separation solution can be adjusted to 6 to 8, thereby promoting the precipitation of aluminum hydroxide to remove aluminum.

[3] The lithium recovery method according to [1] or [2], wherein the oxidation treatment includes any of leaving the separation solution in air, aerating the separation solution with air or an oxidizing gas, and heating the separation solution.

According to the above aspect, the pH of the separation solution can be adjusted without releasing hydrogen sulfide.

[4] The lithium recovery method according to any one of [1] to [3] further including removing impurity anions from the lithium hydroxide aqueous solution using an anion exchange resin.

According to the above aspect, by bringing the lithium hydroxide aqueous solution into contact with the anion exchange resin, trace amounts (on the order of ppm) of chlorine (Cl), bromine (Br), sulfate ions (SO₄²⁻), and the like contained in the lithium hydroxide aqueous solution can be removed.