KR102539126B1 - Lithium recovery system including solid electrolyte membrane and method of manufacturing the solid electrolyte membrane - Google Patents

Abstract

A lithium recovery system is provided. The lithium recovery system includes a positive electrode, a negative electrode, a solid electrolyte membrane positioned between the positive electrode and the negative electrode, and a separator impregnated with an organic electrolyte between the negative electrode and the solid electrolyte membrane, and a cation exchange membrane is formed between the positive electrode and the solid electrolyte membrane. position, and the anode and cathode are applied to an electrochemical cell including a configuration electrically connected through a conducting wire.
The preparation of the solid electrolyte film may include weighing and mixing precursor materials in a predetermined ratio; quenching after melting the mixed precursor materials; cooling the obtained glass after heat treatment; and sintering the glass to crystallize and process it.

Description

Lithium recovery system including solid electrolyte membrane and method of manufacturing the solid electrolyte membrane}

The present invention relates to a lithium recovery system and relates to an apparatus and method for recovering lithium contained in a waste lithium solution or the like.

Lithium is widely used in various industries such as secondary batteries, glass, ceramics, alloys, lubricants, and pharmaceuticals. In particular, lithium secondary batteries are recently attracting attention as a major power source for hybrid and electric vehicles, and The small battery market is also expected to grow into a huge market 100 times larger in the future.

In addition, due to the global movement to strengthen environmental regulations, its application fields will greatly expand not only to the hybrid and electric vehicle industries, but also to electronics, chemicals, and energy in the near future, and domestic and international demand for lithium throughout the 21st century industry will increase. is expected to soar.

Accordingly, many studies are being conducted on the reuse of lithium, such as lithium extraction from waste batteries. Lithium extraction from waste batteries can be performed using an electrochemical process using a lithium ion conductive solid electrolyte membrane.

The production of the lithium ion conductive solid electrolyte membrane may generally be performed by pelletizing solid electrolyte powder obtained through a sol-gel method or the like and then sintering. However, in the case of the solid electrolyte membrane prepared by the above method, there may be a problem in that it has insufficient ion conductivity for practical use. An electrolyte membrane with high density and high ion conductivity can be manufactured by adding a sintering additive, etc., but when applied to a lithium recovery system, the electrolyte membrane is pierced by the solution even if there are only a few pores, and the composition of the recovery system There is a problem that the role of separating the elements cannot be properly performed.

Korean Registered Patent Publication No. 10-2123988

The problem to be solved by the present invention is to provide a lithium recovery device to which a lithium ion conductive solid electrolyte membrane having high ion conductivity and excellent mechanical strength is applied and a lithium recovery method using the same.

The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above technical problem, one aspect of the present invention provides a lithium recovery system. The lithium recovery system includes a positive electrode, a negative electrode, a solid electrolyte membrane positioned between the positive electrode and the negative electrode, a separator impregnated with an organic electrolyte positioned between the negative electrode and the solid electrolyte membrane, and a cation exchange membrane positioned between the positive electrode and the solid electrolyte membrane. An electrochemical cell provided with and a reservoir may be disposed on one side of the electrochemical cell, and the anode may be disposed on a side adjacent to the reservoir.

The positive current collector may be made of carbon felt, carbon paper, carbon fiber, carbon cloth, carbon nanotube layer, or a combination thereof.

As the anode, lithium metal or an alloy of lithium and Mg, Au, Ag, Al, Zn, Sn, or a combination of two or more thereof may be used.

The non-aqueous organic solvent used in the organic electrolyte may be one of carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents.

The separator may be one of a film laminate containing polyethylene or polypropylene, a fibrous nonwoven fabric containing cellulose, polyester or polypropylene, or a porous glass filter.

In the manufacture of the solid electrolyte membrane, precursor materials including Li ₂ CO ₃ and H ₃ PO ₄ , and at least one selected from GeO ₂ , Al(PO ₃ ) ₃ , SiO ₂ and TiO ₂ are measured in a predetermined ratio. mixing, melting the mixed precursor materials and then quenching at 350 ° C to 450 ° C, cooling the obtained glass after annealing, and firing the glass to crystallize and process to obtain a solid electrolyte film And the solid electrolyte membrane has a crystal represented by Formula 1 as a main crystal phase,

[Formula 1]

Li _1+x+y Al _x (Ti, Ge) _2-x Si _y P _3-y O ₁₂

For Chemical Formula 1, 0≤x≤1 and 0≤y≤1 may be satisfied.

