SELECTIVE RECOVERY DEVICE FOR LITHIUM USING FLOW ELECTRODE CAPACITIVE DEIONIZATION AND METHOD FOR SEPARATING AND RECOVERING LITHIUM USING THE SAME

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and the benefit of Korean Patent Application No. 10-2024-0121087, filed on Sep. 5, 2024, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a selective lithium recovery device using flow electrode capacitive deionization and a method for separating and recovering lithium using the same, and more specifically to a selective lithium recovery device using flow electrode capacitive deionization, which has very high selectivity for lithium ions and low energy consumption, and a method for separating and recovering lithium using the same.

Meanwhile, it is disclosed that the present disclosure was invented with the support of the following national research and development projects.

• • [National Research and Development Project 1 That Supported This Invention]
  • [Project Identification Number]1711189842
  • [Project Number]2021R1A2C1092184
  • [Name of Ministry] Ministry of Science and ICT
  • [Name of Project Management (Specialized) Institution] National Research Foundation of Korea
  • [Title of Research Project] Individual Basic Research (Ministry of Science and ICT)
  • [Title of Research Task] Continuous Seawater Desalination and Seawater Power Generation Material/Process Development Based on Flow electrode
  • [Contribution Ratio] 75/100 [Name of Task Performance Institution] Soonchunhyang University Industry-Academic Cooperation Foundation
  • [Research Period] Mar. 1, 2024 to Feb. 29, 2025
  • [National Research and Development Project 2 That Supported This Invention]
  • [Project Identification Number]1345370812
  • [Project Number]2021RIS-004
  • [Name of Ministry] Ministry of Education
  • [Name of Project Management (Specialized) Institution] National Research Foundation of Korea
  • [Title of Research Project] Local Government-University Cooperation-Based Regional Innovation Project
  • [Title of Research Task](Daejeon-Sejong-Chungnam Regional Innovation Platform) Chungnam National University
  • [Contribution Ratio]25/100
  • [Name of Task Performance Institution](Daejeon-Sejong-Chungnam Regional Innovation Platform) Chungnam National University
  • [Research Period] Mar. 1, 2024 to Feb. 28, 2025

RELATED ART

The usage amount of lithium (Li) is increasing worldwide in various fields such as batteries, ceramics, glass and lubricants. In particular, due to its excellent electrochemical properties, the usage amount thereof is skyrocketing in secondary battery applications such as portable electronic devices, electric vehicles (EVs) and large-scale energy storage systems (ESS) integrated with renewable energy sources.

About 35% of lithium is extracted from hard rock minerals, and about 65% is extracted from brine. Despite the steady increase in lithium supply, lithium shortages are expected in the future commodity market due to the significant increase in demand. Two potential solutions have been proposed to address this issue, and one is to extract the approximately 230 billion tons of lithium contained in the ocean, and the other one is to recycle lithium ions from waste batteries (especially lithium-ion batteries (LIBs)). Among these, the method of recovering lithium from waste batteries has the advantage of reducing the need for new resources and protecting the environment from pollution caused by batteries.

Various approaches such as solvent extraction, chemical precipitation and electrochemical processes have been proposed as methods for recovering lithium from spent batteries. However, most of these methods have the disadvantages of being time-consuming and expensive, consuming large amounts of energy, requiring additional chemicals, and requiring complex procedures. In addition, separating specific substances such as lithium from a mixture of various substances is considered as an important challenge in both lithium recycling and production.

Capacitive deionization (CDI) based on the reversible ion adsorption and desorption mechanism has been widely studied for lithium recovery due to its various advantages such as low energy consumption, eco-friendly process, simple cell configuration, and operating procedure. However, capacitive deionization technology also has problems, namely, low ion removal capacity and the need for a discharge step.

In order to solve this problem, flow-electrode capacitive deionization (FCDI) technology, which replaces the conventional solid electrode with a flow electrode, is gaining attention. This technology has greatly improved the efficiency of ion recovery by introducing a recirculation function to enable a continuous process. However, in the case of recovering lithium using the conventional FCDI method, the lithium selectivity, lithium recovery rate and recovery efficiency were still low, it was difficult to separate lithium from a mixture containing various ions, and there were problems of high energy consumption.

SUMMARY

The problems to be solved by the present disclosure are to provide a selective lithium recovery device and a method for separating and recovering lithium, which have a very high selectivity for lithium ions (Li⁺) and can selectively separate lithium ions (Li⁺) from a mixture including various ions, and have a very excellent lithium recovery rate and lithium recovery efficiency such that the lithium recovery time and cost are reduced, the energy consumption is low, and lithium ions (Li⁺) can be recovered from the waste liquid of a waste battery, and thus, it is environmentally friendly, and lithium can be recovered not only through waste liquid treatment but also through desalination treatment and wastewater treatment.

The problems to be solved by the present disclosure are not limited to the problems mentioned above, and other problems that are not mentioned will be clearly understood by a person having ordinary knowledge in the technical field to which the present disclosure pertains from the description below.

In order to solve the above-described problems, provided is a selective lithium recovery device using flow electrode capacitive deionization with enhanced selectivity for lithium ions (Li⁺), the selective recovery device including a selective ion recovery cell, including an electrolyte chamber in which an electrolyte solution containing lithium ions (Li⁺) and polyvalent cations is supplied; an anode and a cathode arranged with the electrolyte chamber therebetween; a cation exchange membrane (CEM) arranged between the electrolyte chamber and the anode; and an anion exchange membrane (AEM) arranged between the electrolyte chamber and the cathode, wherein the anode is a flow electrode and includes a current collector for anode and an anode active material, wherein the cathode is a flow electrode and includes a current collector for cathode and a cathode active material, and wherein at least one of the cation exchange membrane and the anion exchange membrane is bonded with a polymer thin film layer.

In addition, the above-described polyvalent cations may include cobalt ions (Co²⁺) and/or nickel ions (Ni²⁺).

In addition, the polymer thin film layer may be composed of multiple layers, the multilayer polymer thin film layer may be composed of a first polymer electrolyte layer and a second polymer electrolyte layer that are alternately laminated, and the first polymer electrolyte layer and the second polymer electrolyte layer may be configured to have opposite polarities.

In addition, the multilayer polymer thin film layer may be bonded to the cation exchange membrane and be arranged between the cation exchange membrane and the electrolyte chamber, the first polymer electrolyte layer may be configured to have a positive charge, and the second polymer electrolyte layer may be configured to have a negative charge.

In addition, the above-described first polymer electrolyte layer may include poly(allylamine hydrochloride) (PAH), and the above-described second polymer electrolyte layer may include poly(styrene sulfonate) (PSS).

In addition, the above-described multilayer polymer thin film layer may have the first polymer electrolyte layer formed on the outermost surface of surfaces bonded to the cation exchange membrane.

In addition, the above-described multilayer polymer thin film layer may be 3 to 8 layers.

In addition, the anode active material may be disposed between the anode current collector and the cation exchange membrane, the cathode active material may be disposed between the cathode current collector and the anion exchange membrane, and the anode active material and the cathode active material may be porous activated carbon solutions.

Additionally, in the above-described selective recovery device, the ion selectivity

( ρ D Li + )

value for lithium ions (Li+) calculated by Formula 1 below may be 10 or more:

ρ D Li + = ( C Li + 0 - C Li + C Li + 0 ) / ( C D 0 - C D C D 0 ) < Formula ⁢ 1 >

wherein in Formula 1,

C Li + 0 ⁢ and ⁢ C D 0

are an initial lithium ion (Li⁺) concentration and a polyvalent cation concentration in an influent, respectively, and C_Li+ and C_D are a lithium ion (Li⁺) concentration and a polyvalent cation concentration in treated water subjected to selective ion separation, respectively.

In order to solve the above-described problems, provided is a method for separating and recovering lithium, by introducing an electrolyte solution containing lithium ions (Li⁺) and polyvalent cations into an electrolyte chamber of the selective recovery device of claim 1 and applying a voltage.

According to an embodiment of the present disclosure the voltage may be 0.2 to 0.8 V and the pH of the above-described electrolyte solution may be 4 to 7, or the voltage may be 0.8 to 1.6 V and the pH of the above-described electrolyte solution may be 1 to 4.

Furthermore, the flow rate of the electrolyte solution may be 1.2 mL/min or more, and the initial ion concentration of lithium in the electrolyte solution may be 5 mM or more.

The selective lithium recovery device and the method for separating and recovering lithium according to the present disclosure have a very high selectivity for lithium ions (Li⁺) such that lithium ions (Li⁺) can be selectively separated from a mixture including various ions, and the lithium recovery rate and lithium recovery efficiency are very excellent such that the lithium recovery time and cost are reduced, and the energy consumption is low. In addition, the device and method can recover lithium ions (Li⁺) from the waste liquid of a waste battery, and thus, they are environmentally friendly, and lithium can be recovered not only through waste liquid treatment of a waste battery, but also through desalination treatment and wastewater treatment.

The effects of the present disclosure are not limited to the above effects, and should be understood to include all effects that can be inferred from the constitutions of the invention described in the detailed description or claims of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a selective lithium recovery device according to a preferred embodiment of the present disclosure.

FIG. 2 is a result of measuring the contact angle after coating each layer when forming a multilayer polymer thin film layer according to the present disclosure.

