KR102776436B1 - Llzo solid electrolyte manufacturing method using microwave solvothermal synthesis method and llzo solid electrolyte prepared thereby - Google Patents

Abstract

The present invention relates to a method for producing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method, and to an LLZO-based solid electrolyte produced thereby, and more particularly, to a method for producing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method, and to an LLZO-based solid electrolyte produced thereby, and more particularly, to a method for producing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method, which can synthesize a precursor powder in a short period of time using a microwave solvothermal synthesis method, refine the particle size of the LLZO powder, and produce an LLZO-based solid electrolyte having improved electrochemical characteristics through improved sinterability thereby, and to an LLZO-based solid electrolyte produced thereby.
According to the above, the present invention provides a method for manufacturing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method, which can synthesize a precursor powder in a short period of time using a microwave solvothermal synthesis method, refine the particle size of the LLZO powder, and manufacture an LLZO-based solid electrolyte having improved electrochemical characteristics through improved sinterability thereby, and an LLZO-based solid electrolyte manufactured thereby, and the present invention also provides a method for manufacturing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method, which can improve the capacity of a lithium-ion battery while ensuring stability, has high ionic conductivity, and can be used safely without problems of leakage and ignition.

Description

Method for manufacturing LLZO-based solid electrolyte using microwave solvothermal synthesis method and LLZO-based solid electrolyte prepared thereby {LLZO SOLID ELECTROLYTE MANUFACTURING METHOD USING MICROWAVE SOLVOTHERMAL SYNTHESIS METHOD AND LLZO SOLID ELECTROLYTE PREPARED THEREBY}

The present invention relates to a method for producing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method, and to an LLZO-based solid electrolyte produced thereby. More specifically, the present invention relates to a method for producing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method, which can synthesize a precursor powder in a short period of time using a microwave solvothermal synthesis method, refine the particle size of the LLZO powder, and produce an LLZO-based solid electrolyte having improved electrochemical properties through improved sinterability thereby.

As the demand for lithium-ion batteries is increasing as a power source for automobiles and energy storage systems, lithium-ion batteries are pursuing low price, high stability, high capacity, and large area.

However, lithium-ion batteries using existing liquid electrolytes have safety issues due to the high possibility of leakage and ignition, and these safety issues are becoming more prominent as batteries become larger in capacity and area.

Accordingly, research is being conducted on all-solid-state batteries (all-solid-state lithium-ion batteries) using inorganic solid electrolytes, which are non-flammable materials, to increase the capacity of lithium-ion batteries while ensuring stability.

Inorganic solid electrolytes include sulfides and oxides, but sulfide-based solid electrolytes have the disadvantages of reacting with moisture in the air, making it difficult to control the process atmosphere, and causing side reactions at the interface with the electrode. In contrast, oxide-based solid electrolytes have high stability in moisture and the air.

Representative examples of oxide-based solid electrolytes include LLTO and LLZO. LLTO has the disadvantage of high resistance at grain boundaries and low overall ionic conductivity. On the other hand, LLZO has a wide potential window characteristic and low resistance at grain boundaries compared to LLTO, so it has high overall ionic conductivity, and therefore, much research is currently being conducted on it.

LLZO solid electrolytes have a tetragonal or cubic structure. It has been reported that the cubic structure has ionic conductivity about 100 times higher than the tetragonal structure. The cubic LLZO has high ionic conductivity because the lithium ions in the octahedral sites exist in a twisted form, which is due to the short distance between the lithium ions in the tetrahedral sites and the three-dimensional ion conduction channel structure. On the other hand, the tetragonal LLZO has a well-ordered lithium ions structure, which makes the distance between the ions long and has a two-dimensional ion conduction channel structure, which is reported to have lower ionic conductivity than the cubic LLZO.

For this reason, in order to have high ionic conductivity, the cubic structure must be formed, but the cubic structure is unstable at room temperature and requires a high sintering temperature of 1,200℃ or higher. This high temperature also causes lithium volatilization, which results in a decrease in the concentration of lithium ions. For this reason, in order to stabilize the cubic structure at room temperature, prior research is being conducted on doping cations such as Al3 ⁺ , Ga3 ⁺ , Fe3 ⁺ , and B3 ⁺ in the existing lithium ion site and substituting them with lithium, which increases entropy and decreases free energy, thereby stabilizing the cubic structure.

In addition, it has been reported that although it is difficult to synthesize cubic LLZO without doping, it is possible to synthesize cubic LLZO without doping when the particle size is reduced. Conventional methods for synthesizing LLZO powder include the solid-state reaction method and the sol-gel method.

In the case of the above solid-state reaction method, the synthesis process time is long and calcination must be performed at a high temperature of 1,000℃ or higher, so the particle size of the powder increases and the sinterability decreases during sintering, which has the disadvantage of lowering the electrochemical characteristics (ionic conductivity).

Accordingly, research has been conducted to introduce the sol-gel method for synthesis in order to simplify the synthesis process and reduce the particle size of the powder. However, compared to the solid-state reaction method, the sol-gel method has a simple manufacturing process and the particle size of the powder is relatively small, so there is a result of a previous study that relatively improves the electrochemical characteristics (ionic conductivity) due to the increase in sinterability.

As electrochemical properties such as ionic conductivity are proportional to the particle size of the powder and the resulting sinterability, there is a need to develop a technology that can further refine the particle size of the powder, and there is also a need to develop a new synthesis method that pursues reduction and simplification of the process time.

Therefore, a new method to solve these problems became necessary.