As an example, a quenching temperature may be 350 °C to 400 °C when manufacturing the solid electrolyte membrane.

Ionic conductivity of the prepared solid electrolyte membrane may be 1 x 10 ^-5 to 4 x 10 ^-4 S/cm.

The lithium recovery system is driven by a positive electrode, a negative electrode, a solid electrolyte membrane positioned between the positive electrode and the negative electrode, a separator positioned between the negative electrode and the solid electrolyte membrane, and a cation exchange membrane positioned between the positive electrode and the solid electrolyte membrane. Providing a lithium recovery system in which an electrochemical cell and a storage tank are disposed on one side of the electrochemical cell, putting a waste solution into the storage tank and performing a charging operation to deposit lithium metal from the negative electrode, and depositing lithium metal in the storage tank. A step of obtaining a lithium salt such as LiOH and Li ₂ CO ₃ from the positive electrode by adding water instead of the solution and performing a discharging operation.

The waste solution includes a lithium-containing material, and the lithium-containing material may be a waste battery, a waste cathode material, a waste anode material, a material derived from LAS recycled resources (Lithium-Aluminium-Silicate), or a combination thereof.

The water contained in the storage tank used during the discharge may be in a state in which CO ₂ (g) is added to the water in a bubbling manner and dissolved before the reaction.

The present invention can manufacture a solid electrolyte membrane having high ionic conductivity and excellent mechanical strength, and provide a lithium recovery system to which the solid electrolyte membrane is applied.

The technical effects of the present invention are not limited to those mentioned above, and other technical effects not mentioned will be clearly understood by those skilled in the art from the description below.

1 is a schematic diagram showing a lithium recovery system including an electrochemical cell according to an embodiment of the present invention.
2 is a schematic diagram showing movement of lithium ions during a charging process of an electrochemical cell according to an embodiment of the present invention.
3 is a schematic diagram showing movement of lithium ions during discharging of an electrochemical cell according to an embodiment of the present invention.
4 is a photograph of a reduction phenomenon prevention experiment when assembling an electrochemical cell for evaluating an electrolyte membrane according to an embodiment of the present invention.
5 is a graph of XPS analysis results after a charge/discharge experiment when assembling an electrochemical cell for evaluating an electrolyte membrane according to an embodiment of the present invention.
6 is a schematic flowchart of a manufacturing process of a solid electrolyte membrane, which is a component of the electrochemical cell of the present invention.
7 is a graph showing XRD analysis results and SEM observation results of a solid electrolyte membrane prepared at room temperature (25 ° C.) as a quenching temperature.
8 is a graph showing XRD analysis results and SEM observation results of a solid electrolyte membrane prepared at a quenching temperature of 150 °C.
9 is a graph showing XRD analysis results and SEM observation results of a solid electrolyte membrane prepared at a quenching temperature of 250 °C.
10 is a graph showing XRD analysis results and SEM observation results of solid electrolyte membranes prepared at a quenching temperature of 350 °C.
11 is a graph showing XRD analysis results and SEM observation results of a solid electrolyte membrane prepared at a quenching temperature of 400 °C.
12 is a graph showing XRD analysis results and SEM observation results of solid electrolyte membranes prepared at a quenching temperature of 450 °C.
13 is a graph showing the impedance measured for calculating the ionic conductivity of the solid electrolyte membrane according to the preparation example according to the quenching temperature.
14 is a charge/discharge graph of an electrochemical cell to which a solid electrolyte membrane according to an embodiment of the present invention is applied.

Hereinafter, in order to explain the present invention in more detail, preferred embodiments according to the present invention will be described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Like reference numbers indicate like elements throughout the specification.

1 is a schematic diagram showing a lithium recovery system including an electrochemical cell according to an embodiment of the present invention.

Referring to FIG. 1, an electrochemical cell to which a solid electrolyte membrane is applied according to an embodiment of the present invention stores energy using abundant lithium ions in a waste solution and provides the stored energy to generate a lithium salt, and an anode (500 ), a negative electrode 100, and a solid electrolyte membrane 300 disposed between the positive electrode and the negative electrode, and the storage tank 1000 connected to one side of the positive electrode 500 may introduce waste solutions, seawater, etc. .