FIG. 3A is a result of measuring X-ray photoelectron spectroscopy (XPS) for a cation exchange membrane (f-CEM: functionalized cation exchange membrane) having a polymer thin film layer combined according to the present disclosure and a cation exchange membrane (P-CEM: pristine cation exchange membrane) having no polymer thin film layer combined, FIG. 3B is a result of enlarging the N is peak portion in the XPS graph for P-CEM, and FIG. 3C is a result of enlarging the N is peak portion in the XPS graph for f-CEM.

FIG. 4A is an enlarged result of the S 2p peak portion in the XPS graph for P-CEM, and FIG. 4B is an enlarged result of the S 2p peak portion in the XPS graph for f-CEM.

FIG. 5 is a graph showing the ion recovery rate and lithium selectivity measured when the selective lithium recovery device using P-CEM or f-CEM is operated under various operating conditions.

FIG. 6 is a graph showing the current (FIG. 6A) and conductivity change (FIG. 6B; Cout/Cin) over time when the selective lithium recovery device using f-CEM is operated under various operating conditions.

FIG. 7 is a graph showing the ion recovery rates of cobalt, nickel and lithium measured when the selective lithium recovery device using P-CEM or f-CEM is operated under conditions where the applied voltage is 1.2 V and the pH of the electrolyte solution is 6.

FIG. 8 shows the results of the change (FIG. 8A) in current and conductivity (FIG. 8B) over time when the selective lithium recovery device using f-CEM is operated under the conditions of the applied voltage of 1.2 V and the pH of the electrolyte solution of 6.

FIG. 9 shows photographs of the sediment according to the operating time (operation time of FIG. 9A: 30 minutes, operation time of FIG. 9B: 1 hour, operation time of FIG. 9C: 3 hours) when the selective lithium recovery device using f-CEM is operated under the conditions of the applied voltage of 1.2 V and the pH of the electrolyte solution of 6.

FIG. 10A shows the results of the measurement of the ion recovery rate and lithium selectivity according to the number of layers of the polymer thin film layer coupled to the f-CEM of the selective lithium recovery device. In addition, FIG. 10B shows the current measurement value over time according to the number of layers of the polymer thin film layer coupled to the f-CEM of the selective lithium recovery device.

FIG. 11A is a result of lithium selectivity and ion recovery efficiency according to the flow rate of the electrolyte solution when the lithium selective recovery device according to a preferred embodiment of the present disclosure is operated. In addition, FIG. 11B is a result of lithium selectivity measurement according to the initial ion concentration of the electrolyte solution when the lithium selective recovery device using P-CEM or f-CEM is operated. In addition, FIG. 11C is a result of measuring ion recovery rate and lithium selectivity when the lithium selective recovery device using P-CEM or f-CEM is operated.

FIG. 12 is a result of measuring total ion recovery rate according to the initial ion concentration of the electrolyte solution when the lithium selective recovery device using P-CEM or f-CEM is operated under the conditions of an applied voltage of 0.4 V and a pH of the electrolyte solution of 6.

FIG. 13 shows the results of analysis by electrochemical impedance spectroscopy (EIS) for various electrolyte solutions when a selective lithium recovery device using P-CEM (FIG. 13A) or f-CEM (FIG. 13B) is operated under the conditions of an applied voltage of 0.4 V and a pH of 6 of the electrolyte solution.

FIG. 14 shows a circuit configuration for electrochemical impedance spectroscopy (EIS) analysis of a selective lithium recovery device using P-CEM or f-CEM.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, with reference to the attached drawings, embodiments of the present disclosure will be described in detail so that those skilled in the art can easily practice the present disclosure. The present disclosure may be implemented in various different forms and is not limited to the embodiments described herein. In the drawings, parts that are not related to the description are omitted in order to clearly describe the present disclosure, and the same reference numerals are added to the same or similar components throughout the specification.

The terms used in the present specification are used only to describe specific embodiments and are not intended to limit the present disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In the present application, the terms “include” or “have” are intended to specify the presence of features, numbers, steps, operations, components or combinations thereof described in the specification, but should be understood to not preclude the presence or addition of one or more other features, numbers, steps, operations, components or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present disclosure pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant technology, and shall not be interpreted in an ideal or overly formal sense unless explicitly defined in the present application.

As described above, the amount of waste batteries such as lithium-ion batteries is increasing, and environmental pollution is worsening due to the increasing amount of waste batteries, and thus, attempts have been made to recycle waste batteries using flow-electrode capacitive deionization (FCDI). However, when using conventional FCDI technology to prevent environmental pollution caused by waste batteries and recover lithium, the ion selectivity for lithium (lithium selectivity), the ion recovery rate (IRR: Ion Recovery Rate) and the recovery efficiency (Recovery Efficiency) were low, it was difficult to separate lithium from a mixture containing various ions, and there was a problem of high energy consumption.

Accordingly, the present disclosure attempted to solve the above-described problems by providing a selective recovery device 10 for lithium using flow electrode capacitive deionization with enhanced selectivity for lithium ions (Li), the selective recovery device including a selective ion recovery cell 100, including an electrolyte chamber 110 in which an electrolyte solution containing lithium ions (Li) and polyvalent cations is supplied; an anode 120 and a cathode 130 arranged with the electrolyte chamber 110 therebetween; a cation exchange membrane (CEM) 140 arranged between the electrolyte chamber 110 and the anode 120; and an anion exchange membrane (AEM) 150 arranged between the electrolyte chamber 110 and the cathode 130, wherein the anode is a flow electrode and includes a current collector for anode and an anode active material, wherein the cathode is a flow electrode and includes a current collector for cathode and a cathode active material, and wherein at least one of the cation exchange membrane 140 and the anion exchange membrane 150 is bonded with a polymer thin film layer 160.

Through such a device, the amount of waste batteries (particularly, lithium-ion batteries) can be reduced to prevent environmental pollution, lithium selectivity can be increased to selectively separate lithium ions (Li⁺) from a mixture including various ions, and energy consumption can be reduced in lithium separation and recovery. In addition, the lithium recovery rate and lithium recovery efficiency can be increased to reduce the lithium recovery time and cost.

Hereinafter, a schematic diagram of the selective lithium recovery device in FIG. 1 will be described.

First of all, the lithium selective recovery device 10 according to the present disclosure includes a selective ion recovery cell 100 including an electrolyte chamber 110 in which an electrolyte solution containing lithium ions (Li⁺) and polyvalent cations is supplied, an anode 120 and a cathode 130 arranged with the electrolyte chamber 110 therebetween, a cation exchange membrane (CEM) 140 arranged between the electrolyte chamber 110 and the cathode 120, and an anion exchange membrane (AEM) (150) arranged between the electrolyte chamber 110 and the anode 130.

In addition, the selective ion recovery cell (100) of the present disclosure has an ion selectivity that is capable of selectively separating and recovering only lithium ions among different types of ions. To this end, the present disclosure is an invention that maximizes ion separation and recovery for lithium ions by introducing a polymer thin film layer 160 to the ion exchange membranes 140, 150.

The electrolyte chamber 110 into which the electrolyte solution containing lithium ions and polyvalent cations according to the present disclosure is supplied will be described.

The electrolyte solution is a solution including various ions in a solvent, and may be seawater, wastewater or waste liquid of a waste battery, but is not limited thereto. Preferably, the above-described electrolyte solution described may be waste liquid of a waste battery. More preferably, the above-described electrolyte solution may be waste liquid of a lithium-ion battery, and most preferably, it may be waste liquid of a NCM (Lithium nickel manganese cobalt oxides) ternary lithium-ion battery. The electrolyte solution may be introduced into the electrolyte chamber 110 when the selective recovery device 10 of lithium according to the present disclosure is operated.

The above-described electrolyte solution contains polyvalent cations, and the types of polyvalent cations included in the solution may be single or multiple, and herein, the polyvalent cations refer to ions having two or more positive charges, for example, divalent cations, trivalent cations, and tetravalent cations. Specifically, as divalent cations, Co²⁺, Ni²⁺, Ca²⁺, Cu²⁺, Cd²⁺ Fe²⁺, Mn²⁺ and the like may be included, as trivalent cations, Al³⁺ and the like may be included, and as tetravalent cations, Si⁴⁺ and the like may be included. Preferably, the above-described polyvalent cation may be a divalent cation, and more preferably, it may be a cobalt ion (Co²⁺) and/or a nickel ion (Ni²⁺). Meanwhile, since cobalt ions (Co²⁺) and nickel ions (Ni²⁺) have similar physical and chemical properties in the ion recovery process, they may show similarity in the ion recovery behavior.

The initial ion concentration of lithium included in the above-described electrolyte solution is not limited as long as it is a concentration capable of recovering lithium ions, but may be preferably 5 mM or more, and more preferably 5 mM to 1 M.

The concentration of each of the polyvalent cations among the single or multiple polyvalent cations included in the above-described electrolyte solution may be a concentration generally included in the waste liquid of a used battery, but preferably, the concentration of each polyvalent cation may be 1 mM to 10 M.

Since the solvent of the above-described electrolyte solution may be used without limitation if it is a solvent commonly used in the art to dissolve an electrolyte, the present disclosure does not specifically limit the same. Preferably, the above-described solvent may be water.

Meanwhile, the pH (hydrogen ion concentration index) of the above-described electrolyte solution may be neutral or acidic. Specifically, the pH may be 7 or less, and preferably 1 to 7. The appropriate pH of the above-described electrolyte solution may vary depending on the applied voltage of the selective lithium recovery device, which will be described below.

