KR102200967B1 - Galium- gadolinium dopped solid electrolyte material for all-solid-state lithium secondary battery and method for preparing the same - Google Patents

Abstract

The present invention is a garnet structure, gallium (Ga) and gadolinium (Gd) doped lithium lanthanum zirconium oxide (lithium lanthanum zirconium oxide, LLZO) containing a LLZO solid electrolyte is provided. By doping gallium and gadolinium to the LLZO solid electrolyte using the gallium-gadolinium-doped solid electrolyte for an all-solid lithium secondary battery of the present invention and a method for manufacturing the same, there is an excellent effect of ion conductivity and potential window characteristics.

Description

Gallium-Gadolinium-doped solid electrolyte for an all-solid lithium secondary battery, and its manufacturing method {GALIUM- GADOLINIUM DOPPED SOLID ELECTROLYTE MATERIAL FOR ALL-SOLID-STATE LITHIUM SECONDARY BATTERY AND METHOD FOR PREPARING THE SAME}

The present invention relates to a solid electrolyte for an all-solid lithium secondary battery and a method of manufacturing the same, and more particularly, by doping gallium and gadolinium in the LLZO solid electrolyte, gallium-gadolinium for an all-solid lithium secondary battery having excellent ion conductivity and potential window characteristics It relates to the doped solid electrolyte and a method for preparing the same.

Lithium secondary batteries have large electrochemical capacity, high operating potential, and excellent charge/discharge cycle characteristics, so they are in demand for applications such as portable information terminals, portable electronic devices, small household power storage devices, motorcycles, electric vehicles, and hybrid electric vehicles. Is increasing. With the proliferation of such uses, there is a demand for improved safety and high performance of lithium secondary batteries.

As a conventional lithium secondary battery uses a liquid electrolyte, it is easily ignited when exposed to water in the air, and a stability problem has always been raised. This stability problem is becoming more and more an issue as electric vehicles become visible.

Accordingly, in recent years, for the purpose of improving safety, research on an all-solid-state secondary battery using a solid electrolyte made of an inorganic material, which is a non-combustible material, has been actively conducted. All-solid-state secondary batteries are attracting attention as next-generation secondary batteries from the viewpoint of stability, high energy density, high output, long life, simplification of manufacturing processes, and large/compact and low cost of batteries.

The all-solid lithium secondary battery is composed of a positive electrode/solid electrolyte layer/cathode, of which high ionic conductivity and low electronic conductivity are required for the solid electrolyte of the solid electrolyte layer. In addition, a solid electrolyte is also included in the constituent elements of the anode and cathode layers, which are electrode layers, and a mixed conductive material having high ionic conductivity and electron conductivity is advantageous for the solid electrolyte used in the electrode layer.

Solid electrolytes that satisfy the requirements of the solid electrolyte layer of an all-solid secondary battery include sulfide-based and oxide-based solid electrolytes. Among them, the sulfide-based solid electrolyte has a problem in that a resistance component is generated by an interface reaction with a positive electrode active material or a negative electrode active material, has strong hygroscopicity, and generates hydrogen sulfide (H ₂ S) gas, a toxic gas.

Oxide-based solid electrolyte is _{LATP (Li 1. 3 Al 0} . 3 Ti 1 .7 (PO 4) 3), LLTO (Li 3x La 2 / (3x) TiO 3) based, LLZO (Li ₇ La ₃ Zr ₂ O ₁₂ ) and the like are widely known, and among them, LLZO, which is known to have relatively high intergranular resistance compared to LLTO, but has excellent dislocation window characteristics, is attracting attention as a promising material.

Although the LLZO has advantages such as high ionic conductivity, low reactivity with electrode materials, and a wide potential window (0-6V), it is difficult to control process conditions due to volatilization of lithium (Li) in the sintering process. However, the manufacturing process is complicated and difficult due to the incompatibility of sintering, which is difficult to apply in practice. In addition, since the difference in ionic conductivity is large depending on the crystal structure, it is necessary to develop a technology to control the crystal structure of LLZO by controlling the composition of the starting material and sintering characteristics.