The positive electrode 500 may be a porous material having excellent electronic conductivity and capable of transmitting lithium ions. The anode 500 may be a carbon-based compound or a metal mesh. However, it is not particularly limited as long as it has high conductivity without causing chemical change in the device. More specifically, as a carbon-based compound having low density and good electrical conductivity, it may be a carbon felt, carbon paper, carbon fiber, carbon cloth, carbon nanotube layer, or a combination thereof.

The anode 100 may be a lithium metal layer or a lithium alloy layer. In the negative electrode 100, a reaction in which lithium metal is oxidized to lithium ions during discharging and reduced to lithium metal during charging may occur. The lithium metal layer may be a lithium foil, and the lithium alloy layer may be a lithium alloy foil. The lithium alloy may be an alloy of lithium and another metal, such as Mg, Au, Ag, Al, Zn, Sn, or a combination of two or more thereof.

The solid electrolyte film 300 is a film through which only lithium ions can selectively pass, and includes a lithium super ionic conductor (LISICON), an amorphous ion conductive material (phosphorus-based glass, oxide-based glass, oxide/ sulfide based glass), a ceramic ion conductive material (lithium beta-alumina), a lithium sulfide-based solid electrolyte, a lithium oxide-based solid electrolyte, or a combination thereof.

Specifically, the solid electrolyte film 300 is phosphorus-based glass, oxide-based glass, phosphorus-oxynitride-based glass, sulfur-based glass, oxide/sulfide-based glass, selenide-based glass, gallium-based glass, germanium-based glass, or glass. -ceramic active metal ion conductor, LiPON, Li ₃ PO ₄ Li ₂ S SiS ₂ , Li ₂ S GeS ₂ Ga ₂ S ₃ , Li ₂ O 11Al ₂ O ₃ , Li _1+x Ti _2-x Al _x (PO ₄ ) ₃ (0.6≤x≤0.9) and crystallographically related structures, Li ₃ Zr ₂ Si ₂ PO ₁₂ , Li ₅ ZrP ₃ O ₁₂ , Li ₅ TiP ₃ O ₁₂ , Li ₃ Fe ₂ P ₃ O ₁₂ , or Li ₄ NbP ₃ O ₁₂ . More specifically, it may be Li _1+x+y Al _x (Ti, Ge) _2-x Si _y P _3-y O ₁₂ (where 0≤x≤1, 0<y≤1).

A separator 200 impregnated with an organic electrolyte may be inserted between the anode 100 and the solid electrolyte layer 300 . The separator 200 is an insulating porous material, and may be a film laminate containing polyethylene or polypropylene (PP), a fiber non-woven fabric containing cellulose, polyester, or polypropylene (PP), or a porous glass filter.

The organic electrolyte solution (not shown) may include an electrolyte used in a general lithium ion battery and a non-aqueous organic solvent. The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

Carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents may be used as the non-aqueous organic solvent. As the carbonate-based solvent, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used, and the ester-based solvent includes methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methyl propionate , ethylpropionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and the like can be used. Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether-based solvent, and cyclohexanone or the like may be used as the ketone-based solvent. there is. In addition, ethyl alcohol, isopropyl alcohol, etc. may be used as the alcohol-based solvent, and as the aprotic solvent, R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, among which aromatic rings or ether linkages may be included), nitriles such as dimethylformamide, amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like may be used.

Representative examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ ) (C _y F _{2y +1} SO ₂ ) (where x and y are natural numbers), LiCl, LiI, LiB(C ₂ O ₄ ) ₂ (lithium bis(oxalato) borate; LiBOB) or combinations thereof. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, Excellent electrolyte performance can be exhibited, and lithium ions can move effectively.

A cation exchange membrane 400 may be positioned between the solid electrolyte membrane 300 and the anode 500 . The cation exchange membrane 400 may selectively transmit cations, specifically lithium ions, and may be an ion conductor and an electrical insulator at the same time. The cation exchange membrane 400 is a polymeric porous membrane in which an anionic functional group is bonded to the pore surface, and may be a polyolefin membrane in which a sulfonyl (SO ₃ ^- ) group is bonded to an anionic functional group.

2 is a schematic diagram showing movement of lithium ions during a charging process of an electrochemical cell according to an embodiment of the present invention.

Referring to FIG. 2 , during a charging process in which lithium metal is precipitated on the negative electrode 100 , a waste solution is first introduced into the storage tank 1000 . At this time, the lithium salt in the waste solution is ionized at the positive electrode 500, and the lithium ions sequentially pass through the cation exchange membrane 400, the solid electrolyte membrane 300, and the separator 200 to come into contact with the negative electrode 100. .

