JP2022115833A - Solid electrolyte film made of lithium-containing garnet crystal and its manufacturing method, as well as lithium ion secondary battery with the solid electrolyte film - Google Patents

Abstract

To provide a solid electrolyte film that is made of a lithium-containing garnet crystal, dense and robust due to an improvement of relative density and capable of realizing high ionic conductivity by decreasing a resistant component in a particle interface.SOLUTION: A solid electrolyte film made of a lithium-containing garnet crystal characterized by having a composition of LiaM1bM2cOd (5.0≤a≤8.0, 2.5≤b≤3.5, 1.0≤c≤2.5, 10≤d≤14, M1 is an element of one or more kinds selected from Al, Ga, La, Y, Pr, Mg, Ca, Sr, or Ba, and M2 is one or more elements selected from Zr, Hf, Ta, or Nb) that shows a garnet type structure and configured of particles having an average particle size of 30 to 250 μm.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a solid electrolyte membrane made of lithium-containing garnet crystals, a method for producing the same, and a lithium ion secondary battery having the solid electrolyte membrane.

Lithium-ion secondary batteries have a higher energy density than other secondary batteries such as nickel-cadmium batteries and nickel-metal hydride batteries, and can be operated at high potentials. Demand is increasing as secondary batteries for hybrid and electric vehicles.

In recent years, in consideration of safety, research and development of all-solid-state lithium-ion batteries using a solid electrolyte membrane as an electrolyte instead of an electrolytic solution have been actively carried out. Oxides having a garnet-type structure have high lithium-ion conductivity among oxide-based lithium-ion conductors, and are therefore expected as solid electrolytes for next-generation storage batteries such as all-solid-state batteries.

The garnet-type lithium ion conductive oxide has a tetragonal low-temperature phase with poor ion conductivity and a cubic high-temperature phase with high ion conductivity. In order to obtain this cubic garnet-type lithium ion conductive oxide, when synthesizing with a general oxide raw material, synthesis is performed at a firing temperature of 1000 ° C. or higher, and then sintering at a high temperature. and densify to produce a solid electrolyte.

Patent Document 1 mentions an invention relating to a separator that exhibits excellent processability and high ionic conductivity by supporting crystalline oxide-based solid electrolyte particles having an average particle size of 5 to 100 μm in a single layer on a porous membrane. ing. Further, Patent Document 2 discloses a lithium ion battery incorporating a solid electrolyte with enhanced ion conductivity, and Patent Document 3 discloses a lithium ion conductive membrane capable of stably conducting at low temperatures.

In addition, Non-Patent Document 1 reports that a thin-layer electrolyte membrane of a garnet-type oxide was produced using a general tape casting method.

JP 2017-183111 A JP 2017-183115 A JP 2018-6297 A

R.A. Jonson and P.J. McGinn, Solid State Ionics, 323 (2018) 49-55.

In a lithium ion secondary battery, the solid electrolyte serves as a separator separating the positive electrode and the negative electrode. Therefore, the solid electrolyte is required to be dense and robust from the viewpoint of short circuit prevention. Also, in order to reduce the resistance of the solid electrolyte, it is desirable to make it thin. Furthermore, although it is desirable to be made of a material with high ionic conductivity, it is generally desired to reduce the resistance component at the solid electrolyte particle interface in order to lower the ionic conductivity. Therefore, it is desirable that the solid electrolyte particles are thin and few in the cross-sectional direction of the electrolyte.

In the techniques disclosed in Patent Documents 1 to 3, since single particles are supported in the cross-sectional direction of the solid electrolyte membrane, the problem of reducing the resistance component of the solid electrolyte particle interface as described above is solved. However, in the techniques disclosed in Patent Documents 1 to 3, since the oxide-based solid electrolyte particles are supported on a polyolefin microporous membrane or nonwoven fabric having high electrical resistance, the electrolyte partially inhibits ion conduction. There was a problem of becoming

In addition, as in Non-Patent Document 1, in the technique of producing a garnet-type oxide thin-layer electrolyte membrane using a general tape casting method, garnet-type lithium ion conductive oxides are difficult to sinter. However, when fabricating a thin-layer electrolyte membrane using a general tape casting method, it has been difficult to obtain a dense and robust thin-layer electrolyte membrane. There have been problems that prevent achieving ionic conductivity.

The present invention has been made in view of such circumstances, and a lithium-containing garnet crystal that is dense and robust with an improved relative density and can reduce the resistance component at the particle interface to achieve high ionic conductivity. An object of the present invention is to provide a solid electrolyte membrane composed of a solid, a method for producing the same, and a lithium ion secondary battery having the solid electrolyte membrane.

In order to solve the above problems, the present inventors investigated a densification process of a garnet-type lithium ion conductive oxide. is generated, and the decomposition product covers the particle surface. Then, by synthesizing a fine-particle electrolyte powder and fabricating a solid electrolyte membrane using the tape casting method, grain growth of the solid electrolyte powder and an improvement in the sintering density of the solid electrolyte membrane were observed. After confirming this, the present invention was completed.