Domestic registration patent No. 10-2131890 (registered on July 2, 2020) Domestic registration patent No. 10-1752866 (registered on June 26, 2017) Domestic registration patent No. 10-1939142 (registered on January 10, 2019)

The present invention has been made to solve the problems of the prior art as described above, and more specifically, the present invention provides a method for manufacturing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method, which can synthesize a precursor powder in a short period of time using a microwave solvothermal synthesis method, refine the particle size of the LLZO powder, and manufacture an LLZO-based solid electrolyte having improved electrochemical properties through improved sinterability thereby, and an LLZO-based solid electrolyte manufactured thereby.

In addition, the present invention aims to provide a method for manufacturing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method, which can improve the capacity of a lithium ion battery while ensuring stability, has high ion conductivity, and can be used safely without problems of leakage and ignition, and an LLZO-based solid electrolyte manufactured thereby.

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

According to a preferred embodiment of the present invention, a method for preparing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method comprises: a mixed solution preparing step of preparing a mixed solution; a precursor solution preparing step of preparing a precursor solution by treating the mixed solution with microwaves; a cooling and mixing step of mixing a precursor solution including a precipitate produced after cooling the precursor solution; a centrifugation step of centrifuging the precursor solution including the precipitate to separate it into a precipitate and a residual solution including an organic solvent; a dried precipitate powder preparing step of drying the precipitate after separating the precipitate to prepare a dried precipitate powder; a precursor powder preparing step of pulverizing the dried precipitate powder to prepare a precursor powder; a calcination step of heating the precursor powder to prepare lithium lanthanum zirconium oxide (LLZO) powder; It is characterized by including a pellet manufacturing step of putting the lithium lanthanum zirconium oxide (LLZO) powder into a mold and then pressing it to manufacture pellets; and a sintering step of sintering the pellets to manufacture a lithium lanthanum zirconium oxide (LLZO) pellet sintered body.

In addition, in the mixed solution preparation step, the mixed solution is prepared by mixing a lithium salt, a lanthanum salt, a zirconium salt, a complexing agent, and an organic solvent, wherein the lithium salt is at least one selected from _the group consisting of lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), and lithium nitrate (LiNO ₃ ), the lanthanum salt is at least one selected from the group consisting of lanthanum nitrate (La( _{NO 3 ) 3} ) and lanthanum oxide (La ₂ O ₃ ), the zirconium salt is at least one selected from the group consisting of zirconyl nitrate (ZrO(NO 3 ) 2 ) and zirconium oxide (ZrO ₂ ), the complexing agent is at least one selected from the group consisting of citric acid, tartaric acid, and ascorbic acid, and the organic solvent is diethylene glycol (DEG (Diethylene glycol)), It is characterized in that at least one selected from the group consisting of ethylene glycol and propylene glycol is used.

In addition, the mixed solution is characterized in that it is prepared by mixing 2 to 4 parts by weight of a lithium salt, 10 to 15 parts by weight of a lanthanum salt, 4 to 8 parts by weight of a zirconium salt, 20 to 30 parts by weight of a complexing agent, and 800 to 1,200 parts by weight of an organic solvent in a weight ratio, and then stirring at a temperature of 20 to 70°C for 40 to 180 minutes.

In addition, the calcination step is characterized in that the precursor powder is heated at a heating rate of 5°C/min to reach a temperature of 600 to 900°C and then heated for 2 to 8 hours to produce lithium lanthanum zirconium oxide (LLZO) powder, wherein the lithium lanthanum zirconium oxide (LLZO) powder is represented by the following [Chemical Formula 1], and in the sintering step, the pellet is placed into a zirconia crucible and heated at a heating rate of 5°C/min to reach a temperature of 1,000 to 1,200°C and then sintered for 8 to 24 hours to produce a lithium lanthanum zirconium oxide (LLZO) pellet sintered body.

[Chemical Formula 1]

Li _x La _y Zr _z O ₁₂

Here, 4 ≤ x ≤ 9, 2 ≤ y ≤ 4, 1 ≤ z ≤ 3.

In addition, in the mixed solution preparation step, the mixed solution is prepared by mixing a lithium salt, a lanthanum salt, a zirconium salt, a gallium salt, a complexing agent, and an organic solvent, wherein lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), and lithium nitrate (LiNO ₃ ) are used as the lithium salt, lanthanum nitrate (La(NO ₃ ) ₃ ) and lanthanum oxide (La ₂ O ₃ ) are used as the lanthanum salt, zirconyl nitrate (ZrO(NO ₃ ) ₂ ) and zirconium oxide (ZrO ₂ ) are used as the zirconium salt, and gallium nitrate (Ga(NO ₃ ) ₃ ) is used as the gallium salt, citric acid is used as the complexing agent, and diethylene glycol is used as the organic solvent.

In addition, the mixed solution is characterized in that it is prepared by mixing 2 to 4 parts by weight of a lithium salt, 10 to 15 parts by weight of a lanthanum salt, 4 to 8 parts by weight of a zirconium salt, 0.5 to 2 parts by weight of a gallium salt, 20 to 30 parts by weight of a complexing agent, and 800 to 1,200 parts by weight of an organic solvent in a weight ratio, and then stirring the mixture at a temperature of 20 to 70°C for 40 to 180 minutes.

In addition, the calcination step heats the precursor powder at a heating rate of 5°C/min to reach a temperature of 650 to 900°C and then heats it for 2 to 8 hours to manufacture a gallium-doped lithium lanthanum zirconium oxide (Ga-LLZO) powder, wherein the gallium-doped lithium lanthanum zirconium oxide (Ga-LLZO) powder is characterized by being represented by the following [chemical formula 2].

[Chemical formula 2]

Li _x Ga _w La _y Zr _z O ₁₂

Here, 4 ≤ x ≤ 9, 0.1 ≤ w ≤ 1, 2 ≤ y ≤ 4, 1 ≤ z ≤ 3.