The waste solution includes a lithium-containing material, and the lithium-containing material is a waste battery, a waste cathode material, a waste anode material, a material derived from LAS recycled resources (Lithium-Aluminium-Silicate), for example, lithium oxide, lithium salt Or a combination thereof may be dispersed or dissolved in a solvent.

When an external conductor is connected between the positive electrode 500 and the negative electrode 100, the positive electrode 500 generates lithium ions and electrons from the lithium-containing material, and the electrons move to the negative electrode 100 along the external conductor, , Lithium ions may pass through the cation exchange membrane 400, the solid electrolyte membrane 300, and the separator 200 in sequence to move to the negative electrode 100. In the negative electrode 100, the electrons and lithium ions meet and lithium metal may be deposited on the negative electrode.

3 is a schematic diagram showing movement of lithium ions during discharging of an electrochemical cell according to an embodiment of the present invention.

Referring to FIG. 3 , the waste lithium solution may be removed and water may be injected into the storage tank 1000 . By reversing the electrical flow between the positive electrode 500 and the negative electrode 100 connected by an external conductor, the lithium metal deposited on the negative electrode 100 is ionized into lithium ions and moves to water through the positive electrode 500 to form LiOH and Li ₂ A discharging process to obtain a lithium salt such as CO ₃ may proceed.

Specifically, lithium ions and electrons are generated from lithium metal precipitated on the anode 100, and the lithium ions pass through the separator 200, the solid electrolyte membrane 300, and the cation exchange membrane 400 in sequence to reach the anode. will do At this time, electrons may move to the anode 500 along the external conductor.

Lithium ions moved to the positive electrode 500 may react with water as shown in Scheme 1 below.

[Scheme 1]

Li ⁺ + e ^- + H ₂ O (ℓ) → LiOH (aq) + 1/2 H ₂ (g)

LiOH (aq) produced by Reaction Scheme 1 may react with CO ₂ (g) previously dissolved in water as shown in Reaction Scheme 2 below, and prior to the reaction, the CO ₂ (g) is added to water by bubbling. It may be in a sufficiently dissolved state.

[Scheme 2]

2LiOH(aq) + CO ₂ (g) → Li ₂ CO ₃ (s) + H ₂ O (ℓ)

1 to 3 , a cation exchange membrane 400 is disposed between the solid electrolyte membrane 300 and the anode 500 when assembling the electrochemical cell. The cation exchange membrane 400 serves as an electrical insulator to prevent deterioration of the solid electrolyte membrane 300 by blocking the flow of electrons from the adjacent anode 500 to the solid electrolyte membrane 300 when the electrochemical cell is operated. can

4 is a photograph of a reduction phenomenon prevention experiment according to whether a cation exchange membrane 400 is introduced or not when assembling an electrochemical cell for evaluating an electrolyte membrane. 4(a) is a photograph of an electrolyte membrane evaluation without introducing the cation exchange membrane 400 when assembling the electrochemical cell, and FIG. 4(b) shows an electrolyte membrane by introducing the cation exchange membrane 400 during assembly of the electrochemical cell. This is a picture I just reviewed.

Referring to FIG. 4(a), when the cation exchange membrane 400 is not introduced when assembling the electrochemical cell, electrons that have moved to the anode 500 during discharge are injected to the surface of the solid electrolyte membrane 300 to form Ge ⁴⁺ , Ti ⁴⁺ ions are reduced to Ge ²⁺ and Ti ³⁺ , respectively, and discoloration occurs on the surface of the solid electrolyte membrane 300 .

Referring to FIG. 4(b), when a cation exchange membrane 400 is introduced between the anode 500 and the solid electrolyte membrane 300, the cation exchange membrane 400 acts as an electrical insulator, and the solid electrolyte in the anode 500 It can be confirmed that discoloration is prevented by blocking the flow of electrons to the surface of the film 300 by preventing reduction of a metalloid such as Ge or Ti or a transition metal on the surface of the solid electrolyte film 300 of the electrochemical cell.

5 is an XPS analysis result before (a, c) and after (b, d) driving the electrochemical cell after a charge/discharge experiment when assembling an electrochemical cell for evaluating an electrolyte membrane according to an embodiment of the present invention. it's a graph

As a result of XPS analysis in FIG. 5 comparing before and after driving the electrochemical cell, comparing FIGS. 5(a) and 5(b) in which Ge ions were analyzed first, in FIG. 5(a), which is a graph before driving, Ge ⁴ Only ⁺ ions were observed, but Ge ²⁺ ions were additionally observed in FIG. 5 (b), which is a graph after driving.