In addition, the above-described electrolyte chamber 110 may be applied without limitation if it is an electrolyte chamber that can be commonly used in the art.

Preferably, when the anode 120 and the cathode 130 are arranged, the space therebetween may be an electrolyte chamber 110. More preferably, the electrolyte chamber 110 may be a spacer, and even more preferably, it may be a spacer manufactured by using a polyester resin.

The above-described electrolyte chamber 110 is arranged between the anode 120 and the cathode 130, and through this, specific ions may be separated and recovered.

The width of the above-described electrolyte chamber 110 may be applied without limitation as long as it is a width that can be commonly applied in the relevant industry, but may preferably be 0.1 to 1 mm.

The above-described anode 120 is a flow electrode and includes a current collector for anode 121 and an anode active material 122. In addition, any configuration that can be commonly used in the art may be included in the anode 120.

The thickness of the above-described anode 120 may be applied without limitation as long as it is a thickness that can be commonly applied in the art, but preferably, it may be 5 to 50 mm.

The above-described current collector for anode 121 may use a general anode current collector material that can be used in the art, and for example, an anode current collector manufactured using at least one selected from carbon-based materials such as graphite, activated carbon, carbon nanotubes or graphene, redox active materials (organic or inorganic materials), titanium and copper may be applied. Preferably, the current collector for anode 121 of the present disclosure may be an anode current collector manufactured using graphite (graphite-based negative electrode current collector).

The thickness of the above-described current collector for anode 121 may be applied without limitation as long as it is a thickness that can be commonly applied in the relevant industry, but preferably, it may be 1 to 10 mm.

The above-described anode active material 122 may be an anolyte. The above-described anolyte may be an anolyte that can be commonly used in the relevant industry, but preferably, it may be an anolyte that includes at least one selected from porous activated carbon, Prussian blue, organic compounds and inorganic compounds, and most preferably, it may be a porous activated carbon anolyte.

The above-described porous activated carbon anolyte may be a slurry solution in which porous activated carbon and water are mixed. In this case, water may correspond to a solvent, and the porous activated carbon may be mixed in the solution at 10 to 30 wt % based on the total weight of the solution.

Meanwhile, the above-described anode active material 122 may be supplied to an anode flow electrode chamber and included in the anode 120.

The shape of the above-described anode flow electrode chamber may be applied without limitation as long as it is a shape that can be commonly used as a chamber in the art, but preferably, it may be a channel engraved on the surface of the above-described current collector for anode 121.

If the shape of the above-described anode flow electrode chamber is a channel engraved on the surface of the above-described current collector for anode 121, the width and depth of the channel may be applied without limitation as long as it is a thickness that can be commonly applied in the art, but preferably, the width of the channel may be 0.1 to 10 mm, and the depth may be 0.1 to 3 mm.

In addition, the above-described anode active material 122 may be placed between the current collector for anode 121 and the cation exchange membrane 140.

The above-described cathode 130 is a flow electrode and includes a current collector for cathode 131 and a cathode active material 132. In addition, any configuration that can be commonly used in the art may be included in the cathode 130.

The thickness of the above-described cathode 130 may be applied without limitation as long as it is a thickness that can be commonly applied in the art, but preferably, it may be 5 to 50 mm.

The above-described current collector for cathode 131 may use a general positive electrode current collector material that can be used in the art, and for example, a cathode current collector manufactured using at least one selected from carbon-based materials such as graphite, activated carbon, carbon nanotubes or graphene, redox active materials (organic or inorganic materials), titanium and copper may be applied. Preferably, the current collector for cathode 131 of the present disclosure may be a cathode current collector manufactured using graphite (graphite-based positive electrode current collector).

The thickness of the above-described current collector for cathode 131 may be applied without limitation as long as it is a thickness that can be commonly applied in the art, but preferably, it may be 1 to 10 mm.

The above-described cathode active material 132 may be a catholyte. The catholyte may be a catholyte that can be commonly used in the art, but preferably, it may be a catholyte including at least one selected from porous activated carbon, Prussian blue, organic compounds and inorganic compounds, and most preferably, it may be a porous activated carbon catholyte.

The porous activated carbon catholyte described above may be a slurry solution in which porous activated carbon and water are mixed. In this case, water may correspond to a solvent, and the porous activated carbon may be mixed in the solution at 10 to 30 wt % based on the total weight of the solution.

Meanwhile, the above-described cathode active material 132 may be supplied to a cathode flow electrode chamber and included in the cathode 130.

The shape of the above-described cathode flow electrode chamber may be applied without limitation as long as it is a shape that can be commonly used as a chamber in the art, but preferably, it may be a channel engraved on the surface of the above-described current collector for cathode 131.

If the shape of the above-described cathode flow electrode chamber is a channel engraved on the surface of the above-described current collector for cathode 131, the width and depth of the channel may be applied without limitation as long as it is a thickness that can be commonly applied in the art, but preferably, the width of the channel may be 0.1 to 10 mm, and the depth may be 0.1 to 3 mm.

In addition, the above-described cathode active material 132 may be arranged between the current collector for cathode 131 and the anion exchange membrane 150.

The following describes the ion exchange membranes 140, 150.

The selective recovery device 10 of lithium according to the present disclosure includes a cation exchange membrane (CEM) 140, and the cation exchange membrane 140 may be placed between the electrolyte chamber 110 and the anode 120.

The above-described cation exchange membrane 140 may be used without limitation as long as it is commonly used in the art, and thus, the present disclosure does not specifically limit the same. Preferably, it may be a strong acid cation exchange membrane and a weak acid cation exchange membrane, more preferably, it may be a strong acid cation exchange membrane, and most preferably, it may be a strong acid cation exchange membrane having a sulfonic acid group as a functional group.

The thickness of the above-described cation exchange membrane 140 may be a thickness that can be commonly used, but it may be preferably 5 to 500 μm.

In addition, the selective recovery device 10 for lithium according to the present disclosure includes an anion exchange membrane (AEM) 150, and the anion exchange membrane 150 may be placed between the electrolyte chamber 110 and the cathode 130.

Since the above-described anion exchange membrane 150 may be used without limitation as long as it is commonly used in the art, the present disclosure does not specifically limit the same. Preferably, it may be a strong basic anion exchange membrane or a weak basic anion exchange membrane.

The thickness of the above-described anion exchange membrane 150 may be a thickness that can be commonly used, but it may preferably be 5 to 500 μm.

A polymer thin film layer 160 is bonded to at least one of the cation exchange membrane 140 and the anion exchange membrane 150 included in the lithium selective recovery device 10 according to one embodiment of the present disclosure. Hereinafter, the polymer thin film layer 160 will be described in detail with reference to FIGS. 2 to 4.

The above-described polymer thin film layer 160 may be bonded to an ion exchange membrane (a cation exchange membrane 140 or an anion exchange membrane 150) to increase lithium selectivity. Particularly, in the case of the cation exchange membrane 140, the negatively charged functional group, such as —SO^3- or —CO^3-, of the material included in the cation exchange membrane 140 has a greater affinity for polyvalent cations than lithium ions such that polyvalent cations can be recovered more than lithium ions, and accordingly, if the polymer thin film layer 160 is not bonded to the cation exchange membrane 140, the lithium selectivity described below may be low.

Referring to FIG. 2, the above-described polymer thin film layer 160 may be formed of multiple layers, and the above-described multilayer polymer thin film layer 160 may be formed by alternately laminating a first polymer electrolyte layer and a second polymer electrolyte layer. As the number of times the polymer thin film layers 160 are laminated increases, the lithium selectivity may be improved. When the polymer thin film layer 160 formed by alternately laminating the first polymer electrolyte layer and the second polymer electrolyte layer is defined as one layer, in the present disclosure, the first polymer electrolyte layer further formed at the outermost may be expressed as 0.5 layers.

Referring to FIG. 10, the above-described multilayer polymer thin film layer 160 may have 3 or more layers, and preferably 3 to 8 or more layers. More preferably, it may have 3.5 to 7.5 layers. If the multilayer polymer thin film layer 160 has less than 3 layers, there may be a problem in that the lithium selectivity is too low. If it exceeds 8 layers, the lithium selectivity is excellent, but there may be a problem in that the ion recovery efficiency or ion recovery rate is low due to the thick film thickness that acts as a physical barrier to ion recovery. Therefore, it is preferable to form the multilayer within the above range. In addition, if the number of layers of the multilayer polymer thin film layer 160 is 3.5, 4.5, 5.5, 6.5 or 7.5 layers, that is, 3.5 to 7.5 layers, and the first polymer electrolyte layer is positively charged, the first polymer electrolyte layer having a positive charge is located at the outermost layer, and thus, the polyvalent cation has a greater electrical repulsion than the lithium ion, and thus, the lithium selectivity may be higher.

In addition, the thickness of the first layer of the above-described polymer thin film layer 160 may be 5 to 50 nm, and the total thickness may be 15 to 400 nm in the case of 3 to 8 layers. In addition, the thickness of the first polymer electrolyte layer of the above-described polymer thin film layer 160 may be 2 to 30 nm, and the thickness of the second polymer electrolyte layer may be 2 to 30 nm.

