KR102048701B1 - Manufacturing method of lithium lanthanum zirconium oxide-lithium boron oxide composite - Google Patents

Abstract

The present invention provides a step of preparing an LBO (Li ₃ BO ₃ ) -based glass frit, LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte powder having a garnet structure and the LBO (Li ₃ BO ₃₎ A method of manufacturing a lithium lanthanum zirconium oxide-lithium boron oxide-based composite, comprising mixing and shaping a glass frit and sintering the molded product, wherein the sintering is performed at a temperature lower than 1200 ° C. It is about. According to the present invention, liquid sintering can be induced by LBO (Li ₃ BO ₃ ) -based glass frit during sintering of LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte, thereby achieving densification of the sintered compact. It is possible to make low-temperature sintering, and to improve the ion conductivity of the sintered body.

Description

Manufacturing method of lithium lanthanum zirconium oxide-lithium boron oxide composite}

The present invention relates to a method for producing a lithium lanthanum zirconium oxide-lithium boron oxide-based composite, and more particularly, densification of the sintered compact can be induced by liquid phase sintering during LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte The present invention relates to a method for producing a lithium lanthanum zirconium oxide-lithium boron oxide-based composite capable of achieving a low temperature, enabling low temperature sintering, and improving ion conductivity of the sintered body.

Since the first commercialization of lithium secondary batteries by Sony in Japan in 1991, demand has increased rapidly since 1995. Lithium secondary battery has less self-discharge than conventional battery, has no memory effect, high operating voltage of 3.6V, and has various advantages such as light weight, high energy density and excellent output characteristics. come. The reason why lithium secondary batteries are in the spotlight recently is that they are highly applicable as batteries for electric vehicles. As the advanced industries such as electric vehicles, next-generation IT mobile communication devices, and environmentally friendly energy industries are developed, lithium secondary batteries are required for technological development of the industry.

The liquid electrolyte type lithium secondary battery currently commercialized is composed of an organic solvent and a lithium salt, and additionally, a separator is installed. During charging, Li ⁺ ions move from the anode to the cathode, and during discharge, Li is ionized and the generated electrons move from the cathode to the anode. The movement of Li ⁺ ions occurs through the electrolyte, and the ion conductivity of the electrolyte affects the charge / discharge rate of the battery. In addition, the properties of the anode and cathode materials affect the energy density, the ionic conductivity and thickness of the electrolyte affect the output, and the contact area and contact resistance of the electrode and electrolyte, and the electrical conductivity of the electrode affect both energy density and output. Gives.

However, currently used organic liquid electrolytes have a risk of explosion due to problems of dendrite formation, flammability, and leakage. As an alternative to solve this problem, all-solid-state lithium ion batteries using solid electrolytes have been proposed. All-solid-state lithium secondary battery refers to replacing the liquid electrolyte with a solid electrolyte among the components of the existing lithium secondary battery. There is no risk of explosion or fire of the battery, and the manufacturing process is simplified compared to liquid electrolyte, and it is attracting attention as a next-generation secondary battery because it has advantages over existing lithium secondary batteries with high energy density and reliability. In the case of using a solid electrolyte, since the battery design is simple, the process can be minimized, thereby reducing the production cost. However, since the lithium ion conductivity of the solid electrolyte is a solid having no fluidity compared to the lithium ion conductivity of the liquid electrolyte, it is difficult due to the low ion conductivity. Therefore, development of a solid electrolyte material is necessary.

Republic of Korea Patent Publication No. 10-1732003

The problem to be solved by the present invention is to induce liquid phase sintering during the sintering of LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte to achieve densification of the sintered body, to enable low-temperature sintering, ions of the sintered body The present invention provides a method for producing a lithium lanthanum zirconium oxide-lithium boron oxide-based composite capable of improving conductivity.

The invention, LBO (Li ₃ BO ₃₎ based glass frit _{LLZ (Li 7 La 3 Zr 2} O 12) solid electrolyte powder and the LBO (Li ₃ BO ₃ having a phase and a garnet structure to prepare the (glass frit) A method of manufacturing a lithium lanthanum zirconium oxide-lithium boron oxide-based composite, comprising mixing and shaping a glass frit and sintering the molded product, wherein the sintering is performed at a temperature lower than 1200 ° C. To provide.

The sintering is preferably carried out at 1000 ~ 1150 ℃.

The LBO (Li ₃ BO ₃ ) -based glass frit is preferably mixed with 0.1 to 25 parts by weight based on 100 parts by weight of the LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte powder.

Preparing the LBO (Li ₃ BO ₃ ) -based glass frit, (a) mixing the chelating agent and the solvent, (b) a lithium source material and a mixture of the chelating agent and the solvent Dissolving the boron source material, (c) heating the solution in which the lithium source material and the boron source material are dissolved to a first temperature to esterify to form a complex, and (d) in the esterification reaction. Heating the complex formed at a second temperature higher than the first temperature to form a powder precursor in a powder state; and (e) calcining the powder precursor to form a LBO (Li ₃ BO ₃ ) -based glass frit ( glass frit).

The chelating agent is citric acid (C ₆ H ₈ O ₇ ), polyaminocarboxylic acid, polyphosphoric acid, ethylenediamine (C ₂ H ₄ (NH ₂ ) ₂ ) and ethylenediaminetetraacetic acid (C ₁₀ H ₁₆ N ₂ O ₈ ) one or more materials selected from the group consisting of.

The solvent may include one or more substances selected from the group consisting of ethylene glycol, H ₂ O, and dimethyl ether (C ₂ H ₆ O).

In the step (a), the solvent and the chelating agent are preferably mixed in a molar ratio of 2: 1 to 7: 1.

The lithium source material may include at least one material selected from the group consisting of lithium carbonate (Li ₂ CO ₃ ), lithium nitrate (LiNO ₃ ), and lithium chloride (Lithium chloride, LiCl). .

The boron source material is boric acid (Boric acid, H ₃ BO ₃ ), boron carbonate (Boron carbonate, C ₃ B ₂ O ₉ ), tetranitratoborate (B (NO ₃ ) ₃ ) and boron trichloride (Boron trichloride, BCl ₃ ) may include one or more substances selected from the group consisting of.

In the step (b), aluminum nitrate nonahydrate (Al (NO ₃ ) ₃ .9H ₂ O), aluminum chloride, AlCl ₃ and aluminum carbonate, Al ₂ (CO _{3 3} ) one or more substances selected from the group consisting of

In the step (b), made of niobium nitrate (Nobium nitrate, Nb (NO ₃ ) ₅ ), niobium acid (Niobium acid, Nb ₂ O ₅ · nH ₂ O) and niobium chloride (Niobium chloride, NbCl ₅ ) It is also possible to further dissolve one or more substances selected from the group.

In the step (b), 1 selected from the group consisting of tantalum nitrate, TaN ₅ O ₁₅ , tantalum carbonate, Ta ₂ (CO ₃ ) ₅ , and tantalum chloride, TaCl ₅ . More than one substance may be further dissolved.

Heating to the first temperature for the esterification is preferably carried out at a temperature of 90 ~ 250 ℃.

The calcination is preferably carried out in an oxidizing atmosphere at a temperature of 600 ~ 800 ℃ higher than the second temperature.

The method may further include heat treatment at a temperature higher than the second temperature and lower than the calcination temperature in order to remove the organic material contained in the powder precursor before the calcination.

In the step (b), it is preferable to dissolve the lithium source material and the boron source material in a molar ratio of 1: 1 to 5: 1.