An object of the present invention is to solve the above problems, by doping gallium and gadolinium in LLZO solid electrolyte, to provide a gallium-gadolinium doped solid electrolyte for an all-solid lithium secondary battery having excellent ion conductivity and potential window properties, and a method of manufacturing the same I have to.

According to an aspect of the present invention, there is provided a LLZO solid electrolyte comprising a garnet structure, lithium lanthanum zirconium oxide (LLZO) doped with gallium (Ga) and gadolinium (Gd).

The LLZO solid electrolyte may be represented by Formula 1 below.

[Formula 1]

Li _x Ga _p La _y Gd _q Zr _z O ₁₂ (5≤x≤9, 0<p≤4, 0<q≤4, 2≤y≤4, 1≤z≤3)

The LLZO solid electrolyte may be represented by Formula 2 below.

[Formula 2]

Li _(7-3p) Ga _p La _{3 - q} Gd _q Zr ₂ O ₁₂ (0<p≤1, 0<q≤1)

The LLZO solid electrolyte may be represented by Formula 2 below.

The LLZO solid electrolyte may include 0.05 to 0.5 moles of gallium (Ga) and 0.01 to 0.2 moles of gadolinium (Gd) based on 2 moles of zirconium (Zr).

The gallium and gadolinium-doped lithium lanthanum zirconium oxide solid electrolyte may have an ionic conductivity of 6.0 x 10 ^-4 to 2.0 x 10 ^-3 S/cm.

The LLZO solid electrolyte may have an ionic conductivity of 0.5 x 10 ^-3 to 1.5 x 10 ^-3 S/cm.

The LLZO solid electrolyte may have a single-phase cubic structure.

According to another aspect of the present invention, a positive electrode including a first lithium lanthanum zirconium oxide (first LLZO), a first conductive polymer, a positive electrode active material, and a conductive material; A negative electrode containing lithium metal; And a composite solid electrolyte layer comprising a second lithium lanthanum zirconium oxide (second LLZO) and a second conductive polymer between the positive electrode and the negative electrode, wherein the first LLZO and the second LLZO are each independently gallium and It is a gadolinium-doped lithium lanthanum zirconium oxide solid electrolyte, and the gallium and gadolinium-doped lithium lanthanum zirconium oxide solid electrolyte is represented by the following Formula 1, it provides an all-solid lithium secondary battery.

[Formula 1]

Li _x Ga _p La _y Gd _q Zr _z O ₁₂ (5≤x≤9, 0<p≤4, 0<q≤4, 2≤y≤4, 1≤z≤3)

According to another aspect of the present invention, (a) a lanthanum (La) precursor, a zirconium (Zr) precursor, a gallium (Ga) precursor, a gadolinium (Gd) precursor, a complexing agent, and a reactant aqueous solution containing a pH adjusting agent are co-precipitated. Reacting and drying to prepare a solid electrolyte precursor; (b) preparing a mixture by mixing the solid electrolyte precursor with a lithium (Li) source; And (c) heat-treating the mixture to prepare a lithium lanthanum zirconium oxide (LLZO) solid electrolyte doped with gallium (Ga) and gadolinium (Gd) represented by the following Chemical Formula 1; a method for producing a LLZO solid electrolyte comprising: Provides.

[Formula 1]

Li _x Ga _p La _y Gd _q Zr _z O ₁₂ (5≤x≤9, 0<p≤4, 0<q≤4, 2≤y≤4, 1≤z≤3)

The LLZO solid electrolyte may be represented by Formula 2 below.

[Formula 2]

Li _(7-3p) Ga _p La _{3 - q} Gd _q Zr ₂ O ₁₂ (0<p≤1, 0<q≤1)

The step (a) includes (a-1) preparing an aqueous metal precursor solution including a lanthanum (La) precursor, a zirconium (Zr) precursor, a gallium (Ga) precursor, and a gadolinium (Gd) precursor; (a-2) preparing a complexing agent aqueous solution containing a complexing agent; (a-3) preparing a pH adjusting agent aqueous solution containing a pH adjusting agent; And (a-4) a reactant aqueous solution comprising the metal precursor aqueous solution, the complexing agent aqueous solution, and the pH adjusting agent aqueous solution, while the pH of the reactant aqueous solution is adjusted to 8 to 12 with the pH adjuster, followed by co-precipitation reaction and drying. Preparing a precursor; may include.