The above-described first polymer electrolyte layer and the second polymer electrolyte layer may be configured to have opposite polarities. For example, the first polymer electrolyte layer may be configured to have a positive charge and the second polymer electrolyte layer may be configured to have a negative charge, or the first polymer electrolyte layer may be configured to have a negative charge and the second polymer electrolyte layer may be configured to have a positive charge. Preferably, the first polymer electrolyte layer may be configured to have a positive charge, and the second polymer electrolyte layer may be configured to have a negative charge. Since the electrolyte layers having opposite polarities are alternately laminated, stability may be excellent.

The above-described polymer thin film layer 160 may be bonded to the above-described cation exchange membrane (140) or anion exchange membrane 150 through a coating process. The coating process may preferably be a multilayer thin film (LbL: Layer-by-Layer) coating process. A preferred embodiment of the LbL coating process is as follows. After rinsing the ion exchange membrane (CEM 140 or AEM 150) with deionized water, it is immersed in a first polymer electrolyte solution capable of forming a first polymer electrolyte layer for a predetermined period of time, taken out, and washed with deionized water. Then, it is immersed again in a second polymer electrolyte solution capable of forming a second polymer electrolyte layer for a predetermined period of time, taken out, and washed with deionized water to form a first polymer thin film layer. When this is defined as one cycle, the cycle is repeated until the desired number of layers is reached. Finally, the ion exchange membrane, whose cycle has been completed, is immersed in the first polymer electrolyte solution for a predetermined period of time, taken out, and washed with deionized water to form a first polymer electrolyte layer on the outermost layer. Using the multilayer thin film coating process described above, multilayer polymer thin film layers may be formed, and this can be confirmed through the bonding angles of each layer in FIG. 2.

The above-described LbL coating process has an advantage in that it can control the physicochemical properties of the surface in various ways by simply changing the coating conditions such as polymer concentration, pH conditions, salt concentration, coating time and coating procedure. In addition, it does not require expensive or complicated equipment, and the coating process may be performed simply and conveniently.

The above-described polymer thin film layer 160 may be bonded to the above-described cation exchange membrane 140 and may be arranged between the above-described cation exchange membrane 140 and the above-described electrolyte chamber 110. In this case, the above-described first polymer electrolyte layer may be configured to have a positive charge, and the above-described second polymer electrolyte layer may be configured to have a negative charge. Meanwhile, the cation exchange membrane 140 to which the polymer thin film layer 160 is bonded may be referred to as a functional CEM (f-CEM), and the cation exchange membrane 140 to which the polymer thin film layer 160 is not bonded may be referred to as a pristine CEM (P-CEM). XPS graphs for the functional CEM and the pristine CEM according to a preferred embodiment of the present disclosure are shown in FIGS. 3 and 4.

The above-described polymer thin film layer 160 may have the above-described first polymer electrolyte layer formed on the outermost surface of the other surface of the surfaces bonded to the above-described cation exchange membrane 140, and in this case, the first polymer electrolyte layer may be configured to have a positive charge. Since the first polymer electrolyte layer has a positive charge, it repels polyvalent cations more than lithium ions, and thus, the lithium selectivity described below may be better than that of the second polymer electrolyte layer formed on the outermost surface having a negative charge.

The above-described first polymer electrolyte layer may include, without limitation, a polymer that may have an opposite charge to the second polymer electrolyte layer. Preferably, it may include a positively charged polymer, and more preferably, it may include poly(allylaminehydrochloride) (PAH).

In addition, the PAH may have a weight average molecular weight (Mw) of 1,000 to 1,000,000.

The above-described second polymer electrolyte layer may include, without limitation, a polymer that may have an opposite charge to the first polymer electrolyte layer. Preferably, it may include a negatively charged polymer, and more preferably, it may include poly(styrene sulfonate) (PSS).

In addition, the PSS may have a weight average molecular weight (Mw) of 1,000 to 1,000,000.

In addition, when the above-described first polymer electrolyte layer includes PAH and the above-described second polymer electrolyte layer includes PSS, PAH has a positive charge and PSS has a negative charge, but regardless of whether the outermost layer is PAH or PSS, the positive charge may be consistently maintained by the overcharge compensation effect. Accordingly, the above-described polymer thin film layer 160 may have strong resistance to cations with a high charge density by the Donnan charge exclusion effect. Therefore, when the above-described first polymer electrolyte layer includes PAH and the above-described second polymer electrolyte layer includes PSS, the lithium selectivity described below may be high.

The above overcharge compensation effect is expressed when the number of layers of the polymer thin film layer 160 is 4 or more, and PAH is a weak polymer electrolyte whose charge density can vary depending on external conditions, whereas PSS is a strong polymer electrolyte and is fully charged regardless of external conditions. Therefore, the PAH and PSS multilayer thin film pair do not have equivalent charges under normal conditions. For the first few layers, most of the positive charge of the PAH is neutralized by the negative charge of the PSS layer. However, after a couple of sequential stackings of PAH and PSS, the overall charge of the PAH begins to overcome the charge of the PSS, thereby causing all the multilayer thin films to be slightly positively charged, and this trend is accelerated as the number of laminations of the polymer thin film layers 160 increases. Although the total amount of positive charges in the multilayer film 160 is significantly reduced when the lamination is completed with the PSS layer, the total charge value of the polymer thin film layer 160 may have a positive value.

Meanwhile, in the present disclosure, when it is expressed as (PAH/PSS)5.5-CEM, it means that the process cycle of forming the first polymer electrolyte layer including PAH and the second polymer electrolyte layer including PSS is performed 5 times, and the last one is that only the first polymer electrolyte layer including PAH is formed, and the second polymer electrolyte layer forming process including PSS is not performed. In other words, the 0.5 layer means that the first polymer electrolyte layer including PAH is formed.

The selective lithium recovery device 10 according to the present disclosure uses a flow-electrode (or flow electrode) capacitive deionization (FCDI) technology. The FCDI refers to a technology that changes the solid electrode of the existing capacitive deionization (CDI) into a flow electrode. Through this, high ion recovery capacity and efficiency may be achieved, and since a discharge step is not required, a continuous process is possible, which can greatly increase the operating efficiency.

The selective lithium recovery device of the present disclosure may further include a protection member coupled to the electrodes (anode 120 and cathode 130). The protection member may preferably be made of PVC material.

According to a preferred embodiment of the present disclosure, the selective lithium recovery device 10 may have a lithium selectivity of 10 or more, and preferably, 10 to 20. Specifically, the lithium selectivity

( ρ D Li + )

is an ion selectivity for lithium ions (Li⁺), and is calculated by Formula 1 below.

ρ D Li + = ( C Li + 0 - C Li + C Li + 0 ) / ( C D 0 - C D C D 0 ) < Formula ⁢ 1 >

In Formula 1,

C Li + 0 ⁢ and ⁢ C D 0

are an initial lithium ion (Li⁺) concentration and a polyvalent cation concentration in an influent, respectively, and C_Li+ and C_D are a lithium ion (Li⁺) concentration and a polyvalent cation concentration in treated water subjected to selective ion separation, respectively.

If the polyvalent cation is a divalent cation, the lithium selectivity

( ρ D 2 + Li + )

may be calculated by Formula 2 below.

ρ D 2 + Li + = ( C Li + 0 - C Li + C Li + 0 ) / ( C D 2 + 0 - C D 2 + C D 2 + 0 ) < Formula ⁢ 2 >

In this case, in Formula 2,

C Li + 0 ⁢ and ⁢ C D 2 + 0

are an initial lithium ion (Li) concentration and a divalent cation concentration in an influent, respectively, and C_Li+ and C_D2+ are a lithium ion (Li⁺) concentration and a divalent cation concentration in treated water subjected to selective ion separation, respectively.

Furthermore, the selective lithium recovery device 10 of the present disclosure may be applied to various devices, and according to a preferred example, the selective lithium recovery device 10 may be applied to a seawater desalination device, a wastewater treatment device, or a waste battery waste liquid treatment device.

According to the present disclosure, provided is a method for manufacturing a selective lithium recovery device 10, including step 1 of preparing an anode 120 including a current collector for anode 121 and an anode active material 122 and a cathode 130 including a current collector for cathode 131 and a cathode active material 132; step 2 of bonding a polymer thin film layer 160 to at least one of a cation exchange membrane 140 and an anion exchange membrane 150; and step 3 of arranging the anode 120 and the cathode 130 with an electrolyte chamber 110 therebetween, arranging the cation exchange membrane (CEM) 140 between the electrolyte chamber 110 and the anode 120, and arranging the anion exchange membrane (AEM) 150 between the electrolyte chamber 110 and the cathode 130.

In steps 1 and 2 described above, step 1 may be performed first, step 2 may be performed first, or they may be performed simultaneously.

In the above-described method for manufacturing the selective lithium recovery device 10, the anode 120, the cathode 130, the cation exchange membrane 140, the anion exchange membrane 150 and the polymer thin film layer 160 are as described above, and thus, specific details are omitted.

In order to solve the above-described problems, provided is a method for separating and recovering lithium, by introducing an electrolyte solution containing lithium ions (Li⁺) and polyvalent cations into an electrolyte chamber of the above-described selective recovery device and applying a voltage.

In the above-described method for separating and recovering lithium, the polyvalent cations, the electrolyte chamber 110 and the selective recovery device 10 are as described above, and thus, specific details are omitted.