That is, according to the present invention, the following inventions are provided.
[1] Li _a M ¹ _b M ² _c O _d (5.0≦a≦8.0, 2.5≦b≦3.5, 1.0≦c≦2.5, 10 ≤ d ≤ 14, M1 is ^one or more elements selected from Al, Ga, La, Y, Pr, Mg, Ca, Sr or Ba, ^M2 is one or more elements selected from Zr, Hf, Ta or Nb A solid electrolyte membrane composed of lithium-containing garnet crystals, characterized in that it is composed of particles having a particle diameter of 30 to 250 μm.
[2] _{The lithium} -containing _{material according} to claim 1, _wherein the composition is _{Li6.00Ga0.150Al0.100La3.00Zr1.75Ta0.250O12.0 .} A solid electrolyte membrane made of garnet crystals.
[3] Li _a M ¹ _b M ² _c O _d (5.0≦a≦8.0, 2.5≦b≦3.5, 1.0≦c≦2.5, 10 ≤ d ≤ 14, M1 is ^one or more elements selected from Al, Ga, La, Y, Pr, Mg, Ca, Sr or Ba, ^M2 is one or more elements selected from Zr, Hf, Ta or Nb A first step of synthesizing a solid electrolyte having a composition of (element of) and then pulverizing it to produce a solid powder,
a second step of dissolving the obtained particulate electrolyte powder in a solvent to form a slurry;
A third step of coating the slurry on a substrate to produce a green sheet, and
A fourth step of sandwiching the obtained green sheet between a pair of firing substrates and firing to produce a solid electrolyte membrane composed of particles having a particle diameter of 30 to 250 μm,
The first step includes a step of synthesizing a precursor oxide containing a metal raw material excluding a Li raw material, and a step of adding a Li raw material to the precursor oxide and sintering it to synthesize the solid electrolyte. Lithium A method for producing a solid electrolyte membrane comprising garnet crystals contained therein.
[4] _{The lithium} -containing _{material according} to claim ₃ , wherein the composition is _{Li6.00Ga0.150Al0.100La3.00Zr1.75Ta0.250O12.0 .} A method for producing a solid electrolyte membrane composed of garnet crystals.
[5] A lithium ion secondary battery comprising the solid electrolyte membrane according to claim 1 or 2 as a separator, and a positive electrode and a negative electrode provided on both sides of the separator.

According to the present invention, since the above configuration is adopted, the relative density calculated from the mass of the solid electrolyte membrane and the measured volume is improved to 90% or more with respect to the theoretical density of 5.30 g cm ⁻¹ . A solid electrolyte membrane made of lithium-containing garnet crystals that is robust and capable of reducing the resistance component at the particle interface and realizing high ionic conductivity, a method for producing the same, and a lithium ion secondary comprising the solid electrolyte membrane Batteries can be provided.

4 is an SEM image of the solid electrolyte powder described in Example 1. FIG. 4 is a SEM image of a cross section of the solid electrolyte membrane described in Example 1. FIG. 4 shows a cross-sectional SEM image of the solid electrolyte membrane described in Example 1 and the results of elemental mapping analysis. 4 is an SEM image of the solid electrolyte powder described in Comparative Example 1. FIG. 4 is a SEM image of a cross section of a solid electrolyte membrane produced in Comparative Example 1. FIG. 4 shows a cross-sectional SEM image of the solid electrolyte membrane described in Example 1 and the results of elemental mapping analysis. FIG. 2 is a diagram showing impedance measurement results of a solid electrolyte membrane produced in Example 1 in comparison with impedance measurement results of a solid electrolyte membrane produced in Comparative Example 1; 4 is a SEM image of a cross section of the solid electrolyte described in Example 2. FIG. 4 is a SEM image of a cross section of the solid electrolyte described in Comparative Example 2. FIG. FIG. 10 is a diagram showing impedance measurement results of a solid electrolyte membrane produced in Example 2 in comparison with impedance measurement results of a solid electrolyte membrane produced in Comparative Example 2; 4 is a SEM image of a cross section of the solid electrolyte described in Example 3. FIG. 4 is a SEM image of a cross section of the solid electrolyte described in Comparative Example 3. FIG. FIG. 11 is a diagram showing impedance measurement results of a solid electrolyte membrane produced in Example 3 in comparison with impedance measurement results of a solid electrolyte membrane produced in Comparative Example 3; 4 is a SEM image of a cross section of the solid electrolyte described in Example 4. FIG. 4 is a SEM image of a cross section of the solid electrolyte described in Comparative Example 4. FIG. FIG. 10 is a diagram showing impedance measurement results of a solid electrolyte membrane produced in Example 4 in comparison with impedance measurement results of a solid electrolyte membrane produced in Comparative Example 4;

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on embodiments.
The solid electrolyte membrane comprising the lithium-containing garnet crystals of the present invention has a garnet-type structure of Li _a M ¹ _b M ² _c O _d (5.0≦a≦8.0, 2.5≦b≦3.5). , 1.0≤c≤2.5, 10≤d≤14, M1 is ^one or more elements selected from Al, Ga, La, Y, Pr, Mg, Ca, Sr or Ba, ^M2 is Zr , Hf, Ta or Nb), and is composed of particles having a particle diameter of 30 to 250 μm. The particle size of the solid electrolyte membrane is more preferably 40 to 150 μm, still more preferably 50 to 100 μm, in order to achieve the intended purpose.

In the solid electrolyte membrane of the present invention, M1 is selected from ^one or more elements selected from Al, Ga, La, Y, Pr, Mg, Ca, Sr and Ba. It preferably contains La.

In addition, in the solid electrolyte membrane of the present invention, one or more elements selected from Zr, Hf, Ta and Nb are selected as ^M2 , and among these, Zr and Ta are preferably included.

The solid electrolyte membrane made of the _lithium - _{containing garnet crystals} of the present invention has the above-described _composition . Ta _0.250 O _12.0 , Li _6.00 Ga _0.150 Al _0.100 La _3.00 Zr _1.75 Nb _0.250 O _12.0 and the like.

The solid electrolyte membrane comprising the lithium-containing garnet crystals of the present invention is characterized by being composed of single particles in the cross-sectional direction. As a result, the relative density calculated from the mass of the solid electrolyte membrane and the measured volume has improved to 90% or more of the theoretical density, which is dense and robust, and the resistance component at the particle interface is reduced to achieve high ionic conductivity. can be realized.

The solid electrolyte membrane comprising the lithium-containing garnet crystals of the present invention can be suitably used as a separator for lithium ion secondary batteries. In this case, the lithium ion secondary battery has a general configuration in which a positive electrode and a negative electrode are provided on both sides of the separator made of the solid electrolyte film. Of course, other various members conventionally used in lithium secondary batteries can be used as needed.