The step (c) of (c-1) heat-treating the mixture at 800 to 1,000° C. to calcinate; And (c-2) heat-treating the calcined mixture at 1,100 to 1,300°C to sinter to prepare gallium and gadolinium-doped LLZO solid electrolytes.

Before the step (c-1), it may further include a step (c'-1) of raising the temperature to the calcination temperature at a rate of 0.5 to 10°C/min.

Between steps (c-1) and (c-2), a step (c'-2) of raising the temperature from the calcination temperature to the sintering temperature at a rate of 2 to 4°C/min may be further included.

The aqueous solution of the reactant may be adjusted to a pH of 8 to 12 for co-precipitation reaction.

The lithium source may be used in an excess of 5 to 15 wt% so that the lithium content of the lithium source is 105 to 115 parts by weight based on 100 parts by weight of lithium in the LLZO solid electrolyte to be prepared.

The lanthanum precursor is lanthanum nitrate hydrate, the zirconium precursor is zirconium hydrochloride hydrate, the gallium precursor is gallium nitrate hydrate, the gadolinium precursor is gadolinium nitrate hydrate, the complexing agent is ammonium hydroxide (NH ₄ · OH), the The pH adjusting agent may be sodium hydroxide (NaOH), and the lithium source may be lithium hydroxide hydrate.

The LLZO solid electrolyte may include 0.05 to 0.5 moles of gallium (Ga) and 0.01 to 0.2 moles of gadolinium (Gd) based on 2 moles of zirconium (Zr).

By doping gallium and gadolinium to the LLZO solid electrolyte using the gallium-gadolinium-doped solid electrolyte for an all-solid lithium secondary battery of the present invention and a method for manufacturing the same, there is an excellent effect of ion conductivity and potential window characteristics.

1 is a flowchart showing a method of manufacturing a solid electrolyte doped with gallium and gadolinium according to the present invention.
2 is a schematic diagram of a batch type reactor used to prepare the solid electrolyte of the present invention.
3 is an impedance profile of sintered pellets manufactured according to Examples 1 to 3;
4 is an XRD analysis graph for powders of solid electrolytes according to Examples 1 to 3.
5 is an XRD analysis graph of the pellets of solid electrolytes according to Examples 1 to 3.
6 is a graph showing the Miller index of the powder of the solid electrolyte according to Example 2.
7 is a graph showing the Miller index for the pellets of the solid electrolyte according to Example 2.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention.

However, the following description is not intended to limit the present invention to a specific embodiment, and in describing the present invention, when it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted. .

The terms used herein are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, elements, or combinations thereof described in the specification, but one or more other features or It is to be understood that the possibility of the presence or addition of numbers, steps, actions, elements, or combinations thereof is not preliminarily excluded.

Hereinafter, a method for preparing a solid electrolyte doped with gallium and gadolinium of the present invention will be described in detail.

The LLZO solid electrolyte of the present invention has a garnet structure, and may include lithium lanthanum zirconium oxide (LLZO) doped with gallium (Ga) and gadolinium (Gd).

The LLZO solid electrolyte may be represented by Formula 1 below.

[Formula 1]

Li _x Ga _p La _y Gd _q Zr _z O ₁₂ (5≤x≤9, 0<p≤4, 0<q≤4, 2≤y≤4, 1≤z≤3)

The LLZO solid electrolyte may be represented by Formula 2 below.

[Formula 2]

Li _(7-3p) Ga _p La _{3 - q} Gd _q Zr ₂ O ₁₂ (0<p≤1, 0<q≤1)

The LLZO solid electrolyte may include 0.05 to 0.5 moles of gallium (Ga) and 0.01 to 0.2 moles of gadolinium (Gd) based on 2 moles of zirconium (Zr).

The gallium and gadolinium-doped lithium lanthanum zirconium oxide solid electrolyte may have an ionic conductivity of 6.0 x 10 ^-4 to 2.0 x 10 ^-3 S/cm, preferably 0.5 x 10 ^-3 to 1.5 x 10 ^-3 S May be /cm.