In addition, the LLZO-based solid electrolyte using the microwave solvothermal synthesis method of the present invention is characterized by being manufactured by any one of the above methods.

In addition, the doping element of the lithium site of the LLZO-based solid electrolyte using the microwave solvothermal synthesis method of the present invention is at least one or more of Al, B, Be, Br, Fe, Ga, H, and Zn, the doping element of the lanthanum site is at least one or more of Ac, Ba, Bi, Ca, Dy, Er, Gd, Ho, K, Lu, Na, Nd, Pm, Pr, Rb, Sm, Sr, Tb, Tm, and Y, and the doping element of the zirconium site is at least one or more of As, Au, C, Cd, Ce, Cl, Co, Cr, Cu, Eu, Ge, Hf, Hg, I, In, Ir, Mg, Mn, Mo, Nb, Ni, Np, Pa, Pb, Pd, Pt, Pu, Rh, Ru, S, Sc, Se, Si, Sn, Ta, Tc, Te, Th, Ti, V, and W.

Meanwhile, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, and these embodiments are provided only to completely disclose the present invention and to fully inform a person having ordinary skill in the art to which the present invention belongs of the scope of the invention, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

The present invention has been created to solve the problems of the prior art, and more specifically, provides a method for manufacturing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method, which can synthesize a precursor powder in a short period of time using a microwave solvothermal synthesis method, refine the particle size of the LLZO powder, and manufacture an LLZO-based solid electrolyte having improved electrochemical characteristics through improved sinterability thereby, and an LLZO-based solid electrolyte manufactured thereby.

In addition, the present invention can provide a method for manufacturing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method, which can improve the capacity of a lithium ion battery while ensuring stability, has high ion conductivity, and can be used safely without problems of leakage and ignition, and an LLZO-based solid electrolyte manufactured thereby.

FIG. 1 is a flow chart for explaining a method for manufacturing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method according to one embodiment of the technical idea of the present invention.
FIG. 2 is a flow chart for explaining a method for manufacturing a gallium-doped LLZO (Ga-LLZO) solid electrolyte using a microwave solvothermal synthesis method according to another embodiment of the technical idea of the present invention.
FIG. 3 is a graph showing the results of analyzing cubic lithium lanthanum zirconium oxide (Li ₇ La ₃ Zr ₂ O ₁₂ ) powder synthesized according to the present invention using X-ray diffraction (XRD).
FIG. 4 is a photograph taken with a scanning electron microscope (SEM) of cubic lithium lanthanum zirconium oxide (Li ₇ La ₃ Zr ₂ O ₁₂ ) powder synthesized according to the present invention.
FIG. 5 is a graph showing the results of analyzing cubic gallium-doped lithium lanthanum zirconium oxide (Li _5.5 Ga _0.5 La ₃ Zr ₂ O ₁₂ ) powder synthesized according to the present invention using X-ray diffraction (XRD).
FIG. 6 is a photograph taken with a scanning electron microscope (SEM) of cubic gallium-doped lithium lanthanum zirconium oxide (Li _5.5 Ga _0.5 La ₃ Zr ₂ O ₁₂ ) powder synthesized according to the present invention.
FIG. 7 is a graph showing XRD analysis of lithium lanthanum zirconium oxide pellet sintered bodies according to Examples 1 to 9.
FIG. 8 is a graph showing XRD analysis of lithium lanthanum zirconium oxide pellet sintered bodies according to Examples 10 to 15.
FIG. 9 is a graph showing XRD analysis of lithium lanthanum zirconium oxide pellet sintered bodies according to Examples 16 to 17.
FIG. 10 is a graph showing the ionic conductivity through impedance analysis of lithium lanthanum zirconium oxide pellet sintered bodies according to Examples 16 to 17.

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

FIG. 1 is a flow chart for explaining a method for manufacturing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method according to one embodiment of the technical idea of the present invention.

Referring to FIG. 1, the method for manufacturing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method includes a mixed solution manufacturing step (S110), a precursor solution manufacturing step (S120), a cooling and mixing step (S130), a centrifugation step (S140), a dried precipitate powder manufacturing step (S150), a precursor powder manufacturing step (S160), a calcination step (S170), a pellet manufacturing step (S180), and a sintering step (S190), and the manufacturing steps are described in more detail below.

1. Mixed solution preparation step (S110)

The above mixed solution preparation step (S110) is a step of preparing a mixed solution by mixing a lithium salt, a lanthanum salt, a zirconium salt, a complexing agent, and an organic solvent.

In the above mixed solution preparation step (S110), as the lithium salt, at least one selected from the group consisting of lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), and lithium nitrate (LiNO ₃ ) may be used, and preferably, lithium hydroxide (LiOH) may be used as the lithium salt. As the lanthanum salt, at least one selected from the group consisting of lanthanum nitrate (La(NO ₃ ) ₃ ) and lanthanum oxide (La ₂ O ₃ ) may be used, and preferably, lanthanum nitrate (La(NO ₃ ) ₃ ) may be used as the lithium salt. As the zirconium salt, at least one selected from the group consisting of zirconyl nitrate (ZrO(NO ₃ ) ₂ ) and zirconium oxide (ZrO ₂ ) may be used, and preferably, zirconyl nitrate (ZrO(NO ₃ ) ₂ ) may be used as the lithium salt.

In addition, the complexing agent may be at least one selected from the group consisting of citric acid, tartaric acid, and ascorbic acid, and citric acid may be preferably used as the complexing agent.

In addition, the organic solvent may be at least one selected from the group consisting of diethylene glycol (DEG), ethylene glycol, and propylene glycol, and preferably, diethylene glycol (DEG) may be used as the organic solvent.