Next, the method for manufacturing the solid electrolyte membrane of the present invention will be described.
The solid electrolyte comprising a lithium-containing garnet crystal of the present invention has a garnet-type structure of Li _a M ¹ _b M ² _c O _d (5.0≦a≦8.0, 2.5≦b≦3.5, 1.0≤c≤2.5, 10≤d≤14, M1 is ^one or more elements selected from Al, Ga, La, Y, Pr, Mg, Ca, Sr or Ba, ^M2 is Zr, (one or more elements selected from Hf, Ta, and Nb) is synthesized, pulverized to prepare a solid electrolyte powder, and the obtained fine particle electrolyte powder is dissolved in a solvent to form a slurry. It can be produced by coating a slurry on a carrier substrate to produce a green sheet, sandwiching the obtained green sheet between a pair of firing substrates, and firing.

(Synthesis of particulate electrolyte powder (first step))
When producing the solid electrolyte membrane of the present invention, first, each metal raw material is weighed so as to obtain a desired molar ratio.

Here, each metal raw material used in the present invention will be described.

The lithium raw material is not particularly limited as long as it contains lithium, and examples thereof include Li ₂ O and Li ₂ CO ₃ .

The aluminum raw material is not particularly limited as long as it contains aluminum, and examples thereof include Al(NO ₃ ) _{3.9H 2} O and Al ₂ O ₃ .

The gallium source is not particularly limited as long as it contains gallium, and examples thereof include Ga(NO ₃ ) _{3.nH 2} O, Ga ₂ O, GaCl ₂ and GaN.

The lanthanum raw material is not particularly limited as long as it contains lanthanum, and examples thereof include La(NO ₃ ) _{3.6H 2} O, La ₂ O ₃ and La ₂ (CO ₃ ) ₃ .

The yttrium raw material is not particularly limited as long as it contains yttrium, and examples thereof include Y ₂ O ₃ and YCl ₃ .

The praseodymium raw material is not particularly limited as long as it contains praseodymium, and examples thereof include PrO, Pr ₂ O ₃ and PrCl ₃ .

The magnesium raw material is not particularly limited as long as it contains magnesium, and examples thereof include MgO, MgCl ₂ and MgF ₂ .

The calcium raw material is not particularly limited as long as it contains calcium, and examples thereof include CaO, CaO ₂ , Ca(OH) ₂ and the like.

The strontium raw material is not particularly limited as long as it contains strontium, and examples thereof include SrO, SrCl ₂ and Sr(OH) ₂ .

The barium raw material is not particularly limited as long as it contains barium, and examples thereof include BaO, BaO ₂ , BaCO ₃ and the like.

The zirconium raw material is not particularly limited as long as it contains zirconium, and examples thereof include ZrOCl ₂ .8H ₂ O, ZrO ₂ , ZrC and ZrN.

The hafnium raw material is not particularly limited as long as it contains hafnium, and examples thereof include HfO ₂ and HfCl ₄ .

The tantalum raw material is not particularly limited as long as it contains tantalum, and examples thereof include TaCl ₄ and Ta ₂ O ₅ .

The niobium raw material is not particularly limited as long as it contains niobium, and examples thereof include NbO, Nb ₂ O ₅ and NbCl ₅ .

After weighing each metal raw material, the metal raw materials other than the lithium raw material are dissolved in an organic solvent such as ethanol and mixed with a stirrer. Here, a chelate complex ligand such as citric acid and a chelate polymerizing agent such as ethylene glycol may be used.

Next, these mixtures are stirred for 4 to 5 hours while gradually increasing the temperature to about 140 to 150° C. to polymerize (gelate). When the gelation has sufficiently progressed, it is calcined at a temperature of about 300 to 400° C. in a heating device such as an electric furnace to break the C—C bond chain or C—H bond chain.

Thereafter, after pulverizing the calcined powder in an agate mortar or the like, it is fired at a temperature of about 900 to 1000° C. in a heating device such as an electric furnace to synthesize an oxide as a precursor.

Next, a lithium raw material (for example, LiO ₂ ) was added to the obtained precursor so as to have a predetermined ratio, dry-mixed using an agate mortar or the like, and then an atmosphere of an inert gas such as Ar was allowed to flow. Firing is performed at 450 to 600° C. for 6 to 15 hours in a tubular electric furnace or the like to obtain the desired solid electrolyte powder.

(Preparation of slurry (second step))
First, a binder is prepared. As the binder, for example, a polyvinyl butyral-based binder, diamine, and bis(2-ethylhexyl) adipate are prepared so as to have a predetermined mass ratio with respect to the solid electrolyte powder. The material used for the binder is not limited to this.

Next, a binder is dissolved in a solvent in which toluene and butanol are mixed at a predetermined volume ratio, for example, and the solid electrolyte membrane prepared above is added and stirred and dispersed by a kneader. Thereafter, stirring is continued while reducing the pressure to, for example, about 0.2 kPa to concentrate the slurry to obtain the target slurry.

(Preparation of green sheet (third step))
The slurry obtained above is formed on a carrier film such as PET using, for example, a doctor blade method to produce a green sheet.

This green sheet is sandwiched between specific sintering base materials as shown in Examples below, and sintered, for example, in an electric furnace at 1000 to 1100° C. for 3 to 5 hours (fourth step).

As described above, a solid electrolyte membrane comprising the lithium-containing garnet crystals of the present invention is obtained.

EXAMPLES The features of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples described herein.

[Example 1]
( _{Synthesis of solid electrolyte powder Li6.00Ga0.150Al0.100La3.00Zr1.75Ta0.250O12.0 (} first step))
First, Ga raw material, Al raw material, La raw material, Zr raw material, Ta raw materials were weighed, these raw materials were dissolved in ethanol, and mixed with a stirrer.