According to the present invention, liquid sintering can be induced by LBO (Li ₃ BO ₃ ) -based glass frit during sintering of LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte, thereby achieving densification of the sintered compact. It is possible to make low-temperature sintering, and to improve the ion conductivity of the sintered body.

1 is a view showing a cubic Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ) structure.
2 shows a liquid phase sintering mechanism.
3 is a view showing a polymer composite precursor is formed based on the esterification reaction between the metal citric acid complex and ethylene glycol.
4 is a scanning electron microscope (SEM) photograph showing Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ) powder used as a raw material powder in the experimental example.
5 is a process schematic diagram of a complex polymerization method for the synthesis of Li ₃ BO ₃ (LBO) powder according to the experimental example.
6 is a process schematic diagram for forming a composite according to an experimental example.
Figure 7 is a TG-DTA (thermogravimetry-differential thermal analysis) curve of LBO powder nationwide synthesized by the complex polymerization method.
8 is a view showing an X-ray diffraction pattern according to the calcination temperature of the powder precursor prepared by the complex polymerization method.
9 is a diagram showing an X-ray photoelectron spectroscopy (XPS) pattern of LBO powder calcined at 700 ° C. for 5 hours.
10 is a view showing a powder precursor and the powder image according to the calcination temperature of 600 ℃, 700 ℃ and 800 ℃.
11A to 11C are photographs of the powder precursor calcined for 5 hours by temperature after heat treatment at 400 ° C. for 5 hours under a scanning electron microscope (SEM).
Figure 12a is a graph showing the dilator shrinkage behavior of the pure LLZ and LLZ-12wt% LBO complex, Figure 12b is a graph showing the dilator shrinkage of the pure LLZ and LLZ-12wt% LBO complex.
Figure 13a is a view showing the sintered density of the LLZ-LBO composite according to the content of LBO powder calcined at 700 ℃, Figure 13b is a view showing the relative density of the LLZ-LBO composite according to the content of LBO powder calcined at 700 ℃ to be.
14 is a view showing the results of analyzing the crystal phase using an X-ray diffraction (XRD) for the sintered body sintered at 1100 ℃ for 8 hours by adding 0 ~ 16wt% LBO.
15A to 15E are photographs of microstructures of sintered bodies sintered at 1100 ° C. for 8 hours by adding LBO to LLZ powders according to their contents using a field emission-scanning electron microscope (FE-SEM).
FIG. 16 is a diagram illustrating a complex impedance plot of the LLZ-LBO composite according to LBO content at room temperature of 28 ° C. FIG.
17a is a view showing sintered density according to the sintering temperature of the LLZ-12wt% LBO and LLZ-16wt% LBO composite, Figure 17b is a sintering temperature of the LLZ-12wt% LBO and LLZ-16wt% LBO composite A diagram showing relative density according to this.
18 is a view showing an x-ray diffraction (XRD) pattern according to the sintering temperature of the LLZ-12wt% LBO composite.
19 is a view showing an x-ray diffraction (XRD) pattern according to the sintering temperature of the LLZ-16wt% LBO composite.
20A to 20D show the results of observing the microstructure of the sintered body according to the sintering temperature of the LLZ-12wt% LBO composite using FE-SEM.
21A to 21D show the results of observing the microstructure of the sintered body according to the sintering temperature of the LLZ-16wt% LBO composite using FE-SEM.
FIG. 22 is a plot showing impedance plots measured at 28 ° C. according to the sintering temperature of LLZ to which LLZ-12 wt% LBO was added.
FIG. 23 is a plot showing impedance plots measured at 28 ° C. according to the sintering temperature of LLZ to which LLZ-16 wt% LBO was added.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments are provided to those skilled in the art to fully understand the present invention, and may be modified in various forms, and the scope of the present invention is limited to the embodiments described below. It doesn't happen.

According to a preferred embodiment of the present invention, a method for preparing a lithium lanthanum zirconium oxide-lithium boron oxide-based composite may include preparing an LBO (Li ₃ BO ₃ ) -based glass frit, and an LLZ (Li) having a garnet structure. ₇ La ₃ Zr ₂ O ₁₂ ) mixing and molding the solid electrolyte powder and the LBO (Li ₃ BO ₃ ) -based glass frit and sintering the molded product, the sintering at a temperature lower than 1200 ℃ It is characterized by performing.

The sintering is preferably carried out at 1000 ~ 1150 ℃.

The LBO (Li ₃ BO ₃ ) -based glass frit is preferably mixed with 0.1 to 25 parts by weight based on 100 parts by weight of the LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte powder.

Preparing the LBO (Li ₃ BO ₃ ) -based glass frit, (a) mixing the chelating agent and the solvent, (b) a lithium source material and a mixture of the chelating agent and the solvent Dissolving the boron source material, (c) heating the solution in which the lithium source material and the boron source material are dissolved to a first temperature to esterify to form a complex, and (d) in the esterification reaction. Heating the complex formed at a second temperature higher than the first temperature to form a powder precursor in a powder state; and (e) calcination of the powder precursor to form a LBO (Li ₃ BO ₃ ) -based glass frit ( glass frit).

The chelating agent is citric acid (C ₆ H ₈ O ₇ ), polyaminocarboxylic acid, polyphosphoric acid, ethylenediamine (C ₂ H ₄ (NH ₂ ) ₂ ) and ethylenediaminetetraacetic acid (C ₁₀ H ₁₆ N ₂ O ₈ ) one or more materials selected from the group consisting of.

The solvent may include one or more substances selected from the group consisting of ethylene glycol, H ₂ O, and dimethyl ether (C ₂ H ₆ O).

In the step (a), the solvent and the chelating agent are preferably mixed in a molar ratio of 2: 1 to 7: 1.

The lithium source material may include at least one material selected from the group consisting of lithium carbonate (Li ₂ CO ₃ ), lithium nitrate (LiNO ₃ ), and lithium chloride (Lithium chloride, LiCl). .

The boron source material is boric acid (Boric acid, H ₃ BO ₃ ), boron carbonate (Boron carbonate, C ₃ B ₂ O ₉ ), tetranitratoborate (B (NO ₃ ) ₃ ) and boron trichloride (Boron trichloride, BCl ₃ ) may include one or more substances selected from the group consisting of.

In the step (b), aluminum nitrate nonahydrate (Al (NO ₃ ) ₃ .9H ₂ O), aluminum chloride, AlCl ₃ and aluminum carbonate, Al ₂ (CO _{3 3} ) one or more substances selected from the group consisting of

In the step (b), made of niobium nitrate (Nobium nitrate, Nb (NO ₃ ) ₅ ), niobium acid (Niobium acid, Nb ₂ O ₅ · nH ₂ O) and niobium chloride (Niobium chloride, NbCl ₅ ) It is also possible to further dissolve one or more substances selected from the group.

In the step (b), 1 selected from the group consisting of tantalum nitrate, TaN ₅ O ₁₅ , tantalum carbonate, Ta ₂ (CO ₃ ) ₅ , and tantalum chloride, TaCl ₅ . More than one substance may be further dissolved.

Heating to the first temperature for the esterification is preferably carried out at a temperature of 90 ~ 250 ℃.

The calcination is preferably carried out in an oxidizing atmosphere at a temperature of 600 ~ 800 ℃ higher than the second temperature.

The method may further include heat treatment at a temperature higher than the second temperature and lower than the calcination temperature in order to remove the organic material contained in the powder precursor before the calcination.

In the step (b), it is preferable to dissolve the lithium source material and the boron source material in a molar ratio of 1: 1 to 5: 1.