Meanwhile, comparing FIG. 5(c) and FIG. 5(d) in which Ti ions are analyzed, only Ti ⁴⁺ ions are observed in the graph before driving, but additional Ti ³⁺ ions are observed in the graph after driving in FIG. 5(d). can be observed.

4 and 5 simultaneously, the discoloration of the surface of the solid electrolyte membrane 300 of the electrochemical cell can be seen as the reduction of Ge ions and Ti ions, which is used as the anode 500 during discharge of the electrochemical cell. It can be seen that electrons moved to the carbon felt are injected into the surface of the solid electrolyte film 300 and reduction occurs.

FIG. 6 is a schematic flow chart of a manufacturing process of the solid electrolyte membrane 300 among the components of the electrochemical cell shown in FIG. 1 . The manufacturing process of the solid electrolyte film 300 may be performed by a melt-quenching method as follows.

Referring to FIG. 6 , the manufacturing process of the solid electrolyte membrane 300 is described in more detail as follows. First, the raw materials are weighed in a predetermined ratio. In this case, the raw material may be Li ₂ CO ₃ , Al(PO ₃ ) ₃ , TiO ₂ , SiO ₂ , GeO ₂ and H ₃ PO ₄ (S100). After uniformly mixing the raw materials, the mixed raw materials are put into an alumina crucible, which is a thermal analysis crucible, and heated to melt in an electric furnace.

Gas components generated from the raw material components evaporate at 700 ° C., and when the temperature is raised to 1350 ° C. to 1450 ° C. and maintained for about 1 to 2 hours, the raw materials melt. The molten raw materials are cast on a stainless steel plate (SUS plate) to form a glass sheet (quenching) (S200).

The quenching refers to a process of casting the molten raw materials on a stainless steel plate. At this time, the temperature of the stainless steel sheet is called the quenching temperature.

When the quenching temperature is 250 ° C. or higher, cracks may not occur during sintering of the obtained glass. In addition, the ion conductivity of the solid electrolyte membrane fabricated at a quenching temperature of 350 ° C. or higher and 450 ° C. or higher, more specifically, at a quenching temperature of 400 ° C. or higher may have a high ion conductivity of 1 x 10 ^-4 or higher. Additionally, in the case of an electrochemical cell to which a solid electrolyte membrane manufactured at a quenching temperature of 350 ° C. to 400 ° C. is applied, it can be driven with a low charge and discharge overvoltage. Therefore, when the solid electrolyte membrane manufactured by setting the quenching temperature to 350 °C to 400 °C is applied to an electrochemical cell, driving may be advantageous.

The glass obtained through the quenching process is heat treated (annealed) for 2 to 72 hours in the range of 550 ° C to 1000 ° C and then cooled (S300).

The obtained glass is calcined, crystallized, and processed (S400). In detail, crystallinity of the glass can be improved through a firing process to obtain an integrated glass-ceramic that is firmly bonded to each other. The glass-ceramic is Li _1+x+y Al _x (Ti, Ge) _2-x Si _y P _3-y O ₁₂ (provided that 0≤x≤1 and 0≤y≤1, for example 0≤ x≤0.4, 0≤y≤0.6, or 0.1≤x≤0.3, 0≤y≤0.4) may be included as the main crystal phase. In addition to this, the secondary phase (secondary phase) may further include AlPO ₄ .

The firing treatment temperature is not particularly limited as long as it is a temperature at which a desired glass-ceramic can be obtained. If the firing temperature is too low, crystallization does not proceed because the glass transition temperature is not reached, whereas if the firing temperature is too high, a desired crystal structure cannot be formed. Further, the firing treatment duration is within a range of, for example, 1 minute to 10 hours, and preferably within a range of 0.5 to 6 hours.

In the case of the lithium ion conductive glass-ceramic according to an embodiment of the present invention, the above-mentioned composition range is Li _1+x+y Al _x (Ti, Ge) _2-x Si _y P _3-y O ₁₂ (provided that, 0≤x≤1, 0≤y≤1, for example, 0≤x≤0.4, 0≤y≤0.6, or 0.1≤x≤0.3, 0≤y≤0.4) as the main crystal phase. . When the glass-ceramic is a crystal that does not include a grain boundary that inhibits ion conduction, it is advantageous in terms of conductivity. For example, glass-ceramic has high ion conductivity and excellent chemical stability because it has almost no pores or grain boundaries that hinder ion conduction.