The above-described voltage refers to a voltage applied to the anode 120 and the cathode 130, and may be 0.2 to 3.0 V. However, the applied voltage may be appropriately adjusted depending on the pH of the electrolyte solution. The higher the voltage applied to the cathode 130, the more ions included in the electrolyte may be induced to move from the electrolyte, pass through the ion membrane, and be adsorbed on the electric double layers (EDL) formed on the surface of the active material inside the flow electrode chamber in the electrodes (anode 120 and cathode 130), thereby increasing the adsorption capacity. However, a high voltage may increase an unintended faradaic reaction, decompose water molecules included in the electrolyte, deteriorate the electrode, and generate undesirable substances in the electrolyte chamber 110. Therefore, it is preferable that the voltage applied to the cathode 130 be 1.6 V or less. However, since an excessively low voltage may significantly reduce the ion recovery efficiency and ion recovery rate, it is preferable to set it to 0.2 V or more.

Meanwhile, in the past, FCDI devices were often operated in a range where the applied voltage exceeded 0.8 V and was 2.0 V or less and the pH of the electrolyte solution exceeded 4 and was 7 or less. When the selective lithium recovery device 10 of the present disclosure is operated under the above conditions, it can be confirmed that precipitated substances may be generated, as can be seen from FIGS. 7 to 9.

Specifically, when the outermost layer of the polymer thin film layer 160 of the present disclosure is a PAH layer, the above-described voltage exceeds 0.8 V and the pH of the electrolyte solution exceeds 4, a large amount of precipitates may be formed in the polymer thin film layer 160 bonded to the cation exchange membrane 140. More specifically, the ammonium group (NH₃⁺) of the outermost PAH layer, which is positively charged, may temporarily capture OH⁻, and the OH⁻ may interact with the cation (e.g., Ni²⁺) included in the electrolyte to form Ni(OH)₂ precipitate as shown in the chemical reaction formula below. The precipitate may interfere with the movement of the cation, which can reduce the lithium selectivity and ion recovery efficiency of the selective lithium recovery device 10, and can interfere with the long-term operation of the recovery device (10).

Meanwhile, the above-described precipitate is not composed only of Ni(OH)₂, and may also include precipitates due to cobalt ions.

In order to prevent the above-described precipitate, the applied voltage may be lowered or the pH of the electrolyte solution may be lowered. However, it can be confirmed through the results of FIGS. 5 and 7 that the ion recovery rate decreases when the applied voltage is lowered. This is because the driving force is weakened, and the ion recovery efficiency is reduced.

When the pH of the electrolyte solution is lowered, the hydrogen ion (H⁺) content increases such that the hydrogen ion is adsorbed before the lithium ion, which is a monovalent cation, and the ion recovery rate of lithium decreases. In addition, FIG. 6 shows that the measured current and conductivity change increase over time due to the presence of hydrogen ions in the electrolyte solution, which shows that the driving can be more stable when using a neutral electrolyte solution than an acidic electrolyte solution. In other words, it suggests that the acidic electrolyte solution is inefficient and unstable compared to the neutral electrolyte solution.

Ultimately, when the applied voltage and the pH of the electrolyte solution are lowered at the same time, the lithium ion recovery rate may be very low due to the weak electric driving force and competitive adsorption with hydrogen ions, which can be seen through FIG. 5. That is, it can be confirmed that lowering only the applied voltage or only the solution pH in the conventional applied voltage and electrolyte solution pH range described above may be effective in preventing precipitation while increasing the lithium recovery efficiency and selectivity, and especially, considering that the neutral electrolyte solution is stable for long-term operation, lowering the applied voltage while maintaining the pH may be desirable in terms of lithium selectivity or lithium ion recovery rate.

Based on the above-described content, in the present disclosure, the above-described voltage may be 0.2 to 0.8 V, and in this case, the pH of the electrolyte solution may be 4 to 7. Alternatively, the above-described voltage may be 0.8 to 1.6 V, and in this case, the pH of the electrolyte solution may be 1 to 4. If it is out of the above-mentioned range, the lithium ion recovery rate and lithium selectivity may decrease, and when operating for a long period of time, too much sediment may be generated, and the ion separation process itself may not occur. Specifically, when the voltage described above is less than 0.8 V and the pH of the electrolyte solution is less than 4, or when the voltage described above exceeds 0.8 V and the pH of the electrolyte solution exceeds 4, the lithium ion recovery rate and lithium selectivity may be lower than when the voltage described above is 0.2 to 0.8 V and the pH of the electrolyte solution is 4 to 7, or when the voltage described above is 0.8 to 1.6 V and the pH of the electrolyte solution is 1 to 4. In particular, when the above-described voltage exceeds 0.8 V and the pH of the electrolyte solution exceeds 4, precipitates may be formed on the cation exchange membrane, which may decrease the lithium ion recovery rate and lithium selectivity, and when operating for a long period time, too many precipitates may be formed such that the ion separation process itself may not occur.

In conclusion, in summary of the above, the present disclosure may exhibit excellent performance in lithium recovery while ensuring long-term stability when the applied voltage is 0.2 to 0.8 V and the pH of the electrolyte solution is 4 to 7.

Referring to FIG. 11A, in the method for separating and recovering lithium described above, the flow rate of the above-described electrolyte solution may be 1.2 mL/min or more, and preferably 1.2 to 10 mL/min. Referring to FIG. 11, as the flow rate of the electrolyte solution decreases, lithium ions preferentially pass through the cation exchange membrane 140 at the initial inflow of the electrolyte solution such that as ion recovery progresses, the concentration of polyvalent cations may increase in the electrolyte solution, and since lithium ions and polyvalent cations have a competitive ion adsorption relationship, the lithium selectivity may decrease as the concentration of polyvalent cations increases. In contrast, as the flow rate of the electrolyte solution increases, the ion-exchanged electrolyte solution is replaced with a new electrolyte solution more quickly such that all ion concentrations are relatively maintained to be constant compared to when the flow rate is low, and thus, high lithium selectivity may be achieved. That is, when the flow rate of the above-described electrolyte solution is less than 1.2 mL/min, the lithium selectivity may be low, and thus, it may be difficult to efficiently recover lithium.

Referring to FIG. 11B, in the method for separating and recovering lithium described above, the initial ion concentration of lithium in the above-described electrolyte solution may be 5 mM or more, and preferably, 5 mM to 1 M. When it is explained by referring to FIG. 11, as the initial ion concentration of lithium in the above-described electrolyte solution increases, the lithium selectivity may increase. If the initial ion concentration is low, since the ions present near the surface of the ion exchange membranes 140, 150 decrease, when a voltage is applied, all ions present near the surface are affected, potentially generating excessive electric force, which can nullify the difference between lithium and polyvalent cations and reduce the blocking effect for polyvalent cations, thereby decreasing the lithium selectivity. In addition, as the initial ion concentration increases, more ions are located near the ion exchange membranes 140, 150, and thus, the ion recovery efficiency may also increase. That is, when the initial ion concentration is 5 mM or more, the lithium selectivity and ion recovery efficiency may be superior compared to when the initial ion concentration is less than 5 mM.

In the method for separating and recovering lithium according to the present disclosure, the ion recovery rate (IRR) of lithium may be 10 μmol/m²s or more. If it is out of the above range, problems may occur in the practical use of the lithium recovery device. In this case, the ion recovery rate (IRR) may be obtained using Formula 3 below.

I ⁢ R ⁢ R ⁢ ( μmol / m 2 ⁢ s ) = V × ( C X 0 - C X ) t × S < Formula ⁢ 3 >

In this case, V is a volume of the electrolyte solution,

C X 0 ⁢ and ⁢ C X

are initial and final concentrations of ions in the electrolyte solution, respectively, t is a device operation time, and S corresponds to an effective contact area between the flow electrode and the ion exchange membrane. t is 1 hour, and S is 12.7 cm².

Additionally, in the method for separating and recovering lithium described above, the ion recovery efficiency (E: recovery Efficiency) of lithium may be 10% or more. If it is out of the above range, problems may occur in the practical use of the lithium recovery device. In this case, the ion recovery efficiency (E: recovery Efficiency) may be obtained Formula 4 below.

E ⁡ ( % ) = ( C X 0 - C X C X 0 ) < Formula ⁢ 4 >

In this case,

C X 0 ⁢ and ⁢ C X

are initial and final concentrations of ions in the electrolyte solution, respectively.

Additionally, in the method for separating and recovering lithium described above, the specific energy consumption may be 0.9 Wh/mol or less. If the specific energy consumption exceeds 0.9 Wh/mol, excessive energy consumption may occur, which may cause problems in the practical use of the lithium recovery device. The specific energy consumption maybe obtained using Formula 5 below.

SEC ⁢ ( Wh / mol Li ) = ( U × I ( C Li + 0 - C Li + ) × V / t ) < Formula ⁢ 5 >

In this case,

C Li + 0 ⁢ and ⁢ C Li +

are an initial concentration of lithium and a final concentration of lithium in the electrolyte stream, respectively, V/t is a flow rate (mL/min) of the electrolyte solution, and U and I are the constant potential and current applied in the FCDI cell, respectively.

In the above-described method, the type of electrolyte solution, the type of ions included in the electrolyte solution, the ion concentration of the electrolyte solution, and the solvent of the electrolyte solution are as described above, and thus, the specific details are omitted.

The present disclosure will be described more specifically through the following examples, but the following examples do not limit the scope of the present disclosure, and it should be interpreted that they are intended to help understanding of the present disclosure.