Hereinafter, a method of manufacturing a lithium lanthanum zirconium oxide-lithium boron oxide-based composite according to a preferred embodiment of the present invention will be described in more detail.

Currently, the liquid electrolyte used in the commercially available lithium secondary battery is very vulnerable to high temperature or external shock, so the risk of explosion is very high. Efforts have been made to solve the stability problem by replacing the existing liquid electrolyte with a solid electrolyte.

In general, many studies have been made on solid electrolytes, mainly sulfide-based and oxide-based, and various types of solid electrolytes have been studied. Among these solid electrolyte materials, Li ₇ La ₃ Zr ₂ O ₁₂ solid electrolyte with cubic garnet structure has high thermal stability and relatively easy to manufacture and handle, and has lattice constant by substituting other materials for La or M ions. The ion conductivity may be improved due to an increase in and an increase in lithium ion vacancy, which is a path through which lithium ions may move.

LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte must maintain stable cubic structure to have high ion conductivity. In addition, crystalline solid electrolytes such as LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) are highly influenced by ionic conductivity due to resistance between grains, so it is important to obtain a dense sintered body to reduce grain boundary resistance. However, densification of LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) generally requires sintering at high temperatures above 1200 ° C. At this time, lithium ion volatilization and phase transition problems at high temperatures result in a decrease in ion conductivity. The addition of the low melting point additive may lead to liquid phase sintering during sintering, thereby densifying LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ).

In the present invention, unlike the addition of a dopant to the LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ), a lithium boron oxide-based glass frit, more specifically LBO (Li ₃ BO) for densification at low temperatures ₃ ) Add the glass frit. In order to obtain LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) densification at high ionic conductivity and low temperature, Li ₃ BO ₃ (LBO) glass frit having low grain boundary resistance is added. The added Li ₃ BO ₃ (LBO) glass frit is manufactured by the complex polymerization method, and has a low melting temperature, and when it is added as an additive, it induces liquid phase sintering and acts as a binder in sintering, thereby sintering more densely. Can be achieved.

The LBO (Li ₃ BO ₃ ) -based glass frit may be prepared by a polymerization complex method.

The complex polymerization method used in the present invention is a method of obtaining an oxide by heating a solution formed by dispersing a chelating agent and a metal ion material in a solvent to form a complex in which metal ions are uniformly dispersed and coordinated. The complex polymerization method is excellent in uniformity of components even in a multi-component system, has a low synthesis temperature, and particularly, has a small particle size of powder.

Chelating agents and solvents are mixed to prepare LBO (Li ₃ BO ₃ ) -based glass frits. It is preferable that the solvent and the chelating agent are mixed in a molar ratio of 2: 1 to 7: 1. The chelating agent is citric acid (C ₆ H ₈ O ₇ ), polyaminocarboxylic acid, polyphosphoric acid, ethylenediamine (C ₂ H ₄ (NH ₂ ) ₂ ) and ethylenediaminetetraacetic acid (C ₁₀ H ₁₆ N ₂ O ₈ ) one or more materials selected from the group consisting of. The solvent may include one or more substances selected from the group consisting of ethylene glycol, H ₂ O, and dimethyl ether (C ₂ H ₆ O).

 A lithium source material and a boron source material are dissolved in a mixture of the chelating agent and the solvent. It is preferable to dissolve the lithium source material and the boron source material in a molar ratio of 1: 1 to 5: 1. It is preferable to add a lithium source material and a boron source material to the mixture of a chelating agent and a solvent, stirring and dissolving at a rate of about 10 to 500 rpm while maintaining a temperature of 60 to 100 ° C.

At this time, aluminum nitrate nonahydrate (Al (NO ₃ ) ₃ · 9H ₂ O), aluminum chloride (Aluminum chloride, AlCl ₃ ) and aluminum carbonate (Aluminum carbonate, Al ₂ (CO ₃ ) ₃ ) It is also possible to further dissolve one or more substances selected from the group.

Niobium nitrate (Nb (NO ₃ ) ₅ ), at least one material selected from the group consisting of niobium acid, Nb ₂ O ₅ · nH ₂ O, and niobium chloride (NbCl ₅ ) May be further dissolved.

Tantalum nitrate (TaN ₅ O ₁₅ ), tantalum carbonate (Ta ₂ (CO ₃ ) ₅ ) and tantalum chloride (Tatal ₅ ) It may be.

The lithium source material may include at least one material selected from the group consisting of lithium carbonate (Li ₂ CO ₃ ), lithium nitrate (LiNO ₃ ), and lithium chloride (Lithium chloride, LiCl). .

The boron source material is boric acid (Boric acid, H ₃ BO ₃ ), boron carbonate (Boron carbonate, C ₃ B ₂ O ₉ ), tetranitratoborate (B (NO ₃ ) ₃ ) and boron trichloride (Boron trichloride, BCl ₃ ) may include one or more substances selected from the group consisting of.

The solution in which the lithium source material and the boron source material are dissolved is heated to a first temperature to esterify to form a complex. Heating to the first temperature for the esterification is preferably carried out at a temperature of 90 ~ 250 ℃. The esterification reaction is preferably carried out by putting a solution in which the lithium source material and the boron source material are dissolved in a heating stirrer such as a heating mantle and raising the temperature to the first temperature. Preferably, the esterification reaction is performed for about 1 minute to 12 hours.

The complex formed by the esterification reaction is heated at a second temperature higher than the first temperature to remove the solvent to form a powder precursor. The powder precursor is black. The second temperature is preferably about 250 to 350 ° C. as a temperature at which the solvent may be volatilized (evaporated).

The powder precursor is calcined to yield LBO (Li ₃ BO ₃ ) based glass frit. The calcination is preferably carried out in an oxidizing atmosphere at a temperature of 600 ~ 800 ℃ higher than the second temperature.

The heat treatment may be performed at a temperature higher than the second temperature and lower than the calcination temperature in order to remove the organic material contained in the powder precursor before the calcination. The heat treatment is preferably carried out at a temperature of 300 ~ 500 ℃.

A LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte powder having a garnet structure and the LBO (Li ₃ BO ₃ ) -based glass frit are mixed and molded. In this case, Li ₂ O, Li ₄ SiO ₄ and the LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte powder and the LBO (Li ₃ BO ₃ ) -based glass frit The one or more materials that are selected from the group consisting of Li ₃ PO ₄ may further be mixed. Li ₂ O, Li ₄ SiO ₄ and At least one material selected from the group consisting of Li ₃ PO ₄ is preferably mixed with 0.1 to 10 parts by weight based on 100 parts by weight of the LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte powder.

The LBO (Li ₃ BO ₃ ) -based glass frit is preferably mixed with 0.1 to 25 parts by weight based on 100 parts by weight of the LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte powder. Lithium lanthanum zirconium oxide solid electrolyte, more specifically LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte is generally sintered at a temperature higher than 1200 ℃. In addition, LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte has a property that is not sintered well. Therefore, in order to lower the sintering temperature of the LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte, a lithium boron oxide-based glass frit is used. LBO (Li ₃ BO ₃ ) -based glass frit can induce liquid phase sintering during sintering of LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte, which makes densification of sintered compact and low temperature sintering possible. It is possible to improve the ion conductivity of the sintered body.

The molded result is sintered. The sintering is carried out at a temperature lower than 1200 ° C. Preferably, the sintering is preferably performed at 1000 ~ 1150 ℃.