Ga(NO ₃ ) _{3.nH 2} O (manufactured by Kojundo Chemical Co., Ltd., 99.9%, at this time n was 8.5), Al(NO ₃ ) _{3.9H 2} O (Fuji Film Wako Pure Chemical, 99.9%), La(NO ₃ ) _{3.6H 2} O (Fuji Film Wako Pure Chemical, 99.9%), ZrOCl _{2.8H 2 O} (Fuji Film Wako Pure Chemical, 99 .0%) and TaCl ₅ (manufactured by Rare Metallic, 99.9%) were used. In addition, citric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 98%) was used as a chelate complex ligand, and ethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.5%) was used as a chelate polymerization agent.

The mixture was stirred for about 4 to 5 hours while gradually raising the temperature to about 140° C. to polymerize (gelate). At the stage when gelation has sufficiently progressed, calcination was performed at 350° C. in an electric furnace to carbonize. That is, the C--C bond chain or the C--H bond chain was cut.

After that, the calcined powder was lightly pulverized in an agate mortar and fired again in an electric furnace at 1000° C. for 4 hours to obtain oxide Ga _0.150 Al _0.100 La _3.00 Zr as a precursor _{. 75} Ta _0.250 O _9.00 was synthesized.

Li ₂ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.9%) was added to this precursor at a predetermined ratio, and after dry-mixing using an agate mortar, the mixture was heated to 600 in a tubular electric furnace in which Ar was flowed. C. for 24 hours to obtain the desired solid electrolyte powder.

(Preparation of slurry (second step))
First, a polyvinyl butyral binder (BM-S, manufactured by Sekisui Chemical Co., Ltd.), diamine (manufactured by Kao Corporation), and bis(2-ethylhexyl) adipate (manufactured by Fujifilm Wako Pure Chemical Industries, first grade reagent) were prepared as described above. They were adjusted to 6 wt %, 2 wt %, and 1 wt % with respect to the solid electrolyte powder.

After that, this was dissolved in a solvent in which toluene:butanol was mixed at a volume ratio of 85:15. After confirming dissolution, the solid electrolyte powder was added and dispersed by stirring with a kneader (ARV-310LED, manufactured by Thinky) at 1000 rpm together with YSZ balls (manufactured by Nikkato). Thereafter, the YSZ balls were removed, and stirring was continued while the pressure was reduced to 0.2 kPa to concentrate the slurry and obtain the target slurry.

(Preparation of green sheet (third step))
Using the slurry obtained above, a 10 cm wide and 30 cm long piece was formed by a doctor blade method. Coating was performed on the PET film using an automatic coating machine (Model PI-1210 manufactured by Tester Sangyo Co., Ltd.) at a blade gap of 400 μm and a molding speed of 1 cm/sec.

(Firing of green sheet (fourth step))
A specific firing substrate was used for firing the green sheet. In order to prepare a sintered base material, synthesis was performed from powder. Li: La: Zr = 7: 3: 2 molar ratio lithium carbonate (manufactured by Fujifilm Wako Pure Chemical, reagent special grade), lanthanum oxide (Kanto Chemical Industry Co., Ltd., special grade reagent), zirconium oxide (Kanto Chemical Kogyo Co., Ltd., special grade reagent) was weighed. After mixing these, it was filled in an alumina crucible (manufactured by Nikkato Co., Ltd., C5 type) and fired in an electric furnace at 850° C. for 3 hours. The obtained fired product was simply pulverized, pelletized using a uniaxial pressure press, and fired in an electric furnace at 1100° C. for 3 hours to obtain a fired base material. The aforementioned green sheet was sandwiched between a pair of firing substrates and fired in an electric furnace at 1100° C. for 4 hours to obtain the desired solid electrolyte membrane. The thickness of the solid electrolyte membrane was 70 μm.

FIG. 1 shows a scanning electron microscope image (SEM image) of the solid electrolyte powder produced in Example 1. As shown in FIG. As is clear from FIG. 1, although secondary particles of several μm are observed due to agglomeration, they are solid electrolyte powders having primary particle diameters on the order of submicrons.

FIG. 2 shows a scanning electron microscope image (SEM image) of a cross section of the solid electrolyte membrane produced in Example 1. As shown in FIG. As is clear from FIG. 2, the solid electrolyte membrane is composed of single particles in the cross-sectional direction. The particle size of the particles forming the solid electrolyte membrane in the cross-sectional direction was measured by observing the SEM image. The particle diameter of the particles was 70 μm. Further, the relative density obtained from the measured values of the mass and volume of the solid electrolyte membrane of Example 1 was 91% with respect to the theoretical density (5.30 g·cm ⁻¹ ) of the solid electrolyte membrane.

FIG. 3 shows an SEM image (SEI) of the cross section of the solid electrolyte membrane prepared in Example 1 and elemental mapping analysis ((Al, Ga) and (La, Zr and Ta)) by an energy dispersive X-ray spectrometer (EDS). shows a diagram of As is clear from FIG. 3, each metal element other than Li in the solid electrolyte membrane is uniformly dispersed in the particles without segregation.

[Comparative Example 1]
( _{Synthesis of Solid Electrolyte Powder Li6.00Ga0.150Al0.100La3.00Zr1.75Ta0.250O12.0 )}
First, Li raw material, Ga raw material, Al raw material, La raw material, Zr raw material, and Ta raw material were weighed and mixed.

Ga ₂ O ₃ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.9%), Al(OH) ₃ (manufactured by Kojundo Chemical Co., Ltd., 99.9%), Li ₂ CO ₃ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as each metal raw material 99.9%), La ₂ O ₃ (manufactured by Fujifilm Wako Pure Chemical, 99.99%), ZrO ₂ (manufactured by Kojundo Chemical, 99.9%), Ta ₂ O ₅ (manufactured by Fujifilm Wako Pure Chemical 99.9%) was used.