In addition, in the mixed solution preparation step (S110), the mixed solution can be prepared by mixing 2 to 4 parts by weight of a lithium salt, 10 to 15 parts by weight of a lanthanum salt, 4 to 8 parts by weight of a zirconium salt, 20 to 30 parts by weight of a complexing agent, and 800 to 1,200 parts by weight of an organic solvent in a weight ratio, and then stirring at a temperature of 20 to 70°C for 40 to 180 minutes, and preferably stirring at a temperature of 20 to 30°C for 40 to 80 minutes.

2. Precursor solution preparation step (S120)

The above precursor solution preparation step (S120) is a step of preparing a precursor solution by treating the mixed solution with microwaves.

In the precursor solution preparation step (S120), the mixed solution is divided into 40 to 60 parts by weight units, the divided mixed solution is placed in a microwave Teflon, and stirred at 400 to 800 watts (W) and a temperature of 200 to 280°C for 2 to 15 minutes to prepare the precursor solution. Preferably, the precursor solution is prepared by dividing the mixed solution into 45 to 55 parts by weight units, and the divided mixed solution is placed in a microwave Teflon, and stirred at 400 watts (W) and a temperature of 240 to 260°C for 5 to 15 minutes.

3. Cooling and mixing step (S130)

The above cooling and mixing step (S130) is a step of mixing the precursor solution including the precipitate generated after cooling the precursor solution.

In the above cooling and mixing step (S130), the precursor solution is cooled to a temperature of 20 to 30°C, and then the precursor solution including the generated precipitate can be uniformly mixed using a known stirrer.

4. Centrifugation step (S140)

The above centrifugation step (S140) is a step of centrifuging the precursor solution containing the precipitate to separate it into the precipitate and a residual solution containing the organic solvent.

In the centrifugation step (S140), the precursor solution containing the precipitate can be separated into the precipitate and the residual solution containing the organic solvent by centrifuging the precursor solution containing the precipitate using a centrifuge at a speed of 8,000 to 12,000 RPM for 50 to 100 minutes.

5. Dry sediment powder manufacturing step (S150)

The above-mentioned dry sediment powder manufacturing step (S150) is a step of manufacturing dry sediment powder by separating the sediment and then drying the sediment.

In the above dry sediment powder manufacturing step (S150), the dry sediment powder can be manufactured by separating only the sediment from the residual solution containing the sediment and the organic solvent using a known filter, placing the sediment in an alumina crucible, heating at a heating rate of 15°C/min to reach a temperature of 240 to 260°C, and then heating for 100 to 150 minutes.

6. Precursor powder manufacturing step (S160)

The above precursor powder manufacturing step (S160) is a step of manufacturing precursor powder by grinding the dried sediment powder.

In the above precursor powder manufacturing step (S160), the dried sediment powder is pulverized using a known pulverizer, thereby manufacturing a precursor powder formed into fine particles from the dried sediment powder formed into lumps.

7. Calcination stage (S170)

The above calcination step (S170) is a step of heating the precursor powder to manufacture lithium lanthanum zirconium oxide (LLZO) powder.

The above calcination step (S170) heats the precursor powder at a temperature rising rate of 5°C/min to reach a temperature of 650 to 900°C, and then heats it for 2 to 8 hours, preferably 650 to 750°C, and then heats it for 4 to 6 hours to remove volatile components or impurities remaining in the precursor powder and synthesize precursor materials, thereby manufacturing lithium lanthanum zirconium oxide (LLZO) powder.

The lithium lanthanum zirconium oxide (LLZO) powder manufactured in the above calcination step (S170) can be represented by the following [chemical formula 1].

[Chemical Formula 1]

Li _x La _y Zr _z O ₁₂

Here, 4 ≤ x ≤ 9, 2 ≤ y ≤ 4, 1 ≤ z ≤ 3.

The above chemical formula 1 is preferably Li ₇ La ₃ Zr ₂ O ₁₂ , and the solid electrolyte using Li ₇ La ₃ Zr ₂ O ₁₂ has the effect of being stabilized in a cubic phase by synthesizing the powder in a nano size, and more specifically, the powder size is about 100 to 500 nm.

8. Pellet manufacturing step (S180)

The above pellet manufacturing step (S180) is a step of manufacturing pellets by putting lithium lanthanum zirconium oxide (LLZO) powder into a mold and then pressing it.

For example, in the pellet manufacturing step (S180), the lithium lanthanum zirconium oxide (LLZO) powder may be injected into a mold and then compressed at a pressure of 1,500 to 5,000 PSI to manufacture a pellet.

9. Sintering step (S190)

The above sintering step (S190) can manufacture a lithium lanthanum zirconium oxide (LLZO) pellet sintered body by sintering the pellet.

For example, in the sintering step (S190), the pellets may be placed in a zirconia crucible and heated at a heating rate of 5°C/min to reach a temperature of 1,000 to 1,200°C, and then sintered for 8 to 24 hours to manufacture a lithium lanthanum zirconium oxide (LLZO) pellet sintered body.

Hereinafter, with reference to FIG. 2, a preferred embodiment of a method for manufacturing a gallium-doped LLZO (Ga-LLZO) solid electrolyte using a microwave solvothermal synthesis method according to another embodiment of the technical idea of the present invention will be described in detail.

FIG. 2 is a flow chart for explaining a method for manufacturing a gallium-doped LLZO (Ga-LLZO) solid electrolyte using a microwave solvothermal synthesis method according to another embodiment of the technical idea of the present invention.