The lithium lanthanum zirconium oxide-lithium boron oxide-based composite (Li ₇ La ₃ Zr ₂ O ₁₂ -Li ₃ BO ₃ -based composite) thus prepared is liquid sintered when sintered by LBO (Li ₃ BO ₃ ) -based glass frit. It has high densification characteristics and excellent ion conductivity.

Hereinafter, experimental examples according to the present invention are specifically presented, and the present invention is not limited by the following experimental examples.

1.1. Solid electrolyte

Currently, the liquid electrolyte used in the commercially available lithium secondary battery is very vulnerable to high temperature or external shock, so the risk of explosion is very high. Efforts have been made to solve the stability problem by replacing the existing liquid electrolyte with a solid electrolyte.

In general, many studies have been made on solid electrolytes, mainly sulfide-based and oxide-based, and various types of solid electrolytes have been studied. Among these solid electrolyte materials, Li ₇ La ₃ Zr ₂ O ₁₂ (hereinafter referred to as 'LLZ') solid electrolyte having a cubic garnet structure has a high thermal stability and is relatively easy to manufacture and handle, and La or M By replacing other materials with ions, the ion conductivity may be improved due to an increase in lattice constant and an increase in lithium ion vacancy, which is a path through which lithium ions may move.

LLZ solid electrolyte must maintain stable cubic structure in order to have high ion conductivity. In addition, crystalline solid electrolytes such as LLZ are highly influenced by ionic conductivity due to the resistance between many grains, so it is important to obtain a compact sintered body to reduce grain boundary resistance. However, densification of LLZ generally requires sintering at high temperatures above 1200 ° C. At this time, lithium ion volatilization and phase transition problems at high temperatures result in a decrease in ion conductivity. The addition of low melting point additives can lead to liquid phase sintering during sintering, resulting in densification of LLZ.

In the present invention, Li ₃ BO ₃ (LBO) additives having low grain boundary resistance were added to obtain LLZ densification at high ionic conductivity and low temperature. The added LBO was prepared by the complex polymerization method and has a low melting temperature. When the additive is added as an additive, the LBO can be sintered more precisely by inducing liquid phase sintering and acting as a binder in sintering. Unlike the addition of dopants to the LLZ, low melting point sintering additives were added for densification at low temperatures. Li ₃ BO ₃ (hereinafter referred to as 'LBO') by the temperature of each of the contents to determine the effect of the additive to the effect on the phase change and ionic conductivity, and confirmed the sintering behavior.

1.2. Garnet Structure Li ₇ La ₃ Zr ₂ O ₁₂ Solid electrolyte properties

Oxide-based solid electrolytes are classified into crystalline and amorphous solid electrolytes. In the case of solid electrolytes having crystallinity, passages through which lattice defects can easily move due to lattice defects are formed to have ion conductivity. Representative crystalline oxide solid electrolytes are typically classified into NASICON, LISICON, Perovskite and Garnet type oxides.

Although the solid electrolyte of the garnet structure has a low ion conductivity, a high heat treatment temperature is required. However, the solid electrolyte of the garnet structure has many possibilities as a solid electrolyte due to its chemical stability and does not react with Li metal. According to the garnet structure, LLZ is classified into two types of tetragonal and cubic crystal systems according to the heat treatment temperature. The tetragonal phase (space group I4 ₁ / acd) is synthesized at relatively low temperatures and has an ion conductivity of approximately 10 ⁻⁶ Scm ^{− 1} . However, the cubic phase (space group Ia3d) has a higher ion conductivity of 10 ⁻⁴ Scm ⁻¹ and forms a phase at a high temperature (1200-1230 ° C.). The LLZ structure of cubic phase is shown in FIG. The basic form of the garnet structure is A ₃ B ₂ C ₃ O ₁₂ , where the La atom is located coordinating with 8 oxygen at position A (24c) and Zr is coordinating with 6 position oxygen at position B (16a) . Lithium is also present at three sites in two forms: tetragonal site (24d) coordinated with four oxygen and octahedral site coordinated with six positions oxygen. (96h, 48g) in the form. They exist by 1/3 and 2/3, respectively, to form lithium ion vacancy, and lithium ions conduct through the voids.

1.3. Li ₇ La ₃ Zr ₂ O ₁₂ Low temperature sintering

Crystalline solid electrolytes are strongly affected by ion conductivity due to the resistance between numerous grains. Therefore, LLZ must maintain a stable cubic phase in order to have high ion conductivity, and densification is also very important to reduce grain boundary resistance.

In order to densify LLZ, sintering additives that form a liquid phase under a solid-phase sintering temperature with a low melting point were added. By adding the sintering additive, the liquid phase is formed by melting the glass at a low temperature of 1000 ° C. or less during the sintering of the LLZ to not only improve the densification of the LLZ particles through liquid phase sintering, but also as shown in FIG. 2. It is possible to obtain high ion conductivity of LLZ by forming a thin layer on the substrate to reduce the resistance of grain boundaries. In low temperature LLZ densification, it is effective to use a liquid phase sintering process by adding a low melting point sintering aid that forms a liquid phase at a temperature lower than the solid phase sintering temperature. LLZ sintering aids include Li ₂ O (720 ° C.), Li ₄ SiO ₄ (823 ° C.), Li ₃ PO ₄ (837 ° C.), Various Li-based glass ceramics such as Li ₃ BO ₃ (700 ° C.) may be used. Among these various Li-based ceramic glasses, Li ₃ BO ₃ (LBO) additive has a high ion conductivity in bulk, has the lowest melting point, and is well distributed between LLZ grain boundaries with the advantage of reducing grain boundary resistance. This increases sinterability and is the most effective sintering aid for densification at low temperatures of LLZ.

1.4. Li ₃ BO ₃ by the complex polymerization method Glass frit collage

Synthesis of ceramic powder has various synthesis methods for other physical properties besides high purity powder and crystal phase. Among them, one of the chemical synthesis methods for producing a composite oxide powder having high purity and uniform composition is the Polymerization Complex Method of the Pechini process. This method is based on the bonding with metal elements, and is a powder production method using a polymer precursor made of citrate acid and ethylene glycol (Ethylene glycol). The complex polymerization method is a liquid phase method of dissolving a substance, and when a multicomponent composite oxide is produced, since the cations are stoichiometric, a uniform chemical composition is maintained and due to the low mobility of the cations, aggregation does not occur, thereby making it uniform and fine. A powder having particles can be obtained. In addition, chemically and physically produced powders have the advantage of being prepared at high purity and low temperature and without the grinding and resintering steps required by solid phase methods. Resin is used for the synthesis of ceramic powder. In this experiment, ethylene glycol was used to promote polymerization during the esterification reaction with citric acid as a chelating agent. Using an ethylene glycol solvent and α-hydroxy carboxylic acid such as citric acid, each metal ion is uniformly distributed in the resin phase to form a metal-chelate complex and then titrated. A polymer resin is prepared based on a polyesterification reaction at a temperature (90 ° C. to 100 ° C.). The principle of this process is that dissolved metal ions are chelated by the carboxylic acid end of citric acid, which has an ideal arrangement by chelating. Citric acid, with three carboxylic acid and one alcohol functional groups, forms stable chelates with metal ions. This is because various metal ions are uniformly distributed and irregular macromolecular chains are connected by ester bonds as shown in FIG. 3. The prepared polymeric resin can maintain the cations in the starting solution state in the oxide state as a final product due to the excellent thermal stability. Decomposition of the polymer occurs by heating the prepared polymer resin at a temperature of about 250 ~ 300 ℃. The polymer network having a high viscosity can prevent the aggregation effect during the pyrolysis process due to the low mobility of cations.