These raw materials were placed in a container together with YSZ balls (manufactured by Nikkato) having a diameter of 5 mm and ethanol in a planetary ball mill (manufactured by Fritsch, P-7) and mixed at 500 rpm for 1 hour.

This mixture was filled in an alumina crucible (manufactured by Nikkato, C5 type) and fired in an electric furnace at 850° C. for 3 hours to obtain solid electrolyte powder Li _6.00 Ga _0.150 Al _0.100 La _3.00 Zr. _1.75 Ta _0.250 O _12.0 was synthesized.

The obtained solid electrolyte powder was placed in a container together with YSZ balls (manufactured by Nikkato) having a diameter of 5 mm and ethanol in a planetary ball mill (manufactured by Fritsch, P-7) and mixed again at 500 rpm for 1 hour.

(Preparation of slurry, preparation of green sheet, firing of green sheet)
After preparing the slurry in the same manner as in Example 1, a green sheet was prepared. Thereafter, this green sheet was sandwiched between the firing substrates used in Example 1 and fired in an electric furnace at 1100° C. for 4 hours to obtain the desired solid electrolyte membrane.

FIG. 4 shows a scanning electron microscope image (SEM image) of the solid electrolyte powder produced in Comparative Example 1. As shown in FIG. As is clear from FIG. 4, it is a solid electrolyte powder having a primary particle size of several μm.

FIG. 5 shows a scanning electron microscope image of a cross section of the solid electrolyte membrane produced in Comparative Example 1. As shown in FIG. The solid electrolyte membrane of Comparative Example 1 had a particle size of 5 μm or less. The relative density obtained from the measured values of the mass and volume of the solid electrolyte membrane of Example 1 was 73% with respect to the theoretical density (5.30 g·cm ⁻¹ ) of the solid electrolyte membrane.

FIG. 6 shows an SEM image (SEI) of the cross section of the solid electrolyte membrane prepared in Comparative Example 1 and elemental mapping analysis ((Al, Ga) and (La, Zr and Ta)) by an energy dispersive X-ray spectrometer (EDS). shows a diagram of As is clear from FIG. 6, it can be observed that Al and Ga in the solid electrolyte membrane are localized at part of the particle interface. In addition, it can be seen that Zr and Ta have different concentrations inside the particles and are non-uniformly dispersed.

The impedance of the solid electrolyte membranes of Example 1 and Comparative Example 1 was measured by an electrochemical measurement system (manufactured by Biologic, SP-300-AH-2CH). The measurement results are shown in FIG. In Example 1, in which a Li-free precursor was first prepared and then Li was added, and in Comparative Example 1, in which a raw material containing Li was used from the beginning, the solid electrolyte membrane of Example 1 was formed as a single layer in the cross-sectional direction. Since it is composed of one grain, no grain boundary resistance was observed. However, in the solid electrolyte membrane of Comparative Example 1, many grain boundaries that increase the resistance of the grain interface are observed.

[Example 2]
_{( Synthesis} of _{Solid Electrolyte Powder Li5.0Ga0.10Al0.10La3.0Zr0.60Ta1.4O12 )}
As in Example 1, Ga raw material, Al raw material, La A raw material, a Zr raw material, and a Ta raw material were weighed, dissolved in ethanol, and mixed with a stirrer.

Ga(NO ₃ ) _{3.nH 2} O (manufactured by Kojundo Chemical Co., Ltd., 99.9%, at this time n was 8.5), Al(NO ₃ ) _{3.9H 2} O (Fuji Film Wako Pure Chemical, 99.9%), La(NO ₃ ) _{3.6H 2} O (Fuji Film Wako Pure Chemical, 99.9%), ZrOCl _{2.8H 2 O} (Fuji Film Wako Pure Chemical, 99 .0%) and TaCl ₅ (manufactured by Rare Metallic, 99.9%) were used. In addition, citric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 98%) was used as a chelate complex ligand, and ethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.5%) was used as a chelate polymerization agent.

The mixture was stirred for about 4 to 5 hours while gradually raising the temperature to about 140° C. to polymerize (gelate). At the stage when gelation has sufficiently progressed, calcination was performed at 350° C. in an electric furnace to carbonize. That is, the C--C bond chain or the C--H bond chain was cut.

After that, the calcined powder was lightly pulverized in an agate mortar and fired again in an electric furnace at 1000° C. for 4 hours to obtain oxides Ga _0.10 Al _0.10 La _3.0 Zr 0.10 as a precursor _{. 6} Ta _1.4 O _9.5 was synthesized.

Li ₂ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.9%) was added to this precursor at a predetermined ratio, and after dry-mixing using an agate mortar, the mixture was heated to 600 in a tubular electric furnace in which Ar was flowed. C. for 24 hours to obtain the desired solid electrolyte powder.

(Preparation of slurry, preparation of green sheet, firing of green sheet)
After preparing the slurry in the same manner as in Example 1, a green sheet was prepared. Thereafter, this green sheet was sandwiched between the firing substrates used in Example 1 and fired in an electric furnace at 1100° C. for 4 hours to obtain the desired solid electrolyte membrane.

FIG. 8 shows a scanning electron microscope image (SEM image) of a cross section of the solid electrolyte membrane produced in Example 2. As shown in FIG. As is clear from FIG. 8, the solid electrolyte membrane is composed of single particles in the cross-sectional direction. The particle size of the particles forming the solid electrolyte membrane in the cross-sectional direction was measured by observing the SEM image. The particle diameter of the particles was 80.9 μm. Also, the relative density obtained from the actual measurements of the mass and volume of the solid electrolyte membrane of Example 2 was 93% with respect to the theoretical density (6.16 g·cm ⁻¹ ) of the solid electrolyte membrane.