Preparation Example

Preparation Example 1: Purchase of P-CEM (Pristine CEM)

A cation exchange membrane (CEM) 140 was purchased from Fujifilm (Type 10, Tilburg, Netherlands). Since a polymer thin film layer 160 was not formed, the cation exchange membrane 140 is referred to as a P-cation exchange membrane 140.

Preparation Example 2: Manufacture of (PAH/PSS)1.5-CEM

A cation exchange membrane (CEM) 140 was purchased from Fujifilm (Type 10) (Tilburg, Netherlands). In addition, poly(allylamine hydrochloride) (PAH, Mw=17,500) and poly(styrene sulfonate) (PSS, Mw=70,000) were purchased from Sigma-Aldrich Inc. (St. Louis, MO, USA). In addition, deionized (DI) water was produced and used by using a Human Power II+ purification system (Human Corporation) (Seoul, Korea). The cation exchange membrane 140, PAH, and PSS were used as purchased without any additional purification or treatment.

The above-described cation exchange membrane 140 was cut into an appropriate size and soaked in deionized water for 24 hours. The above-described PAH and PSS were each added to a petri dish containing a 1 M NaCl aqueous solution to be 1 mg/mL. Thereafter, the pretreated cation exchange membrane 140 was immersed in the PAH solution for 30 minutes, rinsed with deionized water for 3 minutes, and then immersed again in the PSS solution for 30 minutes, and rinsed with deionized water for 3 minutes, thereby forming a first layer in which a PAH layer and a PSS layer were formed in sequence on the upper surface of the cation exchange membrane 140. The first layer formation process consisting of the PAH layer and the PSS layer is defined as 1 cycle. In addition, the cation exchange membrane 140 that performed 1 cycle was soaked in the PAH solution for 30 minutes, and then rinsed with deionized water for 3 minutes to manufacture an f-cation exchange membrane 140 denoted as (PAH/PSS)1.5-CEM 140.

Preparation Example 3: Manufacture of (PAH/PSS)5.5-CEM

(PAH/PSS)5.5-CEM 140 was manufactured in the same manner as in Preparation Example 2, except that the cycle of Preparation Example 2 was performed 5 times.

Preparation Example 4: Manufacture of (PAH/PSS)8.5-CEM

(PAH/PSS)8.5-CEM 140 was manufactured in the same manner as in Preparation Example 2, except that the cycle of Preparation Example 2 was performed 8 times.

Preparation Example 5: Manufacture of (PAH/PSS)11.5-CEM

(PAH/PSS)11.5-CEM 140 was manufactured in the same manner as Preparation Example 2 except that the cycle of Preparation Example 2 was performed 11 times.

Experimental Example

Experimental Example 1: Contact Angle Analysis

The contact angle was measured using a contact angle goniometer (Kruss DSA25) (Germany). In order to measure the hydrophilicity of the surface of the cation exchange membrane 140 or the polymer thin film layer 160, deionized water manufactured by using a Human Power II+ purification system (Human Corporation) (Seoul, Korea) was used. The deionized water used for the measurement was 5 μL. The contact angle of Preparation Example 1 was measured, and the contact angle of Preparation Example 3 was measured every time the PAH layer and the PSS layer were formed. The results are shown in FIG. 2.

Referring to FIG. 2, it can be confirmed that the PAH layer and the PSS layer were successfully formed. Since PAH is more hydrophobic than PSS, there was a difference in the contact angle values when the two polymers were used alternately. In the pristine CEM 140 of Preparation Example 1, the sulfonate group present in the polymer chain attracted water molecules, showing a low contact angle of 42°. In the case of Preparation Example 3, when the PAH coating was applied, the contact angle suddenly increased to 103° due to the PAH coating, whereas the contact angle decreased again to 51° due to the subsequent PSS coating. Such a distinct and sequential change in the contact angle means that each layer of PAH and PSS was successfully formed on the CEM 140.

Experimental Example 2: X-Ray Photoelectron Spectroscopy (XPS) Measurement

The presence of functional groups in the cation exchange membranes 140 of Preparation Examples 1 and 4 was analyzed using X-ray photoelectron spectroscopy (XPS, Thermo VG, UK), and the results are shown in FIGS. 3 and 4. In FIGS. 3 and 4, pristine CEM 140 means a cation exchange membrane 140 in which a multilayer polymer thin film 160 is not formed, and functionalized CEM 140 means a cation exchange membrane 140 in which a polymer thin film layer 160 is formed. FIG. 3a was investigated with 1.0 eV step and 200 CAE (constant analyzer energy), and FIGS. 3B, 3C and 4 were investigated with 0.1 eV step and 50 CAE (constant analyzer energy).

FIG. 3A is the XPS full spectrum for the cation exchange membranes 140 of Preparation Example 1 and Preparation Example 4, and FIGS. 3B and 3C show high-resolution fitting peaks for nitrogen (N 1s) of Preparation Example 1 and Preparation Example 4, respectively, and FIGS. 4A and 4B show high-resolution fitting peaks for sulfur (S 2p) of Preparation Example 1 and Preparation Example 4, respectively.

In FIG. 3B, the nitrogen peak of Preparation Example 4 can be decomposed into peaks with binding energies of ˜399.6 and ˜401.7 eV, which represent the —NH₂ state and the —NH₃⁺ state in PAH. The nitrogen sub-peaks of these two states may have been generated by the partial protonation of —NH₂ in the salt form in PAH to —NH₃⁺ in the hydrated state under neutral pH conditions. On the other hand, in the case of Preparation Example 1, only one peak appeared at ˜399.8 eV due to the presence of nitrogen-containing compounds present in the CEM 140 polymer.

The two sub-peaks at ˜167.8 and ˜169 eV shown in FIG. 4 correspond to the 2p3/2 and 2p1/2 spin states of —SO₃⁻ bonds, respectively, resulting from spin-orbit coupling. The peak of Preparation Example 1 shown in FIG. 4a indicates the presence of —SO₃⁻ present in the CEM 140 polymer, suggesting that it may have cation exchange properties. It can be seen that the peak of Preparation Example 4 shown in FIG. 4B is derived from the functional group of PSS, not —SO3-, which exists in the CEM (140) polymer, and the reason is because, in the case of Preparation Example 4, most of the peaks at 1072, 831, 685, 497, 348, 154, 102 and 64 eV were hardly observed in FIG. 3A, except for the main nitrogen (N 1s) and sulfur (S 2p) peaks.

In conclusion, as described above, Preparation Example 4 confirmed that a polymer film layer 160 was successfully formed on the surface of CEM 140.

Example

Example 1

Through the process described above, a selective lithium recovery device 10 using a flow electrode capacitive deionization device equipped with the components schematically disclosed in FIG. 1 was manufactured.

The selective lithium recovery device 10 has two graphite-based positive electrode current collectors 131 and graphite-based negative electrode current collectors 121 each having grooves (1 mm wide and 1 mm deep) engraved to allow catholyte (cathode active material) or anolyte (anode active material) to flow, and the engraved grooves mean flow electrode chambers (flow electrode chambers for anode and flow electrode chambers for cathode). In addition, a polyester-based spacer is firmly arranged between the two current collectors to form a space (electrolyte chamber 110) for flowing the electrolyte.

In addition, the CEM 140 of Preparation Example 2 was placed between the current collector 131 for the graphite-based cathode and the electrolyte chamber 110, and the AEM 150 purchased from Fujifilm (Type 10) (Tilburg, Netherlands) was placed between the current collector 121 for the graphite-based anode and the electrolyte chamber 110. Through this, the flow of the electrode solutions (catholyte and anolyte) of the flow electrodes and the electrolyte solution may be separated. Meanwhile, the flow electrode includes the graphite-based current collectors 121, 131, the flow electrode chamber and the electrode solutions, and the total contact area of the flow electrode thereof and the ion exchange membrane (CEM 140 and AEM 150) was 12.7 cm².

Meanwhile, a mixture of 100 mL of deionized water and 20 wt % of porous activated carbon (MSP-20X) purchased from Kansai Coke & Chemical (Hyogo, Kobe, Japan) was introduced into the flow electrode chamber for anode and the flow electrode chamber for cathode as electrode solutions (catholyte and anolyte), respectively.

Example 2

Except that the CEM 140 of Preparation Example 3 was placed between the graphite-based current collector for cathode 131 and the electrolyte chamber 110, the process was carried out in the same manner as Example 1, and it was manufactured as shown in Table 1.

Example 3

Except that the CEM 140 of Preparation Example 4 was placed between the graphite-based current collector for cathode 131 and the electrolyte chamber 110, the process was carried out in the same manner as Example 1, and it was manufactured as shown in Table 1.

Example 4

Except for placing the CEM 140 of Preparation Example 5 between the current collector 131 for the graphite-based cathode and the electrolyte chamber 110, the process was carried out in the same manner as Example 1, and it was manufactured as shown in Table 1.

Comparative Example

Comparative Example 1

Except for placing the CEM 140 of Preparation Example 1 between the current collector 131 for the graphite-based cathode and the electrolyte chamber 110, it was carried as shown in Table 1, and it was manufactured as shown in Table 1.