Therefore, the complex polymerization method forms a metal chelate complex from the initial precursor solution, so that uniformity of dendritic formation and stoichiometric composition through the polymerization reaction is maintained so that cations do not occur to obtain a powder having fine and uniform particles. Can be.

2.1. Raw powder

2.1.1. Li ₇ La ₃ Zr ₂ O ₁₂ powder

In this experiment, a commercial LLZ powder (Schott, Garmany) was used, and the physical properties are shown in Table 1 below.

Specific surface area (㎡ / g) Mean particle size (㎛) 3.28 1.7

As shown in Table 1, the LLZ powder has a specific surface area of 3.28 m 2 / g and a particle size of 1.7 μm, and FIG. 4 shows a distribution in which fine particles are partially aggregated as an image of the LLZ powder.

2.1.2. Li ₃ BO ₃ Powder Synthesis

Citric acid (C ₆ H ₈ O ₇ , 99.5%, DAE JUNG) was used as a chelating agent to synthesize LBO powder, and ethylene glycol (HOCH ₂ CH ₂ OH, 99.0%, DAE JUNG) was used as a solvent. Lithium carbonate (Li ₂ CO _{3 ,} JUNSEI) was used as the lithium source material, and boric acid (H ₃ BO _3, DAEJUNG) was used as the boron source material.

4 mol of ethylene glycol was heated to 90 ° C., and 1 mol of citric acid was added thereto, followed by stirring at 250 rpm for 1 hour to dissolve. Calculate the total amount of ME (Metal) required for the synthesis in a molar ratio of CA (Citric Acid) and 1: 4, and completely dissolve by adding 0.1 mol of lithium carbonate, and then add 0.1 mol of boric acid. Each 40 minutes were dissolved in order. The fully dissolved precursor was stirred at 130 ° C. at 200 rpm for 5 hours to induce esterification, and after the excess ethylene glycol was removed, the reaction solution was heated to 300 ° C. in a heating mantle. The liquid was evaporated to a powder state by heating for 2 hours. This powder was called powder precursor. After heating, heat treatment was performed at 400 ° C. for 5 hours to remove organic substances remaining in the powder precursor. The organic matter-free powder was calcined at 600-800 ° C. for 5 hours. The above experimental method is shown in a schematic diagram in FIG.

2.2. Characterization of Li ₃ BO ₃ Powder

Thermal behavior was measured using a thermal analyzer (TG-DSC Q 600 SDT, TA Instruments, USA) to measure the decomposition temperature of organic materials present in the powder precursor, the weight loss according to the thermal weight, and the endothermic and exothermic reactions. An attempt was made to analyze. In particular, it was measured to analyze the decomposition temperature and phase formation temperature conditions of the organic materials present in the powder precursor (powder precursor). The powder precursor was charged to an alumina cell, mounted on a rod, and measured at 1200 ° C. at a temperature rising rate of 5 ° C./min in an air atmosphere.

40kV using an X-ray diffractometer (D / max-2500, RIGAKU, Japan) set to a λ value of 1.54059Å as the Cu target to confirm the synthesis and the presence of phases in the powder synthesized by the complex polymerization method , 2θ was measured under a condition of 5 ° / min from 10 ° to 60 ° at 200 mA.

X-ray photoelectron spectroscopy (XPS) (PHI-5000 versaprobe ™, ULVAC-PHI Inc.) was measured for quantitative analysis of the synthesized powder. At this time, the pass energy of the hemispherical energy analyzer for analyzing the energy of the photoelectrons was 23.5 eV, and the binding energy of each element was measured in the range of 0 to 1200 eV.

In addition, a scanning electron microscope (FE-SEM, JSM-9701, JEOL, Japan) was used to observe the powder shape.

2.3. Sintering of Li ₇ La ₃ Zr ₂ O _{12 with} Li ₃ BO ₃

Commercial LLZ powder (Schott, Garmany) was used in this experiment. Powder precursor (Powder precursor) was calcined at 600 ℃, 700 ℃, 800 ℃ was used as an additive. As a result of calcining by temperature, the powder (LBO glass frit) obtained by calcining at 700 ° C showed a particle shape of 5 ~ 10㎛, the additive was used LBO glass frit obtained by calcining at 700 ° C.

The LBO additive in the LLZ powder was mixed by milling the content of 0wt%, 4wt%, 8wt%, 12wt%, 16wt% compared to the LLZ powder. At this time, a mixed mill was used as a mini mill (Pulverisette 23, FRITSCH, Germany), and the powder 0.3g, Oscillation 40, 5min.

The mixed powder was charged into a 10 mm cemented carbide mold and molded at a pressure of 10 MPa, and then a disk-shaped molded body was manufactured at a pressure of 200 MPa by cold isotic pressing.

Sintering was used as a box furnace, and the molded body was put in an alumina crucible, and sintered with bed powder in order to prevent sticking to the crucible due to the liquid phase from the molded body during sintering. Sintering was sintered 0 ~ 16wt% at 1100 ℃ for 8 hours by LBO content. In addition, the sintering behavior was confirmed by sintering at 900 ° C., 1000 ° C., 1100 ° C., and 1200 ° C. for 8 hours based on the content of 12 wt% and 16 wt%. The above experimental method is shown in a schematic diagram in FIG.

2.4. Li ₇ La ₃ Zr ₂ O _{12 with} Li ₃ BO ₃ Characterization of Sintered Body

The density of the sintered compact was measured using the dimension measurement. The dimension density value was measured using a vernier caliper and an electronic balance to measure the volume and weight. As the LBO content is different, the density of LLZ is also different. Therefore, the sintered density values of LLZ-LBO composites with different compositions were compared with each other considering the theoretical density of LLZ-LBO composites. The theoretical density values of the LLZ-LBO composite were calculated by the rule of mixure by applying the theoretical density values of LLZ (ρ _LLZ : 5.11 g / cm 3) and LBO (ρ _LBO : 2.16 g / cm 3).

In order to analyze the distribution, densification and grain boundary microstructure of the LBO liquid phase between LLZ particles, the cross section of the sintered body was cut out and observed by using a field emission scanning electron microscope (FE-SEM, JSM-9701, JEOL, Japan).

In addition, X-ray diffractometer (D / max-2500, RIGAKU, Japan) set to λ value of 1.54059 으로 as Cu target for the crystal phase analysis of sintered body according to LBO content and temperature, 10 ° at 40kV, 200mA It measured under the conditions of 5 degrees / min to -60 degrees.

In order to measure the impedance, the LLZ-LBO sintered body having a constant width (A) and thickness (t) was polished with sandpaper. Au electrodes having excellent electron conductivity were coated on both surfaces of the sintered body by dry deposition. An AC voltage was applied through the double-sided electrode to measure impedance (Agilent 4192A, Hewlett Packard) in the signal level of 0.05V and the measurement frequency in the range of 10 Hz to 13 MHz. From the intersection where the measured half circle of the impedance trajectory meets the real axis, the resistance ( _b ) of the bulk electrolyte was obtained, and the ion conductivity (σ) was obtained from the width (A) and thickness (l) of the sample as shown in Equation 1 below. .