[Comparative Example 2]
_{( Synthesis} of _{Solid Electrolyte Powder Li5.0Ga0.10Al0.10La3.0Zr0.60Ta1.4O12 )}
As in Comparative Example 1, first, the molar ratio of Li: Ga: Al: La: Zr: Ta = 5.0: 0.10: 0.10: 3.00: 0.60: 1.4 Li raw material, Ga raw material, Al raw material, La raw material, Zr raw material and Ta raw material were weighed and mixed.

Ga ₂ O ₃ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.9%), Al(OH) ₃ (manufactured by Kojundo Chemical Co., Ltd., 99.9%), Li ₂ CO ₃ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as each metal raw material 99.9%), La ₂ O ₃ (manufactured by Fujifilm Wako Pure Chemical, 99.99%), ZrO ₂ (manufactured by Kojundo Chemical, 99.9%), Ta ₂ O ₅ (manufactured by Fujifilm Wako Pure Chemical 99.9%) was used.

These raw materials were placed in a container together with YSZ balls (manufactured by Nikkato) having a diameter of 5 mm and ethanol in a planetary ball mill (manufactured by Fritsch, P-7) and mixed at 500 rpm for 1 hour.

This mixture was filled in an alumina crucible (manufactured by Nikkato, C5 type) and fired in an electric furnace at 850° C. for 3 hours to obtain solid electrolyte powder Li _5.0 Ga _0.10 Al _0.10 La _3.0 Zr. _0.60 Ta _1.4 O ₁₂ was synthesized.

The obtained solid electrolyte powder was placed in a container together with YSZ balls (manufactured by Nikkato) having a diameter of 5 mm and ethanol in a planetary ball mill (manufactured by Fritsch, P-7) and mixed again at 500 rpm for 1 hour.

(Preparation of slurry, preparation of green sheet, firing of green sheet)
After preparing the slurry in the same manner as in Comparative Example 1, a green sheet was prepared. Thereafter, this green sheet was sandwiched between the firing substrates used in Comparative Example 1, and fired in an electric furnace at 1100° C. for 4 hours to obtain the intended solid electrolyte membrane.

FIG. 9 shows a scanning electron microscope image of a cross section of the solid electrolyte membrane produced in Comparative Example 2. As shown in FIG. The solid electrolyte membrane of Comparative Example 2 had a particle size of 5 μm or less. The relative density obtained from the measured values of the mass and volume of the solid electrolyte membrane of Comparative Example 2 was 74% with respect to the theoretical density (6.16 g·cm ⁻¹ ) of the solid electrolyte membrane.

The impedance of the solid electrolyte membranes of Example 2 and Comparative Example 2 was measured by an electrochemical measurement system (manufactured by Biologic, SP-300-AH-2CH). The measurement results are shown in FIG. In Example 2, in which a Li-free precursor was first prepared and then Li was added, and in Comparative Example 2, in which a raw material containing Li was used from the beginning, the solid electrolyte membrane of Example 2 was formed in a single plane in the cross-sectional direction. Since it is composed of one grain, no grain boundary resistance was observed. However, in the solid electrolyte membrane of Comparative Example 2, many grain boundaries that increase the resistance of the grain interface are observed.

[Example 3]
_{( Synthesis} of solid _{electrolyte powder Li6.8La3.0Zr1.8Ta0.2O12} )
In the same manner as in Example 1, the La raw material, the Zr raw material, and the Ta raw material were weighed so that the molar ratio of La:Zr:Ta=3.0:1.8:0.2, and these raw materials were added to ethanol. Allow to dissolve and mix with a stirrer.

La(NO ₃ ) _{3.6H 2} O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.9%), ZrOCl _{2.8H 2 O} (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.0%), TaCl ₅ (manufactured by Rare Metallic, 99.9%) was used. In addition, citric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 98%) was used as a chelate complex ligand, and ethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.5%) was used as a chelate polymerization agent.

The mixture was stirred for about 4 to 5 hours while gradually raising the temperature to about 140° C. to polymerize (gelate). At the stage when gelation has sufficiently progressed, calcination was performed at 350° C. in an electric furnace to carbonize. That is, the C--C bond chain or the C--H bond chain was cut.

After that, the calcined powder was lightly pulverized in an agate mortar, and fired again in an electric furnace at 1000° C. for 4 hours to obtain oxides La _3.0 Zr _1.8 Ta _0.2 O _{8 . 6} was synthesized.

Li ₂ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.9%) was added to this precursor at a predetermined ratio, and after dry-mixing using an agate mortar, the mixture was heated to 600 in a tubular electric furnace in which Ar was flowed. C. for 24 hours to obtain the desired solid electrolyte powder.

(Preparation of slurry, preparation of green sheet, firing of green sheet)
After preparing the slurry in the same manner as in Example 1, a green sheet was prepared. Thereafter, this green sheet was sandwiched between the firing substrates used in Example 1 and fired in an electric furnace at 1100° C. for 4 hours to obtain the desired solid electrolyte membrane.

FIG. 11 shows a scanning electron microscope image (SEM image) of a cross section of the solid electrolyte membrane produced in Example 3. As shown in FIG. As is clear from FIG. 11, the solid electrolyte membrane is composed of single particles in the cross-sectional direction. The particle size of the particles forming the solid electrolyte membrane in the cross-sectional direction was measured by observing the SEM image. The particle diameter of the particles was 50.2 μm. The relative density obtained from the measured values of the mass and volume of the solid electrolyte membrane of Example 3 was 90% with respect to the theoretical density (5.23 g·cm ⁻¹ ) of the solid electrolyte membrane.

[Comparative Example 3]
_{( Synthesis} of solid _{electrolyte powder Li6.8La3.0Zr1.8Ta0.2O12} )
As in Comparative Example 1, first, Li raw material, La raw material, Zr raw material, and Ta raw material were used so that the molar ratio of Li:La:Zr:Ta=6.8:3.0:1.8:0.2 was obtained. was weighed and mixed.