The gallium and gadolinium-doped lithium lanthanum zirconium oxide solid electrolyte may have a single-phase cubic structure.

In addition, the present invention includes a positive electrode including a first lithium lanthanum zirconium oxide (first LLZO), a first conductive polymer, a positive electrode active material, and a conductive material; A negative electrode containing lithium metal; And a composite solid electrolyte layer comprising a second lithium lanthanum zirconium oxide (second LLZO) and a second conductive polymer between the positive electrode and the negative electrode, wherein the first LLZO and the second LLZO are each independently gallium and It is a gadolinium-doped lithium lanthanum zirconium oxide solid electrolyte, and the gallium and gadolinium-doped lithium lanthanum zirconium oxide solid electrolyte is represented by the following Formula 1, it provides an all-solid lithium secondary battery.

[Formula 1]

Li _x Ga _p La _y Gd _q Zr _z O ₁₂ (5≤x≤9, 0<p≤4, 0<q≤4, 2≤y≤4, 1≤z≤3)

1 is a flowchart showing a method of manufacturing a solid electrolyte doped with gallium and gadolinium according to the present invention. Hereinafter, a method of manufacturing a solid electrolyte doped with gallium and gadolinium of the present invention will be described in detail with reference to FIG. 1.

First, a lanthanum (La) precursor, zirconium ( Zr ) Precursor, gallium (Ga) precursor, gadolinium (Gd) precursor, Complexing agent And a reactant aqueous solution containing a pH adjusting agent Co-precipitation reaction Dry to prepare a solid electrolyte precursor (step a).

The step (a) includes (a-1) preparing an aqueous metal precursor solution including a lanthanum (La) precursor, a zirconium (Zr) precursor, a gallium (Ga) precursor, and a gadolinium (Gd) precursor; (a-2) preparing a complexing agent aqueous solution containing a complexing agent; (a-3) preparing a pH adjusting agent aqueous solution containing a pH adjusting agent; And (a-4) a reactant aqueous solution comprising the metal precursor aqueous solution, the complexing agent aqueous solution, and the pH adjusting agent aqueous solution, while the pH of the reactant aqueous solution is adjusted to 8 to 12 with the pH adjusting agent, followed by coprecipitation reaction and drying Preparing a precursor; may include.

The metal aqueous solution is lanthanum nitrate hydrate (La(NO ₃ ) ₃ ·xH ₂ O), zirconium hydrochloride (ZrO(Cl) ₂ ·xH ₂ O), gallium nitrate hydrate (Ga(NO ₃ ) ₃ ·xH ₂ O) and Including gadolinium nitrate hydrate (Gd(NO ₃ ) ₃ ·xH ₂ O), and each of x may be independently an integer of 1 to 9.

In addition, the complexing agent may be ammonium hydroxide (NH ₄ ·OH), sodium hydroxide, or the like.

In addition, the pH adjusting agent may include sodium hydroxide (NaOH), ammonia, and the like, but is not limited thereto. Any other pH adjuster that can adjust the pH of the mixed solution without affecting the physical properties of the ion conductive solid oxide is possible.

The aqueous solution of the reactant may be adjusted to a pH of 8 to 12 for co-precipitation reaction.

Next, above Solid electrolyte Precursor to lithium ( Li ) Mix with sauce to prepare a mixture (step b).

In addition, the lithium source may be lithium hydroxide hydrate (LiOH·H ₂ O), lithium hydroxide (LiOH), lithium nitrate (LiNO ₃ ), or the like.

The lithium source is 5 to 115 parts by weight based on 100 parts by weight of lithium in the LLZO solid electrolyte prepared by considering the amount of lithium evaporated during calcination or sintering. 15 wt% excess can be used.

Structurally, a cubic structure is advantageous in terms of ionic conductivity, and a tetragonal structure may lower ionic conductivity.

In some cases, the precursor may be pulverized before mixing the precursor and the lithium source.

The pulverization and mixing may be performed by a ball mill process.