[Equation 1]

3.1. Li ₃ BO ₃ synthesis Properties of powder

3.1.1. Thermal behavior analysis

In order to determine the optimum calcination temperature and organic decomposition temperature of the powder precursor obtained by heat treatment at 300 ° C., TG-DTA (thermogravimetry-differential thermal analysis) analysis is shown in FIG. 7. As a result of measuring TG, about 32% weight loss occurred from around 400 ° C, 50% weight loss at 700 ° C, and 12% weight loss at 800 ° C. The reason for the large weight loss behavior in the TG result is thought to be due to dehydration and decomposition of organic matter near 400 ℃. Weight loss at 700 ℃ and 800 ℃ is the most common carbonate containing It is thought to be due to the decomposition of residual organics associated with (carbonate). As a result of the DSC measurement, the exothermic reaction was found to be slightly lower due to the weight loss of carbon dioxide and water vapor which did not burn at 300 ℃. In addition, an exothermic peak was observed to rapidly increase from 700 ° C to 750 ° C, which can be assumed to be a temperature at which the Li ₃ BO ₃ phase is formed after evaporation of ethylene glycol, decomposition of citric acid, and combustion of organic material. In addition, a slightly lower endothermic reaction was observed around 800 ℃, which indicates that the remaining organic matter was burned.

3.1.2. X-ray Diffraction Results

Figure 8 shows the X-ray diffraction pattern according to the calcination temperature of the powder precursor prepared by the complex polymerization method. An amorphous peak was observed in the initial powder precursor. This indicates that citric acid and four metal ions are uniformly formed by metal-chelating. The calcined powder at 600 ° C. was found to be a mixture of amorphous and crystalline. As a crystalline phase, an amorphous peak was not observed in the powder calcined at 700 ° C. and 800 ° C., and a Li ₂ CO ₃ crystal phase was observed. The reason is that the BC bond is not decomposed in the heat treatment process, so Li is not bonded with B, is bonded with C in the air, precipitated as Li ₂ CO ₃ , and volatilized during the heat treatment process without B melting.

3.1.3. XPS Analysis Results

B was not observed in the X-ray diffraction (XRD) results of FIG. 8, so X-ray photoelectron spectroscopy (XPS) (PHI-5000 versaprobe ™, ULVAC-PHI Inc.) was measured for quantitative analysis. It was.

9 shows the results of measuring the chemical bonding state of the LBO powder calcined at 700 ℃ for 5 hours. The binding energy was about 284 eV relative to C 1s, the peak for O 1s was observed at about 530eV, Li 1s about 55eV, and the peak for B 1s was observed at about 182eV.

As a result of quantitative analysis, it was confirmed that Atomic% contained 27.5% C 1s, 46.6% O 1s, 28.4% Li 1s, and 0.5% B.

It is determined that B is volatilized during the heat treatment and is present in a small amount of 0.5% so that no peak appears on the X-ray diffraction (XRD).

3.1.4. Result of particle size and shape analysis

10 shows an image of the powder according to the powder precursor and the calcination temperature. The powder precursor (see 'Black powder' in FIG. 10) was black and the powder calcined at 600 ° C. showed a color close to black. On the other hand, the color of the powder calcined at 700 ° C is white, and the color of the powder is determined to be changed by removing residual organic substances and impurities. The powder calcined at 800 ° C. showed a white color. Image observation showed that the powder calcined at 700 ° C and 800 ° C was excellent.

After heat treatment of the powder precursor at 400 ° C. for 5 hours, the powder calcined for 5 hours by temperature was observed using a scanning electron microscope (SEM) to observe the particle size and shape as a microstructure. FIGS. 11A to 11C. Shown in FIG. 11A shows the powder calcined at 600 ° C., FIG. 11B shows the powder calcined at 700 ° C., and FIG. 11C shows the powder calcined at 800 ° C. FIG.

As a result of observing the size of the powder according to the calcination temperature, the powder calcined at 600 ° C. was observed to be 0.5 to 5 μm. The powder calcined at 700 ° C showed a size of about 1 ~ 10㎛ and the particles of the powder were somewhat unevenly arranged. The powder calcined at 800 ° C. was observed to be about 0.5-10 μm particles. The powder calcined at 600 ° C. did not burn residual organic matter, and the powder calcined at 800 ° C. has a problem of melting above a melting temperature. Therefore, the powder calcined at 700 ° C. was used as an additive through observation of the color of the calcined powder according to the microstructure result and temperature.

3.2. Li ₃ BO ₃ Results of Sintering Characteristics of Li ₇ La ₃ Zr ₂ O _{12 with} Different Contents

3.2.1. Dilatometry Contraction Behavior

In order to investigate the sintering properties of LLZ-LBO composites, shrinkage behavior was investigated using a dilatometer. Figure 12a shows the dilator shrinkage behavior of the pure LLZ and LLZ-12wt% LBO complex. In the case of pure LLZ, shrinkage occurs rapidly at 1000 ° C. or higher, whereas in the case of LLZ-12wt% LBO composite, shrinkage starts at about 700 ° C., which is much lower than LLZ. In order to examine the shrinkage behavior in more detail, as shown in Figure 12b (shirinkage rate) graph. Referring to the shrinkage rate graph of FIG. 12B, it means that the sintering shrinkage of the LLZ-LBO composite proceeds by different sintering mechanisms according to the temperature section. Shrinkage began to occur at the first peak at about 650 ° C., reaching a maximum at 730 ° C. The second sintering step started over 800 ℃ and proceeded over a relatively wide temperature range compared to the first sintering section, the peak temperature showing the maximum shrinkage was 1020 ℃. The first stage shrinkage is due to the particle rearrangement of LLZ due to viscous flow as the viscosity decreases above the softening point of the sintering additive LBO glass and the fluidity of the LBO particles increases, and the second peak It may be related to the rearrangement of LLZ by liquid phase sintering by molten LBO and the solid phase sintering between LLZ particles as LBO melts.

3.2.2. Sintered Density

LBO powder calcined at 700 ℃ was added 0 ~ 16wt% to LLZ, Figure 13a is a view showing the sintered density of the LLZ-LBO composite according to the content of LBO powder calcined at 700 ℃, Figure 13b is calcined at 700 ℃ It shows the relative density of LLZ-LBO composite according to the content of one LBO powder. The sintered density of pure LLZ was 2.98 g / cm ³ , and the density of LLZ was found to increase with increasing LBO content. However, the sintered density is slightly reduced at 16wt%, because the theoretical density value of the LLZ-LBO composite is different when the LBO content is changed. Therefore, the sintered density values of LLZ-LBO composites were compared with each other considering the theoretical density of LLZ-LBO composites. For detailed comparison, the relative values of theoretical density were compared. As a result, it can be seen that the relative density value increases as the LBO content increases. The highest sintered density of 88% was obtained when 16wt% was added. This is a significant improvement over 58% of pure LLZ without LBO.

3.2.3. X-ray Diffraction

14 is a result of analyzing the crystal phase using an X-ray diffraction (XRD) for the sintered body sintered at 1100 ℃ for 8 hours by adding 0 ~ 16wt% LBO. As shown in FIG. 14, the diffraction peaks of the cubic LLZ were mainly observed for the pure LLZ specimens without the addition of the LBO and the 4 wt% LBO, and some La ₂ Zr ₂ O ₇ (LZ) pyrochlore phases were observed. Confirmed. The pure LLZ specimen showed the highest intensity (Intensity) on the La ₂ Zr ₂ O ₇ (LZ) impurity phase and the impurity phase decreased with increasing content. It can be seen that the pure LLZ specimen contains many impurity phases. In addition, in the case of LLZ specimens containing 8 wt% or more of LBO, only cubic LLZ phases were observed, and La ₂ Zr ₂ O ₇ (LZ) phases were observed to disappear. It can be seen that LBO plays a role of inhibiting La ₂ Zr ₂ O ₇ (LZ) formation of LLZ and stabilizing the cubic structure.