Referring to FIG. 2, a method for manufacturing a gallium-doped LLZO (Ga-LLZO) solid electrolyte using a microwave solvothermal synthesis method according to another embodiment of the technical idea of the present invention includes a mixed solution manufacturing step (S210), a precursor solution manufacturing step (S220), a cooling and mixing step (S230), a centrifugation step (S240), a dried precipitate powder manufacturing step (S250), a precursor powder manufacturing step (S260), a calcination step (S270), a pellet manufacturing step (S280), and a sintering step (S290), and the manufacturing steps are described in more detail below.

1. Mixed solution preparation step (S210)

The above mixed solution preparation step (S210) is a step of preparing a mixed solution by mixing a lithium salt, a lanthanum salt, a zirconium salt, a gallium salt, a complexing agent, and an organic solvent.

In the above mixed solution preparation step (S210), as the lithium salt, at least one selected from the group consisting of lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), and lithium nitrate (LiNO ₃ ) may be used, and preferably, lithium hydroxide (LiOH) may be used as the lithium salt. As the lanthanum salt, at least one selected from the group consisting of lanthanum nitrate (La(NO ₃ ) ₃ ) and lanthanum oxide (La ₂ O ₃ ) may be used, and preferably, lanthanum nitrate (La(NO ₃ ) ₃ ) may be used as the lithium salt. As the zirconium salt, at least one selected from the group consisting of zirconyl nitrate (ZrO(NO ₃ ) ₂ ) and zirconium oxide (ZrO ₂ ) may be used, and preferably, zirconyl nitrate (ZrO(NO ₃ ) ₂ ) may be used as the lithium salt. Gallium nitrate (Ga(NO ₃ ) ₃ ) can be used as a gallium salt.

In addition, the complexing agent may be at least one selected from the group consisting of citric acid, tartaric acid, and ascorbic acid, and citric acid may be preferably used as the complexing agent.

In addition, the organic solvent may be at least one selected from the group consisting of diethylene glycol (DEG), ethylene glycol, and propylene glycol, and preferably, diethylene glycol (DEG) may be used as the organic solvent.

In addition, in the mixed solution preparation step (S210), the mixed solution can be prepared by mixing 2 to 4 parts by weight of a lithium salt, 10 to 15 parts by weight of a lanthanum salt, 4 to 8 parts by weight of a zirconium salt, 0.5 to 2 parts by weight of a gallium salt, 20 to 30 parts by weight of a complexing agent, and 800 to 1,200 parts by weight of an organic solvent in a weight ratio, and then stirring at a temperature of 20 to 70°C for 40 to 180 minutes, and preferably stirring at a temperature of 20 to 30°C for 40 to 80 minutes.

2. Precursor solution preparation step (S220)

The above precursor solution preparation step (S220) is a step of preparing a precursor solution by treating the mixed solution with microwaves.

In the precursor solution preparation step (S220), the mixed solution is divided into 45 to 55 parts by weight units, the divided mixed solution is placed in a microwave Teflon, and stirred at 400 to 800 watts (W) and a temperature of 200 to 260°C for 2 to 15 minutes, thereby preparing the precursor solution. Preferably, the precursor solution is prepared by stirring at 400 watts (W) and a temperature of 240 to 260°C for 5 to 15 minutes.

3. Cooling and mixing step (S230)

The above cooling and mixing step (S230) is a step of mixing the precursor solution including the precipitate generated after cooling the precursor solution.

In the above cooling and mixing step (S230), the precursor solution is cooled to a temperature of 20 to 30°C, and then the precursor solution including the generated precipitate can be uniformly mixed using a known stirrer.

4. Centrifugation step (S240)

The above centrifugation step (S240) is a step of centrifuging the precursor solution containing the precipitate to separate it into the precipitate and a residual solution containing the organic solvent.

In the centrifugation step (S240), the precursor solution containing the precipitate can be separated into the precipitate and the residual solution containing the organic solvent by centrifuging the precursor solution containing the precipitate using a centrifuge at a speed of 8,000 to 12,000 RPM for 50 to 100 minutes.

5. Dry sediment powder manufacturing step (S250)

The above-mentioned dry sediment powder manufacturing step (S250) is a step of manufacturing dry sediment powder by separating the sediment and then drying the sediment.

In the above dry sediment powder manufacturing step (S250), the dry sediment powder can be manufactured by separating only the sediment from the residual solution containing the sediment and the organic solvent using a known filter, placing the sediment in an alumina crucible, heating at a heating rate of 15°C/min to reach a temperature of 240 to 260°C, and then heating for 100 to 150 minutes.

6. Precursor powder manufacturing step (S260)

The above precursor powder manufacturing step (S260) is a step of manufacturing precursor powder by crushing the dried sediment powder.

In the above precursor powder manufacturing step (S260), the dried precipitate powder is pulverized using a known pulverizer, thereby manufacturing a precursor powder formed into fine particles from the dried precipitate powder formed into lumps.

7. Calcination stage (S270)

The above calcination step (S270) is a step of heating the precursor powder to manufacture gallium-doped lithium lanthanum zirconium oxide (Ga-LLZO) powder.

The above calcination step (S270) can manufacture gallium-doped lithium lanthanum zirconium oxide (Ga-LLZO) powder by heating the precursor powder at a heating rate of 5°C/min to reach a temperature of 650 to 900°C and then heating for 2 to 8 hours to remove volatile components or impurities remaining in the precursor powder.

The gallium-doped lithium lanthanum zirconium oxide (Ga-LLZO) powder manufactured in the above calcination step (S270) can be represented by the following [chemical formula 2].

[Chemical formula 2]

Li _x Ga _w La _y Zr _z O ₁₂

Here, 4 ≤ x ≤ 9, 0.1 ≤ w ≤ 1, 2 ≤ y ≤ 4, 1 ≤ z ≤ 3.