	TABLE 1
					Comparative
	Example 1	Example 2	Example 3	Example 4	Example 1

Type of	Preparation Example 2	Preparation Example 3	Preparation Example 4	Preparation Example 5	Preparation Example 1
CEM	((PAH/PSS)1.5-CEM)	((PAH/PSS)5.5-CEM)	((PAH/PSS)8.5-CEM)	((PAH/PSS)11.5-CEM)	(p-CEM)

Experimental Example

Experimental Example 3: Measurement of Lithium Selectivity, Ion Recovery, Time-Current and Time-Conductivity Changes According to Applied Voltage and Electrolyte Solution pH

Anhydrous lithium chloride (LiCl, 98.2%) was purchased from Samcheon Chemical (Seoul, Korea), and cobalt (II) chloride hexahydrate (CoCl2·6H2O, 98%) and nickel (II) chloride hexahydrate (NiCl2·6H2O, 98%) were purchased from Thermo Fisher Scientific (Ward Hill, MA, USA). The electrolyte solution was prepared by mixing LiCl, CoCl2·6H2O, and NiCl₂·6H₂O in water such that the concentrations were 10 mM each.

The electrolyte solution, the anolyte and catholyte of the flow electrode were continuously pumped to the selective lithium recovery device 10 at flow rates of 1.5 mL/min, 20 mL/min and 20 mL/min, respectively, by using a peristaltic pump (Miniplus 3) purchased from Gilson, Inc. (Middleton, Wisconsin, USA).

The voltage was applied for 1 hour using a potentiostat (ZIVE MP2A, Won-A-TAK) (Korea), and the conductivity was measured using a conductivity meter (DS-70 Laqua, Horiba) (Japan). The ion concentration was measured after taking a 15 mL sample using an inductively coupled plasma-optical emission spectrometer (ICP-OES) (SPECTROGREEN; SPECTRO) (Kleve, Germany) after all of the conductivity and current values reached stable values after about 15 minutes. The radio frequency power was set to 1,400 W, and the emission lines of 670.78 nm, 228.61 nm and 231.60 nm were used for Li, Co and Ni, respectively, in order to detect the analyte signals.

The lithium selectivity

( ρ D Li + )

can be obtained using Formula 1 below.

ρ D Li + = ( C Li + 0 - C Li + C Li + 0 ) / ( C D 0 - C D C D 0 ) < Formula ⁢ 1 >

In Formula 1,

C Li + 0 ⁢ and ⁢ C Li +

are an initial lithium ion (Li+) concentration and a poly cation concentration in an influent, respectively, and C_Li+ and C_D are a lithium ion (Li⁺) concentration and a polycation concentration in treated water subjected to selective ion separation, respectively.

The ion recovery rate (IRR) was obtained using Formula 3 below.

IRR ⁡ ( μmol / m 2 ⁢ s ) = V × ( C X 0 - C X ) t × S < Formula ⁢ 3 >

In this case, V is a volume of the electrolyte solution,

C X 0 ⁢ and ⁢ C X

are the initial and final concentrations of ions in the electrolyte solution, respectively, t is a device operation time, and S corresponds to the effective contact area between the flow electrode and the ion exchange membrane. t was 1 hour, and S was 12.7 cm².

The lithium selectivity and ion recovery rate of Example 2 and Comparative Example 1 were measured while changing the applied voltage and the pH of the electrolyte solution, and the results are shown in FIG. 5 and FIG. 7.

In addition, the current and conductivity changes over time of Example 2 were measured while changing the applied voltage and the pH of the electrolyte solution, and the results are shown in FIG. 6 and FIG. 8.

The photographs of the sediment appearance at each time point of the recovery device operated at an applied voltage of 1.2 V and an electrolyte solution pH of 6 in Example 2 are shown in FIG. 9B (operating time: 30 minutes), 9B (operating time: 1 hour) and 9C (operating time: 3 hours).

In addition, the lithium selectivity and ion recovery rate of Examples 1 to 4 and Comparative Example 1 were measured by operating the recovery device at an applied voltage of 0.4 V and an electrolyte solution pH of 6, and the results are shown in FIG. 10A, and the current was measured overtime, and the results are shown in FIG. 10B.

The lithium selectivity and ion recovery rate of Example 2 and Comparative Example 1 were measured by operating the recovery device at an applied voltage of 0.4 V and an electrolyte solution pH of 6, and the results are shown in FIG. 11c.

As the device was operated at an applied voltage of 1.2 V and an electrolyte solution pH of 6, it can be confirmed that a green precipitate was accumulated in FIG. 9, and it can be confirmed through FIG. 8 that the green precipitate reduced the current and conductivity changes during long-term operation (the decrease in conductivity change means that the ion permeability is reduced in the CEM 140 of Example 2). As described above, this precipitate included Ni(OH)₂ precipitate. FIG. 9A shows the appearance after 30 minutes of operation, FIG. 9B shows the appearance after 1 hour of operation, and FIG. 9C shows the appearance after 3 hours of operation. Such precipitates changed the ion selectivity, which can lead to unstable operation in the long term.

In order to prevent the green precipitate described above, the applied voltage must be lowered or the pH of the electrolyte solution must be lowered. However, it can be confirmed through the results of Comparative Example 1 of FIGS. 5 and 7 that the ion recovery rate decreased when the applied voltage was lowered. This is because the driving force was weakened by three times, and the ion recovery efficiency was reduced by more than three times. Meanwhile, when the pH of the electrolyte solution was lowered, the ion recovery rate of lithium decreased as the hydrogen ion (H+) content increased and the hydrogen ion was adsorbed before the lithium ion, which is a monovalent cation. In addition, FIG. 6 shows that the measured current and conductivity changes increase over time due to the presence of hydrogen ions in the electrolyte solution, which shows that a neutral electrolyte solution can be more stable in driving than an acidic electrolyte solution. In other words, it suggests that an acidic electrolyte solution is inefficient and less stable than a neutral electrolyte solution. Ultimately, when the applied voltage and the pH of the electrolyte solution are lowered at the same time, the recovery rate of lithium ions can be very low due to the weak electric driving force and competitive adsorption with hydrogen ions, which can be seen through FIG. 5. That is, it suggests that lowering only the applied voltage or only the solution pH at an applied voltage of 1.2 V and an electrolyte solution pH of 6 can be effective in preventing green precipitation while increasing the lithium recovery efficiency and selectivity, and especially considering that a neutral electrolyte solution is stable for long-term operation, lowering the applied voltage while maintaining the pH can be desirable in terms of lithium selectivity or lithium ion recovery rate.

When it is explained by referring to FIGS. 5 and 7, when a polymer thin film layer 160 was combined (Example 2), it showed a significantly higher lithium selectivity and a superior lithium ion recovery rate compared to when it was not combined (Comparative Example 1). Particularly, in the case of Example 2, it was shown that the lithium selectivity was 10.75 at 0.4 V at pH 6, 13.12 at 1.2 V at pH 1.7, and 5.63 at 0.4 V at pH 1.7. In the case of Example 2, since the charge interaction between the surface of the polymer thin film layer and the divalent cations was large, the ion blocking effect due to the Donnan charge exclusion becomes less important than that of the monovalent cations such that the ion selectivity of the monovalent cations is improved when a low voltage is applied.

In addition, referring to FIGS. 5 and 7, when the polymer thin film layer was combined (Example 2), when the voltage was 0.4 V and the pH of the electrolyte solution was 6, or when the voltage was 1.2 V and the pH of the electrolyte solution was 1.7, the lithium ion recovery rate and lithium selectivity were very excellent compared to when the voltage was 1.2 V and the pH of the electrolyte solution was 6. In particular, when the voltage was 1.2 V and the pH of the electrolyte solution was 6, it was shown that the lithium ion recovery rate was much lower than that of nickel and cobalt. When the voltage was 0.4 V and the pH of the electrolyte solution was 1.7, it was shown that the lithium ion recovery rate and lithium selectivity were low. Therefore, it was confirmed that the optimal conditions for lithium recovery were when the voltage was 0.2 to 0.8 V and the pH of the electrolyte solution was 4 to 7, or when the voltage was 0.8 to 1.6 V and the pH of the electrolyte solution was 1 to 4.

As a result, according to the above, when the applied voltage was 0.2 to 0.8 V and the pH of the electrolyte solution was 4 to 7, excellent performance in lithium recovery could be achieved while ensuring long-term stability.

It can be confirmed through FIG. 10a that the lithium selectivity increases as the number of layers of the polymer thin film layer 160 increases. Since the outermost PAH layer with a cation charge existed in Examples 1 to 4, the polyvalent cations present in the electrolyte solution have a higher charge density than lithium ions, and thus, they repel more strongly from the surface of the exchange membrane (140), and as the number of layers increases, the Donnan charge exclusion effect is amplified, which increases the ion blocking effect, thereby affecting the movement of cations, especially divalent cations. In other words, as the number of layers increases, the lithium selectivity increases. However, as the number of layers increases, the physical barrier increases due to the thick film thickness, and the total ion permeability decreases. Therefore, the number of polymer thin film layers may be appropriately between 3 and 8 layers.

Experimental Example 4: Measurement of Lithium Selectivity and Ion Recovery Efficiency According to the Flow Rate of Electrolyte Solution

The same electrolyte solution as in Experimental Example 3 was prepared. The experiment was performed under the same pump conditions as in Experimental Example 3, except that the lithium selectivity and ion recovery efficiency were measured by changing the flow rate of the electrolyte solution. In this case, the pH of the electrolyte solution was set to 6, and the applied voltage was set to 0.4 V.

The ion recovery efficiency (E: recovery efficiency) was obtained using Formula 4 below.