3.2.4. Microstructure

The cross-section of the sintered body sintered at 1100 ° C. for 8 hours by adding LBO to the LLZ powder was observed using a field emission-scanning electron microscope (FE-SEM), and the results of the microstructures are shown in FIGS. 15A to 15E. . 15a shows a cross section of a sintered body obtained by sintering pure LLZ powder at 1100 ° C. for 8 hours, and FIG. 15b shows a cross section of a sintered body sintered at 1100 ° C. for 8 hours by mixing 4 wt% LBO in LLZ powder. 15c shows a cross section of a sintered body sintered at 8100% LLZ powder and sintered at 1100 ° C. for 8 hours. FIG. 15D shows a cross section of a sintered body sintered at 1100 ° C. for 12 hours by mixing 12 wt% LBO in LLZ powder. FIG. 15E shows a cross section of a sintered body sintered at 1100 ° C. for 8 hours by mixing 16 wt% LBO in LLZ powder. As shown in FIG. 15B, many pores between grain boundaries were observed for pure LLZ and 4 wt% sintered specimens. On the other hand, in the case of the sintered body added with more than 8wt% LBO shows a fine microstructure as the content increases. The liquid phase is uniformly distributed between the LLZ interfaces and shows a dense microstructure with greatly reduced pores. In addition, unlike the pure LLZ, the particles of the LLZ can be seen that the growth of the particles greatly occurs as the LBO is added. This confirms that densification of LBO-added LLZ proceeds by solid phase sintering between particles of LLZ and the growth of particles, namely grain growth, as explained in the dilator shrinkage behavior of FIGS. 12A and 12B. Could.

3.2.5. Ion conductivity

FIG. 16 shows a complex impedance plot of the LLZ-LBO composite according to LBO content at room temperature of 28 ° C. FIG. The LLZ solid electrolyte shows a straight line due to polarization by electrodes at high frequencies and semicircles due to ion conduction at high frequencies. A fitting was performed through the Z view program using the equivalent circuit of FIG. 16, Rg represents grain resistance, Rgb represents grain boundary resistance between grains, and CPE represents Constant Phase Element. The total resistance of the specimen can be determined from the intersection of the semicircles in the real part of the impedance. Table 2 shows the ionic conductivity values for each content.

LBO contents Total ionic conductivity
(S / cm ^-1 ) wt% vol% 0 0 5.98 × 10 ^-6 4 9 1.12 × 10 ^-5 8 17 1.54 × 10 ^-5 12 24 1.18 × 10 ^-4 16 31 1.28 × 10 ^-4

Referring to FIG. 16 and Table 2, as the LBO content increases, the ionic conductivity value tends to increase, and as the content increases, the resistance of grain boundaries decreases. If the specimen was added to 16wt% LBO total ionic conductivity was 1.28 × 10 ^-4 5.98 a pure sample as a LLZ Scm ^-1 × 10 ^- could be obtained greatly improved value as compared to ⁶ Scm ^-1. Therefore, when the LBO sintering additive is added to the pure LLZ, the interfacial resistance is judged to be uniformly distributed between the LLZ grain boundaries.

3.3. Sintering Characteristics Analysis of Li ₇ La ₃ Zr ₂ O _{12 with} Li ₃ BO ₃

3.3.1. Sintered Density

17a is a view showing sintered density according to the sintering temperature of the LLZ-12wt% LBO and LLZ-16wt% LBO composite, Figure 17b is a sintering temperature of the LLZ-12wt% LBO and LLZ-16wt% LBO composite A diagram showing relative density according to this. Sintering was performed for 8 hours at each temperature. The sintered density tended to increase when 16 wt% LBO was added (16 wt% LBO) than when 12 wt% LBO was added (12 wt% LBO). When sintered at 900 ° C. based on 16wt%, 72% relative density values were obtained, and when sintered at 1100 ° C., the density increased to 88%. At 900 ° C, LBO showed a 72% lower density than the melting temperature. As the sintering temperature increased, the sintered density increased and the maximum value was 88% at 1100 ℃. From this, sintering of LLZ-LBO composite was confirmed that not only liquid phase sintering by melting LBO but also solid phase sintering of LLZ should work together. On the other hand, the sintered density of both specimens decreased drastically at 1200 ° C. This is because LLZ and LBO are decomposed at high temperature, and a small amount of Li and B having low melting points is volatilized, and thus the density is reduced.

3.3.2. X-ray Diffraction

18 is a view showing the x-ray diffraction (XRD) pattern of the LLZ-12wt% LBO composite according to the sintering temperature, Figure 19 is a view of the x-ray diffraction (XRD) pattern of the LLZ-16wt% LBO composite according to the sintering temperature The figure shown. As shown in Figure 18 and 19, the LZ phase was not observed at 900 ~ 1200 ℃ sintering temperature, only the peak of the cubic LLZ phase was observed. In addition, in the LLZ specimens with LBO added at each temperature, no LBO crystal phase peak was observed, which did not form a new crystal phase because LBO did not react with LLZ and existed in the amorphous phase at the grain boundary of the LLZ after liquid phase sintering. It is judged.

3.3.3. Microstructure

20A to 20D show the results of observing the microstructure of the sintered body according to the sintering temperature of the LLZ-12wt% LBO composite using FE-SEM, and FIGS. 21A to 21D show the LLZ-16wt% LBO composite. The sectional view of the sintered compact according to the sintering temperature of the microstructure was observed using FE-SEM. 20A and 21A show the case of sintering at 900 ° C, FIGS. 20B and 21B show the case of sintering at 1000 ° C, and FIGS. 20C and 21C show the case of sintering at 1100 ° C, and FIGS. 20D and 21D show 1200 ° C. Sintered at. As the temperature increases, the particles of LLZ grow and densify. By adding LBO additive, densification proceeded with grain arrangement of LLZ by liquid phase sintering and grain growth by sintering solid phase with temperature. When sintered at 900 ° C., LBO was not uniformly distributed, and thus a large area occupied by pores was observed. Since sintering between the LLZ particles was hardly occurred because particle growth hardly occurred. When sintered at 1000 ° C, the area occupied by pores was small, and the finest microstructure was observed in the specimen sintered at 1100 ° C. When sintered at 1200 ° C., a new microstructure was observed that was completely different from the microstructure below 1100 ° C. In addition, abnormal grain growth of LLZ particles of 10 µm or more was observed locally.

3.3.4. Ion conductivity

FIG. 22 is a plot showing impedance plots measured at 28 ° C according to the sintering temperature of LLZ added with LLZ-12wt% LBO, and FIG. 23 is plotted according to the sintering temperature of LLZ with LLZ-16wt% LBO. A plot of impedance plots taken at ° C. The ionic conductivity is increased by as the sintering temperature increases, 3.10 × 10 in the case of sintering at 900 ℃ to 12wt% based on ^- were scored ⁷ Scm ^-1, if the sintering at 1100 ℃ is 1.18 × 10 ^{- 4} Scm ^-1 The value was obtained. In the case of sintering at 1100 ° C. or lower, it is considered that the interfacial resistance is large and the pore amount is high to influence the ion migration. In ^{1200 ℃ 2.08 × 10 - 5 Scm} - ¹ was the ionic conductivity is decreased, which is due to a change in the crystal structure, as observed in the microstructure of the increased resistance as a whole. It showed the same tendency even when the addition of 16wt%, 1.28 × 10 in the case of sintering at 1100 ℃ ^- was the highest ion conductivity value to ⁴ Scm ^-1. This confirmed that the ion conductivity of the composite according to the temperature is affected by densification.