The above chemical formula is preferably Li _6.25 Ga _0.25 La ₃ Zr ₂ O ₁₂ , and a solid electrolyte using Li _6.25 Ga _0.25 La ₃ Zr ₂ O ₁₂ does not show evaporation of Li even when sintered at a temperature of 1050℃, and when the Ga content is 0.25, the resistance is smaller and the ionic conductivity is higher.

8. Pellet manufacturing step (S280)

The above pellet manufacturing step (S280) is a step of manufacturing pellets by putting the gallium-doped lithium lanthanum zirconium oxide (Ga-LLZO) powder into a mold and then pressing it.

For example, in the pellet manufacturing step (S280), the gallium-doped lithium lanthanum zirconium oxide (Ga-LLZO) powder may be injected into a mold and then compressed at a pressure of 1,500 to 5,000 PSI to manufacture the pellet, preferably by compression at a pressure of 1,500 to 2,500 PSI.

9. Sintering step (S290)

The above sintering step (S290) can manufacture a gallium-doped lithium lanthanum zirconium oxide (Ga-LLZO) pellet sintered body by sintering the pellet.

For example, in the sintering step (S290), the pellets are placed in a zirconia crucible and heated at a heating rate of 5°C/min to reach a temperature of 1,000 to 1,200°C and then sintered for 8 to 24 hours to manufacture a gallium-doped (Ga-doped) lithium lanthanum zirconium oxide (Ga-LLZO) pellet sintered body, and preferably, the pellets are manufactured by reaching a temperature of 1,000 to 1,100°C and then sintering for 8 to 12 hours.

Meanwhile, the present invention can provide an LLZO-based solid electrolyte using a microwave solvothermal synthesis method manufactured by one method selected from the above methods.

The solid electrolyte and the solid electrolyte sintered body according to the present invention include at least one structure selected from a cubic structure and a tetragonal structure, and preferably, the solid electrolyte and the solid electrolyte sintered body may have a single-phase cubic structure.

In addition, the LLZO-based solid electrolyte may be doped with at least one element among Al, B, Be, Br, Fe, Ga, H, and Zn in the lithium site in order to stabilize the cubic structure with high conductivity. When the above elements are doped, the cubic structure can be further stabilized, and more specifically, when the above elements are doped in the lithium site, the ionic conductivity can be improved due to the formation of Li vacancies, and there is an effect of being able to obtain a sintering temperature that is about 200℃ lower on average than before.

In addition, in order to further improve the ionic conductivity, multiple ion doping is performed instead of single ion doping, and as a preferred embodiment, at least one element among Ac, Ba, Bi, Ca, Dy, Er, Gd, Ho, K, Lu, Na, Nd, Pm, Pr, Rb, Sm, Sr, Tb, Tm, Y can be doped in the lanthanum position, and at least one element among As, Au, C, Cd, Ce, Cl, Co, Cr, Cu, Eu, Ge, Hf, Hg, I, In, Ir, Mg, Mn, Mo, Nb, Ni, Np, Pa, Pb, Pd, Pt, Pu, Rh, Ru, S, Sc, Se, Si, Sn, Ta, Tc, Te, Th, Ti, V, W can be doped in the zirconium position.

Hereinafter, a method for manufacturing an LLZO-based solid electrolyte using a microwave solvothermal synthesis method according to one embodiment of the technical idea of the present invention will be described in more detail with specific examples.

Manufacturing Example 1. Manufacturing of LLZO powder and LLZO pellet sintered body

Lithium hydroxide (LiOH (manufactured by Alfa-Aesar, 98%) 0.2495g or 0.2744g or 0.2994g (+0% or +10% or +20%), lanthanum nitrate (La( _NO3 ) ₃ ) (manufactured by Aldrich, 99.9% trace metal basis) 1.2185g, zirconyl nitrate (ZrO( _NO3 ) ₂ ) (manufactured by Aldrich, 99%) 0.5780g and citric acid (manufactured by Alfa-Aesar, 99.5%) 2.4g were added to 100㎖ of diethylene glycol (DEG (diethylene glycol)) (manufactured by Sigma-Aldrich, 99%), mixed and stirred at 25℃ for 60 minutes to obtain a mixed solution. was manufactured.

Next, 50 mL of the above mixed solution was placed in each microwave Teflon and stirred at 250°C for 10 minutes with a power of 400 W using a microwave to prepare a precursor solution.

Next, the precursor solution was cooled to room temperature (25°C) and separated into a precipitate and a residual solution containing an organic solvent using a vortex mixer.

Next, the precipitate and the residual solution containing the organic solvent were separated using a known filter to separate only the precipitate, and the precipitate was placed in an alumina crucible and heated at a heating rate of 15°C/min to reach a temperature of 250°C and then heated for 120 minutes to produce a dry precipitate powder.

Next, the dried sediment powder was pulverized to prepare a precursor powder, and the precursor powder was heated at a heating rate of 5°C/min to reach a temperature of 700°C, and then heated for 5 hours to remove volatile components or impurities remaining in the precursor powder, thereby preparing lithium lanthanum zirconium oxide (Li ₇ La ₃ Zr ₂ O ₁₂ ) powder.

Next, the lithium lanthanum zirconium oxide (Li ₇ La ₃ Zr ₂ O ₁₂ ) powder was placed into a mold and pressed at a pressure of 2,000 PSI to produce pellets.

Next, the pressed pellets were placed in a zirconia crucible and heated at a heating rate of 5°C/min to reach a temperature of 1,050°C and then sintered for 10 hours to produce a lithium lanthanum zirconium oxide (Li ₇ La ₃ Zr ₂ O ₁₂ ) pellet sintered body.