E ⁡ ( % ) = ( C X 0 - C X C X 0 ) < Formula ⁢ 4 >

In this case,

C X 0 ⁢ and ⁢ C X

are initial and final concentrations of ions in the electrolyte solution, respectively.

The flow rates of the electrolyte solution were set to 0.5 mL/min, 1 mL/min, 1.5 mL/min and 2 mL/min, respectively, and the lithium selectivity and ion recovery efficiency of Example 2 were measured and shown in FIG. 11a.

When it is explained by referring to FIG. 11, it can be confirmed that the ion recovery efficiency of the selective lithium recovery device 10 of Example 2 decreased as the flow rate of the electrolyte solution increased, but the lithium selectivity increased. In other words, since the productivity of lithium and the lithium selectivity are inversely proportional to the flow rate of the electrolyte solution, the flow rate of the electrolyte solution can be controlled according to an appropriate purpose. However, since the lithium selectivity must be guaranteed to a certain extent for proper lithium recovery, the flow rate of the electrolyte solution may be appropriately 1.2 mL/min or more.

Experimental Example 5: Lithium Selectivity and Ion Recovery Rate According to Initial Ion Concentration of Electrolyte Solution

The LiCl concentration (or Li⁺ concentration) of Experimental Example 3 was set to 5, 10, 15 or 20 mM, respectively, and the concentrations of CoCl₂·6H₂O and NiCl₂·6H₂O were mixed in water to be the same as the LiCl concentration, respectively, to prepare an electrolyte solution. The experiment was performed under the same pump conditions as Experimental Example 3. In this case, the pH of the electrolyte solution was set to 6, and the applied voltage was set to 0.4 V.

The specific energy consumption (SEC) was obtained using Formula 5 below.

SEC ⁢ ( Wh / mol Li ) = ( U × I ( C Li + 0 - C Li + ) × V / t ) < Formula ⁢ 5 >

In this case,

C Li + 0 ⁢ and ⁢ C Li +

are an initial concentration of lithium and a final concentration of lithium in the electrolyte stream, respectively, V/t is a flow rate (mL/min) of the electrolyte solution, and U and I are a constant potential and a current applied in the FCDI cell, respectively.

The selective recovery devices of lithium 10 of Example 2 and Comparative Example 1 were operated, and the lithium selectivity and ion recovery rate were measured, and the results are shown in FIG. 11B and FIG. 12.

When it is explained by referring to FIG. 11B and FIG. 12, the initial ion concentration of the electrolyte solution is one of the important parameters in lithium recovery. In the case of Comparative Example 1, the lithium selectivity according to the initial ion concentration was less than 1 at all concentrations, and thus, there was almost no difference. In contrast, the lithium selectivity of the CEM 140 of Example 2 showed an increasing trend as the initial ion concentration increased from 9.44 at 5 mM to 31.55 at 20 mM.

In addition, as the initial ion concentration increased, the total ion recovery rate increased in both Example 2 and Comparative Example 1, because a larger amount of ions were located on the surface of the cation exchange membrane (140).

Additionally, in order to verify the possibility of practical application, selective Li separation was performed in the FCDI system according to the present disclosure using a synthetic lithium-ion battery waste fluid (30 mM: 44 mM: 4 mM for Li:Co:Ni) designed to mimic the actual ion composition of lithium-ion battery waste fluid. As a result, a high Li selectivity of 12.88 was obtained with a specific energy consumption of 0.57 Wh/mol.

Experimental Example 6: Electrochemical Impedance Spectroscopy Measurement According to Electrolyte Solution Composition

EIS data were obtained by changing the composition of the electrolyte solution using a potentiostat (ZIVE MP2A, Won-A Tech, Korea). In this case, the applied voltage of the selective lithium recovery device 10 was set to 0.4 V, the vibration amplitude was set to 10 mV, and the EIS analysis was performed in the frequency range of 0.01 Hz to 10 kHz. In this case, LiCl, CoCl₂·6H₂O and NiCl₂·6H₂O were purchased and used from the same place indicated in Experimental Example 3. In addition, the EIS analysis was performed using the circuit diagram shown in FIG. 14. In FIG. 14, R1 represents the internal resistance including the interfacial resistance between the electrolyte solution, the ion exchange membranes 140, 150, the electrode current collectors 121, 131 and the flow electrode solution (the cathode active material and the anode active material 122, 132), and R2 and CPE1 represent the resistance and the constant phase element (CPE) related to the charge transfer, ion diffusion and ion transport through the ion exchange membranes 140, 150 in the electrolyte solution, respectively. In addition, R3 and CPE2 represent the resistance and the constant phase element (CPE) for the interfacial charge transfer between the electrode particles, ion diffusion and ion transport from the ion exchange membrane to the suspended flow electrode particles, respectively.

EIS analysis was performed on Example 2 and Comparative Example 1 while changing the composition of the electrolyte solution to 30 mM LiCl; 15 mM CoCl₂ and 15 mM NiCl₂; or 10 mM LiCl, 10 mM CoCl₂ and 10 mM NiCl₂, and the results are shown in FIG. 13 and Table 2. Hereinafter, when the composition of the electrolyte solution is 30 mM LiCl, it is indicated as a “Li electrolyte solution”, when it is 15 mM CoCl₂ and 15 mM NiCl₂, it is indicated as a “Co/Ni electrolyte solution”, and when it is 10 mM LiCl, 10 mM CoCl₂ and 10 mM NiCl₂, it is indicated as a “Li/Co/Ni electrolyte solution”.

FIG. 13 shows that the R1 value decreased in the order of Li electrolyte solution, Li/Co/Ni electrolyte solution and Co/Ni electrolyte solution in both Comparative Example 1 and Example 2, but shows a similar trend. Co²⁺ and Ni²⁺ cations have high charge density and additional valence shells, and thus, they have high conductivity and low specific resistance in the electrolyte. On the other hand, lithium ions have low charge density, and thus, they have low conductivity and high resistance. Therefore, the Li electrolyte solution and the Li/Co/Ni electrolyte solution showed relatively higher R1 values than the Co/Ni electrolyte solution.

In the case of R2 of the P-CEM 140 of Comparative Example 1, the R2 value of the Li electrolyte solution (4.92Ω) was higher than that of the Co/Ni electrolyte solution (4.57Ω), showing the divalent ion affinity of the P-CEM 140. In the case of the f-CEM 140 of Example 2, R2 generally increased regardless of the type of cation due to electrostatic repulsion and additional physical barriers occurring in the multilayer polymer thin film layer 160 (14.99Ω for the Li electrolyte solution and 20.21Ω for the Co/Ni electrolyte solution). In particular, the R2 of the f-CEM 140 of Example 2 was much higher in the Co/Ni electrolyte solution (20.21Ω) than in the Li electrolyte solution (14.99Ω). This indicates that the ion affinity was switched from divalent cations to monovalent cations due to the multilayer polymer thin film layers (160), which is in good agreement with the FCDI ion separation results (FIG. 10). This EIS analysis confirmed that coating the CEM 140 with the multilayer polymer thin film layers 160 provided strong lithium selectivity among various ion mixtures.

	TABLE 2
	Comparative Example 1	Example 2

	Li	Co/Ni	Li/Co/Ni	Li	Co/Ni	Li/Co/Ni
	electrolyte	electrolyte	electrolyte	electrolyte	electrolyte	electrolyte
Parameters	solution	solution	solution	solution	solution	solution
R1	5.365	3.981	4.365	8.19	4.633	5.119
(Ω)	(±0.017)	(±0.012)	(±0.013)	(±0.09)	(±0.095)	(±0.295)
R2	4.916	4.568	4.454	14.99	20.21	12.7
(Ω)	(±0.256)	(±0.187)	(±0.188)	(±0.48)	(±0.4)	(±0.83)
CPE1	0.041	0.0458	0.0439	0.0004	0.0001	0.0002
(Ω−1 · s−n)	(±2 × 10−3)	(±1.6 × 10−3)	(±1.7 × 10−3)	(±4.3 × 10−5)	(±5.8 × 10−6)	(±3.4 × 10−5)
n1	0.518	0.5	0.51	0.78	0.938	0.921
	(±0.012)	(±8.9 × 10−3)	(±9.8 × 10−3)	(±0.016)	(±0.009)	(0.033)
R3	44.46	52.17	54.82	493	330	419
(Ω)	(±8.57)	(±16.45)	(±17.41)	(±30.27)	(±10.97)	(±22.15)
CPE2	0.513	0.395	0.366	0.084	0.012	0.022
(Ω−1 · s−n)	(±0.037)	(±0.015)	(±0.014)	(±4.615)	(±0.1 × 10−3)	(±6 × 10−4)
n2	0.632	0.507	0.491	0.311	0.335	0.265
	(±0.029)	(±0.013)	(±0.011)	(±4.124)	(±3.9 × 10−3)	(±9 × 10−3)
χ2	6.8 · 10−4	4.3 · 10−4	4.6 · 10−4	2.4 · 10−3	2.9 · 10−4	2.5 · 10−3

Although one embodiment of the present disclosure has been described above, the spirit of the present disclosure is not limited to the embodiment presented in the present specification, and those skilled in the art who understand the spirit of the present disclosure will be able to easily suggest other embodiments by modifying, changing, deleting or adding components within the scope of the same spirit, but this will also be considered to fall within the spirit of the present disclosure.