Li ₂ CO ₃ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.9%), La ₂ O ₃ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.99%), ZrO ₂ (manufactured by Kojundo Chemical Co., Ltd., 99%) as each metal raw material .9%) and Ta ₂ O ₅ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.9%).

These raw materials were placed in a container together with YSZ balls (manufactured by Nikkato) having a diameter of 5 mm and ethanol in a planetary ball mill (manufactured by Fritsch, P-7) and mixed at 500 rpm for 1 hour.

This mixture was filled in an alumina crucible (manufactured by Nikkato Co., Ltd., C5 type) and fired in an electric furnace at 850 ° C. for 3 hours to obtain a solid electrolyte powder Li _6.8 La _3.0 Zr _1.8 Ta _0.2 O ₁₂ was synthesized.

The obtained solid electrolyte powder was placed in a container together with YSZ balls (manufactured by Nikkato) having a diameter of 5 mm and ethanol in a planetary ball mill (manufactured by Fritsch, P-7) and mixed again at 500 rpm for 1 hour.

(Preparation of slurry, preparation of green sheet, firing of green sheet)
After preparing the slurry in the same manner as in Example 1, a green sheet was prepared. Thereafter, this green sheet was sandwiched between the firing substrates used in Example 1 and fired in an electric furnace at 1100° C. for 4 hours to obtain the desired solid electrolyte membrane.

FIG. 12 shows a scanning electron microscope image of a cross section of the solid electrolyte membrane produced in Comparative Example 3. As shown in FIG. The solid electrolyte membrane of Comparative Example 3 had a particle size of 5 μm or less. The relative density obtained from the measured values of the mass and volume of the solid electrolyte membrane of Comparative Example 3 was 68% with respect to the theoretical density (5.23 g·cm ⁻¹ ) of the solid electrolyte membrane.

The impedance of the solid electrolyte membranes of Example 3 and Comparative Example 3 was measured by an electrochemical measurement system (manufactured by Biologic, SP-300-AH-2CH). The measurement results are shown in FIG. In Example 1, in which a Li-free precursor was first prepared and then Li was added, and in Comparative Example 3, in which a raw material containing Li was used from the beginning, the solid electrolyte membrane of Example 3 was formed in a single plane in the cross-sectional direction. Since it is composed of one grain, no grain boundary resistance was observed. However, in the solid electrolyte membrane of Comparative Example 3, many grain boundaries that increase the resistance of the grain interface are observed.

[Example 4]
_{( Synthesis of Solid Electrolyte Powder Li6.9Mg0.10Ca0.10Sr0.10Ba0.10La2.6Zr1.50Nb0.5O12 ) _}
As in Example 1, Mg:Ca:Sr:Ba:La:Zr:Nb = 0.10:0.10:0.10:0.10:2.6:1.5:0.5 moles Mg raw material, Ca raw material, Sr raw material, Ba raw material, La raw material, Zr raw material, and Nb raw material were weighed so as to have the same ratio, and these raw materials were dissolved in ethanol and mixed with a stirrer.

As each metal raw material, Mg(NO ₃ ) 2.6H ₂ O (manufactured by Fuji Film Wako Pure Chemical, 99.5%), Ca(NO ₃ ) _{2.4H 2} O ₍ manufactured by Fuji Film Wako Pure Chemical, 99.9 %), Sr(NO ₃ ) ₂ (manufactured by Fujifilm Wako Pure Chemical Industries, reagent special grade), Ba(NO ₃ ) ₂ (manufactured by Fujifilm Wako Pure Chemical Industries, 99.9%), La(NO ₃ ) ₃ 6H ₂ O (manufactured by Fuji Film Wako Pure Chemical, 99.9%), ZrOCl ₂ 8H ₂ O (manufactured by Fuji Film Wako Pure Chemical, 99.0%), NbCl ₅ (manufactured by Fuji Film Wako Pure Chemical, 95.0%) It was used. In addition, citric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 98%) was used as a chelate complex ligand, and ethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.5%) was used as a chelate polymerization agent.

The mixture was stirred for about 4 to 5 hours while gradually raising the temperature to about 140° C. to polymerize (gelate). At the stage when gelation has sufficiently progressed, calcination was performed at 350° C. in an electric furnace to carbonize. That is, the C--C bond chain or the C--H bond chain was cut.

After that, the calcined powder was lightly pulverized in an agate mortar and fired again in an electric furnace at 1000° C. for 4 hours to obtain the precursor oxide Mg _0.10 Ca _0.10 Sr _0.10 Ba 0.10 _{. 10La2.6Zr1.50Nb0.5O8.55 was synthesized . _}

Li ₂ O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.9%) was added to this precursor at a predetermined ratio, and after dry-mixing using an agate mortar, the mixture was heated to 600 in a tubular electric furnace in which Ar was flowed. C. for 24 hours to obtain the desired solid electrolyte powder.

(Preparation of slurry, preparation of green sheet, firing of green sheet)
After preparing the slurry in the same manner as in Example 1, a green sheet was prepared. Thereafter, this green sheet was sandwiched between the firing substrates used in Example 1 and fired in an electric furnace at 1100° C. for 4 hours to obtain the desired solid electrolyte membrane.

FIG. 14 shows a scanning electron microscope image (SEM image) of a cross section of the solid electrolyte membrane produced in Example 4. As shown in FIG. As is clear from FIG. 14, the solid electrolyte membrane is composed of single particles in the cross-sectional direction. The particle size of the particles forming the solid electrolyte membrane in the cross-sectional direction was measured by observing the SEM image. The particle diameter of the particles was 54.7 μm. Further, the relative density obtained from the measured values of the mass and volume of the solid electrolyte membrane of Example 4 with respect to the theoretical density (5.80 g·cm ⁻¹ ) of the solid electrolyte membrane was 90%.