In the experimental example of the present invention, in order to improve the properties of the garnet structure Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ) solid electrolyte at low temperature, the effect of sintering behavior of LLZ using Li ₃ BO ₃ (LBO) as a sintering additive and I looked at the ion conductivity. The sintering additive used LBO synthesize | combined using the complex polymerization method. When sintering at 1100 ℃ for 8 hours, the sintering behavior was investigated by adding 0wt% ~ 16wt% according to LBO content. In addition, phase analysis, sintering behavior and ion conductivity were investigated by adding 12wt% LBO and 16wt% LBO at 900 ~ 1200 ℃ according to the sintering temperature.

Through the complex polymerization method, a powder precursor in which two metal ions of citrate, Li, and B are formed by metal-chelating was prepared. LBO powder calcined at 700 ° C. showed excellent conditions and images.

As a result of the shrinkage behavior analysis with the dilatometry, the addition of 12wt% LBO additive to the LLZ powder showed that the shrinkage began at around 700 ° C, which is much lower than Pure LLZ. In addition, two shrinkage behaviors were observed, and the first stage shrinkage was above the softening point of the sintering additive LBO glass, reducing the viscosity and increasing the fluidity of the LBO particles. It is due to the particle rearrangement, and it is believed that the second peak occurs with the rearrangement of the LLZ due to liquid phase sintering by the molten LBO and the solid phase sintering between the LLZ particles.

The overall sintering behavior tended to increase with increasing LBO content. It is confirmed that as the LBO content increases, the densification increases due to melting at the LLZ boundary interface. In addition, as a result of sintering density measurement, when 16 wt% of LBO was added, a relatively high density value of 88% was obtained. On the other hand, in the case of pure LLZ without LBO, the sintered density was as low as 58%. Therefore, it was confirmed that the sintered density was improved when the LBO sintering aid was added to the pure LLZ.

La ₂ Zr ₂ O ₇ who crystal phase X- ray diffraction (XRD) according to the LBO content analysis result exists in the pure LLZ and 4wt% LBO The impurity phase decreased with increasing LBO content, and when added more than 8wt%, cubic LLZ was formed. 12,16wt% .LBO depending on temperature La ₂ Zr ₂ O ₇ Only cubic LLZ was observed which was not observed and was stable.

As the LBO content increased, the ion conductivity value tended to increase, and the resistance of the grain boundary decreased. If the specimen was added to 16wt% LBO full (total) ionic conductivity at 1100 ℃ 1.28 × 10 ^- it could be obtained greatly improved value as compared to ⁶ Scm ^{-1 -} 5.98 × 10 of a pure specimen as LLZ ⁴ Scm ^-1. As the sintering temperature was increased, the ion conductivity increased, and the maximum ion conductivity was obtained at 1100 ° C.

As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment, A various deformation | transformation is possible for a person with ordinary skill in the art.

Claims (16)

Preparing a LBO (Li ₃ BO ₃ ) -based glass frit;
Mixing and molding a LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte powder having a garnet structure and the LBO (Li ₃ BO ₃ ) -based glass frit; And
Sintering the shaped result,
Preparing the LBO (Li ₃ BO ₃ ) -based glass frit (glass frit),
(a) mixing a chelating agent with a solvent;
(b) dissolving a lithium source material and a boron source material in a mixture of the chelating agent and the solvent;
(c) heating the solution in which the lithium source material and the boron source material are dissolved to a first temperature to esterify to form a complex;
(d) heating the complex formed by the esterification reaction at a second temperature higher than the first temperature to form a powder precursor in powder state; And
(e) a step of calcining the precursor powder (calcination) to give the LBO (Li ₃ BO ₃₎ based glass frit (glass frit),
The chelating agent is at least one selected from the group consisting of polyaminocarboxylic acid, polyphosphoric acid, ethylenediamine (C ₂ H ₄ (NH ₂ ) ₂ ) and ethylenediaminetetraacetic acid (C ₁₀ H ₁₆ N ₂ O ₈ ) Contains substances,
The lithium source material includes at least one material selected from the group consisting of lithium carbonate (Lithium carbonate, Li ₂ CO ₃ ), lithium nitrate (Lithium nitrate, LiNO ₃ ) and lithium chloride (Lithium chloride, LiCl),
The boron source material is boric acid (Boric acid, H ₃ BO ₃ ), boron carbonate (Boron carbonate, C ₃ B ₂ O ₉ ), tetranitratoborate (B (NO ₃ ) ₃ ) and boron trichloride (Boron trichloride, BCl ₃ ) comprises one or more substances selected from the group consisting of,
Dissolving the lithium source material and the boron source material in a molar ratio of 1: 1 to 5: 1 in step (b),
The LBO (Li ₃ BO ₃ ) -based glass frit is mixed with 0.1 to 25 parts by weight based on 100 parts by weight of the LLZ (Li ₇ La ₃ Zr ₂ O ₁₂ ) solid electrolyte powder,
The calcination is carried out in an oxidizing atmosphere at a temperature of 600 ~ 800 ℃ higher than the second temperature,
Lithium lanthanum zirconium oxide-lithium boron, characterized in that the sintering is carried out at a temperature of 1000 ~ 1150 ℃ higher than the calcination temperature to obtain the LBO (Li ₃ BO ₃ ) -based glass frit (lower than 1200 ℃) Method for producing an oxide-based composite.
delete delete delete delete The method of claim 1 wherein the solvent is ethylene glycol (Ethylene glycol), H ₂ O and dimethyl ether lithium lanthanum zirconium oxide, characterized in that it comprises one or more materials that are selected from the group consisting of (C ₂ H ₆ O) - Method for producing a lithium boron oxide-based composite.
The method of claim 1, wherein in the step (a), the solvent and the chelating agent are mixed in a molar ratio of 2: 1 to 7: 1.
delete delete The method of claim 1, wherein in step (b),
From aluminum nitrate nonahydrate (Al (NO ₃ ) ₃ 9H ₂ O), aluminum chloride (AlCl ₃ ) and aluminum carbonate (Al ₂ (CO ₃ ) ₃ ) A method for producing a lithium lanthanum zirconium oxide-lithium boron oxide-based composite, characterized by further dissolving at least one selected material.
The method of claim 1, wherein in step (b),
Niobium nitrate (Nb (NO ₃ ) ₅ ), at least one material selected from the group consisting of niobium acid, Nb ₂ O ₅ · nH ₂ O, and niobium chloride (NbCl ₅ ) Method for producing a lithium lanthanum zirconium oxide-lithium boron oxide-based composite, characterized in that further dissolved.
The method of claim 1, wherein in step (b),
Tantalum nitrate (TaN ₅ O ₁₅ ), Tantalum carbonate (Tantalum carbonate, Ta ₂ (CO ₃ ) ₅ ) and tantalum chloride (Tantalum chloride, TaCl ₅ ) to further dissolve one or more substances selected from the group Method for producing a lithium lanthanum zirconium oxide-lithium boron oxide-based composite, characterized in that.
The method for preparing a lithium lanthanum zirconium oxide-lithium boron oxide-based composite according to claim 1, wherein the heating to the first temperature is performed at a temperature of 90 to 250 ° C.
delete The lithium lanthanum zirconium oxide according to claim 1, further comprising a heat treatment at a temperature higher than the second temperature and lower than the calcination temperature in order to remove the organic matter contained in the powder precursor before the calcination. -Method of producing a lithium boron oxide-based composite. delete

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