Manufacturing Example 2. Manufacturing of gallium-doped LLZO powder and gallium-doped LLZO pellet sintered body

Lithium hydroxide (LiOH (manufactured by Alfa-Aesar, 98%) 0.2495g or 0.2744g or 0.2994g (+0% or +10% or +20%), lanthanum nitrate (La( _NO3 ) ₃ ) (manufactured by Aldrich, 99.9% trace metal basis) 1.2185g, gallium nitrate (Ga( _NO3 ) ₃ ) (manufactured by Acros-Organics, 99.9998% trace metal basis) 0.1066g, zirconyl nitrate (ZrO( _NO3 ) ₂ ) (Aldrich, 99%) 0.5780g and citric acid (manufactured by Alfa-Aesar, 99.5%) 2.4g A mixed solution was prepared by adding 100 ml of diethylene glycol (DEG) (manufactured by Sigma-Aldrich, 99%), mixing, and stirring at 25°C for 60 minutes.

Next, 50 mL of the above mixed solution was placed in each microwave Teflon and stirred at 250°C for 10 minutes with a power of 400 W using a microwave to prepare a precursor solution.

Next, the precursor solution was cooled to room temperature (25°C) and separated into a precipitate and a residual solution containing an organic solvent using a vortex mixer.

Next, the precipitate and the residual solution containing the organic solvent were separated using a known filter to separate only the precipitate, and the precipitate was placed in an alumina crucible and heated at a heating rate of 15°C/min to reach a temperature of 250°C and then heated for 120 minutes to produce a dry precipitate powder.

Next, the dried sediment powder was pulverized to prepare a precursor powder, and the precursor powder was heated at a heating rate of 5°C/min to reach a temperature of 700°C, and then heated for 5 hours to remove volatile components or impurities remaining in the precursor powder, thereby preparing a gallium-doped lithium lanthanum zirconium oxide (Li _6.25 Ga _0.25 La ₃ Zr ₂ O ₁₂ ) powder.

Next, the gallium-doped lithium lanthanum zirconium oxide (Li _6.25 Ga _0.25 La ₃ Zr ₂ O ₁₂ ) powder was placed into a mold and pressed at a pressure of 2,000 PSI to produce pellets.

Next, the pressed pellet was placed in a zirconia crucible and heated at a heating rate of 5°C/min to reach a temperature of 1,050°C and then sintered for 10 hours to produce a gallium-doped lithium lanthanum zirconium oxide (Li _6.25 Ga _0.25 La ₃ Zr ₂ O ₁₂ ) pellet sintered body.

Examples 1 to 15.

Using the above Manufacturing Examples 1 and 2, lithium lanthanum zirconium oxide (Li ₇ La ₃ Zr ₂ O ₁₂ ) powder and gallium-doped lithium lanthanum zirconium oxide (Li _5.5 Ga _0.5 La ₃ Zr ₂ O ₁₂ ) powder were manufactured, and the results are shown in Table 1 below.

furtherance Li excess
(%) Rising temperature
(℃/m) Low temperature
(℃) Time to settle
(h) Example 1 Li _5.5 Ga _0.5 La ₃ Zr ₂ O ₁₂ 0 5 700 5 Example 2 10 5 700 5 Example 3 20 5 700 5 Example 4 20 5 700 6 Example 5 20 5 700 4 Example 6 20 5 700 3 Example 7 20 5 700 2.5 Example 8 20 5 650 5 Example 9 20 5 600 5 Example 10 Li ₇ La ₃ Zr ₂ O ₁₂ 0 5 700 5 Example 11 10 5 700 5 Example 12 20 5 700 5 Example 13 70 5 700 5 Example 14 80 5 700 5 Example 15 90 5 700 5

FIG. 3 is a graph showing the results of analyzing lithium lanthanum zirconium oxide (Li ₇ La ₃ Zr ₂ O ₁₂ ) powder having a cubic structure synthesized according to the present invention using X-ray diffraction (XRD). It can be seen that LLZO manufactured by microwave hydrothermal synthesis is synthesized with a powder size of nanometers and stabilized in a cubic phase. FIG. 4 is a scanning electron microscope (SEM) photograph of lithium lanthanum zirconium oxide (Li ₇ La ₃ Zr ₂ O ₁₂ ) powder having a cubic structure synthesized according to the present invention. As a result of analyzing the SEM data, it can be seen that LLZO powder having a size of about 100 to 500 nm, which is smaller than the size of the currently reported LLZO powder, was successfully synthesized.

FIG. 5 is a graph showing the analysis of lithium lanthanum zirconium oxide (Li _5.5 Ga _0.5 La ₃ Zr ₂ O ₁₂ ) powder with a cubic structure doped with Ga, synthesized according to the present invention, using X-ray diffraction (XRD). As can be seen from the cubic XRD pattern, it can be seen that stabilization was successfully achieved as a cubic Ga-LLZO pattern by gallium doping, rather than the tetragonal LLZO pattern that generally appears when no doping is performed.

FIG. 6 is a scanning electron microscope (SEM) photograph of lithium lanthanum zirconium oxide (Li _5.5 Ga _0.5 La ₃ Zr ₂ O ₁₂ ) powder having a cubic structure synthesized according to the present invention. As a result of analysis of the SEM data, it can be seen that Ga-LLZO powder of about 100 to 500 nm, which is smaller than the size of the currently reported LLZO powder, was successfully synthesized.