[Comparative Example 4]
_{( Synthesis of Solid Electrolyte Powder Li6.9Mg0.10Ca0.10Sr0.10Ba0.10La2.6Zr1.50Nb0.5O12 ) _}
As in Comparative Example 1, Li:Mg:Ca:Sr:Ba:La:Zr:Nb=6.9:0.10:0.10:0.10:0.10:2.6:1 Li raw material, Mg raw material, Ca raw material, Sr raw material, Ba raw material, La raw material, Zr raw material, and Nb raw material were weighed and mixed so as to have a molar ratio of 5:0.5.

As each metal raw material, MgO (manufactured by Fuji Film Wako Pure Chemical, 99.9%), CaCO ₃ (manufactured by Fuji Film Wako Pure Chemical, 99.95%), SrCO ₃ (manufactured by Fuji Film Wako Pure Chemical, 99.9% ), BaCO ₃ (manufactured by Fuji Film Wako Pure Chemical, 99%), Li ₂ CO ₃ (manufactured by Fuji Film Wako Pure Chemical, 99.9%), La ₂ O ₃ (manufactured by Fuji Film Wako Pure Chemical, 99.99% ), ZrO ₂ (manufactured by Kojundo Chemical Co., Ltd., 99.9%), and Nb ₂ O ₅ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 99.9%).

These raw materials were placed in a container together with YSZ balls (manufactured by Nikkato) having a diameter of 5 mm and ethanol in a planetary ball mill (manufactured by Fritsch, P-7) and mixed at 500 rpm for 1 hour.

This mixture was filled in an alumina crucible (manufactured by Nikkato, C5 type) and fired in an electric furnace at 850° C. for 3 hours to obtain solid electrolyte powder Li _6.9 Mg _0.10 Ca _0.10 Sr _0.10 Ba. _{0.10La2.6Zr1.50Nb0.5O12 was synthesized . _}

The obtained solid electrolyte powder was placed in a container together with YSZ balls (manufactured by Nikkato) having a diameter of 5 mm and ethanol in a planetary ball mill (manufactured by Fritsch, P-7) and mixed again at 500 rpm for 1 hour.

(Preparation of slurry, preparation of green sheet, firing of green sheet)
After preparing the slurry in the same manner as in Comparative Example 1, a green sheet was prepared. Thereafter, this green sheet was sandwiched between the firing substrates used in Comparative Example 1, and fired in an electric furnace at 1100° C. for 4 hours to obtain the intended solid electrolyte membrane.

FIG. 15 shows a scanning electron microscope image of a cross section of the solid electrolyte membrane produced in Comparative Example 4. As shown in FIG. The solid electrolyte membrane of Comparative Example 4 had a particle size of 5 μm or less. The relative density obtained from the measured values of the mass and volume of the solid electrolyte membrane of Comparative Example 4 was 72% with respect to the theoretical density (5.80 g·cm ⁻¹ ) of the solid electrolyte membrane.

The impedance of the solid electrolyte membranes of Example 4 and Comparative Example 4 was measured by an electrochemical measurement system (manufactured by Biologic, SP-300-AH-2CH). The measurement results are shown in FIG. In Example 4, in which a Li-free precursor was first prepared and then Li was added, and in Comparative Example 4, in which a raw material containing Li was used from the beginning, the solid electrolyte membrane of Example 4 was formed in a single plane in the cross-sectional direction. Since it is composed of one grain, no grain boundary resistance was observed. However, in the solid electrolyte membrane of Comparative Example 4, many grain boundaries that increase the resistance of the grain interface are observed.

Claims (5)

Li _a M ¹ _b M ² _c O _d (5.0≦a≦8.0, 2.5≦b≦3.5, 1.0≦c≦2.5, 10≦d≦ 14, M1 is ^one or more elements selected from Al, Ga, La, Y, Pr, Mg, Ca, Sr or Ba, ^M2 is one or more elements selected from Zr, Hf, Ta or Nb) and having a particle diameter of 30 to 250 μm. _The lithium-containing _garnet crystal _according to claim ₁ , _wherein the composition is _{Li6.00Ga0.150Al0.100La3.00Zr1.75Ta0.250O12.0 .} A solid electrolyte membrane comprising: The following steps:
Li _a M ¹ _b M ² _c O _d (5.0≦a≦8.0, 2.5≦b≦3.5, 1.0≦c≦2.5, 10≦d≦ 14, M1 is ^one or more elements selected from Al, Ga, La, Y, Pr, Mg, Ca, Sr or Ba, ^M2 is one or more elements selected from Zr, Hf, Ta or Nb) A first step of synthesizing a solid electrolyte having the composition of and then pulverizing it to prepare a fine particle electrolyte powder,
a second step of dissolving the obtained particulate electrolyte powder in a solvent to form a slurry;
A third step of coating the slurry on a substrate to produce a green sheet, and
A fourth step of sandwiching the obtained green sheet between a pair of firing substrates and firing to produce a solid electrolyte membrane composed of particles having a particle diameter of 30 to 250 μm,
The first step includes a step of synthesizing a precursor oxide containing a metal raw material excluding the Li raw material, and a step of adding a Li raw material to the precursor oxide and sintering it to synthesize the solid electrolyte. A method for producing a solid electrolyte membrane comprising lithium-containing garnet crystals. _The lithium-containing _garnet crystal _according to claim ₃ , _wherein the composition is _{Li6.00Ga0.150Al0.100La3.00Zr1.75Ta0.250O12.0 .} A method for producing a solid electrolyte membrane comprising: A lithium ion secondary battery comprising the solid electrolyte membrane according to claim 1 or 2 as a separator, and a positive electrode and a negative electrode provided on both sides of the separator.

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