Finally, the mixture is heat-treated to obtain gallium (Ga) and gadolinium ( Gd )this Doped Lithium lanthanum zirconium oxide ( LLZO ) Solid electrolyte Prepared (step c).

[Formula 1]

Li _x Ga _p La _y Gd _q Zr _z O ₁₂ (5≤x≤9, 0<p≤4, 0<q≤4, 2≤y≤4, 1≤z≤3)

The LLZO solid electrolyte may be represented by Formula 2 below.

[Formula 2]

Li _(7-3p) Ga _p La _{3 - q} Gd _q Zr ₂ O ₁₂ (0<p≤1, 0<q≤1)

The step (c) of (c-1) heat-treating the mixture at 800 to 1,000° C. to calcinate; And (c-2) heat-treating the calcined mixture at 1,100 to 1,300°C to sinter to prepare gallium and gadolinium-doped LLZO solid electrolytes.

Before the step (c-1), it may further include a step (c'-1) of raising the temperature to the calcination temperature at a rate of 0.5 to 10°C/min.

Between steps (c-1) and (c-2), a step (c'-2) of raising the temperature from the calcination temperature to the sintering temperature at a rate of 2 to 4°C/min may be further included.

The LLZO solid electrolyte may include 0.05 to 0.5 moles of gallium (Ga) and 0.01 to 0.2 moles of gadolinium (Gd) based on 2 moles of zirconium (Zr).

[Example]

Hereinafter, a preferred embodiment of the present invention will be described. However, this is for illustrative purposes, and the scope of the present invention is not limited thereby.

Example 1: Gallium ( 0.2mole ) And gadolinium ( 0.05mole ) Doped Solid electrolyte Pellet Sintered body manufacturing

Starting materials lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O), zirconium hydrochloride (ZrO(Cl) ₂ ·8H ₂ O), gallium nitrate (Ga(NO ₃ ) ₃ ·9H ₂ O) and gadolinium nitrate ( Gd(NO ₃ ) ₃ ·6H ₂ O) is dissolved in distilled water so that the molar ratio of La:Zr:Ga:Gd, which is their metal element, is 2.95:2:0.2:0.05, and the starting material is 1 molar concentration. Was prepared.

Referring to FIG. 2, gallium (0.2 mole) and gadolinium (0.05 mole) doped LLZO solid electrolytes were prepared using a batch type reactor. The starting material solution, 0.6 mol of ammonia water, and an appropriate amount of sodium hydroxide aqueous solution were added as a complexing agent to obtain a mixed solution whose pH was adjusted to 11, and the reaction temperature was 25° C., the reaction time was 4 hours, and Ga _{0 . 2} La _{2 . 95} Gd _{0 . 05} Zr ₂ O ₂ (OH) _a A precursor slurry in the form of _a liquid slurry was obtained. Here, a is any one of 1 to 15 real numbers, and it was found that a was 13.6 as a result of calculating a in this example.

After washing the precursor slurry with purified water, it was dried at 110° C. for 24 hours. After pulverizing the dried precursor with a ball mill, excess LiOH·H ₂ O was added and mixed with a ball mill to prepare a mixture. The LiOH·H ₂ O content of the mixture was added in an excess of 10 wt% so that the content of Li in LiOH·H ₂ O was 110 parts by weight based on 100 parts by weight of Li in the solid electrolyte. The mixture was calcined at 900° C. for 2 hours (heating rate 5° C./min) and then pulverized to Li ₆ doped with gallium (0.2 mole) and gadolinium (0.05 mole) _{. 4} Ga _{0 . 2} La _{2 . 95} Ga _{0 . 05} Zr ₂ O ₁₂ solid electrolyte was prepared.

Subsequently, the calcined powder was prepared with a molding mold and then sintered at 1,200°C for 5 hours (heating rate 3°C/min) to prepare a pellet sintered body.

Example 2: Gallium ( 0.2mole ) And gadolinium ( 0.05mole ) Doped Solid electrolyte Pellet Sintered body manufacturing

In the calcination step, gallium (0.2 mole) and gadolinium (0.05 mole) were doped in the same manner as in Example 1, except that the heating rate was performed at 3°C/min instead of performing the temperature increase rate at 5°C/min. Li _{6 . 4} Ga _{0 . 2} La _{2 . 95} Ga _{0 . 05} A pellet sintered body of Zr ₂ O ₁₂ solid electrolyte was prepared.