Hereinafter, preferred examples are presented in order to facilitate understanding of the present invention. However, the following experimental examples are only for helping understanding of the present invention, and the present invention is not limited by the following experimental examples.

Manufacture of solid electrolyte membrane

[Example 1]

A solid electrolyte membrane having a quenching temperature as shown in Table 1 below was prepared.

First, Li ₂ CO ₃ , Al(PO ₃ ) ₃ , TiO ₂ , SiO ₂ , GeO ₂ and H ₃ PO ₄ are prepared as raw materials. The raw materials were weighed so as to have a ratio of 36.0 P ₂ O ₅ - 22.0 GeO ₂ - 6.9 Al ₂ O ₃ - 4.8 SiO ₂ -12.6 TiO ₂ - 17.7 Li ₂ O (mol %). After uniformly mixing the raw materials, they are put into an alumina crucible and melted in an electric furnace by heating. CO ₂ , NH ₃ and H ₂ O from raw materials are evaporated at 700 °C. After that, the temperature is raised to 1350 ° C. and heat is applied at that temperature for 1 hour and 30 minutes to melt the raw materials.

The melt is cast in a stainless steel plate (SUS plate) to form a uniform glass sheet. The process of forming a glass sheet by placing the molten material on a stainless steel plate is called quenching, and at this time, the temperature of the stainless steel plate is called the quenching temperature. The glass obtained by setting the quenching temperature to 350 °C was annealed at 550 °C for 2 hours and then cooled.

The glass sample is calcined at 900° C. to crystallize, and processed into a circular sample having a diameter of 20 mm to obtain a glass-ceramic. The prepared glass-ceramic crystal phase can be represented by Li _1+x+y Al _x (Ti, Ge) _2-x Si _y P _3-y O ₁₂ (where 0≤x≤1 and 0≤y≤1) there is.

[Experimental Example 2]

A battery was manufactured in the same manner as in Example 1, except that the quenching temperature was changed to 25 °C (room temperature).

[Experiment 3]

A battery was manufactured in the same manner as in Example 1, except that the quenching temperature was changed to 150 °C.

[Experiment 4]

A battery was manufactured in the same manner as in Example 1, except that the quenching temperature was changed to 250 °C.

[Example 5]

A battery was manufactured in the same manner as in Example 1, except that the quenching temperature was changed to 350 °C.

[Experiment 6]

A battery was manufactured in the same manner as in Example 1, except that the quenching temperature was changed to 400 °C.

[Experiment 7]

A battery was manufactured in the same manner as in Example 1, except that the quenching temperature was changed to 450 °C.

[Comparative example]

Li _1+x+y Al _x (Ti, Ge) _2-x Si _y P _3-y O ₁₂ (0≤x≤1, and 0≤y≤1) was used. The solid electrolyte membrane was purchased from OHARA's LICGC AG-01 product.

Table 1 below is a table showing the quenching temperature and density when preparing the solid electrolyte membranes of Experimental Examples 1, 6, and 7 and Comparative Examples, respectively.

Quenching Temperature(℃) Density (g/cm ³ ) Experimental Example 1 350 2.998 Experimental Example 6 400 2.997 Experimental Example 7 450 2.994 comparative example Use of commercial solid electrolyte membrane 3.05

Referring to Table 1, it can be seen that the density increases as the quenching temperature decreases during the manufacture of the solid electrolyte membrane.

Meanwhile, as the quenching temperature decreases, the strength of the solid electrolyte membrane increases. By controlling the quenching temperature, a solid electrolyte membrane having high strength and high ionic conductivity of 1x10 ^-4 can be manufactured.

Crystal structure and particle shape characteristics according to quenching temperature

XRD analysis results and SEM observation results of the solid electrolyte membrane prepared according to the experimental example are shown in FIGS. 7 to 12 .

When preparing the solid electrolyte membrane, each quenching temperature, room temperature (FIG. 7), 150 ℃ (FIG. 8), 250 ℃ (FIG. 9), 350 ℃ (FIG. 10), 400 ℃ (FIG. 11) and 450 ℃ (FIG. 12 ) are SEM images and XRD analysis graphs for the solid electrolyte membrane composition according to.