FIG. 7 is a graph showing XRD analysis of lithium lanthanum zirconium oxide pellet sintered bodies according to Examples 1 to 9. As a result of XRD analysis according to the Examples, it can be seen that LLZO was successfully synthesized even with a calcination time of 2.5 hours at 700°C, and when looking at data obtained by calcination at conditions of 650°C and 600°C, it can be confirmed that LLZO was synthesized by calcination at 650°C, but LLZO was not properly synthesized at 600°C due to insufficient temperature.

FIG. 8 is a graph showing XRD analysis of lithium lanthanum zirconium oxide pellet sintered bodies according to Examples 10 to 15. As a result of XRD analysis according to Examples, it can be seen that in the case of LLZO without doping, the particle size gradually increases depending on the amount of additional Li content, and accordingly, in the case of an extreme additional Li content of 70 to 90%, tetragonal LLZO was synthesized as the particle size was not nanosized, and in the case of an additional Li content of 0 to 20%, it can be confirmed that the cubic phase was stabilized as the particle size was nanosized.

Examples 16 to 17.

Using the above Manufacturing Examples 1 and 2, gallium-doped lithium lanthanum zirconium oxide powders as shown in Examples 16 and 17 below were manufactured, and the results are shown in Table 2 below.

furtherance Li excess
(%) Temperature rise
temperature
(℃/m) Low temperature
(℃) Time to settle
(h) Sintering temperature
(℃) Sintering time
(h) Ionic conductivity
(bulk)
(S/cm) Example 16 Li _6.1 Ga _0.3 La ₃ Zr ₂ O ₁₂ 20 5 700 5 1050 10 0.88X10 ^-4 Example 17 Li _6.25 Ga _0.25 La ₃ Zr ₂ O ₁₂ 20 5 700 5 1050 10 1.27X10 ^-3

FIG. 9 is a graph showing XRD analysis of lithium lanthanum zirconium oxide pellet sintered bodies according to Examples 16 to 17. As a result of the analysis, it can be confirmed that no evaporation of Li occurred, as the XRD analysis result of cubic LLZO was observed even when sintered at a temperature of 1050°C.

FIG. 10 is a graph showing the ionic conductivity through impedance analysis of lithium lanthanum zirconium oxide pellet sintered bodies according to Examples 16 and 17. As the doping content of gallium decreases, the content of Li increases and the ionic conductivity of Li ions increases. Based on these results, it can be confirmed that in Examples 16 and 17, as the content of Ga decreases from 0.3 to 0.25, the resistance decreases and the ionic conductivity also increases.

Above, although a preferred embodiment of the present invention has been described, it will be understood by those skilled in the art to which the present invention pertains that the present invention may be implemented in other specific forms without changing the technical idea or essential features thereof. Therefore, it should be understood that the above-described embodiment is exemplary in all respects and not restrictive.

As described above, although the present invention has been described by means of limited embodiments and drawings, the present invention is not limited to the above embodiments, and various modifications and variations are possible from this description by those with ordinary skill in the art to which the present invention pertains. Accordingly, the spirit of the present invention should be understood only by the scope of the patent claims described below, and all equivalent or equivalent modifications thereof will be considered to fall within the scope of the spirit of the present invention.

A singular expression should be understood to include the plural expression unless the context clearly indicates otherwise, and terms such as “comprises” or “have” should be understood to specify the presence of a stated feature, number, step, operation, component, part, or combination thereof, but not to exclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

Claims (9)

A mixed solution preparation step _{of preparing} a mixed solution by stirring the mixture of 2 to 4 parts by weight of lithium hydroxide (LiOH), 10 to 15 parts by weight of lanthanum nitrate (La( _No3 ) ₃ ), 4 to 8 parts by weight of zirconyl nitrate (ZrO( _NO3 ) ₂ ), and 0.5 to 2 parts by weight of gallium nitrate (Ga(NO3)3), 20 to 30 parts by weight of citric acid as a complexing agent, and 800 to 1,200 parts by weight of diethylene glycol (DEG) as an organic solvent at a temperature of 20 to 70°C for 40 to 180 minutes.
A precursor solution preparation step of dividing the above mixed solution into 45 to 55 parts by weight units, placing the divided mixed solution into a microwave Teflon, and stirring for 5 to 15 minutes at 400 watts (W) and a temperature of 240 to 260°C to prepare a precursor solution;
A cooling and mixing step of mixing the precursor solution containing the precipitate produced after cooling the precursor solution at a temperature of 20 to 30°C;
A centrifugation step of centrifuging a precursor solution containing the above precipitate to separate the precipitate and a residual solution containing an organic solvent;
A dry sediment powder manufacturing step of manufacturing a dry sediment powder by drying the sediment after separating the sediment;
A precursor powder manufacturing step of manufacturing a precursor powder by grinding the above-mentioned dry sediment powder;
A calcination step of heating the precursor powder at a heating rate of 5°C/min to reach a temperature of 650 to 750°C and then heating for 2 to 8 hours to produce a gallium-doped lithium lanthanum zirconium oxide (LLZO) powder represented by Li _6.25 Ga _0.25 La ₃ Zr ₂ O ₁₂ ;
A pellet manufacturing step of putting the lithium lanthanum zirconium oxide (LLZO) powder into a mold and then pressing it to manufacture pellets; and
A method for producing a lithium lanthanum zirconium oxide (LLZO) solid electrolyte using a microwave solvothermal synthesis method, characterized in that the pellets are placed in a zirconia crucible, heated at a heating rate of 5°C/min to reach a temperature of 1,000 to 1,100°C, and then sintered for 8 to 12 hours to produce a sintered body of lithium lanthanum zirconium oxide (LLZO) pellets doped with gallium.
An LLZO-based solid electrolyte using a microwave solvothermal synthesis method, characterized in that it is manufactured by the method of claim 1. delete delete delete delete delete delete delete