Example 3: Gallium ( 0.2mole ) And gadolinium ( 0.05mole ) Doped Solid electrolyte Pellet Sintered body manufacturing

In the calcination step, gallium (0.2 mole) and gadolinium (0.05 mole) were doped in the same manner as in Example 1, except that the heating rate was performed at 1 °C/min instead of performing the heating rate at 5 °C/min. Li _{6 . 4} Ga _{0 . 2} La _{2 . 95} Ga _{0 . 05 A} sintered pellet of Zr ₂ O ₁₂ solid electrolyte was prepared.

Comparative Example 1: Preparation of sintered pellets of solid electrolyte doped with aluminum (0.25 mole)

Starting materials, lanthanum nitrate (La(NO ₃ ) ₃ ·6H ₂ O), zirconium hydrochloride (ZrOCl ₂ ·8H ₂ O) and aluminum nitrate (Al(NO ₃ ) ₃ ·9H ₂ O), are used as their metal element La: By dissolving in distilled water so that the molar ratio of Zr:Al was 3:2:0.25, a starting material solution having a starting material concentration of 1 was prepared.

A solid electrolyte was prepared using a Quet Taylor vortex reactor. The starting material solution, 0.6 mol of aqueous ammonia, and an appropriate amount of sodium hydroxide aqueous solution are added through the injection part of the Kuet Taylor vortex reactor to obtain a mixed solution whose pH is adjusted to 11, and the reaction temperature is 25°C and the reaction time is 4 hours. , The agitation speed of the stirring rod was co-precipitated at 1000 rpm, and the precursor slurry in the form of a liquid slurry was discharged to the discharge unit.

After washing the precursor slurry with purified water, it was dried for 24 hours. After pulverizing the dried precursor with a ball mill, the molar ratio (Li:Al) of Al of Li of the lithium source LiOH·H ₂ O and the aluminum nitrate (Al(NO ₃ ) ₃ ·9H ₂ O) is 6.25:0.25 LiOH·H ₂ O was added so as to be, and mixed with a ball mill to prepare a mixture. The LiOH·H ₂ O content of the mixture was added to 110 parts by weight (10 wt% excess) based on 100 parts by weight of Li in the solid electrolyte in which the Li content in LiOH·H ₂ O is generated. The mixture was calcined at 900° C. for 2 hours and then pulverized to obtain a 0.25 mole doped Li _{6 of} aluminum (Al) _{. 25} Al _{0 . 25} La ₃ Zr ₂ O _{12 A} solid electrolyte was prepared.

Subsequently, the calcined powder was made into a pellet with a molding mold and then sintered at 1200° C. for 5 hours to prepare a pellet sintered body.

[Test Example]

Test Example 1: Measurement of ion conductivity

3 is an impedance profile of sintered pellets manufactured according to Examples 1 to 3; In addition, the sintered pellets prepared according to Examples 1 to 3 and Comparative Example 1 were calculated as ionic conductivity using the resistance value by the EIS (Electrochemical Impedance Spectroscopy) method, and the results are shown in Table 1 below.

Calcination conditions Sintering condition Ion Conductivity (S/cm) at R.T Example 1 900℃, 2h, 5℃/min 1200℃, 5h,
3℃/min 7.77 x 10 ^-4 Example 2 900℃, 2h, 3℃/min 1.04 x 10 ^-3 Example 3 900℃, 2h, 1℃/min 8.22 x 10 ^-4 Comparative Example 1 900℃, 2h, 1℃/min 1200℃, 5h,
1℃/min 3.03 x 10 ^-4

3 and Table 1, compared with the ionic conductivity of the solid electrolyte doped with aluminum (Al) (Comparative Example 1) of 3.03 x 10 ^-4 S/cm, gallium and gadolinium according to Examples 1 to 3 were doped. It was found that the ionic conductivity of the solid electrolyte showed more excellent properties. In particular, it was confirmed that it had the most excellent ion conductivity (1.04 x 10 ^-3 S/cm @RT) when the heating rate was 3°C/min (Example 2).