Referring to FIG. 7, SEM images and XRD graphs of the composition obtained by controlling the quenching temperature to room temperature and sintering the broken pieces are shown. As a result of analyzing the peaks of the XRD graph shown in FIG. 7(c), it can be seen that (Ge,Si)O ₂ (Germanium silicon oxide), which is an additional secondary phase, is detected in addition to AlPO ₄ .

Referring to FIG. 8(c), as a result of analyzing the peaks of the XRD graph, as at room temperature, an additional secondary phase (Ge,Si)O ₂ (Germanium silicon oxide) is detected, and FIG. 8(a) As a result of the SEM top view image analysis shown in to FIG. 8(b), it can be confirmed that white crystals are partially concentrated.

Referring to FIGS. 7 to 9 , in the case of glass prepared at room temperature, 150 ° C. and 250 ° C. as the quenching temperature, cracks may occur after firing. This may be caused by stress caused by a difference in thermal expansion coefficient (TEC) between the main crystal phase and the secondary phase.

9 to 12, as a result of SEM image analysis, it can be seen that the crystals are densely gathered in both the top view and the cross view, and as a result of analyzing the peaks of the XRD graph, the main crystal phase and AlPO ₄ It can be seen that is detected and no additional secondary phase is detected.

Evaluation of ion conductivity of solid electrolyte membrane according to quenching temperature

Ion conductivity was measured for the electrochemical cell using the solid electrolyte membrane prepared by varying the quenching temperature according to the experimental example. Ionic conductivity was measured by the alternating current impedance method.

The ionic conductivity of the electrolyte used in the experimental example was evaluated by applying a voltage bias of 10 mV in the frequency range of 0.1 Hz to 1 MHz and measuring the resistance at 20 ° C. and 0% relative humidity (RH) conditions, and it is shown in Table 2 below.

Quenching Temperature(℃) Conductivity(S/cm) Experimental Example 1 350 3. 45 X 10 ^-5 Experimental Example 6 400 2. 31 X 10 ^-4 Experimental Example 7 450 3. 46 X 10 ^-4

Table 2 is a table showing the ion conductivity of the solid electrolyte membrane prepared according to the experimental example according to the quenching temperature.

13 is a graph showing the impedance measured for the calculation of the ionic conductivity of the solid electrolyte membrane prepared according to the experimental example according to the quenching temperature, 350 ℃ (a), 400 ℃ (b) and 450 ℃ (c), respectively am.

Referring to Table 2 and FIG. 13, as a result of measuring the ion conductivities of the solid electrolyte membranes prepared at quenching temperatures of 350 ° C, 400 ° C, and 450 ° C according to the AC impedance method, the ionic conductivity values were 3. 45 x 10 ^-5 S/cm, 2. 31 x 10 ^-4 S/cm and 3. 46 x 10 ^-4 S/cm. Through the value of the ionic conductivity, when the quenching temperature is 400 ℃ or more, it can be confirmed that it has a high ionic conductivity of 1 x 10 ^-4 S / cm or more.

7 to 13 and Table 2, considering the characteristics of crystal structure, particle shape and ionic conductivity according to the quenching temperature, the quenching temperature is 250 ℃ or more, in particular, 400 ℃ or more. It can be seen that it is more preferable when

Manufacturing and driving method of electrochemical cell

In order to manufacture the electrochemical cell according to the experimental example of the present invention, a porous carbon felt was used as an anode and lithium metal was used as a cathode. The anode and cathode are electrically connected through an external conductor. A separator impregnated with an organic electrolyte, a solid electrolyte membrane, and a cation exchange membrane are sequentially stacked between the anode and the cathode. Polypropylene (PP) as the separator, LiPF ₆ dissolved in ethylene carbonate (EC) as the organic electrolyte, and Li _1+x+y Al _x (Ti, Ge) _2-x Si _y P ₃ as the solid electrolyte film _-y O ₁₂ (however, 0≤x≤1, 0<y≤1) is used, and CEM-type10 (Fuji film) is used as a cation exchange membrane. A storage tank in which waste solution or water can be contained may be disposed on one side of the anode.

After the waste solution containing lithium salt is contained in the storage tank, when an electric current is applied, the lithium salt is ionized at the anode, and the lithium ions pass through the cathode, the solid electrolyte membrane, the organic electrolyte and the separator in order to form lithium metal on the anode. is precipitated

The discharge of the lithium metal deposited on the negative electrode is performed by applying a reverse direction of electric flow and exchanging the waste solution contained in the storage tank with water. Through the discharging process, the lithium metal on the negative electrode is ionized and sequentially passes through the separator, the organic electrolyte solution, and the solid electrolyte membrane, and reacts with water at the positive electrode to generate a salt such as LiOH or Li ₂ CO ₃ .

Evaluation of charge and discharge characteristics

A charge/discharge cycle experiment was performed at a constant current of 0.05 mA/cm ² for an electrochemical cell using a solid electrolyte membrane prepared by varying the quenching temperature at room temperature and atmospheric pressure. Cut-off voltage was set to 2 to 5V. 14 shows a charge/discharge graph in which voltage values measured after each charge/discharge cycle were performed for 5 hours. However, the commercial solid electrolyte film used at this time is Li _1+x+y Al _x( Ti, Ge) _2-x Si _y P _3-y O ₁₂ (0≤x≤1, and 0≤y≤1). OHARA's LICGC AG-01 product was purchased.

Referring to FIG. 14 at the same time, it can be seen that when the solid electrolyte membranes manufactured at quenching temperatures of 350 ° C and 400 ° C are used, they operate with low charge and discharge and overvoltage similar to commercial solid electrolyte membranes manufactured in the prior art. On the other hand, it can be seen that in the case of using a solid electrolyte membrane manufactured at a quenching temperature of 450 °C, it is driven with a relatively high charge/discharge overvoltage.

7 to 14 and Table 2, the quenching temperature is 350 ℃ to 400 ℃ in consideration of the crystal structure, particle shape, ionic conductivity, and charging and discharging characteristics of the electrochemical cell according to the quenching temperature Solid electrolyte It can be seen that it is more preferable when the production of the membrane is made.

In the above, the present invention has been described in detail with preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications and changes are made by those skilled in the art within the technical spirit and scope of the present invention. this is possible

100: cathode 200: separator
300: solid electrolyte membrane 400: cation exchange membrane
500: anode 1000: reservoir

Claims (11)

anode;
cathode;
a solid electrolyte film positioned between the anode and the cathode and containing a metalloid or transition metal;
a separator impregnated with an organic electrolyte positioned between the anode and the solid electrolyte layer; and
An electrochemical cell equipped with a cation exchange membrane positioned between the anode and the solid electrolyte membrane; and
A storage tank is disposed on one side of the electrochemical cell, and the anode is disposed adjacent to the storage tank,
The solid electrolyte membrane includes a main crystal phase represented by Chemical Formula 1 and a secondary crystal phase represented by AlPO ₄ , but does not include a secondary phase (Ge,Si)O ₂ ,
The ion exchange membrane and the solid electrolyte membrane are in contact with each other, and the cation exchange membrane prevents Ge ⁴⁺ and Ti ⁴⁺ ions on the surface of the solid electrolyte membrane from being reduced to Ge ²⁺ and Ti ³⁺ , respectively. Blocking, lithium recovery system:
[Formula 1]
Li _1+x+y Al _x (Ti, Ge) _2-x Si _y P _3-y O ₁₂
For Formula 1, 0≤x≤1 and 0≤y≤1. According to claim 1,
A lithium recovery system in which carbon felt, carbon paper, carbon fiber, carbon cloth, carbon nanotube layer, or a combination thereof is used as the anode. According to claim 1,
A lithium recovery system in which lithium metal or an alloy of lithium and Mg, Au, Ag, Al, Zn, Sn, or a combination of two or more thereof is used as the negative electrode. According to claim 1,
The non-aqueous organic solvent used in the organic electrolyte solution is one of carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents. According to claim 1,
The separator is a lithium recovery system that is one of a film laminate containing polyethylene or polypropylene, a fibrous nonwoven fabric containing cellulose, polyester or polypropylene, or a porous glass filter. delete delete delete Providing the lithium recovery system of claim 1;
Putting a waste solution into the storage tank and performing a charging operation to deposit lithium metal from the negative electrode; and
A method of driving a lithium recovery system comprising: adding water into the storage tank and performing a discharging operation to obtain LiOH and Li ₂ CO ₃ lithium salt at the cathode. According to claim 9,
The waste solution includes a lithium-containing material, and the lithium-containing material is a waste battery, a waste cathode material, a waste anode material, a material derived from a lithium-aluminium-silicate (LAS) recycling resource, or a combination thereof of a lithium recovery system. driving method. According to claim 9,
The method of driving the lithium recovery system in which the water contained in the storage tank used during discharge is in a state in which CO ₂ (g) is added to the water by bubbling and dissolved before the reaction.

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