Test Example 2: Crystal structure characteristic (XRD) analysis

4 and 5 are XRD analysis graphs of powders and pellets of solid electrolytes according to Examples 1 to 3. 6 and 7 are graphs showing Miller indexes for powders and pellets of the solid electrolyte according to Example 2.

In Tables 2 and 3, the results of XRD analysis of powders and pellets of solid electrolytes according to Examples 1 to 3 using Equations 1 and 2 are described.

[Equation 1]

Sherrer's equation: Crystallite size(Dp) = Kλ/(B cosθ)

K-Scherrer constant (K=0.94 for spherical crystallites with cubic symmetry)

λ-X-ray wavelength (Cu Kα average = 1.542512Å)

B-FWHM (Full Width at Half Maximum) of XRD peak

θ-XRD peak position, one half of 2θ

[Equation 2]

Lattice parameter = d*sqrt(h ² +k ² +l ² ) for cubic symmetry

d: d-spacing (Å)

powder structure a[Å] b[Å] c[Å] Crystallite size[Å] Example 1 cubic 13.00622 13.009622 13.009622 701.6 Example 2 cubic 12.987177 12.987177 12.987177 939.5 Example 3 cubic 12.97567 12.97567 12.97567 551.6

Pellet a[Å] b[Å] c[Å] Crystallite size[Å] Example 1 12.957255 12.957255 12.957255 675.6 Example 2 12.980287 12.980287 12.980287 607.8 Example 3 12.960678 12.960678 12.960678 588.3

According to FIGS. 4 to 7 and Tables 2 and 3, looking at the XRD peak of the solid electrolyte according to Example 2 (calcination conditions of 900°C, 2h, 3°C/min), the peak of 420 Miller index at 2 degree (31°) The highest strength was observed, and the lattice constant of Example 2 was maintained larger than that of Examples 1 and 3 in both the powder and the pellet. In other words, it was confirmed that the lattice constant and crystallite size are highly dependent on the heating rate. Here, when the powder is sintered, the lattice constant shrinks. When sintering under the conditions of 900°C and 3°C/min, the shrinkage rate is the lowest, indicating a stable crystal structure.

The scope of the present invention is indicated by the claims to be described later rather than the detailed description, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention. do.

Claims (18)

Garnet structure, gallium (Ga) and gadolinium (Gd) doped lithium lanthanum zirconium oxide (LLZO) containing LLZO solid electrolyte,
The LLZO solid electrolyte is represented by the following formula (2),
The LLZO solid electrolyte has an ionic conductivity of 0.5 x 10 ^-3 to 1.5 x 10 ^-3 S/cm,
LLZO solid electrolyte for all solid lithium secondary batteries:
[Formula 2]
Li _(7-3p) Ga _p La _3-q Gd _q Zr ₂ O ₁₂ (0<p≤1, 0<q≤1) delete delete The method of claim 1,
LLZO solid electrolyte, characterized in that the LLZO solid electrolyte comprises 0.05 to 0.5 moles of gallium (Ga) and 0.01 to 0.2 moles of gadolinium (Gd) based on 2 moles of zirconium (Zr). delete delete The method of claim 1,
The LLZO solid electrolyte, characterized in that the LLZO solid electrolyte has a single-phase cubic structure. A positive electrode including a first lithium lanthanum zirconium oxide (first LLZO), a first conductive polymer, a positive electrode active material, and a conductive material;
A negative electrode containing lithium metal; And
Between the positive electrode and the negative electrode, a second lithium lanthanum zirconium oxide (second LLZO) and a composite solid electrolyte layer comprising a second conductive polymer; Including,
The first LLZO and the second LLZO are each independently gallium and gadolinium-doped lithium lanthanum zirconium oxide solid electrolyte,
The gallium and gadolinium-doped lithium lanthanum zirconium oxide solid electrolyte is represented by the following formula (2),
An all-solid lithium secondary battery having an ionic conductivity of 0.5 x 10 ^-3 to 1.5 x 10 ^-3 S/cm of the first LLZO and the second LLZO:
[Formula 2]
Li _(7-3p) Ga _p La _3-q Gd _q Zr ₂ O ₁₂ (0<p≤1, 0<q≤1) (a) preparing a solid electrolyte precursor by coprecipitation and drying a reactant aqueous solution including a lanthanum (La) precursor, a zirconium (Zr) precursor, a gallium (Ga) precursor, a gadolinium (Gd) precursor, a complexing agent and a pH adjuster ;
(b) preparing a mixture by mixing the solid electrolyte precursor with a lithium (Li) source; And
(c) heat-treating the mixture to prepare a lithium lanthanum zirconium oxide (LLZO) solid electrolyte doped with gallium (Ga) and gadolinium (Gd) represented by the following Formula 2; Including,
The ionic conductivity of the lithium lanthanum zirconium oxide (LLZO) solid electrolyte doped with gallium (Ga) and gadolinium (Gd) is 0.5 x 10 ^-3 to 1.5 x 10 ^-3 S/cm,
Manufacturing method of LLZO solid electrolyte for all-solid lithium secondary battery:
[Formula 2]
Li _(7-3p) Ga _p La _3-q Gd _q Zr ₂ O ₁₂ (0<p≤1, 0<q≤1) delete The method of claim 9,
The step (a) is
(a-1) preparing an aqueous metal precursor solution including a lanthanum (La) precursor, a zirconium (Zr) precursor, a gallium (Ga) precursor, and a gadolinium (Gd) precursor;
(a-2) preparing a complexing agent aqueous solution containing a complexing agent;
(a-3) preparing a pH adjusting agent aqueous solution containing a pH adjusting agent; And
(a-4) A solid electrolyte precursor by co-precipitation reaction with a reactant aqueous solution including the metal precursor aqueous solution, the complexing agent aqueous solution, and the pH adjuster aqueous solution while adjusting the pH of the reactant aqueous solution to 8 to 12 with the pH adjuster and drying A method for producing an LLZO solid electrolyte comprising a; The method of claim 9,
Step (c)
(c-1) calcining the mixture by heat treatment at 800 to 1,000°C; And
(c-2) sintering the calcined mixture by heat treatment at 1,100 to 1,300°C to prepare a gallium- and gadolinium-doped LLZO solid electrolyte; a method for producing an LLZO solid electrolyte, comprising: The method of claim 12,
Before the step (c-1),
The method of producing an LLZO solid electrolyte further comprising the step (c'-1) of raising the temperature to the calcination temperature at a rate of 0.5 to 10°C/min. The method of claim 12,
Between steps (c-1) and (c-2),
The method of manufacturing an LLZO solid electrolyte further comprising a step (c'-2) of raising the temperature from the calcination temperature to the sintering temperature at a rate of 2 to 4°C/min. The method of claim 9,
A method for producing an LLZO solid electrolyte, characterized in that the reactant aqueous solution is subjected to a coprecipitation reaction with a pH of 8 to 12. The method of claim 9,
The method of manufacturing an LLZO solid electrolyte, characterized in that the lithium source is used in an excess of 5 to 15 wt% so that the lithium content of the lithium source is 105 to 115 parts by weight based on 100 parts by weight of lithium in the LLZO solid electrolyte. The method of claim 9,
The lanthanum precursor is lanthanum nitrate hydrate, the zirconium precursor is zirconium hydrochloride hydrate, the gallium precursor is gallium nitrate hydrate, and the gadolinium precursor is gadolinium nitrate hydrate,
The complexing agent is ammonium hydroxide (NH ₄ ·OH),
The pH adjusting agent is sodium hydroxide (NaOH),
The method of manufacturing an LLZO solid electrolyte, wherein the lithium source is lithium hydroxide hydrate. The method of claim 9,
The method of manufacturing an LLZO solid electrolyte, wherein the LLZO solid electrolyte comprises 0.05 to 0.5 moles of gallium (Ga) and 0.01 to 0.2 moles of gadolinium (Gd) based on 2 moles of zirconium (Zr).

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